1. Energy Production 1 Flashcards
What are the 4 general steps of catabolism?
Stage 1
- breakdown to building block molecules
Stage 2
- breakdown to metabolic intermediates
- release of ‘reducing power’ and ‘energy’
Stage 3
- tricarboxylic acid (Kreb’s) cycle
- release of ‘reducing power’ and ‘energy’
Stage 4
- oxidative phosphorylation: conversion of ‘reducing power’ into ATP
Describe the process of stage 1 catabolism of dietary carbohydrates.
Carbohydrates are broken down into monosaccharides by:
- Saliva: amylase (starch/glycogen to dextrins)
- Pancreas: amylase (to monosaccharides)
- Small intestine: disaccharidases attached to brush border membrane of epithelial cells:
- lactase (lactose)
- sucrose (sucrose)
- pancreatic amylase (alpha1-4 bonds)
- isomaltase (alpha1-6 bonds)
What are the differences between the types of lactose intolerance.
- Primary lactase deficiency
- Cause: absence of lactase persistence allele
- Only occurs in adults
- Secondary lactase deficiency
- Cause: injury to small intestine (gastroenteritis, coeliac disease, Crohn’s disease, ulcerative colitis)
- Occurs in both infants and adults
- Generally reversible
- Congenital lactase deficiency
- Cause: autosomal recessive defect in lactase gene - cannot digest breast milk
- Occurs in both infants and adults
- Extremely rare
What are the symptoms of lactose intolerance?
Bloating/cramps Flatulence Diarrhoea Vomiting Rumbling stomach
How are monosaccharides absorbed into the blood?
- Active transport into intestinal epithelial cells by sodium-dependent glucose transporter 1 (SGLT1): co-transport of 2 Na+ for 1 sugar.
- Transport out of epithelial cells into blood via GLUT2 transporter.
How are monosaccharides absorbed from the blood into tissues? Give examples.
- Via facilitated diffusion using transport proteins (GLUT1-GLUT5).
- GLUT2: kidney, liver, pancreatic beta cells, small intestine
- GLUT4: adipose tissue, striated muscle (insulin-regulated)
What is the major blood sugar and to what is its concentration regulated?
Blood [glucose] regulated to ~5 mM
Which cell types have an absolute requirement for glucose, why?
- Red blood cells (lack mitochondria so can’t do stages 3 and 4 of metabolism)
- Neutrophils (have mitochondria but used for oxidative burst and ROS production)
- Innermost cells of kidney medulla (kidney cortex has very high oxygen requirement so not enough left for medulla)
- Lens of the eye (not vascularised as needs to be translucent, so no oxygen supply)
Which cell type has a preference for glucose as its energy source?
CNS - brain (can use ketone bodies for some of energy requirements in times of starvation but needs time to adapt)
What does glucose uptake into tissues mainly depend on?
[blood glucose] - if falls lower than Km of glucose transporter, can’t be transporter into tissues… hypoglycaemic… coma (as brain doesn’t have enough energy).
Where does glycolysis occur?
Cytosol - in all tissues
What are the functions of glycolysis?
Oxidation of glucose, producing C6 and C3 intermediates, to synthesise:
- NADH (2 per glucose)
- ATP from ADP (net gain of 2 per glucose)
What does the ‘investment’ phase of glycolysis involve?
Conversion of 2 ATP to ADP.
What are the substrate and end product of glycolysis?
Substrate = glucose (C6) Product = pyruvate (C3) x2
Why are there so many steps/enzymes in glycolysis?
- Chemistry easier in small stages
- Efficient energy conservation
- Gives versatility: allows interconnections with other pathways, allows production of useful intermediates, allows part to be used in reverse
- Allows for fine control