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Nutrition and Metabolism > Protein Metabolism > Flashcards

Protein Metabolism Flashcards

1
Q

Explain the structure of an amino acid

A

-Contains a central carbon, with an amino (NH3+) group, a carboxyl (COOH) group, and a variable ‘R’ group that determines the amino acid

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2
Q

How do two amino acids form bonds?

A

-Condensation reaction, removing water, to form a bond between the amino and carboxyl ends to make a peptide chain

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3
Q

What are the essential amino acids for infants?

A
  • Arginine

- Histidine

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4
Q

What are the essential amino acids for adults?

A
  • Leucine
  • Isoleucine
  • Valine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
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5
Q

What are the aliphatic amino acids (and which are BCAAs?)

A
  • Glycine
  • Alanine
  • Valine (BCAA)
  • Leucine (BCAA)
  • Isoleucine (BCAA)
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6
Q

What is a BCAA and why are they important?

A

An aliphatic amino acid with a branch in the R group. They constitute nearly 70% of all the amino acids in the body’s proteins and play important roles in signalling protein synthesis/breakdown

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7
Q

What is the function of Glycine in the body? Is it essential or non-essential?

A
  • Regulate bile acid
  • Inhibitory neurotransmitter
  • Nucleic acid synthesis
  • Development and quality of skeletal muscle and connective tissues (1/3 of collagen is glycine)
  • Non-essential
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8
Q

What is an essential amino acid?

A

An amino acid that is not produced at a high enough rate to meet the demand for it in the body, so it must be consumed in the diet

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9
Q

What is the function of L-alanine in the body? is it essential or non-essential?

A

Non-essential.

  • Plays a central role in the glucose-alanine cycle between body tissues and the liver
  • Required to process B vitamins
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10
Q

What does the L in front of amino acid names mean?

A

The L denotes that the amino acid is in its free form, not associated with or bonded or any other amino acids.

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11
Q

What is the function of Leucine in the body? Is it essential or non-essential?

A

Essential.

  • Necessary to stimulate protein synthesis by stimulating the mTOR pathway
  • Regulates blood sugar by stimulating insulin secretion from pancreatic beta cells
  • Necessary for production of growth hormone
  • Preventing muscle protein breakdown
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12
Q

What is the function of Isoleucine in the body? Is it essential or non-essential?

A

Essential

  • Hemoglobin synthesis
  • Regulation of blood sugar/energy levels
  • Upregulates intestinal and muscular glucose transporters
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13
Q

What is the function of Valine in the body? Is it essential or non-essential?

A

Essential

  • Muscle protein synthesis, blood glucose regulation, like the other BCAAs
  • Inhibiting tryptophan transport across B/B barrier by competing for transporters, like all other LNAAs
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14
Q

What is the difference between and acidic amino acid and an amide? And what are the amides/acidic amino acids?

A

Amides are polar and uncharged. Acidic amino acids are polar negatively charged at physiological pH

Amides: Asparigine and Glutamine
Acidic: Aspartic Acid and Glutamic Acid

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15
Q

What are the 3 things required to build muscle?

A
  • Building blocks (amino acids)
  • Sufficient energy (caloric surplus)
  • Signalling (Leucine is a potent signal for this)
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16
Q

What is a key impact of serine in the body? is it essential or non?

A

Non-essential

Insulinotropic

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17
Q

What is the most insulinotropic amino acid?

A

Phenylalanine

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18
Q

What are tyrosine and tryptophan precursors for?

A

Tyrosine - Dopamine

Tryptophan - Serotonin

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19
Q

What are the Imino acids? and why are they not amino acids?

A

Proline and Hyroxyproline: Because nitrogen is bound to two carbon atoms in the side chain

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20
Q

Why does protein make you feel full?

A
  • Nausea stimulated by hyperaminoacidemia
  • Some amino acids are precursors to neurotransmitters that make you feel full
  • Protein increases fluid surface tension and foams easily. Will provide illusion of fullness if it foams in the stomach
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21
Q

What are the positively charged side chain amino acids?

A

Histidine and Lysine

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22
Q

What are the aromatic amino acids?

A

-Tryptophan, Phenylalanine and Tyrosine

All have a benzene ring in the side chain, and smell strongly.

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23
Q

What is the problem of amino acid metabolism?

