Proteins (AQA AS Level)
Summary of all information in the Nelson Thornes AQA guide for AS Level Biology. Any boxes with a pencil icon inside are for displayed formulas (if the mindmap was to be printed out).
- Created by: Honoria
- Created on: 18-11-13 11:44
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- Proteins
- Most important molecules required for life.
- Structural proteins
- Fibrous proteins
- Collagen
- 3 individual polypeptide chains wound together line fibres in a rope, and linked with cross bridges.
- Strong
- Found in tendons - usded to move bones.
- Points where polypeptides end and beginn are distributed throughout fibre so that there are no specific weak points.
- 3 individual polypeptide chains wound together line fibres in a rope, and linked with cross bridges.
- Collagen
- Fibrous proteins
- Globular proteins
- Enzymes - involved in almost every living process.
- Carry out metabolic functions.
- Transport proteins
- Allow essential molecules/ions to move into/out of cells.
- Structural proteins
- Monomers - amino acids
- About 100 types of amino acid - 20 naturally occuring
- Combine in condensation reactions, where a molecule of water is released and a peptide bond is formed.
- Two combined amino acids: a dipeptide.
- More than 2 combined amino acids - a polypeptide.
- The peptide bond if formed between the -C from the carboxyl group and the -N from the amino group.
- The -OH from the carboxyl group and a -H from the amino group combine to make the molecule of water.
- Products
- Dipeptide + water
- Products
- Reactants
- Amino Acids
- CONDENSATION REACTION
- A peptide bond can be broken down by hydrolysis, involving the addition of a water molecule.
- Poly/dipeptide + water => amino acids
- Amino group - NH2
- Carboxyl group -COOH (acidic)
- Variable R group - a variety of different chemical groups.
- STRUCTURE OF AN AMINO ACID
- Primary Structure
- Sequence of amino acids - the combination will be specific to the function of the protein.
- Determines the protein's shape, as this depends on the bonds that will later be formed between certain amino acids.
- Sequence of amino acids - the combination will be specific to the function of the protein.
- Secondary Structure
- Hydrogen bonds form between the positively-charged H of the -NH group, and the negatively-charged O of the -C=O group.
- Causes the polypeptide chain to coil into an alpha-helix (or fold inot a beta-pleated sheet).
- 3D
- Causes the polypeptide chain to coil into an alpha-helix (or fold inot a beta-pleated sheet).
- Hydrogen bonds form between the positively-charged H of the -NH group, and the negatively-charged O of the -C=O group.
- Tertiary Structure
- The polypeptide chain is coiled (or folded) even more to produce the complex, unique shape of the protein.
- This structure is maintained by various bonds:
- Disulfide bonds (fairly strong)
- Ionic bonds between the carboxyl and amino groups not involved in froming peptide bonds.
- Weaker than disulfide bonds and easily broken down by changes in pH.
- Hydrogen bonds
- Numerous, but weak.
- 3D - shape allows to recognise/be recognised by other molecules + interact. Final structure for some proteins.
- This structure is maintained by various bonds:
- The polypeptide chain is coiled (or folded) even more to produce the complex, unique shape of the protein.
- Quaternary Structure
- Multiple polypeptide chains (in the tertiary structure) linkled together by bonds.
- Often include non-protein groups (prosthetic groups).
- Large proteins - complex molecules.
- Multiple polypeptide chains (in the tertiary structure) linkled together by bonds.
- BIURET TEST
- Test for proteins
- Add equal volume of sodium hydroxide to the sample in a test tube.
- Add few drops of copper(II) sulfate solution (0.05% concentration) and mix gently.
- Purple colouration indicates presence of PEPTIDE BONDS.
- If solution remains blue, no PEPTIDE BONDS present.
- Add few drops of copper(II) sulfate solution (0.05% concentration) and mix gently.
- Most important molecules required for life.
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