PROTEINS C, H, O, N, (S) Polymers made from chains of amino acids 20 amino acids used Linked by a...
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Transcript of PROTEINS C, H, O, N, (S) Polymers made from chains of amino acids 20 amino acids used Linked by a...
![Page 1: PROTEINS C, H, O, N, (S) Polymers made from chains of amino acids 20 amino acids used Linked by a peptide bond.](https://reader036.fdocuments.us/reader036/viewer/2022062519/56649ef45503460f94c07583/html5/thumbnails/1.jpg)
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PROTEINS
• C, H, O, N, (S)
• Polymers made from chains of amino acids
• 20 amino acids used
• Linked by a peptide bond
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In addition fibrous proteins (collagen) form structural components in cells and tissues
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Amino Acids
• Central carbon has attached:– Amine group– Acid group– Functional group (R) – determines nature of amino acid
• R groups fall into 4 categories• Non-polar - only carbons; chains or aromatic rings
(methionine has sulphur)• Uncharged Polar- carbons with amine groups (NH2) or
- hydroxyl groups (OH)• Acidic - carboxylic acid groups (COOH) ionizes to negative
charge COO-
• Basic - terminal amine groups (not next to C=O) ionizes to NH3
+
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Peptide bond
• Amino acids joined by a peptide bond
• Condensation reaction between – COOH of 1st amino acid and NH2 of 2nd amino
acid•Chains are called peptides (short)/ polypeptides (longer)•Peptide bond is rigid•Bonds either side can rotate
–Introduces flexibility allowing proteins to take up variety of shapes.
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Protein Structure
• 4 levels– Primary– Secondary– Tertiary– Quaternary
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PRIMARY STRUCTURE
• Order in which amino acids are linked together– Written starting at the N (amino) terminus– e.g.
– Arg-Lys-Phe-Glu-Ser-Gly-
– R K F E S G
N C
N terminus
C terminus
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SECONDARY STRUCTURE
• Two possible shapes in the protein chain each stabilised by Hydrogen bonds: -pleated sheet -helix
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-pleated sheet
• Peptide chains arranged side by side• Held together by H-bonds between the two chains• Parallel (chains running same direction)
• N C
• N C
• Antiparallel (chains in opposite directions)• N C
• C N
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-pleated sheet
• Silk– Resistant to stretch (very strong)
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-helix
• Peptide chain coils into a helix– Held by H-bond between N-H group and the
C=O 4 residue away
• 4 residues per turn
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-helix• Hair/Wool (keratin)
– Stretchy (er) -helices coiled together to form a superhelix
– For horn/hoof more disulphide bridges are present (covalent)
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Tertiary Structure
• The overall folded shape of a protein held together by (usually) weak forces.– Hydrogen bonding which doesn’t form secondary
structure– Hydrophobic interactions
• Place non-polar amino acids inside protein• Polar amino acids on surface
– Van der Waals forces– Ionic interactions (strong) – Disulphide bridges (strong)
• Covalent bond between cysteine residuesMyoglobin
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• With reference to bonding, explain why enzyme activity decreases as you increase the temperature above the optimum, and as you move pH away from the optimum.
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Proteins fold to take up their shape
Shape is determined by primary structure –
order of hydrophobic/ hydrophilic amino acids & relative positions of polar/charged amino acids.
Loss of tertiary structure is called denaturation.
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Lysozyme
Proteins are 3D
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Primary structure determines tertiary structure
Mutation acid (polar) for non polar changes folding pattern
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Prosthetic groups• Some proteins have permanently bound non
protein groups, called prosthetic groups– e.g. myoglobin & haemoglobin bind to a porphyrin
(haem) chelating an Iron atom– e.g. Chlorophyll has a similar prosthetic group
chelating Mg
• The protein without its prosthetic group is called an apoprotein, with its group it is called a holoprotein
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Co-factors/ Co-enzymes
• Other proteins have inorganic ions temporarily bound to them– E.g. copper/ zinc on enzymes
• Others have carbon containing molecules temporarily attached– e.g. Coenzyme A, NAD, FAD
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Quaternary Structure
• Only present if protein has more than one polypeptide chain
• Describes the shape adopted by the interacting polypeptide chains
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Nucleic Acids
• DNA– Deoxyribonucleic Acid
• RNA– Ribonucleic Acid
• Video
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Nucleic Acids
• Summary Knowledge– DNA deoxyribose sugar,– RNA ribose sugar– DNA double stranded (antiparallel)– RNA single stranded– DNA thymine,– RNA uracil– A double (hydrogen) bonds to T (A 2 T)– G triple (hydrogen) bonds to C (G 3 C)– G & A purines (small word, big molecule –A Giant)– C,T & U pyrimidines (big word, small molecule)
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