LEARNING OUTCOMES Flashcards
glucokinase vs hexokinase
involved in the phosphorylation of glucose to glucose-6-phosphate so that it can be trapped in the cells.
Glucokinase-has a High Km and Vmax. Found in liver
Hexokinase-has a low Km and a low Vmax. Found in other tissues
After a meal when Blood glucose high-
Glucokinase will grab a lot of the glucose very quickly, hence why there is a high storage in liver
A long time after a meal i.e. when blood glucose levels low.
Hexokinase will grab onto glucose effectively-can be used in other tissues
major carbohydrates in our diet
1- Starch: made up of amylose and amylopectin.
2-Glycogen: animal version of starch. D-glucose is branched every 8-12 residues
3-oligosaccharides : broken down into CH4 and H2
4-Cellulose and hemicellulose: Not digested. Increase digestion time and faecal bulk.
5- Lactose, Sucrose, Maltose
6- Glucose and Fructose
Digestion and absorption of carbohydrates
1- mouth: salivary amylase 2-stomach: no carbohydrate digestion 3- small intestine: absorption of glucose via co-transport with sodium and then release into blood via GLUT carriers. -duodenum : pancreatic amylase. -jejunum : cell-surface mucosal enzymes. 4- In cells: -liver: Glucokinase -other tissues: Hexokinase 5- glycolysis/ citric acid cycle
synthesis/degradation of glycogen:
Sythesis:
1- Glycogenin: Binds 8 glc residues from UDP-glucose
2- glycogen syntase : increases chain length
3- branching enzymes : breaks bonds formed by glycogen synthase and forms alpha-1,6 bonds
Degradation:
1- Glc residues removed from non-reducing ends
2- 3 Glc residues removed from branch and bonded to closest non-reducing end
3- glucosidase: breaks alpha 1,6 bonds.
4-G-1-P–> G-6-P
compare and contrast function in liver and S.M.
In liver
glycogen-G-6-P- glucose bc of glucose-6-phosphorylase
In Skeletal Muscle
glycogen- G-6-P to lactate
used in substrate-level phosphorylation to produce ATP
describe the function and process of glycolysis?
Function : produce small amounts of ATP via substrate-level phosphorylation in the absence of 02 in the cytoplasm.
irreversible steps:
- Glucose to G-6-P
- F-6-P tp F-1,6-biP
- PEP + ADP to Pyruvate and ATP
where is NAD+ needed: glyceraldehyde-3-
final products: lactate and ethanol
describe the function of the lactate and alcohol dehydrogenase reactions
-pyruvate- lactate: uses lactate dehydrogenase .
In muscle during contraction or in RBCs with no mitochondria.
-pyruvate- acetaldehyde- ethanol uses pyruvate carboxylase and then alcohol dehydrogenase.
In yeast cells
PRODUCE NAD+
describe the fate of lactate?
GLUCONEOGENESIS:
in the liver lactate in converted back into PEP by bypass reactions which allow the irreversible reactions in glycolysis to take place.
lactate-pyruvate-OAA-PEP.
CORI CYCLE
Interaction between the liver and the muscle when vigorous exercise takes place.
Allows ATP to be produced via substrate-level phosphorylation in muscle- LACTATE produced which is then transported through blood to liver.
Liver builds up a debt to muscle. Break down lactate into glucose during gluconeogenesis which then transported to muscles.
describe the precursors and the processes involved in gluconeogenesis?
Precursors : lactate, pyruvate, fructose and galactose
Lactate-pyruvate- OAA–PEP
Pyruvate- OAA-malate- PEP
Fructose-F-1-P- DAH + glyceraldehyde- G-3-P
Galactose-Galactose-1-Phosphate- UDP-galactose- UDP-glucose
Describe the functions of the phosphate pentose pathway
1- produces NADPH which is required in the liver and mammary gland for FA synthesis, in the adrenal gland for steroid production, in the RBCs as an antioxidant
2- Produces pentoses which are used as a precursor for ATP, DNA, proteins…
Oxidative:
- G-6-P to ribulose-6-phosphate produces a lot of NADPH.
- ribulose-6-phophate to nucleic acids,DNA
Non-oxidative:
-ribulose-6-phosphate to G-6-P during cell reproduction
