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25 Cards in this Set
- Front
- Back
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PROTEIN FUNCTIONS |
- Structural support - Protection - Catalysis transport - Defence - Movement |
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SIZE |
Variable between 5-500 kDa |
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FORMATION OF PEPTIDE BONDS |
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N-TERMINUS AND C-TERMINUS |
- N-terminus: The end of the polypeptide with a free amine group.
- C-terminus: The end of the polypeptide with a free carboxyl group. |
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PRIMARY PROTEIN STRUCTURE [2] |
- Amino acid sequence - Only takes one amino acid difference in the sequence to cause problems. Ie: normal haemoglobin beta chain and sickle cell haemoglobin beta chain. |
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SECONDARY PROTEIN STRUCTURE [3] |
- Regular repeated folding patterns in the polypeptide chain. - Stabilised by hydrogen bonding (amine and carboxyl groups) between amino acids brought into close proximity. - Alpha helix or Beta pleated sheet. |
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ALPHA HELIX; [3] |
- Hydrogen bonding between carboxyl oxygen and amine hydrogen. - 3.6 amino acid residues per turn. - Amino acid residues on the outside of the helix. |
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BETA PLEATED SHEET; [2] |
- Parallel: Both polypeptide chains start with the same group (carboxyl-carboxyl, amine-amine) - Antiparallel: Both polypeptide chains start with different group (carboxyl and amine) |
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TERTIARY STRUCTURE [2] |
- 3D structure resulting from folding of polypeptide chain due to interactions between R groups of amino acids. - Which may be linearly distant but brought into close proximity by folding. |
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FORCES STABILISING TERTIARY STRUCTURE [3] |
- Covalent: Disulfide bridges - Apolar: Hydrophobic - Polar: Hydrogen bonding - Ionic: Electrostatic |
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CHAPERONES/CHAPERONINS [4] |
2 classes of proteins which assist in correct folding of newly synthesised (nascent) polypeptides. both require ATP energy.
- Chaperones: Bind to unfolded protein and assist its folding - Chaperonins: Form a cage around the protein allowing it to fold correctly |
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DENATURATION [2] |
-Changes in environment: heat, salt concentration, pH disrupt weak non-covalent interactions and destabilise tertiary structure resulting in loss of biological function
- Usually irreversible |
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QUATERNARY PROTEIN STRUCTURE [3] |
- Protein structure resulting from interactions between individual polypeptide subunits (protomers) of an oglimeric protein.
- Homogenous: with identical subunits (phosphorylase) - Heterogenous: with differing subunits (haemoglobin) |
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HIV PROTEASE [3] |
- Enzyme produced by virus - Dimer of 2 identical proteins, held together by interacting anti-parallel beta sheets - Active site consists of a carboxylic acid group from single aspartate residues from each peptide providing acid catalysed hydrolysis of peptide bonds in viral proteins, that require processing to make the virus active. |
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REGULATION OF PROTEIN ACTIVITY [3] |
Most common mechanism of switching on and off biological processes regulating protein activity is the phosphorylation of specific amino acid residues (most commonly serine, threonine or tyrosine) in the protein. Catalysed by kinase enzymes. |
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MECHANISM OF PROTEIN KINASES; [3] |
- Kinase binds ATP and protein at the active site. - Transferring gamma-phosphate to relevant amino acid - Phosphorylated protein and ADP then released.
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PROTEIN KINASE STRUCTURE; [2] |
- 2 lobes (one mainly beta pleated sheet one mainly alpha helix) - Cleft in the middle provides active site |
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PROTEIN KINASE SPECIFICITY; [2] |
- Different kinases for different groups of proteins. - Different specificities due partly to difference in charge and hydrophobicity of surface residues. |
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SERINE/THREONINE KINASES; [3] |
- CDK2: Cyclin dependent kinase 2 - PKA: Protein Kinase A - PHK: Phosphorylase Kinase |
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TYROSINE KINASE: |
IRK - Kinase domain of insulin receptor |
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CONTROL OF PROTEIN ACTIVITY DUE TO PHOSPHORYLATION; [4] |
- Active proteins (usually phosphorylated - Kinases) - Inactive proteins (usually dephosphorylated - Phosphatase) - Change in conformation on phosphorylation is due to negative charge of phosphate group interacting with other charges in amino acids in the protein (eg: charge repulsion) leading to a change in shape (active site changes). |
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GLYCOGEN PHOSPHORYLASE; [3] |
- Enzyme that breaks down glycogen - Dimer of 2 identical subunits - Regulated by phosphorylation of Serine 14 (ringed) - leads to a change from inactive T (tense) confomation where catalytic site is buried away to an R (relaxed) conformation which has a much more open catalytic site |
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MYOGLOBIN |
- Protein with a prosthetic group - 1st ever protein whose 3D structure was determined - Monomeric - single polypeptide chain (153 aa) - Oxygen storage and release in muscle - Haem prosthetic group buried in hydrophobic interior - Oxygen binds to Fe2+ ion in the haem - Typical saturation curve (increasing then levels off) with a high affinity for oxygen |
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HAEMOGLOBIN |
- Oxygen storage and release in blood - Composed of 4 monomeric proteins (2 alpha, 2 beta) similar to myoglobin and haem to bind to oxygen - Allosteric proteins: when one oxygen binds affinity at other binding sites increases and as each molecule dissociates it becomes easier for other molecules to dissociate. Giving a sigmoidal curve (S-shape) |
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ALLOSTERIC PROTEIN |
- Several binding site (binding at one affects binding at the others increasing or decreasing affinity constant of other sites)
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