L34 - introduction To Cell Metabolism 1

Question 1

What is metabolism?

Answer 1

The inter-conversion of biomolecules using chemical reactions

Question 2

What are catabolic reactions (degradative)?

Answer 2

• production of ATP and ion gradients
• production of mechanical energy (muscle contraction)
• production of reducing equivalents (NADH, NADPH)
• production of biosynthetic precursors

Question 3

What are anabolic reactions (biosynthetic)?

Answer 3

• storage of energy
• production of macromolecules and cellular structures

Question 4

What is the gibbs free energy eqn?

Answer 4

DeltaG = deltaG^degrees +RT ln [products]/[reactants]

Question 5

What is GFE like?

Answer 5

• under standard conditions
• temp fixed at ~310.15K (37) R is constant (8.314 J.K^-1.mol^-1)

Question 6

What are reactions like?

Answer 6

• in a state of flux (chemicals interconverted through successive series of steps)
• endothermic (need energy)
• driven by ATP or pyrophosphate hydrolysis

Question 7

What does metabolism need to do?

Answer 7

Balance energy (ATP), reducing agents and the amounts of small molecules

Question 8

What is stage 1 of glycolysis?

Answer 8

• in the cytosol
• activates glucose for meatbolism (2ATP) and rearrangement (2 C3 sugars in stage 2)
• double phosphorylation causes ring openeing of sugar

Question 9

What is stae 2 of glycolysis?

Answer 9

• fructose-1,6-bisphosphate -> dihydroxyacetone phosphate, glyceraldehyde-3-phosphate
• dihydroxyacetone phosphate -> glyceraldehyde-3-phosphate
• NET 2glyceraldehyde-3-phosphate

Question 10

What is stage 3 of glycolysis?

Answer 10

• each step repeated twice (2glyceraldehyde-3-phosphate produced)
• energy producing phase (2NADH, 4ATP)

Question 11

What is anaerobic respiration?

Answer 11

• occurs in muscle, absence of oxygen
• pyruvate reduced to R-lactate (D-lactate)
• oxidises NADH to NAD+ = glycolysis continues
• R-lactate reoxidised to pyruvate with NAD+

Question 12

What does the cori cycle do?

Answer 12

recycles R-lactate to glucose

Question 13

What is the cori cycle?

Answer 13

• lactate transported, muscle -> liver by blood
• lactate dehydrogenase R-lactate -> pyruvate
• requires 6ATP/glucose, 2ATP from glycolysis

Question 14

What is gluconeogenesis?

Answer 14

• in liver
• 2pyruvates/glucose
• ATP, CO2, pyruvate = oxaloacetate, exported to cytosol -> phosphoenolpyruvate
• 2ATP, NADH required
• additional enzymes needed
• phosphate allows export of glucose to other tissues

Question 15

What enzymes are needed in gluconeogenesis?

Answer 15

• pyruvate carboxylase (ATP, CO2)
• PEP carboxykinase (ATP)
• bisphophatase
• phosphatase

Question 16

What is mitochondria important for?

Answer 16

• aerobis respiration
• degradation of glucose and fats
• gluconeogenesis

Question 17

How does the structure of mitochondria relate to its functions?

Answer 17

• matrix contains enzymes for tricarboxylic acid (TCA) cycle
• membranes required for ETS

Question 18

What does the pyruvate dehydrogenase complex control?

Answer 18

Entry of pyruvate into TCA cycle

Question 19

What are the pyruvate dehydrogenase complex subunits?

Answer 19

• pyruvate dehydrogenase (E1)
• pyruvate transferase (E2)
• dihydrolipoyl dehydrogenase (E3)

Question 20

What does E1 do?

Answer 20

Decarboxylates pyruvate

Question 21

What does E2 do?

Answer 21

Makes CoA (requires lipoamide)

Question 22

What does E3 do?

Answer 22

Converts reduced lipoamide to disulfide form (requires FAD)

Question 23

What are the steps in the reaction for formation of acetyl-CoA?

Answer 23

• TPP anion adds to pyruvate and CO2
• lipoamide disulfide added to acetyl group, redox
• disulfide exchange occurs = acetyl-CoA, reduced lipoamide
• reduced lipoamide oxidised -> disulfide form (FAD)
• FADH2 oxidised (NADH), into ETS

Question 24

What is the TCA cycle?

Answer 24

• in catabolic and anabolic reactions
• 4 phases (8 steps)
• Acetyl-CoA -> 2CO2 (+ 3NADH, H+, FADH, GTP)
• O2 present -> reoxidation of reduced cofactors by ETS

Question 25

What are the 4 phases in TCA cycle?

Answer 25

• condensation, rearrangement (1 and 2)
• decarboxylation (3 and 4)
• formation og GTP using phosphate anhydride bond (5)
• conversion of succinate to oxaloacetate (6-8)

Question 26

What is step 1 in the TCA cycle?

Answer 26

• citrate synthase catalyses cond of Acetyl-CoA and oxaloacetate
• hydrolysis of CoA ester = irreversible reaction
• citrate undergoes rearrangement = isocitrate

Question 27

What is stage 2 in TCA cycle?

Answer 27

• isocitrate -> B-ketoacid using NAD+
• B-ketoacid loses CO2
• 2-oxoglutarate -> succinyl-CoA by multi-enzyme complex