Faculty of Science

Interesting facts in biochemistry

1. What does DNA do?

DNA is the material that every living cell and creature inherits from its parents.

DNA is found in a special part of the cell, the nucleus, and every one of the millions of cells we have contains the same DNA. Our DNA originally came from our parents, half from each parent, and came together when the DNA of the sperm cells joined with the egg's DNA to form a fertilised egg. All the many different types of cells in an adult human - liver, skin and brain cells etc, develop from this single cell.

The DNA molecules within our cells direct what types of proteins the cell makes, and therefore what sort of work that cell will do. Although all of our cells contain the same DNA, the types of proteins made differ between cell and tissue types, depending on what proteins the DNA tells the individual cell to make.

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2. If you stretched out your entire DNA from just one cell, how long would it be?

Two metres.

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3. Why aren't identical twins really identical?

Although identical twins inherit the same DNA from their parents, the genome (DNA) is subject to changes as an organism grows.

Although identical twins are very similar as adults, the genome of each individual may be slightly different - due to mutations and the rearrangement of pieces of DNA - that have occurred uniquely in each twin, since the egg split. A genome is also subject to environmental influences, and so the same genes can be expressed in different ways in different individuals.

Identical, or monozygotic, twins result when a single fertilised egg splits into two parts, each of which then forms a foetus in the womb. Therefore, identical twins are always of the same sex, and always contain identical DNA in their nuclei.

However, DNA also exists in another part of the cell, the mitochondrion. When a cell splits into two new cells to form the twins, the mitochondrial DNA is not divided equally between the two cells. So, even so-called "identical twins" are not truly identical if we compare their level of DNA or genetics.

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4. What is it in an egg white that makes it turn hard when boiled?

Protein molecules.

Proteins are normally neatly folded chains of amino acids. When you heat an egg, the protein gains energy and shakes apart until the proteins unfold and then link together to form a solid.

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5. Why are leaves green?

Light is made up of electromagnetic radiation with different wavelengths, and consequently, colours. Orange and blue light is absorbed best by chlorophyll molecules, allowing photosynthesis to take place. Green light is reflected or transmitted, and this is what we see.

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6. Why is breast milk best for babies?

We often hear that breast milk is best for babies, but do we really understand the reasons why?

Many of the body's systems that we take for granted in adults are not yet fully functional in newborn babies. The digestive, immune (defence) and central nervous systems are some examples of these. However, breast milk contains many different compounds that can assist in developing these immature systems.

There are enzymes, which help the baby to digest the fats and proteins present in breast milk. Antibodies, similar to those of the mother, help protect the baby from infection. And the long chain polyunsaturated fatty acids found in breast milk assist in the development of the baby's brain.

These are just three examples of how breast milk is tailored to the developmental requirements of the baby. So, breast milk does more than provide nutrients to the baby; it also assists in the baby's development. Infant formulae do not contain these compounds, and it is unlikely that many of them could be added. It is for these reasons - and many others - that breast milk is best for babies.

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7. What takes the oxygen from your lungs to cells in your body?

A protein called haemoglobin, which is found in red blood cells, carries most of the oxygen in your blood. It does this by having an iron atom at its core that is very good at binding oxygen.

When carrying oxygen, the haemoglobin is bright red. When the oxygen is released, the haemoglobin is dark red and appears blue through your skin.

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8. What is the most abundant protein in the world?

Ribulose 1,5 bisphosphate carboxylase - the protein found in algae and the leaves of plants, that fixes CO2 to make carbon, which our world depends upon.

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9. Which parts of the glucose molecule do you think the cell can access for energy?

Glucose provides much of the energy your body uses each day. Some tissues, like your brain, use nothing but glucose as a source of energy. Which parts of the glucose molecule do you think the cell can access for energy?

The cell can only access the energy in the bonds between the carbons, and between the carbons and the hydrogens, that is C-C and C-H bonds. The C-O bonds do not provide any energy to the cell. The atoms themselves, even though they contain a lot of energy (think nuclear fission in nuclear power stations and nuclear weapons), are not accessible as a source of energy for the cell.

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10. How many of these C-C + C-H bonds are actually required by a human?

An average human at rest on an average day requires the energy from 1.4 x 1022 bonds each minute. One of these bonds is only enough to propel a marathon runner 1.3 x 10-21 metres of the 42.2 km course.

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11. How much energy in a molecule of glucose can a cell actually access?

The cell can only access 1 x 1010th of the energy contained in a molecule of glucose. If the cell could access the nuclear energy in a molecule of glucose (why do you think this is not possible?), a human would only need three millionths of a gram of glucose to supply the energy required for a lifetime.

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12. How much energy to do you need to climb Bluff Knoll?

Bluff Knoll is about the only place in Western Australia where you are ever likely to see snow.

It is the highest peak in the south west of Western Australia at 1095 metres above sea level. You need extra energy to climb up Bluff Knoll. How many Mars Bars will provide you with that energy?

One 65 gram Mars Bar provides about 1230 kilojoules of energy. Assuming your body weight is about 75 kilograms, you will expend about 3200 kilojoules. So, three Mars Bars will get you comfortably to the top. However, the Mars Bars should not really be necessary - our fat stores typically provide 540,000 kilojoules, enough for about 170 climbs.

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