Amino acids and protein structureAQA A-Level Biology: Flashcards
Card 1 of 140 of 14 known
Question
What is the monomer of proteins?
Tap or press Space to reveal
Tap card or press Space to flip
See all 14 cards
- What is the monomer of proteins?
- The amino acid.
- What are the parts of an amino acid?
- An amine group (NH₂), a carboxyl group (COOH), a hydrogen and an R group on a central carbon.
- What makes the twenty amino acids different from each other?
- Only their R group.
- What bond forms between two amino acids?
- A peptide bond, formed in a condensation reaction.
- What is a dipeptide?
- Two amino acids joined by a peptide bond.
- What is primary structure?
- The sequence of amino acids in a polypeptide.
- What holds secondary structure together?
- Hydrogen bonds between the peptide groups, giving an α-helix or β-pleated sheet.
- What is tertiary structure?
- The specific three-dimensional folding of a polypeptide, held by bonds between R groups.
- Name the three bonds in tertiary structure.
- Hydrogen bonds, ionic bonds and disulfide bridges.
- What is a disulfide bridge?
- A strong covalent bond between sulfur atoms in the R groups of two cysteine molecules.
- What is quaternary structure?
- The association of two or more polypeptide chains, for example haemoglobin.
- Why can a change in primary structure change a protein's function?
- The R groups are in different places, so the bonds and three-dimensional shape change.
- How do you carry out the biuret test?
- Add sodium hydroxide and dilute copper(II) sulfate; purple means protein.
- Why do free amino acids not give a positive biuret test?
- There are no peptide bonds.
Exam questions on Amino acids and protein structure
- Alanine is an amino acid whose R group is a methyl group, CH₃. Cysteine is an amino acid whose R group is CH₂SH, which contains sulfur.Explain why two cysteine molecules in a polypeptide can form a bond between their R groups that two alanine molecules cannot.2 marks
- Haemoglobin is a protein made from four polypeptide chains: two α chains of 141 amino acids each and two β chains of 146 amino acids each.Explain why a change in the sequence of amino acids in a protein can change its function.2 marks
- Ribonuclease is an enzyme made from a single polypeptide of 124 amino acids, folded into a compact three-dimensional shape. Its tertiary structure is held together by hydrogen bonds, ionic bonds and four disulfide bridges.Describe the primary, secondary and tertiary structure of ribonuclease.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).