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FNH 350 > Protein > Flashcards

Protein Flashcards

1
Q

what is the average nitrogen content?

A

Average nitrogen of proteins = 16%
Convert nitrogen cont into protein content:
1/0.16 = 6.25
N x 6.25 = protein content

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2
Q

What is the significance of protein?

A

Acceptable Macronutrient Distribution Range: 10-35%
Protein in the human body:
- 40% in skeletal muscle
- 25% in body organs
- 35% in skin and blood
Proteins Functions:
1. structural
2. regulatory
3. energy

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3
Q

What are the structural functions?

A
  • contractile proteins => actin, smooth muscle
  • fibrous protein => collagen, elastin, certain
  • globular proteins=> spherical shape e.g. myoglobin
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4
Q

What are the regulatory functions?

A

Enzymes/catalysts: changing rate of reactions
- cofactors => minerals (metalloprotein), folate, B-vitamins

Hormones/Messagners: acting as chemical messengers

Transporters:
- in blood - hemoglobin, albumin (fatty acids), prealbumin = transthyretin (thyroxine and RBP), transferring (iron), ceruloplasmin (copper), lipoprotein

Immunoglobins/antibodies

Buffers=> amino acids act as acids or bases

Fluid balance:
- ascites => fluid balance is impaired in protein deficiency - abnormal accumulation of fluid in the abdominal

Acute Phase Reactant Proteins:
- formed in the liver - in response to infection, injury/inflammation
functions:
- stimulate the immune system, wound healing, chelate and remove iron from circulating
C-reactive protein = clinical indicator for inflammatory status

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5
Q

What are other functions?

A

Storage proteins:

Conjugated proteins: Glycoproteins

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6
Q

What is the storage protein for glucose storage?

A

glycogenin

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7
Q

Which glycoprotein has a role in clinical diagnosis?

A

glycated hemoglobin (A1C, blood glucose level)

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8
Q

What are the sources of energy at excessive intake?

A

Deaminination of amino aids; enters into:
- TCA cycle -> formation of ATP
- glucogenesis -> energy storage
- fatty acid synthesis -> energy storage

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9
Q

Describe the protein structures.

A

Primary: polypeptide backbone does not differ btw polypeptide chains but side chains differ

Secondary: alpha (cylindric) and beta-pleated sheets (stretched out backbone) => both stable

tertiary: interaction among the amino acids residues or side chains

Quaternary: oligomers = 2 or 4 polypeptides chains => held together by hydrogen bonds and electrostatic attraction

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10
Q

What are the essential amino acids?

A

phenylalanine, valine, threonine, methionine, tryptophan, histidine, isoleucine, leucine, lysine

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11
Q

What is phenylketonuria (PKU)?

A

missing phenylalanine hydroxylase => converts phenylalanine to tyrosine
- instead into phenylpyruvic acid
- interferes with neurotransmitter synthesis saying retaration
Is an essential amino acid
- classic diet therapy

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12
Q

what are exogenous sources of amino acid?

A

Animal-sourced foods: meats, poultry, fish, dairy
plant-sourced foods: almond milk, tofu, grains, legumes
Protein supplements/protein bars
amino acids supplements

in GI tract:
- desquamated mucosal cells
- digestive enzymes and glycoproteins

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13
Q

In the case of proteins, the small intestine can only absorb

A

amino acids, dipeptides, tripeptides

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14
Q

How is protein digested in the stomach?

A
  1. release of hydrochloric acid (HCl) from parietal cells, which is stimulated by: gastrin, acetylcholine, histamine
    - protein degradation => protein unfolding; disrupts hydrogen and electrostatic bonds (quaternary, tertiary, secondary)
  2. Pepsinogen
    - released from chief cells => pepsin
    - hydrolysis of peptide bonds
    - protein -> large polypeptides, oligopeptides, free amino acids
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15
Q

How is protein digested in the small intestine?

A

the major site of protein digestion, absorption

acidic chyme enters the duodenum
- stimulation of secretion of secretin and cholecystokinin
- stimulate pancreatic juice secretion from acinar cells -> containing digestive enzymes (zymogens)
- stimulates the secretion of enteropeptidases released from brush border
trypsinogen => trypsin
chymotrypsinogen => chymotrypsin
proelastase => elastase
procollagenase => collagenase
procarboxypeptidases A and B => Carboxypeptidases A and B -> only exopeptidase => release of amino acids from C-terminal end of a peptide chain

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16
Q

Aminopeptidases

A

hydrolyze AA from the N-terminal end of oligopeptides

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17
Q

Dipeptideylaminopetidases

A

hydrolyze AA from the N-terminal and of dipeptides

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18
Q

tripeptidase

A

hydrolyze specific AA to yield dipeptide and 1 free AA

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19
Q

How much amino acids aborbed in different parts of the body?

