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Metabolism - Alex's Cards (ESA2) > Session 3 Lecture Notes > Flashcards

Session 3 Lecture Notes Flashcards

1
Q

Where is the majority of alcohol metabolised?

A

The liver (over 90%)

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2
Q

Name the 3 steps by which alcohol is converted to acetyl-CoA

A
  1. Alcohol to acetaldehyde (by alcohol dehydrogenase)
  2. Acetaldehyde to acetate (by aldehyde dehydrogenase
  3. Acetate (conjugated to CoA) to form Acetyl-CoA - can be used in TCA cycle or for fatty acid synthesis
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3
Q

What is the recommended alcohol limit for men and women per week?

A

14 units a week - spread over at least 3 days

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4
Q

What is 1 unit of alcohol in grams?

A

8g

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5
Q

What redox reaction takes place alongside enzymatic activity of alcohol dehydrogenase and aldehyde dehydrogenase?

A

NAD+ to NADH (at each step)

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6
Q

What metabolism when accumulated causes a hangover?

A

Acetaldehyde (it is a toxic metabolite)

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7
Q

How is acetaldehyde normally kept to a low level?

A

Because aldehyde hydrogenase has a low kM for acetaldehyde

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8
Q

Alcohol oxidation results in conversion of NAD+ to NADH. What 3 effects does lack of NAD+ have?

A
  1. Not enough NAD+ for conversion of lactate to pyruvate
  2. Not enough NAD+ for glycerol metabolism
  3. Not enough NAD+ for fatty acid oxidation
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9
Q

What happens when there is an increase in Acetyl-CoA?

A

There is increased synthesis of fatty acids and ketone bodies

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10
Q

Disulfiram can be used in treatment of alcohol dependence. Explain how it works

A

It is an inhibitor of aldehyde dehydrogenase

Acetaldehyde accumulates giving the person the symptoms of a hangover

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11
Q

What is used in the treatment of alcohol dependence?

A

Disulfiram

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12
Q

What is a free radical?

A

An atom or molecule that contains one or more unpaired electrons
They are very reactive and can cause damage to cells

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13
Q

Most reactive oxygen species are free radicals. What other type of molecules cause damage?

A

Reactive nitrogen species

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14
Q

Oxygen is a biradical. What does this mean?

A

It has 2 unpaired electrons but in different orbitals

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15
Q

What is produced by adding an electron to oxygen?

A

Superoxide

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16
Q

What is produced when 2 hydrogen atoms and an electron are added to superoxide?
Is this a free radical?

A

Hydrogen peroxide

No it is not a free radical but it can react with iron to produce free radicals

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17
Q

What is the most damaging free radical?

A

Hydroxyl radical

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18
Q

What does superoxide react with to produce peroxynitrite?

A

Nitric oxide

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19
Q

When nitric oxide reacts with superoxide what does it form?

A

Peroxynitrite

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20
Q

What are the 2 types of damage reactive oxygen species can cause to DNA?

A
  1. ROS reacting with the base = can lead to mispairing and mutation
  2. ROS reacting with the sugar = can cause strand break and mutation on repair
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21
Q

What can be used as a measure of the amount of oxidative damage?

A

The amount of 8-oxo-dG present in cells

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22
Q

What 2 parts of the protein can reactive oxidative species damage?

A

The backbone

The sidechain

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23
Q

What can happen if ROS damages the side chain of a protein?

A

Lots of chemical modifications can occur such as disulphide bonds can form
This can lead to gain or loss of function

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24
Q

Because which groups are disulphide bonds in proteins usually formed?

