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MOLECULAR BIOLOGY > WEEK 5 (Energy generation in mitochondria) > Flashcards

WEEK 5 (Energy generation in mitochondria) Flashcards

1
Q

What are the two ways animal cells make ATP?

A
  • An energetically unfavourable reaction [ADP + Pi = ATP] that occurs during the breakdown and oxidation of food molecules
  • Oxidative phosphorylation in the inner mitochondrial membrane that produce both ATP and the additional activated carriers that will help drive the production of much larger amounts of ATP
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2
Q

What is the composition of the mitochondria?

A

A mitochondrion contains two membranes and a large internal space called the matrix

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3
Q

What does NADH stand for?

A

Nicotinamide Adenine Dinucleotide Hydride

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4
Q

Describe the stages of the breakdown of food molecules

A

1) Digestion - physical/mechanical breakdown occurs in the mouth via teeth and chemical hydrolysis occurs in the gut via digestive enzymes and intracellular lysosomes
2) Glycolysis - a linear metabolic pathway of enzyme-catalyzed reactions that converts glucose into two molecules of pyruvate in the presence of oxygen or two molecules of lactate in the absence of oxygen. (occurs in the cytoplasm)
3) Begins with the citric acid cycle (Krebs cycle) in the mitochondrial matrix and concludes with oxidative phosphorylation on the mitochondrial inner membrane

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5
Q

Where does Glycolysis usually take place?

A

Mainly in the Cytosol, except for the final step of conversion of pyruvate to acetyl groups on acetyl CoA which occurs in the mitochondrial matrix

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6
Q

How do the products of Glycolysis contribute to oxidative phosphorylation?

A

The conversion of Pyruvate (3C) to Acetyl CoA (2C) produces NADH & CO2 . The NADH adds to the NADH produced by the citric acid cycle (Krebs cycle) to drive the production of ATP by oxidative phosphorylation

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7
Q

What are the net products of the complete oxidation of food?

A
  • ATP (30-32)
  • NADH
  • CO2
  • H2O

ATP and NADH provide the energy and electrons needed for biosynthesis and CO2 and H2O are waste products

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8
Q

In eukaryotic cells, where is acetyl CoA produced?

A

In the mitochondria from molecules derived from sugars and fats

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9
Q

What happens to the acetyl groups in acetyl CoA via the citric acid cycle?

A

They become oxidised to produce CO2

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10
Q

Describe how activated carriers generated during the citric acid cycle power the production of ATP

A

1) Pyruvate and fatty acids enter the mitochondrial matrix where they are converted to acetyl CoA
2) acetyl CoA is metabolised by the citric acid cycle which produces NADH
3) During oxidative phosphorylation, high energy electrons donated by NADH are passed along the electrontransport chain in the inner membrane to O2 to produce H2O (it requires four electrons from four NADH molecules to convert O2 to two H2O molecules)
4) Electron transport generates a proton gradient across the inner membrane which is used to drive the production of ATP by ATP synthase

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11
Q

In which cells does oxidative phosphorylation take place?

A

Eukaryotic cells and in aerobic bacteria

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12
Q

In oxidative phosphorylation, what is the importance of the energy released by the oxidation of NADH to NAD+?

A

The energy released is harnessed through energy-conversion processes in the inner mitochondrial membrane to drive the energy-requiring phosphorylation of ADP to form ATP

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13
Q

What are the three respiratory enzyme complexes that transfer high-energy electrons?

A
  • NADH dehydrogenase complex
  • Cytochrome c reductase complex
  • Cytochrome c oxidase complex
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14
Q

What are the names of the mobile carriers that carry electrons from one complex to the next in the inner mitochondrial membrane?

A
  • Ubiquinone (Q)
  • Cytochrome C
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15
Q

What happens to the protons during the transfer of high-energy electrons from NADH to oxygen?

A

Protons derived from water are pumped across the membrane from the matrix into the inter membrane space by the complexes

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16
Q

What are the final products on Glycolysis?

A

2 NADH (cytosolic) + 2 ATP

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17
Q

What are the final products of pyruvate oxidation to acetyl CoA?

A

2 NADH (mitochondrial matrix)

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18
Q

What are the final products on complete acetyl CoA oxidation?

A

6 NADH + 2 FADH2 + GTP

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19
Q

What is the final ATP yield per molecule of glucose?

A

30

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20
Q

NADH produced in the cytosol yields __________ ATP molecules than NADH produced in the mitochondrial matrix

A

fewer

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21
Q

What are the stages that Oxidative phosphorylation could have evolved from?

A

Stage 1) Could have involved the evolution of an ATPase that pumped protons out of the cell using the energy of ATP hydrolysis
Stage 2) Could have involved the evolution of a different proton pump driven by an electron-transport chain
Stage 3) Would have linked these two systems together to generate an ATP synthase that uses the protons pumped by the electron-transport chain to synthesis ATP (a bacterium with this final system would have a selective advantage over bacteria with neither of the systems or only one)

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22
Q

Where has mitochondria most likely evolved from?

