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Mitochondria Flashcards

1
Q

What are the 2 methods used to convert ADP to ATP?

A

Substrate level phosphorylation

oxidative phosphorylation

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2
Q

How does substrate level phosphprylation differ from oxidative phosphorylation?

A

It occurs in the cytosol in the Krebs cycle and in glycolysis

Directly phosphorylates ADP using energy from a coupled reaction as opposed to indirectly from the oxidation of NADH and FADH

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3
Q

What are the 2 main substrates that are turned into acetyl CoA for the Krebs cycle?

A

Fatty acids and glucose

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4
Q

Explain why mitochondrial damage is so bad with respect to the possible methods of turning ADP to ATP

A

Only glycolysis can occur

Since Beta oxidation and oxidative phosphorylation occur inside the mitochondria

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5
Q

What is another name for complex 1?

A

NADH CoQ reductase

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6
Q

What is another name for complex 2?

A

Succinate CoQ reductase

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7
Q

What is another name for complex 3?

A

Cytochrome CoQ reductase

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8
Q

What is another name for complex 4?

A

Cytochrome C oxidase

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9
Q

What is another name for complex 5?

A

ATP synthase

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10
Q

Which complexes in the ETC pump protons into the intermembrane space?

A

1, 3 and 4

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11
Q

How does oxidative phosphorylation work?

A

Drop in energy of e- as they pass from one protein to another, driving movement of protons into the intermembrane space

H+ gradient drives ADP –> ATP

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12
Q

Which makes more energy, glucose or fatty acids?

A

Fatty acids because they can have very long tails

Glucose is always going to only phosphorylate about 34 ADP molecules

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13
Q

What are 2 enzymes involved in substrate level phosphorylation in glycolysis?

A

Pyruvate kinase

Phosphoglycerate kinase

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14
Q

Uses of ATP

A

Normal cellular functions

Nerve conduction

Muscle contraction

etc

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15
Q

What are very efficient generators of high energy stores?

A

ATP

Phosphocreatine

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16
Q

Where is phosphocreatine found/used?

A

Heart and muscle

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17
Q

TRUE or FALSE?

Mitochondrial content reflects the energy demand of a cell

A

TRUE

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18
Q

Which cells have lots of mitochondria?

A

Muscle, neuron, retina, heart, liver

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19
Q

What cell type has no mitochondria?

A

RBCs

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20
Q

What are important functions of mitochondria (other than respiration)?

A

Intracellular calcium regulation - sucking calcium out of cells

Cellular iron handling

Generation of important intermediary metabolites for other pathways - makes NTs

Key regulation of apoptosis

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21
Q

In what cells is the intracellular Ca2+ regulation of mitochondria important?

A

Muscles and Nerves

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22
Q

What are some ways mitochondria help with cellular iron handling?

A

Synthesizing iron sulphur centres

Key steps in haem biosynthesis

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23
Q

Which NT is made in mitochondria?

A

Glutamate

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24
Q

How do mitochondria regulate of apoptotic cell death?

A

Release of pro-apoptotic factors when stressed

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25
Q

How many subunits are there in each respiratory complex protein?

A

I-45

II-4

III-11

IV-13

V-14

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26
Q

How many copies of mtDNA is in a mitochondrion?

A

2-10

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27
Q

What kinds genes are in mtDNA and how many of each kind?

A

13 mRNA

22 tRNA

2 rRNA

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28
Q

How many proteins out of each respiratory complex protein does mtDNA code for?

A

I - 7

II -0

III - 1

IV - 3

V - 2

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29
Q

Which genomes code for MRC proteins?

A

The nuclear AND mitochondrial genomes

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30
Q

How do proteins from outside the mitochondria get in?

A

They have a specific sequence added to them so that they are imported after they are translated

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31
Q

Why do mitochondria contain their own DNA?

A

Originally there were early anaerobic prokaryotic cells

Some of these went on to form the nucleus and made anaerobic eukaryotic cells without mitochondria

Then, the eukaryotic cell engulfed the aerobic prokaryotes by endocytosis to make an eukaryote carrying aerobic prokaryotic endosymbiont

The mtDNA got smaller as the nuclear DNA got larger

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32
Q

What is a feature of mtDNA that proves its bacterial origin?

