Genetics and DNA by Varun Shirhatti

    Genetics and DNA

DNA is the genetic material of all plants and animals. It resides in the nucleus of every cell of every plant, animal and, actually, every organism with a nucleus in the first place.

DNA stands for DeoxyriboNucleic Acid. The ‘De-oxy-ribo’ part of its name is from the sides of the DNA ‘ladder’, which are composed of a sugar called ribose, but with one less oxygen atom-Deoxyribose. The ‘nucleic’ is because it’s found in the nucleus. ‘Acid’ sort of explains itself.

Most people think of DNA as just a ‘twisty ladder’ shape. Actually, it’s a bit more complex than that. See the rest of the article for confirmation.

DNA has a shape known as a ‘double helix’, which is like a twisted rope ladder. The ‘rungs’ of the ladder are comprised of four bases: Adenine, Cytosine, Guanine and Thymine. These are abbreviated as A,C,G and T. A always pairs with T and C always pairs with G. Two bases form one ‘rung’.

RNA

DNA takes all the credit for making us who we are, but in fact, it does practically nothing. All the real work is done by RNA and proteins.

RNA is a molecule similar to DNA. However, there are some major differences between the two. First, the name. RNA stands for ribonucleic acid as opposed to deoxyribonucleic acid. This is because the base sugar for RNA is ribose, which I mentioned earlier. Second, RNA isn’t a ‘ladder’ like DNA is, just a sort of floppy noodle with bases tacked onto it.

Also, in RNA, the base Thymine is replaced by the base Uracil, or U.

When RNA is being made, the DNA ‘unzips’ itself, splitting into two strands. Then, extra bases come swooping in, connect themselves with ribose and make strands of RNA: C and G pair up, T and A pair up, but instead of T, U pairs up with A. The RNA made, the DNA  quickly ‘zips’ itself back up.

The newly made RNA then leaves the nucleus to perform its most important function: It is read by proteins called ribosomes to make amino acids, which combine to make proteins.

AMINO ACIDS AND PROTEINS

Proteins are what make you who you are. Literally. Your hair? Protein. Your eyes and eye colour? Protein. Your muscles? Protein. Even the male/female hormones are protein. Having said that, imagine what would happen if just one of those thousands of proteins were wrong somehow.  For example, your body could stop  making hair all over your body and start making nails instead; both of them are proteins. And that is only one possibility.

Proteins are composed of long chains of amino acids. These are the molecules that RNA is used to make. There are a total of 20 different types of amino acids. Out of these, 9 are not able to be made by the body and must be taken in through the diet. Because of this, the environment in which an organism lives affects its growth and development, not genetics alone. This is a debate that has been going on for years: is it primarily genetics that determines the sort of person we are, or is it the environment?

My stance on the matter is that both contribute equally to a person’s development. If a person has genes that say they are going to be 6 feet tall, and the person is wildly malnourished, they probably won’t grow to 6 feet tall.

But back to proteins. RNA is used to build proteins through a process called translation.

During translation. a ribosome goes along the length of the RNA, ‘reading’ the bases in chunks of 3 called codons. Each codon stands for an amino acid, except for ‘start’ and ‘stop’ codons. A start codon tells the ribosome to start making amino acids and stringing them together. A stop codon tells the ribosome to stop making amino acids. Every amino acid has a specific combination of bases. This is why single-base mutations (where one base is changed into another) aren’t as bad as mutations are inserted or removed entirely.

For example:

ORIGINAL                                                                                      EXTRA BASE

RNA SEQUENCE                                                                           RNA SEQUENCE

AUGUAUGACCGUCGCUGA                                                     AUGUAUAGACCGUCGCUGA

CODON SEQUENCE                                                                   CODON SEQUENCE

AUG, UAU, GAC, CGU, CGC, UGA                                            AUG, UAU,AGA,CCG,UCG,CUG

AMINO ACID SEQUENCE                                                          AMINO ACID SEQUENCE

Start, Tyrosine, Aspartic Acid,                                                Start,Tyrosine,Arginine,Proline,

Arginine,Arginine, Stop                                                          Serine,Leucine

OBSERVATION:The sequence from the third base onwards has been changed completely and the protein will be larger than necessary, as the ‘stop’ codon has been removed.

MUTATIONS

You’re a mutant.Yes,you.

To most people, the word ‘mutation’ means either bad things like extra eyes or no fingers, or  X-Men-esque superpowers. However, a mutation isn’t necessarily a bad thing. Case in point: A long time ago, all humans were lactose intolerant. This meant that beyond a certain age, their bodies stopped making a milk-digesting enzyme called lactase. Eventually, a mutation arose: lactose tolerance. People with this new mutation were more biologically successful than people without it. This mutation spread until, today, lactose tolerance is part of practically the whole world’s genomes.

Mutations can be detrimental to health and even survival, it’s true.  But some, like blue eyes or curly hair, are perfectly harmless.

Most mutations occur naturally: a base is removed, added or changed into another. Some mutations, though, can be caused by exposure to radioactivity and other harmful substances.

EPIGENETICS

This is one of the most intriguing parts of the study of genetics. Epigenetics is the study of how the environment affects the genome. Because of this, it closely ties in to the Nature vs Nurture debate.

Not all the parts of the genome are read at once. Some parts of it are ‘blocked off’ by methyl markers, rendering them unreadable. Different kinds of food, like sesame seeds and broccoli can cause methyl markers to lift or land on genes. This can cause serious problems- for example if a gene to prevent cancer is suppressed. In this event, cells would start multiplying madly and cause problems across the body.

This, however, can also be used to our advantage. Epigenetics can be used to stop the growth of a cancer tumour so that it can be safely removed.  This method is much safer than chemotherapy and radiation therapy and has much fewer side effects.

This is another piece of evidence that the environment plays a part in making us who we are.

Bibliography

‘What’s In Your Genes?’ by Katie McKissick