Protein Synthesis II

Discussed in protein synthesis I

A gene is a sequence of DNA nucleotides.
Each nucleotide has one of four bases (A, T, C, G). So, a gene will contain a particular sequence of bases.
- This sequence instructs the cell to make a particular protein.
Proteins are made up of amino acids linked together by peptide bonds.
What determines the type of protein formed is the type and sequence of the amino acids that are joined together.
- As mentioned before, the sequence of bases in a gene determines the sequence of amino acids used to make a specific protein.
Each base triplet codes for one particular amino acid.

The basic structure of a protein is the sequence of amino acids in the chain.
- It determines the eventual shape of the protein and hence its function.
There are 20 different amino acids and all their different combinations can build the 100,000 known proteins.
- It is important to be aware that proteins are three dimensional structures instead of amino acid chains lying flat. They form of helices, which twist and fold around themselves.
The result is a complex 3D structure held together by a number of different chemical bonds. This structure gives the protein its function.
The only genes that are expressed are those that code for the proteins that each cell needs to function correctly.
- Most body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific protein it needs.

DNA controls cell function by controlling the production of proteins, including enzymes, membrane carriers, and receptors for neurotransmitters.

Enzymes control the chemical reactions that take place in a cell. All enzymes are proteins. So:
- the genetic code of DNA, by determining which proteins (particularly enzymes) are made in the cell, will determine the cell’s structure and function.
The 3D shape of an enzyme is critical to its function.
Remember that the active site on the surface of the enzyme has a complementary shape to the enzyme’s substrate. This is important because it gives the enzyme its specificity.

Antibodies are proteins that are made by white blood cells called lymphocytes.
Each antibody has a binding site that can attach to pathogens like bacteria.
- This either directly destroys the pathogen or labels it in a way that can be detected by other white blood cells called phagocytes.
Each pathogen has antigens on its surface that have a particular shape, so only specific antibodies, with a complementary shape can attach to a particular antigen.

Membrane carriers are proteins that control the movement of water-soluble ions and certain molecules across the cell membrane.
They are able to maintain different concentrations of ions on either side of the cell membrane.

Receptors for neurotransmitters are proteins found in the membrane at the synapses between neurones.
They have a complementary structure to the transmitter molecules, which attach to them and enable an impulse to pass across the synapse.