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BMSC 220 > Topic 9: Mitochondria > Flashcards

Topic 9: Mitochondria Flashcards

1
Q

Mitochondira

A
  • energy generating “factories” of the cell
  • the site of metabolic energy generated in the form of ATP by the breakdown of carbs and lipids (oxidative phosphorylation)
  • critical for cell viability**
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2
Q

Structure of a Mitochondrion

A
  • double membrane bound cytoplasmic organelle

- “semi-autonomous”

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3
Q

Outer Membrane

A
  • defines outer perimeter
  • contains PORINS
  • similar chemical composition to plasma membrane
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4
Q

Porins

A
  • specialized proteins that form transmembrane channels permeable to all molecules below a size of 10 kDa
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5
Q

Inner Membrane

A
  • primary site of ATP production by oxidative metabolism
  • only effective permeability barrier between matrix and cytoplasm
  • contains Cardiolipin
  • 80% protein (by weight)
  • contains Cristae
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6
Q

Cardiolipin

A
  • specialized phospholipid with 4 fatty acyl tails found in mitochondrial inner membrane
  • decreases permeability of inner membrane to protons
  • synthesized within mitochondria
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7
Q

Cristae

A
  • folds of inner membrane
  • number of cristae varies with energy demands of cell
  • more cristae = higher energy demand
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8
Q

Intermembrane Space

A
  • similar chemical composition to cytoplasm (due to porin channels)
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9
Q

Matrix

A
  • 50% protein solution
  • contains majority of enzymes involved in oxidative metabolism
  • higher pH and negative charge relative to cytoplasm
  • site of mitochondrial DNA, RNA, protein synthesis
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10
Q

Endosymbiotic Origin of Mitochondria

A
  • thought to arisen by colonization of primitive eukaryotic cell by bacteria that became symbiotic relationship
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11
Q

Support of Endosymbiotic Origin Theory

A
  • presence of mitochondrial DNA
  • presence of unique RNA and DNA polymerases within mitochondria
  • presence of unique ribosomes and tRNAs within mitochondria
  • unique genetic code
  • capable of division
  • Rickettsia sp
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12
Q

Rickettsia sp.

A
  • intracellular parasitic proteobacteria

- many similarities between Rickettsia and mitochondrial genomes

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13
Q

Human Mitochondrial Genome

A
  • genes encode: rRNAs for mitochondrial ribosomes
  • mitochondrial tRNAs (22)
  • 13 proteins involved in electron transport chain/oxidative phosphorylation
  • remainder (95%) of human mitochondrial proteins are encoded by nuclear DNA
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14
Q

Human Mitochondrial Genome tRNAs

A
  • separate tRNAs
  • the 22 tRNAs in the mitochondria are the only ones used in mitochondrial protein synthesis
  • -> vs. 61 tRNA encoded in nucleus
  • mitochondria tRNAs have “extreme wobble” therefore 22 tRNAs are sufficient to recognize 20 amino acids
  • the mitochondria use a slightly different genetic code than in the nuclear genome
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15
Q

Shape and Intracellular Organization

A
  • some cells require selective positioning of mitochondria to location of high energy
  • size and shape = highly variable based on needs
  • different cells have different # of mitochondria based on energy needs
  • each mitochondria can contain diff. # of DNA molecules
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16
Q

Mitochondria Division

A
  • FISSION and/or FUSION
  • continual fusion and fission allow the mitochondria to modify their morphology within the cell
  • can divide semi-autonomously
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17
Q

Fission

A
  • division
  • is important:
    1. to distribute mitochondria evenly to daughter cells
    2. increase the # of mitochondria in a cell when more energy is needed
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18
Q

Fusion

A
  • fusion of pre-existing mitochondrial
  • allows mitochondria to share genetic material and proteins
  • each mitochondria can contain diff. # of DNA molecules
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19
Q

Fission Requires

A
  • DNA replication
  • RNA synthesis
  • membrane generation via phospholipid transfer from ER
  • protein synthesis within mitochondria & protein importation from cytoplasm
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20
Q

Localization

A
  • localized to sites of greatest energy requirements in cell

- localized predominantly through cytoskeleton

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21
Q

Nuclear Encoded Mitochondrial Proteins

A
  • most are synthesized on free ribosomes in cytoplasm

- imported into mitochondria complex b/c of double-membrane

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22
Q

4 Targets of Imported Proteins

A
  1. Outer membrane
  2. Inner membrane
  3. Intermembrane space
    - contain specific internal compartment targeting sequence
  4. Matrix
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23
Q

