Biochemistry Flashcards
what are the 3 main glycogen metabolic pathways
glycogenesis: synthesis of glycogen from glucose
glycogenolysis: breakdown from glycogen to from glucose
gluconeogenesis: de novo synthesis pf glucose from metabolic precursors (AAs, lactate)
what is glycogen?
a polymer of glucose
what 2 substances are needed for glycogenesis?
UDP & Glycogen synthase
what is UDP?
activated form of glucose
what is glycogen synthase?
key enzyme that synthesises glycogen from UDP-glucose.
True/False…
glycogen synthase is rate limiting
True…
it can only add 1 glucose molecule to glycogen at a time
what is the key enzyme for glycogenolysis?
glycogen phosphorylase
what does glycogen phosphorylase do?
cleaves off 1 glucose from glycogen at a time.
which organ can dephosphorylate glucose-6-phosphate to form glucose?
the liver, muscle can’t do this
when does gluconeogenesis usually kick in?
during prolonged starvation
what are the precursors, energy supply and location of gluconeogenesis?
precursors: AAs, lactate, glycerol
energy: oxidation of fatty acids from adipose tissue
location: liver
what determines glycolysis or gluconeogenesis?
hormones, high AMP/ADP, high ATP, acetyl-coA etc
what is the Cori Cycle?
lactate formation
describe the Cori Cycle…
lactate formed in fast twitch muscles > lactate transported to liver by blood > liver converts lactate to glucose
what are the 3 classes of lipids
simple (fatty acids, triglycerides)
compound (phosphorylase, glycol, lipo)
steroids (cholesterol, steroid hormones)
True/False…
fatty acids are a straight chain
True
True/False…
fatty acids have an odd number of C atoms
False…
even number
what does saturated, unsaturated and polyunsaturated in terms of bonds mean?
saturated- single bond
unsaturated- double bond
polyunsaturated- several double bonds
what are fats broken down to?
monoglycerides
short and medium FAs absorbed by…
mucosal cells
long FAs and monoglycerides are…
resynthesised into triglycerides
what are chylomicrons?
triglycerides coated with protein, cholesterol, phospholipid
what happens to chylomicrons
cleaved by lipases to form free fatty acids which can be resynthesised or oxidised
triglycerides are composed of…
1 glycerol & 3 FAs, have a high energy yield
what happens during lipolysis
- initial cleavage of triglycerides by hormone sensitive lipases
- FAs are then converted o acetyl-CoA (in cytoplasm- req 2 ATP)
- FAs undergo oxidation to provide energy (matrix of mitochondria)
what is the carnitine shuttle
allows acetyl CoA to travel to matrix for B-oxidation
what does b-oxidation produce?
produces 1 acetyl-coA, 1 FADH, 1 NADH + H+, 1 fatty acyl-CoA
how are ketone bodies formed?
formed in mitochondria of liver and eventually converted back to acetyl CoA
what does fatty acid oxidation usually yield if carb and fat degradation is balanced?
acetyl co-A which enter Citric Acid Cycle
what happens in fatty acid oxidation if in starvation or a diabetic?
oxaloacetate is used for gluconeogenesis, fatty acids are oxidised to provide energy so acetyl-CoA converted to ketone bodies
what is dangerous about ketosis
ketoacidosis may occur
where does de novo synthesis of fatty acids occur?
in the liver, kidney, mammary glands, adipose tissue and brain
why does denovo synthesis of FAs occur?
during excess energy intake
where does lipogenesis occur
cytoplasm
what is citrate’s role in acetyl co A transport?
carries acetyl co-A from mitochondria to cytoplasm for lipogenesis
once in cytoplasm, what happens to the acetyl co-A?
activated to malonyl-CoA which donates carbon atoms to new lipid
what is the cycle of lipogenesis?
- condensation
- reduction
- dehydration
- reduction & release
once what no of carbon atoms is reached, does the FA release itself?
C16
what enzyme is needed for the synthesis of FAs from acetyl-coA
fatty acid synthase
what enzyme controls lipogenesis?
acetyl-coA Carboxylase - activates acetyl-CoA to malonyl-CoA
what is acetyl-coA Carboxylase activated and inhibited by?
activated: insulin, glucagon, epinephrine, citrate
inhibited: palmitoyl-CoA
what does triglyceride synthesis require?
glucose-3-phosphate
where does amino acid metabolism occur?
liver
what happens if AAs can’t be degraded?
are absorbed into intestinal cells and released into blood
what are AA produced ammonium ions excreted by and why?
they are toxic so excreted by urea, uric acid, creatinine
how is urea synthesised?
AA > glutamic acid > NADH + NH4+ + aspartic acid > urea
after removal of an amino group in transmission stage of urea synthesis, what are remaining carbon skeletons converted to?
either glucose or oxidised to join TCA cycle
