New News Biology #45

DNA (Part 1): Genes and the Genome

DNA = deoxyribonucleic acid

It is a polymer, which means it is made up of parts that are quite similar to each other.

There are two strands, which form the so-called ‘double helix’ shape (‘double helix’ is just a fancy name for a double stranded spiral.

Fun-fact: If you took the two strands of DNA from the nucleus of a single cell, and unraveled it into a single long strand, it would be roughly 2 meters long. In order to stop this DNA from being tangled up, it is tightly coiled and split into 46 different sections which are known as ‘chromosomes’. However, there are only actually 23 different types, and with two of each type, one from each parent. Each of these are a ‘pair’.

The 23rd pair is special, as it’s the ‘sex chromosomes’. There are two types: the X chromosome and the Y chromosome. Women have two X chromosomes, while men have one of each.

The most confusing part of chromosomes are that they are usually drawn in a ‘x’ shape. However, this shape only occurs when the cell is about to undergo cell division. When they are at rest, they look more like half of the ‘x’ shape.

Gene = a small section of DNA that codes for a protein = a ‘small segment of a chromosome’

It’s basically a code for a particular sequence of amino acids, and when they are combined, they make a protein. There are only 20 different types of amino acids, but they can be combined in countless ways, and can make more than 1000 different proteins. It is what fundamentally determines the type of cell.

For example, a red blood cell has to have a lot of haemoglobin to transport oxygen. And muscle cells have to contain the proteins frequently used for muscular contraction.

Genome = entire set of genetic material in an organism

The genome of a person may be very different from that of a stranger, but more similar to those of their parents. If it happened that the person had an identical twin, the genome of these two people would be the same.

Scientists have worked out the complete human genome, meaning they can now identify genes that can be linked specific diseases. Some genes directly cause diseases, in which case they are known as inherited disease, because the genes that cause them are inherited from the patient’s parents. Another type are genes that increase risk of a particular disease but don’t directly cause it. For example, the BRCA genes increase the risk of breast cancer.

By looking at a person’s genes, doctors can develop better treatments for that particular patient.

It can also be used to trace the migrations of our ancestors. Most people share most of their genomes, however small differences can be found in the genomes of different populations. These differences can tell when they separated, like when people migrated outwards from Africa.