Proteins of Inner Membrane

A
  • located in electron transport chain
  • encoded on mitochondrial DNA
  • synthesized within matrix
  • unique mechanism for insertion into inner membrane
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24
Q

Mechanism to Target Proteins to Interior Compartments of Mitochondria

A
  • amino terminal mitochondrial targeting pre sequence of matrix proteins plus additional internal compartment sequences for some inner membrane proteins
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25
Q

Mechanism to Target Proteins to Outer Compartments

A
  • Internal mitochondrial targeting sequence plus internal compartment targeting sequences
  • -> for inter membrane space, outermsmbrane, and some inner membrane proteins
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26
Q

Tom complex

A
  • translocate of outer membrane
27
Q

Tim complex

A
  • translocate of inner membrane
28
Q

Hsp70

A
  • chaperones that keep proteins unfolded until reaching final desination
29
Q

MPP

A
  • matrix processing peptidase that cleaves targeting sequence following transport
30
Q

Inner Membrane Proteins with Amino Terminal Presequence

A
  • Tom complex
  • Tim complex
  • Hsp70
  • MPP
    Protein
    1. in inner membrane
  • contains internal inner membrane targeting sequence
    2. in matrix
  • no inner membrane targeting sequence (default pathway is thus to matrix)
31
Q

Sorting Proteins Containing Internal Targeting Sequences to Inner Membrane

A
  • Tim9, Tim10
  • Oxa
  • Proteins
    1. multiple folds in inner membrane
  • inner membrane protein encoded by nuclear DNA
    2. single in inner membrane
  • inner membrane protein encoded by mitochondrial DNA
32
Q

Tim9 and Tim 10

A
  • inter membrane space chaperones that “carry” protein to Tim22 channel complex
  • “tiny Tims”
33
Q

Oxa

A
  • translocase within inner membrane for proteins synthesized within matrix of mitochondria
  • ex) encoded by mitochondrial genome
34
Q

Sorting Proteins Containing Internal Targeting Sequences to Intermembrane and outer membrane

A
  • Mim1
  • SAM
    Proteins
    1. in outer membrane
  • outer membrane protein with alpha-helix transmembrane domain (similar to stop-transfer mechanism of rough ER)
    2. beta-barrel protein
  • outer membrane protein with beta sheet (beta barrel) transmembrane domains (e.g porin)
    3. intermembrane space protein (interacting with chaperones that are unique to intermembrane space proteins)
35
Q

Mim1

A
  • inserts proteins with a single alpha helical transmembrane domain inserted into the outer membrane
36
Q

SAM

A
  • Sorting and Assembly Machinery
  • moving some proteins from inter membrane space to outer membrane
  • ex) beta barrel proteins such as porins
37
Q

Phospholipids in Mitochondria

A
  • predominantly phosphatidylcholine and phosphatidylethanolamine
  • synthesized in ER
  • transferred to mitochondria by cytoplasmic phospholipid transfer proteins
  • cardiolipin
38
Q

Catabolism

A
  • breakdown of large, complex molecules into smaller, simpler molecules with release of chemical energy
  • majority of energy captured by ATP to form phosphoanhydride bonds
  • ATP is a molecule that stores “free energy” (ΔG)
  • hydrolysis of phophoanhydride bonds provides energy for most cellular reactions (releases free energy)
  • ATP generated in mitochondria
39
Q

phosphoanhydride bonds

A

high energy bonds

40
Q

2 Sources of Acetyl CoA

A
  1. pyruvate - product of glucose breakdown through glycolysis
  2. fatty acids - product of fat (triglyceride) breakdown
41
Q

Citric Acid Cycle

A
  • produces 2 molecules of NADH and 1 FADH2

- used to make ATP through oxidative phosphorylation via the electron transport chain

42
Q

NADH

A
  • reduction of NAD+ to NADH in citric acid cycle it accepts Both a proton (H+) and 2 e-
  • oxidation of NADH releases a proton and 2 e-
43
Q

Electron Transport Chain

A
  • electrons enter during oxidative phosphorylation from NADH and FADH2 combine with O2 to produce H2O
  • energy released during process is through chemiosmotic coupling
  • involves storage of proton gradient used to drive ATP synthesis
44
Q

Chemiosmotic coupling

A
  • electron transport through the electron transport chain is coupled to ATP synthesis
  • releases energy from the oxidative/reduction reactions that drive ATP synthesis
45
Q

