proteins

Question 1

amino acids

Answer 1

monomers from which proteins are made
NH2 - amine group
COOH - carboxyl group
R - side chain
- 20 amino acids that are common in all organisms differ only in side group

        R H2N - C - COOH
      H

Question 2

bond - proteins

Answer 2

a condensation reaction between two amino acids forms a peptide bond

dipeptides - two amino acids
polypeptides - many amino acids

Question 3

functional protein

Answer 3

may contain one or more polypeptides

Question 4

R groups

Answer 4

side chain

some are polar while others non-polar

Question 5

hydrolysis of proteins

Answer 5

proteins are digested by breaking the peptide bond and adding water across the bond by the protease enzymes

Question 6

primary structure

Answer 6

the order or sequence of amino acids in a polypeptide joined together by peptide bonds

this is determined/coded by the DNA base sequence

determined by sequence of codons on mRNA

Question 7

secondary structure

Answer 7

the polypeptide is folded into alpha-helices or beta-pleated-sheets

forming hydrogen bonds in the amino acid backbone

alpha - all N-H bonds on same side of protein chain
- spiral shape
- H-bonds parallel to helical axis

beta - N-H and C=O groups alternate from one side to another

Question 8

tertiary structure

Answer 8

further holding of alpha-helices and beta-pleated sheets into a complex 3D shape/structure by forming 3 types of bonds between R-groups

H-bonds (weakest)
Ionic bonds (weak)
- both can be broken by high temp or change in pH causing denaturing
- disulphide bonds (covalent - strong)

Question 9

quaternary structure

Answer 9

2 or more polypeptides are folded together using the same bonds as in tertiary structure

contain a prosthetic group - non-protein molecule attached to a protein molecule eg haeme group in haemoglobin

Question 10

collagen

Answer 10

• 3 identical polypeptide chains
• 3 chains are twisted around each other to form a triple helix
• no prosthetic group
• insoluble in water
• connective tissue eg tendons

Question 11

haemoglobin

Answer 11

• 4 polypeptide chains
• form a globular protein showing 3 and 4 str
• contains haeme prosthetic group which contains an Fe2+ ion
• wide range of amino acids used
• soluble in water
• transport of oxygen in red blood cells

Question 12

test for proteins

Answer 12

biuret test

• add biuret solution/reagent to the sample and mix
• if protein is present, colour changes from blue to purple/lilac

Question 13

functions of proteins

Answer 13

1. Fibrous proteins have a structural role. eg. Keratin in nails and hair; Collagen in connective tissue
   
   2. Enzymes: eg. amylase, trypsin etc
   3. Protein hormones: eg. Insulin
   4. Receptor proteins on cell membrane: eg. Insulin receptor, receptors for neurotransmitters on neurones
   5. Antibodies: immunoglobulins to bind to antigens
   6. Channel proteins: transport polar substances across membranes by FD
   7. Carrier proteins: transport polar substances across membranes by FD and AT
   8. Glycoproteins: on cell membrane for cell-cell signalling
   9. Motor proteins: eg. myosin and actin in muscle
   10. Capsid proteins in viruses
   11. Proteins used to transport specific molecules around the body: eg. Haemoglobin in red blood cells to transport oxygen around the body
   12. Proteins can be deaminated, and the remaining keto acid can be used as an energy source in respiration
   13. DNA-binding proteins for gene regulation: to switch on or off specific genes
   14. Buffer protein in blood: albumen
   15. Blood clotting protein: fibrinogen (globular protein) is converted to fibrin (fibrous protein) to form a clot

Question 14

proteins

Answer 14

form many cell structures

also important as enzymes, chemical messengers and components for the blood

Question 15

dipeptide

Answer 15

formed by the condensation of two amino acids

Question 16

polypeptide

Answer 16

formed by the condensation of many amino acids

Question 17

how do amino acids differ from one another

Answer 17

20 amino acids - differ only by side ‘R’ group

Question 18

describe types of bond in tertiary structure

Answer 18

disulfide bridges - strong covalent S - S bonds between molecules of the amino acid cysteine

ionic bonds - relatively strong bonds between charged R groups - pH changes cause these bonds to break

hydrogen bonds - numerous and easily broken

Question 19

structure and function of globular proteins

Answer 19

spherical and compact

hydrophilic R groups face outwards and hydrophobic R groups face inwards = usually water-soluble

involved in metabolic processes eg enzymes and haemoglobin

Question 20

structure and function of fibrous proteins

Answer 20

can form long chains or fibres

insoluble in water

useful for structure and support eg collagen in skin

Question 21

outline how chromatography could be used to identify amino acids in a mixture

Answer 21

use capillary tube to spot mixture onto pencil origin line and place chromatography paper in solvent

allow solvent to run until it almost touches other end of paper

amino acids move different distances based on relative attraction to paper and solubility in solvent

use revealing agent or UV light to see spots

calculate Rf values and match to database