Medical Biochemistry Test 2

Front 1

The main chains of glycogen exist as what kind of bonds?

Back 1

Alpha 1-4

Front 2

The branched chain of glycogen exist as what king of bond?

Back 2

Alpha 1-6

Front 3

Animals use the ___ anomer of glucose for glycogen synthesis while plants use the ___ anomer for cellular biosynthesis and the _____ anomer for starch synthesis?

Back 3

Animals use the alpha to make glucose, plants use the beta to produce cellulose (we cant break it down) and they use the alpha anomer to produce starch. (we can digest starch)

Front 4

The enzyme that produces glycogen from glucose?

Back 4

Glycogen synthase.

Front 5

Before a molecule of glucose can be converted to glycogen, what must happen to it?

Back 5

It must be converted to glucose 6 phosphate by the glucokinase (or hexokinase), then the G6P is converted to G16P, then G1P by phosphoglucomutase. Glucose 1 phosphate becomes UDP-glucose by the action of uridylyl transferase on UTP. The UDP glucose may now be acted upon to form the A1-4 chain of glycogen.

Front 6

What role does pyrophosphate play in the production of glycogen?

Back 6

When UTP and glucose are combined using an uridylyl transferse both UDP-glucose and pyrophophate are formed. Pyrophosphare is rapidly converted by pyrophosphatase, a ubiquitouse enzyme, into two inorganic phosphates. This reactions makes to overal production of glycogen very energetically favored.

Front 7

What role does UDP play in the production of glycogen?

Back 7

It acts as a byproduct of the reaction that supplies the energy (from the phophate bonds) for the reaction.

Front 9

How does glycogenin help to produce glycogen?

Back 9

It acts as the template for the firt polymerization of glucose.

Front 10

Where does glycogenin react with UDP-glucose?

Back 10

There is a tyrosine group on the chain of glycogenin. This tyrosine has an OH- group bound to it on the end. This OH- acts as a neucleophile and binds to glucose kicking off UDP.

Front 11

How many times of glycogenin react with UDO-Glucose?

Back 11

It reacts 7 times to produce an octomer primer (the eighth is the tyrosine.)

Front 12

After Glycogenin has reacted with UDP-glucose seven times to produce an octomer of glycogen, what happens?

Back 12

glycogen synthase and more UDP-glucose create a single chain of alpha 1-4 bonded glycogen.

Front 13

Is glycogen generally a single chain of molecules or a branched chain? What causes the branching?

Back 13

Branched, the branching enzyme adds a new chain of alpha 1-4 glycogen to to an existing chain of alpha 1-4 glycogne by using a single alpha 1-6 bind.

Front 14

What does the branching enzyme do and how does it do it?

Back 14

It adds a terminal 6 to 7 fragment chain of alpha 1-4 glucose to an existing chain of alpha 1-4 glucose by using an alpha 1-6 chain.

Front 15

What enzyme breaks glycogen down into individual glucose 1 phophate molecules?

Back 15

Glycogen phosphorylase.

Front 16

What is important in the way glycogen phophorylase breaks doen glycogen?

Back 16

It does not use a hydrolysis reaction, rather it uses inorganic phosphate to break the 1-4 linkage leading to the product glucose1phosphate.

Front 17

What end of the glycogen chain doen glycogen phosphorylase react with?

Back 17

It reacts with the non-reducing end of glycogen 1 glucose1phophate at a time.

Front 18

What is the advantage of phophorolytic cleavage of glycogen over hydrolysis?

Back 18

Glucose 1 phophate is formed without the need for ATP. This reaction is energentically favorable due to the excess amount of inorganic phosphate in the cell.

Front 19

When does glycogen phosphorylase stop reacting with a glycogen chain?

Back 19

It stops 4 residues before the branching point.

Front 20

After glycogen phophorylase stops reacting with a glycogen, what enzyme is used?

Back 20

The debranching enzyme cuts three of the last 4 residues and replaces them on another end of the molecule, effectively straightening out the chain.

Front 21

What breaks the alpha 1-6 bond in glycogen?

Back 21

the alpha 1-6 glucosidase by hydrolysis.

Front 22

What happens to the glucose1phosphate that is created by the degredation of glycogen?

Back 22

It is rapidly converted to glucose6phosphate by phosphoglucomutase so it can enter into glycolysis.

Front 23

Is the liberated glucose1phosphate created by cleaving glycogen capable of entering glycolysis?

Back 23

No, it must be converted into glucose6phophate by phosphoglucomutase.

Front 24

In the liver, glucose6phosphate is converted to what to create glucose?

Back 24

Glucose6phosphatase.

Front 25

In muscle, what happens to the glucose1phosphate that is poduced due to the breakdown of glycogen?

