My name is cholesterol

CHOLESTEROL is a type of fat that is a normal component of most body tissues, and is required for good health. Yet, high levels can increase the risk of developing diseases (eg heart disease).

High cholesterol levels are asymptomatic, and in many cases, the first sign of any problem is a serious health issue. To help reduce the risk of this occuring, cholesterol levels are measured by a simple blood test. Your healthcare professional can organise this for you, along with other measurements of your cardiovascular health, such as blood pressure testing.

Cholesterol is transported through the blood stream in particles known as lipoproteins. The two most important varieties of lipoproteins to be aware of are low-density lipoproteins (LDL) and high-density lipoproteins (HDL).

High levels of LDL-cholesterol can lead to fatty deposits in the artery walls, referred to as atherosclerosis, or “hardening of the arteries”. Atherosclerosis makes the blood vessels narrower and stiffer, and consequently, increases the risk of heart disease and stroke.

This form of cholesterol is sometimes referred to as “bad” cholesterol.

High-density lipoproteins (HDL-cholesterol) help to reduce the risk of heart disease as they have the ability to help remove excess cholesterol from the arteries and other parts of the body. For this reason, they are sometimes referred to as “good” cholesterol.

The narrowing of the arteries associated with high cholesterol levels can sometimes cause symptoms that include chest pain (angina), or leg pain (intermittent claudication), especially with exercise.

High production of cholesterol by the liver may contribute to the development of gallstones, symptoms of which include episodic abdominal and back pain, especially after consumption of fatty foods.

Cholesterol levels in the blood depend on dietary factors and the amount of cholesterol manufactured by the body. High consumption of saturated fat, trans fat and cholesterol in foods may make your total cholesterol and LDL cholesterol levels rise.

Genetics also play a role in some people with high cholesterol. Your genes will partly determine how much cholesterol you naturally produce. Familial hypercholesterolaemia is more likely to be present in people who experience a heart attack at an early age or who have a family member who had a heart attack at an early age.

Being overweight contributes to increased LDL-cholesterol.

Other blood markers that may be associated with high cholesterol levels and are also risk factors for cardiovascular disease include high levels of a compound called homocysteine and high blood levels of triglycerides (fats).

Free radical damage to cholesterol molecules is believed to increase their ability to damage blood vessels.

Remember that cholesterol is not a disease in itself, but an indicator of the risk of developing heart disease. Your healthcare professional will consider your cholesterol level in the context of other risk factors, such as your family history, blood pressure, level of physical activity, and whether you are diabetic or smoke cigarettes.

Measures you can take to help reduce cholesterol levels include:

● To help maintain healthy cholesterol levels, reduce the quantity of cholesterol and saturated and trans fats in your diet. This involves avoiding animal fats (meat and full-fat dairy products) and sources of hidden fat such as pastries and pies.

● At the same time, increase the amount of fish in your diet (but not deep fried fish), and eat more fruit, vegetables and whole grains.

● A diet high in soluble fibre is highly recommended in order to promote the excretion of cholesterol. Good sources include legumes, oats and psyllium.

● Eating moderate amounts of foods that contain monounsaturated fats may support the management of healthy normal cholesterol levels. Important foods to include in your diet include nuts (especially walnuts), seeds and olive oil.

● Garlic and onion have cholesterol-lowering properties and are valuable additions to your diet.

● Limit your alcohol consumption to one to two standard drinks per day, and avoid binge drinking.

● Quit smoking. Cigarette smoking significantly increases the risk of cardiovascular disease and other health problems, and can exacerbate the negative effects of high cholesterol levels.

● Regular aerobic exercise can be of benefit to those with high cholesterol levels. Aim for at least 30 minutes of brisk walking per day. Always seek the advice of your healthcare professional before commencing an exercise programme.

● If you are overweight, talk to your healthcare professional about ways to address this, as being overweight may contribute to raised LDL and triglyceride levels.

There are also certain natural alternatives you can consider:

● Plant sterols (also known as phytosterols) may help reduce LDL-cholesterol levels and assist in improving the LDL:HDL ratio to healthier levels. They work by lowering cholesterol absorption and reabsorption. Take a daily dose of 2-3 grams of plant sterols, as recommended by the National Heart Foundation of Australia. Choose a formula that also supplies a healthy dose of betacarotene, which may become depleted when taking plant sterols.

● Coenzyme Q10 helps maintain heart and artery health and inhibits the oxidation of LDL–cholesterol.

● Omega-3 fatty acids EPA and DHA from fish oil, may help decrease fat in the blood (triglycerides) in healthy people. Omega-3s also help to maintain the flexibility of the blood vessels, help maintain healthy heart rates, and help maintain healthy blood pressure.

