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3 MEH Flashcards

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1
Q

By which organ is most alcohol metabolised?

A

> 90% is metabolised by the liver

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2
Q

The alcohol not metabolised by the liver is excreted passively by…

A

Urine and breath

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3
Q

What is the final product of alcohol metabolism?

A

acetyl-CoA

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4
Q

Which two major enzymes are involved in alcohol oxidation?

A
  1. Alcohol dehydrogenase

2. Aldehyde dehydrogenase

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5
Q

Describe alcohol metabolism pathway. (3 molecules, 2 enzymes)

A 
1. Alcohol (ethanol)
... alcohol dehydrogenase ...
2. Acetaldehyde
... aldehyde dehydrogenase ...
3. Acetate
Acetate is then conjugated to coenzyme A to give acetyl-CoA
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6
Q

Which moleucle is associated with the feling of “hangover”?

A

Acetaldehyde (produced by covnersion of enthanol by alcohol dehydrogenase)

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7
Q

Why is alcohol metabolism detrimental to the liver?

A

Because the 2 enzymes responsible for alcohol metabolism use NAD and produce NADH

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8
Q

Why it is useful that alcohol metabolism gives acetyl-CoA as a final product?

A

Acetyl-CoA is the central molecule to metabolism and will be able to enter TCA cycle or be utilised for fatty acid synthesis

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9
Q

What can you say abiut aldehyde dehydrogenase’s Km, and what impact does it have on the liver?

A

aldehyde dehydrogenase has a LOW Km. This means that it will work at a high rate, so keep on top of the production of acetaldehyde which is very toxic for the liver.
But in excessive consuption context, acetaldehyde dehydrogenase can’t cope with all the acetaldehyde and it builds up causing liver damage.

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10
Q

Which molecules (involved in alcohol metabolism) cause changes in liver metabolism if present in excessive amounts?

A
  • excessive NADH

- excessive Acetyl-CoA

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11
Q

What is corrhosis?

A

Cirrhosis means scarring. It is the fibrosis in the liver associated with scarring.

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12
Q

Why is it a problem that alcohol metabolism uses NAD? (3 consequences)

A
  1. Inadequate NAD for comversion of lactate into pyruvate so lactic acid builds up = lactic acidosis
  2. Inadequate NAD for glycerol metabolism - deficit in gluconeogenesis and so hypoglycaemia
  3. Inadequate NAD for fatty acid oxidation - increased synthesis of triacylglycerol
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13
Q

What impact does lactic acid build up have on the kidneys (eg. when lactate can’t be converted to pyruvate for lack of NAD)

A

Lactate inhibits excretion of uric acid becasue they use the same mechanism. So if there is accumulation of uric acid, there can be appearance of gout.

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14
Q

How is gout associated with alcohol oxidation?

A

Alcohol oxidation necessitates 2 enzymes: alcohol DH and aldehyde DH. Both these enzymes use NAD that they convert to NADH. But by using NAD they deplete the store needed to convert lactate into pyruvate. So lactate will accumulate. But lactate and uric acid use the same mechanism to be excreted by the kidney, so the excess lactate will block uric acid excretion. So there is build up of uric acid which could form cristals (monosodium urate) which deposit especially in big toe joint causing gout.

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15
Q

How does alcohol oxidation cause hypoglycaemia?

A

alcohol oxidation will reduce the NAD/NADH ratio, as the 2 enzymes involved in alcohol metabolism (alcohol DH and acetaldehyde DH) use NAD. Therefore, if there is excessive alcohol consumption, NAD stocks will be depleted, and inadequate NAD is available for glycerol metabolism and therefore there will be a deficit in gluconeogenesis causing hypoglycaemia.

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16
Q

What is disulfiram?

A

It is a drug given to wncourage alcohol addicts not to drink.

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17
Q

How does disulfiram work?

A

Disulfiram discourages from alcohol consumption as it increases the “hangover” feeling. Hangover feeling is caused by acetaldehyde, and by inhibiting aldehyde dehydrogenase, acetaldehyde will build up, therefore increasing “hangover” symptoms.
So basically disulfiram is an inhibitor of aldehyde DH.

