Biochemistry Flashcards
Rate limiting step
e slowest step of a chemical reaction that determines the speed (rate) at which the overall reaction proceeds
primer
a molecule whose presence is required for the formation of another molecules
glycogenesis
synthesis of glycogen form glucose
glycogenolysis
break down of glycogen to form glucose
glycogen
storage form of glucose
present in liver and muscle cells
liver glycogen
can be released into the blood stream to maintain blood glucose levels
muscle glycogen
cannot be released into the blood stream, is used in the cell to form energy via glycolysis and citric acid cycle
when does glycogenesis occur?
between meal times to maintain blood glucose levels
when does gluconeogenesis occur?
when the liver glycogen stores are depleted and glucose is required to be produced from non carbohydrate precursors
what bond holds glucose molecules in the chain together
α 1-4 glycosidic bonds, between the no1 carbon on one carbon on one glucose and the number 4 carbon on another glucose
what bonds attach the branches to glycogen molcules
α 1-6 glycosidic bonds
where is the glycogenin protein and what does it do
centre of glycogen molecule, catalytic activity
adds a few glucose molecules to itself
Why is the glycogenin protein so crucial?
because the enzyme glycogen synthase cannot start glycogen from scratch, it can only add glucose to an existing chain
what does hexokinase do?
phosphorylates glucose to form glucose 6 phosphate
what does phosphoglucomutase do?
transfers glucose 6 phosphate to glucose 1 phosphate
moves the position of glucose
UDP glucose pyrophosphorylase
transfers glucose 1 phosphate to UDP glucose
UDP glucose
activated form of glucose
what happens to the UDP glucose
convalently bonded onto glycogen by glycogen synthase
what does glycogen synthase do
adds a glucose molecule to the end of glycogen
does not add branches
rate limiting step
how are branches added to glycogen
via the enzyme transglycosylase
summary of gycogenolysis
glucose molecule removed from glycogen and a phosphate added to the glucose
products of glycogenolysis
glucose 1 phosphate
glycogen chain minus 1 glucose
what happens to glucose 6 phosphate in the liver
dephosphorylated by glucose 6 phosphatase to form free glucose thats released into the blood stream via GLUT 2
what happens to glucose 6 phosphate in muscle
cannnot be dephosphorylated. produces energy via glycolysis and citric acid cycle
how is glucose 1 phosphate converted to glucose 6 phosphate?
phosphoglucomutase
can glycogen phosphorylase remove branches?
no additional enzymes are required
what hormones regulate glycogenesis and glycogenolysis
insulin
glucagon
adrenaline
cortisol
urea
a colourless crystalline compound which is the main nitrogenous breakdown product of protein metabolism in mammals and is excreted in urine
gluconeogenesis
synthesis of glucose from non-carbohydrate precursors
e.g lactate, amino acid, glycerol
requires energy
where does gluconeogenesis mainly occur
liver
does gluconeogenesis require energy
yes, very energy expensive
In lipid catabolism, how is the fatty acid transferred to acetyl coA?
Beta oxidation
lipid anabolism
transfer of starch to triglycrides
where does amino acid catabolism take place
liver
how is nitrogen secreted
urea
stages of urea synthesis
transamination
deamination
degradation
