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Cytology > Mitochondria/peroxisomes > Flashcards

Mitochondria/peroxisomes Flashcards

1
Q

General functions of mitochondria (6)

A
  1. aerobic ATP production
  2. lipid/phospholipid metabolism
  3. steroid hormone synthesis
  4. Ca2+ homeostasis
  5. Heat production
  6. Apoptosis initiation
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2
Q

2 theories of mitochondrial biogenesis (and which one is more supported)

A
  1. ENDOSYMBIOSIS:
    - descendants of ancient prokaryotes
    -engulfed by phagocytosis to become part of bacterium
  2. AUTOGENOUS:
    -event in eukaryotes which caused separation of genomic parts and encircling them in a plasma membrane

!! Endosymbiotic is supported because: mitochondria have their own genome, can synthesise some of their own substances and replicate similarly to bacteria

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3
Q

General structure of mitochondria

A

3 REGIONS:
1. outer membrane
2. intermebrane space
3. matrix

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4
Q

2 important characteristics of mitochondria

A
  1. Shape can change via fusion/fission
  2. Organelle can move throughout cytoplasm bcos of attachment to microtubules
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5
Q

how can mitochondria be separated and visuallised?

A

SEPARATED: centifugation, diff speeds have an output of different regions

VISUALISED: either fluorescent microscopy (allows visualisation of the motility as well as the structure) or TEM

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6
Q

Structure of outer membrane

A

-enzymes used for lipid synthesis
-VDAC channels for ATP to exit mitochondria and into cell cytoplasm
-PORINS: Transmembrane proteins which allow it to be mostly permeable
-membrane receptors for proteins and peptides that translocate into intermembrane space

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7
Q

Structure of intermembrane space

A

-enzymes that use ATP generated in inner membrane
-cytochrome C for apoptosis

!! size is variable and depends on activity levels

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8
Q

Structure of inner membrane

A

2 SUBDIVISIONS:
1. Inner boundary
-contains double phospholipid CARDIOLIPIN (with 4 fatty acid tails) that makes membrane impermeable to ions
-!!! no cholesterol

  1. Cristae
    -contains elementary particles: transmembrane proteins needed for respiratory chain/ ATP synthesis
    -dehydrogenases for oxidative phosphorylation
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9
Q

2 possible organisations of cristae

A
  1. LAMELLAR: perpendicular to longitudinal axis
    !! most common
  2. TUBULAR: shorter and tubular invaginations into inner membrane
    !! present in steroid synthesising cells
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10
Q

structure of matrix

A

-contains circular mtDNA
-contains mRNA, tRNA, ribosomes
-contains Ca2+ and Mg2+ ions stored in granules
-contains enzymes needed for Krebs and Ox, phosphorylation

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11
Q

Cell types that mitochondria are in higher concentration in (than average) [6]

A
  1. cardiomyocytes
  2. skeletal muscle fibers
  3. liver cells
  4. sperm cells
  5. neurons
  6. kidney tubular cells
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12
Q

Mitochondria organisation in cardiomyocytes

A

-mitochondria positioned inbetween actin and myosin filaments –> along myofibrils

3 different types:
1. subsarcolemmal mitochondria (SSM):located just under sarcolemma

  1. interfibrillar mitochondria (IFM): major population, between the myofibrils
  2. perinuclear mitochondria (PNM): located in region adjacent to nucleus
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13
Q

Mitochondria in sperm cells

A

-present within the ‘collar’
-provides energy needed for motility

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14
Q

Mitochondria in neurones and function

A

-biogenesis occurs in the soma, and mitochondria are then moved (via cytoskeletal attachment) to the synapse

FUNCTION:
-supply ATP for neurotransmitters
-act as buffering for local Ca2+ concentration

RELATIONSHIP BETWEEN MITOCHONDRIA AND ACTIVITY OF SYNAPSE: higher activity means mitochondria with higher volume, higher cristae density and lamelarity, higher cytochrome C expression

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15
Q

Role of mitochondria in Ca2+ homeostasis and its purpose

A

Ca2+ homeostasis regulates:
-cardiac energy metabolism
-apoptosis
-oxygen free radical production
-autophagy
-oxidative phosphorylation and redox balance

!! regulated by mitochondria via influx/efflux mechanisms

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16
Q

Pathologies associated with mitochondrial abnormalities

A
  1. Morphological abnormalities:
    -childhood myopathy: larger mitochondria with paracrystalline structures of regular cristae (dense packing of inner membrane proteins)
  2. Mutational defects (present a slight amount in everyone but become a disease when they cross the threshold of expression):
    -autism
    -muscular dystrophy
    -parkinsons/alzheimers
17
Q

Orthodox vs condensed mitochondral configuration

A

ORTHODOX:
-healthy cells
-matrix occupies the majority of volume
-cristae are prominent
-occurs when ADP is low

CONDENSED:
-unfolded cristae
-decreased volume
-increased intermembrane space
-facilitates secretion of cytochrome C
-occurs due to H+ accummulation at high ADP

18
Q

Role of mitochondria in heat production

A

-occurs in brown adipose tissue (get their colour because of high abundance of mitochondria and capilaries)
-H+ leak in the brown fat cells occurs via uncoupling proteins which generates ATP