● Antioxidant nutrients such as vitamin C and vitamin E help reduce the oxidation of LDL-cholesterol. Antioxidants are often taken with folic acid and the vitamins B6 and B12. Low intake of these B-group vitamins is a common cause of elevated plasma homocysteine.

● If you’re overweight, achieving a healthy body weight may aid the management of healthy cholesterol levels.

Your cholesterol level is only one aspect of your cardiovascular health profile and should be addressed in conjunction with other risk factors. Talk to your healthcare professional for more information.

Regulation of Kidney Function

One of the most important aspects of the mammalian kidney is its ability to adjust both the volume and osmolarity of urine, depending on the animal′s water and salt balance and the rate of urea production. In situations of high salt intake and low water availability, a mammal can excrete urea and salt with minimal water loss in small volumes of hyperosmotic urine. But if salt is scarce and fluid intake is high, the kidney can get rid of the excess water with little salt loss by producing large volumes of hypoosmotic urine (as dilute as 70 mosm/L, compared to about 300 mosm/L for human blood). This versatility in osmoregulatory function is managed with a combination of nervous and hormonal controls.

One hormone that is important in regulating water balance is antidiuretic hormone (ADH).

ADH is produced in the hypothalamus of the brain and is stored in and released from the posterior pituitary gland, which is positioned just below the hypothalamus. Osmoreceptor cells in the hypothalamus monitor the osmolarity of blood; when it rises above a set point of 300 mosm/L (perhaps due to water loss from sweating or to ingestion of salty food), more ADH is released into the bloodstream and reaches the kidney. The main targets of ADH are the distal tubules and collecting ducts of the kidney, where the hormone increases the permeability of the epithelium to water. This amplifies water reabsorption, which reduces urine volume and helps prevent further increase of blood osmolarity above the set point. By negative feedback, the subsiding osmolarity of the blood reduces the activity of osmoreceptor cells in the hypothalamus, and less ADH is then secreted. But only the gain of additional water in food and drink can bring osmolarity all the way back down to 300 mosm/L.

Conversely, if a large intake of water has reduced blood osmolarity below the set point, very little ADH is released. This decreases the permeability of the distal tubules and collecting ducts, so water reabsorption is reduced, resulting in increased discharge of dilute urine. (Increased urination is called diuresis, and it is because ADH opposes this state that it is called anti diuretic hormone.) Alcohol can disturb water balance by inhibiting the release of ADH, causing excessive urinary water loss and dehydration (which may cause some of the symptoms of a hangover). Normally, blood osmolarity, ADH release, and water reabsorption in the kidney are all linked in a feedback loop that contributes to homeostasis.

A second regulatory mechanism involves a specialised tissue called the juxtaglomerular apparatus (JGA), located near the afferent arteriole that supplies blood to the glomerulus. When blood pressure or blood volume in the afferent arteriole drops (for instance, as a result of reduced salt intake or loss of blood), the enzyme renin initiates chemical reactions that convert a plasma protein called angiotensinogen to a peptide called angiotensin II. Functioning as a hormone, angiotensin II raises blood pressure by constricting arterioles, decreasing blood flow to many capillaries, including those of the kidney. Angiotensin II also stimulates the proximal tubules of the nephrons to reabsorb more NaCl and water. This reduces the amount of salt and water excreted in the urine and consequently raises blood volume and pressure. Another effect of angiotensin II is stimulation of the adrenal glands to release a hormone called aldosterone. This hormone acts on the nephrons′ distal tubules, making them reabsorb more sodium (Na+) and water and increasing blood volume and pressure. In summary, the renin–angiotensin–aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis. A drop in blood pressure and blood volume triggers renin release from the JGA. In turn, the rise in blood pressure and volume resulting from the various actions of angiotensin II and aldosterone reduce the release of renin.

The functions of ADH and the RAAS may seem to be redundant, but this is not the case. Both increase water reabsorption, but they counter different osmoregulatory problems. The release of ADH is a response to an increase in the osmolarity of the blood, as when the body is dehydrated from excessive water loss or inadequate intake of water. However, a situation that causes an excessive loss of both salt and body fluids—an injury, for example, or severe diarrhea—will reduce blood volume without increasing osmolarity. This will not induce a change in ADH release, but the RAAS will respond to the fall in blood volume and pressure by increasing water and Na+ reabsorption. ADH and the RAAS are partners in homeostasis; ADH alone would lower blood Na+ concentration by stimulating water reabsorption in the kidney, but the RAAS helps maintain balance by stimulating Na+ reabsorption.

