Questions

• describe how mRNA is produced in the nucleus of a cell?

  • helicase breaks hydrogen bonds between bases.
  • only one DNA strand acts as a template.
  • RNA nucleotides are attracted to exposed bases according to base pairing rule.
  • RNA polymerase joins RNA nucleotides together.
  • pre-mRNA spliced to remove introns.
• describe the structure of proteins?

  • proteins are polymers of amino acids.
  • they are joined by peptide bonds.
  • formed by condensation reactions.
  • primary structure is the sequence of amino acids in a polypeptide chain.
  • secondary structure is the folding of polypeptide chain due to hydrogen bonding.
• describe how proteins are digested in the human gut?

  • hydrolysis of peptide bonds.
  • endopeptidases break polypeptides into smaller peptide chains.
  • exopeptidases remove terminal amino acids.
  • dipeptidases hydrolyse dipeptides into amino acids.
• explain why maltase only breaks down maltose?

  • maltase is an enzyme which has a specific tertiary shape complimentary to the active site on maltose.
  • this forms an enzyme-substrate-complex.
  • it has an induced fit.
  • the enzyme is a catalyst so lowers the activation energy.
• describe competitive and non-competitive inhibitors?

  • inhibitors prevent the formation of enzyme-substrate complexes.
  • competitive inhibitors have a similar shape to the substrate.
  • binds to the active site of the enzyme.
  • inhabitation can be overcome by more substrate.
  • non-competitive inhibitors bind to the enzyme away from its active site.
  • this changed the shape of the active site.
  • cannot be overcome by more substrate.
• describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst?

  • substrate binds to the active site.
  • active site changed shape slightly so distorts bonds in the substrate.
  • enzyme reduces the activation energy.
• why does the formation of enzyme substrate complexes increase the rate of reaction?

  • activation energy is reduced.
  • without enzyme, very few substrates have sufficient energy for reaction.
• describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.

  • condensation reaction.
  • between phosphate and deoxyribose.
  • catalysed by DNA polymerase.
• describe the role of DNA polymerase.

  • joins adjacent DNA nucleotides.
  • catalyses condensation reactions.
  • former phosphodiester bonds.
• describe how HIV is replicated?

  • attachment proteins attach to receptors on helper T cell.
  • RNA enters the cell.
  • reverse transcriptase converts RNA to DNA.
  • viral proteins produced.
  • virus particles assembled and released from cell.
• pathway red blood cell takes when travelling in the human circulatory system from kidney to lungs.

  • renal veins.
  • vena cava to right atrium.
  • right ventricle to pulmonary artery
• explain how water from tissue fluid is retuned to the circulatory system.

  • plasma protein remain.
  • this reduced water potential of the blood.
  • water moves to the blood by osmosis.
  • return to blood by lymphatic system.
• explain how an arteriole can reduce the blood flow into capillaries.

  • muscle contracts.
  • narrows lumen
• the mass flow hypothesis is used to explain the movement of substances through phloem.

  • sucrose is actively transported into phloem.
  • reduces water potential.
  • water moves into the phloem by osmosis from the xylem.
• describe the role of tRNA in translation?

  • bonds with a specific amino acid using energy from ATP.
  • carries specific amino acids to the ribosome to build proteins.