Transcript PROTEINS - Hyndland Secondary School

PROTEINS
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C, H, O, N, (S)
Polymers made from chains of amino acids
20 amino acids used
Linked by a peptide bond
In addition fibrous proteins (collagen) form structural
components in cells and tissues
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+
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.
Protein Structure
• 4 levels
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Primary
Secondary
Tertiary
Quaternary
PRIMARY STRUCTURE
• Order in which amino acids are linked
together
– Written starting at the N (amino) terminus
– e.g.
N – Arg-Lys-Phe-Glu-Ser-Gly- C
– RKFESG
C terminus
N terminus
SECONDARY STRUCTURE
• Two possible shapes in the protein chain
each stabilised by Hydrogen bonds:
– -pleated sheet
– -helix
-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
-pleated sheet
• Silk
– Resistant to stretch (very strong)
-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
-helix
• Hair/Wool (keratin)
– Stretchy (er)
– -helices coiled together to form a superhelix
– For horn/hoof more disulphide bridges are present
(covalent)
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 residues
Myoglobin
• 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.
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.
Proteins are 3D
Lysozyme
Primary structure determines tertiary structure
Mutation acid (polar) for non polar changes folding pattern
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
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
Quaternary Structure
• Only present if protein has more than one
polypeptide chain
• Describes the shape adopted by the
interacting polypeptide chains
Nucleic Acids
• DNA
– Deoxyribonucleic Acid
• RNA
– Ribonucleic Acid
• Video
Nucleic Acids
• Summary Knowledge
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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)