Exam 3 Flashcards
(31 cards)
What are restriction enzymes?
They cut DNA at a specific recognition nucleotide sequences.
How do they work?
They work by making two incisions, once through each sugar-phosphate backbone of the DNA double helix.
By what type of mechanism do they work?
Direct Hydrolysis of a phosphodiester bond in the DNA back bone and Covalent intermediate.
Why is MG2+ required for activity?
Mg2+ ion helps to activate a H20 molecle & positions it so it can attack phosphate. Without Mg the enzyme cannot determine the infcted DNA.
How can the host DNA protect itself?
Host DNA can be mehtylated on specific Adenine bases within the host recognition sequence done by methylases. This prevents hydrogen bonding on the active sites.
What are myosins?
Catalyzes the hydrolysis of ATP to form ADP + Pi (inorganic phosphate).
What do they do?
They use the energy from the rxn to drive motion in cells.
Why is Mg2+ important and where does it bind?
Myosins are inactive without Mg2+ or Mn2+. Metal binds to ATP & that is the actual substrate for the enzyme.
How is transcarbamoylase inhibited?
Allosterically inhibited by its own end product in the reaction path.
How would CTP binding shift the rate curve?
Curve goes lower and levels off
How are allosteric inhibitors different from other types of inhibition?
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What is meant by regulatory and catalytic sites?
both sites occur in different peptide chains ???
How does the quaternary structure change when substrates are bound?
The trimers move approx. 12 Amstrong apart & rotate 10 degrees.
When are regulators bound?
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What are the T/R states?
T state is less active and favored by CTP binding. R state is more active and favored by substrate binding.
What can give positive feedback to transcarbamoylase?
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How would that shift the rate curve?
R state shift to the left and T state shifts to the right.
What are isozymes?
Enzymes that differ in amino acid sequence but catalyzes the same reaction.
Why are they important?
Because they can permit the fine tuning of metabolism to meet the needs of tissue or develop stages.
How does Phosphorylation happen in Covalent Modification?
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What molecules mediates it?
Protein Kinase enzyme catalyzes phosphorylation
What types of changes occur when phosphorylation happens?
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What is cAMP? Why is it important?
An intracellular messenger formed by cyclization of ATP. It is important because it activates the enzyme protein kinase A (PKA).
What is proteolytic cleavage?
The folded forms of other enzymes are inactive until the cleavage of one of a few specific peptide bonds.
