Practise Amino acids. 13 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Two molecules of glycine can join together: 2 H2NCH2COOH → H2NCH2CONHCH2COOH + X Identify substance X.
Water
The –COOH group of a glycine molecule reacts with the –NH2 group of an alanine molecule to form a dipeptide. Write the structure of the dipeptide.
H2N–CH2–CO–NH–CH(CH3)–COOH
Calculate the number of water molecules released when this chain formed.
59
Amino acids are the monomers used to make proteins. Name the two functional groups in an amino acid molecule.
amine group and carboxylic acid group
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Amino acids are the monomers used to make proteins.
(a) Which formula shows an amino acid? Tick (✓) one box.[1]
CH3COOH
H2NCH2COOH
C2H5OH
C2H4
(b) Name the two functional groups in an amino acid molecule.[2]
(c) Many amino acid molecules join together to form a long chain. Name this type of polymer.[1]
Show the answer and mark scheme
(a)Answer: H2NCH2COOH
(b)Answer: amine group and carboxylic acid group
amine (group) / –NH2
carboxylic acid (group) / –COOH
(c)Answer: polypeptide
polypeptide / protein
Question 2Medium5 marks
Two molecules of glycine can join together: 2 H2NCH2COOH → H2NCH2CONHCH2COOH + X
(a) Identify substance X.[1]
(b) Calculate the relative formula masses of glycine and of H2NCH2CONHCH2COOH. Relative atomic masses (Ar): H = 1 C = 12 N = 14 O = 16[2]
(c) Explain why glycine can form a long polymer chain but ethanoic acid, CH3COOH, cannot.[2]
Show the answer and mark scheme
(a)Answer: Water
water
(b)Answer: Glycine 75; product 132
glycine: 75
product: 132
(c)Answer: Glycine has a functional group at each end, so it can join at both ends; ethanoic acid has only one functional group.
glycine has two functional groups, one at each end, so it can join to other molecules at both ends
ethanoic acid has only one functional group, so the chain cannot keep growing
Question 3Hard5 marks
(a) Glycine, H2NCH2COOH, polymerises to form a polypeptide and water. Draw the repeating unit of the polypeptide.[2]
(b) Alanine is another amino acid. Its formula is H2NCH(CH3)COOH. How many different dipeptides (two amino acids joined together) can be made from glycine and alanine? Explain your answer.[2]
(c) A protein molecule is a single chain of 120 amino acids. How many molecules of water were produced when the chain formed?[1]
Show the answer and mark scheme
(a)Answer: –NH–CH2–CO– (with the C=O shown), in brackets with n.
–NH–CH2–CO– with the C=O shown
bonds extending through brackets at both ends, with n
(b)Answer: 4: glycine–glycine, alanine–alanine, glycine–alanine and alanine–glycine.
4
glycine–glycine, alanine–alanine, glycine–alanine and alanine–glycine (the order matters because each molecule has different groups at each end)