Still another hormone, a peptide called atrial natriuretic factor (ANF), opposes the RAAS. The walls of the atria of the heart release ANF in response to an increase in blood volume and pressure. ANF inhibits the release of renin from the JGA, inhibits NaCl reabsorption by the collecting ducts, and reduces aldosterone release from the adrenal glands. These actions lower blood volume and pressure. Thus, ADH, the RAAS, and ANF provide an elaborate system of checks and balances that regulate the kidney′s ability to control the osmolarity, salt concentration, volume, and pressure of blood. The precise regulatory role of ANF is an area of active research.

Mammalian Kidney

The excretory system of mammals centres on the kidneys, which are also the principal site of water balance and salt regulation. Mammals have a pair of kidneys. Each kidney, bean–shaped and about 10 cm long in humans, is supplied with blood by a renal artery and drained by a renal vein.

Blood flow through the kidneys is voluminous. In humans, the kidneys account for less than 1% of body weight, but they receive about 20% of resting cardiac output. Urine exits each kidney through a duct called the ureter, and both ureters drain into a common urinary bladder. During urination, urine is expelled from the urinary bladder through a tube called the urethra, which empties to the outside near the vagina in females or through the penis in males. Sphincter muscles near the junction of the urethra and the bladder, which are under nervous system control, regulate urination.

The mammalian kidney has two distinct regions, an outer renal cortex and an inner renal medulla. Packing both regions are microscopic excretory tubules and their associated blood vessels. The nephron—the functional unit of the vertebrate kidney—consists of a single long tubule and a ball of capillaries called the glomerulus. The blind end of the tubule forms a cup–shaped swelling, called Bowman′s capsule, which surrounds the glomerulus. Each human kidney contains about a million nephrons, with a total tubule length of 80 km.

Filtration of the Blood

Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman′s capsule. The porous capillaries, along with specialised cells of the capsule called podocytes, are permeable to water and small solutes but not to blood cells or large molecules such as plasma proteins. Filtration of small molecules is nonselective, and the filtrate in Bowman′s capsule contains salts, glucose, amino acids, and vitamins; nitrogenous wastes such as urea; and other small molecules—a mixture that mirrors the concentrations of these substances in blood plasma.

Pathway of the Filtrate

From Bowman′s capsule, the filtrate passes through three regions of the nephron: the proximal tubule; the loop of Henle, a hairpin turn with a descending limb and an ascending limb; and the distal tubule. The distal tubule empties into a collecting duct, which receives processed filtrate from many nephrons. This filtrate flows from the many collecting ducts of the kidney into the renal pelvis, which is drained by the ureter.

In the human kidney, approximately 80% of the nephrons, the cortical nephrons, have reduced loops of Henle and are almost entirely confined to the renal cortex. The other 20%, the juxtamedullary nephrons, have well–developed loops that extend deeply into the renal medulla. Only mammals and birds have juxtamedullary nephrons; the nephrons of other vertebrates lack loops of Henle. It is the juxtamedullary nephrons that enable mammals to produce urine that is hyperosmotic to body fluids, an adaptation that is extremely important for water conservation.

The nephron and the collecting duct are lined by a transport epithelium that processes the filtrate to form the urine. One of this epithelium′s most important tasks is reabsorption of solutes and water. Between 1,100 and 2,000 L of blood flows through a pair of human kidneys each day, a volume about 275 times the total volume of blood in the body. From this enormous traffic of blood, the nephrons and collecting ducts process about 180 L of initial filtrate, equivalent to two or three times the body weight of an average person. Of this, nearly all of the sugar, vitamins, and other organic nutrients and about 99% of the water are reabsorbed into the blood, leaving only about 1.5 L of urine to be voided.

Blood Vessels Associated with the Nephrons

Each nephron is supplied with blood by an afferent arteriole, a branch of the renal artery that subdivides into the capillaries of the glomerulus. The capillaries converge as they leave the glomerulus, forming an efferent arteriole. This vessel subdivides again, forming the peritubular capillaries, which surround the proximal and distal tubules. More capillaries extend downward and form the vasa recta, the capillaries that serve the loop of Henle. The vasa recta also form a loop, with descending and ascending vessels conveying blood in opposite directions.

Although the excretory tubules and their surrounding capillaries are closely associated, they do not exchange materials directly. The tubules and capillaries are immersed in interstitial fluid, through which various substances diffuse between the plasma within capillaries and the filtrate within the nephron tubule. This exchange is facilitated by the relative direction of blood flow and filtrate flow in the nephrons.

