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Biochem 2 > 1. Nitrogen balance. Digestion of proteins. Function of proteases, their regulation. Absorption of amino acids, amino acid transporters > Flashcards

1. Nitrogen balance. Digestion of proteins. Function of proteases, their regulation. Absorption of amino acids, amino acid transporters Flashcards

1
Q

What is the role of nitrogenase complex?

A

Convert nitrogen to amonia

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2
Q

Give the whole equation representing the role of nitrogenase complex

A

(In lect)

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3
Q

Give the percentages of biological nitrogen fixation on earth and oceans

A

60% on earth
40% oceans

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4
Q

Definition of nitrification

A

the oxidation (as by bacteria) of ammonium salts to nitrites and the further oxidation of nitrites to nitrates.

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5
Q

Definition of denitrification

A

the microbial process of reducing nitrate and nitrite to gaseous forms of nitrogen, principally nitrous oxide (N2O) and nitrogen (N2)

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6
Q

What is the normal protein intake?

A

45 - 60g protein/day

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7
Q

What is the normal protein intake in case of pregnancy, breastfeeding?

A

45 - 60g/ day + 50%

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8
Q

What is nitrogen balance?

A

total daily intake equals total daily excretion 0.8 g/bw.kg/day

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9
Q

What is positive nitrogen balance?

A

Positive nitrogen balance: 1.0-1.1 g/bw.kg/day: childhood, pregnancy

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10
Q

What are the symptoms of Kwashiorkor?

A
  1. Decreased body weight
  2. Oedema (decreased albumin)
  3. Diarrhoea (decreased intestinal epithelial cells)
  4. Steatorrhoea (decreased pancreas enzyme)
  5. Skin atrophy
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11
Q

Some special aspects of the vegetarian diet
-> What is the energy content (in comparison to mixed diet)

A

30 - 50 cal./100g (vs. 150 - 300 cal/100 g for mixed diet)

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12
Q

Some special aspects of the vegetarian diet
-> What is the protein content (in comparison to mixed diet)?

A

Protein content: 1 - 2 g/100 g (vs 15 - 20g/100 g for mixed diet)

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13
Q

Some special aspects of the vegetarian diet
-> Is the protein nutritional value of vegetarian diet low or high?

A

Low

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14
Q

Some special aspects of the vegetarian diet
-> Is the digestibility of the protein low or high?

A

Low

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15
Q

Is the vegetarian diet suitable for adults? How?

A

Yes, it is generally enough, if the limitations are considered (legumes are low in methionine while cereals are low in lysine)

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16
Q

Is the vegetarian diet suitable for children and pregnancy? Why?

A

No, it is problematic
-> Cause low birth weight, slower growth in the first 5 years of life

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17
Q

What are the 9 essential AAs? (definition based on N-balance)

A
  1. Histidine (His)
  2. Isoleucine (Ile)
  3. Leucine (Leu)
  4. Valine (Val)
  5. Lysine (Lys)
  6. Methionine (Met)
  7. Threonine (Thr)
  8. Tryptophan (Trp)
  9. Phenylalanine (Phe)
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18
Q

What are the 3 semi-essential amino acids?

A
  1. Arginine (Arg)
  2. Tyrosine (Tyr)
  3. Cysteine (Cys)
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19
Q

Protein Digestion
-> Are whole proteins absorbed? Why?

A

No, whole proteins are not absorbed
-> Why? - Too large to pass through intact membranes

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20
Q

Whole proteins cannot be absorbed
-> How do our body absorb them? Is there any additional digestion?

A

The proteins must be digested into di- and tri- peptide or individual amino acids priot to absorption
-> Additional digestion occur in the cytosol

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21
Q

Are structures of protein more diverse than carbohydrates?
-> What is the consequence?

A

Yes, proteins structures are more diverse than carbohydrate structures
-> Proteins require broad spectrum peptidases and transporters

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22
Q

Protein digestion - stomach
-> What is the first step?

A

Chief cells secrete pepsinogen

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23
Q

Protein digestion - stomach
1st step: chief cells secrete pepsinogen
-> This process is stimulated by ____

A

Cephalic vagal input

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24
Q

Protein digestion stomach

1st step: chief cells secrete pepsinogen
-> What are the 3 substances that enhance this secretion?

A
  1. Acetylcholine
  2. cholecystokinin (CCK)
  3. Gastrin
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25
Q

Protein digestion stomach

Pepsinogen is auto-activated to pepsin at which pH?

A

< 4

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26
Q

Pepsinogen is auto-activated to which substance? (at pH < 4)

A

Pepsin

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26
Q

Protein digestion stomach

the Pepsinogen is auto-activated to which substance? (at pH < 4)

A

Pepsin

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27
Q

Protein digestion - stomach

What is the role of pepsin?

