Cell Biology Flashcards
What are the 2 functions of the plasma membrane?
What is so useful about membrane-bound organelles in eukaryotes?
What is the most common phospholipid & what is it made up of?
What is the fundamental characteristic of it?
- Enable composition of cell to differ from its environment
- Prevent molecules inside mixing with outside/Separates compartments
Internal membranes around organelles allows difference in composition of organelles & environments to allow different environments & processes
Phosphatidylcholine- 2 hydrocarbon chains, glycerol, hydrophilic head (choline & phosphate)
Amphipathic (polar & non-polar)
What does a hydrophilic substance do in water?
Hydrophobic substance?
What do amphipathic molecules form in water/aq solutions?
Forms H bonds & electrostatic attractions with it
Hydrophobic effect- adjacent water molecules form cage-like structure around to maximise hydrogen bonds with eachother- minimises energy to form droplets
Bilayer
Why are planar phospholipid bilayers energetically unfavourable?
What is more favourable?
What is crucial about this?
What different proteins are in the phospholipid membrane?
Edges are exposed to water
Forming sealed compartments (bilayers spontaneously close on themselves)
Can’t completely seal (communication, information, expand)- aided with proteins
Transporters, ion channels, anchors, receptors, enzymes
How thick is the lipid bilayer membrane & what percentage of its mass accounts for proteins?
What are the 4 ways a protein can associate with a membrane?
What does a transmembrane cross the layer as and why?
How long does the helix have to be to span the membrane?
5nm , 50%
Transmembrane- goes through bilayer
Monolayer associated a-helix-
Lipid linked- proteins with covalently linked lipids
Protein-attached- non cov interactions with membrane
a-helix: polar ends of the peptides allow hydrogen bonds with hydrophilic heads & also exterior hydrophobic side chains surrounded by hydrophobic tails
20AA
What is the Central Dogma of Life & who was it proposed by? What transfers are possible/not?
How did Louis Pasteur prove the Generation of Life that cells arise from all-cells-from-cells hypothesis & not the spontaneous generation hypothesis?
What was Pasteur’s cell theory?
DNA -> RNA -> Protein
Transfer of NA to protein is possible
Protein to protein and protein to NA not possible
Francis Crick
Straight neck flask- boiled broth & let sit in open = cells
Swan-neck flask- boiled broth but cells accumulated in condensation in the neck = no cells in broth
- tilted flash microbes from neck enter broth = cells
living organisms are made up of cells with are the unit for all organisms & they come from pre-existing cells & are made through growth & division
What are the resolutions of: unaided eye light microscope super resolution microscopy electron/x-ray/cyro-em
E.coli bacteria: what is unique about its genome? Does it have membranes? How large is it?
What types of organisms are e.coli bacteria?
What are the 3 different cells in cyanobacteria & what do they do?
How are these cells separated & why?
What have they evolved & why?
0.2mm
200nm/2E-4mm
20nm/2E-5mm
2-0.2nm
circular DNA lies freely in cytoplasm, no internal membranes/compartmentalisation, unicellular & 0.1-1 micrometres
phototrophs & chemolithotrophs
H = heterocyst: fixes atmospheric nitrogen into ammonia S = spore (resistant & dormant) V = fixation carbon (light to chemical energy)
H & V separated- nitrogenase sensitive to oxygen in carbon fixation
Thylakoids- large SA for carbon fixation/photosynthesis
What organelles can you see in eukaryotes in light vs electron microscope?
Nucleus:
What is it enclosed in & how does this enable its function?
How is genetic info contained in the nucleus?
What occurs in the nucleolus?
Light = nucleus & shapes, electron = organelles (ribosomes, mitochondria etc)
Nuclear envelope with pore- allow transport DNA/RNA in & out of cell
chromatin (associated w/ histones & TFs)
genes transcribe rRNA & assemble ribosomal proteins with ribosomal subunits
What is the ER the site of?
What is the structure of the ER?
What does it store?
What does the RER produce?
What does the golgi apparatus do?
What does the golgi apparatus look like?
Protein & lipid synthesis
Labyrinthine space enclosed in a membrane
Calcium ions
Transmembrane proteins & lipids
Receives the lipids & proteins from the ER & modifies them & sends to other organelles
Stacked membranes
What does the cytoplasm contain?
What occurs in the cytosol?
What do the lysosomes receive?
What do lysosomes contain & as a result what is their function?
What do the endosomes receives?
What do endosomes do?
