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Cell Biology & Physiology BIOL1024 > Organelles & Cytoskeleton > Flashcards

Organelles & Cytoskeleton Flashcards

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1
Q

Cytosol vs cytoplasm

A

Cytosol:
- water
- small molecules
- cytoskeleton
- ribosomes

Cytoplasm:
- cytosol
- organelles

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2
Q

Features of mitochondria

A
  • thought to be prokaryotic in origin
  • double membrane - inner membrane highly folded for large SA
  • mobile organelles, associated with microtubules, can change shape and position, motor proteins can bind allowing them to move
  • outer membrane contains porins - permeable to small molecules
  • intermembrane space, similar composition to cytoplasm
  • inner membrane - cristae - contains double phospholipid called cardiolipin making the membrane permeable to ions
  • electron transport chain
  • matrix - space enclosed by cristae
  • mitochondrial DNA= circular
  • granular
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3
Q

Mitochondrial fission

A
  • Midzone fission - forms 2 mitochondria
  • Peripheral fission - used to remove damaged material
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4
Q

Mitochondria generating ATP

A

Chemiosmotic Coupling:

Stage 1: Electron Transport Chain
- high energy electrons are derived from oxidation of food
- electrons are transferred along electron carriers in membrane
- electron transfer releases energy which is used to pump hydrogen ions across the membrane - electrochemical proton gradient

Stage 2:
- proton gradient provides an energy store used to drive ATP synthesis (cardiolipins involved)
- flow of protons through ATP synthase forming ATP
- fats and carbs broken down releasing electrons
- 2 electrons picked up by NAD+ converts to NADH, electrons carried to inner membrane
- glucose converted to pyruvate (glycolysis)
- pyruvate oxidised forming CO2 + H2O + 15 ATP

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5
Q

Mitochondrial DNA - mtDNA/mDNA

A
  • 16569 bases and encodes for 13 proteins
  • evolves much faster than genomic DNA and is used in phylogenetic studies
  • maternally inherited in most organisms
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6
Q

Mitochondrial diseases

A
  • can be a defect in a nuclear genome or mitochondrial genome gene - inherited or acquired
  • can be caused by drugs, infections or environmental factors
  • mitochondrial replacement therapy - 3 parent babies
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7
Q

Features of ribosomes

A
  • Prokaryotic - 70s
  • large subunit = 50s, small = 30s
  • Eukaryotic - 80s
  • large subunit= 60s, small = 40s
  • rRNA + ribosomal proteins
  • facilitate synthesis of polypeptides, protein synthesis, move 5’ to 3’ along mRNA
  • A site - incoming aminoacetyl tRNA
  • P site - most recent amino acid (peptidyl tRNA)
  • E site - exit of deacylated tRNA
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8
Q

Ribosome inactivating proteins (RIPs)

A

Type 1 - cannot pass cell membrane (non-cytotoxic)
Type 2 - binding domain allows entry of toxins to cells

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9
Q

Features of peroxisomes

A
  • single membrane
  • no DNA or ribosomes
  • protein import from ER or Golgi
  • adaptable to conditions
  • vary in shape
  • contain oxidative enzymes
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10
Q

Reactions of peroxisomes

A
  • important in detoxification +breakdown of fatty acids to acetyl CoA
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11
Q

Biogenesis and maturation of peroxisomes

A
  • budding off of vesicles from ER
  • can undergo fission to replicate
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12
Q

Features of lysosomes

A
  • membrane bound
  • contain hydrolytic enzymes e.g. proteases and nucleases - function in acidic conditions, all acid hydrolases pH 4/5
  • diverse shape/size
  • proton pumps - maintain low pH, us ATP as an energy source
    Involved in:
  • endocytosis - waste material taken into cell to be degraded
  • phagocytosis
  • autophagy
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13
Q

What are endosomes?

A
  • intracellular sorting organelles
  • fuse to lysosomes once matured
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14
Q

Why don’t lysosomes digest themselves?

A
  • modified lipid membrane
  • highly glycosylated proteins
  • membrane transporters to remove digestion products
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15
Q

What are VAULT complexes?

A
  • ribonucleoprotein structures
  • contain multiple subunits
  • true function is unknown, thought to be involved in mRNA localisation, drug resistance and cell signalling
  • essential for cell function but other genes can compensate - gene redundancy
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16
Q

Features of proteasomes

A
  • important for correctly folded and functional proteins
  • incorrectly folded proteins can be fatal
  • destroy those that are incorrectly folded or short lived proteins
  • made up of a complex of multiple proteins
  • 4 heptametric rings
  • contain ubiquities to target proteins to be destroyed
  • polyubiquitin tail removed and destroyed
17
Q

Features of vacuoles

A
  • maintain turgor pressure
  • plant and fungal cells
  • fluid filled, membrane bound
  • contain hydrolytic enzymes
  • nutrient and waste storage
  • regulate pH - pump protons in and out of
18
Q

