1.5 - Key Control of Glycolysis and Gluconeogenesis

Question 1

isoenzymes

Answer 1

group of enzymes that catalyse same reaction but have different enzyme forms and catalytic efficiencies (Km)

Question 2

erythrocytes

Answer 2

red blood cells

Question 3

hepatocytes

Answer 3

functional cells of the liver

Question 4

what inhibits glycolysis?

Answer 4

ATP

Question 5

which enzymes are regulated when glycolysis is inhibited? (2)

Answer 5

1. phosphofructokinas kinase
   (accumulates inhibiting hexose kinase)
2. pyruvate kinase

Question 6

key control points in glycolysis (3)

Answer 6

1. phosphofructokinase (PFK)
2. pyruvate kinase (PK)
3. hexokinase (HK)

Question 7

phosphofructokinase (PFK) isozymes in human genome (3)

Answer 7

1. PFKM - muscle type
2. PFKL - liver type
3. PFKP - platelet type

Question 8

pyruvate kinase (PK) isozymes in human genome (2)

Answer 8

1. PKM
2. PKLR

Question 9

isoforms of PKM gene (2)

Answer 9

1. PKM1
2. PKM2

Question 10

PKM1

Answer 10

predominantly expressed through alternative splicing in muscle and brain tissues

Question 11

PKM2

Answer 11

found in various tissues, including tumour cells

Question 12

PKLR gene isozymes (2)

Answer 12

1. PKL
2. PKR

Question 13

where are PKL and PKR expressed (separately) (2)

Answer 13

1. PKL - expressed in liver
2. PKR - found in erythrocytes (red blood cells)

Question 14

primary pyruvate kinase (PK) isozymes (2)

Answer 14

1. M-type - muscle and brain
2. L-type - liver

Question 15

what happens to L-type pyruvate kinase isozyme when blood glucose is low?

Answer 15

covalently phosphorylated

Question 16

why is L-type pyruvate kinase isozyme phosphorylated?

Answer 16

less active compared to non phosphorylated, prevents liver cells consuming glucose when there is demand in other parts of body

Question 17

Km of hexokinase I (HK1) in erythrocytes and skeletal muscle cells?

Answer 17

Km = 0.05 - 0.1mM

Question 18

Km of hexokinase II (HK2) in skeletal muscle cells and adipose cells

Answer 18

Km = 0.1mM

Question 19

Km in glucokinase/hexokinase IIII (HK4) in hepatocytes and pancreatic beta cells

Answer 19

kM = 5 - 6mM

Question 20

how is hexokinase (HK1) allosterically inhibited?

Answer 20

high levels of G-6-P

Question 21

how is hexokinase (HK1) an important control step in glycolysis?

Answer 21

prevents over consumption of cellular ATP to form G-6-P when glucose is not limiting

Question 22

What happens to HK1 in hepatic cells/pancreatic B-cells when glucose is not limiting glycolysis?

Answer 22

replaced by glucokinase/HK4

Question 23

Why is HK1 replaced by glucokinase/HK4 in hepatic cells/pancreatic B-cells when glucose is not limiting glycolysis? (4)

Answer 23

1. has high Km
2. activated by high blood glucose and insulin, not inhibited by G-6-P
3. Allows liver to remove excess glucose in CVS for glycogen synthesis
4. helps reduce blood glucose after eating (reducing hyperglycaemia)

Question 24

GLUT2 Km/affinity for glucose (2)

Answer 24

1. highest Km
2. lowest affinity for glucose

Question 25

why do hepatocytes and pancreas express GLUT2

Answer 25

exposed to relatively high glucose concentration via hepatic portal vein

Question 26

why do hepatocytes and pancreatic B-cells express GK instead of HK for phosphorylation of glucose?

Answer 26

GKs have higher Km than HK (relatively low affinity to glucose)

Question 27

lactic acid fermentation for NAD+ (3)

Answer 27

1. accumulation of pyruvate 2. accumulation of NADH without enough oxygen 3. pyruvate converted to lactate

Question 28

fate of lactic acid (4)

Answer 28

1. lactate is biproduct of NAD+ recovery by lactate dehydrogenase 2. in excess, lactate inhibits many cellular activities in cytoplasm 3. monocarboxylate transporter (MCT) transports lactate across plasma membranes of muscle cells (allow lactate to move to CVS) 4. lactates recycled by hepatic cells

Question 29

Cori cycle (4)

Answer 29

1. in oxygen deficit anaerobic respiration muscle cells produce lactate 2. lactate released into blood 3. in liver, conversion lactate to pyruvate and to glucose uses 6 ATP by gluconeogenesis 4. glucose released from liver cells into blood (taken up by peripheral tissues)

Question 30

where does gluconeogenesis occur?

