protein metabolism Flashcards
1
Q
what happens after the ingestion of protein, where does digestion begin?
A
- digestion begins in the stomach where food is mixed with gastric juices due to the activity of smooth muscle in the stomach wall
2
Q
what is secreted in response to ingestion and what does it secrete in turn?
A
- gastrin secreted in stomach
- stimulates secretion of hydrochloric acid and pepsinogen
3
Q
what are the key components of gastric juices needed for protein breakdown?
A
- gastrin, hydrochloric acid and pepsinogen
4
Q
where is HCL secreted from and what does it cause?
A
- secreted via gastric glands
- causes stomach to reach 1.5-3.5 pH
5
Q
what does the low pH via HCL cause? what is the equation?
A
- low pH causes the denaturation of proteins
HCL - H+ + Cl-
6
Q
where is pepsinogen secreted from and what does it generate?
A
- secreted via gastric glands
- generates pepsin
7
Q
why must pepsinogen be converted to be effective? when does this happen?
A
- converted to pepsin
- happens when pepsinogen encounters the gastric juices and unfolds
8
Q
what pH does pepsin work at? what does it catalyse?
A
- works at 1-2 pH
- catalyses the hydrolysis of peptide bonds
9
Q
what happens after the stomach contents pass into the duodenum?
A
- acidic pH causes the secretion of bicarbonate (HC03-) into intestinal lumen
10
Q
what does bicarbonate cause?
A
- secretion of the hormone secretin into circulation
11
Q
what does secretin cause?
A
- causes the pancreas to release more HC03- into intestinal lumen via pancreatic duct
12
Q
what is the role of neutralisation?
A
- protects the intestinal wall from high acidic stomach acids
13
Q
what do pancreas cells release?
A
- pancreatic enzymes as inactive precursors called zymogens, or the generation of enzymes
14
Q
what is the role of the synthesis of inactive enzymes?
A
- protects against degradation of its own proteins
15
Q
what is cholecystokinin?
A
- hormone which triggers secretion of pancreatic zymogens to the duodenum
16
Q
where is protein present in the body?
A
- present in every cell in the body, as well as extracellular fluids (interstitial fluid & plasma) and solids (connective tissues)
17
Q
how much percentage of protein is in a male?
A
- 16%
18
Q
how much percentage of protein is in a female?
A
- 14% total proteins
19
Q
what are the differences in total proteins in men and women?
A
- due to body composition, and women in particular have larger amount of adipose tissue
- adipose tissue is low in protein and high in triglycerides
20
Q
what state do proteins in the human body exist in?
A
- exist in a constant state of muscle protein synthesis and breakdown
21
Q
what happens to protein turnover in a fastened state?
A
- muscle protein breakdown exceeds protein synthesis
- negative net balance
22
Q
what happens to protein turnover following exercise?
A
- both protein synthesis and breakdown increase
- but negative net balance is still apparent
23
Q
what happens to protein turnover in a fed state following protein feeding ?
A
- protein synthesis far exceeds protein breakdown so there is a positive protein balance
24
Q
why can the fed state differ slightly?
A
- depends on type of exercise, population and training status
25
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
26
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
27
what can individuals rates of hypertrophy exceed?
- 50% baseline
28
what factors influence muscle adaptations of resistance exercise?
- volume/ intensity
- frequency
29
does endurance exercise contribute to muscle hypertrophy?
- no
30
what are the common adaptations of endurance training?
- increase in mitochondrial content
- mitochondrial biogenesis (increase in new mitochondria)
- mitochondrial hypertrophy (enlargement of mitochondria)
31
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
32
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
33
what do catabolic processes of all amino acids involve?
- involves the removal of a- amino acid group
34
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
35
what does aerobic catabolism of amino acids produce?
- carbon dioxide
- ATP
36
what is deamination?
- serine, threonine and glutamine discard of their amino acids via this process
37
what does deamination form?
- a- keto acids and ammonium
- highly toxic
38
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
39
what is transamination?
- transfer of one amino acid group from one molecule to another
40
what is transamination catalysed by? what type of reaction is it?
- catalysed by aminotransferase
- reversible reaction
41
what is the most useful and major keto acid involved with transamination?
- alpha- ketoglutarate
- intermediate in the citric acid cycle
42
what can a-keto acids be converted into?
