9.2 Glycolysis [HY]

Question 1

What cells can carry out glycolysis?

Answer 1

• All cells
• being unable to carry out glycolysis is incompatible with life

Question 2

Why do RBCs undergo glycolysis?

Answer 2

• Glycolysis is the only energy-yielding pathway available because red blood cells lack mitochondria, which are required for the citric acid cycle, electron transport chain, oxidative phosphorylation, and fatty acid metabolism (β oxidation).

Question 3

Glycolysis

Answer 3

• a cytoplasmic pathway that converts glucose into two pyruvate molecules, releasing a modest amount of energy captured in two substratelevel phosphorylations and one oxidation reaction

Question 4

What happens (in glycolytic cycle) when either the mitochondria or oxygen is lacking? (such as in
erythrocytes or exercising skeletal muscle)

Answer 4

• glycolysis may occur anaerobically, although some of the available energy is lost

Question 5

What is glycolytic process for in the liver?

Answer 5

• part of the process by which excess glucose is converted to fatty acids for storage

Question 6

What’re the first step in glucose metabolism?

Answer 6

• phosphorylation by kinase enzymes inside the cell to prevent glucose from leaving via the transporter
• kinases attach a phosphate group from ATP to their substrates.
• convert glucose to glucose 6-
  phosphate
• Because the GLUT transporters are specific for glucose (not phosphorylated glucose), the glucose gets “trapped”

Question 7

Hexokinase

Answer 7

• widely distributed in tissues and is inhibited by its product, glucose 6-phosphate.
• Present in most tissues
• Low Km (reaches maximum
  velocity at low [glucose])
• Inhibited by glucose 6-
  phosphate

Question 8

Glucokinase

Answer 8

• Present in hepatocytes and pancreatic β-islet cells (along
  with GLUT 2, acts as the glucose sensor)
• High Km (acts on glucose proportionally to its concentration)
• Induced by insulin in hepatocytes

Question 9

Phosphofructokinase-1 (PFK-1)

Answer 9

• the rate-limiting enzyme and main control point in glycolysis
• inhibited by ATP and citrate
• activated by AMP

Question 10

Citrate

Answer 10

• an intermediate of the citric acid cycle
• high levels of citrate imply that the cell is producing sufficient energy

Question 11

Which pathway allows production of glycogen & fatty acids (which are storage molecules) instead of them being used for ATP?

*overrides the inhibition caused by ATP

Answer 11

Insulin-> PFK-2 -> Fructose 6-P -> Fructose 2,6 biphosphate -> PFK-1

Question 12

What pathway provides energy for ATP synthesis by oxidative phosphorylation?

Answer 12

Glyceraldehyde-3-Phosphate Dehydrogenase -> inorganic phosphate to glycogen-3-phosphate (makes) -> 1,3 biphosphoglycerate & NAD to NADH (if aerobic) -> oxidative phosphorylation to ATP

Question 13

What is the pathway that has substrate-level phosphorylation forming ATP and 3-phosphglycerate?

Answer 13

3-Phosphoglycerate Kinase (takes phosphate from) -> 1,3 biphosphoglycerate [1,3 BPG] (to) -> ADP (makes) -> ATP + 3-phosphoglycerate

*only ATP gained in anaerobic respiration

Question 14

What is the pathway for substrate lvl phosphorylation of ADP using high-energy substrate phosphoenolpyruvate (PEP)?

Answer 14

PK1 rxn (feed forward rxn) -> Fructose 1,6 biphosphate -> pyruvate kinase (takes p from) -> [PEP] Phosphoenolpyruvate (gives to) -> ADP (makes) -> ATP

*only ATP gained in anaerobic respiration

Question 15

Fermentation

Answer 15

• Occurs in the absence of oxygen
• key fermentation enzyme in mammalian cells is lactate dehydrogenase which oxidizes
  NADH to NAD+, replenishing the oxidized coenzyme for glyceraldehyde-3-phosphate dehydrogenase

Question 16

What would happen without mitochondria and oxygen?

Answer 16

• glycolysis would stop when all the available NAD+ had been reduced to NADH. By reducing pyruvate to lactate and oxidizing NADH to NAD+, lactate dehydrogenase prevents this potential problem from developing

Question 17

What happens when oxygenation is poor (during strenuous exercise in
skeletal muscle, a heart attack, or a stroke)?

Answer 17

• most cellular ATP is generated
  by anaerobic glycolysis, and lactate production increases

Question 18

What is the result of both both mammalian and yeast fermentation?

Answer 18

• replenishing NAD+

Question 19

What is the pathway for triacylglycerol synthesis?

Answer 19

Fructose 1,6 biphosphate (forms) -> DHAP -> isomerized to glycerol 3-phosphate -> glycerol

*glycerol is the backbone of triacylglycerols

Question 20

Irreversible steps of glycolysis (Mnemonic)

Answer 20

How Glycolysis Pushes Forward the Process: Kinases
- Hexokinase
- Glucokinase
- PFK-1
- Pyruvate Kinase

Question 21

Mutases

Answer 21

• enzymes that move a functional group from one place in a molecule to another

Question 22

RBC pathway for ATP production?

Answer 22

• have bisphosphoglycerate mutase, which produces 2,3-
  bisphosphoglycerate (2,3-BPG) from 1,3-BPG
• the phosphate is moved from the 1-position to the 2-position. - 2,3-BPG binds allosterically to the β-chains of hemoglobin A (HbA) and decreases its affinity for oxygen.
• Causes right shift of oxygen dissociation curve

Question 23

Physiological Changes that promote right shift of dissociation curve (the Bohr effect)?

Answer 23

• High 2,3-BPG
• Low pH
• High [H+]
• High pCO2

Question 24

Why does HbF have a higher affinity for oxygen than
maternal HbA?

Answer 24

• B/c 2,3-BPG doesn’t bind well to fetal hemoglobin

Question 25

Rate-limiting enzymes

Answer 25

• Glycolysis: phosphofructokinase-1
• Fermentation: lactate dehydrogenase
• Glycogenesis: glycogen synthase
• Glycogenolysis: glycogen phosphorylase
• Gluconeogenesis: fructose-1,6-bisphosphatase
• Pentose Phosphate Pathway: glucose-6-phosphate dehydrogenase

Question 26

How many carbons are involved in Glycolysis?

Answer 26

Start with 6 carbon glucose and make two three carbon molecules of pyruvate