Energy production : carbohydrate 2

Question 1

What are the important intermediates in glycolysis?

*state function andenyzyme involved

Answer 1

• Glycerol phosphate
  
  • glycerol 3-phosphate dehydrogenase converts DHAP to GP in adipose tissue and liver
  • Important to triglyceride and phospholipid biosynthesis
• 2,3-BPG
  
  • BPG mutase converts1,3-BPG to 2,3-BPG
  • Important regulator of O2 affinity in haemoglobin
  • present in RBC

Question 2

Why lactate production occurs?

Answer 2

• RBC : have no stage 3 or 4 metabolism to regenerate NAD+
• Muscle cell : Supply of O2 to muscle cell often reduced for stage 4 to occur
• Low O2 conditions : pyruvate converted to lactate

Question 3

What causes Lactate production?

Answer 3

• strenuous exercise
• pathological situations : shock, congestive heart disease

Question 4

What enzyme is involved in lactate metabolism?

Answer 4

Lactate dehydrogenase, LDH

Question 5

How is lactate produced?

Answer 5

• Produced from glucose via pyruvate
• NADH + H+ + pyruvate —LDH—> NAD+ + lactate

Question 7

Where does the metabolsim of lactate occur ?

Answer 7

• Heart
• Liver

Question 8

What are the clinical conditions associated with plasma lactate concentration elevations

*Normal con <1mM

Answer 8

• Hyperlactaemia
  
  • 2-5mM
• Lactic acidosis
  
  • >5mM
  • blood pH lower

Question 9

What are the other sugars metabolised in the body?

Answer 9

• fructose
• galactose

Question 10

Where is fructose metabolised in body?

*huge organ

Answer 10

liver

Question 11

What are the 4 enzymes involved in Fructose metabolism?

Answer 11

• fructokinase
• aldolase
• triose kinase
• TPI

Question 12

What are the clinical conditions related to deficienciesin fructose metabolism enzymes?

Answer 12

• Essential fructosuria
  
  • x fructokinase
  • x clinical signs
• Fructose intolerance
  
  • x aldolase
  • Fructose-1-P accumulates in liver
  • liver damage

Question 13

What is the treatment for Fructose intolerance?

Answer 13

remove fructose from diet

Question 14

What is the Galactosaemia?

Answer 14

Inability to metabolise galactose

Question 15

Where does galactose metabolism occur?

*same as fructose metabolism

Answer 15

liver

Question 16

What are the 2 types of galactosaemia?

Answer 16

• Galactokinase deficiency (rare) : causes accumulation of galactose
• Transferase deficiency (common) : causes accumulation of galactose and galactose-1-P

Question 17

What are the three important enzymes involved in galactose metabolism

Answer 17

• galactokinase
• galactose-1-P uridyl transferase
• UDP-galactose 4’-epimerase

Question 18

How cataract is formed?

Answer 18

• Galactose enters other pathways
• galactose reduced to galactitol by NADPH and aldose reductase
• NADPH levels in lens deplete
• prevents maintenance of free sulphydryl groups on proteins
• Disulphide bonds formed
• crystallin protein denatured

Question 19

What are the metabolic consequences of an absence of galactose 1-P uridyl transferase?

Answer 19

• accummulation of galactose 1-P
• affects liver, kidney and brain

Question 20

What are the stages involvedin Pentose phosphate pathway? Describe the

Answer 20

• Oxidative decarboxylation
  
  • Glucose-6-P —> C5 sugar + CO2 by glucose-6-P dehydrogenase
  • NADP+ to NADPH
• Rearrangement to glycolytic intermediates
  
  • 3C5sugars —> 2 Fructose-6-P + 1 Glyceraldehyde-3-P

Question 21

What is the characteristics of pentose phosphate pathway?

Answer 21

• no ATP production
• Loss of CO2 - irreversible
• controlled by NADP+/NADPH ratio
• catalysed by G6P dehydrogenase

Question 22

What is the function of pentose phosphate pathway

Answer 22

• produce NADPH in cytoplasm
• Produce C5 sugar for nucleotides
  
  • nucleic acid synthesis

Question 23

What happens in G6PDH deficeincy?

Answer 23

Depletion of NADPH

Question 24

What is the metabolic consequence of G6PDH deficiency?

Answer 24

• Cataract
• Haemolysis of RBC
  
  • decrease NADPH in RBC - disulphide bonds formed - proteins aggregate causing haemoglobin to denature