Biochem Exam 5

Where is α-amylase stated to be present?

In saliva and pancreatic secretions

α-amylase is described as which type of enzyme?

Exoglycosidase

Which product results from α-amylase cleavage of amylopectin or glycogen

All of the above

In starch and glycogen degradation, what does the debranching enzyme cleave?

Limit dextrins

Which is one of the two activities of the debranching enzyme described on the slide?

It transfers trisaccharide groups

Which is one of the two activities of the debranching enzyme is described:

Cleaving the remaining single glucose units from the main chain

As α-amylase nears branch point its going to reduce activity and end up with:

Highly branched limit dextrins

The debranching enzyme’s glucanotransferase activity transfers what?

A trisaccharide unit

In order for alpha amylase to easily digest, we have a debranching enzyme called ____ activity

glucanotransferase

The digestive breakdown of starch and dietary glycogen is:

Unregulated

Which form of glycogen is described as tightly regulated?

Synthesis and degradation of storage glycogen

Tissue glycogen is described on the slide as:

An important energy reservoir

___ cleaves a sugar unit from which part of the glycogen chain and uses inorganic phosphate to phosphorylate the glucose. (cleaves and phosphorylates at the same time)

Glycogen phosphorylase

What does glycogen phosphorylase use to phosphorylate the released glucose?

Inorganic phosphate

True or False: Glycogen phosphorylase requires the use of ATP and inorganic phosphate to phosphorylate glucose

False

After glycogen phosphorylase activity, what enzyme degrades the resulting limit dextrins?

Debranching enzyme

Which statement best describes the enzymes present in glycogen granules?

Catabolic and anabolic enzymes are present

True or False: In the phosphorolysis reaction, the glycosidic bonds are split by phosphates and NOT H2O

True

If glycogen is degraded in muscles, the reaction enters:

Enters glycolysis

If glycogen is degraded in liver then:

Glucose-6-phosphate is hydrolyzed to glucose

If glycogen is degraded in the liver, glucose-6-phosphate is hydrolyzed to glucose for:

Transport to other tissues

Where is the active site located within each glycogen phosphorylase subunit?

At the center of the subunit

The allosteric effector active site of glycogen phosphorylase lies near which region?

The subunit-subunit interface

Which residue serves as the regulatory phosphorylation site on each subunit of glycogen phosphorylase?

Ser14

Regulatory control of glycogen phosphorylase is influenced by which structural site?

Glycogen-binding site

Which molecules act as allosteric inhibitors of glycogen phosphorylase?

ATP and glucose-6-phosphate

Which molecule serves as an allosteric activator of glycogen phosphorylase?

AMP

What happens to glycogen breakdown when ATP and glucose-6-phosphate levels are abundant?

Breakdown is inhibited

True or False: When cellular energy reserves are LOW (meaning high AMP and low ATP-G6P), glycogen metabolism is stimulated.

True

Which condition would most strongly activate glycogen phosphorylase?

High AMP and low ATP

What general rule describes the relationship between cellular energy status and glycogen breakdown?

Both

Phosphorylation of which Ser14 converts phosphorylase b into phosphorylase a causing:

A large conformational change that decreases allosteric sensitivity

Which form of glycogen phosphorylase is less sensitive to allosteric regulation?

Phosphorylase a

Phosphorylation of glycogen phosphorylase shifts the enzyme’s equilibrium toward which state?

R state

Once phosphorylated, glycogen phosphorylase becomes more active because it no longer requires:

AMP as an allosteric activator

Phosphorylation converts glycogen phosphorylase into a form that is:

Active without allosteric activation

Phosphorylase kinase, which activates glycogen phosphorylase, is itself activated by which mechanism?

Phosphorylation

Which hormones stimulate the signaling cascade that activates phosphorylase kinase?

Epinephrine and glucagon

Epinephrine’s role in regulating glycogen breakdown is to:

Prepare the body for large energy demands

Which hormone inhibits glucagon secretion?

Insulin

Which abnormal pattern occurs in diabetes regarding glycogen breakdown?

Glycogen is degraded even when glucose levels are high

cAMP is classified as what type of molecule in hormone signaling?

Second messenger

Which enzyme converts ATP into cAMP?

Adenylyl cyclase

What happens when cAMP binds to the regulatory subunits of cAMP-dependent protein kinase?

The catalytic subunits dissociate and become active

The catalytic subunits of cAMP-dependent protein kinase phosphorylate which target in the glycogen breakdown pathway?

Phosphorylase kinase

Which molecule activates glucose needed for glycogen synthesis? (not what activates glycogen synthesis, there’s a difference)

UDP

Glycogen synthesis differs from glycogen degradation because synthesis requires:

Activation of glucose as a sugar nucleotide