L5 glucose metabolism

Question 1

what is catabolism/anabolism?

Answer 1

catabolism: breaking down complex molecules (exergonic)
anabolism: building of complex molecules (endergonic)

Question 2

what are the fates of nutrients?

Answer 2

• supply energy
• serve as building blocks
• stored

Question 3

sources of carbohydrate?

Answer 3

starch (plant storage)
glycogen (branched glucose)
lactose (glucose and galactose)
sucrose (fructose and glucose)

Question 4

normal blood glucose levels?

Answer 4

90mg/100ml (2-3g)

Question 5

what is ATP made up of?

Answer 5

• purine base (adenine)
• five carbon sugar (ribose)
  = adenosine
• 3 phosphate (attached to sugar by phosphodiester bond)

Question 6

fate of glucose?

Answer 6

• ATP production
• Amino acid synthesis
• Glycogen Synthesis
• Triglyceride synthesis

Question 7

GLUT1?

Answer 7

• most tissues
• low Km/High affinity
• not affected by insulin
• works with GLUT3 to allow glucose across blood brain barrier - GLUT1 deficiency therefore impairs flu one transport into the brain (also over expressed in cancers)

Question 8

GLUT2?

Answer 8

• Hepatocytes
• regulated by insulin
• high Km (only transports glucose into cells when blood glucose is high e.g. after eating)

Question 9

GLUT3?

Answer 9

• has the highest affinity for glucose and high expression in neuronal tissues.

Question 10

GLUT4?

Answer 10

• striated muscle and adipose tissue
• in intracellular vesicles in insulin sensitive tissues
• blood flu raises, insulin released from pancreatic B cells - binds to insulin receptors on plasma membrane - activates insulin signal pathway, GLUT4 translocates from intracellular vesicle to membrane allowing glucose transport.

Question 11

which GLU transporters are sensitive to insulin?

Answer 11

GLUT4

GLUT2

Question 12

which GLUT are no affected by insulin?

Answer 12

GLUT1 and GLUT3

Question 13

what are the products of glycolysis?

Answer 13

net gain of 4 ATP
2 pyruvate
2 NADH+H

Question 14

fate of pyruvate?

Answer 14

• aerobic = converted to acetyl-coenzyme A and enters TCA cycle
• anaerobic = reduced to lactic acid by lactate dehydrogenase (or ethanol)

Question 15

where does galactose enter glycolysis?

Answer 15

Galactose is converted to Glu-6-P

Question 16

where does fructose enter glycolysis?

Answer 16

fructose is phosphorylated by hexokinase (in muscle and adipose tissue) to Fruc-6-P

Question 17

describe hexokinase?

Answer 17

• glucose to glucose-6-p
• inhibited allosterically by its product (G-6-P) - prevents HK using up all the free inorganic phosphate (Pi)
• low Km/High affinity = all glucose that enters cell is phosphorylated by HK
• Maintains glucose conc gradient
• unaffected by insulin
• will phosphorylate other sugars (fructose - but slower)

Question 18

What happens if Hexokinase is inhibited?

Answer 18

Inhibition of HK will suppress Glu uptake into cell bc intracellular conc of glucose will rise

Question 19

describe glucokinase?

Answer 19

• isoenzyme of HK
• specific for glucose
• dominant role in liver and kidneys
• much higher Km (when glucose conc are high GK is only enzyme responding)
• not inhibited by G-6-P

Question 20

describe phosphofructokinase 1?

Answer 20

• fruc-6-p to fruc,1,6,BP
• ATP both substrate and allosteric inhibitor
• inhibited by high levels of ATP
• AMP and ADP relieve inhibition of PFK1 (therefore the rate of glycolysis depends on the ratio of AMP/ADP)

Question 21

where does gluconeogenesis occur?

Answer 21

liver (major store of glucose)

Question 22

what produces insulin?

Answer 22

beta cells in pancreas

Question 23

what produces glucagon?

Answer 23

alpha cells in pancreas

Question 24

describe pyruvate kinase?

Answer 24

• inhibited by high ATP levels, high ACoA levels, high Glucagon levels
• regulated by fruc-1,6-BP and insulin

Question 25

function of insulin?

Answer 25

lower blood glucose

- stimulates glycolysis and glycogenesis

Question 26

function of glucagon?

Answer 26

raise blood glucose

- stimulates gluconeogenesis and glycogenolysis