Organelles & Cytoskeleton Flashcards
1
Q
Cytosol vs cytoplasm
A
Cytosol:
- water
- small molecules
- cytoskeleton
- ribosomes
Cytoplasm:
- cytosol
- organelles
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
3
Q
Mitochondrial fission
A
- Midzone fission - forms 2 mitochondria
- Peripheral fission - used to remove damaged material
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
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
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
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
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
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
10
Q
Reactions of peroxisomes
A
- important in detoxification +breakdown of fatty acids to acetyl CoA
11
Q
Biogenesis and maturation of peroxisomes
A
- budding off of vesicles from ER
- can undergo fission to replicate
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
13
Q
What are endosomes?
A
- intracellular sorting organelles
- fuse to lysosomes once matured
14
Q
Why don’t lysosomes digest themselves?
A
- modified lipid membrane
- highly glycosylated proteins
- membrane transporters to remove digestion products
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
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
Regulation of microfilament association
- 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
Features of microtubules
- 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
Formation of microtubules
- 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
Regulation of microtubule assembly
- 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
Stabilisation of microtubules
- 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
Features of intermediate filaments
- 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
Movement through cytoskeleton
- mitochondria and lysosomes move via saltatory conduction, rapid then pauses
- in plants, cellulose biosynthesis, protein complexes move along filamentous pathways
32
Movement along microtubules
- 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
Movement along axons via microtubules
- bidirectional movement
- inward (toward cell body) - retrograde transport
- outward (away from cell body) - anterograde transport
34
Directionality of movement
- depends on polarity of cytoskeleton
- without polarity, movement would be random
- important for bidirectional movement
35
Characteristics of motor proteins
- 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
Features of kinesin
- 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
