KEGS Biology Blog

Monday 22nd October Section 1
October 21, 2012, 6:35 pm
Filed under: Uncategorized

Nucleotides and DNA


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Nucleotides are the monomers of all nucleic acids. Each nucleotide is formed by bonding together a phosphate group, a sugar molecule and a nitrogenous base. These are joined by condensation reactions to form a single nucleotide.

DNA – Deoxyribonucleic acid (sugar is deoxyribose) and can contain the bases Adenine, Thymine, Cytosine and Guanine (A-T, C-G are complementary bases)

RNA – Ribonucleic acid (sugar is ribose) and can contain the bases Adenine, Uracil, Cytosine and Guanine (A-U, C-G are complementary bases)

Bases are joined by hydrogen bonds:
A-T has 2 hydrogen bonds
C-G has 3 hydrogen bonds

RNA has an extra oxygen atom compared to DNA and is a single strand compared to DNA which is a double strand (Double Helix)

Purpose of DNA:
> Genetic code for primary sequence of amino acids
> Genetic code details shape of polypeptides
> A gene is a sequence of DNA nucleotides that code for a polypeptide

DNA is synthesised in the nucleus but the organelles needed to make the proteins are in the cytoplasm (outside the nucleus). DNA is a massive molecule and is too large to fit through the pores in the nucleus so RNA is needed as it is smaller. RNA leaves nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein. Ribosome is a small organelle that either floats free in the cytoplasm or is attached to rough endoplasmic reticulum. Proteins are made here.

3 types of RNA : mRNA, rRNA, tRNA

Each amino acid is coded for buy a sequence of three bases in a gene (triplet code)

Comment by charlieshah

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