Cells and membranes Flashcards
1
Q
Why are membrane compartments important?
A
Cell function an in disease
2
Q
Plasma membrane
A
Maintains cell contents, semi-permeable battier only some molecules can pass
3
Q
Nuclear membranes
A
Contain and organise genome
4
Q
Mitochondria and chloroplasts
A
Localise and facilitate ATP synthesis
5
Q
ER and golgi apparatus
A
Organise glysosylation or proteins, protein modification and sorting
6
Q
Lysosomes
A
Degradation of unwanted contents - intracellular digestion
7
Q
Convex lens
A
Converges parallel beams to focal point
8
Q
What does focal length depend on?
A
Curvature of lens - long and less curved = less magnifiying
9
Q
Concave lens
A
Diverges parallel beams
10
Q
Single lens
A
Enlarged visual image if object is closer than focal point
11
Q
Decreasing focal length…
A
Increases magnification as fatter lens
12
Q
Object further from focal length
A
Real image is formed
13
Q
Objective lens
A
Magnified real image, eye piece lens produces magnified virtual image of real image
14
Q
Bright field microscope
A
Light through specimen - image magnification and focussed on retina
15
Q
Phase contrast
A
Can amplify refractive index differences in cell composition - live cells
16
Q
Fluorescence microscopy
A
Different parts if cell specifically stained using spec dyes of antibodies to individual proteins, attached to fluorescent molecules. These are excited by a wavelength of light which emits light of another wavelength - image magnification focussed on retina/detector. Compare by immunofluorecese - secondary antibody - GFP
17
Q
Confocal microscopy
A
Physical filter e.g. pin-hole prevents out of focus light reacting detector
18
Q
Deconvolution
A
Remove out of focus light in silico
19
Q
Resolution of EM vs LM
A
0.1nm vs 200nm
20
Q
TEM
A
2D projection image of thin specimen. Focuses e- onto specimen, focuses and magnification
21
Q
SEM
A
Surface image of specimen of unlimited thickness - e- emitted or reflected from surfaces - detection = image
22
Q
Resolution
A
The closest 2 objects can be and still be distinguishable - depends on wavelength
23
Q
Non-polar molecules with water
A
No interaction - order on water molecules (thermodynamically unfavourable)
Entropy decreases, but aggregation releases water molecules, increasing entropy = favoured - reduced number of water molecules affected - SA reduced
Cages around non-polar to reduce H bonding = stronger and more stabled
24
Q
Amphipathic molecule
A
No interaction with water - affects H bonds, therefore forced together to reduce water contact
25
Aggregation of lipids
Reduces water order - more aggregation = less water molecules involved per lipid, therefore water n a system is less ordered overall.
26
How can you prove that membrane lipids are highly mobile?
Fluorescent molecules bleach with laser beam, fast recovery as bleached diffuse out and outside bleached area move in
27
Monoglyceride
Fatty acid and C1 on glycerol - mediated by CoA --> di/triglyceride
28
Phosphatidate
Phosphate to C3 (simplest head group) - alcohols may be added
29
How does shape affect reactions?
Different alcohol head groups added with different chem and phys properties. Affects reactions with other molecules, affecting packing in bilayer - fluidity, affects other physical properties e.g. curvature
30
How are kinks formed in fatty acids?
Double bonds - less flexibility
31
How can lipids be more/less packed?
Saturated = less fluid (closer packed) than unsaturated
32
What affects the mpt of FAs?
Saturated = higher mpt as more van der waals and need to disrupt order. Longer = higher mpt and more van der waals stabilising
33
Sphringolipids
Long chain amino alcohol, 2nd HC tail held by amide bond. Fit into membrane like phospholipids but usually saturated strong van der waals - tend to partition.
