L5: Energy production- Carbohydrates Flashcards
Define catabolism?
- Breakdown of larger molecule into smaller ones (intermediate metabolite)
- Exergonic→ release large amount of energy -G
- Oxidative reactions→ H atoms→ get a reducing power
(OIL)
Briefly describe the four stages of metabolism?
Stage 1
- Extracellular → GI tract
- Breakdown to building blocks for absorption
- Convert nutrients into a form that can be taken up into cells
- No energy produced
- Breakage of C-N and C-O bonds
Stage 2
- Cystolic and mitochondrial
- Breakdown to metabolic intermediates (many pathways e.g glycolysis)
- Oxidation- release of ‘reducing power’ NAPD and ATP
- Requires co-enzymes which are then reduced
Stage 3
- Mitochondrial
- Tricarboxylic acid cycle (kreb’s cycle)
- Oxidative- release of reducing power (NADP, FAD2H) and some energy GTP
- Acetyl CoA oxidised to CO2
- Molecules for biosynthesis pathway
Stage 4
- Mitochondiral
- Oxidative phosphorylation
- Conversion of reducing power into energy currancy ATP
- Oxygen required
- Large amount of energy produced
What is the general structure of a carbohydrate?
Formula (CH20)n
Aldehyde (C=0 next to C-H) or ketose sugars (C=0 next to two R groups)
What different types of carbohydrates are there?
Monosaccharide (single sugar unit) → glucose, galactose, fructose
Disaccharide (two sugar unit)→ lactose, maltose, sucrose
Oligosaccharide (3-12 units)→ Dextrins
Polysaccharide (10-100 units)→ Glycogen, starch, cellulose
What is the glucose requirements in tissues?
- Major sugar in blood, concentration regulated to 5mM
- All tissue metabolise glucose but some have an absolute requirement for it - RBC, neutrophils, inner mast cell of kidney medulla, lens of eye
- CNS prefers glucose as a fuel source
How does stage 1 catabolism occur?
Occurs in GI tract
Polysaccharides are broken down into dextrins
Glycosidase enzymes
What enzymes are involved in stage 1 catabolism?
- Amylase
- Saliva→ starch, glycogen into dextrins
- Pancreas→ Dextrins into monosaccharides - Glycosidase enzymes attached to brush border in SI
- Lactase (lactose)
- Sucrase (sucrose)
- Pancreatic amylase (α-1,4 bonds)
- Isomaltase (α-1,6 bonds)
What are humans unable to digest cellulose?
Unable to break the ß1-4 glycosidic bond found between C atoms
What does lactose intolerance mean?
Insufficient lactase enzyme
Unable to break down lactose
Lactose appear in colon- broken down by bacteria
Alters osmotic gradient/pressure- water moves into colon- diarrhoea
Bacteria causes methane, CO2 and hydrogen production→ bloating and discomfort
What are the different types of lactose intolerance?
- Primary lactase deficiency
- Absence of lactase persistence allele
- Highest prevalence in Northwest Europe
- Only occurs in adults - Secondary lactase deficiency
- Injury to SI
→ Coeliac disease
→ Gastroenteritis
→ Ulcerative collitis
→ Crohn’s disease
- Occurs in infants and in adults
- Generally reversible
Congential lactase deficiency
- Extremely rare
- Autosomal recessive defect in lactase gene
- Cannot digest breast milk
How are monosaccharides absorbed from the intestine?
Transported into epithelial cells → blood stream
- Into epithelial cell→ active transport (low to high), Sodium-dependent glucose transporter 1 (SGLT1)
- Into blood stream→ passive transport, (high to low) GLUT2
- Blood into target cell→ facilitated diffusion (high to low concentration), GLUT1-5
What are the different glucose transporters?
- Facilitated diffusion via GLUT1-5
- Hormonally regulated
GLUT2- pancreatic ß cells, kidney, SI
GLUT4- adipose tissue, striated muscle
Where does Stage 2 catabolism occur?
Cystolic
Lots of different pathways
Glycolysis is a good example
What are the key features of glycolysis?
Central pathway for carbohydrate metabolism
All tissues
Exergonic and oxidative
10 enzyme catalysed steps
C6 → 2C3 (no loss of CO2)
Additional lactase dehydrogenase (LDH) enzyme can act anaerobically
Irreversible pathway
What is the function of glycolysis?
Oxidation of glucose NADH production (2 per glucose) Net ATP= 2ATP per glucose Produce C6 and C3 intermediates Split into two phases 1. preparative phase 2. ATP generating phase
