BCHM2072/2972 Semester 2, 2005 Page 1

HOW TO ENSURE YOUR MCQ ANSWERS ARE COUNTED

MCQ answer sheets are fed through a scanner and read in comparison to a blank answer sheet. The scanner can’t cope with any change in the configuration of the answer sheet, whiteout, crossed-out answers, etc

Here are some tips for ensuring a safe passage for your answer sheet through the scanner:

•DO use the answer sheet provided for this particular assignment (ie MCQs 1-15). Sheets for other assignments won’t be read by the scanner

•DON’T photocopy an answer sheet. Photocopied sheets are invariably changed in size and won’t be read by the scanner

•DO include your NAME and PRAC GROUP at the top (so that we can locate you if necessary)

•DO fill in your FULL SID (ALL 9 numbers)

•DO use a DARK pen/pencil and COMPLETELY fill in your choice

•DON’T use whiteout. If you make a mistake, use a fresh sheet

•DO put only ONE answer for each question

•DON’T cross out or write over mistakes on a sheet. Use a fresh one

•DON’T staple anything to the sheet

•DON’T curl over the corners of the sheet

•DON’Tfold or crease the sheet

IF YOU DON’T ATTEND TO ALL OF THESE THINGS, YOUR DETAILS AND EACH ANSWER WILL HAVE TO BE FILLED IN MANUALLY – this will delay the return of marks

ASSIGNMENT4, WEEK 9

This assignment is due in the box at the front of the lecture theatre by no later than 10.10 am on Wednesday 5thOctober. Late assignments, assignments not answered on the grid provided, or assignmentsnot covered by a plagiarism statement (universal or individual) will not be marked. Remember, submission of assignments is entirely voluntary. Enter your SID and answer all questions by filling in the relevant circles on the grid provided. Grids can be collected from under the green notice boards in the BCHM2 labs.

  1. Which of the following statements concerning protein folding is incorrect?
  1. The ER is a reducing environment so disulphide bonds readily form, unlike the oxidizing environment of the cytoplasm
  2. Proteins destined for secretion are folded in the ER and released via the Golgi Apparatus
  3. Proteins folded in the ER often have sugars attached which are first assembled on dolichol
  4. Protein disulphide isomerase (PDI) catalyses the breaking and reforming of disulphide bonds on proteins folded in the ER
  5. Proteins destined for the nucleus are translated and folded in the cytoplasm
  1. Glucose units are added and removed from proteins in the ER. What is the function of this process?
  1. To tag proteins for export to the cell surface
  2. To increase the solubility of cell surface proteins
  3. To provide unique antigen determinants for cell surface markers
  4. As an indicator of the extent of folding or how complete the folding process is
  5. To prevent aggregation and precipitation in the ER
  1. Which of the following statements about signal recognition particles (SRPs) is incorrect? A SRP:
  1. Contains RNA and protein
  2. Docks with SNARE proteins on the inner face of the outer cell membrane to facilitate the secretion of proteins from cells
  3. Docks with a receptor on the surface of the ER membrane
  4. Enables translation of proteins into the ER
  5. Binds to localization signals on the N terminal of the emerging polypeptide chain
  1. A mutation in v-SNARE proteins would result in:
  1. Secretion of proteins normally found embedded on the cell surface
  2. An inability to bind to phosphotyrosines
  3. Aggregated proteins which would precipitate in the lumen
  4. Defective glycosylation of proteins in the lumen
  5. An inability to fuse vesicles with the cell membrane
  1. Which of the following is not a step in the secretion of proteins?
  1. Soluble proteins destined for export often have sugars added post translationally
  2. Chaperones such as BiP proteins prevent protein aggregation during folding
  3. Proteins destined for export from the cell have a localization signal contained in the mRNA sequence at the 5’ untranslated region which enables a SRP to bind and direct translation into the ER
  4. Proteins destined for export are ferried to the inner face of the cell membrane in vesicles which bud off from the Golgi Apparatus
  5. Secretion involves the hydrolysis of ATP catalysed by an NSF protein
  1. Which of the following methods of anchoring proteins to the outer cell membrane requires functional translocons?
  1. Alpha helical protein domains containing hydrophobic residues
  2. Disulfide bond anchors
  3. Palmitoyl anchors
  4. GPI (glycosylphosphatidylinositol) anchors
  5. Ionic interactions with phospholipid head groups
  1. What is the role of –SH2 domains on proteins?
  1. To phosphorylate specific tyrosine residues on receptor proteins
  2. To slowly hydrolyse GTP to GDP
  3. To exchange GDP for GTP
  4. To bind to phosphotyrosine, but not tyrosine residues
  5. To catalyse the formation of disulfide bonds from SH groups
  1. Which of the following does not occur during the activation of G-coupled protein receptors?
  1. The dissociation of the alpha subunit from the beta/gamma dimer during activation
  2. The displacement of a GDP with a GTP
  3. The phosphorylation of tyrosines within the receptor upon ligand binding
  4. The dissociation of the G protein trimer from the 7-TMS receptor upon ligand binding
  5. The slow hydrolysis of GTP to restore the receptor to its inactive form
  1. Binding of a cytokine to a cytokine receptor would be generally expected to lead to:
  1. Autophosphorylation of a tyrosine kinase bound to the receptor
  2. An influx of Ca2+ through activation of a ligand-gated ion channel
  3. Displacement of GDP by GTP on a G protein bound to the receptor
  4. Dissociation of the receptor from a dimer to a monomer form
  5. Inhibition of intra-cellular adenyl cyclase
  1. A common structural theme in the 7-TMS family of receptors is:
  1. They all contain seven strands of -sheet which span the cell membrane
  2. They all mediate signal transduction through G-protein coupled events
  3. They all contain protein tyrosine kinase domains at their C-termini
  4. They are all GPI-anchored proteins
  5. None of them are glycoproteins
  1. Which of the following statements about the JAK-STAT signalling pathway is correct?