A

Bacteria that were engulfed by an ancestral pre-eukaryotic and survived inside it

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23
Q

Where have chloroplasts most likely evolved from?

A

Photosynthetic bacteria that were engulfed by an early eukaryotic cell

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24
Q

What do chloroplasts and mitochondria have in common?

A
  • contain their own DNA-based genome and the machinery to copy this DNA and to make RNA and protein
  • Inner compartments contain DNA and a special set of ribosomes
  • membranes contain the protein complexes involved in ATP production
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25
Q

What are the characteristics of the number of mitochondria in cells?

A
  • Present in large numbers
  • Numbers vary depending on the cell type and can change with the energy needs of the cell

e.g mitochondria can divide until their numbers increase to 5-10 fold if muscle has been repeatedly stimulated to contract

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26
Q

What is the composition of liver mitochondria?

A
  • 67% in the matrix
  • 21% in the inner membrane
  • 6% in the outer membrane
  • 6% in the intermembrane space
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27
Q

What are the four separate compartments of mitochondria?

A
  • MATRIX - contains a highly concentrated mixture of hundreds of enzymes including those for oxidation of pyruvate and fatty acids and for the citric acid cycle
  • INNER MEMBRANE - folded into numerous cristae and contains proteins that carry out oxidative phosphorylation (electron transport chain and ATP synthase)
  • OUTER MEMBRANE - contains large channel-forming proteins (PORINS) and is permeable to all molecules
  • INTERMEMBRANE SPACE - contains several enzymes that use the ATP passing out of the matrix to phosphorylate other nucleotides and proteins that are released during apoptosis
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28
Q

Where are mitochondria located in heart muscle cells and sperm cells?

A

In heart muscle cells mitochondria are located close to the contractile apparatus. In sperm cells they are wrapped tightly around the motile flagellum

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29
Q

Human mitochondrial DNA (mtDNA) encodes how many RNAs, tRNAs and polypeptides?

A
  • 2 ribosomal RNAs (rRNAs)
  • 22 transfer RNAs (tRNAs)
  • 13 polypeptides

all essential to the oxidative respiration functions of the organelle

30
Q

What is distinguishable about vertebrate mtDNA?

A
  • the two DNA strands vary in density with one heavy (H) strand and one other light (L) strand
  • introns are absent from mitochondrial genes and gene repetitions are infrequently present
31
Q

Yeast DNA is ____________ than human DNA

A

larger

32
Q

What is the replication in mitochondria dependent on?

A

Enzymes encoded by nuclear DNA and proteins encoded by nuclear genes

33
Q

Describe mitochondrial inheritance regarding maternal influence

A

1) An offspring’s phenotype for a particular trait is under the control of nuclear gene products present in the egg
2) Nuclear genes of the female gamete are transcribed and the genetic products accumulate in the egg cytoplasm
3) After fertilisation, products are distributed among newly formed cells and influence the patters or traits established during early development

34
Q

Describe the three scenarios regarding the influence of the maternal genome on mitochondrial disease

A
  • Father with the disease + Mother without = Children do not have the disease
  • Mother with the disease (all mitochondria mutant) + Father without the disease = Children have the disease
  • Mother with disease (some mitochondria normal, other mutant) + Father without the disease = Children may or may not have the disease (severity may vary)
35
Q

What is Myoclonic epilepsy and ragged-red fibre disease (MERRF) and what are the symptoms?

A

Myoclonic epilepsy with ragged red fibers (MERRF) is a multisystem mitochondrial syndrome characterized by progressive myoclonus and seizures. Patients with MERFF have a mutation in one of the mitochondrial genes encoding a transfer RNA and is maternally transmitted. Symptoms begin in childhood, adolescence or early adulthood.

Ragged-red fibers in skeletal muscle cells has mild proliferation of mitochondria which has replaced most cellular structures

  • Myoclonus (involuntary twitching)
  • Seizures
  • Ataxia
  • Muscle weakness
  • Dementia
  • Worsening eyesight
  • Hearing loss
  • Altered sensation feeling
36
Q

What is Leber Hereditary Optic Neuropathy (LHON)?

A

Leber’s hereditary optic neuropathy (LHON) is a mitochondrially inherited (transmitted from mother to offspring) degeneration of retinal ganglion cells (RGCs) and their axons that leads to an acute or subacute loss of central vision; Vision loss occurs because the cells in the optic nerve die.

Four mutations have been identified at a gene encoding a subunit of NADH dehydrogenase which disrupt normal oxidative phosphorylation. MT-ND1, MT-ND4, MT-ND4L or MT-ND6

Average age of vision loss is 27 and affects predominantly young adult males

37
Q

What can hereditary optic neuropathies be inherited as?

A
  • Autosomal dominant
  • Autosomal recessive
  • X-linked traits
38
Q

What is Kearns-Sayre syndrome (KSS) and what are the symptoms?

A

Kearns-Sayre syndrome (KSS) is a rare neuromuscular disorder with onset usually before the age of 20 years. The most common deletion removes 4,997 nucleotides, including twelve mitochondrial genes. Deletions of mtDNA result in impairment of oxidative phosphorylation and a decrease in cellular energy production. All steps of oxidative phosphorylation are affected.