A

NH3 is produced by amino acid metabolism, which is ammonia, which is toxic, we cannot oxidise it which means it must be disposed of

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24
Q

What are the major sources of addition and removal of amino acids from the dynamic endogenous amino acid pool

A

Catabolism/Anabolism
Dietary interconversion of non-EAAs
Protein Hydrolysis

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25
Q

Approximately how much protein is synthesised in adult humans per day?

A

ABOUT 300g but this is not accurate. It is an estimate based off of a study done on rats. 120 of this is muscle, 80 is liver.

26
Q

What is the muscle protein synthetic rate of adult humans per day? g/kg/day

A

1.4-1.7g per day

27
Q

What are examples of anabolic processes that take away from the endogenous amino acid pool?

A 
Synthesis of:
peptides
small hormones
neurotransmitters
nitrogenous bases of DNA/RNA
28
Q

What are examples of catabolic processes that take away from the endogenous amino acid pool?

A

Nitrogen removal
CHO metabolism
Lipid metabolism

29
Q

Protein is digested by the small intestine. Then what?

A

It is absorbed into the blood stream and heads to the liver, where it can be used for protein synthesis, or it can be sent to other tissues for protein synthesis, or excess can be converted into glucose/fatty acids

30
Q

Define Transamination

A

Transfer of the amine group of one amino acid to another amino acid (alpha keto glutarate, usually)

31
Q

Define Deamination

A

Taking the amine group off to do something with the leftover carbon skeleton of the amino acid

32
Q

Explain the process of transamination generally

A
  • An amino acid, a pyridoxal phosphate and an alpha keto acid (usually alpha ketoglutarate) bind to a transaminase enzyme.
  • Via the pyridoxal phosphate, the amino acid trades its amine group for the keto group of the alpha keto acid.
33
Q

Explain how an amino acid can give its nitrogen/amine group to an alpha keto acid via pyridoxal phosphate during transamination

A

Amino acid forms a schiff base via a condensation reaction with pyridoxal phosphate, and then rearranges its hydrogen ion into the base, which is split by hydrolysis and then bound to the alpha keto acid by another condensation reaction using water

34
Q

What are the 3 types of amino acids in terms of their ability to be converted into fuel?

A
  • Glycogenic (can be turned into glucose/precursors of glucose or glycogen)
  • Mixed (can be turned into either)
  • Ketogenic (can be turned into acetyl coa)
35
Q

If not used for converting amino acids to other forms of fuel, what can transamination be used for?

A

Creating alanine, which carries excess nitrogen to the liver for disposal.

36
Q

Explain the transamination of alanine in the liver to dispose of excess nitrogen

A

Alanine enters the liver, is transaminated with either alpha keto glutarate or oxaloacetate to make pyruvate (which can be used for hepatic gluconeogenesis) and either glutamate or aspartate, which then releases the nitrogen as ammonium ions via oxidative deamination to head to the urea cycle in the mitochondria

37
Q

What enzyme deaminates glutamate?

A

glutamate dehydrogenase

38
Q

what amino acids other than glutamate can be directly deaminated?

A

serine and threonine

39
Q

What does elevated alanine/aspartate transaminase in the blood suggest?

A

Heart or liver damage

40
Q

What is anaplerosis?

A
  • Replenishment of TCA cycle intermediaries.
  • E.g. Fumarate from the Urea Cycle, or
  • aspartate from the Urea Cycle transaminated into oxaloacetate.
41
Q

What is cataplerosis?

A
  • Removal of TCA cycle intermediates (sometimes to prevent accumulation in the mitochondrial matrix) for use elsewhere.
  • E.g. Aspartate transaminated from oxaloacetate from the TCA cycle being used in the Urea cycle
42
Q

What is the alternative pathway other than the urea cycle that we can dispose to ammonia/amine/nitrogen?

A

Glutamate or Aspartate conversion into their neutral amides, Glutamine and Asparagine, which go straight to the kidneys instead of urea, where the ammonia diffuses into the filtrate to buffer the increase in urinary hydrogen ions, forming benign ammonium ions.

43
Q

Do athletes need more protein than average sedentary people? What does Tarnopolsky et al 1988 say?

A

Tarnopolsky et al 1988 found that Sedentary individuals need about 0.8g per kg per day of protein to stay in nitrogen balance. Athletes need 1.2 g per kg per day.

44
Q

What is the recommended upper limit of protein intake to avoid protein toxicity? According to whom?

