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Biochem > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

Where does glycolysis occur

A

cytosol

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2
Q

Preparatory phase (5) vs payoff phase (5)

A
  • Preparatory phase:
    • Investment of energy into the system from hydrolyzing 2 ATP
      • Locks glucose into glycolytic pathway
    • Split glucose into two, 3-carbon molecules

Payoff phase: 4ATP and 2NADH are produced

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3
Q

First step - what is it? how is it possible? is it irreversible?

A

Glucose +ATP -hexokinase -> glucose-6- phosphate + ADP

Phosphorylation coupled to ATP hydrolysis.

Irreversible.

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4
Q

Glucokinase

A

IA lvier-specific hexokinase isoform with a higher Km

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5
Q

Importance of glucose phosphorylation in the first step

A
  1. Invests energy
  2. Trap glucose in the cell
    1. Glucose-6-phosphate is too negative to leave the cell
    2. Decreases [glucose] in the cell so more unphosphorylated glucose can diffuse into the cell via transport channels
  3. Use glucose-6-phosphate in other cell pathways
    1. The negative phosphate charge can interact through weak ionic forces to stabilize the substrate in the active site of various enzymes
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6
Q

Substrate flux- what is it and what steps do it?

A

a reaction that can go in either direction is pushed in one direction because its product is rapidly used as a substrate for the next reaciton

Seen in step 2 (Isomerization of glucose-6-phosphate to fructose-6-phosphate) and step 5 (isomerization of DHAP into GAP)

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7
Q

Step 3 - what is it? how is it possible? is it irreversible?

A

Fructose-6-phosphate + ATP -PFK-1-> Fructose-1,6-bisphosphate + ADP

Coupled to ATP hydrolysis

Irreversible

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8
Q

Importance of fructose-6-phosphate phosphorylation

A

Invests ATP

Commitment step

PFK-1 is the most highly regulated glycolytic enzyme

Product has an axis of symmetry- cleavage in step 4 into DHAP and GAP molecules generates twice the E in the payoff phase

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9
Q

When are ATP molecules hydrolyzed?

A

steps 1 and 3

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10
Q

Step 6

A

GAP is oxidized, NAD reduced.

Glyceraldehyde-3-phosphate + Pi + NAD+

-GAP dehydrogenase->

1,3-bisphosphoglycerate + NADH + H+

  • NADH will be used to donate e- to the ETC
  • 1,3BPG is very high energy
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11
Q

Step 7

A

1,3BPG is hydrolyzed; substrate level phosphorylation

1,3BPG + ADP -phosphoglycerate kinase-> 3PG + ATP

  • 1,3BPG’s phosphate bond is broken and the E is transferred to generate ATP
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12
Q

Which steps involves substrate level phosphorylation ?

A

7 & 10

7: 1,3BPG is hydrolyzed to 3PG to make an ATP
10: PEP is hydrolyzed to pyruvate to make na ATP

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13
Q

Step 10

A

PEP is hydrolyzed into pyruvate to make ATP.

PEP + ADP -pyruvate kinase-> pyruvate + ATP

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14
Q

Which steps of the payoff phase generated energy ?

A

Step 6- oxidation - NADH

Step 7 - sub lvl phos - ATP

Step 10 - sub lvl phos - ATP

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15
Q

End products of glycolysis of one glucose molecule

A

2 pyruvate

2 NADH

2 ATP (net, because Step1&3 used 2 ATP)

2 H2O

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16
Q

Bleeding can lower your hemoglobin and hematocrit, so your body is low oxygen. What do you expect to find in this patient’s blood test

A

High lactate

Acidic blood

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17
Q

COPD (poor gas exchange in the lungs) can cause ___ due to the increase in the partial pressure of CO2

A

Respiratory acidosis

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18
Q

What happens to pyruvate in aerobic vs anaerobic conditions?

A

Aerobic: pyruvate converted to acetyl-CoA for the citric acid cycle to make more NADH

Anaerobic: pyruvate converted to lactate by lactate dehydrogenase in a redox rxn; this oxidizes NADH from step6 into NAD+

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19
Q

Anaerobic glycolysis

A

One molecule of glucose –> 2 lactate + 2 net ATP

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20
Q

What causes metabolic acidosis?

