Carbohydrates 2 Flashcards
Carbohydrates in diet
Starch Glycogen sucrose, maltose, fructose cellulose and hemicellulose Oligosaccharides => 1-6 glucose, roughage Glucose, fructose
Digestion in mouth
Salivary amylase breakdown alpha 1-4 of starch
Digestion in stomach
Nothing
Digestion in duodenum (small intestine)
Pancreatic amylase enters through duct
Digestion in jejenum
Enzymes in mucus break 1-6
Glucoamylase remove glucose from non reducing end
Sucrase hydrolyse sucrose and lactase hydrolyse lactose
Main products of carbohydrate digestion
Glucose, galactose and fructose (monosaccharide)
Absorption of glucose
High sodium forces glucose in cell together
Low cellular sodium maintained by pump
Glucose move cell==> blood
Absorption of galactose
Similar to glucose
Absorption of fructose
Binds to GLUT5 channel and moves down gradient - not ATP dependent
What do cellulose and hemicellulose do?
Increase faecal bulk
Decrease transit time
What are cellulose polymers broken down by and to?
Bacteria
Methane and hydrogen
Deficiencies in disaccharides
- severe intestinal infection or removal
- inflammation of gut
- drugs injuring gut wall
What are disaccharide deficiencies categorised by?
Abdominal pain and cramps
Lactose intolerance
Most common disaccharide deficiency
Loss of lactase activity
Undigested lactose ==> methane
Lactose drains water from gut => lumen
What is glucose immediately phosphorylated to?
Glucose-6-phosphate by hepatocytes in liver
Why phosphorylate glucose?
- trapped In cell
- Glycolysis
Glucokinase
In liver
High km and vmax
Only pick up glucose for liver in high conc
Hexokinase
Low km and k max
Found in other tissues which are easily satisfied
What enzyme G6P => Glucose
Glucose - 6 - phosphatase
Is Synthesis of glycogen directly from glucose monomers?
No
What does glycogenin do?
Covalently bind glucose from UDP to form chains of 8 glucose residues
Step 2 of glycogen synthesis
Glycogen synthase extends the chain
Chains broken by glucose branching enzyme
Reattached via alpha 1-6 for branch points
Degradation of glycogen
- Glucose removed one at a time from non reducing ends as G1P by glycogen phosphorylase
- De branching enzyme removes glucose near branch
- transferase release glucose and reattach at non reducing end
- Glucosidase removes final glucose by breaking alpha 1-6
- unbranched chain further degraded
G6P -> with glucose 6 phosphatase
Glucose -> blood
G6P with substrate level phosphorylation
Lactate
Von Gierke’s disease
G6P deficient
little and often carb eating
McArdles disease
Skeletal muscle phosphorylase deficiency
Avoid strenuous activity
