The four bases that make up this code are adenine A , thymine T , guanine G and cytosine C. Bases pair off together in a double helix structure, these pairs being A and T, and C and G. RNA molecules, by comparison, are much shorter 3. Eukaryotic cells, including all animal and plant cells, house the great majority of their DNA in the nucleus, where it exists in a tightly compressed form, called a chromosome 4.
This squeezed format means the DNA can be easily stored and transferred. In addition to nuclear DNA, some DNA is present in energy-producing mitochondria, small organelles found free-floating in the cytoplasm, the area of the cell outside the nucleus. The three types of RNA are found in different locations. If it receives the correct signal from the ribosome, it will then hunt down amino acid subunits in the cytoplasm and bring them to the ribosome to be built into proteins 5.
Ribosomes are formed in an area of the nucleus called the nucleolus, before being exported to the cytoplasm, where some ribosomes float freely. Other cytoplasmic ribosomes are bound to the endoplasmic reticulum, a membranous structure that helps process proteins and export them from the cell 5.
Meet The Author. Ruairi J Mackenzie. Chosen for you. Deoxyribonucleic Acid. These pages are written to be read one after the other, so unless you already understand the structure of DNA , follow this link to start from the beginning.
You will probably know that the sequence of bases in DNA carries the genetic code. Scattered along the DNA molecule are particularly important sequences of bases known as genes. Each gene is a coded description for making a particular protein. Note: It would be more accurate to say that each gene coded for a particular polypeptide, because some proteins are made of more than one polypeptide chain. For simplicity, I'm going to refer from now on to the synthesis of a protein, rather than a polypeptide - it sounds less scary!
To be really accurate, some genes code for other sorts of molecule apart from proteins, but we are only going to be looking at the genes involved in protein synthesis. The code is first transcribed "copied", although with one important difference - see later to messenger RNA.
That then travels out of the nucleus of the cell where the DNA is found into the cytoplasm of the cell. The cytoplasm contains essentially everything else in the cell apart from the nucleus.
We'll talk a lot more about those in a later page. DNA contains the code for making lots and lots of different proteins. Messenger RNA contains the information to make just one single polypeptide chain - in other words for just one protein, or even just a part of a protein if it is made up of more than one polypeptide chain.
DNA deoxyribonucleic acid has a backbone of alternating deoxyribose and phosphate groups. In RNA ribonucleic acid , the sugar ribose replaces deoxyribose. If you have read this sequence of pages from the beginning, you will already have come across the difference between these two sugars.
But to remind you. Note: If you don't understand what 2' means, you obviously haven't read the first page in this sequence of pages. It's a bad idea trying to take short cuts with this! The nitrogen shown in blue in the uracil is the one which attaches to the 1' carbon in the ribose. In the process, the hydrogen shown in blue is lost together with the -OH group on the 1' carbon in the ribose.
The only difference between the two molecules is the presence or absence of the CH 3 group. Uracil can form exactly the same hydrogen bonds with adenine as thymine can - the shape of the two molecules is exactly the same where it matters.
In DNA the hydrogen bonding between A and T helps to tie the two strands together into the double helix. That isn't relevant in RNA because it is only a single strand. However, you will find several examples in what follows on this and further pages where the ability of adenine A to attract and bond with uracil U is central to the processes going on. Transcription is the name given to the process where the information in a gene in a DNA strand is transferred to an RNA molecule. The important thing to realise is that the genetic information is carried on only one of the two strands of the DNA.
This is known as the coding strand. The other strand is known as the template strand , for reasons which will become obvious is a moment. Note: These two strands are often given other names as well, sometimes in a very confusing way at least to a non-biochemist! DNA words are three letters long. A gene is a discrete sequence of DNA nucleotides. The RNA message is sometimes edited. Some viruses store genetic information in RNA. RNA was the first genetic molecule. Mutations are changes in genetic information.
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