protein metabolism Flashcards
what happens after the ingestion of protein, where does digestion begin?
- digestion begins in the stomach where food is mixed with gastric juices due to the activity of smooth muscle in the stomach wall
what is secreted in response to ingestion and what does it secrete in turn?
- gastrin secreted in stomach
- stimulates secretion of hydrochloric acid and pepsinogen
what are the key components of gastric juices needed for protein breakdown?
- gastrin, hydrochloric acid and pepsinogen
where is HCL secreted from and what does it cause?
- secreted via gastric glands
- causes stomach to reach 1.5-3.5 pH
what does the low pH via HCL cause? what is the equation?
- low pH causes the denaturation of proteins
HCL - H+ + Cl-
where is pepsinogen secreted from and what does it generate?
- secreted via gastric glands
- generates pepsin
why must pepsinogen be converted to be effective? when does this happen?
- converted to pepsin
- happens when pepsinogen encounters the gastric juices and unfolds
what pH does pepsin work at? what does it catalyse?
- works at 1-2 pH
- catalyses the hydrolysis of peptide bonds
what happens after the stomach contents pass into the duodenum?
- acidic pH causes the secretion of bicarbonate (HC03-) into intestinal lumen
what does bicarbonate cause?
- secretion of the hormone secretin into circulation
what does secretin cause?
- causes the pancreas to release more HC03- into intestinal lumen via pancreatic duct
what is the role of neutralisation?
- protects the intestinal wall from high acidic stomach acids
what do pancreas cells release?
- pancreatic enzymes as inactive precursors called zymogens, or the generation of enzymes
what is the role of the synthesis of inactive enzymes?
- protects against degradation of its own proteins
what is cholecystokinin?
- hormone which triggers secretion of pancreatic zymogens to the duodenum
where is protein present in the body?
- present in every cell in the body, as well as extracellular fluids (interstitial fluid & plasma) and solids (connective tissues)
how much percentage of protein is in a male?
- 16%
how much percentage of protein is in a female?
- 14% total proteins
what are the differences in total proteins in men and women?
- due to body composition, and women in particular have larger amount of adipose tissue
- adipose tissue is low in protein and high in triglycerides
what state do proteins in the human body exist in?
- exist in a constant state of muscle protein synthesis and breakdown
what happens to protein turnover in a fastened state?
- muscle protein breakdown exceeds protein synthesis
- negative net balance
what happens to protein turnover following exercise?
- both protein synthesis and breakdown increase
- but negative net balance is still apparent
what happens to protein turnover in a fed state following protein feeding ?
- protein synthesis far exceeds protein breakdown so there is a positive protein balance
why can the fed state differ slightly?
- depends on type of exercise, population and training status
when combined with sufficient protein intake, what does resistance exercise contribute to?
- contribute to an increase in cross- sectional area of muscle fibres known as a muscle hypertrophy
- increase in muscle strength
what are the daily rates of hypertrophy? when is plateau?
- daily rates of hypertrophy are 0.1- 0.2%
- until plateau is reached that is -335 above baseline levels
what can individuals rates of hypertrophy exceed?
- 50% baseline
what factors influence muscle adaptations of resistance exercise?
- volume/ intensity
- frequency
does endurance exercise contribute to muscle hypertrophy?
- no
what are the common adaptations of endurance training?
- increase in mitochondrial content
- mitochondrial biogenesis (increase in new mitochondria)
- mitochondrial hypertrophy (enlargement of mitochondria)
what do the adaptations of endurance exercise allow?
- allows the muscle to generate larger amount of ATP through the aerobic breakdown of carbs, lipids & proteins
- more economical source of energy
what is amino acid degradation?
- amino acids are building blocks for muscle hypertrophy as well as an energy source
- each individual AA follows an individualised catabolic route
what do catabolic processes of all amino acids involve?
- involves the removal of a- amino acid group
what happens after the removal of a- amino acid group?
- carbon skeleton of the amino acids lead to intermediate compounds of carb and lipid metabolism
what does aerobic catabolism of amino acids produce?
- carbon dioxide
- ATP
what is deamination?
- serine, threonine and glutamine discard of their amino acids via this process
what does deamination form?
- a- keto acids and ammonium
- highly toxic
what is ammonia converted to? where is it excreted?
- converted into urea in the liver
- excreted by kidneys
- urea/ ammonia can be excreted in urine/ sweat
what is transamination?
- transfer of one amino acid group from one molecule to another
what is transamination catalysed by? what type of reaction is it?
- catalysed by aminotransferase
- reversible reaction
what is the most useful and major keto acid involved with transamination?
- alpha- ketoglutarate
- intermediate in the citric acid cycle
what can a-keto acids be converted into?
- pyruvate, acetyl CoA, acetoacetyl CoA, succinyl CoA, fumarate, oxaloacetate (compounds of citric acid cycle)
how does glutamate dispose of its a - amino group?
