Biochemistry Lecture 11- Enzyme Controls

Front 1

The sodium-potassium ATPase is an example of

Back 1

The sodium-potassium ATPase is an example of a protein whose activity includes a transient step in which it is phosphorylated using phosphate from ATP.

Front 2

A very common type of covalent modification is phosphorylation, as exhibited by

Back 2

A very common type of covalent modification is phosphorylation, as exhibited by Glycogen Phosphorylase

Front 3

Phosporylation converts glycogen phosphorylase ___________ to glycogen phosphorylase_________

Back 3

Phosporylation converts glycogen phosphorylase b (less active) to glycogen phosphorylase a (more active).

Front 4

The kinase that puts the phosphates on in Glycogen Phosphorylase is controlled by

Back 4

In Glycogen Phosphorylase, the kinase that puts the phosphates on is controlled by epinephrine (adrenalin) and the phosphatase that takes the phosphates off is controlled by insulin.

Front 5

zymogens

Back 5

Zymogens are enzymes made in an inactive form and then activated by cleavage of one or more peptide bonds in them.

Front 6

Which kind of modification activates zymogens?

Back 6

Covalent modification is that which activates zymogens.

Front 7

Chymotrypsinogen is

Back 7

Chymotrypsinogen is a zymogen that get activated by peptide cleavage to form chymotrypsin.

Front 8

Where is Chymotrypsinogen made?

Back 8

Chymotrypsinogen is made in the pancreas and normally activated in the digestive system.

Front 9

What happens if Chymotrypsinogen gets activated too soon?

Back 9

If Chymotrypsinogen gets activated too soon, pancreatitis results from attack of the enzyme on the proteins in the pancreas.

Front 10

Chymotrypsin is an enzyme that catalyzes a reaction in _____ phases

Back 10

Chymotrypsin is an enzyme that catalyzes a reaction in two phases -a slow phase and a fast phase. The fast phase occurs first.

Front 11

Chymotrypsin is an enzyme that catalyzes a reaction in two phases -a slow phase and a fast phase. The fast phase occurs first. What happens there?

Back 11

Chymotrypsin is an enzyme that catalyzes a reaction in two phases - a slow phase and a fast phase. The fast phase occurs first. In this phase, the peptide bond is broken and the first peptide is released.

Front 12

What is a result of Chymotrypsin's first phase?

Back 12

In Chymotrypsin's first phase phase, the peptide bond is broken and the first peptide is released. As a result of this action, the other peptide is covalently linked to the enzyme transiently.

Front 13

What happens in chymotrypsin's slow phase? What is involved?

Back 13

The release of the second peptide from Chymotrypsin is the slow phase and involves the action of water.

Front 14

What is a serine protease? and what is is an example?

Back 14

Chymotrypsin is a so-called serine protease, meaning that it uses the side chain of serine to catalyze proteolytic cleavage.

Front 15

What is the side chain of Serine?

Back 15

A hydroxyl group

Front 16

What happens to Serine when Chymotrypsin is catalyzing?

Back 16

The side chain of serine (hydroxyl group) is ionized in the reaction as a result of removal of its proton by a nearby histidine. This occurs when the substrate binds the active site, moving the histidine slightly closer to the serine. serine becomes covalently attached to one peptide when the other peptide is released. Release of the second peptide from serine requires the action of water.

Front 17

Serine proteases act by creation of a

Back 17

Serine proteases act by creation of a reactive alkoxide ion.

Front 18

How is the reactive alkoxide ion made?

Back 18

Serine proteases act by creation of a reactive alkoxide ion. This is made by 1) binding of the proper substrate at the active site; 2) slight changes in shape that bring the catalytic triad (aspartic acid, histidine, and serine) closer together; 3) removal of a proton from the hydroxyl group of serine (creating the alkoxide ion).

Front 19

The alkoxide ion is reactive and

Back 19

The alkoxide ion is reactive and attacks the peptide bond in the active site, breaking it. One piece from the break is released and the other piece becomes transiently attached to the oxygen of the serine. Detachment of the attached peptide requires action of water in the active site. This is the slow step of the reaction.