 



Secretion and reabsorption in the proximal tubule substantially alter the volume and composition of filtrate. For example, the cells of the transport epithelium help maintain a relatively constant pH in body fluids by the controlled secretion of H+. The cells also synthesise and secrete ammonia, which neutralises the acid and keeps the filtrate from becoming too acidic. The more acidic the filtrate, the more ammonia the cells produce and secrete, and the urine of a mammal usually contains some ammonia from this source (even though most nitrogenous waste is excreted as urea). The proximal tubules also reabsorb about 90% of the important buffer bicarbonate (HCO3−). Drugs and other poisons that have been processed in the liver pass from the peritubular capillaries into the interstitial fluid, and then are secreted across the epithelium of the proximal tubule into the nephron′s lumen. Conversely, valuable nutrients, including glucose, amino acids, and potassium (K+), are actively or passively transported from the filtrate to the interstitial fluid and then are moved into the peritubular capillaries.

One of the most important functions of the proximal tubule is reabsorption of most of the NaCl (salt) and water from the huge initial filtrate volume. Salt in the filtrate diffuses into the cells of the transport epithelium, and the membranes of the cells actively transport Na+ into the interstitial fluid. This transfer of positive charge is balanced by the passive transport of Cl− out of the tubule. As salt moves from the filtrate to the interstitial fluid, water follows by osmosis. The exterior side of the epithelium has a much smaller surface area than the side facing the lumen, minimizing leakage of salt and water back into the tubule. Instead, the salt and water now diffuse from the interstitial fluid into the peritubular capillaries.

Reabsorption of water continues as the filtrate moves into the descending limb of the loop of Henle. Here the transport epithelium is freely permeable to water but not very permeable to salt and other small solutes. For water to move out of the tubule by osmosis, the interstitial fluid bathing the tubule must be hyperosmotic to the filtrate. The osmolarity of the interstitial fluid does in fact become progressively greater from the outer cortex to the inner medulla of the kidney. Thus, filtrate moving downward from the cortex to the medulla within the descending limb of the loop of Henle continues to lose water to interstitial fluid of greater and greater osmolarity, which increases the solute concentration of the filtrate.

The filtrate reaches the tip of the loop, deep in the renal medulla in the case of juxtamedullary nephrons, then moves back to the cortex within the ascending limb. In contrast to the descending limb, the transport epithelium of the ascending limb is permeable to salt but not to water. The ascending limb has two specialized regions: a thin segment near the loop tip and a thick segment adjacent to the distal tubule. As filtrate ascends in the thin segment, NaCl, which became concentrated in the descending limb, diffuses out of the permeable tubule into the interstitial fluid. This movement increases the osmolarity of the interstitial fluid in the medulla. The exodus of salt from the filtrate continues in the thick segment of the ascending limb, but here the epithelium actively transports NaCl into the interstitial fluid. By losing salt without giving up water, the filtrate is progressively diluted as it moves up to the cortex in the ascending limb of the loop.

The distal tubule plays a key role in regulating the K+ and NaCl concentration of body fluids by varying the amount of the K+ that is secreted into the filtrate and the amount of NaCl reabsorbed from the filtrate. Like the proximal tubule, the distal tubule also contributes to pH regulation by the controlled secretion of H+ and reabsorption of bicarbonate (HCO3−).

The collecting duct carries the filtrate through the medulla to the renal pelvis. By actively reabsorbing NaCl, the transport epithelium of the collecting duct plays a large role in determining how much salt is actually excreted in the urine. Though its degree of permeability is under hormonal control, the epithelium is permeable to water. However, it is not permeable to salt or, in the renal cortex, to urea. Thus, as the collecting duct traverses the gradient of osmolarity in the kidney, the filtrate becomes increasingly concentrated as it loses more and more water by osmosis to the hyperosmotic interstitial fluid. In the inner medulla, the duct becomes permeable to urea. Because of the high urea concentration in the filtrate at this point, some urea diffuses out of the duct and into the interstitial fluid. Along with NaCl, this urea contributes to the high osmolarity of the interstitial fluid in the medulla. This high osmolarity enables the mammalian kidney to conserve water by excreting urine that is hyperosmotic to the general body fluids.

Weird Facts

Can you feel the pulse in your wrist? For humans the normal pulse is 70 heartbeats per minute. Elephants have a slower pulse of 27 and for a canary it is 1000!

If all the blood vessels in your body were laid end to end, they would reach about 60,000 miles.
 

Abraham Lincoln probably had a medical condition called Marfans syndrome. Some of its symptoms are extremely long bones, curved spine, an arm span that is longer than the persons height, eye problems, heart problems and very little fat. It is a rare, inherited condition.
 

In one day your heart beats 100,000 times.
 

By the time you are 70 you will have easily drunk over 12,000 gallons of water.
 

Coughing can cause air to move through your windpipe faster than the speed of sound - over a thousand feet per second!
 

