BY 330 Spring 2015Mock Exam 3

  1. The three nucleotides always present at the 3’ end of a molecule of tRNA are CCA. The variable loop also contains three nucleotides called the anticodon that are complementary to the codon on a molecule of mRNA.
  1. Initiation factors help to begin the process of protein synthesis in a eukaryotic ribosome. IF3 aligns the first codon, AUG, in its proper position. IF1 and IF2 act as escorts for the first tRNA molecule bringing in the first amino acid, methionine. IF2 can be phosphorylated to block the process of protein synthesis.
  1. True or False: The full 80S ribosome is assembled prior to the introduction of an mRNA molecule. False
  1. List and describe the function of the four proteins used during the elongation phase of translation.

Tu and Ts – transport proteins used to help direct tRNA into lumen of ribosome so that it can bind to mRNA

Peptidyl transferase – breaks bond between adenine on tRNA and carboxyl carbon of amino acid  releases enough energy to form a bond between first and second amino acids

G-translocase – moves mRNA through the ribosome during process of translation

  1. Termination factors will bind to stop codons to terminate protein synthesis. What are the three stop codons and which factors will bind to each?

UAG, UAA, or UGA – R1 will bind to UAG and UAA; R2 will bind to UAA and UGA

  1. A polysome is a single message that contains multiple ribosomes. One ribosome can bind every 80 nucelotides.
  1. Circle all of the following that can be found in both monolayers of the plasma membrane.

a). Phosphotidyl-choline

b). Phosphotidyl- inositol

c). Cholesterol

d). Phosphotidyl-serine

e). Glycoplipids

f). Proteins

  1. The plasma membrane regulates the transport of which of the following? Circle all that apply.

a). Na+ ions

b). Water

c). O2 molecules

d). CO2 molecules

e). Glucose

  1. True or False: All membrane of the cell is made up of the exact same components. False
  2. The majority of the cytoplasm is made up of which organic molecule?

Proteins

  1. Circle all of the following whose gene had a leader sequence.

a). R1

b). Pyruvate kinase

c). Voltage-gated sodium channel

d). F1ATPase

e). Aminoacyl-tRNA-synthetase

  1. Circle all of the amino acids in the following protein that the rough ER will attach a sugar to through the process of glycosylation. Underline all of the amino acids that the Golgi will attach a sugar to. (bolded is ER, underlined is Golgi)

gly-cys-thr-tyr-gln-asn-val-ser-met-asn-arg-lys-his-trp-thr-phe-ser-leu-asn

  1. List three ways to increase the fluidity of the plasma membrane.

Decrease length of fatty acid tails

Decrease amount of cholesterol

Decrease saturation/increase unsaturation

  1. Metastatic cancer cells are generally missing which component of the plasma membrane? What are the parts of this molecule and in which organelle(s) are these parts synthesized?

Glycolipids – lipid + oligosaccharide  lipid synthesized in smooth ER, oligosaccharide synthesized in Golgi

  1. Describe and draw one mechanism by which a peripheral protein can be anchored in the plasma membrane.

Three mechanisms possible – add more hydrophilic/hydrophobic domains, conjugate to fatty acid, attach to transmembrane protein with weak bonds

  1. The sodium-potassium pump is an example of which specific type of transport protein.

Antiport carrier

  1. What effect does an action potential have on a carrier protein? Voltage-gated channel proteins?

None; Will open voltage-gated

  1. A membrane-bound vesicle/endosome forms to bring molecules into the cell during endocytosis. The (luminal, cytoplasmic) side of the vesicle contains high amounts of phosphotidyl-choline. Once this vesicle enters the cells, actin fibers will pull it to where it needs to go. If the vesicle is involved in receptor-mediated endocytosis, a clathrin protein coat will form around it. This protein coat will eventually be (discarded, recycled).
  1. The calcium ion acts as a signal to promote exocytosis.
  1. A protein found in the plasma membrane is involved in cell signaling. What type of protein is this? Describe in general how and where this protein was translated from its mRNA code, how and where the other components of this protein was synthesized, and how this protein reached its functional location.

Glycoprotein

From mRNA code – first 20 amino acids synthesized in cytoplasm  moved to rough ER by leader sequence to continue synthesis

Other component is oligosaccharide – synthesized in rough ER  built on dolichol on cytoplasmic side of ER, add phosphorus + sugars needed, flip to luminal side, cut off with glycosylases and attach to protein

Reaches functional location by traveling through transitional ER and pinching off membrane to form vesicle

  1. The rough ER will synthesize all proteins, except for the proteins that function in the cytoplasm and the mitochondria.
  1. The process of glycosylation in the rough ER is often times called N-linked glycosylation. This is because the oligosaccharide will be attached to the asparagine amino acid in the protein, which has a amino group present in its R group. This oligosaccharide was built on a lipid called dolichol, which is present on the cytoplasmic side of ER membrane. Once the oligosaccharide is synthesized it will be flipped to the luminal side of the membrane and enzymes called glycosylases will cut it from the lipid on which it was built. It will eventually be attached to the luminal side of the protein. Circle all of the following sugars that can be used in this process: (mannose, fucose, sialic acid, glucose, galactose).
  1. This molecule is used in the detoxification process that occurs in the smooth ER. Cytochrome P450
  1. List four functions of the Golgi.

There are five possible answers – glycosylation, proprocessing, membrane recycling, secretion, lysosome production

  1. The cis face of the Golgi is closest to the ER, while the trans face is closest to the plasma membrane. The Golgi will turn over its membrane approximately every 40 minutes. The zone of exclusion around the Golgi restricts which molecules can move around the organelle.
  1. Describe how the lysosome activates its enzymes for digestion.

Proton transporters use ATP to pump protons into lysosome, which decreases pH from 7 to around 5  activates enzymes

  1. List two diseases that can be caused because of problems with lysosomes.

Three possibilities – gout, Tay-Sachs, arthritis

  1. Which two organelles produce metabolic water?

Peroxisome, mitochondria

  1. Describe how functional catalase is assembled. Did catalase have a leader sequence? What organelle does this enzyme function in and what reaction does it catalyze?

4 catalase monomers moved from cytoplasm to peroxisome and put together with a heme ring; no leader sequence; peroxisome  catalyzes peroxidative reaction of reduced compound with hydrogen peroxide to produce oxidized compound and metabolic water

  1. Apoptosis is caused by a build-up of hydrogen peroxide outside of the peroxisome. It can be solved by glutathione peroxidase, which will convert the excess hydrogen peroxide intro water.