Proteins Ial Edexcel Unit 1 1n716v

Mahmoud AbuAlSamen

Addendum (2) to 1A:5 Proteins 1. Primary structure of proteins: linear sequence of amino acids ed together by peptide bonds in a polypeptide chain 2. Secondary structure of proteins: further folding of the polypeptide chain to alpha helix and beta pleated sheets bonded by hydrogen bonds between COO- and NH3+

3. Tertiary structure of proteins: further folding forming a 3D shape held by different bonds: 1. Hydrogen bonds (between amine and carboxyl groups) 2. Covalent bonds (disulfide bridges S-S) 3. Ionic bonds (between oppositely charged ions of the R-groups) 4. Polar interactions (hydrophilic groups arrange themselves on the outside of the protein while those that are hydrophobic arrange themselves on the inside) 5. Hydrophobic interactions 4. Quaternary structure of proteins: two or more polypeptide chains held together by hydrogen bonds in place (e.g: Haemoglobin)

Mahmoud AbuAlSamen

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Mahmoud AbuAlSamen 20 Amino Acids:

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Mahmoud AbuAlSamen Practice Question

How does the primary structure of a protein determine its tertiary structure? Primary structure determines 3D folding Types of amino acids determine the type of the bonds Position of amino acids determine the type of bonds Eg: Cys formed between two S-S (disulfide bridge) Bonds in primary and secondary determine tertiary (H-bonding, ionic bonds and polar interactions) Tertiary determines shape and structure of proteins and hence their shapes and functions

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Mahmoud AbuAlSamen Describe how does the primary structure determine the secondary structure of a protein? 1. Primary is the linear sequence of amino acids ed by peptide bond in a polypeptide chain. + 2. Hydrogen bonds arise between COO and NH3 3. Between amino and carboxyl terminals 4. Causing folding of the polypeptide chains into alpha helix and beta pleated sheets

Explain how the primary structure determines the tertiary structure of a protein /enzyme and its properties. 1. Primary structure is a sequence of amino acids 2. The primary structure determines the positioning and the type of the bonds and folding 3. Mention examples on bonds: disulfide bond (Cys-Cys), hydrogen, ionic bonds, hydrophobic interactions, (between R groups) 4. for globular (soluble) 5. Hydrophilic R groups on the outside of enzymes and hydrophobic R groups on the inside  soluble (globular) 5. Determining the shape and structure of the active site 6. Determining its specificity (for enzymes)

Examples on Globular proteins (soluble): Enzymes, membrane proteins, antibiotics and oxygen transport pigments (haemoglobin etc..) Fibrous proteins tend to be stable Examples on fibrous proteins (insoluble): Keratin (skin and nails), collagen in skin. Globular proteins tend to be metabolically active.

Mahmoud AbuAlSamen

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