Name:
BIOCHEMISTRY
HOMEWORK 9
Due: November 13, 2013
1.
The “generic” enzyme shown below can be regulated from active to inactive form
(and back again) by
covalent modification catalyzed by different enzymes which
are identified according to their functions.
Kinase
Inactive Enzyme
Active Enzyme
Enzyme X
1.1.
1.2.
2.
Identify the nature of the covalent modification in the “inactive”
enzyme” (what is the usual function of a kinase?)
Classify Enzyme X according to its function.
Valinomycin is an anti-bacterial that kills bacteria by disrupting a secondary transport
processes that depend on K+ ion concentration gradient.
Explain the details of the process and identify the structural features of valinomycin
which enables the antibacterial activity mentioned.
3.
Glucose enters some cells by simple diffusion through channels and pores, but glucose
enters red blood cells by passive transport. On the plot below, indicate which line
represents diffusion through a channel or pore, and which line represents passive
transport. Explain why the rates of the two processes (and the shapes of the two plots) are
different.
3.1.
4.
Once inside the cell glucose undergoes a reaction which prevents it from crossing
the membrane and leaving the cell again. What is the reaction mentioned above
and how/why does it prevent glucose from leaving the cell?
The Na+, K+-ATPase exchanges 3 Na+ for 2 K+ ions across the membrane in
different directions. Since it generates concentration gradient of these ions, it
requires input of energy. Which of the following features correctly describes
Na+, K+-ATPase?
(1) passive uniporter
(4) active uniporter
(2) passive symporter
(5) active symporter
(3) passive antiporter
(6) active antiporter
5.
Why does glycogen degradation involve phosphorylation instead of simple hydrolysis?
You might need to give a “speculative” answer here (which will serve as a mental
exercise). Refer to the details of the degradation mechanism.
6.
Although gluconeogenesis is “more or less” reverse of glycolysis there is one
intermediate product in the early stages, which clearly differentiates gluconeogenesis
from glycolysis. Write the structure of the unique intermediate. Outline how the “unique
intermediate” is formed and how it is converted into a common (for both in
gluconeogenesis and glycolysis) intermediate.
Give you thoughts on why this additional step might be necessary in gluconeogenesis.