A

It cleaves proteins at large aliphatic or aromatic side groups (~ complete 10 - 20% of digestion)

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28
Q

Protein digestion stomach

At which pH that pepsin is inactivated? Why?

A

> 4.5; protects intestinal tissues

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29
Q

Protein digestion stomach
-> Protein leaves stomach as __

A

Mix of insoluble protein, soluble protein, peptides and amino acids

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30
Q

What are the 2 major enzymes that participate in digestion of proteins in intestine?

A
  • Proteases
  • Enteropeptidases
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31
Q

Protein digestion in the intestine
-> How are proteases produced?

A

They are produced as zymogens in the pancreas

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32
Q

Protein digestion in the intestine
-> How is the secretion of zymogens occur?

A

Into the intestine for secretin and cholecystokinin stimuli

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33
Q

Protein digestion in the intestine
-> What is the role of enteropeptidases?

A

It converts trypsinogen to trypsin by limited proteolysis, which in turn activates other enzymes (chymotrypsinogen, prelastase, procarboxypeptidase)

34
Q

Protein digestion in the intestine
-> Enteropeptidase converts trypsinogen to trypsin by limited proteolysis, which in turn activates other enzymes which are ___ (3)

A
  1. Chymotrysinogen
  2. Proelastase
  3. Procarboxypeptidase
35
Q

Where are pancreatic proteases stored?

A

In acinar cells as pro-enzymes (zymogens)

36
Q

The role of pancreatic proteases

A
  1. Trypsinogen -> Trypsin
  2. Chymotrypsinogen -> chymotrypsin
  3. Procarboxypeptidase A & B -> Carboxypeptidase A & B
  4. Proelastase -> Elastase
37
Q

What are the 3 amino acids that are a part of serin-proteases?

A
  1. Aspartic acid (active center)
  2. Histidine
  3. Serine (reactive)
38
Q

Locations of Asp, His, Ser during activation of serin-proteases

A

These 3 AAs are located at very distant locations in the polypeptide chain, but are just spatially juxtaposed during activation

39
Q

What are the 3 major members of the serine-proteases family?

A

Trypsin, chymotrypsin, elastase

40
Q

What is SERPIN-s?

A

a broadly distributed family of protease inhibitors that use a conformational change to inhibit target enzymes.
-> another possibility to regulate protease activity

41
Q

What is the role of SERPIN-s?

A

An ester bond is formed between COO group of the inhibitor and the Ser OH

42
Q

Give a major example of an inhibitor of elastase

A

α1-protease inhibitor –also an inhibitor of elastase

43
Q

Why is Met358 important?

A

It is essential for enzyme binding

44
Q

How is methionine affected in smokers?

A

In smokers, this methionine is oxidized to methionine sulfoxide and inactivated.
=> As a result, elastases function uncontrollably, consequence: lung emphysema

45
Q

How is protein digestion occur in cytosol?

A
  1. The vast majority of di- and tri- peptides are digestied into AAs by cytoplasmic peptidases
  2. Peptidases -> cleave N-terminal amino acids
46
Q

What is the role of peptidases?

A

Cleaving N-terminal AAs

47
Q

Protein Absorption — Amino acids
-> How many transporters of free amino acids are there in the brush border?

48
Q

Protein Absorption — Amino acids

There are 7 transporters of free amino acids in the brush border
-> What are their mechanisms?

A
  1. Na+ - independent carriers (2)
    - Proton-co transport
    - Facilitated diffusion
  2. Na+ dependent (5)
    - Carriers are coupled to Na+ concentration gradient
49
Q

How is protein transport occurred in basolateral membrane of the enterocyte?

A

The basolateral membrane of the enterocyte contains transporters which export AAs from the cell into the blood
- Diffusion
- Both Na+ depedent and indepedent carriers

50
Q

Type(s) of AAs that can be absorbed into blood

A

Only free AAs

51
Q

Protein Absorption Overview
-> Where does most protein absorption take place?

A

In the duodenum and jejunum

52
Q

Protein Absorption Overview
-> Most AAs are absorbed into the bloodstream, but why do some AAs still remain in the enterocytes?

A

They are used to support the cells

53
Q

Protein Absorption Overview
-> more than 99% of protein enters the bloodstream as ___

54
Q

What is ubiquitinilation?

A

A signal for degrading denatured unfolded proteins

55
Q

The ubiquitin ligases recognize different degradation signals which are ___

A
  1. Denatured, unfolded proteins
  2. Oxidated AA
  3. Modified or non-functional AA
56
Q

What is an example for unbiquitinilation?