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18
Q

What is oxidative stress?

A

Oxidative stress is an imbalance between cell damage (caused by reactive oxygen species and reactive nitrogen species) and cell defences (antioxidants).
It results in cell damage.

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19
Q

Which diseases are examples involving oxidative stress? (give 4)

A
  • multiple sclerosis
  • parkinson’s
  • pancreatitis
  • cancer
  • ischaemia/reperfusion injury
  • COPD
  • rhumatoid arthritis
  • Alzheimer’s
  • Crohn’s
  • CV disease
    So cellular damage caused by ROS & RNS is a significant component in a wide range of disease states
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20
Q

What are free radicals?

A

A free radical is an atom or molecule that contains one or more unpaired electrons and is capable of independent (“free”) existence.
These species will therefore want to steal an electron form another molecule in order to stabilise.
Therefore these free radicals are VERY REACTIVE. Reaction of a radical with a molecule typically generates a second radical thereby propagating damage! = chain reaction

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21
Q

How are free radicals denoted?

A

With a superscript dot after the atomical “name”

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22
Q

Which is the most reactive and damaging free radical that reacts with anything?

A

Hydroxyl radical, ie. OH⚫️

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23
Q

Which are the two RNS

reactive nitrogen species (one isnt technically speaking but it is a powerful oxidant that causes cellular damage)

A
  1. Nitric oxide NO⚫️

2. Peroxynitrite ONOO-

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24
Q

How is the RNS peroxynitrite produced?

