Glycolysis

Question 1

*Be able to describe the process of glycolysis.

Answer 1

Glycolysis- process of breaking down glucose.

Converting one molecule of glucose to 2 molecules of pyruvate with generation of 2 net molecules of ATP

Question 2

*What does hexokinase do?

Answer 2

Hexokinase- transfer phosphoryl group from ATP to glucose to form Glucose 6-phosphate (at expense of ATP)
Hexokinase- requires Mg^2+ or Mn^2+ as a cofactor, catalyzes the reaction.
Hexokinases also employ substrate-binding induced fit to minimize hydrolysis of ATP (increases specificity, decreases chance of becoming indiscriminate ATPase)
upon entering cell through specific transport protein, glucose phosphorylated into G6P.

Question 3

*Understand the two stages of glycolysis and what is consumed and produced at each stage.

Answer 3

Stage 1: TRAPS glucose in the cell and modifies it so it can be cleaved into pair of phosphorylated 3-carbon compounds (HIGH PHOSPHORYL TRANSFER POTENTIAL), no ATP produced yet. (you used up 2 ATP). (investment)
Stage 2: Oxidizes the 3 carbon- compounds to pyruvate while generating 2 molecules of ATP (Pay off stage)

Question 4

*Understand what substrate-level phosphorylation is.

Answer 4

Substrate-level phosphorylation- process of forming ATP from ADP through a phosphoryl donor that is a substrate with HIGIHER PHOSPHORYL TRANSFER POTENTIAL than ATP.
Ex: 1,3 Bisphosphoglycerate (Phosphate donor, with higher PTP than ATP) reactis with ADP to form 3-phosphoglycerate and ATP.

Question 5

*Know where ATP is utilized and synthesized and where NADH is generated in the steps of
glycolysis.

Answer 5

ATP is utilized in 1st and 3rd steps of glycolysis:
-Glucose to form Glucose 6-phosphate
- Fructose 6-phosphate to form fructose 1, 6-bisphosphate.
ATP is synthesized in 2 steps
1. in 1,3 Bisphosphogylcerate to form 3-phosphogylcerate (1,3 BPG to 3PG) using phosphoglycerate kinase.
2. Phosphoenolpyruvate to form pyruvate (through pyruvate kinase)
NADH is generated in 6th step:
Glyceraldehyde 3-phosphate forms 1,3 bisphosphoglycerate (using G3P DH)

Question 6

*Understand table 16.1 in terms of the free-energy changes

Answer 6

a

Question 7

*What are the enzymes that catalyze the three irreversible steps in glycolysis?

Answer 7

hexokinase, phosphofructokinase, pyruvate kinase

Question 8

*Be able to describe the three fates of pyruvate. What does the conversion of pyruvate to
lactate or ethanol actually do for the cell?

Answer 8

3 fates:

1. pyruvate can be converted into acetyl CoA, with presence of both Oxygen and mitochondria. (3c to 2c)
2. Pyruvate can be converted to Lactate (absence of oxygen), oxidizing NADH to NAD+ (3c to 3c)
3. Pyruvate can be converted to ethanol through oxidation of NADH to NAD+ (absence of Oxygen, 2c to 2c)

Question 9

*Understand how galactose and fructose enter into glycolysis.

Answer 9

Fructose from table sugar or high fructose and galactose (milk sugar) are converted into glycolytic intermediates.
They are both metabolized in the liver.
Galactose reacts with ATP to from glucose-1 phosphate (which can then be converted to glucose 6-phosphate by phosphoglucomutase.
In liver, fructose is metabolized by fructose 1-phosphate pathway.
other tissues, such as adipose tissue, fructose is directly phosphorylated to hexokinase.

Question 10

*How is glycolysis regulated in skeletal muscle? Why is glycolysis regulated differently in
the liver? How is it regulated in the liver?

Answer 10

a

Question 11

*What is aerobic glycolysis?

Answer 11

a

Question 12

*Become familiar with the family of glucose transporters (Table 16.3)

Answer 12

GLUT1-5 facilitate the movement of glucose.
GLUT 1- all mammalian tissues; basal glucose uptake in BRAIN-BARRIER
GLUT 2- acts as glucose sensor. in PANCREAS beta cells, regulates insulin; in LIVER remove excess glucose from blood (insulin dependent)
GLUT 3- in all mammalian tissues, basal glucose uptake in NEURONS, WBC.
GLUT 4- MUSCLE and FAT cells, insulin sensitive/dependent. The am amount in muscle PM increases with endurance training
GLUT 5 - in small intestine, transporter for fructose

Question 13

Why is glucose such a prominent fuel in all life forms?

Answer 13

1. Glucose may have been available for primitive biochemical systems, because it can form under prebiotic conditions
2. Glucose is the most stable hexose
3. Glucose has a low tendency to non-enzymatically glycosylate proteins.

Question 14

What is the rate limiting step in glycolysis?

Answer 14

converting fructose-6-phosphate into fructose 1, 6 bisphosphate using PHOSPHOFRUCTOKINASE (PFK). irreversible step

Question 15

What are the three enzymes that catalyze irreversible reactions in metabolic pathways, and serve as potential control sites?