A.Activation of JAK kinases allows them to enter the nucleus and phosphorylate STAT proteins

B.JAK kinases use GTP to phosphorylate small GTP-binding proteins such as Ras

C.Dephosphorylation of STAT proteins allows them to dimerise through their SH2 domains

D.JAK-dependent phosphorylation of protein kinase C leads to inhibition of phospholipase C

E.Up-regulation of SOCS protein expression would be expected to down-regulate STAT activity

  1. Which of the following statements about activation of protein kinase C is correct?

A.An influx of Ca2+ from the extra-cellular medium leads to conversion of protein kinase C into its active form

B.Protein kinase C could be activated via both growth factor and 7-TMS receptor signalling

C.Protein kinase C becomes activated after dissociation of its regulatory subunits

D.Phospholipase C hydrolyses phospholipids in the ER membrane, leading to Ca2+ release

E.Diacyl glycerol is phosphorylated and becomes incorporated into the cell membrane

  1. In general, binding of growth factors to their receptors might be expected to:

A.Lead to dissociation of receptor dimers into their active monomer forms

B.Lead to inhibition of export of proteins from the nucleus

C.Lead to the inhibition of protein kinase C because of increased levels of intra-cellular Ca 2+

D.Lead to production of both phosphotyrosine and phosphoserine- modified proteins

E.Have no effect in cells which do not express the NFKB transcription factor

  1. The NF-KB transcription factor:

A.Requires removal of inhibitory phosphate groups in order to become active

B.Is an example of a steroid hormone receptor

C.Is activated by protein kinase A

D.Is unusual because is does not contain a signal peptide

E.Is normally present in the cytoplasm

  1. Which one of the following would indicate involvement of calcium ions in the signalling mechanism of a receptor?

A.Activation of Ras and the MAP kinase cascade

B.Cytoplasmic protein kinase C in cells in which the receptor is expressed

C.Phosphotyrosine binding sites for phospholipase C on the activated receptor

D.Receptor-stimulated synthesis of cAMP

E.Receptor-stimulated activation of a heterotrimeric G protein