MCBG Session 6 - Catabolic Pathways (Part 1) Flashcards
What is catabolism?
The conversion of biological molecules into smaller ones (intermediary metabolites)
Give a brief overview of the 4 major stages of catabolism
1) Breakdown of macromolecules (carbs, proteins, fats, alcohol) into building block molecules.
2) Degradation of building block molecules into smaller precursors (e.g.: pyruvate) - AKA: Glycolysis
3) TCA cycle (Krebs) - oxidation of acetyl CoA into CO2 and production of NADH/FADH2
4) Electron transport & oxidative phosphorylation to produce large amounts of ATP.
- What is the general formula of carbohydrates?
- What 4 different kinds of carbohydrate can you get (give an example of each)
- What are the 3 kinds of monosaccharide sugars?
- (CH2O)n
- Monosaccharide (glucose), Disaccharide (lactose), Oligosaccharide (dextrin), Polysaccharide (starch)
- Triose, Pentose & Hexose sugars
What are the constituents of lactose, sucrose + maltose
Lactose = Glucose + Galactose Sucrose = Glucose + Fructose Maltose = Glucose + Glucose
How are carbohydrates initially digested?
- In the mouth, salivary amylase break polysaccharides into dextrins.
- Pancreatic amylase breaks down polysaccharides into monosaccharides
- Small intestine - disaccharides attached to brush border of epithelial cells broken down by respective enzymes, e.g.: lactase for lactose (breaking a-1,4 glycosidic linkages)
Why is cellulose not digested in the human GIT?
- Humans do not contain enzymes required to break down B1,4-glycosidic linkages present in cellulose.
- What is the biochemical basis of lactose intolerance?
- What leads to the symptoms?
- Lack of lactase enzyme - can be primary (absence of lactase persistance allele), secondary (damage to SI epithelium) or congenital (autosomal recessive defect in lactase gene).
- Lactose not broken down, remains in GIT as osmolyte, draws water into GIT, leads to bloating, flatulence, Diarrhoea, Vomiting etc.
- Which 4 tissues need glucose as an absolute requirement?
- How much glucose does the brain use per day?
- RBC’s, Neutrophils, Innermost cells of the kidney medulla & Lens of the eye (approx 40g glucose/day)
- 140g per day
What transporters take up glucose into cells via facilitated transport?
-GLUT1-5 - different locations have different GLUT transporters.
What are the 4 main functions of glycolysis?
1) Oxidation of glucose to 2 x 3C pyruvate molecules
2) Production of NADH (2 per glucose)
3) Synthesis of ATP from ADP (4 produced, 2 used therefore net of 2xATP per glucose)
4) Produces 6C and 3C intermediates
- Where does glycolysis occur?
- What type of reactions occur in glycolysis?
- Is there any loss of CO2?
- Is it a reversible or irreversible pathway?
- Glycolysis is cytosolic
- Oxidative (exothermic) reactions
- 6C molecules –> 2 x 3C molecules (so no loss of CO2)
- Irreversible
What are the 3 irreversible steps in glycolysis + the enzymes that catalyse them? (and the steps therefore subject to regulation)
1) Step 1 - phosphokinase (PK)
2) Step 3 - phosphofructokinase-1 (PFK1) - key control enzyme
3) Step 10 - Pyruvate kinase
What 2 important intermediate metabolites can produced during glycolysis
1) Glycerol Phosphate (from DHAP via glycerol-3-phosphate dehydrogenase) - important in triglyceride and phospholipid synthesis,
2) 2,3-BPG (from 1,3-BPG via bisphosphoglycerate mutase) - regulates Hb O2 affinity (makes it favour oxygen release)
What is the role of Lactate Dehydrogenase (LDH) in glucose metabolism?
- In low O2 conditions, NADH must be re-oxidised to NAD+ for ATP synthesis in glycolysis to occur.
- LDH catalyses the reaction of NADH, protons + pyruvate to reform NAD+.
- However this also produces lactate, which is converted back into pyruvate in the liver - also by LDH.
- What is the normal blood conc of lactate?
- What is the blood conc for hyperlactaemia + lactic acidosis
- <1mM lactate
- 2-5 mM
- > 5mM - critical marker of acutely unwell patient
