Glycolysis

Question 1

Glycolysis

Answer 1

Occurs in all human cells

“Anaerobic” process (Oxygen is not required)

It sets the stage for AEROBIC OXIDATION of glucose in the cells via the Krebs Cycle

Question 2

(TRUE/FALSE)

Many of our tissues rely solely on glycolysis, such as RBCs that do not have mitochondria.

Answer 2

TRUE

They require a high level of glucose and they will convert glucose to ATP in order to meet their energy needs.

Question 3

How much does 1 glucose molecule yield in glycolysis?

Answer 3

2 pyruvate
2 ATP
2 NADH

Question 4

What is the energy investment phase? What does it require?

Answer 4

2 ATP are required to get glycolysis started. By the end of glycolysis, we will yield 4 ATP; however, the net is going to be only 2 ATP.

Question 5

In the adipose and muscle tissue, what enzyme phosphorylates glucose, as the first step in glycolysis?

Answer 5

HEXOKINASE

Question 6

In the hepatocytes, what enzyme phosphorylates glucose, as the first step in glycolysis?

Answer 6

GLUCOKINASE

Question 7

Why is glucose-6-phosphate important?

Answer 7

Once glucose has been phosphorylated into glucose-6-P, it can enter a number of different pathways, including glycolysis.

*1 ATP is used

Question 8

What is the second step in glycolysis?

Answer 8

Glucose-6-P is isomerized to Fructose-6-P.

*1 ATP is used, as this is part of the PRIMING PHASE of glycolysis

Question 9

Why is substrate level phosphorylation important?**

Answer 9

**Does NOT require the ETC and we have been able to generate some ATP to be used for energy, which has been done completely independent of the MITOCHONDRIA.

Question 10

Why is it essential to regenerate NAD from NADH in the cytoplasm for glycolysis? In which 2 ways is this done?

Answer 10

Glycolysis will be inhibited if NAD is not regeneration by:

1. NADH to go to oxidative phosphorylation, drop off it’s electrons and cycle. back to the cytoplasm as NAD (during aerobic glycolysis, when oxygen and mitochondria are present).
2. NADH can reduce pyruvate to lactate, so NAD can be reformed (during anaerobic glycolysis).

It will be inhibited in the reaction of glyceraldehydrate-3-P to 1,3-bisp

Question 11

(TRUE/FALSE)

There is an unlimited supply of NAD (coenzyme form of niacin) available for glycolysis in the cytoplasm.

Answer 11

FALSE

There is a VERY limited amount, which is why NAD regeneration is so important!

Question 12

Besides RBCs, what other tissues lack mitochondria? How much glucose do they require?

Answer 12

Cornea, lens, part of the retina
Testis
Leukocytes
White muscle fibers (few mito)

These require 40g of glucose daily in adults

Question 13

How much glucose is required by the brain per day?

Answer 13

120g glucose in an adult is used by the brain to meet ATP needs

Remember: the brain relies HEAVILY on glucose, it can switch over to ketones during prolonged starvation but it is NOT able to utilize beta-oxidation.

Question 14

Explain glucose metabolism in RBCs.

Answer 14

GLUT-1 transporter

Glucose is metabolized mainly by GLYCOLYSIS

Since RBC lack mitochondria, the end product is LACTATE.

In the RBCs, some glucose is also used by the PPP (Pentose Phosphate Pathway) to provide NADPH to keep GLUTATHIONE in a reduced state, which has an IMPORTANT role in destruction of organic peroxides.

Question 15

Explain glucose metabolism in the BRAIN.

Answer 15

GLUT-3

Glucose is FULLY OXIDIZED BC THERE IS MITOCHONDRIA PRESENT*** through glycolysis and into the TCA Cycle

The PPP is activated to generate NADPH for reductive synthesis and to keep glutathione in a reduced state.

Question 16

Explain glucose metabolism in the MUSCLE and HEART.

Answer 16

Insulin stimulates the transport of glucose into these cells via GLUT-4.

1. Glucose can be FULLY oxidized bc of mito being present through glycolysis.
2. Go to PPP to produce NADH

OR,

3. GLYCOGENESIS: they can synthesize significant amounts of GLYCOGEN

Question 17

Explain glucose metabolism in ADIPOSE TISSUE.

Answer 17

Insulin stimulates the transport of glucose into these cells via GLUT-4.

1. and will go through Glycolysis (which is similar to Muscle and Heart); however, the PYRUVATE is going to enter into the MITOCHONDRIA and be converted to acetyl-CoAs which will be mainly used for FA SYNTHESIS, which will then be converted to TRIACYLGLYCEROL and stored in adipose tissue.
2. NADPH is also produced through PPP for the reductive synthesis of FA. **Very important in the reduction of FAs.

In other words: there is NOT a lot of mito in adipose tissue, there is some, but for the most part the acetyl-CoA is NOT going to be fully oxidized, rather it will be shuttled back where they will participate in the synthesis of FA.

3. Minimal amount will be stored as glycogen

Question 18

Explain glucose metabolism in HEPATOCYTES.

Answer 18

GLUT-2 transporter which is INDEPENDENT*** of insulin

Once within the LIVER, glucose has the greatest number of different pathways:

1. Glucose –> Pyruvate —> CO2 & H20 (Glycolysis & FULL oxidation)
2. Glycogen synthesis and breakdown
3. Excess Glucose will be converted to pyruvate, then acetyl-CoA for FA synthesis
4. PPP
5. Gluconeogenesis