Organelles & cytosol
Protein synthesis & chemical reactions
Proteins & lipids from ER
Lysozymes & low pH degrade non-functioning organelles/large particles/endocytosis
Lipids from golgi
Endocytosed material enters & then is delivered to lysosome- as a result has low pH
What are the structural features of the mitochondria?
What is its functions?
In what organisms are chloroplasts found?
What do peroxisomes contain & what is its function?
What other organelles do eukaryotes contain?
Surrounded by double membrane, circular mitrochondrial DNA
Oxidise sugar to generate ATP & site of biochem pathways like cell death
Plants & algae
Enzymes for oxidative reactions to inactivate toxic molecules- in lipid metabolism
Ribosomes, transport vesicles (trafficking between organelles), cytoskeleton (utility, transport, cell shape), actin & intermediate filaments
How are organelles without membrane formed and why?
How do these characteristics compare in prokaryotes & eukaryotes: Nucleus Diameter cell Cytoskeleton Cytoplasmic organelles DNA content (bp) chromosomes
Lipid phase separation in situations of stress- they demonstrate a control of gene expression
E = yes, P = no E = 10-100 micrometre, P = 1micrometre E = yes P = no E = yes P = no E = 1.5E7-5E9, P = 1E6-5E6 E = many linear DNA molecules, P = single circular DNA molecule
How are organelles without membrane formed and why?
How do these characteristics compare in prokaryotes & eukaryotes: Nucleus Diameter cell Cytoskeleton Cytoplasmic organelles DNA content (bp) chromosomes
Lipid phase separation in situations of stress- they demonstrate a control of gene expression
E = yes, P = no E = 10-100 micrometre, P = 1micrometre E = yes P = no E = yes P = no E = 1.5E7-5E9, P = 1E6-5E6 E = many linear DNA molecules, P = single circular DNA molecule
The Endosymbiotic theory discusses how an archaebacterium develops into an animal cell & plant cell.
How does it form a eukaryotic animal cell?
Plant cell?
What is the evidence to support this theory?
- Archaebcterium grows & develops infoldings = endomembrane system & membrane around nucleus
- Aerobic protobacterium with its own membrane is engulfed by the cell as a parasite & becomes endosymbiont
- The bacterium’s use oxygen to produce energy allows host thrive in rich oxygen environment = form mitrochondria
Cyanobacterium/photosynthetic bacteria becomes endosymbiont to form a chloroplast
- Chloroplasts & mitochondria are the same size as prokaryotic cells & also divide by binary fission
- They both have their own circular DNA
- Both have 30S & 50S ribosomes
How is a transmembrane hydrophilic pore different to a transmembrane cross layer?
What is the composition of a bacterial transmembrane filled water channel?
How can membrane proteins be transported out of the golgi with vesicles?
What are the 4 ways lateral mobility of plasma membrane proteins are restricted?
Elaborate on how the 4th one restricts some membrane proteins’ access in the epithelial cell of the gut
Aq is on the inside-
5 transmembrane helices form a water filled channel in the bilayer where the hydrophilic side chains are on the inside
16 strand beta sheet curved around itself in the bilayer & porin proteins associate to form a trimer with 3 different channels
Vesicle buds from golgi apparatus membrane with membrane protein inside & forms transport vesicle- then fuses to plasma membrane to release protein extracellularly
- Proteins tethered to cell cortex
- Proteins bound in extra cellular matrix
- Cell-cell interactions
- Restricted movement from 1 part of cell to the other by tight junctions
Tight junctions between the epithelial cells stop proteins moving from blood stream into gut lumen & vice versa
What do cytoskeletons do?
What is the diameter of intermediate filaments?
What are they made of?
What do they look like?
What are their characteristics?
What are they used for?
Give cell shape, & allow organise internal components & movement
10nm
Fibrous intermediate filament proteins
Rope like structures/fibres
Flexible, strong, deform under stress but don’t rupture
Forms nuclear lamina beneath inner nucleus membranes, span cytoplasm between cell-cell junctions to distribute mechanical stress in epithelial tissue
What is the diameter of a microtubule? What does this say about its characteristics?
What are they made up of?
What are their characteristics?
25nm (more rigid intermediate & actin filaments)
Hollow cylinders made of tubulin (protein), long & straight with a centrosome at one end
Rupture when stretched
What are the structures of actin filaments?
What is their diameter?
Where are they found most?
Helical polymers of actin- organised into linear bundles, 2D networks or 3D gels- very flexible
7nm
Cortex (layer cytoplasm beneath plasma membrane)
How is a growing intermediate filament formed?
