Lecture 20: Glycolysis

Question 1

Describe the fates of glucose in mammals… Which cells require glucose as their main source of fuel? Where do we get glucose in our diets?

Answer 1

The brain (even under non-starvation) and Red blood cells use glucose as fuel

Diet: Disaccharides, starch, glycogen

pyruvate and lactate can be salvaged and resynthesized to glucose

Question 2

Where is GLUT 1 mainly expressed?

Answer 2

brain and RBCs; has a high affinity for glucose

Km= 1mM

Question 3

Describe GLUT 2

Answer 3

Main transporter in the liver, and it has a low affinity for glucose

Km= 10 mM

Question 4

Describe GLUT 3

Answer 4

Main transporter in the neurons and has a high affinity for glucose

Km= 1 mM

Question 5

Describe GLUT 4

Answer 5

present in skeletal muscle, heart, and the adipose tissue. Insulin dependent

Km=5mM

Question 6

Which steps of glycolysis are in the “trapping of glucose” stage?

Answer 6

Glucose–>G6P–>F6P->F1,6BP–G3P

Question 7

Which steps of glycolysis are involved in the generation of ATP?

Answer 7

G3P–>1,3BPG–>3PG–>2PG–>PEP–> Pyruvate

Question 8

Describe stage 1 of glycolysis

Answer 8

Has 5 steps
2 ATP are consumed, nothing is generated

There are 3 reactions; phosphorylation, isomerization, and another phosphorylation

Question 9

What is Step 1 of glycolysis and describe the differences that are present if it is occurring in the liver versus in all of the tissues

Answer 9

Step 1 is taking Glucose to Glucose 6 phosphate (G6P)
hexokinase is used in the tissues and glucokinase is used in the liver

ATP is consumed

Question 10

What is Step 2 of glycolysis

Answer 10

G6P is isomerize to fructose 6 phosphate (F6P) with phosphoglucoisomerase

Question 11

What is step 3 of glycolysis

Answer 11

F6P is phosphorylated to F1,6BP with phosphofructokinase

ATP is consumed

RATE LIMITING STEP OF GLYCOLYSIS

Question 12

What is the rate limiting step of glycolysis?

Answer 12

Taking F6P to F16BP with phosphofructokinase

Question 13

What is step 4 of glycolysis?

Answer 13

F1,6BP is broken down into G3P and DHAP with aldolase

Question 14

What is step 5 of glycolysis?

Answer 14

DHAP is converted to G3P with triose phosphate isomerase

Question 15

In the first stage of glycolysis, which steps require ATP?

Answer 15

Step 1 from glucose to G6P and Step 3 from F6P to F1,6BP

Question 16

Describe what happens to the G3P as it is transitioning into the generation of ATP stage of glycolysis

Answer 16

Glyceraldehyde 3-phosphate dehydrogenase converts G3P to 1,3BPG

NAD+ and phosphate is reduced to make NADH that goes to the electron transport chain

Question 17

Describe the phosphoglycerate kinase step of glycolysis

Answer 17

Converts 1,3BPG to 3-PG with the use of phosphoglycerate kinase

this reaction makes ATP

Question 18

Describe the phosphoglycerate mutase step of glycolysis

Answer 18

Takes 3-PG to 2-PG with the phosphoglycerate mutase

Question 19

Describe the enolase step of glycolysis

Answer 19

Enolase Takes 2 PG to PEP and H2O is released

Question 20

Describe the conversion of PEP to pyruvate

Answer 20

pyruvate kinase takes PEP to pyruvate and creates an ATP molecule; irreversible step

Question 21

After the pyruvate is made by glycolysis, what are the various fates that she has?

Answer 21

1. reduced to lactate if there is a low O2 content
2. can be oxidized aerobically via the CAC(citric acid) to form acetyl coA
3. Can be converted to acetaldehyde and to ethanol

Question 22

Define sucrose

Answer 22

glucose and fructose

Question 23

Define lactose

Answer 23

glucose and galactose

Question 24

Describe the entry points of galactose and fructose in glycolysis, distinguishing between fructose in adipose tissue and the liver

Answer 24

Galactose enters into the cycle as G6P

Fructose from adipose tissue F6P

Fructose from the liver is able to form into DHAP and then transformed into G3P which SKIPS the rate limiting step; can be used in times of high energy

Question 25

What are the major regulatory enzymes of glycolysis

Answer 25

1. hexokinase
2. phosphofructokinase
3. pyruvate kinase

Question 26

Describe the differences between glycolysis in muscle versus the liver

Answer 26

In the muscle, the ATP levels regulate whether or not glycolysis happens; so if you are at rest, then glycolysis will not occur, but if you are exercising, then it will

In the liver, the goal is to maintain the blood glucose levels; it is regulated by the major kinases in the liver. Phosphofrutokinase is activated by F2,6BP and inhibited by citrate

Glucokinase is the (hexokinase) of the liver and is not inhibited by G6P so the glucose is permanently trapped

Pyruvate kinase is regulated by allosteric effectors and covalent modification

Question 27

Why is high fructose corn syrup bad for you?

Answer 27

It is able to bypass the regulatory step of glycolysis the phosphofructokinase-catalyzed reaction which leads excess triacylglycerols in the adipose tissue, resulting in obesity

Question 28

Describe galactosemia

Answer 28

disruption of galactose metabolism; cannot process galactose or lactose (because it has galactose in it) and can cause CNS problems, cataracts, and cognitive issues, because there are some extreme physiological problems that result