A

60% => form of di- or tripeptides
pept1 => transporter into enterocytes
40% of absorbed AA as free amino acids

30-50% of AA used by intestine
50-70% of amino acids transported vis basolateral membrane to portal blood

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20
Q

Amino acid transport

A

y+ => passive
ASC => active transport; binding of Na+
- amino acids need to be transported out of the enterocytes -> reach blood

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21
Q

How is the uptake of polypeptides or proteins directly into the bloodstream bad?

A
  • leaks btw epithelial cell junctions
  • transport by vesicles to the submucosa
    potential consequences:
  • acute immune response
  • development of sensitivity to polypeptides
  • food allergy, asthma
  • idiosyncratic drug reaction

vulnerable population:
- atopic heredity
- infants => feed formula solely -> resolution breastfeed for 6 months or use partially or extensively hydrolyzed infant formula (smaller protein fragments)
- GI tract diseases

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22
Q

How are amino acids used in enterocytes?

A

synthesis of proteins, nitrogen-containing compounds and energy
- new digestive enzymes
- hormones
-structural proteins and nucleotides for new intestinal cells

Retained amino acids include: glutamine, glutamate, aspartate, arginine, methionine

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23
Q

What is the role of glutamine?

A
  • the primary source of energy
  • formation of alanine
  • trophic effects -> stimulates GI mucosal cell proliferation
    -> prevents atrophy of gut mucosa
    -> creates a barrier against bacterial translocation
    w/ threonine => synthesis of mucin
    -> produced in skeletal muscles => taken up by intestinal cells
    -> Enteral and parental nutrition products are enriched with glutamine
24
Q

What is the role of glutamate?

A

90% of absorbed glutamate used by the intestine
- energy
- formation of alanine
- formation of proline => released into portal blood for delivery to the liver
- with aspartate -> ornithine -> citrulline (urea cycle)
- with glycine and cysteine -> glutathione (antioxidant)

25
Q

What is the role of arginine?

A
  • used in intestinal cells; source of energy
  • little found in portal blood
  • transaminated to => oxaloacetate (TCA cycle); ornithine (urea cycle)
26
Q

what is the role of arginine?

A
  • critulline (formation) and urea
  • intestinal injury => conditionally indispensable amino acid; arginine or citrulline supplementation in the diet
27
Q

what is the role of methionine?

A

50% -> metabolized in the intestine
- precursor for S-adenosylmethionine (SAM) -> one-carbon donor => formation of neurotransmitter, DNA methylation
- transformed to cysteine via tran-sulfuration pathway (vit B-6 dependent) => used for formation of glutathione and taurine (bile salts)

28
Q

Role of the liver

A
  • monitor the passage of AA from the gut to the peripheral circulation
  • monitors AA concentration in plasma
  • uses AA for protein synthesis
  • primary site of AA catabolism
29
Q

Which hormone regulates protein anabolism?

A

Insulin
- promotes cellular AA uptake ‘
- simulates transcellular movement of AA transporter to membrane
- inhibition of AA oxidation
- stimulates protein synthesis
After/during meal: inc. protein synthesis and dec. degradation of proteins

30
Q

Protein formation in liver

A

For release into plasma:
Albumin
- most abundant plasma proteins
- critical for fluid balance
- indicator of visceral protein status
- transports proteins: nutrients (Ca, Zn, B-6, FA) and drugs & hormones

Transthyretin:
- transports thyroid hormones (T4) and vit A
- a more sensitive indicator of visceral protein status -> rapid protein turnover

More transport proteins:
VLDL -> lipid transport
HDL-> reverse cholesterol transport
ceruloplasmin -> transport of Fe

others:
prothrombin -> blood coagulation
immunoglobins -> immune response
acute phase proteins -> infection, injury, inflammation

purines and pyrimidines are synthesized in the liver

31
Q

interorgan amino acid transport

A

provide amino acids for protein synthesis and other functions to all tissues
- happens in all states

32
Q

Dietary proteins: whey vs. casein

A

whey protein:
- ‘fast protein’ => digested faster, amino acid reached, quicker
- fast, high, transient
- inc, protein synthesis and amino acid oxidation
- no change in protein breakdown

casein protein:
- ‘slow proteins’ => slow digestion; amino acids in blood deposited slowly
- slow, lower, prolonged
- protein synthesis slightly inc,
- amino acid oxidation is moderately stimulated
- protein breakdown is marked inhibited by 30%

33
Q

When do protein and AA catabolism occur?