What properties does it have?
Where are the 2 main regions intermediate filaments are found?
What are they used in more specifically? (4)
- a helical region = monomer
- monomer is coiled in pairs to form a dimer
- Staggered tetrameter of 2 coiled-coil dimers
- then lateral association of 8 tetrameters
Rope like- high tensile strength
Cytoplasm & nucleus
Keratin filaments in epithelial cells
Vimentin & its filaments in connective, muscle & glial tissue
Neurofilaments in nerve cells
Nuclear lamins in all animal cells for shape
How is the structure of a microtubule built up?
What is special about a microtubule’s structure?
What are the organising sites microtubules grow from?
How do microtubules grow out of centrosomes? What happens to the centrioles?
What causes dynamic instability in microtubules and what happens?
What do capping proteins do then?
1 subunit = tubulin heterodimer is encoded by 2 genes
Tubulin heterodimers make up a protofilament, and 13 of these make 1 microtubule
Has polarity- due to the tubulin dimers being arranged in the same direction means theres a + (top) and - end (bottom)
In dividing cells = centrosome (spindles)
Cilia & flagella = basal (cilia)
Tubulin nucleates out of ring nucleating sites in the centrosome- where - end is anchored and + end grows. Pair of centrioles at right angles inside centrosome
GTP hydrolysis. GTP-tubulin dimers add to the end of a growing microtubule causing + GTP cap. GTP hydrolysis/GDP-tubulin peels away from microtubule wall & released into cytosol causing shrinking microtubule
Stabilise microtubules (prevent shrinking) with +ve capping
What 2 microtubule binding proteins are involved in movement? What kind of proteins are they?
Which end of the microtubule do they move towards?
What are their structures?
How does this contribute to their walking movement?
What can they transport with them?
Kinesins & dyneins- motorproteins
Kinesins = + Dyneins = -
Both have globular heads with ATPase activity
ATP hydrolysis results in the heads interacting with the microtubules
On the tails- large protein complexes, vesicles, organelles
How are microtubules arranged in cilia/flagella?
How is a powerstroke in cilia caused?
9 + 2
Dynein motorproteins move along by 1 microtubule causing it to bend = powerstroke if all the doublets are coordinated
What is actin filaments characteristics? (4)
How is polarity caused?
What do many lateral interactions help with?
What is treadmilling? What else can occur due to the hydrolysis of ATP?
What do these processes regulate?
Thin, flexible proteins, polarised, 2 stranded helix with twist every 37nm
ATP binding cleft in the actin monomers (+ end has site, - site doesn’t)
Prevents separation
ATP-actin monomers bind to +ve end. Hydrolysis of ATP causes instability due to ADP-bound monomers, so actin at -ve end fall off. Dynamic instability
Polymer length
How can actin filaments help with cell movement? in steps
What is myosin?
What is myosin I’s function & how does it move? What is its structure?
myosin V?
myosin II?
muscle cells contain sarcomeres- what are these?
What are the lighter and darker filaments in muscles?
how does an entire muscle contract?
how does muscle relax?
- Actin polymerises at the +ve end of lamellipodium & attaches to integrins in the focal contact = anchorage
- Cell uses anchorage to drag itself forward by contracting at other cell end as myosin motor proteins slide the actin filaments
- Repeating cycling = further protrusion
Motor protein that moves along actin filaments due to their globular head with ATPase activity
membrane association & endocytosis
tail anchors plasma membrane & myosins move towards +ve end actin with hydrolysis of ATP as globular heads.
1 head with short tail
2 heads, biggest tail, carries cargo on tail region
muscle contraction, 2 heads & smaller tail than V
2 dimers of myosin II interact between tails to form a bipolar dimer where tails inwards & heads outwards. 2 actin fibres bound either side of 1 myosin, where + faces heads and - faces inner tails.
when myosin active- moves towards the + ends causing actin slide outwards = contraction
+=======–=======+ (actin)
ooo——————ooo (myosin)
+=======–=======+ (actin)
contractile units of microfibrils
dark = myosin II (bound to sarcomere) light = actin (attached to Z disc)
myosin moves to + end causing actin slide outwards = contraction of sarcomere. if all sarcomeres contract = muscle contracts
myosin stops moving
What are the 4 parts of the cell cycle?
What are cyclin-dependent protein kinases Cdpks used for in the cell cycle? What is the enzyme & protein?
