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BIOC 384 Exam 3

Terms in this set (54)

Acetylcholinesterase is an important enzyme in the nervous system. Acetylcholinesterase activity is blocked by the nerve agent sarin gas, which forms a covalent bond with a Ser in the active site of the enzyme. Sarin gas is a(n)__________________.
irreversible inhibitor
Signal transduction is part of a cell's response to an external signal. Although signal transduction pathways can differ in their details, there are some common elements. Determine which of the statements below accurately describe signal transduction pathways. Select the three correct statements.
A receptor changes conformation upon binding, transmitting a signal across the cell membrane

A receptor may pass on a signal by interacting with another protein or by acting as an enzyme

signal transduction cascades, often involving protein kinases, amplify a signal intracellularly
What characteristic is true for both RTKs and GPCRs?
The receptor undergoes a conformational change on activation
Procathepsin B is a lysosomal protease that is first translated as a proenzyme. On autocleavage it is fully activated. Procathepsin B is ________________.
a zymogen
Which of the following are characteristics of allosteric enzymes like ATCase? Choose the THREE that apply. Allosteric enzymes:
may have binding sites for regulatory molecules that are separate from active sites

interconvert between a more active form and less active form

tend to have a sigmoidal (s-shaped) curve of V0 vs. [S]
Which of the following choices below includes only first messenger signaling molecules?
cortisol

insulin

prostaglandins
Signaling activity of G proteins is controlled by GTPase activating proteins (GAPs) and Guanine exchange factors (GEFs). What are the mechanisms by which GAPs and GEFs control G proteins?
GAPs inhibit G proteins by stimulating GTP hydrolysis; GEFs activate G proteins by stimulating GDP-GTP exchange
Binding of first messengers to G protein-coupled receptors results in ___________.
recruitment of heterotrimeric G proteins to the GPCR cytoplasmic tail
Put the following steps of the G protein cycle into the correct order
(1) ligand stimulation of the GEF function of a GPCR

(2) dissociation of G-alpha and G-beta/gamma from a GPCR

(3) GAPs stimulate the GTPase activity of G-alpha

(4) reassociation of the heterotrimeric G complex with a GPCR
What is the function of the GTPase activity in G proteins?
The GTPase cleaves GTP to generate GDP and inactivate signaling
The alpha subunit of trimeric G proteins can function to _________________.
activate adenylate cyclase
The common structural pattern that is a distinguishing characteristic specific to all G-protein-coupled receptors is that they __________________.

video about Heterotrimeric G Proteins
contain seven transmembrane helices
A pH/enzyme activity curve is shown above. Which of the following pairs of amino acids would be likely candidates as catalytic groups?

Vmax vs pH graph
His and Cys
An enzyme undergoes a mutation that causes it to lose the ability to be regulated via phosphorylation. Which of the following mutations may lead to this loss of regulation? Assume that the overall structure is not altered by the mutation and multiple kinases can phosphorylate the wild-type protein.
Ser-->Phe
Cyclic GMP is the __________ during vasodilation.
second messenger
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