CELLS Flashcards
What’s a chimera?
having parts of different origins
e.g. a eukaryotic cell
What’s an endosymbiont?
organisms forming symbiotic relationships with another cell/organism
2 types of endosymbiont
intracellular
extracellular
what’s a plastid?
membrane-bound organelle
How are phylogenetic trees formed?
inferred from nucleotide/ amino acid sequence data
most common phylogenetic marker
small sub-unit ribosomal RNA (SSUrRNA)
ARCHEZOA hypothesis
eukaryogenesis involving exogenous origins of mitochondrion via phagocytosis of an alphaproteobacterium to form mitochondrion
remnant genome of mitochondria
*what does it encode
rRNA and protein-coding genes
2 rRNA’s (12S and 16S)
22 tRNA’s
13 essential genes
*encodes sub-units for oxidative phosphorylation enzyme complexes
origins of ER
Endogenous
gram-negative bacteria
don’t retain crystal-violet stain
- double membrane systems
chloroplast exogenous origin
cyano bacteria
plasma membrane functions
- enclose cell content/ separate from environment
- maintain concentrations of cell substances
- communication w environment/other cells
- barrier
- cell growth/ shape change/ movement/ division
cytosol function
protein synthesis/ metabolic pathways
endoplasmic reticulum
lipid synthesis/ protein synthesis
golgi apparatus function
modification/sorting/packaging of proteins/ lipids
endosome function
sorting of endocytosed material
plasma membrane sub-unit
* polarity of parts
phospholipid
- hydrophilic phosphate head
hydrophobic fatty acid tails
* amphiphilic!
cholesterol effect on PM
decreases membrane permeability to small/ water-soluble molecules
prevent crystallization
4 phospholipids in plasma membrane
phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin
function of glycolipid asymmetry
extracellular to intracellular signal conversion
charge differences
binding sites
live and dead cell distuinguishment
sugar group addition
self-association of glycolipids
H-bonds from sugars / Van der Waals between hydrocarbon chains
oligosaccharides charge and function
net negative charge
alters electric field and ion concentrations
lectins
carb binding proteins
bind to sugar groups on other glycolipids/ glycoproteins
how is the PM fluid
rapid lateral diffusion
flexible hydrocarbon chains
flippases catalyzing movement
cis-double bonds create kinks in fatty acid tail/ shorter tail lengths
temp effect on cis bonds
more cis bonds as temp drops
types of membrane proteins
integral
peripheral
lipid attached
when are integral proteins released?
when detergents dissolve PM
where are lipid-attached proteins made?
ER
prior to cleaving and GPI anchor added via vesicle
when are peripheral proteins released?
when protein-protein interaction disrupting agents arrive
functions of membrane proteins
transporters
linkers
receptors
catalysis
how are transmembrane domains identified?
bioinformatic analysis ‘in silico’
glycocalyx components
glycoproteins/ glycolipids
glycocalyx function
protect cell chemically, physically, biologically
adhesion
recognition
storage
affect health and disease
glycoprotein links
N-linked
O-linked
proteoglycans
N-glycans
asparagine-linked
O-linked
serine/threonine-linked
proteoglycans
glycoproteins w GAGs
polysaccharide chains covalently linked to a protein core> GPI anchor
GAG
glycosaminoglycans
ruthenium red
stains carbohydrate layer of glycocalyx
detergents
small, amphiphilic molecules of variable structure
(more soluble than lipids)
detergent behaviour
aggregate to form micelles/ rapidly diffuse in/out
affected by temp, pH and salt conc
displace lipid molecules
affect crystallization/purification
tpes of membrane diffusion
rotational
lateral
how are PM diffusion rates measured
FRAP
fluorescence recovery after photobleaching
FRAP process
- mark membrane protein w fluorescent group
- fluoresecnce group bleached w laser beam
- time for diffusion measured and diffusion coefficient measured
disadvantages of FRAP
can’t follow individual protein molecules
cortical cytoskeleton