How more specifically is the cell cycle activity controlled? e.g activation & inhibition
What Cdks & cyclins control the S phase & M phase?
Where in the cycle are the concentrations of these cyclins highest?
What is it that actually triggers these phases?
G1, S (DNA rep), G2, M (mitosis & cytokinesis)
Enzymes that attach phosphates to proteins covalently- can activate or inhibit the proteins hence control the cell cycle
Cdk = enzyme, cyclin = protein
Activation = cdk associate with cyclin
Phosphorylation of Cdk = both activation & inhibition
Inhibition = association with p27 or p21
S-Cdk with S cyclin
M-Cdk with M cyclin
S cyclin is between G1-S and beginning of M
M cyclin is between G2-M and beginning M
Activation of cdks due to the high concentration of the cyclins (low conc inactivates them)
How would you halt the G1 to S phase?
Why does this happen?
What does p53 do?
How would you halt the G2 to M phase?
How would you halt the M to G1 phase?
S-Cdk already formed- so inhibit with p27/p21 proteins to form inactivated p27-cyclin-Cdk complex
damaged DNA means protein kinases activate p53 by phosphorylation (tumour suppressor/protoncogene)
stimulates transcription p21 gene and induces DNA repair & sometimes activates programmed cell death
M-Cdk already assembled- so kinase phosphorylates Cdk enzyme at its inhibitory site
Cyclin is degraded with ubiquitylation (adding protein tag) & then destruction in proteosome
How can you inhibit DNA replication in G1 & S? in 4 steps
what else is S-Cdk useful for?
- in G1 origin recognition complex ORC assembled on the origin of replication on the DNA
- DNA helicase binds so Cdc6 dissociates
- prereplicative complex preRC is inactive, but is activated when S-Cdk activity is high at end of G1
- S-Cdk activates helicase, pre-RC & DNA polymerase
because it dissociates Cdc6 it prevents re-replication
How can you inhibit DNA replication in G1 & S? in 4 steps
what else is S-Cdk useful for?
- in G1 origin recognition complex ORC assembled on the origin of replication on the DNA
- DNA helicase binds so Cdc6 dissociates
- prereplicative complex preRC is inactive, but is activated when S-Cdk activity is high at end of G1
- S-Cdk activates helicase, pre-RC & DNA polymerase
because it dissociates Cdc6 it prevents re-replication
What do cohesin rings do during the S phase? Why?
What do condensin rings do in the M phase? Why?
What is a chromosome made up of?
How are the cytoskeletons recruited in mitosis?
Do plant cells contain these same structures?
Tie 2 adjacent sister chromatids in each duplicated chromosome- forms large protein rings to prevent chromatids coming apart
coil each sister chromatid/DNA double helix into smaller & compact structures- so more easily segregated in mitosis
2 sister chromatids with centromere
Microtubules- to separate duplicated chromosomes via pulling chromatids apart as spindles
Contractile rings- actin & myosin filaments that form around the spindles for division
Microtubules but not contractile rings
What are the 6 steps for the formation of the mitotic spindles/division of the centrosome & metaphase?
- Microtubules nucleate from centrosomes
- In interphase (animals G1 S G2) centriole pair in centrosome associate with the centrosome matrix so microtubules grow out
- Centrosome duplicates at same time as DNA rep in S phase by S-Cdks
- Early M phase- centrosome starts divide & nucleate own aster microtubules
- Centrosomes move apart & form bipolar mitotic spindles with aster at each pole
- Mitotic spindle waits for breakdown of nuclear envelope & then when it does break down- spindle microtubles interact with chromosome
- What happens in prophase? t=0 of M phase
- Prometaphase t=79min
- Metaphase t = 250
- anaphase t=279
- telophase t=315
- cytokinesis t=362
- Chromosomes condense, mitotic spindles assemble between 2 centrosomes & chromosomes have duplicated and start to move apart
- Breakdown nuclear envelope so chromosomes attach to spindle microtubules via their kinetochores & move
- Chromosomes align equator of spindle between spindle poles & kinetochore of each sister chromatid attach to opposite poles of spindle
- chromatids pulled opposite spindle poles = segregation of chromosomes, kinetochores of microtubules get shorter & spindle poles move apart
- 2 sets chromosomes arrive poles of spindle & nuclear envelope builds around each set. contractile ring for cytokinesis forms
- cytoplasm divides in 2- separation of cytosome & daughter cells where the division is due to contractile ring of actin & myosin perpendicular to spindle
Which region of the microtubules binds to the kinetochores?
