BIOCHEM BRS AND ICS SECTION 2 EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED LATEST UPDATE
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BIOCHEM BRS AND ICS SECTION 2 EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED LATEST UPDATE
D. GIcNAc-phosphate
Bacterial pneumonia can be caused by the gram-positive bacteria Streptococcus pneumoniae. Treatment with tunicamycin, which inhibits bacterial cell wall glycoprotein synth...
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BIOCHEM BRS AND ICS SECTION 2 EXAM QUESTIONS
AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
LATEST UPDATE
D. GIcNAc-phosphate
Bacterial pneumonia can be caused by the gram-positive bacteria Streptococcus
pneumoniae. Treatment with tunicamycin, which inhibits bacterial cell wall glycoprotein
synthesis, blocks the attachment of which of the following to the nascent
oligosaccharide core?
A. Glucose
B. Mannose
C. GICNAC
D. GIcNAc-phosphate
E. A phosphate group
C. Segregating membrane or secretory proteins from cytoplasmic proteins during
synthesis.
- The signal hypothesis describes how proteins destined for secretion or
insertion into membranes are directed to the endoplasmic reticulum (ER) during
their synthesis. Signal recognition particles (SRPs) bind to the signal sequence of
nascent proteins and guide them to the ER membrane, where docking proteins
(receptors) help transfer the ribosome-protein complex to the ER for further
,synthesis and processing. This process helps segregate membrane or secretory
proteins from cytoplasmic proteins.
The signal hypothesis, involving signal recognition particles (SP) and docking proteins
(DP), pertains to:
A. Facilitating receptor-mediated signal transduction across the plasma membrane.
B. Removing and replacing incorrect nucleotides or aminoacyl-tRNAs.
C. Segregating membrane or secretory proteins from cytoplasmic proteins during
synthesis.
D. Overseeing the cleavage of a sequence at the carboxyl end of a secretory protein
after secretion.
E. It does not involve the formation of cyclic nucleotides (CAMP or cGMP).
a) A stretch of hydrophobic amino acids
- The signal peptide that directs a nascent protein to the endoplasmic reticulum
contains a central stretch of hydrophobic amino acids. This hydrophobic region
is key to binding the signal recognition particle (SRP), which recognizes and
binds to the signal peptide, facilitating the targeting of the protein to the ER
membrane.
Which feature of the signal peptide
increases its affinity for the signal recognition particle (SRP)?
a) A stretch of hydrophobic amino acids
b) Glutamic acid residues
c) A Lysine residue
,d) Its length
e) Serine residues
b) Lys-Asp-Glu-Leu (aka KDEL)
- The enzyme responsible for transferring glucose from dolichol phosphate to the
core oligosaccharide during glycosylation in the endoplasmic reticulum (ER)
would be an ER-resident protein. The KDEL sequence (Lys-Asp-Glu-Leu) is a
retention signal for proteins that need to remain in the ER after their synthesis.
Which tag (signal sequence) would you expect on the enzyme responsible for
transferring glucose from dolichol phosphate to the core oligosaccharide during its
biosynthesis?
a) Ser-Lys-Leu
b) Lys-Asp-Glu-Leu (aka KDEL)
c) Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val
d) No-tag
e) A mannose-6-phosphate
B. Halt sequence
- Membrane-bound immunoglobulins have a halt sequence, also known as a stop-
transfer sequence, that ensures the immunoglobulin is anchored in the plasma
membrane as an integral protein. This sequence allows the protein to be
embedded in the membrane rather than being fully secreted.
Plasma cells produce immunoglobulins in two forms: membrane-bound (integral
proteins) for lymphocyte activation and proliferation upon antigen binding, and the
soluble form found in blood plasma. Which of the following is present in mature
, membrane-bound immunoglobulins but not in plasma immunoglobulins?
A. Signal peptide
B. Halt sequence
C. Lys-Asp-Glu-Leu
D. Mannose-6-phosphate
E. Ubiquitination sites
E. None of the above
- High-speed centrifugation at 75,000 x g for an extended period sediments most
organelles, leaving the cytosolic fraction in the supernatant. The enzymes found
in this non-sedimented fraction are typically cytosolic proteins, which do not
possess specific targeting sequences like KDEL, nuclear localization signals
(NLS), peroxisomal targeting signals (Ser-Lys-Leu), or signal peptides.
As a researcher working with mammalian liver tissue, you prepared a liver homogenate
and performed high speed centrifugation at 75,000 x g for 3 hours. This process
sediments all organelles, leaving a supernatant with enzymes from the non-sedimented
fraction. Assuming no organelles disrupted, which tag elements would be present in
these enzymes?
A. A stretch of hydrophobic amino acids ending with a lysine residue
B. Lys-Asp-Glu-Leu-COO- (KDEL sequence)
C. A Ser-Lys-Leu
D. Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val
E. None of the above
D. No tag
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