A

Supoeroxide O2⚫️ can react with nitric oxide NO⚫️ to produce peroxynitrite ONOO-

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25
How is superoxide produced?
By adding an electron to molecular oxygen O2 (normally has 2 freeeelctorms so happy, but if add on, then only 1 free, and unhalpy)
26
Which free radical can react with anything thus is very damaging?
Hydroxyl radical OH⚫️
27
Which two types of damage can ROS casue to DNA.
1. ROS reacts with base - the midified base can lead to misoairing and mutation 2. ROS reacts with sugar (ribose or deoxyribose) - can cause strand break and mutation on repair
28
What is the link between reactive oxygen species and cancer?
ROS and react with DNA bases or sugars thus causing mispairing thus mutation or mutation on repair
29
With which 2 elements of a protein can ROS interact and therefore cause damage?
1. Backbone - causing protein fragmentation | 2. Sidechain - therefore changing an amino acid
30
A change in protein structure due to ROS can have which 3 consequences?
1. Protein degradation 2. Loss of function 3. Gain of function
31
What is the link between ROS and disulphide bond formation?
If a ROS steals an electron from a cysteine residue, then this might cause inappropriate disulphide bond formation between cysteine residues. - misfolding - crosslinking - function disruption
32
Between which groups of which amino acid residues do disulphide bonds form?
disulphide bonds form between thiol groups of cysteine residues.
33
How do ROS damage lipids?
free radicals can extract hydrogen atom from a polyunsaturated fatty acid in membrane lipid. A lipid radical is formed, which can then react with ixygen to form a lipid peroxyl radical. a CHAIN REACTION occurs as lipid peroxyl radical extracts hydrogen from nearby fatty acid, etc. => hydrophobic environment of bilayer is disruoted and membrane integrity fails.
34
Give 3 sources of endogenous biological oxidants?
1. Electron transport chain 2. Nitric oxide synthases 3. NADPH oxidases
35
How is the electron transport chain a source of ROS?
NADH and FADH2 supply electrons from metabolic substrates to the complexes of the electron transprot chain in the internal mitochondrial membrane. e- pass along ETC and reduce oxygen to form H2O at the IVth complex. BUT OCCASIONALLY, electron can accidently ESCAPE the chain and react with dissolved O2 to form superoxide,
36
What are nitric oxide synthases NOS?
NOS produces citrulline form arginine and releases NO Nitric Oxide. There are 3 types of NOS, we just remember that they are a source of endogenous biological oxidants.
37
NO is involved in biological functions such as... (3)
1. Signalling molecule 2. Neurotransmission 3. S-nitrosylation
38
What is a respiatory burst?
It is rapid release of superoxide and H2O2 from phagocytic cells (eg. neutrophils and monocytes). They are produced by NADPH oxidase (ie. source of endogenous oxidants). - NADPH is a membrane bound compex in phagocyte membrane that oxidyses NADPH into NADP and transfers electron to O2, creating O2⚫️. This DELIBERATE production of superoxide can be converted into hydrogen peroxyde and then myeloperoxidase converts it into BLEACH. - bleach = hypochlorite!
39
In which cotnedt are ROS produced deliberately by the body, and by which cells?
Phagocytes produce ROS deliberately for their antimicrobial power. - hydrogen peroxide H2O2 can be converted into BLEACH by myeloperoxidase - superoxide can be combined with nitric oxide to make peroxynitrite. Hypochlortie (bleach) and peroxynitrite are both powerful antibacterials!
40
What does a genetic defect in NADPH ixdase compelx cause?
enhanced susceptibility to bacterial infections. Why? Because NADPH oxidase is important in phagocyte membranes to produce superoxide and H2O2 for antimicrobial actions. - atypical infections - pneumonia - abcesses - impetigo - cellulitis
41
Which 4 types of compound defend us against ROS and RNS.
1. Superoxide dismutase SOD 2. Catalase 3. Glutathione 4. Free radical scavengers like Vitamins E and C
42
Why do superoxide dismutase and catalase have to work together?
Because SOD converts superoxide OH- to hydrogen peroxide H2O2 and oxygen. But H2O2 is still a ROS. So now need catalase to convert H2O2 into water and oxygen.
43
Why is catalase an impotant defense enzyme against ROS.
Because it will convert H2O2 (hydrogen peroxide) into H20 and water. It is a widespread enzyme, important in immune cells to protect against oxidative burst.
44
Decline in which defense mechanism against ROS could explain grey hair?
A decline in catalase in hair follicules, which normally converts H2O2 (hydrogen peroxide) into water and oxygen, could explain grey hair. => hair is literally bleaching itself from the inside!!
45
What is glutathione?
It is a cellular defense against ROS. - tripeptide synthesised by body to protect against oxidative stress - glutathione peroxidase requires selenium - exists in a reduced form and an oxidised form - glutathione works by giving an electron to H2O2 therefore producing H2O. It is willing to give e- and will then simply form a disulphide bond between its cysteine residues (oxidised form)
46
Give the name of the defense molecule that is willing to give away an electron from its cysteine residue to protect from H2O2 (hydrogen peroxide) and will then form a disulphide bond.
