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Biochemistry Muscoskeletal > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

4 ways glucose can be used in cells

A

Synthesis of structural polymers

Storage as glycogen

Oxidation via PPP

Oxidation via glycolysis

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2
Q

Preparatory phase (general)

A

Steps 1-5

2 ATP = investment energy

Glucose splits into 2 3C molecules
(Glyceraldehyde-3-phosphates)

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3
Q

Payoff phase (general)

A

Steps 6-10

4ATP (net 2ATP)

2 NADH —> e-chain for reducing power

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4
Q

Hexokinase

A

Step 1

Phosphorylation

Glucose —> G6P (1 ATP used)

Irreversible

**this locks glucose inside the cell…and thus will bring glucose into the cell because the concentration of glucose will be lower inside than outside

G6P can used in glycolysis, PPP, or glycogen synthesis

Analog in liver = glucokinase (higher affinity for glucose)

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5
Q

Phosphohexose isomerase

A

Isomerization of an aldose into a ketose

G6P—>F6P

Reversible (so [subrate] dictates)

Mg2+ is required

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6
Q

phosphofructokinase-1 (PK1)

A

F6P —> F-1,6-BP (1 ATP used)

Committment step

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7
Q

Aldolase

A

Cleaves F1,6BP —> DHAP and GAP

DHAP will proceed to step 5

GAP will proceed to step 6 (payoff phase)

Reversible

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8
Q

Triose phosphate isomerase

A

DHAP GAP

Favors making GAP since GAP is being used in payoff phase

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9
Q

GAP dehydrogenase

A

GAP from step 4 is oxidized

NAD+ is reduced to NADH

Prodcut = 1,3-biphosphoglycerate

Very high energy product so rxn is readily reversible

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10
Q

Phosphoglycerate kinase

Named for the reverse reaction

A

1,3-BPG +ADP —> 3-PG +ATP

Coupled reaction to make formation of ATP favorable

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11
Q

Phosphoglycerate mutase

A

3-PG —> 2-PG

Reversible

Mg2+ needed

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12
Q

Enolase

A

2-PG —> phosphenolpyruvate (PEP)

PEP = top of free energy list

Largest -deltaG value (but this reaction has a +deltaG) —>

Reversible

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13
Q

Pyruvate kinase

Named for reversible reaction

A

PEP + ADP —> Pyruvate + ATP

Irreversible

Very regulated step

Mg2+ and K+ needed

Diseases associated with this step

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14
Q

Net reaction for glycolysis

A

Glucose + NAD+ + 2ADP + 2Pi —>

2 pyruvate + 2NADH + 2ATP + H2O

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15
Q

Importance of 1,3-bisphosphoglycerate

And

3-PG

A

From step 6 and 7 respectively

Both of them can be converted to 2,3-BPG

Compound in RBCs used for regulating O2 release from hemoglobin

High 2,3-BPG levels —> lower hemoglobin’s affinity of O2 —> O2 unloading

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16
Q

Glycolytic intermediates can be converted into…

A

Amino acids

17
Q

Pyruvate can be converted into

A

Acetyl CoA —> enter citric acid cycle which those intermediates can also be turned into amino acids

Acetly -CoA can also be converted into FAs

18
Q

DHAP (Step 4) can be convereted into

A

Glyceride3-phosphate with fatty acids

—> triglycerides

19
Q

Metabolic acidosis

A

E-chain and the CAC require O2…so it patient does not have enough O2 circulating…pyruvate enters anaerobic glycolysis

Reduced to lactate (lactate dehydrogenase)
Since NADH —> NAD+ net energy is reduced

RBCs use anaerobic because they do not want to use the O2 they are transporting

20
Q

Normal glucose concentration

A

5mM

21
Q

GLUT1

A

Almost all tissues (most importantly the brain)

Km = 1-2mM

Not regulated

Almost always active

22
Q

GLUT2

A

Liver and pancreas
Basolateral membrane on SI

Only active in high [blood glucose] = high Km

Removes excess blood glucose (liver stores it)

NOT regulated by insulin

23
Q

GLUT4

A

Muscle and fat cells

Km = 5mM (at normal blood glucose its at 50% of Vmax)

Regulated by insulin…high glucose —>insulin—>GLUT4 brought to the membrane

24
Q

GLUT5

A

Mucosal (apical) membrane of SI

Spermatoza

Fructose transport (does not transport glucose)

Main fructose transporter in the body

25
Q

Mechanism for GLUT 2 in pancreatic beta inslet cells

A
  1. Increased blood glucose caused glucose to flow into beta cell via GLUT2
  2. Glucose undergoes glycolysis —> results in ATP formation, so the concentration of ATP in the beta cells increase
  3. This causes the closure of an ATP-gated K+ channel
  4. (Normally K+ concentration is much higher inside than outside…closing that channel results in less K+ being able to leave the cell) —> increase in K+ retention causes depolarization
  5. Stimulates voltage-gated Ca2+ channels to open
  6. Ca2+ moves down its concentration gradient into the cell
  7. Increased Ca2+ in the beta cell stimulates secretory vesicles (containing insulin) to undergo exocytosis
26
Q

