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DNA LIFE March 2013

DNA STRUCTURE

DNA STRUCTURE: BACK TO THE BASICS

A DNA nucleotide is made of the sugar deoxyribose, a base (which can be either adenine, guanine, cytosine or thymine) and a phosphate group. These nucleotides combine to form a strand. A covalent bond forms between the sugar of one nucleotide and the phosphate group of another nucleotide.

How is a double helix formed? DNA is made up of two nucleotide strands. The nucleotides are connected together by covalent bonds within each strand. The two strands themselves are connected by hydrogen bonds. The hydrogen bonds are found between the bases of the two strands of nucleotides. Adenine forms hydrogen bonds with thymine whereas guanine forms hydrogen bonds with cytosine. This is called complementary base pairing. Play the DNA Double Helix Game now, here!

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DNA REPLICATION

Fun Fact DNA Replication is semi-conservative. This is because DNA Replication produces two copies that each contain one of the original strands and one entirely new strand.

What is the process of DNA Replication? DNA replication is semi-conservative as both of the

fork which then bond to the template strands. The free

DNA molecules produced are formed from an old

nucleotides form hydrogen bonds with their

strand and a new one. The first stage of DNA replication involves the unwinding of the double strand of DNA (DNA double helix) and separating them by breaking the hydrogen bonds between the bases. This is

complimentary base pairs on the template

Try the DNA Replication Quiz

done by the enzyme helicase. Each separated

guanine will pair up with cytosine. DNA polymerase is the enzyme responsible for this. The new DNA strands then rewind to form a double helix. The replication process

strand now is a template for the new strands.

has produced a new DNA molecule which is

There are many free nucleotides around the replication

Significance of Complementary Base Pairing in the Conservation of the Base Sequence in DNA

strand. Adenine will pair up with thymine and

identical to the initial one.

PAIRING UP

IDENTICAL STRANDS

COMPLEMENTARY

Adenine always pairs up with thymine and guanine always pairs up with cytosine.

This complementary base pairing allows the two DNA molecules to be identical to each other.

The new strands formed are complementary to their template strands but also identical to the other template.

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Translation Translation is the process

These two form a hydrogen

through which proteins are

bond together. Another

synthesized. It uses

transfer RNA molecule then

ribosomes, messenger RNA

bonds. Two transfer RNA

which is composed of codons molecules can bind at once.

Gene

and transfer RNA which has a Then the two amino acids on

RELATIONSHIP BETWEEN ONE GENE AND ONE POLYPEPTIDE

triplet of bases called the

the two transfer RNA

anticodon. The first stage of

molecules form a peptide

A polypeptide is formed by amino acids liking together through peptide bonds. There are 20 different amino acids so a wide range of polypeptides are possible. Genes store the information required for making polypeptides. The information is stored in a coded form by the use of triplets of bases which form codons. The sequence of bases in a gene codes for the sequence of amino acids in a polypeptide. The information in the genes is decoded during transcription and translation leading to protein synthesis.

translation is the binding of

bond. The first transfer RNA

messenger RNA to the small

then detaches from the

subunit of the ribosome. The

ribosome and the second one

transfer RNA’s have a specific takes it’s place.The ribosome amino acid attached to them

moves along the messenger

which corresponds to their

RNA to the next codon so that

anticodons. A transfer RNA

another transfer RNA can

molecule will bind to the

bind. Again, a peptide bond is

ribosome however it’s

formed between the amino

anticodon must match the

acids and this process

codon on the messenger

continues. This forms a

RNA. This is done through

polypeptide chain and is the

complementary base pairing.

basis of protein synthesis.

Polypeptide

Translate a Gene here! [3]


Transcription DNA

Composed of a double helix. Contain cytosine, adenine, guanine and thymine.

RNA

Consist of nucleotides which contain a sugar, a base and a phosphate group

Composed of one strand. Contains uracil, adenine, guanine and cytosine.

DNA transcription is the formation of an RNA strand which is complementary to the DNA strand. The first stage of transcription is the uncoiling of the DNA double helix. Then, the free RNA nucleotides start to form an RNA strand by using one of the DNA strands as a template. This is done through complementary base pairing, however in the RNA chain, the base thymine is replaced by uracil. RNA polymerase is the enzyme involved in the formation of the RNA strand and the uncoiling of the double helix.

View a video of Transcription here!

The RNA strand then elongates and then separates from the DNA template. The DNA strands then reform a double helix. The strand of RNA formed is called messenger RNA.

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The Genetic Code A triplet of bases (3 bases) forms a codon. Each codon codes for a particular amino acid. Amino acids in turn link to form proteins. Therefore DNA and RNA regulate protein synthesis. The genetic code is the codons within DNA and RNA, composed of triplets of bases which eventually lead to protein synthesis.

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