A

Increased lactate (an acid) or ketone bodies in the blood

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21
Q

What is muscle cramping caused by? Why does massaging help it?

A

Lactate build up

Massaging sends more oxygenated blood there while removing CO2 and lactate –> lactate dehydrogenase rxn is reversed

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22
Q

Why do RBCs only do anaerobic glycolysis?

A

No mitochondria

They don’t want to use up the oxygen they’re carrying

23
Q

Why does increased CO2 cause respiratory acidosis?

A

It’s converted by carbonic anhydrase into carbonic acid, which is how CO2 is carried in blood.

24
Q

GLUT_ transporter is found in almost all tissues and is the basal transporter for glucose in most cells. Km is ~1-2

A

GLUT1

Low Km to make sure that even at lower glucose levels it’s still pretty active.

25
Q

GLUT_ is the main transporter in muscle & fat cells. Regulated by insulin. It has Km of 5mM.

A

GLUT4

Insulin sensitive

26
Q

GLUT_ doesn’t transport glucose, but transports fructose, such as in small intestine and sperm

A

5

27
Q

GLUT_ is the main glucose transporter for the liver and pancreas. Also seen in the basoslateral membrane of small intestine. It has a high Km of 15-20mM and is __sensitive to insulin

Why?

A

GLUT2

Insensitive to insulin

High Km to ensure liver will only take up excessive glucose to store as glycogen and the pancreas will only secrete insulin when glucose is excessive.

28
Q

GLUT2 & insulin secretion

A
  1. Excessive glucose enters B islet cells through GLUT2
  2. Glycolysis increases intracellular ATP
  3. ATP closes an ATP-sensitive K+ channel, depolarizing the cell.
  4. Depolarization opens a voltage-gated Ca++ channel.
  5. Increased intracellular Ca++ stimulates exocytosis of insulin-containing secretory vesicles
29
Q

Sulfonylureas and Meglitinides

A

Anti-hyperglycemic drugs that stimulate insulin secretion by mimicking ATP to close K+ channels.

30
Q

Diazoxide

A

drug that opens the K+ channel to maintain membrane polarization and inhibit insulin release

31
Q

When blood glucose is low, what happens to GLUT4 in muscle & adipocytes?

A

Low glucose -> no insulin secreted by the pancreas

Without insulin signaling, GLUT4 becomes sequestered by endocytosis in the membrane of intracellular vesicles.

-> no glucose transported into muscle or fat

32
Q

When well-fed, as glucose levels rise, the pancreas secretes insulin that binds to the insulin receptor on muscle & adipocyte plasma membranes, signaling through the ___ pathway to promote__

A

signal through the protein kinase B pathway to promote exocytosis of GLUT4 back to the plasma membrane to transport glucose into cells.

-> glucose is metabolized to pyruvate for ATP or glucose-6-phosphate can be converted to ribulose 5-phosphate for the pentose phosphate pathway

33
Q

Type 1 Diabetes- impact on insulin & blood glucose

A

No insulin produced

Blood glucose is dramatically elevated

34
Q

Why does type 1 diabetes cause ketoacidosis?

A
  1. Lack of insulin causes adipocytes to hydrolyze triglycerides, increasing fatty ACIDs in the blood.
  2. FA is taken up by liver hepatocytes to be
    1. metabolized by betaoxidation for energy or
    2. converted to ketone bodies (alternative fuel source fo rbrain), which are acidic
35
Q

At normal physiologic blood glucose levels, hexokinase I is___. What about hexokinase IV (glucokinase)?

A

Hexokinase I is saturated, near Vmax. (Very low Km)

Glucokinase (hexokinase IV) is only active at much higher blood glucose levels.

36
Q

Regulation of hexokinase I - III

A

Allosteric regulation - if glucose 6-phosphate builds up, this prevents further glucose phosphorylation by hexokinase I

37
Q

In the fasting state, is glycolysis inactivated or activated?

A

Glycolysis is inactivated to favor glycogen breakdown and/or gluconeogenesis pathway.

Thus, glucokinase has to be turned off.

38
Q

Glucokinase locks glucose in the cell, so it needs to be regulated when hepatocytes are performing

A

Gluconeogenesis or glycogen rbeadkwon

39
Q

How is glucokinase regulated at low blood glucose?

