Nucleic Acids and Cell Division

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  • Created by: Glamour
  • Created on: 24-12-12 12:10

Structure of nucleotide

A nucleotide contains three components :

 - A phosphate group 

 - A pentose sugar

 - An organic nitrogenous base

An organic base comes under one of two different groups :

 - The PYRAMIDINE bases - thymine and cytosine

 - The PURINE bases - adenine and guanine

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DNA Structure

DNA is a double-stranded polymer

The pentose sugar is always deoxyribose

DNA contains four organic bases : adenine, thymine, cytosine and guanine

Pairs of organic bases link each of the strands to the other

The bases are joined by hydrogen bonds 

Adenine pairs with thymine

Guanine pairs with cytosine


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DNA is well suited to carry out its function

DNA is a very stable molecule and can pass from generatio to generation without change

It is a very large molecule and carries a large amount of genetic information

The two strands are able to separate easily because they're held together by weak hydrogen bonds

As the base pairs are held within the deoxyribose-phosphate backbone, the genetic information is protected from outside forces

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RNA structure

RNA is a single-stranded polymer

The pentose sugar is ribose

RNA contains four organic bases :

 - Adenine

 - Guanine

 - Cytosine

 - Uracil (in place of thymine)

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Types of RNA

There are three types of RNA 

All are involved in the process of protein synthesis

They are :

tRNA (transfer RNA) - small, single-stranded molecule which forms the clover-leaf shape, with one end of the chain ending in cytosine-cytosine-adenine sequence at which point the amino acid it carries attaches itself. At the opposite end of the chain is a sequence of three bases called the anticodon. tRNA molecules transport amino acids to the ribosome so that the proteins can be synthesised. 

mRNA (messenger RNA) - long, single-stranded molecule formed into a helix, maunfactured in the nucleus. It carries the genetic code from the DNA to the ribosomes in the cytoplasm

rRNA (ribosomal RNA) - Large complex molecule made up of both single and double helices, found in the cytoplasm. Ribosomes are made up of rRNA. It is the site of translation of the genetic code. 

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DNA -vs- RNA

Pentose sugar :

In DNA - Deoxyribose

In RNA - Ribose

                                                      Helix :

                                                      In DNA - double helix

                                                      In RNA - single helix

 Bases :

In DNA - CGAT

In RNA - CGAU

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