- oxidative deamination
- used as glutamate loses its AA, oxidised by NAD+ / NADP+
what does oxidative deamination produce?
- both generate ammonium and a- ketoglutarate which can also enter the citric cycle
how do you prevent ammonium build up?
- glutamine and alanine
how does glutamine prevent ammonium build up?
- enzyme glutamine synthetase catalyses the conversion of glutamate to gluatamine
- using ATP
- travels to liver for processing
what is the glutamate equation?
Glutamate + NH4- + ATP ==> glutamine + ADP + Pi + H+
how does alanine prevent ammonium build up?
- produced when pyruvate recieves the amino group of glutamine
- reaction is catalysed by alanine aminotransferase
- a- ketoglutarate is also formed
how many amino acids can’t we synthesis? and why?
- 9 out of 20 cannot be synthesised as these our EAA’s
(essential amino acids)
how do we get essential amino acids into the body?
- need to ingest amino acids as part of our diet
what happens to degradation in active fibres?
- AA degradation is favoured by glutamate dehydrogenase
what is degradation inhibited by? what is it activated by?
- inhibited by ATP/GTP
- activated by ADP/GDP
what process happens during exercise and what does it produce?
- glutamate deamination occurs
- produces a- ketoglurate, allowing for potential amino acid oxidation
what amino acids increase oxidation during exercise?
- only branched chain amino acids increase with exercise
- leucine, isoleucine and valine
why can’t the liver convert BCAA into a- keto acids? what does this increase?
- liver lacks aminotransferase
- increased BCAA content in skeletal muscles
what is often used as a measure of BCAA catabolism?
- a- ketoisocaproate
what happens to branched chain a- keto acids?
- decarboxylated by the branched chain a- keto acid and dehydrogenase complex
what is the amino acid content in the liver?
- 3g/kg
- similar to content in skeletal muscle
how is the pool of amino acids in the liver used primarily?
- used for glucose synthesis via gluconeogenesis
how many amino acids can be converted to glucose? what name are they given?
- 18 out of the 20 amino acids
- called glucogenic
how many amino acids can’t be synthesised? what are they called?
- 2 cannot be synthesised
- leucine and lysine
- ketogenic
what helps to speed up gluconeogenesis during exercise?
- increased secretion of glucagon
- decreased secretion of insulin
what else does the liver use amino acids from the muscle as?
- precursors for glucose production
what is glutamine converted to? what is the enzyme involved?
- converted back to glutamate
- catalysed by glutaminase
Glutamine+ H20- glutamate + Nh4+
-2.7kcalmol-1
what is alanine converted into? what enzyme is involved?
- converted into pyruvate
- alanine amino transferase
what does pyruvate from glycolysis form in the first step of the glucose alanine cycle?
- forms amino acceptor (transamination)
- to form alanine (NE)
where is alanine transported and what happens?
- transported to the liver
- converted to pyruvate and glutamate
- to be used via gluconeogenesis
what does the alanine conversion in the liver help to produce?
- helps to produce glucose, which can then be transported back to the muscle to support exercise
- up to 15% total energy demands
how much nitrogen is excreted from the body? what is it incorporated into?
- 90% of nitrogen excreted
- incorporated in urea
describe urea
- non- toxic compound bearing two amino groups and is synthesised through 4 reactions in the urea cycle
what do amino acids from protein breakdown form? what is this during?
- form ammonia
- during deamination
what happens to the excess toxic ammonia in the urea cycle?
- it is neutralised and converted to urea via oxidative deamination in the mitochondria or liver cells (hepatocytes)
what does urea link to? what is this then converted to?
- urea linked to ornithine to produce citrulline
- converted to argininosuccinate
what does arginosuccinate split into? what happens to the products?
- splits to arginine and fumarate
- arginine is hydrolysed via arginase to form urea
what does urea/ nitrogen ratio give an estimate of?
- whole- body protein breakdown
what is the concentration of amino acids in plasma? what are the most abundant ?
- 3 to 4 mmol/ L
- glutamine and alanine are the most abundant
what happens to amino acid concentrations during exercise?
- largely unaffected with durations of around 60 mins
> 2 hours amino acid concentration decreases 30%
how much endogenous amino acid is used during 1 hour of moderate exercise? how many folds?
- 10g of endogenous amino acid used
- 2.5 fold increase
what happens to plasma ammonia during exercise? what is it related to?
- plasma ammonia increases with exercise
- related to plasma lactate concentration
what other factors lead to plasma urea concentration increasing?
- increase in exercise lasting > 30 minutes
- intensity of 60% V02 max
why might plasma urea not increase during intense exercise?
- reduction in blood flow to the liver
what are the two factors that can assess protein quality?
- amino acid composition, particularly leucine and BCAA’s
- digestibility; easier digestion, quicker absorption
