Topic 6 - Energy Production Carbohydrates (glycolysis/krebs cycle/oxidative phosphorylation) Flashcards
(40 cards)
What are the 4 stages of catabolism?
Stage 1 - Complex molecules are converted to building block molecules that can be taken up by cells, absorbed into circulation by G tract, no energy released, Extracellular (GI tract)
Stage 2 - Building block molecules converted into even simpler molecules, oxidative, coenzymes are reduced, some energy produced in ATP form, intracellular (cytosolic and mitochondrial) e.g glycolysis
Stage 3 - Krebs cycle, oxidative, requires FAD and NAD+, mitochondrial
Stage 4 - electron transport, oxidative phosphorylation, ATP synthesis, O2 required (reduced to H20), NADH and FAD2H oxidised, large amounts of ATP produced, mitochondrial
What are the classes of carbohydrate?
Monosaccharide = one monomer,single sugar unit Disaccharide = 2 units Oligosaccharide = 3-12 units (dextrins) Polysaccharides = 10 -1000s units (glycogen, starch, cellulose)
What are the three main dietary monosaccharides?
Glucose, fructose and galactose
Which cells have an absolute requirement of blood glucose?
- red blood cells
- neutrophils
- innermost cells of kidney medulla
- lens of the eye
What constitutes stage 1 metabolism of dietary carbs?
- salivary amylase in mouth (breaks em into dextrins), pancreatic amylase in duodenum (breaks em into monosaccharides), disaccharidases (lactase/sucrase/isomaltase) in small intestine brush border lining of epithelium (monosaccharides as well)
Why can humans not hydrolyse the polysaccharide cellulose?
- no present enzyme to break the beta 1-4 glycosidic bonds in cellulose
Explain briefly in very broad terms lactose intolerance.
- a deficiency of lactase enzyme
Describe the types of lactose intolerance.
Primary lactase deficiency - absence of lactase persistence allele so cannot produce enzyme after infancy (grow out of production)
Secondary lactase deficiency - caused by injury to small intestine (Gastroenteritis, coeliac, crohns, ulcerative colitis)
Congenital lactase deficiency - autosomal recessive defect in lactase gene, very rare, means production is hindered from birth
Why does lactose intolerance cause vomiting, flatulence and bloating/cramps?
Lactose cannot be digested so remains in GI system, it is an osmalite which means it will attract water
Explain the absorption of monosaccharides by intestinal epithelia.
- Active transport into epithelium cell via Sodium dependant glucose transporter
- Then passive transport into blood supply via glucose transporter
- Blood carries to target tissues
- Target cells take it in via facilitated diffusion using transport proteins (GLUT 1-5)
What is the basic overall goal of glycolysis?
Glucose (6C) ——> 2x pyruvates (2x 3C)
Cleavage
Why does phosphorylation of glucose occur in early stage of glycolysis?
Makes glucose negatively charged so it cannot be passed back across the membrane
Why so many steps in glycolysis?
- Chemistry is easier in small stages
- Efficient energy conservation
- Allows interconnections with other pathways
- Can be controlled
How could glycolysis be used for the imaging of tumours?
- glycolysis rate elevated in cancerous cells (200x)
- can measure uptake of modified, radioactive enzyme used in first stage of glycolysis using PET scanning
Why is the glycolytic intermediate DHAP (dihydroxyacetone-p) important?
- goes on to form glycerol phosphate under enzyme action
- Glycerol phosphate is important to synthesis of triglycerides and phospholipids
Why is the glycolytic intermediate BPG (bisphosphoglycerate) important?
- goes onto form an isomer under enzyme action
- This isomer is produced in erythrocytes and regulates haemoglobin O2 affinity (promotes release)
Why is it important to have an alternate pathway after stage 2?
- if there are low O2 conditions, this is bad because stage 4 requires oxygen
- some cells like RBCs don’t have stage 3 or 4 so need another way of producing NAD+
- need NAD+ to be regenerated
What is the name of the enzyme used in lactate production?
- lactate dehydrogenase
What is lactate production?
NADH + H+ + pyruvate = NAD+ + lactate
- NAD IS REGENERATED YAY!
What happens to lactate once its been produced?
Travels in blood:
The heart - LDH catalyses reformation of pyruvate and its entered back into stage 3 and oxidation
Liver and kidney - LDH catalyses reformation of pyruvate and its used for gluconeogenesis
What are the boundaries of lactate plasma for hyperlactaemia and lactic acidosis?
Hyperlactaemia = 2-5mM, below renal threshold, no change in blood pH
Lactic acidosis = above 5mM, above renal threshold, lowers blood pH (buffering capacity exceeded)
What is Essential fructosuria?
- fructokinase enzyme missing, fructose passes into urine and excreted no clinical signs
What is Fructose intolerance?
- adolase B enzyme missing, fructose-1-p accumulates in liver, leads to liver damage
What is galactosaemia?
- Accumulation of galactose and/or galactose-1-p
- problem is galactose enters other pathways like becoming galactitol which oxidises NADPH to NADP+
- This causes improper formation of disulphide bridges
- structural damage to the lens of the eye, cataracts
