B5 - DNA

DNA

A DNA molecule has two strands coiled together in the shape of a DOUBLE HELIX (Two spirals)

Each strand is made up of lots of small units calls nucleotides

Each nucleotide contains a small molecule called a BASE . DNA has 4 bases:

• Adenine (A)
• Cytosine (C)
• Gunanine (G)
• Thymine (T)

The bases always pair up the same = BASE PAIRING

A-T             C-G

Gene = Section of DNA that contains the instructions for one particluar protein

Cells make proteins by joining amino acids together in a particular order .

Its the order of bases in a gene that tells the cell in what order to put the amino acids together

Each set of three bases (a triplet) codes for one amino acid

Ribosomes = Organelles that make proteins in the cytoplasm

DNA is found in the cell nucleus and can't move out because it's really big so to get the information from the DNA to the ribsosme , a copy of the DNA is made using 'mRNA'.

mRNA = Very similar to DNA but it's much shorter and is only a single strand:

• 1. The two DNA strands unzip. A molecule of mRNA is made using ONE strand of the DNA as a template. The base pairings ensure it is an exact match.
• 2. The mRNA molecule moves out of the nucleus and joins with the ribosome in the cytoplasm
• 3. The job of the ribosome is to stick amino acids together in a chain to make a PROTEIN, folowing the order of bases in the mRNA