Germs only cause disease, right? But a common bacterium, E. coli, found in the intestine helps us digest green vegetables and beans (also making gases - pew!). These same bacteria also make vitamin K, which causes blood to clot. If we didn't have these germs we would bleed to death whenever we got a small cut!
 

It takes more muscles to frown than it does to smile.
 

That dust on rugs and your furniture is not only dirt. It's mostly made of dead skin cells. Everybody loses millions of skin cells every day which fall on the floor and get kicked up to land on all the surfaces in a room. You could say, "That's me all over."

It takes food seven seconds to go from the mouth to the stomach via the oesophagus. 

A human's small intestine is 6 meters long.
 

The human body is 75% water.

Your blood takes a very long trip through your body. If you could stretch out all of a human's blood vessels, they would be about 60,000 miles long. That's enough to go around the world twice. 

The width of your armspan stretched out is the length of your whole body. 

The average human dream lasts only 2 to 3 seconds.
 

The average American over fifty will have spent 5 years waiting in lines.
 

The farthest you can see with the naked eye is 2.4 million light years away! (140,000,000,000,000,000,000 miles.) That's the distance to the giant Andromeda Galaxy. You can see it easily as a dim, large gray "cloud" almost directly overhead in a clear night sky. 

The average person has at least seven dreams a night.

Your brain is move active and thinks more at night than during the day.

Your brain is 80% water.
 

85% of the population can curl their tongue into a tube.
 

Your tongue has 3,000 taste buds.
 

Your forearm (from inside of elbow to inside of wrist) is the same length as your foot.  

A sneeze travels at over 100 miles per hour. Gesundheit!
 

Your thigh bone is stronger than concrete.
 

Your fingernails grow almost four times as fast as your toenails.
 

You blink your eyes over 10,000,000 a year.
There were about 300 bones in your body when you were born, but by the time you reach adulthood you only have 206.

Nucleic Acids

If the primary structure of polypeptides determines the conformation of a protein, what determines primary structure? The amino acid sequence of a polypeptide is programmed by a unit of inheritance known as a gene. Genes consist of DNA, which is a polymer belonging to the class of compounds known as nucleic acids.

The Roles of Nucleic Acids

There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) . These are the molecules that enable living organisms to reproduce their complex components from one generation to the next. Unique among molecules, DNA provides directions for its own replication. DNA also directs RNA synthesis and, through RNA, controls protein synthesis. 

The figure above shows DNA → RNA → protein: a diagrammatic overview of information flow in a cell. In a eukaryotic cell, DNA in the nucleus programs protein production in the cytoplasm by dictating the synthesis of messenger RNA (mRNA), which travels to the cytoplasm and binds to ribosomes. As a ribosome (greatly enlarged in this drawing) moves along the mRNA, the genetic message is translated into a polypeptide of specific amino acid sequence.

DNA is the genetic material that organisms inherit from their parents. Each chromosome contains one long DNA molecule, usually consisting of from several hundred to more than a thousand genes. When a cell reproduces itself by dividing, its DNA molecules are copied and passed along from one generation of cells to the next. Encoded in the structure of DNA is the information that programs all the cell’s activities. The DNA, however, is not directly involved in running the operations of the cell, any more than computer software by itself can print a bank statement or read the bar code on a box of cereal. Just as a printer is needed to print out a statement and a scanner is needed to read a bar code, proteins are required to implement genetic programs. The molecular hardware of the cell—the tools for most biological functions—consists of proteins. For example, the oxygen carrier in the blood is the protein haemoglobin, not the DNA that specifies its structure.

How does RNA, the other type of nucleic acid, fit into the flow of genetic information from DNA to proteins? Each gene along the length of a DNA molecule directs the synthesis of a type of RNA called messenger RNA (mRNA). The mRNA molecule then interacts with the cell’s protein–synthesizsng machinery to direct the production of a polypeptide. We can summarise the flow of genetic information as DNA → RNA → protein. The actual sites of protein synthesis are cellular structures called ribosomes. In a eukaryotic cell, ribosomes are located in the cytoplasm, but DNA resides in the nucleus. Messenger RNA conveys the genetic instructions for building proteins from the nucleus to the cytoplasm. Prokaryotic cells lack nuclei, but they still use RNA to send a message from the DNA to the ribosomes and other equipment of the cell that translate the coded information into amino acid sequences.

The Structure of Nucleic Acids

Nucleic acids are macromolecules that exist as polymers called polynucleotides.

The components of nucleic acids. 

(a) A polynucleotide has a regular sugar–phosphate backbone with variable appendages, the four kinds of nitrogenous bases. RNA usually exists in the form of a single polynucleotide, like the one shown here. (

b) A nucleotide monomer is made up of three components: a nitrogenous base, a sugar, and a phosphate group, linked together as shown here. Without the phosphate group, the resulting structure is called a nucleoside.

