Module 7 - enzyme regulation, cell signaling pathways, and GPCR Flashcards
What is DFP?
irreversible enzyme inhibitor, forms covalent links with reactive serine residues such as chymotrypsin and phospholipases
What two things regulate enzyme activity?
bioavailability of enzymes and catalytic efficiency
Allosteric control involves…
the binding of small molecules called metabolites to regulatory sites on enzymes (not the active site)
What processes affect enzyme bioavailability?
RNA synthesis, processing, protein synthesis, protein degradation, and protein targeting
What affects catalytic efficiency?
inhibition, allosteric control, covalent modification, and proteolytic processing
What is reversible inhibition vs. irreversible inhibition?
reversible - noncovalent binding of small molecules
irreversible - inhibitory molecule forms a covalent bond to enzyme active site
Malonate is a —– —– of succinate dehydrogenase
reversible inhibitor
What are the three types of reversible inhibition, and describe each
competitive inhibition:
binds in active site of E
uncompetitive inhibition:
binds outside active site on the ES complex
mixed inhibition:
binds outside active site, but to the E or ES complex
How does the graph change when a competitive inhibitor is present?
same Vmax, but increased Km (higher substrate to reach 1/2 Vmax)
How does the graph change when a uncompetitive inhibitor is present?
lower the Vmax and the Km
(uncompetitive inhibition is not overcome by increasing the substrate concentration)
How does the graph change when a mixed inhibitor is present? What is a noncompetitive inhibitor?
can look many different ways
noncompetitive inhibitors are one specific type of mixed inhibitors, graph shows no change in Km but lowering of Vmax
What is papaya enzyme called, and what is it good for? Why?
papain, good for meat tenderizing because it is a cysteine protease that degrades proteins
How does a Vo vs. [S] graph change with the presence of allosteric effectors?
shifts right (>Km) with a negative allosteric effector and shifts left (<Km) with a positive allosteric effector
Describe the regulation of ATCase and how the allosteric effectors would effect the graph of Vo vs. [S]
What is the quaternary structure of ATCase?
binding of ATP shifts ATCase to the R state (and shifts graph to the left)
binding of CTP shifts ATCase to the T state (and shifts graph to the right)
ATCase is a dimer with a catalytic subunit (where substrate binds) and a regulatory subunit (where allosteric effector binds), 3 dimers come together to form the C3R3 complex
What are the three most common enzyme covalent modification? How do they happen?
What is an example of an enzyme that is activated by each modification?
Phosphorylation:
- of Ser, Thr, and Tyr residues by a kinase (removed by a phosphatase)
- adds an inorganic phosphate
- glucogen phosphorylase
Adenylylation:
- added and removed by an adenylyltransferase
- glutamine synthetase
Uridylylation:
- uridylyltransferase
- control of adenylyltransferase activity for glutamine synthetase activation
What is a zymogen?
inactive precursor proteins that are synthesized with an active site that is inaccessible to protein substrates
How does proteolysis regulate enzymes?
What is an example?
when a protein is synthesized as a zymogen, proteases can be used to remove segments and expose the active site, generating the active form of the enzyme
process is irreversible
ex: pepsinogen (inactive) has its N terminal cleaved to reveal the active site and generate pepsin (active)
ex: trypsin cleaves chymotrypsinogen to create p-chymotrypsin, which then cleaves other p-chymotrypsin molecules to generate the fully active a-chymotrypsin enzyme
What are the 6 general steps of second messenger pathways?
What is the overall effect of a second messenger pathway?
- first messenger (substrate)
- receptor protein (conformational change)
- upstream signaling proteins
- second messengers
- downstream signaling proteins
- target proteins
effect: amplification through the activation of one or more downstream target proteins
What percent of protein coding genes in the human genome are involved in signal transduction? How many signaling genes are there?
9%
about 2,000 signaling genes
What are endocrine, paracrine, and autocrine?
endocrine - target tissue is far away
paracrine - target tissue is a nearby cell
autocrine - target tissue is the same cell
What are examples of first messengers?
peptide hormones, lipids (like steroids), and small molecules like nitric oxide, Ca2+, and CO2
B-estradiol, epinephrine, acetylcholine, etc.
How does insect saliva cause cGMP production?
At pH of 5, NO is bound to the heme of the nitrophorin protein.
At pH of 7, NO is released. A histamine binds to the heme where the NO was released.
The released NO binds to guanylate cyclase to stimulate cGMP production and cause vasodilation.
How does sildenafil work?
prolongs NO mediated vasodilation by inhibiting cGMP phosphodiesterase (which breaks down cGMP)
What enzymes cause ATP to generate cAMP and then AMP?
adenylate cyclase turns ATP to cAMP
cAMP phosphodiesterase turns cAMP to AMP