Answer 15

The three enzymes that have irreversible reactions:

1. Hexokinase
2. phosphofructokinase
3. pyruvate kinase

Question 16

What facilitates them movement of glucose across the cell membrane?

Answer 16

A family of 5 glucose transporters called GLUT1-5 facilitate the movement of glucose.

Question 17

What kind of isoforms do pyruvate kinase have?

What happens to pyruvate kinase, with low blood glucose?

Answer 17

L form- Liver
M form- Muscle
allosteric regulation is similar for both forms except alanine (only L form affected)
Only L form controlled by phosphorylation/dephosphorylation.
Low blood glucose:
-Glucagon triggers cAMP cascade that leads to phosphorylation of pyruvate kinase (LOWERS ACTIVITY) minimizes liver from consuming glucose, when it is needed by brain and muscle.

Question 18

Which compounds are key regulators of phosphofructokinase in the liver?

Answer 18

CITRATE (reports on status of citric acid cycle) and FRUCTOSE-2, 6 BISPHOSPHATE.
Citrate INHIBITS phosphofructokinase, while 2,6, bisphosphate is POWERFUL ACTIVATOR (overriding other molecules)

Question 19

What is the cause of lactose intolerance, or HYPOLACTASIA?

Answer 19

Lactose intolerance, occurs because most adults lack the enzyme to degrade lactose. (they do not have lactase that will convert lactose to glucose and galactose).

Question 20

What are pathological conditions caused by excess fructose consumption?
What enzyme gets bypassed in the liver and why?

Answer 20

Excess fructose consumption linked to obesity, fatty liver, and development of type 2 diabetes.
Due to manner in which fructose is processed in liver, PFK (key regulatory enzyme of glycolysis) is bypassed in liver
-excess acetyl COA is then synthesized and converted to fats.

Question 21

What must be present for Glycolysis and ATP synthesis to continue? How is NAD+ regenerated?

Answer 21

Conversion of glucose into pyruvate generates ATP, but for ATP synthesis to occur, NADH must be REOXIDIZED to NAD+.
NAD+, coenzyme is derived from vitamin B3 (NIACIN).
NAD+ can be regenerated by further oxidation of pyruvate to CO2, or by formation of ethanol and lactate from pyruvate.

Question 22

What is the net reaction for glycolysis?

Answer 22

1 glucose molecule + 2 ADP and 2 Pi + 2 NAD+ will form 2 pyruvate + 2 ATP +2 NADH + 2H and 2 H20.

Question 23

How is PEP (Phosphoenolpyruvate) formed? What makes this a special compound and why? What happens after this compound made?

Answer 23

1. 3-phosphoglycerate is converted into 2-phosphoglycerate by phosphoglycerate mutase.
2. Then a dehydration reaction catalyzed by ENOLASE, results in production of phosphoenol pyruvate (PEP).

PEP is special because it is HIGH phosphoryl-transfer compound due to the presence of phosphate trapping the compound in unstable enol tautomer.

ADP is then phosphorylated at expense of PEP, generating ATP and pyruvate, catalyzed by pyruvate kinase.

Question 24

What compounds and enzyme are used to form fructose 6-phosphate in glycolysis?

Answer 24

Glucose 6-phosphate will convert to fructose 6-phosphate using PHOSPHOGLUCOSE ISOMERASE ENZYME.
reaction is readily reversible.

Question 25

What compound forms next after fructose 6-phosphate? what are the compounds and enzymes involved?

Answer 25

Fructose 6-phosphate will be converted to fructose 1,6 bisphosphate through enzyme phosphofructokinase (PFK).
This step is where carbohydrate is trapped in fructose form by addition of second phosphate to form fructose 1,6 bisphosphate.
irreversible reaction (by allosteric enzyme PFK).

Question 26

what compounds does the second phase of glycolysis begin with?
Which of the compounds cannot be used to yield ATP?

Answer 26

Second phase of glycolysis begins with:
cleavage of fructose 1,6 bisphosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3- phosphate (GAP).
this reaction is readily reversible and is catalyzed by enzyme ALDOLASE
GAP can be processed to pyruvate to yield ATP.
But DHAP can NOT be continued to make ATP.
Hence enzyme TRIOSE PHOSPHATE ISOMERASE interconverts GAP and DHAP allowing DHAP to be metabolized into G3P.

Question 27

What results as an effect of triose phosphate isomerase deficiency?

Answer 27

triose isomerase deficiency is lethal and can cause severe homeolytic anemia, and neurodegeneration.

Question 28

What is alcoholic fermentation?

Answer 28

conversion of glucose into two molecules of ethanol

The NADH generated by glyceraldheyde 3-phosphate Dehydrogenase is oxidized by alcohol H, regenerating NAD+

Question 29

What is the purpose of fermenatation?

Answer 29

Fermentations are ATP-generating pathways in which electrons are removed from one organic compound to another organic compound. formation of ethanol from pyruvate regenerates NAD+
pyruvate carboxylase requires vitamin thiamine B1.