(c) The components of the nucleoside include a nitrogenous base (either a purine or a pyrimidine) and a pentose sugar (either deoxyribose or ribose).

As indicated by the name, each polynucleotide consists of monomers called nucleotides . A nucleotide is itself composed of three parts: a nitrogenous base, a pentose (five–carbon sugar), and a phosphate group. The portion of this unit without the phosphate group is called a nucleoside.

The DNA double helix and its replication. The DNA molecule is usually double–stranded, with the sugar–phosphate backbone of the antiparallel polynucleotide strands (symbolized here by blue ribbons) on the outside of the helix. Holding the two strands together are pairs of nitrogenous bases attached to each other by hydrogen bonds. As illustrated here with symbolic shapes for the bases, adenine (A) can pair only with thymine (T), and guanine (G) can pair only with cytosine (C). When a cell prepares to divide, the two strands of the double helix separate, and each serves as a template for the precise ordering of nucleotides into new complementary strands (orange). Each DNA strand in this figure is the structural equivalent of the polynucleotide diagrammed below.

DNA double helix

The RNA molecules of cells consist of a single polynucleotide chain like the one shown in  the figure above .In contrast, cellular DNA molecules have two polynucleotides that spiral around an imaginary axis, forming a double helix.

The figure above shows the DNA double helix and its replication. The DNA molecule is usually double–stranded, with the sugar–phosphate backbone of the antiparallel polynucleotide strands (symbolised here by blue ribbons) on the outside of the helix. Holding the two strands together are pairs of nitrogenous bases attached to each other by hydrogen bonds. As illustrated here with symbolic shapes for the bases, adenine (A) can pair only with thymine (T), and guanine (G) can pair only with cytosine (C). When a cell prepares to divide, the two strands of the double helix separate, and each serves as a template for the precise ordering of nucleotides into new complementary strands (orange). Each DNA strand in this figure is the structural equivalent of the polynucleotide in the diagram.

James Watson and Francis Crick, working at Cambridge University, first proposed the double helix as the three–dimensional structure of DNA in 1953. The two sugar–phosphate backbones run in opposite 5′ → 3′ directions from each other, an arrangement referred to as antiparallel, somewhat like a divided highway. The sugar–phosphate backbones are on the outside of the helix, and the nitrogenous bases are paired in the interior of the helix. The two polynucleotides, or strands, as they are called, are held together by hydrogen bonds between the paired bases and by van der Waals interactions between the stacked bases. Most DNA molecules are very long, with thousands or even millions of base pairs connecting the two chains. One long DNA double helix includes many genes, each one a particular segment of the molecule.

Only certain bases in the double helix are compatible with each other. Adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C). If we were to read the sequence of bases along one strand as we traveled the length of the double helix, we would know the sequence of bases along the other strand. If a stretch of one strand has the base sequence 5′–AGGTCCG–3′, then the base–pairing rules tell us that the same stretch of the other strand must have the sequence 3′–TCCAGGC–5′. The two strands of the double helix are complementary, each the predictable counterpart of the other. It is this feature of DNA that makes possible the precise copying of genes that is responsible for inheritance. In preparation for cell division, each of the two strands of a DNA molecule serves as a template to order nucleotides into a new complementary strand. The result is two identical copies of the original double–stranded DNA molecule, which are then distributed to the two daughter cells. Thus, the structure of DNA accounts for its function in transmitting genetic information whenever a cell reproduces.

DNA and Proteins as Tape Measures of Evolution

We are accustomed to thinking of shared traits, such as hair and milk production in mammals, as evidence of shared ancestors. Because we now understand that DNA carries heritable information in the form of genes, we can see that genes and their products (proteins) document the hereditary background of an organism. The linear sequences of nucleotides in DNA molecules are passed from parents to offspring; these sequences determine the amino acid sequences of proteins. Siblings have greater similarity in their DNA and proteins than do unrelated individuals of the same species. If the evolutionary view of life is valid, we should be able to extend this concept of “molecular genealogy” to relationships between species: We should expect two species that appear to be closely related based on fossil and anatomical evidence to also share a greater proportion of their DNA and protein sequences than do more distantly related species. In fact, that is the case. For example, if we compare a polypeptide chain of human hemoglobin with the corresponding hemoglobin polypeptide in five other vertebrates, we find the following. In this chain of 146 amino acids, humans and gorillas differ in just 1 amino acid, humans and gibbons differ in 2 amino acids, and humans and rhesus monkeys differ in 8 amino acids. More distantly related species have chains that are less similar. Humans and mice differ in 27 amino acids, and humans and frogs differ in 67 amino acids. Molecular biology has added a new tape measure to the toolkit biologists use to assess evolutionary kinship.