Answer 30

primarily in liver and kidney cells

Question 31

major precursors of gluconeogenesis (3)

Answer 31

1. glycerol 2. amino acids 3. lactic acid

Question 32

ATP economy of gluconeogenesis (2)

Answer 32

1. pyruvate -> glyceraldehyde 3-phosphate = 3 ATP - need 2x GAP = 6 ATP 2. glycerol -> DAHP = 1 ATP - need 2x DAHP = 2 ATP

Question 33

carboxylases to regenerate phosphoenolpyruvate (2)

Answer 33

1. phosphoenolpyruvate carboxylase 2. pyruvate carboxylase

Question 34

How can glycerol be used to regenerate DHAP? (dihydroxyacetone phosphate) (2)

Answer 34

1. glycerol --> glycerol phosphate - via glycerol kinase 2. glycerol phosphate --> dihydroxyacetone phosphate (DHAP) - via glycerol phosphate dehydrogenase

Question 35

4 key enzymes of gluconeogenesis (4)

Answer 35

1. glucose 6-phosphatase (hexokinase) 2. fructose 1,6-bisphosphatase (phosphofructokinase) 3. phosphoenol-pyruvate carboxylase (pyruvate kinase) 4. pyruvate carboxylase (pyruvate kinase)

Question 36

why do human erythrocytes (RBCs) rely entirely on glycolysis for ATP?

Answer 36

no mitochondria, nucleus or other cellular organelles

Question 37

why do human erythrocytes (RBCs) require ATP?

Answer 37

for Na+/K+ ATPase pump keeping membrane potential, which contributes to maintenance of biconcave shape

Question 38

sole source of ATP for human erythrocytes (RBCs)

Answer 38

glycolysis in the cytosol

Question 39

what can result in haemolytic anaemia?

Answer 39

genetic conditions such as deficiency in glycolytic processes

Question 40

why is pyruvate kinase (PK) so important for RBC availability? (2)

Answer 40

1. pyruvate kinase (PK) is last enzymatic reaction in glycolysis 2. aids conversion of phosphoenolpyruvate (PEP) to pyruvate, thereby producing ATP

Question 41

effect of deficit pyruvate kinase (PK)/defficiency in glycolytic processes on erythrocytes (RBC)

Answer 41

amount of ATP insufficient for erythrocyte survival

Question 42

how are deficient glycolytic processes countered in erythrocytes? (2)

Answer 42

1. corrupted erythrocytes removed by reticuloendothelial cells (particularly by spleen) 2. build up of 2,3-DPG occurs which aids oxygen offloading into tissues

Question 43

Warburg effect

Answer 43

in tumours/other proliferating or developing cells, rate of glucose uptake dramatically increases and lactate is produced, even in presence of oxygen and fully functioning mitochondria

Question 44

cancer cell expression of hexokinases

Answer 44

1 and 2, speed up glycolytic pathway

Question 45

hypoxia-inducible factor (HIF) regulated genes role

Answer 45

oxygen deprived hypoxia known to allow HIF transcription factor to turn on many enzymes of glycolysis

Question 46

how do cancer cells fall short for oxygen?

Answer 46

due to spread of cell division and proliferation (tumour cells in core become hypoxic)

Question 47

result of tumour cells becoming hypoxic (oxygen deficient)

Answer 47

makes tumour cells more likely to rely on glycolysis

Question 48

2 enzymes of glycolysis cancer cells have alterations of (2)

Answer 48

1. hexokinase 2. pyruvate kinase

Question 49

2 forms of pyruvate kinase M2 (PKM2)

Answer 49

1. low activity dimeric form 2. high activity tetrameric form

Question 50

role of less active dimeric form of PKM2

Answer 50

phosphorylated by tyrosine kinases and promotes conversion of pyruvate to lactate

Question 51

role of high activity tetrameric form of PKM2

Answer 51

promotes conversion of pyruvate to acetyl-CoA

Question 52

role of tumour form of pyruvate kinase M2 (PKM2)

Answer 52

undergoes tyrosine phosphorylation and gives rise to Warburg effect