4. Many beneficial drugs work by inhibiting enzymes. Penicillin blocks an enzyme that bacteria use in making cell walls. Ibuprofen inhibits an enzyme involved in sending pain signals. Many cancer drugs inhibit enzymes that promote cell division. (3.5 pt.) a. Recall the two mechanisms of enzyme inhibition. Which of these alters the shape of the enzyme? (1 pt.) b. Nerve gases (a form of chemical warfare) irreversibly bind to the active site of an enzyme called acetylcholinesterase vital to transmitting nerve impulses, leading to rapid paralysis and death. What mechanism of enzyme inhibition is exemplified? (1 pt.) c. The enzyme acetylcholinesterase normally binds the neurotransmitter acetylcholine and breaks it down to acetic acid and choline. What is the enzyme’s substrate(s)? What is the enzyme’s product(s)? (1.5 pt.)

a. Non-Competitive

b. Competitive

c. The substrate is acetylcholine. The products are acetic acid and choline.

Explanation:

a. Non-Competitive. Here, the inhibitor binds to the enzymes allosteric site. This action changes the shape of the enzymes active site, so that it can no longer bind to the correct substrate.

b. Competitive. Here, the inhibitor binds directly to the enzymes active site, thereby blocking other substrates.

c. A "substrate" is the molecule that binds to an enzyme. The "product" is what the enzyme produces after it acts upon the substrate.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

b a mature ovary of a plant.