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biochemistry > protein metabolism > Flashcards

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
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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
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3
Q

what are the key components of gastric juices needed for protein breakdown?

A
  • gastrin, hydrochloric acid and pepsinogen
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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
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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-
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6
Q

where is pepsinogen secreted from and what does it generate?

A
  • secreted via gastric glands
  • generates pepsin
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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
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8
Q

what pH does pepsin work at? what does it catalyse?

A
  • works at 1-2 pH
  • catalyses the hydrolysis of peptide bonds
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9
Q

what happens after the stomach contents pass into the duodenum?

A
  • acidic pH causes the secretion of bicarbonate (HC03-) into intestinal lumen
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10
Q

what does bicarbonate cause?

A
  • secretion of the hormone secretin into circulation
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11
Q

what does secretin cause?

A
  • causes the pancreas to release more HC03- into intestinal lumen via pancreatic duct
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12
Q

what is the role of neutralisation?

A
  • protects the intestinal wall from high acidic stomach acids
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13
Q

what do pancreas cells release?

A
  • pancreatic enzymes as inactive precursors called zymogens, or the generation of enzymes
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14
Q

what is the role of the synthesis of inactive enzymes?

A
  • protects against degradation of its own proteins
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15
Q

what is cholecystokinin?

A
  • hormone which triggers secretion of pancreatic zymogens to the duodenum
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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)
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17
Q

how much percentage of protein is in a male?

A
  • 16%
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18
Q

how much percentage of protein is in a female?

A
  • 14% total proteins
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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
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20
Q

what state do proteins in the human body exist in?

A
  • exist in a constant state of muscle protein synthesis and breakdown
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21
Q

what happens to protein turnover in a fastened state?

A
  • muscle protein breakdown exceeds protein synthesis
  • negative net balance
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22
Q

what happens to protein turnover following exercise?

A
  • both protein synthesis and breakdown increase
  • but negative net balance is still apparent
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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
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24
Q

why can the fed state differ slightly?

A
  • depends on type of exercise, population and training status
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25
Q

when combined with sufficient protein intake, what does resistance exercise contribute to?

A
  • contribute to an increase in cross- sectional area of muscle fibres known as a muscle hypertrophy
  • increase in muscle strength
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26
Q

what are the daily rates of hypertrophy? when is plateau?

A
  • daily rates of hypertrophy are 0.1- 0.2%
  • until plateau is reached that is -335 above baseline levels
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27
Q

what can individuals rates of hypertrophy exceed?

A
  • 50% baseline
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28
Q

what factors influence muscle adaptations of resistance exercise?

A
  • volume/ intensity
  • frequency
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29
Q

does endurance exercise contribute to muscle hypertrophy?

A
  • no
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30
Q

what are the common adaptations of endurance training?

A
  • increase in mitochondrial content
  • mitochondrial biogenesis (increase in new mitochondria)
  • mitochondrial hypertrophy (enlargement of mitochondria)
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31
Q

what do the adaptations of endurance exercise allow?

A
  • allows the muscle to generate larger amount of ATP through the aerobic breakdown of carbs, lipids & proteins
  • more economical source of energy
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32
Q

what is amino acid degradation?

A
  • amino acids are building blocks for muscle hypertrophy as well as an energy source
  • each individual AA follows an individualised catabolic route
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33
Q

what do catabolic processes of all amino acids involve?

A
  • involves the removal of a- amino acid group
34
Q

what happens after the removal of a- amino acid group?

A
  • carbon skeleton of the amino acids lead to intermediate compounds of carb and lipid metabolism
35
Q

what does aerobic catabolism of amino acids produce?

A
  • carbon dioxide
  • ATP
36
Q

what is deamination?

A
  • serine, threonine and glutamine discard of their amino acids via this process
37
Q

what does deamination form?

A
  • a- keto acids and ammonium
  • highly toxic
38
Q

what is ammonia converted to? where is it excreted?

A
  • converted into urea in the liver
  • excreted by kidneys
  • urea/ ammonia can be excreted in urine/ sweat
39
Q

what is transamination?

A
  • transfer of one amino acid group from one molecule to another
40
Q

what is transamination catalysed by? what type of reaction is it?

A
  • catalysed by aminotransferase
  • reversible reaction
41
Q

what is the most useful and major keto acid involved with transamination?

A
  • alpha- ketoglutarate
  • intermediate in the citric acid cycle
42
Q

what can a-keto acids be converted into?

A
  • pyruvate, acetyl CoA, acetoacetyl CoA, succinyl CoA, fumarate, oxaloacetate (compounds of citric acid cycle)
43
Q

how does glutamate dispose of its a - amino group?

A
  • oxidative deamination
  • used as glutamate loses its AA, oxidised by NAD+ / NADP+
44
Q

what does oxidative deamination produce?

A
  • both generate ammonium and a- ketoglutarate which can also enter the citric cycle
45
Q

how do you prevent ammonium build up?

A
  • glutamine and alanine
46
Q

how does glutamine prevent ammonium build up?

A
  • enzyme glutamine synthetase catalyses the conversion of glutamate to gluatamine
  • using ATP
  • travels to liver for processing
47
Q

what is the glutamate equation?