Glutathione
47
Selenium is an essential element for which defense mechanism against ROS?
glutathione
48
What does glutathione reductase do?
It catalyses the reduction of GSSG back to 2GSH (= recycling) by transfering electrons from NADPH to NADP. Therefore NADPH that comes from the pentose pathway is essential! If no NADPH, then no recycling of glutathione (back to its reduced for, that can give away electon to H2O2) and so no protection against damage!
49
Which is the rate limiting enzyme of the pentose pathway?
Glucose-6P DH (dehydrogenase)
50
What is the substrate for the oentose pathway?
Glucose-6-phosphate
51
What are the 2 important products of the pentose pathway? (1 actual end product, other is by-product)
1. C5 ribose sugars for nucleotide and DNA/RNA synthesis | 2. NADPH essential for maintaining pool of reduced glutathione (the form that is willing to give electron to H2O2)
52
How do vitamin A and E work to defend from cellular damage by ROS?
They are called free radical scavengers. They reduce free radical damage by donating hydrogen atom and its electron to free radicals in a NONENZYMATIC reaction. - Vitamin E is a lipid soluble antioxidant. - Vitamin E gives the free lipid radical an electron. - Vitamin C is water soluble and will reduce Vitamin E back to its "pre-defense" reduced form.
53
What is galactosaemia?
It is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose properly. Galactosemia follows an autosomal recessive mode of inheritance that confers a deficiency in an enzyme responsible for adequate galactose degradation.
54
Which are the 2 types of galactosaemia?
Type 1 = uridyl transferase deficiency Type 2 = galactokinase deficiency Type 3= UDP-gaalctose epimerase
55
Which symptom is common to all types of galactosaemia?
Cataract
56
Which tyoe of galactosaemia is the most severe?
Type 3. UDO-gaalctose epimerase deficiency.. Ineed even a galactose-free diet will not be abke to save these patients.
57
Which is the most mild type of galactosaemia?
Type 2, galactokinase deficiency. The only symptom they will have is cataract.
58
What is type 1 galactosaemia?
It is a deficiency in Uridyl transferase enzyme that converts galactose 1P into glucose 1P. These patients will have accumulation of galactose-1P in tissues such as liver, kidneys, GIT and brain damage. The treatment is simply a galactose free diet, and they will be fine.
59
What is type 2 galactosaemia?
It is a deficiency in galactokinase. These patients will then have build up of galactose. Increased levels of galactose activate aldose reductase which produces galactitol from galactose. But aldose reductase uses NADPH from this conversion, therefore compromising the stock of NADPH used to protect against ROS damage. Kndeed NADPH is essential to reduce glutathione back to its form that is willing to give electron to H2O2 (hydrogen peroxide)
60
Why do cataract occur in people with galactosaemia?
Because all types of gaalctosaemia induce build up of gaalctose. Increased levels of galactose activate aldose reductase. Aldose reductase uses NADPH to convert galactose into galatitol. So aldose reductase depletes stock of NADPH. The defenses against ROS are compromised. Crystallin protein of the eye lens is denatured by ROS. = cataract
61
How can one discriminate between type 1 and 3 of galactosaemia?
Type 1 will be helped by galactose-free diet, but type 3 will develop other problems due to lack of galactose that they cant
62
What is G6PDH deficiency?
It is a deficiency in the enzyme Glucose-6-phosphate dehydrogenase. It is an enzyme of the pentose pathway. Decreased amount of G6PDH activity limits amounts of NADPH. Indeed, G6PDH converts glucose 6P into 6-phosphogluconate, transferring H to NADP, thus creating NADPH. And NADPH will be used to reduce glutathione GSSG back to its form able to defend against H2O2 (hydrogen peroxide), said GSH form.
63
What are Heinz bodies?
They are aggregates of cross-linked haemoglobin that are seen within red blood cells. They resukt form precipitated haemoglobin. They bind to cell membrane and alter rigidity. Zhey induce increased mechanicla stress when cells squeeze thriugh small capillaries. The spleen removes bound Heinz bodies resulting in blister cells. They are a clinical sign of G6PDH deficiency!
64
What is a typical clinical signof G6PDH?
Heinz bodies in red blood cells!They result form damaged haemoglobin proteins that aggregate.
65
At prescribed dosage, paracetamol can be safely metabolised by conjugation with ... or ...
a) Glucuronide | b) Sulphate
66
What is the molecular name for paravetamol?
acetaminophen
67
Which toxic metabolite accumulates if high levels of paracetamol are taken?
NAPQI
68
Waht us the antidote to paracetamol OD.
Acetylcysteine
69
How does the oxidative damage occur from paracetamol OD?
NAPQI accumulates. it is a toxic metabolite of paracetamol. 1. NAPQI causes direct liver damage 2. The liver tries to compensate by using glutathione. But this depletes the stocks, and so we have less protection against oxidative damage. - lipid peroxidation - damage to proteins - damage to DNA
70
What is creatinine?
