1. Processes SL
2.4, 2.6, 2.7

2. 2.4: Proteins

3. Polypeptides Chains of amino acids joined together by peptide bonds
Result of condensation reactions (also know as translation).
How many amino acids are in a dipeptide?
30 seconds – what do you know about polypeptides?
Polypeptide = many amino acids
Oligopeptide = less than 20 amino acids

4. Contains two polypeptide chains
Human insulin
Contains two polypeptide chains -
Insulin is a small protein, one chain has 21 amino acids, the other has 30.

5. Titin One of the largest polypeptides found so far Found in muscles
Contains 34, 350 amino acids in humans.
In mice there are 35, 213 amino acids!

6. R-groups You do not need to memorise the different R-groups.
BUT, you do need to know that amino acids vary due to the R-group.
There are 20 different amino acids, and they can be categorised based on the R-group. Pg. 89, table 1.
Although there are only 20 amino acids, they can be modified. E.g collagen can be modified to be more stable by exchanging proline for hydroxyproline.

7. Patterns, trends & discrepancies…
Most organisms on Earth use the same 20 amino acids to form proteins.
Theories as to why include:
These 20 amino acids were the ones produced when life first developed.
Natural selection: these are the most favourable amino acids for making proteins.
Common ancestry
Not all species use the same 20 amino acids, there are of course some exceptions to this rule.
Why do you think this happened?

8. Diversity
A dipeptide contains two amino acids. These can be any combination of the 20.
A ribosome can link any of the amino acids. Therefore the possibilities can be calculated by:
20n (n = number of amino acids in a polypeptide
Number of amino acids
Number of possible amino acids sequences 1
201 20 2
202
400 3
203
8,000 4
204
160,000

9. The ‘open reading frame’
This is the section of a DNA strand containing genes which code for a polypeptide.
Each amino acid is coded for by 3 bases
Therefore, in theory, a polypeptide with 400 amino acids would require a gene with a base sequence of 1,200 bases.
The open reading frame is only a small part of the total DNA code.

10. Lysozyme
1 polypeptide
Nasal mucus, tears. Kills bacteria by digesting the substance in the cell wall.

11. Integrin
Two polypeptides
Membrane protein

12. Collagen Three polypeptides
Structural protein (tendons, ligaments, skin & blood vessels)
High strength, limited stretch.

13. Haemoglobin
Four polypeptides
Oxygen binding protein in RBC.

14. The Conformation of proteins
Polypeptides do not remain in long chains. Attractions/bonding between the R-groups can lead to four basic structures.
Conformation is another term for 3D structure

15. Functions Catalysis (enzymes to catalyse reactions)
Immunity (antibodies)
Muscle contraction
DNA packing
Cytosketeton (structure within membrane)
Recepetors (binding sites on membrane)
Tensile strengthening (fibrous proteins in skin)
Hormones (insulin, FSH etc.)
Blood clotting
Membrane transport
Transport (including nutrients & gas)
Cell adhesion
How many functions of proteins can you think of? 12!
HWK: Write a short report (no more than 1000 words) explaining the biotechnological applications of proteins e.g. stain removers.

16. Examples to know Rubisco Insulin Immunoglobulin Rhodopsin Collagen
Spider silk
Research, prepare notes and present to the class.

17. Proteomes
The total of all the proteins produced by a cell, a tissue or an organism.
Gel electrophoresis is used to identify the proteins in a sample – florescent markers are attached to antibodies for specific proteins.
Proteomes vary, because different cells produce different proteins. The proteome for each individual is unique.

18. Assessment
Design an experiment to investigate the effect of either temperature or pH on egg albumin.
You will conduct this experiment next lesson. You will be assessed on your data collection & processing skills ONLY.