Holy Cell Biology Flashcards
Week 2
What are glycolipids important for?
cell recognition and adhesion
In which leaflet are almost all phosphatidylethanolamine and phosphatidylserine located?
cytoplasmic leaflet
In which leaflet are phosphatidylcholine and sphingomyelin mostly found?
non cytosolic leaflet
Where is the glycocalyx and what is it used for?
inside lumen or outside cell, used for protection, identification, and adhesion
What are the main functions of the RER and SER?
RER: synthesize proteins, synthesize lipids
SER: synthesize lipids, metabolize and detoxify, regulate Ca2+
Where is N-linked glycosylation done?
In ER, sugar is attached to asparagine
What complex helps transport misfolded proteins into lumen for degradation?
sec61 translocator complex
What is cytochrome p450 used for in the SER?
detoxification
What are the cis and trans face of the Golgi body?
cis = entry trans = exit
Where does O-linked glycosylation occur?
Golgi- adds oligosaccharides to proteoglycans
What 3 places does Golgi direct transport to?
lysosomes, secretory vesicles, plasma membrane
Where does Mannose-6 phosphate target to?
lysosomes, from golgi
What are lysosomes used for?
Digestive organelles filled with hydrolytic enzymes, pH about 5 (by proton pumps)
What does mitochondrial release of cytochrome C cause?
cell death
Where to mitochondrial localization sequences TOM, TIM, and OXA direct things?
TOM= to outer mito membrane TIM = to inner mito membrane OXA = out of mito matrix
What are peroxisomes?
single membrane bound organelles, do oxidation reactions, produce and decompose H2O2
How are microfilaments formed?
actin polymerization happens at + end
- hydrolyzes ATP to ADP and becomes unstable
- alpha beta actin dimers
What do the Rho proteins (Rac, Rho, CDC42) do to actin?
Overall actin organization:
Rac- promotes gel like network, cell cortex
Rho- stress fibers, contractile bundle
CDC42- promotes tight parallel bundle
What are type 1 and type 2 myosin?
type 1 = short tail, can’t form filaments
type 2 = long tail, can form filaments (thick filaments)
What are microtubules?
heterodimers of alpha and beta tubulin
- organize cytoplasm and intracellular transport
- responsible for sperm mobility (flagella)
- start with gamma tubulin at centrosome
- grows - end to + end (also GTP to GDP decreases stability)
What does the drug taxol do?
stabilizes microtubules, arrests cells in metaphase and results in cell death
-chemo drug for cancer (inhibits tubulin depolymerization)
What do the 2 motor MAPs (microtubule associated proteins) dyneins and kinesins do?
Dyneins- move things toward MT - end
kinesins- move things toward MT + end
What does the drug colchicine do?
inhibits tubulin polymerization
What are intermediate filaments?
middle size, in both cytoplasm and nucleus
- strengthen cytoplasm, nucleus, and cell to cell EC junctions
- proteins are linear (rick in alpha helices)
- 2 ends are structurally similiar
How does phosphorylation affect intermediate filament growth?
low phosphorylation promotes polymerization
high levels phosphorylation promotes depolymerization
What are sites of ribosomal RNA transcription and ribosomal unit assembly called?
nucleoli
What is clathrin used for?
involved in endocytosis, assembles to form cage-like structures to deform membrane and begin vesicle formation
- forms coated vesicles
- Golgi to endosomes/ lysosomes
What does the early endosome do?
receives pinocytotic vesicles
What does the late endosome do?
located deeper in cytoplasm, digests internalized material
Endosomes are formed from the fusion of..
vesicles from Golgi with hydrolytic enzymes and vesicles containing endocytosed cargo
What does KDEL do?
identifies proteins that should stay in ER or come back to ER from Golgi
What do coat proteins COP1 and COP2 do?
COP 2- coats ER vesicles that fuse with cis Golgi
COP 1- coat Golgi vesicles that fuse with ER
What do SNARE proteins do?
help fuse PM of vesicle and correct target. V-SNARES on vesicle membrane correspond with t-SNARES on target organelle membrane
What does cholesterol do in membranes?
inhibits phase transitions
What are the 3 important lipids in membranes?
phospholipids, cholesterol, glycolipids
Where are phosphoglycerides synthesized?
ER
Where is sphingomyelin made?
Golgi apparatus
Where are glycolipids made?
From sphingosine in Golgi apparatus
What is the difference between flippases and scramblases?
flippases flip specific phospholipids between leaflets and scramblases are not specific
What are lipid rafts?
specialized patches of lipids and proteins, asymmetry in PM, active in cell functioning and endocytosis
What do cadherins do?
bind to proteins on adjacent cells, held together by calcium
What are proteoglycans?
special class of very heavily glycosylated proteins
- sugar chains are glycosaminoglycan (GAG) chains (repeating disaccharide units that are highly charged by sulfate (neg) groups)
- O linked glycosylation
What does accumulation of misfolded proteins trigger?
heat shock response (increased expression of chaperone proteins in cytoplasm)
Where are phospholipids and cholesterol synthesized?
ER, active sites face cytoplasm but scramplases equilibrilate lipids between leaflets
What is familial hypercholesterolemia (FH)?
deficit in an endocytotic pathway, cells don’t take up enough LDL from blood
-macrophages take up LDL and cause plaques
What do GEF enzymes do?
convert GDP to GTP
What are the 3 paths to lysosomes?
autophagy, phagocytosis, endocytosis
What integral membrane protein is found in many uncoated vesicles?
caveolin
what are peroxisomes used for?
detoxification reactions (ethanol to acetaldehyde), beta oxidation of FAs, formation of myelin phospholipids
How are proteins destined for the nucleus targeted?
nuclear localization signal (NLS) which is a short region of AAs
How is directionality of transport directed for nucleus?
Imported proteins: bind import receptors with GDP bound and dissociate in presence of GTP
Exported proteins: bind export receptors in presence of GTP and dissociate in presence of GDP
What are Ran proteins?
G proteins that facilitate nuclear transport, Ran-GEF is concentrated in nucleus to make more Ran-GTP there
What are the main functions of microfilaments?
support/ organize PM, cell shape, cell division, cell motility
What are the main functions of microtubules?
organize cytoplasm, intracellular transport, cell division, cilia/flagella motility
What are the main functions of intermediate filaments?
strengthen cytoplasm, support nucleus, epidermal appendages (hair and nails)- keratin
What is the power stroke in contraction?
dissociation of ADP (not the hydrolysis step)
What does integrin do?
links to EC matrix and provides traction to moving cell
What is the centrosome?
- a pair of centrioles and pericentriolar material
- used for microtubule nucleation and organization
