Unit 3, AoS 1

• What is the function of an enzyme?


  Enzymes catalyse a biological reaction by limiting the activation energy to initiate a reaction. Eg: lipase
• What is the function of a hormone?


  Act as a chemical messenger to communicate changes to the cell. Eg: insulin
• What is the function of structural protein?

  supports cell and tissue shape. Eg: collagen
• What is the function of a transport protein?


  Moves substances across a membrane. Eg: glucose channel
• What is the function of a receptor protein?


  Receives signals from the environment. Eg: hormone receptor
• What is the function of a defence protein?

  involved in the immune system to recognise and destroy pathogens. Eg: antibodies
• What is the function of a motor/contractile protein?

  allows muscles to move/contract. Eg: myosin
• What is the function of a storage protein?

  stores metal irons. Eg: ferritin (iron storage)
• Describe primary protein structure

  The sequence of amino acids in a polypeptide chain, which will become a protein.
• Describe secondary protein structure

  The three-dimensional format of segments of a polypeptide chain, through interactions between amino acids. Alpha helix and beta-pleated sheets are formed.
• What is the difference between alpha helix and beta-pleated sheets?

  Alpha helix is an organised coiled secondary structure of proteins, whereas a beta-pleated sheet is an organised, folded secondary structure of proteins.
• Describe tertiary protein structure

  The overall three-dimensional shape of a protein
• Describe quaternary protein structure

  More than one polypeptide chain, each with its own primary, secondary and tertiary structure
• What are amino acids?


  Monomers of which a protein is created
• What is a proteome?

  All proteins that are produced by either a cell, tissue or organism
• What are enzymes, and how do they work?

  Enzymes catalyze a biological reaction by lowering the activation energy to initiate a reaction. A reaction is catalysed when substrate binds to the complimentary active site of the enzyme, reducing activation energy.
• What is the difference between catabolic and anabolic reactions?

  A chemical reaction that breaks big molecules into smaller molecules is catabolic, whereas a reaction that builds larger molecules from smaller is anabolic
• What is the difference between exergonic and endergonic reactions?

  Reactions that release energy = exergonic (catabolic), reactions that absorb energy = endergonic (anabolic)
• What is activation energy?

  the amount of energy which a molecule must possess in order to undergo a reaction
• How does temperature effect enzyme action?

  Increase of temperature beyond optimal leads to rapid decline of reaction rate due to the change of shape at the active site (denaturation). At its optimal, the enzyme will have an optimal amount of collisions, with reaction rate at its fastest. Below optimal temperature, a low amount of collisions will occur, reducing rate of reaction.
• How does pH effect enzyme action?

  Altering pH below the optimal, concentration of hydrogen ions increases, interfering with hydrogen bonds (which hold the active site in place). Altering pH above optimal causes bonds holding complementary active site to break, meaning substrate cannot bind. Precise collisions occur at optimal pH
• How does enzyme concentration effect enzyme action?

  Additional enzyme concentration means more enzyme-substrate complexes are formed, increasing reaction rate as more products can be created.
• How does substrate concentration effect enzyme action?

  Increasing substrate concentration increases reaction rate, as more successful collisions are made between substrate and the active site, increasing product formation (until enzyme concentration becomes the limiting factor)
• what is an inhibitor?

  An inhibitor is any molecule that binds to an enzyme, preventing the enzyme binding to normal substrate
• Describe competitive inhibitors

  bind to the active site of the enzyme and prevent substrate binding to the same active site. Sits in an active site, competing with substrate to get into the active site first
• describe non-competitive inhibitors

  bind to the allosteric site on the enzyme, changing enzyme shape so that the substrate is not complimentary to the shape of the active site. Allosteric site – any part of the enzyme other than the active site
• What is the difference between irreversible and reversible inhibitors?

  Irreversible inhibitors form a covalent bond with part of the enzyme, causing a permanent change to the enzyme, whereas reversible inhibitors bind non-covalently (weak interaction), causing no permanent change
• What are cofactors?

  Cofactors are non-protein molecules that assist enzymes in carrying out their catalytic functions. Sits in the active site to allow substrate binding to occur. Coenzymes are a type of organic cofactor, that bind loosely to enzymes and are 'thrown out' after a reaction occurs
• What is RNA polymerase?


  an enzyme that runs along the template strand in a 3’ to 5’ direction, unwinding DNA to build complimentary strand of RNA
• What is the difference between introns and exons?

  Introns: contain non-coding DNA, are removed from pre-mRNA strand before translation

  Exons: transcribed regions of a gene that are also translated
• Where does transcription occur, and what happens?

  Where: nucleus

  What: DNA - pre-mRNA
• What strand are pre-mRNA molecules built onto?

  Coding strand
• Where does RNA processing occur and what does it produce?

  Where: nucleus

  What: pre-mRNA - mRNA
• What end are nucleotides built onto?

  3' end
• What is splicing?


  Splicing: the process whereby introns are removed, and exons joined together by a spliceosome
• Where does translation occur and what does it produce?


  Where: in the cytosol

  What: mRNA - polypeptide
• Explain the four stages of transcription

  • Initiation: RNA polymerase and transcription factors unwind DNA and bind to promoter region
  • Elongation: RNA polymerase builds complimentary pre-mRNA by reading template strand
  • Elongation: join nucleotides by condensation polymerisation
  • Terminator: finishes when RNA polymerase reaches terminator sequence, and is released by DNA
• Explain the four stages of translation

  • Initiation: 5' methyl cap end of mRNA attaches to ribosome, which starts reading at AUG (start) codon
  • Elongation: ribosome reads codons, and matches specific tRNA with complimentary anticodons
  • Elongation: amino acids are joined together by condensation polymerisation, forming peptide bonds
  • Terminator: polypeptide bond formation continues until ribosome reads STOP codon, and translation is complete
• What three things occur in RNA processing?

  • Introns cut out of pre-mRNA and exons joined together
  • Poly-A tail added to 3' end of mRNA
  • Methyl cap added to 5' end of mRNA
• Explain the process of gene repression when trp is abundant

  When trp is present in a cell, 2 trp molecules bind to a repressor, causing a conformational shape change. This therefore enables the repressor to attach to the operator, preventing awaiting RNA polymerase from transcribing genes