Proteins and Enzymes

What Proteins and Enzymes covers

Proteins and Enzymes is examined in all three written papers — the specification states that Components 01, 02 and 03 can each assess content from any of the five modules, so nothing is confined to one paper. It covers amino acids, peptide bonds and chromatography, globular protein structure: enzymes and haemoglobin, enzyme action and the rate of reaction, blood clotting and first aid, enzymes and inhibitors in medicine and blood donation and stored blood products.

The 6 subtopics

Each one has its own page.

• Amino acids, peptide bonds and chromatographyRecall questions on the structure of amino acids and their R groups, peptide bond formation, running a paper chromatogram of amino acids, developing it with ninhydrin safely, calculating and using Rf values, and two-way chromatography.Open →
• Globular protein structure: enzymes and haemoglobinRecall questions on primary, secondary, tertiary and quaternary protein structure, the bonds including disulfide bridges that hold it, haemoglobin and its haem prosthetic group, the features and solubility of globular proteins, and denaturation.Open →
• Enzyme action and the rate of reactionRecall questions on enzyme specificity and the induced fit model, activation energy, the effects of temperature, Q₁₀, pH, substrate and enzyme concentration, competitive and non-competitive inhibitors, and measuring initial rates of catalase activity with a gas syringe.Open →
• Blood clotting and first aidRecall questions on platelets and calcium ions at a wound, the enzyme cascade that produces an insoluble mesh, why its precursors circulate inactive, and first aid for heavy bleeding.Open →
• Enzymes and inhibitors in medicineRecall questions on why tissue damage raises blood enzyme levels, what a raised amylase suggests, how streptokinase clears a clot, aspirin and warfarin as anticoagulants, and monitoring during treatment.Open →
• Blood donation and stored blood productsRecall questions on ABO antigens and antibodies, agglutination after a mismatched transfusion, universal donors and recipients, the rhesus factor in pregnancy, donor criteria, screening and deferral, and leuco-depleted blood, packed red cells, platelets, clotting factor concentrates and stored plasma.Open →

What you need to know

Answer each one before you reveal it.

Take Proteins and Enzymes further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Secondary structure vs Tertiary structure

  Secondary structure: the regular local folding of the polypeptide backbone into an α-helix or β-pleated sheet, held by hydrogen bonds alone. Tertiary structure: the overall three-dimensional shape of the whole polypeptide, held by interactions between R groups that may lie far apart in the chain.

• Fibrinogen vs Fibrin

  Fibrinogen: the soluble plasma protein that circulates ready to be converted when a clot is needed. Fibrin: the insoluble threads formed from that precursor by thrombin, which mesh across a wound and trap blood cells.

• Prothrombin vs Thrombin

  Prothrombin: an inactive plasma protein that circulates until thromboplastin and calcium ions convert it. Thrombin: the active enzyme that catalyses the conversion of soluble fibrinogen into insoluble fibrin.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is the general structure of an amino acid?

   Model answer

   A central carbon atom is bonded to an amino group −NH₂, a carboxyl group −COOH, a hydrogen atom and a variable side chain known as the R group.

2. 2

   How many different amino acids are commonly found in the proteins of living organisms, and what distinguishes them?

   Model answer

   There are twenty, and they differ only in their R groups.

3. 3

   Why does the R group of an amino acid matter so much to the protein it is part of?

   Model answer

   The R groups may be charged, polar, non-polar or able to form disulfide bridges, and the interactions between them determine how the polypeptide folds and therefore the shape and function of the finished protein.

4. 4

   How is a peptide bond formed?

   Model answer

   The carboxyl group of one amino acid reacts with the amino group of the next in a condensation reaction, releasing a molecule of water and leaving a −CO−NH− link between them.

5. 5

   How many water molecules are released when a polypeptide of 100 amino acids is assembled?

   Model answer

   Ninety-nine, because there is one peptide bond, and therefore one condensation reaction, between each adjacent pair.

6. 6

   Why is paper chromatography able to separate a mixture of amino acids?

   Model answer

   Each amino acid has a different solubility in the mobile solvent and a different attraction to the water held in the stationary paper, so each travels a different distance as the solvent moves up the paper.

What is inside Levo

Six ways to work the same material.

Proteins and Enzymes revision questions

What does Proteins and Enzymes cover in OCR A-Level Biology B?

6 subtopics: amino acids, peptide bonds and chromatography, globular protein structure: enzymes and haemoglobin, enzyme action and the rate of reaction, blood clotting and first aid, enzymes and inhibitors in medicine and blood donation and stored blood products. Each one has its own page with questions and model answers.

How is Proteins and Enzymes organised?

By the OCR H422 specification, subtopic by subtopic, so it matches the order you are taught it in.