A

Thiol groups

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25
What happens when ROS damage to lipids takes place?
It starts a chain reaction A lipid radical is formed which can react with oxygen to form a lipid peroxyl radical Lipid peroxyl radical extracts hydrogen from a nearby fatty acid and sets of a chain reaction within the lipid bilayer
26
Give 4 examples of exogenous source of ROS/RNS
1. Toxins 2. Drugs eg antimalarial drug 3. Radiation eg x-rays 4. Pollutants
27
Give 3 examples of endogenous source of ROS/RNS
1. Electron transport chain 2. Nitric oxide synthases 3. NADPH oxidases
28
How can ROS be formed during the electron transport chain?
Normally, electrons in ETC reduce oxygen to form H20 | Sometimes electrons can escape and react with oxygen to form superoxide
29
There are 3 types of nitric oxide synthase. 2 are used in signalling and 1 in used by phagocytes to produce toxic effects. What are they?
1. Inducible NO synthase (used by neutrophils in particular to kill bacteria) 2. Endothelial NO synthase 3. Neuronal NO synthase
30
What is respiratory burst?
The rapid release of superoxide and hydrogen peroxide from phagocytic cells to destroy bacteria
31
What do superoxide and NO form?
Peroxynitrite radicals
32
What are released from secretory granules within phagocytes?
Myeloperoxidase
33
How is superoxide formed by the phagocytes?
NADPH oxidase oxidises NADPH and oxygen to form superoxide
34
What role does superoxide dismutase have? | What is it's role in cellular defence?
SOD - superoxide dismutase converts superoxide to hydrogen peroxide and oxygen It is involved in cellular defence because superoxide can initiate chain reactions
35
What role does catalase have in cellular defence? | What happens if you have reduced catalase?
It converts hydrogen peroxide to oxygen and water | Reduced catalase = why hair follicles turn grey (increased levels of hydrogen peroxide)
36
How does glutathione play a role in cellular defense?
Glutathione = tripeptide One residue = cysteine The thiol group of cysteine donates its election to a ROS Cysteine then forms a bond with another cysteine residue (forming a disulphide bond)
37
What is disulphide? How is it formed?
It is the oxidised form of glutathione (2 cysteine residues come together forming a disulphide bond)
38
What enzyme removes an electron from the thiol group on cysteine? What does this enzyme require?
Glutathione peroxidase | It requires selenium
39
How is disulphide reduced back to glutathione?
By glutathione reductase | It uses the electron from NADPH to do this
40
Why is the pentose phosphate pathway essential for cellular damage?
Because the NADPH from the pentose phosphate pathway is required to provide the electron for reducing GSSG back to GSH (Glutathione)
41
What do free radical scavengers do? | Give 2 examples
They reduce free radical damage by donating a hydrogen atom and its electron to free radicals in a non-enzymatic reaction Examples: Vitamin E and Vitamin B
42
What is oxidative stress?
An imbalance of oxidants vs cell defense
43
Deficiency in which 3 enzymes can result in galactosaemia?
1. Uridyl transferase 2. Galactokinase 3. UDP-galactose epimerase
44
Explain how build up of galactose can lead to cataracts
- increase in galactose increases activity of aldose reductase which converts galactose to galactitol - aldose reductase uses NADPH in the reaction - NADPH is required for cellular defense (in the reduction of oxidised glutathione to glutathione) - when this is used up there is an increased risk of damage by ROS (as glutathione levels decreased) - damage can occur to proteins especially proteins in lens of eye (crystallin) which leads to cataracts
45
How can a G6PDH deficiency lead to oxidative stress?
Glucose-6-phosphate dehydrogenase is needed to convert glucose 6P to 6-phosphogluconate. At the same time NADP is reduced to NADPH. If G6PDH is deficient there will not be enough NADPH needed to supply the electron for reduction of oxidised glutathione to glutathione
46
What are heinz bodies? | What are they a sign of?
They are clumps of damaged haemoglobin within the RBC | They are a sign of G6PDH deficiency
47
At prescribed dosage what is paracetamol normally metabolised by?
Glucuronide or sulphate
48