A

Translation inhibited by Chloramphenicol (typical of bacteria)

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33
Q

What is affected by mtDNA disorders?

A

Everything except RBCs

34
Q

Name 7 clinical syndromes associated with mtDNA defects

A

KSS - Kearns Sayre Syndrome

MELAS - Mitochondrial Encephalopathy Lactic Acidosis and Stroke-like episodes

MERRF - Myoclonic Epilepsy and Ragged Red Fibres

LD - Leigh’s disease

LHON - Leber’s Hereditary Optic Neuropathy

NARP - Neurogenic weakness, Ataxia, Retinitis Pigmentosa

MNGIE- mitochondrial neuro gastro intestinal encephalopathy

35
Q

What are the symptoms of Kearns Sayre syndrome?

A

Chronic progressive external ophthalmoplegia (CPEO)

Myopathy

Encephalopathy

36
Q

What are the symptoms of MELAS?

A

Encephalopathy

Stroke-like episodes

Myopathy

Lactic acidosis

Stunted growth

Seizures

37
Q

Name as many primary MRC defect-caused clinical symptoms as you can

A 
Encephalopathy 
Ataxia Epilepsy 
Stroke like episodes
optic neuropathy
neurodegeneration
myopathy
Chronic progressive external ophthalmoplegia (CPEO)
Retinopathy 
Cardiomyopathy Diabetes Deafness
Short stature 
Lactic acidosis
38
Q

What is a typical symptom of LHON?

A

Acute bilateral visual loss between 18-30 yrs

39
Q

Which gender is LHON more common in?

A

Men - 85% male

40
Q

What is LHON prognosis like?

A

Rapid progression but symptoms can improve slightly

41
Q

What is the most common symptom of mitochondrial disorders?

42
Q

How does CPEO present?

A

Limited eye movement usually present with ptosis

Muscle weakness and fatigue are usually present

CNS symptoms in about 50% of patients

43
Q

When is CPEO onset?

44
Q

TRUE or FALSE?

There is usually a family history of CPEO

45
Q

What is unique about MELAS?

A

Lacks any CPEO, optic atrophy and heart symptoms

46
Q

When is MELAS onset?

A

Subject is normal until around 30s

47
Q

What is MELAS prognosis?

A

Stroke-like episodes –> premature death

48
Q

What are the additional neurological symptoms of MELAS?

A

Ataxia

Cognitive decline

Spasticity

49
Q

Which mitochondrial diseases have early onset?

A

Leighs

NARP

KSS (mixture: birth - 20s)

LHON (varying onsets)

50
Q

Which mitochondrial diseases have late onset?

A

CPEO

MELAS

LHON (varying onsets)

51
Q

What kind of prognosis do infantile onset patients have?

A

Bad - often fatal due to infantile cardiomyopathy

52
Q

Which mitochondrial diseases lead to premature death?

A

Leigh’s

MELAS

53
Q

Which mitochondrial diseases are just disabling?

54
Q

What do aerobic exercise tests show in mitochondrial disease patients?

A

High levels of lactic acid which take longer to decrease

Because they use mainly glycolysis/anaerobic respiration

55
Q

How does anaerobic respiration work?

A

Glucose –> Pyruvate (produces NADH and ATP)

Pyruvate –> Lactate (recycles NADH to NAD)

56
Q

What do you see in the histology of a person with mitochondrial disease?

A

High oxidative (type 1 ) fibres

Decreased activity of one complex while increased activity of another complex

Sometimes shows ragged red fibres

57
Q

What are the main anormalities of the MRC proteins and what disease do they cause?

A

Complex 1: LHON, MELAS

Complex 4: Leigh’s

Combined complex 1 and 4: CPEO

58
Q

What are the rare anormalities of the MRC proteins and what disease do they cause - if any?

A

Complex 2

Complex 3

Complex 5 - NARP

59
Q

What can cause primary defects in MRC?