Sulfonylureas and meglitinides

Drugs that affect GLUT2

A

Mimic ATP…outisde of the ATP-gated K+ channels, closing the channels

Results in depolarization and released insulin

27
Q

Diazoxide

A

Used to treat hypoglycemia associated with hyperinsulimia

Could be due to a insulin secreting tumor

Caused voltage K+ channels to remain open —> no insulin released

28
Q

Mechanism of GLUT4 regulation

A

During fasting —> blood glucose is low…below the 5mM Km of GLUT4

So we don’t want GLUT4 activity b/c we need glucose available for our brain

Low insulin too —> so GLUT4 is sequestered in an inactive form inside the cell via endocytosis

High glucose —> high insulin —> insulin binds to insulin receptors to the cell membrane, stimulating a signlaing pathway that activates protein kinase B (PKB)

PKB causes exocytosis of GLUT4 to the membrane where it is active

29
Q

Type I Diabetes

A

Lack of insulin produced by beta cells

Cells cannot take up glucose —> no energy

Adipocytes will mobilize triglycerides and released FAs into the bloodstream…live will take these up and can form energy from them in the form of ketones

Can accumulate —> acidosis —> diabetic ketoacidosis

30
Q

Regulation of hexokinase (step 1 of glycolysis)

A

At normal glucose levels the enzyme is almost completely saturated and functioning maximally

Allosterically inhibited by the product of the reaction (G6P)

31
Q

Regulation of glucokinase (hexokinase IV)

A

Much higher Km for glucose compared to the other hexokinase

In liver —> glycolysis does not occur in these cells until glucose levels are fucking high bro!

Not inhibited by G6P…so really controlled by its high Km and thus the [glucose]

It is regulated for F6P which is the product of step 2

When glucose is low…PK1 (step 3 enzyme is inactivated) so F6P builds up in the cytoplasm…thus keeps glucokinase inactive…also allows liver glucose to be available to replenish low glucose levels

32
Q

Regulation of PK1

A

Mostly regulated by allosteric factors

Allosteric activation —> high levels of ADP/AMP and F2,6BP (aka low energy levels)

Allosteric inhibition —> high ATP and citrate

Non-allosteric activation —> increase [F6P]

Non-allosteric inhibition —> increase in acidity (H+ ion concentration)

33
Q

Mechanism of allosteric regulation via F26BP on PK-1

A

F26BP is the most potent allosteric activator of PK1…it is producted by PFK-2 (other domain of this enzyme is FBPase-2)

Low glucose —> glucagon —> activation of PKA through cAMP pathway —> PKA phosyphorylates enzyme —> activates FBPase-2 domain —> Pk-1 deactivated via increase in Km —> GLUCONEOGENESIS

High glucose —> insulin —> activation of phosphoprotein phosphatase —> activation of PK-2 domain —> glycolysis

34
Q

PK-1 allosteric inhibition via ATP

A

Increasing ATP shifts the kinetics curve of PK-1 activity such that Km is increased

ATP = means we have energy and do not need to make any more

35
Q

Regulation on FBPase-2

A

Activity leads to gluconeogenesis

Inhibited allosterically by F26BP…what stimulates PK1

The regulation between PK1/2 and FBPase-2 helps ensure that glycolysis and gluconeogenesis are not occuring at the same time

36
Q

Pyruvate kinase

A

PEP —> pyruvate (irreversible)

Makes ATP

Stimulated by the reation substrates (ADP and PEP) and F16BP

Inhibited by ATP, acetyl-CoA, long chain FAs, and alanine

In the liver…glucagon can start a signaling pathway via PLA which phosphorylates PK —> inactivating it (insulin would lead to dephosphorylation of PK in the liver)

37
Q

2,3-biphosphoglycerate pathway in RBCs

A

Stimulates the release of O2 from hemoglobin

1,3BPG (substrate for step 7 gly) is converted into 2,3-BPG in red blood cells (BPG mutase)

Then 1,3BPG —> 3PG (BPG phosphatase)

3PG is the normal product of step 7…but the normal step was bypassed…therefore 2 fewer ATPs are produced

Mutase is stimulated when O2 needs to be unloaded from hemoglobin and enter tissues

Increase in mutase acvitity —> increase 23BPG levels

38
Q

Clinical correlation to donating blood

A

When donated blood is stored the 23BPG in it are reduced

So blood transfused into someone has low 2,3BPG…

Which means the O2 has really really high affinity for hemoglobin and cannot unload enough into the tissues

Resolved within 24-48 hours

So if you transfuse too much blood —> serious issues since patient cannot oxygenate their tissues

39
Q

Hemolytic anemia

A

RBCs do not have mitochondria…so cannot do oxidative phosphorylation…so all ATP comes from glycolysis

Too little ATP —> changes in shape and membrane in a RBCs

Common enzymes that get fucked

  • G6P dehydrogenase
  • pyruvate kinase

Biochemistry Muscoskeletal (8 decks)

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