Proteins encoded by

A
  1. the mitochondrial genome
  2. the nuclear genome
    - transcription of genes in both the nucleus and mitochondria have to be coordinated very closely to ensure the correct synthesis of the the electron transport chain = cellular communication
46
Q

Transport from NADH down electron transport chain (inner membrane)

A
  1. pairs of electrons enter the electron transport chain from NADH in complex I
  2. electrons transferred to Coenzyme Q, carried to complex III
  3. electrons transferred from cytochrome b to cytochrome c, carried to complex IV
  4. complex IV transfers electrons to molecular oxygen
  5. electron tranfers in complexes I, III, IV decrease in free energy which pump protons from matrix to inter membrane space
    - establishes proton gradient to drive ATP synthesis
47
Q

Coenzyme Q (Ubiquinone)

A
  • lipid soluble electron carrier
  • electrons carried to complex III
  • carried through membrane
48
Q

Cytochrome C (Cyt c)

A
  • peripheral membrane protein on outer face of inner membrane
  • electrons carried to complex IV
49
Q

Transport from FADH2 down electron transport chain (inner membrane)

A
  1. succinate is reduced by succinate dehydrogenase in complex II to generate FADH2
  2. FADH2 is reduced to FADH+H2, a process which donates electrons to coenzyme Q
  3. electrons are transported through complex III and IV, driving proton pump, as described for complex I
50
Q

Succinate

A
  • produced in citric acid cycle
51
Q

Proton Transfer

A
  • release of “small packets” of energy as electrons transferred down chain of carriers and complexes that are then used to move protons from matrix into intermembrane space
52
Q

Complexes I and III

A
  • transfer of 4 protons per pair of electrons per complex
53
Q

Complex IV

A
  • transfer of 2 protons per pair of electrons plus 2 protons combined with O2 to form water in matrix
54
Q

Mechanism of Oxidative Phosphorylation

A
  • a electrochemical gradient is formed across the inner membrane, corresponding to a ΔG of approx. -5 kcal/mol per proton (proton motive force)
  • phospholipid binary of inner membrane is impermeable to ions (cardiolipin plays a role in this)
  • protons can cross the membrane only through a protein channel
  • allows energy in electrochemical gradient to be harnessed and converted to ATP in complex V (ATP synthase)
55
Q

Electrochemical Gradient

A
  • formed when pH gradient and electric potential combine

- protons have a charge therefore proton gradient is both chemical and electrical in nature

56
Q

Complex V

A
  • ATP synthase
  • 2 subunits: F0 and F1
  • flow of protons through F0 drives the rotation of part of F1, which acts as a rotary motor to drive ATP synthesis
  • 4 protons requires to synthesize one ATP
  • oxidation of 1 NADH = 3 ATP
  • oxidation of FADH2 = 2 ATP
57
Q

F0

A
  • spans the inner membrane and forms a channel through which the protons move
58
Q

F1

A
  • catalyzes the synthesis of ATP

- contains ATP synthase

59
Q

Transport of Metabolites

A
  • across the mitochondrial inner membrane relies on electrochemical proton gradient
60
Q

Transport of Small Molecules

A
  • across inner membrane also driven by the electrochemical gradient including exporting ATP from matrix to cytosol, inorganic phosphate, pyruvate are moved into the matrix
61
Q

Inhibitors of Electron Transport

A

Cyanide

  • inhibits final electron transfer to oxygen
  • drives all electron transfer to a halt
62
Q

Mitochondrial Myopathies and Neuropathies

A
  • numerous and varied group of diseases
  • generally affect electron transport chain
  • can arise through mutations in nuclear or mitochondrial DNA
  • mitochondrial mutations can happen spontaneously in oocyte or inherited through maternal lines
63
Q

Chloroplasts

A
  • plastids: plant organelles
  • photosynthetic organelles of plants (conversion of CO2 to carbs)
  • carry out other metabolic functions
  • ETC uses photons from sun and generate ATP
  • endosymbiotic origin
  • contain three membrane system (inner, outer, thylakoid)
64
Q

Peroxisomes

A
  • single membrane organellles of eukaryotic cells
  • can replicate but don’t contain own genetic material
  • carry out various metabolic function, particularly oxidation reactions
  • -> can oxidize purines, amino acids, methanol, fatty acids
  • -> oxidation of fatty acids produce energy
  • -> FA oxidation in plants and yeast only occur in peroxisomes
  • -> FA oxidation in mammals also occur in mitochondria
  • another site of lipid synthesis

BMSC 220 (6 decks)

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