Back 25

Since muscle does not have the enzyme glucose6phosphatse, glucose6phosphate is used directly in the glycolytic pathway

Front 26

What can the liver do with glucose6phosphate?

Back 26

It can either use it in glycolysis to produce ATP, or it can use glucose6phosphatase to produce glucose to be distributed into the blood.

Front 27

What can skeletal muscle cells do with glucose 6 phosphate?

Back 27

Since they lack the enzyme glucose6phosphatase, they cannot create glucose, and must use glucose6phosphate directly in the glycolytic production of energy.

Front 28

In what 2 ways is glycogen phosphorylase regulated?

Back 28

Allosteric regulation and covalent modification.

Front 29

describe allosteric regulation?

Back 29

An effector or metabolite binds to an allosteric site on the enzyme. This may be either a positive or a negative effect.

Front 30

Describe the two states of the glycogen phosphorylase enzyme?

Back 30

An R state (relaxed) and a T state (tense). Phophorylase is capable of binding to glycogen in the R state.

Front 31

What stabilizes the R state of glycogen phosphorylase?

Back 31

AMP, thus AMP is a positive effector for the breakdown of glycogen into glucose1phosphate.

Front 32

What inhibits the R state of glycogne phosphorylase, thus stabilizing the T state?

Back 32

ATP, thus ATP is a negative effector in the breakdown of glycogen.

Front 33

T/F High levels of cellular ATP would lead to the breakdown of glycogen?

Back 33

False. ATP is a negative effector of the breakdown of glycogen. Why would the cell need to breakdown glycogen if there was plenty of energy around?

Front 34

When is glycogen phosphorylase turned into glycogne phosphorylase A?

Back 34

During times of great energy need like exercise.

Front 35

In response to lowering blood glucose, the alpha cells of the pancreas secrete what?

Back 35

Glucagon.

Front 36

What does glucagon do?

Back 36

It binds to cell receptors located on the liver cell membrane causes the activation of adenylate cyclase wich forms the second messenger cAMP.

Front 37

What does adenylate cyclase do?

Back 37

In the liver, it catalyzes the reaction of ATP to cAMP.

Front 38

What does cAMP do in the liver?

Back 38

2 molecules of cAMP bind to protein kinase A causing the the molecule to split into two parts. One of the parts, known as catalytically active PKA activates phosphorylase kinase.

Front 39

What are two other ways that glyogenolysis may be stimulated other than by direct activity of the glycogen phosphorolase enzyme?

Back 39

Epinephrine released by the adrenal medulla in response to neural signaling will bind to muscle cells and activate glycogenolysis. Also, high levels of Ca in the cell will activate phosphorylase kinase which will in turn activat glycogen phosphorylase A from glycogen phosphorylase (b).

Front 40

What does phophorylase kinase do?

Back 40

It turns glycogen phosphorylase into glycogen phosphorylase A, the more active enzyme.

Front 41

Increased intracellular calcium levels in muscles does what?

Back 41

Both increase the rate of muscle contraction and the rate of glycogenolysis, producing even more ATP for contractions.

Front 42

How does epinephrine work in the cell?

Back 42

Epinephrine binds to the A adrenergic receptor through Gprotiein reaction that activates PLC.

Front 43

What does PLC do in the cell?

Back 43

PLC hydrolyzes PIP2 into IP3 and DAG.

Front 44

What does DAG do in the cell?

Back 44

DAG binds to and activates protein Kinase C which phosphorylates glycogen synthase stopping its reaction.

Front 45

What does phophorylating glycogen synthase do?

Back 45

It lowers the molecules affinity for UDP-Glucose.

Front 46

What does IP3 do in the cell?

Back 46

It binds to receptors on the surface of the ER leading to the release of Ca, thus increasing the cellular concentration of Ca.

Front 47

Phosphorylating glycogen phosphorylase does what?

Back 47

Speeds up the reaction of turning glycogen into glucose1phosphate.

Front 48

How is the synthesis of glycogen not carried out while g glycose is being degrated?

Back 48

The phosphorylation of glucogen synthase stops the creation of glycogen, however the phosphorylation of glycogen phosphorylase creates glycogen phosphorylase A which speeds up the breakdown of glycogen into glucose1phosphate.

Front 49

the effects of phosphorylating glycogen synthase are?

Back 49

Decreased affinity for glycogen synthase to UDPglucose, and it increases the ammount of the allosteric activator G6P needed to activate glucose synthase.

Front 50

Von Gierkes disease is a lack of what enzyme?

Back 50

Glucose 6 phophatase.

Front 51

Is muscle tissue affected by Von Gierkes disease?

Back 51

Only secondarily, as muscle tissue does not have glucos6phosphatase anyway.