spectrin meshwork maintaining integrity and shape of PM
*anaemia doesn’t have
cell cortex
actin filaments attached to PM
cell cortex functions
cell movement
endocytosis
filopedia production
restricts free diffusion of proteins
types of active transport
coupled
ATP-driven
light/redox driven
membrane-bending protein function
deforms bilayers
(dynamic control of membrane shape)
membrane-bending protein mechanisms
insertion of hydrophobic protein domains/ lipid anchors
rigid scaffold formation
clustering of specific membrane lipids
selectivity filter
narrowest region of gated ion channel, limiting rate of passage
types of gated ion channels
voltage-gated
ligand-gated extracellular
ligand-gated intracellular
mechanically gated
Vmax in relation to gated membrane carriers
rate at which carrier can flip between conformational states
Km
concentration of solute when rate of transport is half the maximum value
location of nuclear localization signal
at N-terminal end and cleaved after synthesis
functions of nuclear pores in envelope
small molecule diffusion
dynamic in/out movement
export mRNA/ribosome components
import structural proteins and gene transcription/ regulation proteins
SV40 virus nuclear localization signal
mutation means short sequence is lacking (Thre replacing Lys)
nuclear localization signal function
responsible for selectivity of active nuclear import processes
how is nuclear localization regulated?
regulated by turning signals on/off via phosphorylation of amino acids close to signal sequences
transcription regulator mechanisms
bound to cytosolic proteins either anchored via cytoskeleton/ mask nuclear localization signal
gene released by stimuli
NF-AT
nuclear factor of activated T-cells
what is NF-AT
transcription regulatory protein in cytosol
phosphorylated state
what are T-cells activated by in NF-AT?
foreign antigen
calcium ion concentration increase
T cell nuclear activation mechanism
Reacting to the increase in calcium ion concentration, protein phosphatase binds to NF-AT, dephosphorylates and exposes nuclear import signals/ blocks export signal
what happens to the NF-AT once in the nucleus ?
activates gene txn of genes required for T-cell activation
Use of NF-AT pharmaceutically
used in immunosuppressive drugs when inhibited to block T-cell activation
How is the NF-AT response stopped?
Ca2+ concentration decreases
NA-FT released from calcineurin
re-phosphorylation inactivates import signals and exposes export
3 types of cytoskeleton
actin
microtubules
intermediate filaments
actin in plasma membrane
thin, flexible stress fibres
maintains cell shape
aids surface movement
6-8nm
requires ATP to build
regulates binding protein
actin in cytoplasm
polar, flexible filaments in cortex, found in bundles
dynamic polymerisation/ depolymerisation
microtubules structure/ location/ formation
25nm diameter tubes
made up of tubulins, requiring GTP to build up
grow from centrosome
microtubules function
motor proteins
intracellular movement
chr movement in cell division
organelle/vesicle shuttling
breakdown mitotic spindle
intermediate filaments structure
10nm diamter
alpha-helical coiled coil
assembly regulated by phosphorylation
staggered tetramer = 1 filament
intermediate filament functions
mechanical strength
flexible
excess stress prevention
tensile force distribution
actin functions
cell motility
contraction/ adhesion/ mechanosensation
actin formation
G-actin monomers added to either end (more rapidly at+)
ATP hydrolysis fuels polymerisation
actin-binding proteins regulate assembly
villi
non-motile actin filaments increasing SA for absorption
microtubule assembly
dimers of alpha (-) and beta (+) tubulin formed up of 13 protofilaments via GTP
kinesins
motor proteins w head/tail regions
globular
bind ATP
tails bind cargo
dyneins
drive cilia/ flagella
9+2 microtubule arrangement
bends structure via microtubule sliding
cilia
motile
numerous/ short
aid locomotion
microtubules
flagella
few/ long
aid cell locomotion
microtubules