34
Cholesterol
Amphipathic, small head group, too hydrophobic to form own bilayers, can insert into membrane, interaction with FA tail - heads form "umbrella" stiffens FA tails and thickens membrane - less fluid, introduces order into tail, increasing tight packing but maintaining fluidity
35
Micro domains - lipid rafts
Concentration thicker domains rich in sphingomyelin and cholesterol - rafts thicker than rest of the membrane, proteins long and transmembrane domains partition to rafts, short domains partition to phospholipid contain domains. Recruit proteins with lipid anchors or long TM domains.
36
Single pass transmembrane proteins
Alpha helix most common structural motif
H bonds in backbone stable in membrane - lack of competing water
Side chains mostly uncharged, non-polar
Unusual number of glycine - flexibility
Hydropathy measure of energy need to pass a segment of pp into water from solvent - hydrophobic = energy - measures hydrophobicity
37
Multi-pass transmembrane proteins
Light driven proton pump, H bonding to alpha helix, Gly is rate in alpha helices of soluble proteins, common in alpha helices of trans-membrane domains. Gly allows chain flexibility as it is small - tight packing in multi-pass proteins
38
Functions of integral membrane proteins
Transporters, anchors, receptors, enzymes
39
How to study trans-membrane proteins
Solublisiation - use detergents
Isolation - column chromatography
Characterisation - gel electrophoresis to determine Mr
Functional/structural incorporation into artificial membrane - clone genes/isolate proteins
40
Detergents
Amphipathic - incorporate into membranes at high doc to displace phospholipids. Extract P and lipids. Mild non-ionic maintain functions, ionic detergents denature proteins --> gel electrophoresis. Form micelles at critical micelle conc
41
Simple diffusion
Only gases and small uncharged molecules high --> low. Rate depends in diffusion gradient and hydrophobicity of molecule
42
Osmosis
Semi-permeable membrane allows water, not solutes
Water molecules to equalise water concentration - dilute solute, osmotic pressure = pressure to prevent water flow. Channels also allow flow if water in plasma membrane - isotonic no net flow, hypnotic water in and cell swells, hypertonic water out and shrinks.
43
Uniporter
High --> low e.g. glucose. Faster than diffusion but saturable. Conformational change
44
Symporter
Co-transporter. One against and one with conc grad - energy provided (facilitated) by conformational changes
45
Antiporters
Co-transporter. One against, one with in opposite directions
46
Active transport
Movement against gradient driven by ATP hydrolysis
47
Secreted proteins
Synthesised by ribosomes on ER - mediated by signal sequence at N-terminus, proteins into ER lumen, modified, passed to golgi, further modified, transport
48
Protein synthesis
RNA out of nuclear envelope => ER => golgi => membrane. Chaperones mediate protein folding, disulphide bonds added and oligomerisation occurs
49
Docked ribosomes
Synthesise integral membrane proteins or lumenal proteins. Dock to translocation channel, mediated by signal peptide
50
Type I integral protein
LDL receptor, insulin receptor etc. Single pass, C-terminus on cytosolic side, N-terminus of lumenal side
51
Type II/III synthesis
If internal signal preceded by positive aa side chains. N-terminus of cytosolic side if positive side chains after pos side chains = type 3, C-terminus cytosol
52
Where are proteins glycosylated?
In ER - add polysaccharide => N linked, more Philic, stops aggregation and aids folding, protects from degradation
53
Function of RER
Membrane and secretory protein synth, folds protein in lumen, glycosylates proteins,makes disulphide bridges, checks protein quality, ca2+ store
54
SER
Connects to RER, exit sites for transport vesicles, synthesis of lipids and steroids, abundant in lipid metabolising cells
55
Golgi apparatus
Further glycosylation and protein sorting. Incoming cis-face towards nucleus, outgoing trains-face towards plasma membrane. Flat sac like cisternae, distinct compartments. Secretory proteins move on cis to trans direction. Further glycosylation in each Golgi stack - complex specific polysaccharide
56
Forward traffic
ER => Golgi => plasma memb
57
Retrograde transport
Golgi => Golgi; golgi => ER
58
Endocytosis
Used to internalise certain molecules e.g. nutrients. Used to control cell surface proteins e.g. receptors mediated by clathrin and adapters e.g. LDL particle internalisation, dietary lipids and cholesterol transport in LDL particle => binds LDL receptor => formation of clathrin coat => coated pit/vesicle => endosome => lysosome => mutation LDL causes familial hypercholesterolemia.