A
  1. During starvation
  2. low CHO => TCA cycle intermediates, brain glucose

Protein intake > needs for growth and maintenance

34
Q

hormones involved in catabolism

A

glucagon
catecholamines
glucocorticoids
thyroxin

35
Q

Transamination

A

transfer of -NH2 group from one amino acid to alpha-keto acid (carbon skeleton of amino acids)
- involved in alanine, glutamate, aspartate

36
Q

Deamination

A

release of -NH2 group form of ammonia
serine to pyruvate

37
Q

Deamidation

A

loss of an amide functional group -NH2 in the side chain of amino acids glutamine and asparagine in the form of ammonia
glutamine to glutamate

38
Q

Pathways for ammonia removal in the skeletal muscle:

A

glutamate and glutamine formation
alanine-glucose cycle

39
Q

Glutamine and glutamate formation:

A

disposal pathway in extrahepatic tissues
- glutamate is generated in the muscle -> deaminate by glutamate dehydrogenase to alpha-ketoglutarate and ammonia -> in the form of glutamine carried out of the cells to the liver, kidney, and intestine;
- glutamine-> also made in the brain and adipose tissues; greated formation in muscle and lungs

40
Q

Alanine-glucose cycle

A

in the fed state: glutamate => form glutamine for disposal of ammonia

in fasting state:
- between meals and excessive glucose needs of the muscle
- glutamate -> alanine -> released into blood -> liver takes up alanine and catabolizes it and releases ammonia to urea cycle

41
Q

Hyperammonemia [NH3]

A

impaired urea cycle
- liver damage, liver disease
- urea cycle enzyme defects

Consequences -> brain malfunction and coma

Treatments:
- nitrogen-restricted diet, drugs that acidify the GI tract, antibiotics

42
Q

What can the carbon skeleton be used for?

A

energy, glucose (TCA cycle), ketone bodies (pyruvate acetyl-CoA, acetoacetate), cholesterol (directly from leucine), fatty acids

43
Q

Dietary proteins are required for:

A
  • supply of nitrogen for the synthesis of non-essential AA
  • supply of essential AA
44
Q

What factors do the quality of protein depend on:

A

1) amount and proportion of essential amino acids
2) Protein digestibility
3) amino acid availability

45
Q

high-quality or complete proteins

A

proteins containing all essential AA in approximate amounts as needed by humans
- animal sources, soy proteins, quinoa

46
Q

Low-quality or incomplete proteins

A

proteins having too low amounts of one or more essential AA than needed by humans
- plant sources

47
Q

limiting amino acid

A

the essential amino acid present in the lowest amount in the food relative to the requirement for this AA in the human body
- mutual supplementation
ex. legumes are high in lysine but low in methionine and cysteine
grain products are low in lysine but high in methionine and cysteine

48
Q

Protein digestibility

A

amount of amino acids being absorbed after ingestion of given proteins

49
Q

Amino acid availability

A

diminished during food processing because of:
- extensive heating => creates protein side chains that cannot be hydrolyzed during protein digestion
- Maillard reaction => presence of sugars -> reduced availability of lysine
- oxidation of amino acids

50
Q

How can you evaluate protein quality?

A
  1. chemical or amino acid score
  2. protein digestibility corrected amino acid score
  3. protein efficiency ratio
  4. Biological value
  5. net protein utilization
51
Q

Chemical or amino acids score

A

analytical determination of AA composition of the
test protein
Procedure:
1. Quantification of essential AA conc. in the protein
2. comparison to the value of reference proteins considered to have a value of 100

the essential amino acid with the lowest score (in %) in the test protein = limiting amino acid of the test protein determines the amino acid score

52
Q

protein digestibility corrected amino acid score

A

= amino acid score (in %) x true digestibility (in %)

Nitrogen => indirect method to quantify protein content

53
Q

protein efficiency ratio

A

= gain in body weight/grams of protein consumed
measurements: body weight before and after diet total grams of test proteins consumed

54
Q

Biological value

A

measure for the amount of retained amino acids => part of amino acids that were absorbed + being utilized
= Nitrogen retained/nitrogen absorbed x 100

high biological value -> provides amino acids in amounts consistent w/ the individual amino acid requirements

55
Q

net protein utilization

A

measure how well the ingested proteins are digested and absorbed and how well the amino acids absorbed are utilized
= nitrogen retained/nitrogen consumed x 100

FNH 350 (6 decks)

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