Flashcards in MEH 3 - Energy Production Deck (35):
What is stage 1 of catabolism?
Breakdown to building blocks
Where/how is stage 1 of catabolism carried out in the body?
- SALIVA contains amylase
- the PANCREAS contains amylase
- SMALL INTESTINE contains disaccharidases
What are the three types of lactase deficiency?
- primary lactase deficiency (absence of lactase persistence allele)
- secondary lactase deficiency (caused by injury to small intestine)
- congenital lactase deficiency (autosomal recessive defect in lactase gene)
What are the symptoms of lactose intolerance?
- 'rumbling' stomach
How are monosaccharides absorbed into the blood?
- active transport by sodium dependent glucose transporter (SGLT1)
- facilitated diffusion via GLUT2 transport proteins into blood supply
Where are GLUT2 and GLUT4 proteins found?
- GLUT2 - kidney, liver, pancreatic beta cells, small intestine
- GLUT4 - adipose tissue, striated muscle
Which cells have an absolute requirement for glucose as a food?
- red blood cells
- innermost cells of kidney medulla
- lens of the eye
- brains prefers glucose but can use ketone bodies
What is stage two of catabolism?
- breakdown to metabolic intermediates
- release of reducing power and energy
What are the functions of glycolysis?
- oxidation of glucose
- NADH production
- synthesis of ATP from ADP
- production of C6 and C3 intermediates
Can glycolysis occur anaerobically?
Yes - with the addition of an enzyme (PDH) it is the only pathway that can operate anaerobically.
How much ATP and NADH is produced in glycolysis?
- 2 ATP produced per glucose
- 2 NADH produced per glucose
Which enzyme converts glucose into glucose-6-P?
Hexokinase (or glucokinase in the liver)
Which enzyme converts fructose-6-P into fructose 1,6-bis-P?
Which enzyme converts phosphoenolpyruvate into pyruvate?
Why is glucose phosphorylated?
It makes glucose negatively charged so it cant pass back through the plasma membrane. It also increases reactivity to permit subsequent steps.
How many steps are there in glycolysis?
Which steps of glycolysis use ATP?
1 and 3
Which steps of glycolysis form ATP?
7 and 10, which occur twice per glucose
Why is reaction 10 (conversion of phosphoenolpyruvate to pyruvate) irreversible?
Large -ve delta G
How is glycolysis regulated?
- Phosphofructokinase is the main regulator.
- allosteric regulation in muscle
- hormonal regulation in liver
- hexokinase product inhibition
- metabolic regulation
- pyruvate kinase regulation
How do hormonal and allosteric regulation take place?
- inhibited by high ATP
- stimulated by high AMP
- stimulated by insulin
- inhibited by glucagon
What is glycerol phosphate?
- byproduct of step 4 and 5 of glycolysis
- important to triglyceride and phospholipid synthesis
What is 2,3-bisphosphoglycerate?
- 1,3-bisphopsphoglycerate (glycolysis intermediate) can be converted into this
- produced in red blood cells
- regulator of haemoglobin O2 affinity
What is lactate dehydrogenase used for?
It converts NAD+ to NADH and vice versa, allowing continued aerobic respiration in tissues, the heart and the liver and kidney
What is lactic acidosis?
Occurs when plasma lactate rises above 5 mM, and blood pH is lowered
What is hyperlactaemia?
A less severe form of lactic acidosis when plasma lactate reaches 2-5mM, but there is no change in blood pH due to its buffering capacity
What is normal plasma lactate concentration?
Less than 1 mM
How is the galactose from milk digested?
- milk splits into glucose and galactose
- galactose turned into galactose-1P by galactokinase
- galactose-1P converted into glucose-1P by uridyl transferase, then converted into glucose-6P and undergoes glycolysis
- galactose-1P can also be converted into UDP-galactose by UDP-galactose epimerase
- it is then converted into UDP-glucose, which forms glycogen
Describe fructose metabolism
- using ATP, converted into fructose-1P by fructokinase
- aldolase converts into glyceraldehyde and DHAP
- triose kinase (uses ATP) and TPI convert these into 2 x glyceraldehyde-3-P
- these undergo glycolysis
What is the difference between essential fructosuria and fructose intolerance?
Essential fructosuria is fructose in urine due to missing fructokinase.
Fructose intolerance is fructose-1P accumulating in liver due to missing aldolase.
What does the pentose phosphate pathway start with?
The pentose phosphate pathway is an important source of NADPH. What is this required for?
- reducing power for biosynthesis
- maintenance of GSH levels
- detoxification reactions
The pentose phosphate pathway produces C5-sugar ribose. What is this required for?
Synthesis of nucleotides, DNA and RNA.
What is the rate limiting enzyme in the pentose phosphate pathway?