Carbohydrate Metabolism Flashcards
What is the critical blood glucose level?
2.5 mM
What are the symptoms of hypoglycaemia?
Muscle weakness Loss of coordination Mental confusion Sweating Hypoglycaemic coma and death
What are the hyperglycaemic symptoms?
Non enzymatic modification of proteins which could lead to cataracts
Hyperosmolar coma
What is glycogensis
Glycogen synthesis
How much glycogenesis takes place (in grams) in the liver and skeletal muscle?
100g in liver
300-400g in skeletal muscle
When does glycogenesis take place?
When blood glucose levels are high
What is glycogen?
Branched polymer of glucose
How is glycogen formed?
Alpha 1-4 and 1-6 glycosidic bonds
Where is glycogen formed
On a protein primer called glycogenin
What is glycogenesis regulated by?
Glycogen synthase
How are the branched points formed?
by a branching enzyme
What enzyme performs G6P-G1P
Phosphoglucomutase
What enzyme performs G1P+UTP->UDP
UDP glucose pyrophosphorylase
What enzyme adds more glucose residues to the glycogenin?
Glycogen synthase
How long is the original glycogen chain before branching happens?
11 glucose residues
Why is glycogen formed?
Glucose is osmotically active so it cant be stored (affects the water potential of the cells)
What is glycogenolysis?
Glycogen breakdown
Where does glycogenolysis happen?
Liver, muscle and (sometimes) kidney
When does glycogenolysis happen?
When glucose levels are low
What is glycogenolysis stimulated by?
Glucagon, Adrenaline, noradrenaline, growth hormone
What enzyme breaks the 1-4 glycosidic bonds between the glucose residues?
Phosphorylase
What does the breakdown of 1-4 glycosidic bonds produce?
G1P
What does phosphoglucomutase facilitate?
G1P-G6P
What enzyme removes the last 3 glucose residues on a branch?
Transferase
Where do the last 3 glucose residues go when they are debranched?
Added to the non-reducing end of the chain
What enzyme breaks the 1-6 glycosidic bonds?
Alpha 1-6 glucosidase
What happens to the glucose when it is freed from the glycogen?
Phosphorylated by hexokinase in the muscle to form G6P
What breaks down the glucose chains to produce G1P?
Phosphorylase
In the liver what enzyme does the G6P->glucose reaction?
G6-phosphatase
What are the products of glycolysis?
G1P, glucose
What is glycogen phosphorylase?
Large multi-subunit enzyme that plays a key role in glycogenolysis
What is glycogen phosphorylase regulated by?
Allosteric interactions that signal the energy state of the cell
What are the two isoforms of glycogen phosphorylase?
Active - phosphorylase A
Inactive - phosphorylase B
What is phosphorylase A phosphorylated by?
Phosphorylase B kinase
What inhibits phosphorylase?
Insulin
What stimulates phosphorylase in the liver?
Glucagon
What stimulates phosphorylase in the muscle?
Adrenaline
What weakly stimulates phosphorylase?
Cortisol
In muscle what can glycogen phosphorylase B be activated by?
5’AMP
What blocks 5’ AMP activation?
ATP and G6P
In the liver what is phosphorylase A inhibited by?
Glucose
When and how is glycogen synthase activated?
In times of plenty of glucose, by insulin
When and how is glycogen phosphorylase activated?
When blood glucose is low, by glucagon, adrenaline and noradrenaline
What does the pentose phosphate pathway start and end with?
Starts with G6P and ends with ribose 5 phosphate
What is ribose 5 phosphate included in?
Nucleotide and Nucleic acid synthesis
Where is NADPH formed?
In the pentose phosphate pathway
What is GSH used in?
In the protective mechanism of the self and to oxidative stress
What is NADPH important to?
The formation of GSH and fatty acids
What molecules do gluconeogenesis?
Triglycerides
Lactate
Amino acids
What is gluconeogenesis?
Creation of new glucose
Where does gluconeogenesis take place?
Mainly in the liver and the kidney, but also a bit in the intestine
When does gluconeogenesis take place?
When the blood glucose levels are very low (fasting or starving)
What is gluconeogenesis the reverse of?
Glycolysis
What enzyme takes pyruvate to oxaloacetic acid?
Pyruvate carboxylase
What enzyme takes oxaloacetic acid to phosphoenol pyruvate?
Phosphoenol pyruvate carboxykinase
What enzyme reverses phosphofructokinase?
Fructose 1-6 bisphosphate
What enzyme reverses hexokinase?
Glucose-6-phosphatase
Where are the fatty acids fed into the TCA cycle?
Glycerol components feed in where F1-6 bisphosphate is split
Where is pyruvate synthesised?
In the cytosol
Where does pyruvate carboxylase work?
In the mitochondria
3 most important substrates are
Amino acids (Alanine)
Lactate
Glycerol from triglycerides
What is gluconeogenesis used for?
To maintain blood glucose
What is the daily requirement for blood glucose?
160g
What is the daily requirement for blood glucose in the brain?
120g
What are the total body reserves of glucose?
210g
What does the gluconeogenic pathway do?
Pyruvate to glucose
Where does the gluconeogenic pathway take place?
Mostly in the liver and a little in the kidney
Where does the gluconeogenic pathway take place during starvation?
Kidney productions rise to 40% and a little in the liver