A

Glutamate + NH4- + ATP ==> glutamine + ADP + Pi + H+

48
Q

how does alanine prevent ammonium build up?

A
  • produced when pyruvate recieves the amino group of glutamine
  • reaction is catalysed by alanine aminotransferase
  • a- ketoglutarate is also formed
49
Q

how many amino acids can’t we synthesis? and why?

A
  • 9 out of 20 cannot be synthesised as these our EAA’s
    (essential amino acids)
50
Q

how do we get essential amino acids into the body?

A
  • need to ingest amino acids as part of our diet
51
Q

what happens to degradation in active fibres?

A
  • AA degradation is favoured by glutamate dehydrogenase
52
Q

what is degradation inhibited by? what is it activated by?

A
  • inhibited by ATP/GTP
  • activated by ADP/GDP
53
Q

what process happens during exercise and what does it produce?

A
  • glutamate deamination occurs
  • produces a- ketoglurate, allowing for potential amino acid oxidation
54
Q

what amino acids increase oxidation during exercise?

A
  • only branched chain amino acids increase with exercise
  • leucine, isoleucine and valine
55
Q

why can’t the liver convert BCAA into a- keto acids? what does this increase?

A
  • liver lacks aminotransferase
  • increased BCAA content in skeletal muscles
56
Q

what is often used as a measure of BCAA catabolism?

A
  • a- ketoisocaproate
57
Q

what happens to branched chain a- keto acids?

A
  • decarboxylated by the branched chain a- keto acid and dehydrogenase complex
58
Q

what is the amino acid content in the liver?

A
  • 3g/kg
  • similar to content in skeletal muscle
59
Q

how is the pool of amino acids in the liver used primarily?

A
  • used for glucose synthesis via gluconeogenesis
60
Q

how many amino acids can be converted to glucose? what name are they given?

A
  • 18 out of the 20 amino acids
  • called glucogenic
61
Q

how many amino acids can’t be synthesised? what are they called?

A
  • 2 cannot be synthesised
  • leucine and lysine
  • ketogenic
62
Q

what helps to speed up gluconeogenesis during exercise?

A
  • increased secretion of glucagon
  • decreased secretion of insulin
63
Q

what else does the liver use amino acids from the muscle as?

A
  • precursors for glucose production
64
Q

what is glutamine converted to? what is the enzyme involved?

A
  • converted back to glutamate
  • catalysed by glutaminase
    Glutamine+ H20- glutamate + Nh4+
    -2.7kcalmol-1
65
Q

what is alanine converted into? what enzyme is involved?

A
  • converted into pyruvate
  • alanine amino transferase
66
Q

what does pyruvate from glycolysis form in the first step of the glucose alanine cycle?

A
  • forms amino acceptor (transamination)
  • to form alanine (NE)
67
Q

where is alanine transported and what happens?

A
  • transported to the liver
  • converted to pyruvate and glutamate
  • to be used via gluconeogenesis
68
Q

what does the alanine conversion in the liver help to produce?

A
  • helps to produce glucose, which can then be transported back to the muscle to support exercise
  • up to 15% total energy demands
69
Q

how much nitrogen is excreted from the body? what is it incorporated into?

A
  • 90% of nitrogen excreted
  • incorporated in urea
70
Q

describe urea

A
  • non- toxic compound bearing two amino groups and is synthesised through 4 reactions in the urea cycle
71
Q

what do amino acids from protein breakdown form? what is this during?

A
  • form ammonia
  • during deamination
72
Q

what happens to the excess toxic ammonia in the urea cycle?

A
  • it is neutralised and converted to urea via oxidative deamination in the mitochondria or liver cells (hepatocytes)
73
Q

what does urea link to? what is this then converted to?

A
  • urea linked to ornithine to produce citrulline
  • converted to argininosuccinate
74
Q

what does arginosuccinate split into? what happens to the products?

A
  • splits to arginine and fumarate
  • arginine is hydrolysed via arginase to form urea
75
Q

what does urea/ nitrogen ratio give an estimate of?

A
  • whole- body protein breakdown
76
Q

what is the concentration of amino acids in plasma? what are the most abundant ?

A
  • 3 to 4 mmol/ L
  • glutamine and alanine are the most abundant
77
Q

what happens to amino acid concentrations during exercise?

A
  • largely unaffected with durations of around 60 mins
    > 2 hours amino acid concentration decreases 30%
78
Q

how much endogenous amino acid is used during 1 hour of moderate exercise? how many folds?

A
  • 10g of endogenous amino acid used
  • 2.5 fold increase
79
Q

what happens to plasma ammonia during exercise? what is it related to?

A
  • plasma ammonia increases with exercise
  • related to plasma lactate concentration
80
Q

what other factors lead to plasma urea concentration increasing?

A
  • increase in exercise lasting > 30 minutes
  • intensity of 60% V02 max
81
Q

why might plasma urea not increase during intense exercise?

A
  • reduction in blood flow to the liver
82
Q

what are the two factors that can assess protein quality?

A
  • amino acid composition, particularly leucine and BCAA’s
  • digestibility; easier digestion, quicker absorption

biochemistry (15 decks)

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