With happens when high levels of paracetamol accumulates?
NAPQI is produced and accumulates which can have direct toxic effects on the liver
49
What does the liver do to try and combat accumulation of NAPQI?
It reacts NAPQI with glutathione
50
Reaction of glutathione with NAPQI can lead to glutathione depletion (and increased risk of oxidative stress). How can you combat this?
Giving the patient acetylcysteine treatment = it works by replenishing glutathione levels
51
Name 3 major nitrogen containing compounds and 1 smaller key nitrogen containing compound
1. Amino acids 2. Proteins 3. Purines and pyrimidines 4. Creatine
52
What is creatinine?
It is the breakdown product of creatine and creatine phosphate in muscle
53
What is creatinine a marker of? | Explain how it is excreted
Marker of renal function - it is raised when nephrons are damaged Creatinine is filtered via kidneys into urine The amount of creatinine excreted is proportional to muscle mass
54
When might you expect to see a positive nitrogen balance?
When the intake of nitrogen is greater than output such as when a person is pregnant or growing
55
What happens to dietary proteins when digested?
They are broken down to free AAs and stored in the "AA pool" Some are used to make proteins used for hair skin and nails Some are used to synthesise nitrogen containing compounds
56
In the liver what are AAs broken | down into it needed for energy?
Carbon skeleton and amine group Carbon skeleton is broken down into either ketogenic AAs or glucogenic AAs depending on side chain Amine group is broken down into urea and excreted in urine
57
Give an example of a glucogenic AA and a ketogenic AA | What are they converted into?
``` Glucogenic: Alanine Glycine Cysteine Serine Ketogenic: Lysine Leucine ``` Glucogenic AAs go through gluconeogenesis to produce glucose Ketogenic AAs are converted to ketone bodies to produce energy
58
What are the 3 largest stores of fuel?
1. Triacylglycerol 2. Glycogen 3. Muscle protein
59
What are the 2 main pathways that remove nitrogen from AAs?
1. Transamination | 2. Deamination
60
What happens to the amino group of AAs? | What do most of them get funnelled to?
They can be funnelled to either glutamate or aspartate to produce Most are funnelled to glutamate via alpha ketoglutarate
61
What 2 aminotransferase enzymes are measured in liver function tests and what do they do?
1. Alanine aminotransferase (ALT) - converts alanine to glutamate 2. Aspartate aminotransferase (AST) - converts glutamate to aspartate
62
What can death cap mushrooms cause?
Acute liver failure as plasma ALT (plasma alanine transferase) levels are 20 times the normal levels
63
What happens in transamination?
The amine group of 1 AA is swapped for an oxygen in a keto acid to produce a different AA and a different keto acid
64
What happens in deamination?
The amino group from an AA is liberated and becomes a free ammonia (toxic) It is converted to urea or excreted directly in urine
65
What are the input and output of the urea cycle?
``` Input= glutamate and aspartate Output = urea excreted in the urine ```
66
Where does the urea cycle occur and how many enzymes are involved?
In the liver | 5 enzymes are involved
67
How is ammonia removed from tissues?
1. Combination of ammonia and glutamate to form glutamine which can be transported to kidney or liver 2. Combination of ammonia and pyruvate to form alanine which can be transported to liver
68
What are the 2 inborn errors of amino acid metabolism?
PKU | Homocystinuria
69
What is PKU?
Most common inborn error of AA metabolism Deficiency in phenylalanine hydroxylase so accumulation of phenylalanine in tissue plasma and urine and phenylketones in urine
70
What happens if there is a deficiency in phenylalanine hydroxylase? What is this condition called?
If there is a deficiency in this phenylalanine cannot be converted to tyrosine which is needed to produce catacholamines and thyroid hormones for example Condition = PKU
71
What is homocystinurias?
``` Problem breaking down methionine (often from defect in cyststhionine b-synthase) Excess homocystine (oxidised homocysteine) which affects CT, muscles, CNS, CVS ```

Metabolism - Alex's Cards (ESA2) (8 decks)

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