A

2-2.5g of Protein per kg per day or 25% of daily energy, according to a review by Bilsborough and Mann in 2006

45
Q

What is the theoretical boundary of safe, but not recommended protein intake? According to whom? What are the dangers?

A

> 35% of Daily Energy, or 3.3-4.5g of protein per kg per day, according to a review by Bilsborough and Mann in2006.

Dangers include hyperaminoacidemia, hyperammonemia, hyperinsulinemia, nausea, diarrhoea and even death.

46
Q

How can increasing dietary intake of protein at the expense of carbohydrate actually reduce net protein gain? (Bilsborough and Mann 2006)

A
  • Reduced training effectiveness due to limited muscle fuel.

- Increased demand for urea cycle causing cataplerosis to the TCA cycle, limiting its rate of energy production

47
Q

What is the recommended protein intake to provide nitrogen balance in trained female endurance athletes? According to whom?

A

1.63g per kg per day, according to Houltham and Rowlands 2013

48
Q

How does protein intake relate to nitrogen balance? According to whom?

A

Linear relationship between nitrogen balance and protein intake, Tarnopolsky et al 1988

49
Q

What is the optimal dose of protein in a single meal? What are the differing opinions? Give evidence. 3 Points

A

Curvilinear relationship between protein dose and MPS up to 40g.

Moore et al 2009 found no significant difference between 20 and 40g. But only single leg exercise.

Macnaughton et al 2016 found 40g significantly better than 20g, so 40g best. But for whole body exercise.

50
Q

How do protein requirements differ with age and body composition?

A

Younger people need less protein to elicit optimal response than older people due to inefficiency in dealing with protein (Moore et al 2015)

51
Q

How much of your passive oxygen consumption is used on protein synthesis/turnover/dealing with protein intake?

A

approximately 1/3

52
Q

What evidence is there about the ability or lackthereof for nitrogen balance to be achieved in energy defecit?

A

Calloway and Spector 1954 showed that even on a massively high protein diet, you cannot be in nitrogen balance unless you are in energy balance.

53
Q

You cannot gain muscle and lose fat in the exact same instance, but can you lose it at the same ‘time’ over time? give evidence

A

Longland et al 2016 showed that over 28 days, eating 60% of TDEE with resistance exercise, comparing a high (2.4) and normal (1.2) protein diet. High protein diet gained muscle and lost fat with overall mass decrease.

54
Q

How does BCAA/EAA intake affect protein balance after exercise? Give evidence

A

Tipton et al 1999 found 40g of EAA resulted in higher synthesis/lower breakdown of protein compared to water trial. Water trial had net negative protein balance, EAA had net positive.

55
Q

How does CHO-BCAA coingestion impact protein balance when ingested pre vs post exercise? Give evidence

A

Tipton et al 2001 found that net protein balance and net protein uptake was higher in the pre exercise ingestion than post. This is likely due to increased blood flow during exercise aiding in uptake

56
Q

How does intact protein ingestion impact protein balance when ingested pre vs post exercise? Give evidence

A

Lipton et al 2006
No difference in pre vs post 4 hours later. This supports the idea that bloodflow causes better uptake in BCAA ingestion pre compared to post, because intact protein would not be available in the bloodstream as quickly.

57
Q

To what degree is the benefit of protein and training to do with acute spikes in hormones such as test, HGH and IGF-1? Give evidence

A

No degree. Spikes in these hormones are balanced out later in the day via negative feedback/autoregulationto maintain hormonal homeostasis. (Schroeder et al 2013)

58
Q

How does Whey protein compare with milk in terms of effect on protein synthesis? Give 2 evidence

A

Very similar increase, according to Phillips et al 2009 and Mitchell et al 2015

59
Q

What impact does increased protein intake frequency have on oberweight individuals during energy balance or deficit?

A

6x a day protein intake reduced bodyfat and abdominal bodyfat, increases lean body mass and favourably affects adipokine function. Aciero 2013.

60
Q

What are the recommendations for protein intake for preserving lean mass during injury, inactivity or energy deficit?

A

Much higher protein intake, from 1.2 to 2.3g of protein per kg per day. Churchward-Venne et al 2013

61
Q

What evidence is there to suggest that BCAAs reduce central fatigue?

A

Mittleman et al 1993 showed increased time to fatigue with BCAAs compared to sweetener

Nutrition and Metabolism (5 decks)

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