Breakdown product of creatine and creatine phosphate in muscle. It is produced at a constant rate depending on muscle mass. Filtered into urine via the kidneys. Creatinine urine excretion over 24 hours is proportional to muscle mass! for this reason it is a useful CLINICAL MARKER. It provides an estimate of muscle mass! Also commonly used as an indicator of renal function (raised levels if nephron damage)
71
Creatinine is a useful clinical marke rof what?
Muscle mass! as it is found in urine proportionately to muscle mass. Indicator of renal function - raised on damage to nephrons.
72
What is the "nitrogen balance"?
The input and output of nitrogen are usually equal. Ie. there is no change in total body protein, this is the nirmal state in an adult.
73
What does a positive nitrogen balance indicate?
Intake>output So an increase in total body protein. Thus is normal in growth, and lregnancy or in adults recovering from malnutrition.
74
In which cases can a positive nitrogen balance be normal?
1. Pregnancy 2. Growth 3. Adult recovering from malnutrition
75
What does a negative nitrogen balance indicate?
Net loss of body protein
76
Are there physiological situations in which a negative nitrogen balance observed?
No! a negative nitrogen balance is never nirmal!
77
In which cases does one see a negative nitrogen balance?
- trauma - infection - malnutrition
78
What oercentage of protein is nitrogen?
16%
79
Which are the two constituents of a free amino acid?
1. Carbon skeleton - potential energy | 2. Amino group
80
Amino acids can potentially be a siurce of energy. Which two pathways will amino acids follow to give energy?
1. Glucogenic - gluconeogenesis | 2. Ketogenic
81
Under which form is the amino group of an amino acid broken diwn for energy excreted?
Amino groups are transformed into urea and excreted in urine.
82
Give an example of glucogenic amino acids
``` alanine cysteine glycine serine aspartate asparagnie arginine proline histidine glutamine methionine valine glutamate ``` All aas starting with an A are glucogenic
83
Give an example of a ketogenic amino acid.
Lysine Leucine All aas that start with an L are ketogenic
84
Give an example of an amino acid that can be both keto- or glucogenic
``` Threonine Tryptophan Tyrosine Phenylalanine Isoleucine ``` All aas starting with a T are both gluco and ketogenic
85
What is the effect of insulin or growth hormone on protein synthesis?
Increases protein synthesis
86
What is the effect of insulin and growth hormone on protein degradation?
Insulin and growth hormone decrease protein degradation
87
What effect do glucocorticosteroids (cortisol) have in protein synthesis?
Glucocorticosteroids decrease protein synthesis.
88
What effect do glucocorticosteroids have on protein degradation?
Glucocorticosteroids increase protein degradation.
89
In which disease can excessive protein breakdown occur?
In cushings syndrome (excessive cortisol). this will weaken skin structure leading to striae formation.
90
Which are the 9 essential amino acids?
``` Isoleucine Histidine Threonine Lysine Leucine Methionine Phenylalanine Tryptophan Valnie ```
91
Why is protein of animal origin considered to be "high quality"?
Because they contain all essential amino acids
92
Why are proteins of plant origin generally considered "lower quality"?
because most of them are deficient in one or more essential amino acids.
93
Which amino acid is essential for glutathione production? (and so for protection against oxidative stress)
Cysteine!
94
Tyrosine is an important amino acid for the synthesis of which 3 products?
1. Catecholamines 2. Melanin 3. Thyroid hormones
95
Which two main pathways facilitate removal of nitrogen from amino acids?
1. Transamination 2. Demanination need to understand the distinction! - transamination is the exchange of amine group of amino acid with the O of a keto acid. This produces a different amino acid, typically glutamate or aspartate. This requires an aminotransferase, which in turn requires the coenzyme pyridoxal phosphate which is a Vitamin B6 derivative.
96
Which two key aminotransferases are routinely measured as part of tion tests?
1. ALT - alanine aminotransferase, it converts alanine to glutamate 2. AST - it converts glutamate to aspartate
97
In which clinical situation will AST and ALT be particularly high?
1. Viral hepatitis 2. Autoimmune liver disease 3. Toxic injury = conditions that cause extensive cellular necrosis
98
What is deamination?
liberates amino group of a,ino acids as free ammonia. Can ONLY occur where the urea cycle is able to run, so in the liver and kidney! otherwise would have accumualtion of ammonia. - also important in deamination of dietary D-amino acids. They are those found in plants and microorganisms.
99
What is ammonia?
Ammonia occurs from amino acid breakdown. It is very toxic and must be removed. It is ultimately converted to urea or excreted directly in urine.
100
Which 3 enzymes can deaminate amino acids?
1. Amino acid oxidases 2. Glutaminase 3. Glutamate dehydrogenase
101
4 characteristics of urea?
1. High nitrogen content 2. Non-toxic 3. Extremely water soluble 4. Chemically inert in humans (bacteria can break it down to release NH3) 5. Most urea is excreted in urine via the kidneys 6. Also performs useful osmotic role in kidney tubules

MEH (4 decks)

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