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Fundamentals of Biomedicine > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

Tissues that can only use glucose as a metabolic fuel:

A

brain, RBCs, renal medulla, cornea, testes, exercising muscle

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2
Q

What is the end product of glycolysis?

A

2 pyruvates

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3
Q

What occurs to the 2 pyruvates after glycolysis?

A

converted into 2 acetyl coAs, which enters the TCA cycle

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4
Q

How does glucose enter cells?

A
  • can’t simply diffuse into cells

- carried by either facilitated diffusion (GLUT transport proteins in membrane) or Na+-dependent co-transport (SGLT)

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5
Q

What are the GLUT transporter isoforms and their locations?

A
  • GLUT1: brain and RBCs
  • GLUT2: hepatocytes
  • GLUT3: neurons
  • GLUT4: adipose tissue and skeletal muscle
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6
Q

What is the phosphorylation of glucose to trap it in cells catalyzed by?

A
  • Hexokinase: most cell types

- Glucokinase: liver and pancreatic islet cells

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7
Q

Describe the enzymatic activity of glucokinase vs. hexokinase:

A

Hexokinase has a lower Km than glucokinase but also has a lower Vmax

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8
Q

Functions of glucokinase:

A
  • helps beta-cells in pancrease sense rising glucose concentrations in order to trigger insulin release
  • allows liver to mop up high conc. of glucose in the portal circulation after a meal
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9
Q

How are glucokinase and hexokinase regulated?

A
  • glucokinase regulated by fructose-6-phosphate

- hexokinase regulated allosterically by glucose-6-phosphate

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10
Q

What is the rate limiting step of glycolysis?

A

phosphofructokinase-1 (PFK1)

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11
Q

What is the PFK1 in glycolysis regulated by?

A
  • inhibited by ATP and citrate

- stimulated by AMP and fructose-2,6-bisphosphate

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12
Q

What is the function of PFK2?

A

converts fructose-6-phosphate into fructose-2,6-bisphosphate

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13
Q

How does PFK-2 exist in the body?

A

exists in a bifunctional enzyme complex with FBP-2–activity controlled by phosphorylation

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14
Q

Describe the hormonal regulation of glycolysis:

A
  1. high insulin/glucagon ratio–> decreased cAMP and reduced levels of active PKA
  2. decreased PKA favors dephosphorylation of PFK2/FBP2
  3. dephosphorylated PFK2 active whereas FBP2 is inactive–> favors formation of F2,6BP
  4. elevated conc. of F2,6BP activates PFK1, leading to increased rate of glycolysis
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15
Q

What happens to F2,6BP in response to insulin after a high carbohydate meal?

A

increases and therefore acts as a signal of high glucose levels, promoting glycolysis

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16
Q

What happens after the formation of F1,6BP

A
  • Aldolase A produces glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP)
  • triose phosphate isomerase can interconvert G3P and DHAP
17
Q

How is ATP produced?

A
  • Directly: substrate level phosphorylation

- Indirectly: oxidative phosphorylation (NADH+H and FADH2 generation)

18
Q

What is the approximate conversion of electron intermediates to ATP in the ETC?

A
  • NADH+H–> 3 ATP

- FADH2–> 2 ATP

19
Q

Why is aerobic metabolism much more efficient than anaerobic metabolism?

A

allows the complete oxidation of fuel molecules to CO2 and H2O

20
Q

What is the net energy production from aerobic glycolysis?

A
  • glucose–> pyruvate
  • 2 ADP–> 2 ATP
  • 2 NAD+–> 2 NADH
21
Q

What is the net energy production from anaerobic glycolysis?

A
  • glucose–> 2 lactate

- 2 ADP–> 2 ATP

22
Q

What is the total max ATP that can be produced from one molecule of glucose?

A

38 ATP

23
Q

Lactic acidosis:

A
  • elevated plasma lactic acid secondary to: circulatory collapse (MI, PE, hemorrhage) or shock
  • potentially fatal
24
Q

Where does the TCA cycle occur?

A

in the mitochondrial matrix

25
Q

Pyruvate dehydrogenase

A

converts pyruvate to acetyl coA in the matrix (irreversible reaction, glucose cannot be made from acetyl coA)

26
Q

What is pyruvate dehydrogenase regulated by?

A
  • regulated by phosphorylation (PDH kinase/phosphatase activity)
  • ATP, acetyl coA and NADH promote phosphorylation–> inactive
  • pyruvate levels inhibit PDH kinase activity–> promoting active form
  • Ca2+ promotes dephosphorylation (activation)
27
Q

Pyruvate dehydrogenase complex

A
  • a multi-enzyme complex
  • three distinct enzyme activities: pyruvate decarboxylase, dihydrolipoyl transacetylase, dihydrolipoyl dehydrogenase
  • needs 5 coenzymes
  • intermediates passed from one active site to the next without being released
28
Q

Describe the PDH complex reactions

A
  1. pyruvate decarboxylated into a hydroxyethyl derivative bound to the reactive carbon of thiamine pyrophosphate, the coenzyme of pyruvate dehydrogenase
  2. the hydroxyethyl intermediate is oxidized by transfer to the disulfide form of lipoic acid covalently bound to dihydrolipoyl transacetylase
  3. the acetyl group, bound as a thioester to the side chain of lipoic acid, is transferred to CoA
  4. the sulfhydryl form of lipoic acid is oxidized by FAD-dependent dihydrolipoyl dehydrogenase, leading to the regeneration of oxidized lipoic acid
  5. the reduced flavoprotein is reoxidized to FAD by dihydrolipoyl dehydrogenase as NAD+ is reduced
29
Q

Pyruvate dehydrogenase deficiency: what is it, symptoms, treatment

A
  • x-linked disease resulting in congenital lactic acidosis
  • pyruvate converted to lactic acid instead of acetyl coA
  • Symptoms: developmental defects (esp. of CNS), muscular spacticity, early death
  • no effective therapy exists
30
Q

Arsenic poisoning

A
  • arsenic is an inhibitor of enzymes that use lipoic-acid as a cofactor
  • inhibits pyruvate dehydrogenase
  • symptoms: neurological disturbances and death
31
Q

What vitamins do the following coenzymes require for their synthesis?

A
  • CoA–> panthotenic acid (B5)
  • NAD–> niacin (B3)
  • FAD–> riboflavin (B2)
  • TPP–> thiamine (B1)
32
Q

Symptoms of vitamin deficiencies affecting pyruvate dehydrogenase and its coenzymes:

A
  • increased pyruvate, lactate and alanine levels (pyruvate reduced to lactate or transaminated to alanine)
  • severe lethargy and fatigue
  • complications affecting the cardiovascular, nervous, muscular and GI systems
  • examples: Wernicke-Korsakoff and Beri Beri
33
Q

Hereditary myopathy with lactic acidosis: presentation, symptoms, biochemical features

A
  • presentation in childhood
  • symptoms: muscle becomes hard and tender with exercise, cramping, dyspnea, heart palpitations
  • Biochemical features: conc. of lactate and pyruvate in the blood increased disproportionately for the workload (increased lactate and pyruvate w/ exercise, increased arterial alanine conc. during exercise in patients)
34
Q

What are the biochemical defects in hereditary myopathy and lactic acidosis?

A
  • succinate dehydrogenase and iron-sulphur proteins in muscle mitochondria
  • markedly reduced capacity of TCA cycle and Ox-phos
  • increased production of lactate by muscle glycolysis
  • high levels of pyruvate are converted to alanine

Fundamentals of Biomedicine (6 decks)

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