intermediate filaments in the nucleus
nuclear lamins (inner membrane meshwork) act as chr/nuclear pore anchorage sites
strong > coiled fibrillar protein-packing
cytoplasmic intermediate filaments
keratins in epithelia
vimentin/ vimentin-related tissue
neurofilaments
N-/C- terminal domains vary in size
examples of vimentin
connective tissue, muscle cells, neuroglial cells
nuclear lamins
LMNA/LMNB/LMNC
fibrous meshwork of inner nuclear envelope
provide structural support
cell division breakdown
keratin
structural/ mechanical strength in cytoplasm
indirect connection via desmosomes
myosin I
all cells
head/tail
intracellular organization
moves cargo along actin
myosin II
muscle cells
dimer
filaments
contractile
spectrin
inner plasma membrane
provides mech strength/ stability/ shape
link membranes
motor proteins / filament systems
RBC membranes
interphase
normal functions
DNA replication for 2 identical chromatids
S phase
G1
cells produce RNA, enzymes and growth proteins
main growth
checkpoint
G2
cell growth
errors corrected
tubulin increase
checkpoint
early prophase
centrosomes replicated prior
chromatin coils
late prophase
centrosomes to opposite nuclear ends
nucleolus dissapears
2 chromatids appear
metaphase
centrosome reaches pole
spindles appear
chromosomes line along equator via centromeres
anaphase
chromosomes to opposite poles
telophase
nuclear envelope/ nucleolus reformation
spindle breakdown
cytokinesis
chromosomes uncoil
Meiosis 1 middle prophase I
synapsis to form bivalents
centrosomes to opp nuclear ends
Meiosis 1 late prophase I
nuclear envelope breakdown
crossing over
nucleolus disappears
Meiosis I metaphase 1
bivalent alignment
spindle forms
Meiosis 1 anaphase 1
whole chr movement to poles
Meiosis I telophase I
nuclear envelope/ nucleolus reformation
cytokinesis
meiosis II
mitosis behaviour
somatic
non-reproductive cells
2 phases of prokaryotic division
replication
division (binary fission)
4 phases of eukaryotic division
M
G1
G2
S
G1 checkpoint
assesses size
environment favorability
DNA damage
space availability
G2 checkpoint
assesses DNA replication
correct DNA
cell size
environment availability
M checkpoint
assesses whether spindles are attached to centromeres
CdK
cyclin dependent kinases
cyclin-dependent kinases
require cyclins to activate
add phosphate from ATP to amino acid in protein
differ and destroyed at different checkpoints
quiescent state
G0/pause
maintenance period
reversible/ irreversible depending on cell type
PDGF
platelet-derived growth factor
FGF
Fibroblast growth factor
EGF
epidermal growth factor
growth factor concentration
10^-10 M
where are growth factors found/ recognised
found in serum
receptors in PM
apoptosis
cell shrinks
nuclear fragmentation
apoptotic bodies digested/ recycled
necrosis
accidental cell death due to physical/chemical injury
necrosis process
cell/ nucleus swells leading to leakage
cell lysis
triggers inflammatory response
2 types of apoptosis triggers
physiological
pathogenic
physiological activation of apoptosis
used in embryonic development, removing/remodelling tissues
homeostasis maintenance
cell number control
pathogenic activation
viral infection
heat shock
toxins
cytotoxic T cells
stressed/damaged cell removal
apoptosis activators
hormonal signals
cell signalling
apoptosis suppressors
survival factors
extracellular matrix contact
consequences of apoptosis
P53 activation
mitochondria leak
caspase activation
caspase
enzyme, when activated, cleaving nuclear lamins, activating DNAase, cleaving cytoskeleton
leaves apoptotic bodies
what happens when the cytoskeleton is cleaved?
cells detach from neighbours and lose contact with ECM
p53 weight
53KDa
p53
transcription factor acting as tumour suppressor
DNA damage mechanism
- damage activates p53
- p53 blocks progression of cell cycle at G1 checkpoint
- mitochondrial membrane rupture > cytochrome C leaks between inner/outer membrane
- cytochrome C in cytosol activates caspases which activate DNAase to cleave lamins and cytoskeletons
- apoptosis