19
Q

Importance of the fission:fusion ratio in mitochondria

A

determines overall morphology of mitochondrion

  1. FUSION>FISSION: produces interconnected mitochondria
    !! occurs in actively metabolising cells for energy dissipation
  2. FISSION>FUSION: produces mitochondrial fragments. Can also eliminate damanged mitochondria via mitophagy
    !! occurs in quiescent cells
20
Q

Proteins involved in the fusion and fission mechanisms

A

! proteins of the DYNAMIN family

  1. FUSION:
    - Mfn 1/2 (mitofusin) protein mediates fusion of outer membrane
    - Opa1 mediates fusion of inner membrane
  2. FISSION:
    -Drp1 squeezes mitochondria to help separation
21
Q

Outline of mitophagy

A

MITOPHAGY: process by which damaged mitochondria are lysed

  1. damaged organelle
  2. phagophore
  3. autophagosome
  4. phagolysosome
  5. lysis
  6. recycling of fragments
22
Q

structure of mtDNA

A

-double membrane
-circular (nucleoid)
-each nucleoid contains 4/5 copies of the mtDNA
-linked to cristae membrane
-maternal inheritance

23
Q

Where do the proteins needed by the mitochondria come from?

A
  1. they synthesise it themselves
  2. imported from the cytosol (main method): either through TIM complex (on inner membrane) or TOM complex (on outer membrane)
    !! signaling sequences on the proteins are picked up by complexes
24
Q

4 ways that mitochondria can be exhnaged between cells

A
  1. tunelling nanotubes
  2. extracellular vesicles
  3. gap junction channels
  4. cell fusion
25
Q

INTRINSIC (mitochondrial) apoptotic pathway cause and detailed mechanism

A

CAUSE: triggered by intracellular stress signals (usually derived from DNA damage). Relies on proteins of the Bcl-2 family (which can be either pro or anti apoptosis depending on the number of BH domains they contain)

PROCESS:
1. Peristimulus, the cytosolic antiapoptotic molecules (of Bcl2 family) are active: hence prevent cell death

  1. Arrival of apoptotic stimulus inactivates antiapoptotic molecules and hence pro-apoptotic functions are allowed to interact
  2. interactions induce formation of the MOMP (mitochondrial outer membrane permeabilization) pore)
  3. Pore allows exit of certain molecules from mitochondrial space into cytoplasm (eg. cytochrome C or p53)
  4. Cytochrome C binds to cytoplasmic APAF1 which is found in its inactive state
  5. Binding causes a conformational shape change which causes APAF1 to exhibit a CARD domain
  6. CARD domain exposure induces formation of an apoptosome (macromolecular structure)
  7. recruiting of caspase 9 (initiator which shows a CARD domain) by apoptosome
  8. activated caspase 9 activates executioner caspases triggering proteolytic cascade
  9. executioner caspases cleave and degrade substrates (eg. cytoskeletal elements) and activate endonucleases
  10. cytoskeleton breaks down, forming a cytoplasmic bud which forms the apoptotic body
  11. recognition of apoptotic body and internalization by professional phagocytes
26
Q

Process by which mitochondria replicate/divide

A

-segmentation
-similar to bacteria (endosymbiotic theory proof)
-squeezing of the organelle from its center into 2

27
Q

what is the morphology of mitochodria in each phase of the cell cycle

A

G1: various morphologies as they become replicated

G1-S transition : fusion and elongation (high metabolic demand for DNA replication)

G2/M phases: undergo fission to form individual organelles spatially distributed (for equal distribution of mitochondria to the daughter cell in mitosis)

28
Q

2 organelles that dont possess mitochondria

A
  1. RBCs
  2. terminal stage keratinocytes
29
Q

General functions of a peroxisome (5)

A
  1. lipid synthesis & storage
  2. production of bile acids
  3. remove free radicals and reactive oxygen species
  4. synthesis of plasmalogens (phospholypids where one fatty acid chain is attached to glycerol present in the brain and heart)
  5. role in immune response
30
Q

structure of peroxisomes

A

-membrane bound organelle
-enclosed granular matrix
-40% enzyme content = catalase
-sometimes present: paracrystalline central structure made of urate oxidase
-variable shape (rod/circular)
-increased numbers in cells with higher metabolic activity

31
Q

biogenesis of peroxisomes

A

!! either synthesised de novo or derived from pre-existing peroxisomes

  1. Classical model: growth and division of preexisting peroxisomes give rise to new ones
  2. Alternative model: membrane proteins are acquired from SER and matrix proteins are acquired from cytoplasm

-initiated by the budding off of pre-perixosomal vesicles from SER which undergo fusion
-some synthesis of proteins on free ribosomes of cytoplasm
-proteins needed for assembly contain PTS (peroxisomal targeting signal) – PTS1 & PTS2
-proteins inserted into membrane using chaperones

32
Q

how can peroxisomes be visualised?

A
  1. fluorescent miroscopy via probes
  2. stains that target specific enzymes within the matrix (eg. DAB)
33
Q

main differences between lysosomes and peroxisomes (5)

A
  1. microscopically: L is pale and P is dark
  2. L has lytic enzymes, P has oxidative enzymes
  3. L derived from Golgi/ER, P derived from ER and can self replicate
  4. L are larger than P
  5. L doesnt generate energy, P generates ATP

Cytology (8 decks)

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