What are the 3 types of microtubules that make up the mitotic spindle?
+ve
aster microtubules, kinetochore microtubules, interpolar (binds to motor proteins)
What are the 3 steps for triggering the separation of sister chromatids after metaphase?
What occurs in anaphase A? What is the force driving this?
What are the 2 driving forces in anaphase B?
- Separase (proteolytic) is inactivated by securin inhibitory protein
- APC degrades cohesin when chromosomes aligned properly in metaphase
- Separase’s activation means cohesin complex/rings degraded to allow separation chromatids in anaphase (stops this occurring prematurely)
Kinetochore microtubules depolarise while attached to chromosomes- shortening & pulling them to opposite poles. loss tubulin subunits on kinetochore microtubules
interpolar microtubules slide part eachother & pull poles apart by kinesins
dyneins pull poles outwards towards cell cortex
How does the nuclear envelope break down in prometaphase?
How does it reform at telophase?
How do plant cells not divide by?
What are plant cells division affected by?
How do plant cells divide?
Phosphorylation of nuclear pore proteins & lamin = triggers disassembly of nuclear envelope into small vesicles
dephosphorylation of nuclear pore proteins & lamin = vesicles come together around chromosome & reassemble envelope
contractile rings (only in animals)
cell wall
- new cell wall forms inside equator of old spindle after telophase (chromosome segregation)
- interpolar microtubules of spindle form a phragmoplast & golgi-derived vesicles fuse at equator (filled with cell wall materials) to form growing cell wall towards cell wall perpendicularly
- pre-existing plasma membrane & the membrane surrounding the new cell wall fuse to separate the 2 daughter cells
What type of amino acids are present in the following functions of signal sequences:
Import into ER retention in lumen of ER import into mitochondria import into nucleus import into peroxisomes
By what way do materials enter the nucleus?
hydrophobic & negative charge polar positive positive positive & 3 AA long
gated transport
What are the 4 steps importing cargo protein into the nucleus via gated transport?
Exporting cargo protein? (3)
What converts Ran-GTP into Ran-GDP & where is it found?
What about Ran-GDP to Ran-GTP?
How to nuclear import receptors bind to cargo?
Export receptors?
- Cargo protein interacts with importers in cytosol with nuclear localisation signal & complex can move in/out pores
- Complex diffuses into nucleus & interaction of complex disrupted by binding ran-GTP to importer
- Ran-GTP displaces cargo = release cargo & Ran-GTP free to move in/out pore
- Ran-GTP enters cytosol- causes conversion to Ran-GDP releasing importer from Ran-GTP so it’s free to bind to cargo
- Ran-GTP binds to exporter allows complex move with nuclear export signal so can diffuse in/out cytoplasm
- In cytosol: Ran-GTP converted Ran-GDP = disruption & release of cargo
- Exporter free in cytoplasm diffuse back into nucleus
GAP (GTP-ase activating protein) found exclusively in cytoplasm
GEF(Guanine nucleotide exchange factor) found in nucleus & bound to chromatin
nuclear localisation signal
nuclear export signal
What is transmembrane translocation and in which organelles does it affect?
What kind of translocation is it?
What kind of translocation is it when the proteins are made on the RER?
In post translational translocation in mitochondria:
To what exterior complex does the protein bind and where is it?
What precursors enter this way?
What is the pathway for a soluble protein?
What are the 2 requirements for the proteins to get through both complexes?
Proteins synthesised on free ribosomes in cytoplasm are translocated into mitochondria & peroxisomes with protein channels/transporters
Post-translational
Travels into ER lumen- co-translational translocation
TOM complex- outer membrane
Pre-sequence, hydrophobic or beta barrel
TIM23 complex in inner membrane & then matrix
Electrochemical gradient in inner membrane (+ intermembrane space - matrix from electron transfer chain), activity of TIM chaperones (help proteins fold & pull them into matrix)
What is vesicular trafficking & what is it mediated by?
What 2 pathways does it occur in?
How does an mRNA signal sequence on a cystolic protein send it to the lumen of the ER?
What is the signal sequence recognised by?
If translocation of the protein is halted, what can this particle do?
What happens to the particle after?
When & where is the signal sequence cleaved off? How is this different from the mitochondria?
