Biochemistry: Storage Of Energy- Carbohydrates

Front 1

What's the structure of glycogen?

Back 1

It is a branched glucose polymer, between 10K and 40K of glucose residues. Has a reducing end with a free OH at carbon 1, but a large number of non-reducing ends with a free OH and carbon 4.

Front 2

What is the osmotic advantage of glycogen?

Back 2

Individual glucose molecules would create an osmotic gradient that would cause the cell to suck up water and burst. Glycogen reduces this problem.

Front 3

Which end of the glycogen molecule reacts with Fehling's solution?

Back 3

Reducing end

Front 4

Which bonds are glycosidic bonds?

Back 4

a-1,4 glycosidic bonds are linear
a-1,6 glycosidic bonds are branching

Front 5

What is the role of glycogenin in limiting the size of glycogen molecules?

Back 5

For glycogen synthesis to occur, there must be contact between glycogenin and glycogen synthase. In synthesis, a size is eventually reached where that association can no longer occur, so it stops.

Front 6

What does "reducing sugar" mean?

Back 6

The carbonyl group (C1) of the monosaccharides has reducing properties. The reducing properties are lost when the carbonyl carbon forms a glycosidic bond. Of the disaccharides, only sucrose is not a reducing sugar because both anomeric carbons participate in glycosidic bonds.

Front 7

What's the difference between the structure of glycogen and starch?

Back 7

Glycogen are only branched (branching 8-12 residues). There are no linear forms. The reducing end could open up and react with fehling's reagent (glucose, fructose, galactose are reducing monosaccharids), however, reducing end attached to glycogenin (glycoprotein) can't open up.

Starch is linear (amylose) and branched (amylopectin, branching 24-30 residues)

Front 8

What is the activation step of glycogen synthesis?

Back 8

Glucose ----> G6P (Hexokinase, ATP)
G6P --> G1P (phosphoglucomutase)
G1P--> UDP-glucose (UDP-glucose pyrophosphorlase, DP -->2Pi)

Front 9

What is the polymerization step of glycogen synthesis?

Back 9

UDP-glucose + Glycogen --> Glycogen (w/ one more glucose attached) + UDP (Glycogen synthase)

1-4 bonds

UTP is regenerated using ATP.

Front 10

How does the branching enzyme work?

Back 10

By translocating 7 glucose residues from the growing end and reattaches them to C6 of a glucose residue in a more interior location.

Front 11

How is glycogen broken down (glycogenolysis)?

Back 11

Phosphorylase releases glucose-1P from glycogen up to four carbons from the branching point. Glucose-1P is then turned into G6P by mutase.

Phosphorylase can not break branching bonds. It uses the debranching enzyme (transferase) to transfers three of the four remaining glucose to the other branch, and then, glucosidase removes the final branched glucose (1-6 link) as free glucose, which is then rapidly phosphorylated.

Front 12

Which end does phosphorylase act?

Back 12

Non-reducing ends to cleave off G1P.

Front 13

Is a phosphorylated glycogen synthase fully active or less active?

Back 13

Less

Front 14

Is a phosphorylated phosphorylase fully active or less active?

Back 14

Fully

Front 15

How does cAMP increase the activity of protein kinase A?

Back 15

Without cAPM, protein kinase A is made up of two catalytic subunits that are bound to two regulatory subunits. This is the inactive form of PKA.

cAMP can bind to the regulatory subunits, which triggers the release of the catalytic units, each one of which can operate on its own.

Front 16

What's the effect of insulin on cAMP concentration?

Back 16

Reduces it by activating cAMP degrading phosphodiesterase.

Front 17

What is the effect of increased cAMP? Of reduced cAMP?

Back 17

Phosphorylation of a whole bunch of proteins: Phosphorylated glycogen synthase inactivates it, while phosphorylation of phosphorylase A activates it.

Reduced cAMP dephosphorylates a whole bunch of proteins, which means that glycogen synthase is active, and phorphorylase A is inactive.

Front 18

What tissue responds to epinephrine? To glucagon?

Back 18

Liver and muscle
Muscle only

Front 19

What's the defective enzyme and symptoms for Von Gierke's disease?

Back 19

Glucose-6-phosphatase (makes G6P into glucose)

Hypoglycemia (b/c no glucose is not released into blood from gluconeogenesis) reduces insulin and increases glucagon, gluconeogenesis is accelerated (b/c of glucagon). Pyruvate is shunted to lactate. Inactive form of glycogen synthase is stimulated by excess G6P

Affected organs: Liver, Kidney

Symptoms: Severe heptomegaly, sever hypoglycemia, lactic acidosis, ketosis, hyperuricemia.

Front 20

What's the defective enzyme and symptoms for Pompe's disease?

Back 20

a-1,4 glucosidase (the one that cleaves off the remaining glucose into free glucose as a part of the debranching enzyme)

Illustrates role of lysosomes in glycogen turnover

Affects all organs

Symptoms: Death from cardiac failure in infants

Front 21

What's the defective enzyme and symptoms for Cori's disease?

Back 21

Debranching enzyme. Limited amount of glucose is available beyond last branch point. Gluconeogenesis must make up the shortfall.

Organs: Muscle, liver

Symptoms: milder heptomegaly, lactic acidosis, ketosis, hyperuricemia.

Front 22

What's the defective enzyme and symptoms for Andersen's disease?

Back 22

Branching enzyme. Unbranched long chain (amylopectin) causes cirrhosis.

Organ: Liver, myocardium

Symptoms: Death from liver cirrhosis, usually before age 2

Front 23

What's the defective enzyme and symptoms for McArdles disease?

Back 23

Phorphorylase. Patients can not make glycogen. Injection of epinephrine has no effect, can make lactate from glucose. Myoglobin appears in urine (produced by severe cramping)

Organ: Muscle

Symptoms: Muscle cramps and pain upon exertion. Easy fatigability, normal life expectancy.

Front 24

What's the defective enzyme and symptoms for Her's disease?

Back 24

Phosphorylase. Gluconeogenesis and diet permit normal lifestyle

Organ: Liver

Symptoms: Heptomegaly, hypoglycemia, lactic acidosis, ketosis, hyperuricemia.

Front 25

What's the defective enzyme and symptoms for Tauri's

Back 25

Phosphofructokinase

Organ: Muscle, RBCs

Symptoms: Muscle cramps and pain upon exertion, easy fatigability, normal life.

Front 26

What's the defective enzyme and symptoms for VIII glycogen storage disease?

Back 26

Phosphorylase kinase

Organ: Liver

Symptoms: mild hepatomegaly and hypoglycemia.