Biochemistry: Chapter 9

Front 1

What are the four glucose transporters? Which two are the most significant as they are only present in certain cells and highy regulated?

Back 1

These transporters include GLUT 1, 2, 3, and 4. The 2 most important are GLUT2, and GLUT4.

Front 2

Directly after a meal, blood traveling through the hepatic portal vein from the intestine is very rich in glucose. What does GLUT2 have to do with this? Where is glut2 found? What is its affinity like?

Back 2

GLUT2 is a transporter found in hepatocytes and pancreatic cells. GLUT2 captures the excess glucose-primarily for storage. The Km of glut2 is quite high (15 mM). In the B-islets of the pancreas, glut2 along with glucokinase serves as the glucose sensor for insulin release.

Front 3

Where is GLUT4 found? What is its affinity like? What does it do?

Back 3

GLUT4 is found in adipose tissue and muscle tissue. It responds to glucose concentrations in peripheral blood. The Km of glut4 is close to the glucose levels in human blood (~5 Mm).

Front 4

How does increasing the insulin increase the amount of glut4 transporters on a cell?

Back 4

If insulin increases, the amount of glut 4 transporters will increase as well. This is done by exocytosis of transporters to the cell membrane.

Front 5

What purpose does glyceraldehyde-3-phosphate dehydrogenase accomplish during glycolysis?

Back 5

Glyceraldehyde-3-phosphate dehydrogenase catalyzes an oxidation and addition reaction of inorganic phosphate to its substrate glyceraldehyde-3-phosphate. This reaults in a high energy intermediate 1,3-bisphosphoglycerate along with the reduction of NAD+ to NADH.

Front 6

What does 3-phosphoglycerate kinase afford in glycolysis? What is its substrate?

Back 6

3-phosphoglycerate kinase transfers a high energy phosphate from 1,3-bisphosphoglycerate to ADP, thus forming ATP. This action is known as substrate level phosphorylation. The product of the reaction is 3-phosphoglycerate.

Front 7

What is the last enzyme in the glycolitic pathway? What does it do? What activates this enzyme?

Back 7

The last enzyme in the aerobic glycolitic pathway is pyruvate kinase. This enzyme reduces ADP to ATP while phosphoenolpyruvate is converted to pyruvate. This is known as a feed forward activation as fructose 1,6-bisphosphate activates pyruvate kinase.

Front 8

What three wnzymes of glycolysis are irreversible?

Back 8

Hexokinase

PFK-1

Pyruvate kinase

Front 9

In the absence of oxygen, fermentation will occur. What is the key fermentation enzymes in mammalian cells? Why is fermentation important?

Back 9

Fermentation is accomplished through lactate dehydrogenase. This enzyme uses NADH as a coenzyme to produce lactate from pyruvate. This is important to drive anaerobic glycolysis because this replenishes the oxidizing agent NAD+ in order for glyceraldehyde-3-phosphate dehydrogenase to use NAD+ as a coenzyme.

Front 10

Dihydroxyacetone phosphate (DHAP) is used in hepatic and adipose tissues for triacylglycerol synthesis. How does this occur?

Back 10

DHAP is formed from from fructose 1,6 bisphosphate. It can be isomerized to glycerol-3-phosphate, which can then be converted to glycerol in order to form triacylglycerols.

Front 11

Explain how glycolysis occurs in erythrocytes.

Back 11

1,3-bisphosphoglycerate is converted to 2,3 BPG by an enzyme known as bisphosphoglycerate mutase. It's important to remember that mutases are enzymes that move functional groups.

Front 12

How many ATPs are produced per molecule of glucose in red blood cells? How does 2,3 BPG effect the saturation of hemoglobin?

Back 12

2,3 BPG binds allosterically to the Beta chains of hemoglobin (HbA). This decreases the erythrocytes affinity for oxygen. This causes a right shift in a dissociation curve. This right ahift caused by 2,3 BPG allows for full saturation at the lungs, but still affords rapid unloading of O2 at target tissues.

Front 13

Glycogen synthase os the rate limiting enzyme of glycogen synthesis. What type of linkages does this enzyme create? What activates/inhibits this enzyme?

Back 13

Glycogen synthase is activated by insulin and glucose-6-phosphate, while it is inhibited by glucagon and epinephrine. This enzyme grows already existing chains of glucose by creating alpha-1,4 bonds.

Front 14

What does the branching enzyme do?

Back 14

The branching enzyme takes existing alpha 1,4 bonds and creates branched by literally moving them to alpha 1,6 branch points.

Front 15

What is the rate limiting enzyme of glycogenolysis? What activates and inhibits this enzyme?

Back 15

Glycogenolysis is determined by glycogen phosphorylates. This enzyme works to break alpha-1,4 bonds in glycogen. This enzyme is activated by glucagon in the liver, and also activated by epinephrine and AMP in the skeletal muscle. It is inhibited by ATP.

Front 16

What does glycogen phosphorylase release glucose as?

Back 16

Glucose-1-phosphate.

Front 17

What does dbranching enzyme do? What does it release a single glucose as?

Back 17

Debranching enzyme moves all of the glucose except the alpha 1,6 sugar. Afterwards, it reattaches the branch to a continuing alpha 1,4 chain and frees the alpha 1,6 single sugar as a free glucose.

Front 18

What are three inportant substrates for gluconeogenesis?

Back 18

Glycerol 3-phosphate

Lactate

Glucogenic amino acids

Front 19

What does pyruvate carboxylase accomplish? Where is it found? What activates it?

Back 19

Pyruvate carboxylase is an important gluconeogensis enzyme that works to form oxaloacetate (OAA) and deliver it to the cytoplasm outside of the mitochondria through the malate-aspartate shuttle. Acetyl-coA activates pyruvate carboxylase.

Front 20

Phosphoenolpyruvate carboxykinsae is in the cytoplasm of the cell. What does it do for the gluconeogenic pathway?

Back 20

(PEPCK) is induced by cortisol and glucagon. It works to convert OAA into phosphoenolpyruvate.

Front 21

What does fructose-1,6-bisphosphotase do?

Back 21

Fructose-1,6-bisphosphotase works to circumvent PFK-1. it does so by hydrolyzing phosphate from fructose-1,6-bisphosphate. This produces fructose 6-phosphate.

Front 22

Acetyl coA that drives gluconeogensis comes from where?

Back 22

Beta oxidation of fatty acids.

Front 23

What is the main goal of the pentose phosphate pathway (hexose monophosphate shunt)?

Back 23

The PPP serves to produce NADPH as well as creating ribose 5-phosphate for nucleotide synthesis.

Front 24

What is the inportant, rate limiting enzyme of the PPP?

Back 24

this would be glucose-6-phosphate dehydrogenase. This enzyme produces NADPH.

Front 25

What activates G6PD? What inhibits G6PD?

Back 25

This enzyme is induced by insulin as well as NADP. NADPH acts to serve as an inhibitor to the enzyme.

Front 26

What is the role of NAD+ and NADPH?

Back 26

NAD+ acts as a high energy electron acceptor. This makes it an extremely good oxidizing agent. The resulting NADH can then be fed into oxidative phospborylation to provide high energy molecules (ATP). On the other hand, NADPH primarily acts as an electron donor for biosynthesis.

Front 27

What 3 main roles does NADPH play in the body?

Back 27

NADPH serves to form reduced glutathione. Reduced glutathione is the bodies natural antioxidant. NADPH is involved in buosynthesis of fatty acids, as well as cholesterol. NADPH assists in cellular bleach production of certain white blood cells.