1.8 — proteins: amino acids

Question 1

what are proteins made up of?

Answer 1

amino acids

Question 2

what are proteins?

Answer 2

essential macromolecules which are involved in various functions within living organisms

Question 3

what bonds join amino acids together?

Answer 3

peptide bonds

Question 4

what is an amino acid dimer called?

Answer 4

a dipeptide

Question 5

what is an amino acid polymer called?

Answer 5

a polypeptide

Question 6

what are the functions of proteins in living organisms? (6)

Answer 6

1. enzymes — used to breakdown and synthesise molecules
2. antibodies — involved in immune response
3. transport — move molecule or ions across membranes
4. structural components — proteins like keratin are used to create strong fibres
5. hormones — some are proteins that act as chemical messengers in the body
6. muscle contraction — muscles are made of proteins

Question 7

how many amino acids are commonly found in living organisms?

Answer 7

20

Question 8

what is the general structure of an amino acid?

Answer 8

• a central carbon atom
• an amino group (-NH₂)
• a carboxyl group (-COOH)
• a hydrogen atom (-H)
• an R group or a variable side group

Question 9

what does an R group do?

Answer 9

determine the amino acid’s properties

Question 10

what atom does cysteine have in its R group and what bonds does it allow it to form?

Answer 10

cysteine’s R group contains a sulphur atom which allows disulphide bonds to form

Question 11

what bonds form between amino acid monomers after a condensation reaction?

Answer 11

peptide bonds

Question 12

what happens during a condensation reaction?

Answer 12

the hydroxyl (OH) in the carboxyl group of one amino acid reacts with the hydrogen (H) in the amino group of another amino acid. this releases a water molecule (H₂O) and forms a peptide bond between the carbon of one amino acid and the nitrogen of another

Question 13

what are the steps to find out whether a sample contains a protein?

Answer 13

• place food sample into a test tube
• add equal volume of Biuret solution
• if peptide bonds are present (and in turn proteins) the solution will turn from blue to violet and remain blue if not

Question 14

what is Biuret solution made up of?

Answer 14

sodium hydroxide (NaOH) and copper sulphate (CuSO₄)