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Metabolism > Week 3 > Flashcards

Week 3 Flashcards

1
Q

What is ATP?

A

Adenosine triphosphate

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2
Q

What do we get when we split ATP and move the terminal phosphate with hydrolysis?

A

Release of energy and ADP

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3
Q

What makes the hydrolysis of ATP energetically favourable?

A
  • Relieves electrostatic repulsion between phosphate groups
  • increased entropy
  • the released phosphate ion is resonance stabilised
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4
Q

What is enthalpy?

A
  • Chemical bond energy symbol H
  • the enthalpy change is the sum of the energy used to break bonds and the energy released when new bonds are formed (triange H sign)
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5
Q

What is gibbs free energy change?

A

determines whether a reaction can take place considering both enthalpy and entropy changes. Δ G = Δ H − T Δ S

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6
Q

What determines the direction of a reversible reaction in the cell?

A

The value of ΔG and hence the direction of the reaction depends on concentrations of reactants and products

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7
Q

How can an energetically unfavourable reaction be achieved in the cell?

A

By coupling it to a favourable one. often to hydrolysis of ATP

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8
Q

What is OILRIG

A

Oxidation is loss (of electrons)

Reduction is gain

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9
Q

What is a redox carrier?

A

The reactions of the electron transport chain are redox reactions

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10
Q

What do spontaneous reactions look like?

A

Spontaneous reactions proceed downhill to create products with lower free energy than reactants

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11
Q

What are the 3 stages of cellular respiration?

A

1- Production of acetyl-CoA
2- Oxidation of acetyl CoA
3- Electron transport and chemiosmosis

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12
Q

What are flavoproteins?

A

Flavin nucleotide can accept either 1e- or 2e-

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13
Q

What is ubiquinone?

A

Coenzyme Q10. Electron carrier not bound to a protein complex. Freely diffusible in the non-polar interior of the IMM

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14
Q

What are cytochromes?

A

c1, c, a, a3.

Capable of absorbing visible light due to haem groups

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15
Q

What is NADH dehydrogenase?

A

Oxidises NADH from the TCA cycle, fatty-acid oxidation and glycolysis

  • Reduces ubiquinone for the rest of the respiratory chain
  • transports protons across inner mitochondrial membrane to support ATP synthesis
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16
Q

What does chemiosmotic coupling do?

A

Generates a proton motive force

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16
Q

What does chemiosmotic coupling do?

A

Generates a proton motive force

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17
Q

What is the rotary catalysis model in mitochondria?

A

in the ‘‘open state’’, ADP and phosphate enter the active site.

  • the protein then closes up around the molecules and binds them loosely
  • the enzyme then undergoes another change in shape and forces these molecules together, with the active site in the resulting tight state binding the newly produced ATP molecule with very high affinity
18
Q

What are the causes of mitochondrial dysfunction?

A
  1. Impairment of electron transport and ATP-synthesis machinery -single enzyme disorder
  2. Inadequate number of mitochondria- impaired mitochondrial dynamics/biogenesis
  3. accumulation of damaged mitochondria- impaired mitophagy
19
Q

What is a single enzyme disorder in mitochondria dysfunction?

A

Disruption of a single enzyme disrupts the energy production by the mitochondria

20
Q

What is an example of a single enzyme disorder?

A

Complex 1 disorders.
range of symptoms and severity
50% fatal under 2 years
-mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes

21
Q

What is heteroplasmy?

A
  • Presence of <1 type of mitochondrial genome

- multiple copies of mtDNA per cell and not segregated like nuclear genome

22
Q

What happens in mitochondrial fission?

A
  • Cytosolic dynamin-related protein is phosphorylated
  • Drp1 recruited to mitochondria and binds receptors
  • Forms cuff around mitochondrion which constricts the organelle
  • constriction severs both membranes
  • generates new mitochondria
23
Q

Explain mitochondrial fusion

A

Mitofusin 1 and 2 localise to the outer membranes and dock the two mitochondria together, fusing the outer membrane

  • Optic atropy localised on the inner membrane, responsible for fusing the two inner membranes together
  • sharing contents of mitochondria diltues any effect of damage
24
Q

What is mitophagy

A

Mitochondrial quality control

  • selective mitochondrial degradation/recycling
  • usually upregulated in response to stress
25
Q

What is the importance of haem?