Membrane proteins & lipids transport from one cell/organelle to another, mediated by cytoskeleton elements & motor proteins
ER to golgi
Golgi to plasma membrane/lyosomes/endomes
mRNA encoding cytosilic protein is free in cytosol- ribosomal subunits assemble to synthesise the polyribosome from the protein’s sequence. If the terminus of mRNA has ER signal sequence (binds to ER membrane) & the ribosome & proteins are recruited to ER & protein is co-translated into the lumen
SRP (signal recognition particle) protein
SRP binds to ribosome to form complex- which then allows binding to the SRP receptor protein on the RER membrane so nasant protein is translocated with translocators on RER
SRP dissociates to be recycled
in the RER (its N terminus)- in translation. Mitochondria is during translocation
What helps with folding of proteins in the ER lumen?
What is the process for misfolded proteins degradation?
What is a proteasome?
What is the protein tagged with before the process?
Chaperones
Enter cytosol from ER lumen via an ER protein translocation (sec61 complex).
Protein is tagged with ubiquitin (signal for degradation) & will then be degraded in proteasome
Multi enzyme complex with lots proteases & peptides
Blue sugar tag from ER
What was the purpose of the Pulse-Chase experiments?
What cells are the most ideal for this experiment?
How do you prepare the cell of interest?
What was the path found?
What are the 2 methods of analysis?
Identify the paths that proteins take in the cell
Secretory cells e.g from pancreas
Label leucine 3H for 3 mins & wash with cold leucine
3 min in ER, 20 mins golgi, 87 mins plasma membrane & vesicles
- EM autoradiography: image of radioactively labelled proteins
- Cell fractionation: homogenisation & centrifugation & put supernatant on sucrose gradient allowing separation of organelles by density
What are the 5 steps of forward anterograde transport of vesicular trafficking from the ER to golgi?
What about the backwards retrograde transport? What is it mediated by?
- Vesicles build from ER facing the golgi containing secretory proteins & KDEL receptor
- Vesicles gain COPII coat
- Vesicle pinches. off & transported to vesicular tubular cluster
- Coat removed & vesicle fuses with vesicular tubular structure to release secretory proteins its lumen & present receptor onto membrane
- both proteins transported to golgi & golgi stacks (orientation of receptor same)
- Vesicles builds from golgi containing the proteins & gain COPI coat
- Fuse with vesicular tubular cluster where coat is removed
- Then fuses with ER
KDEL receptor- can bring proteins back to ER
How does a vesicle form from the ER?
What is a cargo receptor made of?
How does the vesicle dock with the target membranes?
What is fusion triggered by? What happens?
What happens to the snares after?
What are RAB proteins used for?
Subunits of COPII coat & their assembly mends the membrane outwards. Exit signals on cargo receptors are packaged into transport vesicles when coat assembles
Exit signal, receptor and soluble cargo protein
Coat disassembles. V snares (in transmembrane vesicle) and t snares (on target) need to be correctly matched
GTP-ase (GAP) of Rab-GTP into Rab-GDP causing change of snare proteins & brings vesicle close to target membrane = fusion
disassembled & recycled- v snares need return to ER to be packaged back into vesicles
fusion, coat assembly, vesicle budding, transport & cytoskeleton elements
What happens in the ER & Golgi as well as transport & distribution?
From where does secretion/exocytosis take place?
What are the 2 secretory pathways?
What does exocytosis of secretory vesicles depend on?
Protein & lipid modifications with glycosylation (covalent addition of sugar group)
Golgi apparatus to plasma membrane
- Constitutive (in all cells & causes secretion proteins destined for extracellular matrix)
- Regulated (specific cells, not all time & secretion neurotransmitters from synapse to respond to action potential)
GTPase (GAP) & snare proteins docking & fusion
What is endocytosis?
What is it triggered by?
What happens after?
what is wrong with LDL?
what do statins do?
what is a clathrin coat? What does it require?
How is it different to COPII or COPI?
Transporting material from outside cell to endosomes & lysosomes
binding of LDL to LDL receptors on plasma membrane
- forms a pit & coat is assembled to form vesicle containing receptor & LDL
- vesicle then uncoats & fuses with endosome
- receptor is packed into vesicles & transported back to the membrane
- LDL is transported from endosome to lysosome containing lots hydrolytic enzymes at low pH
- LDL is degraded by enzymes into free cholesterol- released into cytosol & recycled
causes heart disease- mutations in the gene required in endocytosis can cause conditions
increase uptake of LDL to reduce the amt of LDL circulating
coat that covers endocytotic vesicles- requires dynamin (type of GTPase) to pinch vesicle off
requires an enzyme