How to study Biology and succeed



There are no tricks or short-cuts when it comes to succeeding in Biology class. Biology is difficult and there is no substitute for hard work. But what is meant by "hard work"? One component is time spent on task. When we speak of time, we should consider both the quantity of time spent and the quality of time spent.

There is so much material to be understood that a substantial time commitment is required. There is time spent in class, but also time spent preparing for class, reading the assigned pages, upgrading notes, and studying for tests (which might cover as many as 15 chapters). Yet, a student can devote a lot of time to these activities and still do poorly in Biology. This is because the quality of time spent is also an important factor. Many students become discouraged when, though they spend hours and even days studying for tests, they still get unsatisfactory scores. Usually this occurs because what they do when they study is low-quality work.

What are some examples of low-quality work? One example would be reading the textbook just to get the reading assignment out of the way. A student who reads properly, on the other hand, reads with a critical eye, constantly asking him/herself questions like: "If I had to teach this to someone, could I do it?" or "What if this process where screwed up somehow; then how would the results differ?" or "The text's treatment of this topic differs from what I learned in lower secondary (or what I learned in class today); what question could I ask in class that might clear this up?"

Another example of low-quality work is going over and over your class notes. This is an activity that assumes one will be tested in a low-quality fashion, i.e. with test items that require you to do nothing but recall and repeat. This is a false assumption. You will be asked to integrate concepts from different classes, to apply the principles of biology covered in class to situations that were not covered in the class or text, to evaluate new situations in light of the material covered during the test unit. High-quality work entails preparing for such questions. Preparing entails organising the mass of new information in such a way that it helps you understand the way the concepts are related to each other.

A final example of low-quality work is coming to class regularly and just taking notes. Why is this low-quality work? Because many people go on auto-pilot when they takes notes. They switch off their brains and become passive sponges or tape recorders, assuming that later on, they will only need to act like a pair of speakers to play back what was written down. As in other things, your attendance at classes or tuitions  can be either low-quality or high-quality. High-quality attendance entails being critical during the classes, asking questions like: "Why does it work that way?" or "How do we know that? What is the evidence?" "How does that relate to what the teacher said the other day about...?" There is a world of difference between questions such as those listed above and questions like: "Could you repeat that?" or "Could you spell that?" or "Do we have to know this for the test?" The answers to these questions might be important, but asking them does not indicate that critical thinking has been going on, as do the earlier questions.

As you can see, the successful student will necessarily have to work hard. The suggestions above are labour-intensive; they require more mental gymnastics. But just as a gymnast would be foolish to expect to succeed at a complex manoeuver on the first try at an important competition, as foolish would be a student who expected to pass tests requiring higher-order thought processes without first practicing these same processes.

Successful students take pains to carry out some sort of class follow-up activity. For many, this means rewriting their class notes. A lot of students find this activity to be very tedious. An alternative follow-up activity is a strategy known as Concept Mapping. Like rewriting notes, this is an activity that helps you reorganise the information in a way that conforms to your mental "landscape." Better than rewriting your notes, it helps you to discern the patterns and relationships between concepts. Much research supports the effectiveness of this strategy in helping students learn complex material. The process will be detailed in the presentation that accompanies this handout. Below is a summary of the steps in constructing a concept map, followed by guidelines to use in constructing the most helpful maps possible.

Steps in Making A Concept Map

1. Make a list of the concepts from the class.

2. Rank the concepts from most general to most specific.

3. Start each map at the center of the top of the page with the most general concept, which will generally be the chief topic of a particular topic. Below it, place the second-most general concept(s), etc...

4. Circle these two concepts and link them with a solid line.

5. Label the line with a linking phrase.

6. Work your way down the page, adding increasingly specific concepts and looking for crosslinks, which should be drawn with dashed lines.

7. Add details (examples).

8. Do a second version of the map with the goal being to add formerly unnoticed crosslinks and to organise the map so that it flows as logically and as clearly as possible.

Guidelines for the Most Helpful Maps

1. A typical 80-minute class should contain at least 20 (and not more than 45) concepts. Concepts are usually nouns.

2. Label ALL links and crosslinks with linking phrases. Links generally consist of verbs, but other words may be used where appropriate.

3. Circle the concepts, leave examples uncircled.

4. Each concept should only appear once in a given map. Redundancy of concepts usually indicates that you missed an important conceptual relationship.