A
  1. oxygen transport and storage
  2. oxygen metabolism
  3. electron transfer and drug metabolism
  4. signal transduction
  5. interacts with transcriptional factors to regulate gene expression
26
Q

Where is haem synthesised in the largest amount?

A

Liver and erythron

27
Q

How is haem transported?

A

Haem transported in plasma bound to hemopexin or as hemoglobin bound to haptopexin

28
Q

Where are the main sites of haem breakdown?

A

Macrophages, liver

29
Q

What is haem broken down into?

A

Bilirubin

30
Q

What is haem required for in hepatocytes?

A

Incorporation into the cytochrome p450

31
Q

What are the two mechanisms of haem biosynthetic pathway?

A
  1. Nonerythroid cells: transcriptional regulation via haem also regulation of mitochondrial import of ALAS1 by haem and direct inhibition of the enzyme by haem]
  2. Erythroid precursor cells: transcriptional regulation- iron responsive element located in the 5’ end of the mRNA. Iron regulatory protein (IRP) interact with (IRE) and inhibits translation
32
Q

How is haem synthesis regulated?

A

Feedback mechanisms important
-inhibition of ALA synthase by a transcriptional control whereby haem acts as a feedback exerts a feedback regulation on the enzyme.

33
Q

Explain the pathway for the degradation of haem

A
  • Haem is oxidised, with the haem ring being opened by the endoplasmic reticulum enzyme, haem oxygenase
  • The oxidation occurs on a specific carbon producing the linear tetrapyrrole biliverdin, ferric iron and Co2
  • bilirubin conjugated with glucuronic acid and excreted in bile
  • some is reabsorbed and can be excreted in urine
  • rest is metabolised by colon by bacteria to stercobilin
34
Q

What makes the yellow colour in our urine?

A

Some bilirubin being reabsorbed and excreted in urine

35
Q

What makes our stools brown?

A

The bilirubin to urobilinogen being metabolised in colon by bacteria to stercobilin

36
Q

What is porphyria?

A
  • A group of disorders caused by deficiencies in the activities of the enzymes of the haem biosynthesis pathway
  • porphyrins and/or their precursors such as ALA and PBG are abnormally produced in excess accumulate in tissues and are excreted in urine and stool
37
Q

How are porphyrias classed?

A
  • Hepatic or erythropoietic
  • Acute hepatic: neurologic disturbances and overproduction of porphyrin precursors eg ALA or PBG
  • Cutaneous porphyria: cutaneous photosensitivity and excessive production of porphyrins
38
Q

Explain acute intermittent porphyria

A
  • Partial porphobilinogen deaminase deficiency
  • triggered by drugs that induce hepatic cytochrome P450 eg barbiturates
  • Causes a reduced haem level which disrupts the regulation of ALAS by haem
  • Leads to accumulation of ALA and PBG
  • Neurological and psychiatric symptoms and abdominal pain
39
Q

What is the treatment for acute intermittent porphyria?

A

Reducing ALA and PBG excretion by intravenous hematin injection

40
Q

What is the most common form of porphyria?

A

Porphyria cutanea tarda (PCT)

41
Q

Explain porphyria cutanea tarda

A

Heterogeneous group of cutaneous porphyric diseases due to uroporphyrinogen decarboxylase deficiency

42
Q

What causes porphyria cutanea tarda?

A

Uroporphyrinogen decarboxylase deficiency or acquired through: increased amount of hepatic iron, alcohol, hep C, HIV, oestrogens, smoking, low vitamin C and carotenoid status

43
Q

What is variegate porphyria?

A

South African genetic porphyria- heterozygous deficiency in protoporphyrinogen oxidase activity and is inherited in an autosomal dominant manner

Metabolism (5 decks)

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