Biochemistry Flashcards
What is glycogenesis?
synthesis of glycogen from glucose
what is glycogenolysis?
breakdown of glycogen to form glucose
what is gluconeogenesis?
de novo synthesis of glucose from metabolic precursors (lactate, amino acids, glycerol)
what is glycogen?
main storage form of glucose in liver and muscle cells.
what does liver glycogen do?
broken down between meals and released to maintain blood glucose levels for red blood cells and brain.
what does muscle glycogen do?
provides energy via glycolysis and the TCA during bursts of physical activity
what does a glycogen ‘primer’ covalently attach to?
a protein called glycogenin
what does glycogen synthase do?
- synthesises glycogen from UDP-glucose
- adds one glucose molecule to glycogen at a time
- can only extend the chains of glycogen
what is the rate limiting enzyme of glycogensis?
glycogen synthase
what is glycogenolysis catalysed by?
glycogen phosphorylase
what is the rate limiting enzyme for glycogenolysis?
glycogen phosphorylase
where does lactate as a precursor for gluconeogenesis come from?
synthesised by skeletal muscle under anaerobic conditions
where does amino acids as a precursor for gluconeogenesis come from?
derived from muscle protein by proteolysis
where does glycerol as a precursor for gluconeogenesis come from?
derived from triglycerides by lipolysis in adipose tissue
what does gluconeogenesis require?
four unique liver enzymes.
what happens during the cori cycle?
blood transports lactate to liver, liver converts lactate back to glucose, glucose is released into blood stream.
when is lactate formed?
in fast-twitch muscle under conditions of heavy exercise
what do high levels of AMP or ADP mean?
low energy
what do high levels of ATP mean?
high energy
what do high/low levels of fructose 2,6-bisphosphate mean?
high in fed state
low in starved state
what do high levels of citrate, alanine, acetyl-CoA mean?
high when intermediates or building blocks abundant
what are glycogen storage diseases?
group of diseases with increased glycogen deposits in liver or muscle or both
what does increased fat intake without appropriate energy expenditure lead to?
- increase in number of adipocytes
- more fat in adipocytes
what does control of energy balance depend on?
- genetically linked factors e.g. protein messengers regulating appetite
- environmental factors e.g. food abundance, fashionable foods
what can a deficiency in essential fatty acids lead to?
membrane disorders, increased skin permeability and mitochondrial damage
what are the fat soluble vitamins?
vitamins A,D,E and K
what are triglycerides?
main energy storage form in adipose tissue
what is the structure of triglycerides?
consist of glycerol and 3 fatty acids
what does aliphatic mean?
no rings
what are the main natural fatty acids?
palmitic acid, stearic acid and oleic acid
what lowers melting point?
double bonds
what are the main products of fat absorption?
glycerol, fatty aids and monoglycerides
what is lipolysis?
breakdown of lipids
what has to happen to fatty acids before they can be oxidised to generate energy?
they have to be converted to CoA derivatives
how much energy does fatty acid oxidation require?
2 ATP
where does fatty acid oxidation occur?
cytoplasm
what is the carnitine shuttle?
in the cytoplasm, fatty acids are transferred from acyl-CoA to carnitine.
net result - acyl-CoA located in mitochondrial matrix
what does acyl-carnitine transporter in inner membrane do?
faciliates antiport of acyl-carnitine into the mitochondria and carnitine out
where does beta oxidation occur?
mitochondrial matrix
how many steps in beta oxidation?
four
what are the products of each cycle of beta oxidation?
1 acetyl-CoA
1 FADH2
1 NADH + H+
1 fatty acyl-CoA, shortened by 2 carbon atoms
what is glycerol broken down by/to?
activated to glycerol-3-phosphate by glycerol kinase
what is glycerol dehydrogenated to?
dihydroxyacetone phosphate
what are ketones formed from?
acetyl-CoA from beta oxidation
where are ketones important?
energy metabolism for heart muscle and renal cortex
what is the precursor of all new fatty acids called?
malonyl-CoA
what happens to amino acids which are not used as building blocks?
they are degraded
what is the major site of amino acid degradation?
liver
what does amino acid breakdown produce?
ammonia and ammonium ions
what amino acid product is toxic at high concentrations?
ammonium ions
what are the major nitrogen-containing excretory molecule?
Urea, uric acid, creatinine and ammonium ions.
where is urea formed?
liver
what are the three steps in the synthesis of urea?
transamination, de-amination and urea (or ornithine) cycle
what enzyme moves the amino group from alpha-amino acids to alpha-keta acids during transamination?
aminotransferases usually alpha-ketoglutarate
During transamination what are the major carriers of nitrogen in the blood to liver?
alanine and glutamine
How is alanine made during transamination?
amino group of glutamate is transferred to pyruvate, giving alanine
How is glutamine made during transamination?
glutamine synthase adds NH4+ to glutamate giving glutamine
where does deamination/urea cycle happen?
in the liver
what happens during deamination/urea cycle?
amino group of glutamate is converted to free ammonium ion and then urea is synthesised in a complex series of reactions
What are ketogenic amino acids degraded to?
acetyl-CoA or acetoacetyl-CoA, can give rise to ketone bodies or fatty acids
what are glucogenic amino acids degraded to?
degraded to pyruvate or TCA cycle intermediates, can be converted into phosphoenolpyruvate and then into glucose
what happens during alcaptonuria?
degradation of phenylalanine and tyrosine is blocked
what is maple syrup urine disease?
degradation of phenylalaine and tyrosine is blocked, urine smells like maple syrup, mental and physical retardation and prevented by appropriate diet
what is phenylketonuria?
phenylalanine accumulates in all body fluids, leads to severe mental retardation if untreated, as therapy must go as low phenylalanine diet
what happens during a defect in a urea cycle enzyme?
- accumulation of urea cycle intermediates
- glutamine levels increase in the circulation
- alpha-ketoglurarate is no longer regenerated
- alpha- ketoglurarate levels become too low to fix more free ammonium ion
how do you treat urea cycle disorders?
treatment with low-protein diet, drugs which remove nitrogen
