National 5 Biology

DNA and protein synthesis

Deoxyribonucleic acid (_DNA__) is found in the __NUCLEUS___ of a cell. DNA consists of two strands twisted into a double _HELIX__. Each strand is held together by the _COMPLIMENTARY__ base pairing of 4 bases.

The four bases are _ADENINE_, thymine, _CYTOSINE__ and guanine.

Adenine always pairs with __THYMINE____ ; guanine always pairs with _CYTOSINE__.

The bases along a DNA strand take the form of a molecular language called the genetic _CODE__. Each triplet of bases codes for a particular amino acid.

Messenger RNA (mRNA) is copied from a strand of DNA and carries this genetic message from the nucleus out into the cytoplasm. At a _RIBOSOME__ the code on the mRNA is used to ensure the amino acids are joined together in the correct order to produce a _POLYPEPTIDE__ chain.

Wordbank

Adenine Code Cytosine DNA Cytosine Helix Nucleus

Polypeptide Ribosome thymine complimentary

Chromosome

Section of DNA double helix

DNA base

National 5 Biology

Protein Structure Summary

Wordbank

Amino acids antibodies structural haemoglobin

Long polypeptide chains coiled around each other to form fibres

A protein consists of sub-units called amino acids which are joined together to form a polypeptide.

Proteins can have a structural function

Examples are keratin in skin and hair and collagen in bone, tendons and ligaments.

Proteins can be enzymes, hormones and antibodies

Another example of a protein is haemoglobin which is found in red blood cells and transports oxygen.

Non-protein part Globular protein

Oxygen polypepetide