Biology - AS Level - 10.1 - Biological Molecules - .2 - Proteins (copy)
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- 3 Structural proteins and their functions:
-
collagen (bone, cartilage, tendon)
keratin (hair, nails, rhino horn)
actin (muscle) - Enzymes:
- pepsin, amylase, carbohydrase, bromilase, protease, lipase (+>10 000 others)
- Transport (2):
- haemoglobin (oxygen), transferrin (iron)
- Pumps:
- EG Na+ K+ pump in cell membranes
- Motors (2):
- eg. myosin (muscle), kinesin (cilia)
- Hormones (8):
- estrogen, testosterone, LH, FSH, ADH, glucagon, insulin.
- Receptors:
- Rhodopsin (light receptor in retina)
- Antibodies:
- eg immunoglobulins
- Storage (2):
- eg albumins (egg white pure) in eggs and blood, caesin in milk
- Blood clotting (2):
- eg thrombin, fibrin
- Lubrication:
- glycoproteins in synovial fluid.
- Toxins:
- (organic poisons) e.g. diptheria toxin
- antifreeze:
- e.g. glycoproteins in arctic flea
- glycoprotein:
- type of protein with CH chain - antenna - sensor
- All proteins contain 4 elements:
- nitrogen, oxygen, carbon and hydrogen.
- amino acids are:
- the basic units (monomers) of proteins
- basic structure of an amino acid:
-
NCC spine
2 Hs bonded to N
R above and H below middleC
x2bondto O above right C and bond to OH below
OR
H2N, C, COOH, R above and H below middle C - NH2 group is the...
- amino group (in chemistry, the naming group)
- COOH group is the...
- carboxyl group
- R group...
- varies between different amino acids. 20 R groups so 20 different amino acids.
- Glycine structure:
- H for R group.
- 7 R groups:
- Simple (5), Basic (5), hydroxyl (2, end with OH), acidic (2, end with C bonded to O and x2 bonded to O- (extra proton)), sulphur (2, contain sulphur), ringed (3, all ringed but not only ringed amino acids) and cyclic (proline).
- What bond joins two amino acids together?
- Peptide bond. OH from bottom right of left mol and H from bottom left of right mol make water, C and N bond. The line between is peptide bond (glycosidic is when oxygen is left behind). NCCNCC is the pattern for di and poly spines.
- Primary Protein structure:
- 1. Final configuration depends on the primary struct. - The Primary Structure is the number, type and sequence of amino acids in the chain. There are specific interations between different parts of the chain which give a final 3-dimensional shape of the protein.
- Secondary Protein Structure:
-
H-bonds form between a.a.s in the cahin. Between O atoms of the COOH group (delta-) and Hs of the NH2 groups (delta+). When the groups are v close together they attract. This folds or coils the chain giving rise to the 2ndary structure. 2nd structs include the alpha-helix and the beta-pleated sheet.
Due to backbone interactions and is thus largely independant of primary sequence. - Tertiary Protein Structure:
-
2ndary structure may then fold and coil forming the 3ry structure. This is held in a specific 3-d shape by electrostatic interaction (between rs with quite strong +/- charges) and disulphide bridges (covalent S-S bonds between 2 cysteine amino acids, which are strong).
Due to side chain interactions - thus depends on the amino acid sequence. - Quaternary protein structure:
- Found in prots containing more than one polypeptide chain - simply means how the different polypeptide chains are arranged together. Individual chains are usually globular, but can arrange themselves into a variety of 4ry structs eg haemoglobin, immunoglobulins, actin and tubulin.
- Haemoglobin structure:
- 4 globular subunits arranged in a tetrahedral structure. Each sub contains one FE atom and can bind 1 O2 mol.
- Immunoglobulin structure:
- Proteins that make antibodies. 4 polypep chains in a y-shape. Held together via sulphide bridges. This shape allows antibodies to link antigens together, causing them to clump.
- Actin structure:
- One of prots found in muscles. Consists of many globular subunits arranged in a 2 helix to form long filaments.
- Tubulin structure:
- globular prot that polymerises to form hollow tubes called microtubules. These form part of the cytoskeleton and make cilia and flagella move.
- Fibrous proteins:
- Long chains of aas which are folded into a helix. Sometimes can be several polypep chains together. Can join to form long fibres. Insoluble (ext. R-groups are non-polar.) Provide strenght and flexibility - structural. Eg. keratin, collagen.
- Keratin:
-
Keratin alpha-helix is basically a secondary structure. Microfibril (1 mol k is made of 3 a-helices). Hair fibre, macrofibril, microfibril.
Hair made up of many keratin molecules which form fibers. - Protein test:
- To test for protein in solution add Biuret reagent (alkaline copper sulphate). If protein is present the solution turns purple.
- What causes the 2ndary strucutre to differ in length from the primary?
- H bonds form between O atoms of Cooh groups and H atoms of NH2 groups, causing the chain to fold or coil.
- Explain what is meant by the tertiary structure of a protein?
- The way in which the whole molecule is folded or the way it forms a globular shape.
- Heating may affect the tertiary structure of a protein. Explain why.
- It causes the bonds which hold the tertiary structure together to break. The shape is no longer maintained / The protein is denatured.
- What is meant by a receptor molecule?
- A molecule in which another molecule can fit
- Explain how it's tertiary structure might allow a protein molecule to act as a receptor molecule
- The tertiary strucutre gives the receptor a particular shape, which provides the site into which another molecule can fit.
- Why electron can see protein but not light.
- The fibrils are thin / close together. The electron has a greater resolution than a alight microscope.
- Hydrolysis of protein -
- into amino acids. The reaction involves the addition of water.
- Suggest how a change in the structure of a protein could make it resistant to the action of protein - digesting enzymes.
- A change in the secondary structure would change the shape of the PrP molecule. No longer fits the active site of the enzyme.
- Biuret test in detial:
- Add 10 drops of each Biuret reagent (A and B) to a small sample of the protein. Shake the mixture. If it turns lilac protein is present.
- Amino acid structure:
- NCC, two Hbonds N, RaboveHbelow middle C, C 2bondO bondOH