- pyruvate, acetyl CoA, acetoacetyl CoA, succinyl CoA, fumarate, oxaloacetate (compounds of citric acid cycle)
43
how does glutamate dispose of its a - amino group?
- oxidative deamination
- used as glutamate loses its AA, oxidised by NAD+ / NADP+
44
what does oxidative deamination produce?
- both generate ammonium and a- ketoglutarate which can also enter the citric cycle
45
how do you prevent ammonium build up?
- glutamine and alanine
46
how does glutamine prevent ammonium build up?
- enzyme glutamine synthetase catalyses the conversion of glutamate to gluatamine
- using ATP
- travels to liver for processing
47
what is the glutamate equation?
Glutamate + NH4- + ATP ==> glutamine + ADP + Pi + H+
48
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
49
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)
50
how do we get essential amino acids into the body?
- need to ingest amino acids as part of our diet
51
what happens to degradation in active fibres?
- AA degradation is favoured by glutamate dehydrogenase
52
what is degradation inhibited by? what is it activated by?
- inhibited by ATP/GTP
- activated by ADP/GDP
53
what process happens during exercise and what does it produce?
- glutamate deamination occurs
- produces a- ketoglurate, allowing for potential amino acid oxidation
54
what amino acids increase oxidation during exercise?
- only branched chain amino acids increase with exercise
- leucine, isoleucine and valine
55
why can't the liver convert BCAA into a- keto acids? what does this increase?
- liver lacks aminotransferase
- increased BCAA content in skeletal muscles
56
what is often used as a measure of BCAA catabolism?
- a- ketoisocaproate
57
what happens to branched chain a- keto acids?
- decarboxylated by the branched chain a- keto acid and dehydrogenase complex
58
what is the amino acid content in the liver?
- 3g/kg
- similar to content in skeletal muscle
59
how is the pool of amino acids in the liver used primarily?
- used for glucose synthesis via gluconeogenesis
60
how many amino acids can be converted to glucose? what name are they given?
- 18 out of the 20 amino acids
- called glucogenic
61
how many amino acids can't be synthesised? what are they called?
- 2 cannot be synthesised
- leucine and lysine
- ketogenic
62
what helps to speed up gluconeogenesis during exercise?
- increased secretion of glucagon
- decreased secretion of insulin
63
what else does the liver use amino acids from the muscle as?
- precursors for glucose production
64
what is glutamine converted to? what is the enzyme involved?
- converted back to glutamate
- catalysed by glutaminase
Glutamine+ H20- glutamate + Nh4+
-2.7kcalmol-1
65
what is alanine converted into? what enzyme is involved?
- converted into pyruvate
- alanine amino transferase
66
what does pyruvate from glycolysis form in the first step of the glucose alanine cycle?
- forms amino acceptor (transamination)
- to form alanine (NE)
67
where is alanine transported and what happens?
- transported to the liver
- converted to pyruvate and glutamate
- to be used via gluconeogenesis
68
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
69
how much nitrogen is excreted from the body? what is it incorporated into?
- 90% of nitrogen excreted
- incorporated in urea
70
describe urea
- non- toxic compound bearing two amino groups and is synthesised through 4 reactions in the urea cycle
71
what do amino acids from protein breakdown form? what is this during?
- form ammonia
- during deamination
72
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)
73
what does urea link to? what is this then converted to?
- urea linked to ornithine to produce citrulline
- converted to argininosuccinate
74
what does arginosuccinate split into? what happens to the products?
- splits to arginine and fumarate
- arginine is hydrolysed via arginase to form urea
75
what does urea/ nitrogen ratio give an estimate of?
- whole- body protein breakdown
76
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
77
what happens to amino acid concentrations during exercise?
- largely unaffected with durations of around 60 mins
> 2 hours amino acid concentration decreases 30%
78
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
79
what happens to plasma ammonia during exercise? what is it related to?
- plasma ammonia increases with exercise
- related to plasma lactate concentration
80
what other factors lead to plasma urea concentration increasing?
- increase in exercise lasting > 30 minutes
- intensity of 60% V02 max
81
why might plasma urea not increase during intense exercise?
- reduction in blood flow to the liver
82
what are the two factors that can assess protein quality?
- amino acid composition, particularly leucine and BCAA's
- digestibility; easier digestion, quicker absorption