A
  1. PFK-1 is inactivated at low blood glucose, so fructose-6-phosphate builds up
  2. Glucokinase sequestration in the nucleus

As blood glucose concentration rises in the well fed state, glucokianse can return to the cytosol.

40
Q

Allosteric regulation of PFK-1- what are the inhibitors and activators?

A

PFK is inhibited by high ATP and citrate.

Activated by ADP/AMP and fructose 2,6-bisphosphate**

41
Q

___is the enzyme of the commitment reaction for glycolysis, so it’s the most highly regulated glycolytic enzyme

A

PFK-1

42
Q

PFK-_2_ catalyzes the production of ___ from fructose-6-phosphate. The enzyme that catalyzes the dephosphorylation of this product is ____.

A

PFK-2 makes fructose 2,6-bisphosphate

It’s broken down/dephosphorylated by fructose 2,6-bisphosphatase (FBPase-2) back to fructose-6-phosphate

43
Q

Fructose 1,6 bisphosphate vs fructose 2,6 bisphosphate

A

Fructose 1,6 bisphosphate is the 3rd glycolytic intermediate, the product of the PFK-1 reaction

Fructose 2,6 bisphosphate is the most potnet allosteric activator of the PFK-1 enzyme

44
Q

FBPase-1 catalyzes the dephosphorylation of ___, a glycolytic intermediate.

FBPase-2 catalyzes the dephosphorylation of ___, an allosteric activator of PFK-1

A

FBPase-1 dephosphorylates fructose 1,6-bisphosphate

FBPase-2 dephosphorylates fructose 2,6-bisphosphate

45
Q

In the presence of F2,6BP, glycolysis is ___ and gluconeogenesis is ___.

A

F26BP –> glycolysis activated, gluconeogenesis inhibited

46
Q

F26BP _creases the Km of PFK-1 and

_creases the Km of FBPase-1

A

decreases the Km of PFK-1

increases the Km of FBPase-1

47
Q

___ and ___ are two domains of a bifuncitonal enzyme - what determines which functional domain will be active?

A

PFK-2 (glycolysis) and FBPase-2 (gluconeogenesis)

Glucagon (low blood glucose) activates FBPase2 -> FB2,6BP is inactivated -> can’t activate PFK-1 for glycolysis

Insulin (well-fed) -> phosphoprotein phosphatase -> activate PFK-2

48
Q

What is 2,3-BPG

A

Promotes unloading of oxygen from hemoglobin in RBCs to be released into srurounding tissues

49
Q

Pyruvate kinase (last enzyme) is stimulated by what molecules and inhibited by what molecules?

A

Stimulators:

  • ADP + PEP (its substrates)
  • Fructose 1,6-bisphosphate (feedforward activation)

Inhibitors:

  • ATP, acetyl-CoA, long chain fatty acids (means high E)
  • Alanine (from transamination of pyruvate)
  • Glucagon (PKA signaling phosphorylates it)
50
Q

How to bypass step 7, resulting in 2 less ATP per glucose

A
  1. Bisphosphoglycerate mutase turns 1,3BPG to 2,3-BPG in RBCs
  2. 2,3BPG is then hydrolyzed by bisphosphoglycerate phosophatase to 3PG

Results in 2 less ATP per glucose during glycolysis

51
Q

Hemolytic anemia

A

RBCs have to depend on glycolysis for ATP

ATP deficiency changes the cell’s shape -> cell lysis (hemolysis) and phagocytosis of damaged cells

52
Q

The most common enzyme deficiency causing hemolytic anemia

A

2: Pyruvate kinase

GLUCOSE 6-PHOSPHATE DEHYDROGENASE in the pentose phosphate pathway

53
Q

What happens to 2,3BPG if you go to a higher altitude?

A

Higher altitude has more oxygen.

You would make more 2,3BPG to release that oxygen to the tissues

(Going to lower altitudes would hydrolyze 2,3BPG)

54
Q

If too much 2,3-BPG is produced, you might get

A

hemolytic anemia

Because producing 2,3 BPG bypasses step 7 –> not enough ATP to support RBCs

Biochem (28 decks)

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