A

Genetic mutations (mitochondrial or nuclear)

Toxins (MPTP or lack of oxygen)

60
Q

What does MPTP do?

A

Inhibits complex 1 and gives PD-like symptoms

61
Q

What does lack of oxygen do for MRC?

A

It acts like a complex IV inhibitor

62
Q

Which is more common, mtDNA or nuclear DNA mutations leading to mitochondrial diseases?

A

mtDNA mutations (70%)

63
Q

Which diseases are caused by mtDNA deletions and which genes are affected by this?

A

4977bp deletion - various mRNAs/tRNAs genes

CPEO, KSS

64
Q

Which diseases are caused by mtDNA point mutations and which genes are affected by this?

A

mRNA mutations:
A3460G-ND1 gene ->LHON
T8993G-ATPase8->NARP

tRNA mutations:
A3243G-tRNA Leu -> MELAS
A8344G-tRNA Lys -> MERRF

65
Q

TRUE or FALSE?

People with mitochondrial diseases have only the mutated mtDNA copies

A

FALSE

They have 2 versions

(Heteroplasmy!)

66
Q

What % of mtDNA mutations are deletions and how may are mtDNA tRNA/mRNA/rRNA point mutations?

A

mtDNA deletion 30%

mtDNA tRNA point mutation 30%

mtDNA mRNA point mutation 9%

mtDNA rRNA point mutations 1%

The rest are nuclear ones or new mtDNA mutations

67
Q

Describe the inheritance of mtDNA diseases

A
  • Maternal inheritance

Affects all offspring and is passed down the female line

  • Variable penetrance
68
Q

What are secondary MRC defects?

A

The MRC defects contribute to disease but do not cause it

69
Q

What kinds of proteins are affected in secondary MRC defects?

A
  • Regulate mtDNA
  • Regulate the degradation of damaged mitochondria
  • Defects of cellular biosynthetic pathways
  • Cellular Stress / damage caused by excessive free radical generation
70
Q

What is a secondary MRC defect in a nuclear gene that regulates mtDNA?

A

TWINKLE mutations

Cause multiple deletions of mtDNA

71
Q

What is a secondary MRC defect in a nuclear gene that regulates the degradation of damaged mitochondria?

A

PINK1 or parkin mutations in Parkinson’s disease

Control mitophagy

72
Q

What is a secondary MRC defect in a nuclear gene that controls cellular biosynthesis pathways?

A

FXN mutations decreasing iron sulphur centre synthesis in Friedreich’s ataxia

73
Q

Where can we see a secondary MRC defect in a nuclear gene that controls cellular stress?

A

Various neurodegenerative diseases: Parkinson’s disease, motor neuron diseases

Caused by too many free radicals

74
Q

Are there many therapeutic options for mitochondrial diseases?

A

No, it’s very limited

75
Q

What are the current therapeutic options for mt diseases?

A
  • Agents that improve electron transfer in MRC – Coenzyme Q10
  • Protect against free radical damage – vitamin E
  • Shift to lower mutant mtDNA levels & amplify WT mtDNA levels
76
Q

What are methods used to shift to lower mutant mtDNA and higher WT mtDNA levels?

A
  • mitoTALENS
  • Zinc finger
  • CRISPR cas9
  • Small molecules

All targeted to mitochondria

77
Q

What does coenzyme Q10 do?

A

Moves e- from complex 1 to 3 and is an antioxidant

78
Q

What % decrease in mutant load do you need to get significant improvement?

79
Q

What can be currently done for mitochondrial disease patients?

A

Genetic counselling

Ovum donation

Triple parent babies

80
Q

How are triple parent babies made?

A
  1. The mom’s spindle is taken and isolated
  2. The nucleus is discarded from a donor egg with healthy mtDNA
  3. The above 2 are combined to make a healthy egg with mom’s DNA
  4. Egg is fertilised –> embryo with normal mitochondria
81
Q

Which is the most common mtDNA mutation in patients with mitochondrial respiratory chain disease ?

A

Point mutations in the mtDNA for tRNA

Neuro (23 decks)

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