SYMPTOMS:
- loss of vision
- hearing loss
- heart conditions
- muscle weakness
- deafness
- kidney problems
- deterioration of cognitive functions (dementia)
- short

39
Q

What other major diseases are mitochondrial dysfunction associated with?

A
  • Type II diabetes
  • Parkinson
  • Alzheimer
  • Huntington disease
  • Schizophrenia
40
Q

Where does most of the energy released by electron transfers along the electron transport chain go?

A

It’s harnessed to pump protons (H+) out of the matrix creating an electrochemical proton gradient. Proton pumping is carried out by three large respiratory enzyme complexes embedded in the inner membrane.

41
Q

What does the electrochemical proton gradient across the inner mitochondrial membrane do?

A
  • makes ATP when protons move back into the matrix through an ATP synthase located in the inner membrane
  • drives active transport of selected metabolites into and out of the mitochondrial matrix
42
Q

What is the function of electron-transport chains in photosystems?

A

Transfer high-energy electrons from water to NADP+ to form NADPH which produces O2 as a by-product

43
Q

What is specific for transcription of the Mitochondrial Genome?

A

Mitochondrial DNA is circular and does not contain histones therefore both strands of DNA are transcribed simultaneously (different from nuclear DNA in which only one strand is transcribed)

44
Q

What is the size of human mitochondrial DNA?

A

16kb

45
Q

Typically how many copies of DNA are there in each mitochondrion?

A

2-10

46
Q

How many human mitochondrial proteins are encoded in the mitochondrial genome and synthesised within mitochondria?

A

13

47
Q

What best describes mitochondrial DNA?

A

a simple, double stranded circular DNA molecule

48
Q

_______________ can occur at any stage, including within the zygote

A

De novo mutations

49
Q

Why is the phrase “The mitochondrial genome has a very high density and accordingly the mutation frequency in mtDNA is low” wrong?

A

Mutation frequency has nothing to do with gene density and the frequency of mutations in mtDNA exceeds that of mutations in nuclear DNA by a factor of about 10 or more

50
Q

Mitochondrial DNA is advantageous for evolutionary studies because?

A

It is inherited only through the female parent and thus evolves in a way that allows relationship trees to be easily constructed

51
Q

The mitochondrial DNA differs from the nuclear DNA because of ___________________

A

Lacking binding histones

52
Q

How does mitochondria arise?

A

By growth and division of pre-existing mitochondria

53
Q

The presence of DNA in mitochondria and chloroplast supports the hypothesis that _________________________

A

Mitochondria and chloroplasts both originated as independent free living organisms

54
Q

The inner membrane of mitochondria is fairly smooth (TRUE or FALSE)

A

false

55
Q

How do the small molecules pass through the outer membrane of mitochondria?

A

Porins

56
Q

What products of glucose oxidation are essential for oxidative phosphorylation?

A

NADH and FADH2

57
Q

What is the effect of increased levels of hydrogen ions in the intermembrane space of the mitochondria?

A

Increased ATP production

58
Q

In aerobic respiration, carbohydrates are ultimately broken down into?

A

CO2

59
Q

Most ATP produced in aerobic respiration occurs in the process of _________

A

Chemiosmosis

Chemiosmosis is the movement of ions across a semipermeable membrane bound structure down their electrochemical gradient

60
Q

What is the final electron receptor in aerobic respiration?

A

Oxygen

61
Q

Which stage of aerobic respiration produces ATP and NADH and releases CO2?

A

Krebs cycle

62
Q

As protons flow through the ____________, energy is released and exploited to combine ADP and inorganic phosphate to form ATP

A

ATP Synthase

63
Q

What is the term for metabolic pathways that release stored energy by breaking down complex molecules?

A

catabolic pathways

64
Q

When electrons move closer to a more electronegative atom, what happens?

A

Energy is released and the more electronegative atom is reduced

65
Q

Why are carbohydrates and fats considered high energy foods?

A

They have a lot of electrons associated with hydrogen

66
Q

During cellular respiration, acetyl CoA accumulates in which location?

A

Mitochondrial matrix

67
Q

During aerobic respiration, which of the following directly donates electrons to the electron transport chain at the lowest energy level?

A

FADH2

68
Q

What is the primary role of oxygen in cellular respiration?

A

Acts as an acceptor for electrons and hydrogen, forming water

69
Q

Energy released by the electron transport chain is used to pump H+ ions into which location?

A

Mitochondrial intermembrane space

70
Q

Describe the transcription of mitochondrial RNA

A
  1. A specialised RNA polymerase encoded in the nuclear genome is used to transcribe the mitochondrial genome (which contains two related promoter sequences - one for each strand of the circular genome)
  2. Each strand is transcribed in its entirety
  3. Mitochondrial transcripts are processed to generate the various individual mitochondrial mRNAs, tRNAs and rRNAs

MOLECULAR BIOLOGY (11 decks)

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