Features of the cytoskeleton

A
  • gives cell shape
  • capacity to move/alter shape
  • organisation and transport of organelles and chromosomes
  • cell division
  • Microfilaments (actin)
  • intermediate filaments
  • microtubules (tubulin)

Decrease in abundance as you go down

19
Q

Features of microfilaments

A
  • made of actin
  • have 4 domains, central nucleotide (ATP/ADP) binding site and Ca2+/Mg2+ binding site
20
Q

Cycling of microfilaments

A
  • Unpolymerised = globular actin, tightly bound Ca2+ and non covalently bound ATP
  • Polymerised = ATP hydrolysed, polymerised actin forms part of actin chain
  • unpolymerised reused/added to other chains
21
Q

Assembly of actin

A
  • polar - pear shaped
  • barbed (plus) end and pointed (minus) end
  • barbed end = easier to elongate chain/add subunits
  • pointed end = harder to add subunits, requires conformational change
  • 2 chains of filamentous actin - twisted
  • 1 twist = 13 actin monomers, then repeats
22
Q

Dynamic structure of cytoskeleton

A
  • microfilaments allow cells to move and change shape
  • disassemble at lagging end and reassemble at leading edge, pushing the cell forwards
23
Q

Regulation of actin polymerisation

A
  • ARP2 + ARP3 (similar structure to actin but cannot polymerise)
  • act as a primer for actin polymerisation
  • bind to microfilaments forming branches of the microfilament network
  • profilin ( positive regulation, extends)
  • thymosin (negative regulation, inhibits)
  • levels of both can modulate rate of microfilament synthesis
24
Q

Regulation of microfilament length

A
  • Gelsolin - protein that binds to microfilaments causing cleavage, leaves 2 free ends, can then elongate further
  • gelsolin/microfilament complex acts as a primer for chain elongation
25
Q

Regulation of microfilament association

A
  • associate with eachother - create crosslinks e.g. filamin, protein that forms dimers, each part can then bind to another microfilament
  • e.g. villin - doesn’t cleave but forms crosslinks
26
Q

Features of microtubules

A
  • present in animal and plant cells
  • made up of alpha and beta tubulin
  • high sequence similarity
  • form 110 kDa heterodimer = polymerising subunit
  • polymerisation forms tubular structure
  • alpha tubulin has a bound GTP - not hydrolysed
  • beta tubulin may have bound GTP/GDP
27
Q

Formation of microtubules

A
  • created by complex of proteins = gamma tubulin subunit - found within microtubule organising centre (MTOC)
  • alpha and beta subunits add on and elongate the microtubule
  • polymerisation is driven by GTP hydrolysis
28
Q

Regulation of microtubule assembly

A
  • Stathmin (protein) binds to alpha and beta tubulin subunits, preventing elongation, decreasing rate of assembly
  • if insufficient subunits, GTP hydrolysis occurs at minus end causing disassembly of the microtubule.
  • releases new subunits which can be used to elongate other microtubules
29
Q

Stabilisation of microtubules

A
  • Microtubule associated proteins (MAPs) e.g. MAP2 and Tau
  • allow crosslinking of microtubules - also mediate interaction with other cellular components.
  • binding of MAPs forms ‘arms’ on microtubules controlling the spacing of them
30
Q

Features of intermediate filaments

A
  • most stable in cytoskeleton
  • least soluble
  • perform structural function
  • size differs between cell type
  • made of protein subunits which form dimers
  • helical and non-helical regions
  • 40kDa - 200 kDa
31
Q

Movement through cytoskeleton

A
  • mitochondria and lysosomes move via saltatory conduction, rapid then pauses
  • in plants, cellulose biosynthesis, protein complexes move along filamentous pathways
32
Q

Movement along microtubules

A
  • microtubule motors - use ATP derived energy
  • kinesins - towards positive end
  • dyneins - towards negative end
  • e.g. for transport of vesicles for exocytosis between ER and Golgi
  • 1 conformation stabilised by bound ATP following hydrolysis
  • cycling of conformational changes allows ‘walking’ along the filament
  • 1 leading and 1 trailing foot
33
Q

Movement along axons via microtubules

A
  • bidirectional movement
  • inward (toward cell body) - retrograde transport
  • outward (away from cell body) - anterograde transport
34
Q

Directionality of movement

A
  • depends on polarity of cytoskeleton
  • without polarity, movement would be random
  • important for bidirectional movement
35
Q

Characteristics of motor proteins

A
  • globular head - engages filament and actively moves it along
  • tail region - point of attachment of motor protein
  • power stroke - ATP hydrolysis causing conformational change, head thrusts back creating tension in tail, moving tail forwards
  • recovery stroke - occurs when protein is loosely attached to filament, head slides along via thermal motion/diffusion
36
Q

Features of kinesin

A
  • dimer of heavy and light chain (gives specificity)
  • tetrametric structure
  • 3 domains
    1) large globular head - binds microtubules and ATP
    2) stalk region
    3) small globular head - binds to vesicles

Cell Biology & Physiology BIOL1024 (3 decks)

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