5. Concept maps should flow down the page only.

6. Concept maps should NOT resemble flow charts or chronologically based outlines of the class. They should not be sentences with some words diagrammed. An important goal is to accurately relate as many concepts as possible using crosslinks. Maps with long strings of concepts or with several isolated and unlinked branches indicate misunderstanding of the goal of concept mapping.

Further Suggestions:

1. Attend ALL classes: This gives you a good idea of what the teacher(s) think most important. It also allows you to learn by hearing and seeing simultaneously -- much more effective than either one of these alone.

2. Make a regular appointment with your teacher to go over questions you have, or test your own understanding by explaining material back to him/her. It is always better not to be an anonymous face in a crowd -- get to know you teachers.

3. Come to class prepared by having outlined the assigned pages ahead of time. This will help you make more sense of the class as you listen to it and this, in turn, will help you to...

4. Engage your brain in the class. Don't allow yourself to become a note-taking automaton. Think! Be critical! Be skeptical! Ask questions! If you are shy, ask questions after class or during office hours.

5. Put proper closure on each class. Within 24 hours of each class -- the sooner the better -- (1) ask yourself what the class was about without using your notes, and (2) write your answer in the form of a concept map. This is the best time to spot points of confusion or discrepancies between text and notes, which you should write down and follow-up on. It is very important to spend time in this fashion if you are serious about succeeding in biology.

6. Pay attention to the figures in your text, especially the summary figures, like Fig. 17.26 in Campbell's Biology, 7th edition. Figures are expensive to produce and publishers try to use them sparingly in order to reinforce main points.

7. Budget your time. There is such a huge amount of material to be mastered that studying cannot be put off into an all-night cram session before tests. This is a time-tested recipe for failure; if not failure of the test itself, then failure to understand biology. Will you have a cumulative final exam? What is your plan for keeping material from the beginning of the semester fresh and in mind? You would be well-advised to have such a plan.

8. Don't be a hermit. Once you have studied a good bit on your own, get together with a few others who are interested in understanding biology in order to bounce questions off each other, compare concept maps, create sample test questions, explain concepts to each other, and to be able to answer your colleagues' questions regarding those same explanations.

9. Don't miss the forest for the trees. Concentrate on the concepts, not on the minutiae. You will not be asked to recall picky details or to memorise tables (like the genetic code). You will be asked to apply broad concepts to solve specific problems.

Good luck.

Fake Egg



Fake eggs are still going strong in China. Danwei.org published a small report in 2004 and several blogs reported on fake eggs such as The Raw Feed and Chinaview (in 2007 and 2006), but a look at the stories from Chinese language sources show that the problem is still there, if not bigger than before.

The profit margin for fake eggs, estimated at USD$70 per day, is more than enough for the common Chinese to engage in the business and there’s nothing China’s poor won’t do to get ahead. The list of faulty (or deadly) products coming out of China is long and will continue to lengthen for some time to come. It’s simply a matter of economy and history.

A cursory search of Chinese language news sites brought up more than 8,000 hits for “man-made eggs” including numerous news reports, instructional videos and most galling of all, dozens of ads for training manuals for interested entrepreneurs

In order to tell the difference between man-made and natural eggs, the first method is to inspect the shell. Man-made eggshells are particularly shiny and if the egg is opened, the egg white is not as sticky as a natural egg and is easily mixed in with the egg yolk. There may also be a light chemical smell coming from the egg yolk/white, whereas natural eggs have a fresh smell.

Man-made eggshells are made from Calcium Carbonate. The egg whites and egg yolks are made from the following materials: Alginic Acid, Potassium Alum, Gelatin, Calcium Chloride (with water) and artificial colouring. If fake, the yolk will quickly break up when fried

Man-made eggs are manufactured with chemicals, most importantly through the calcification of Alginic Acid. Man-made eggs are basically solidified gel. Most of the ingredients are additives that are regulated under Chinese law. None of these additives have any health benefits; man-made eggs cannot be considered a viable alternative to natural eggs.

Many of the ingredients involved in the manufacture of man-made eggs come in industrial and commercial forms. Considering the extremely low cost price of man-made eggs, it is uncertain what form of these additives the manufacturers are using. Research has shown that long-term consumption of man-made eggs can lead to memory-loss and dementia.

Check out this Health News Sohu story written by a journalist for the Qilu Evening News in Shandong.

In this story, the journalist follows the trail of one of the ads to a man in Shandong who claims to be the “Father of Man-made eggs”. The man, never named, tells how he charges 800RMB (US$120) per student. In his classes, the “Father” teaches how to make the egg-shell (the most important part of the process) as well as the yolk and white. According to the report, the man has taught college graduates as well as peasants and enjoys a comfortable living — safe from the authorities or anyone else — teaching down and out Chinese how to make fake eggs and get rich.