59
Cathrin cage
Assembly drives membrane curvature. Vesicle formation involves coating. Endocytosis => clathrin coats - attaches to membrane via adaptor. Drives membrane deformation by assembling into curved cages - form multiple hexametric complexes - triskelions.
60
Intra-cellular vesicle transportation
ER => golgi = COPII; Golgi => ER = COPI Golgi => golgi = COPI
61
Protein through golgi
Cisternal progression
Each golgi stack has a cis-golgi network formed by a fusion of COPII vesicles from ER. Cis-golgi formed when COPI vesicles from cis-golgi stack fuse with cis-golgi networks. Medial-golgi formed COPI fuse cis-golgi network. Trans-golgi => COPI vesicles fuse medial goggle network,
COPII ER => golgi vesicle formation (forward)
COP I golgi => ER vesicle formation (retrograde transportation)
62
+ SNARES (target) and V-SNARES (vesicle)
Target correct compartment and membrane fusion. SNARES also in fusion of vesicle target. V-SNARES to + SNARE tight complex. SNARES unstructured until bound - 4 helix bundle. Z membranes close - fusion
63
Nuclear envelope
Double membrane separating nucleus and cytoplasmic compartments. Nuclear pores mediate - move nuclear proteins => nucleus and mRNA to cytoplasm => transport and transport separation. Nuclear transport receptor mediation - uses internal non-cleaved signal sequences.
64
Purpose of cell cycle
To produce 2 new separate daughter cells from 1 mother cell
65
Phases of cell cycle
G1: Gap 1 - each chromosome has a single chromatid, cell gets ready for DNA replication, varies in time from 0-several years
S-Phase: DNA replication - each duplicated to contain 2 joined chromatids
G2: ago 2 - two chromatids, cell prepares for metaphase and cell division
Mitosis
G0: exit phase - cell leaves cell cycle, needs external signals to re-enter
66
Stages of mitosis
Prophase: centrosomes separate, chromosome condenses, nuclear envelope disassembles, spindle forms, chromosomes attach to spindle
Metaphase: Chromosomes align on spindle equator
Anaphase: Sister chromatids separate and move to poles, organised central spindle disassembles, poles separate, cleavage furrow assembles
Telophase: Cleavage furrow contracts, nuclear envelope reassembles
Cytokinesis: New membrane inserted, acth-myosin contractile ring forms, chromatin condenses, nuclear substructures for,
67
Check points of cell cycle check for...
DNA damage to prevent replication of incorrect sequences
Incomplete replication to ensure only whole chromosomes are pass on
Spindle attachment to ensure correct chromatid separation into daughter cells
68
How are checkpoints controlled?
Controlled by kinases which phosphorylate proteins. - Cyclin dependent kinases (CDKs) are activated by cyclins.
69
G1/S cyclins
Activate CDKs during G1, destroyed at end. Phosphorylate and inactivate proteins that block progression through restriction point, activate synthesis of S-cyclins, S-cyclins activate S-CKDs, S-cyclin/S-CDKs phosphorylate and activate DNA replication proteins, so allow entry to S-phase
70
What level are CDK proteins at throughout the cell cycle?
Constant. Cyclin only present at specific times. CDK only active when appropriate once is present.
71
S-cyclin
Synthesised in G1, destroyed during mitosis.
72
M-cyclin
Synthesised in G2, activated M-CDK phosphorylation of may proteins and triggers massive reorganisation of cell for division. M-cyclin rapidly destroyed at end of metaphase, destruction via unquitination by APC/C with target protein to proteasome, reverses mitotic changes.