A

Transcriptional regulation of erithropoietin gen (EPO) by hypoxia induced factor

57
Q

What are the 3 types of intracellular proteolysis? (tissue proteases)

A
  1. Lysosomal
  2. Proteasomal
  3. Autophagosomal
58
Q

Tissue proteases
-> What are the 2 enzymes participating in extracellular proteases?

A
  1. Matrix metalloproteases
  2. Elastase
59
Q

What are tissue proteases?

A

proteases degrading endogen proteases

60
Q

What is the role of metalloproteases and cysteine Cathepsin?

A

Shaping dentin

61
Q

What are the enzymes degrading ECM components? (teeth)

A
  1. Kollagenases
  2. Gelatinases
  3. Stromeolysine
  4. Enamelysine
  5. Cathepsin-K
62
Q

Enzymes degrading ECM (teeth) derive from __

A
  1. Pulp odontoblasts
  2. Saliva enzymes
63
Q

The organic material of dentin is 90% __

64
Q

Give a major example of Zn-proteases

A

Matrix metalloproteinases (MMPs)

65
Q

What is the role of matrix metalloproteinases?

A

Degrade ECM components

66
Q

Matrix metalloproteinase (MMP) is synthesized as ___

A

an inactive proenzyme

67
Q

Matrix metalloproteinases (MMPs) are activated by __

A

conformational change/limited proteolysis)

68
Q

What are the inhibitors for matrix metalloproteinases (MMPs)?

A

TIMP (tissue inhibitors of metalloproteinases)

69
Q

Degradation of dentin ECM by host matrix metalloproteases (MMP)
-> What will cariogenic bacteria do if they are present in the caries cavity?

A

They will release lactic acid and reduce the local pH

70
Q

Degradation of dentin ECM by host matrix metalloproteases (MMP)
-> Degradation of dentin ECM by host matrix metalloproteases (MMP)
-> What is the consequence?

A

Acidic environment demineralizes the dentin matrix and induces the activation of host MMPs derived from dentin or saliva

71
Q

3 steps of degradation of dentin collagen with Cathepsin - K

A
  1. Binding of catK monomers to glycosaminoglycans (GAGs) to collagen fibrils
  2. Dimerization of catK at the edges of gap regions
  3. Disintegration of collagen fibers by liberation of alpha-chain sized fragments
72
Q

What is the fate of amino group in degradation of amino acids?

A
  1. Transamination
  2. Deamination
  3. Incorpration of free ammonia (Ornithine cycle)
73
Q

Degradation of amino acids - Fate of amino-group
-> What happen during transamination?

A

Reversible exchange of the amino- and oxogroup

74
Q

Degradation of amino acids - Fate of amino-group
-> What are the 2 enzymes with corresponding locations participate in the exchange of amino group?

A
  1. ALAT: Ala aminotransferase (liver)
  2. ASTA: Asp aminotransferase (heart and muscle)
75
Q

Degradation of amino acids - Fate of amino-group
-> Characteristics of prosthetic group of the transaminases

A

The prosthetic group binds to Lys side chain of the enzyme

76
Q

Degradation of amino acids - Fate of amino-group
-> What happen during oxidative deamination?

A
  1. Glutamate-dehydrogenase reaction
  2. Production of free ammonia
77
Q

Degradation of amino acids - Fate of amino-group
-> What are the enzymes involving in deamination?

A
  1. a-aminogroup–oxidativedeamination
    – Glu Dehydrogenase
  2. a-amino group
    – Ser(Thr) dehydratase
    – His és Gly (Glycine cleavage enzyme
  3. a-amino group oxidation with flavoproteins
    – L- aminoacid oxidases (FMN, H2O, O2)
  4. b or g amid group (deamination) – glutaminase
    – asparaginase
78
Q

What happen if there is a mutation in glycine cleavage enzyme?

A

Glycine encephalopaty

79
Q

Deamination
-> What is the enzyme involving in oxidative deamination of alpha-amino group?

A

Glu dehydrogenase

80
Q

Deamination of alpha amino group
-> What are the enzymes involving?

A

– Ser(Thr) dehydratase
– His és Gly (Glycine cleavage enzyme

81
Q

What is the enzyme involving in alpha-amino group oxidation with flavoproteins?

A
  1. L-amino acid oxidases (FMN, H2O, O2)
  2. D-amino acid oxidases (FAD, H2O, O2) (bacterial AA degradation)
82
Q

What are the 2 enzymes involving in deamination of beta or gamma amid group?

A
  1. Glutaminase
  2. Asparaginase
83
Q

Free ammonia is incorporated into which cycle?

A

Ornithine cycle

Biochem 2 (38 decks)

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