Intro to the Cell and Cell Membrane Flashcards
more integral membrane proteins are associated with the E or P face?
E = external face
P = protoplasmic/cytoplasmic face
more integral membrane proteins associated with P face, stabilized by cytoskeleton
hereditary spherocytosis
mutations in spectrins - cytoskeleton proteins that associate with membrane proteins to stabilize biconcave shape of erythrocytes
characterized by spherical RBCs, more susceptible to destruction in spleen
how is the plasma membrane of enterocytes in the brush border modified
tall, columnar - to increase surface area for nutrient absorption
micorvilli increase absorption as well (extend from apical surface)
glycocalyx
carbohydrate layer of eukaryotic cells
contains transmembrane glycoproteins, membrane glycolipids, proteoglycans
the main structural protein in microvilli is ____, which extends downward to terminate at _____ at apical surface of cell
actin, terminates at terminal web
[microvilli also contain myosin motor protein to move material along actin filament]
what are the 4 types of specializations of junctional complexes
- tight/occluding junctions (zonula occludens)
- belt desmosomes (zonula adherens)
- spot desmosomes (macula adherens)
- gap (communicating) junctions
what are microtubules composed of and how does this contribute to how they work
alpha-beta diametric tubulin molecules that assemble/disassemble into cylindrical structures
[form centrioles, cilia, mitotic spindle, cytoskeleton]
site of protein and lipid synthesis and calcium storage in cell
endoplasmic reticulum:
-SER (agranular): lipid and steroid biosynthesis, calcium storage, detoxification
-RER (granular): ribosomes for protein synthesis (secretory)
where are secretory proteins sent after they are made in RER
golgi apparatus for sorting
vesicles are usually used to transport material between Golgi cisternae (flattened sacs of membrane)
cis golgi is directed towards RER (proteins enter here)
trans golgi is directed towards secretory granules and peripheral cytoplasm (proteins leave here)
constitutive vs regulated secretion (all together makes exocitosis)
constitutive secretion: continual secretion of proteins that are not stored
regulated secretion: initiated by external stimulus, fusion of granules with cell surface to release contents
internalized vesicles fuse with the ____
early endosome - receptors and ligands are separated, receptors recycled to the surface
nutrients are routed to the lysosome and released from carrier proteins to become available
inner membrane of mitochondria is folded into ___
cristae
more cristae = higher energy need
most mitochondrial proteins are encoded by ___
nuclear DNA
enter from cytosol, not RER/golgi
site of intracelular digestion
lysosomes: contain hydrolytic enzymes that become active at acidic pH
ATP-driven proton pump in lysosomal membrane maintains pH
degrade external molecules, worn-out organelles, entire cells following phagocytosis
hydrogen peroxide metabolism and fatty acid metabolism occurs in what part of the cell
peroxisome
have high enzyme concentrations, so have dense material in matrix that forms crystalline core
what are the 4 classes of membrane lipids
- phosphoglycerides: derived from 3C glycerol and 2 fatty acid chains attached (3 subtypes)
- sphingolipids
- glycolipids: sphingosine backbone with carbohydrate
- sterols (primarily cholesterol)
basic structure of phosphoglycerides
2 or 3C of glycerol backbone + fatty acid chains
one chain usually non-saturated —> has kink that inhibits dense packaging (—> increases fluidity)
remaining hydroxyl attached to phosphate and one of 3 major head groups (at head of structure)
what are 3 major phosphoglyceride subtypes
- phosphatidyl-ethanolamine
- phoshatidyl-serine (NEG charge)
- phosphatidyl-choline
structure of sphingomyelin (major sphingolipid of PM)
sphingosine with fatty acid tail and phosphotidylcholine attached
structure of cholesterol
polar sterol, contains:
-polar OH near membrane surface in both leaflets
-rigid sterol ring (stiffens membrane)
-aliphatic region keeps FA chains of phospholipids apart
what type of glycolipid is charged
ganglioside
(GM1 ganglioside mediates entry of cholera toxin)
structure of glycolipids
sphingosine + sugar (instead of phosphate)
asymmetric - sugar on external PM surface only
ganglioside class is charged
why is cholesterol absent from bacteria and plants?
bacteria and plants have cell walls - don’t need it
cholesterol takes on the role of cell wall in eukaryotes in a way by providing structural rigidity around it
(note that cholesterol doesn’t show leaflet asymmetry - evenly distributed)
these areas of non-random lipid distribution can occur within inner or outer PM leaflet. They have a thicker structure (longer hydrophobic chains) and can sequester subsets of membrane proteins to segregate function. what are?
lipid raft
phosphatidyl serine imparts a __ charge to internal face of PM
negative
describe the ability of each of these to pass through PM:
a. hydrophobic molecules
b. small uncharged polar
c. large uncharged polar
d. ions
a. hydrophobic (O2, CO2, N2, steroids) —> YES
b. small uncharged polar (H2O, urea, glycerol) —> some
c. large uncharged polar (glucose, sucrose) —> less
d. ions —> NO
what are the 3 types of ion transporters and their characteristics
- pump: specific enzymes, against gradient (ATP required)
- carrier: downhill gradient, passive transports, conformational change
- channel: ion specific pore, downhill gradient, open/close in regulated manner
very important in intestinal epithelial, kidney epithelial, nerve
what do tetrodotoxin and lidocaine both do
sodium channel blockers
tetrodotoxin (puffer fish) - causes paralysis
lidocaine - anesthetic to treat tachycardia
what does curare do
blocks Na/K ion channel by competitively antagonizing nicotinic Ach receptors at neuromuscular junction
causes paralysis
Glut1 glucose transporter is an example of:
a. uniporter
b. symporter
c. antiporter
Glut1 is uniporter - transport rate depends on concentration gradient, binding affinity (Km), flipping rate (Vmax)
conformational change dumps glucose to other side quicker than diffusion
(transporters follow enzyme kinetics)
in the Na+/glucose symporter, which molecule is moving against its concentration gradient
binding of Na+ increases affinity of symporter for glucose. Both Na+ and glucose sites need to be occupied for conformational change
glucose moves against gradient without direct energy expenditure
glucose transport from digestive system through epithelial cells uses 2 glucose transporters:
first step: symporter with Na+ (sodium moving down gradient, glucose against) - at lumen of GI tract (apical surface)
second step: uniporter (glucose goes down gradient) - at basal domain of cell
-Na+/K+ pump compensates for increased sodium that is not leaving with glucose this side
key here is there is high glucose concentration in the brush border cells
two types of transporter pumps (active transport)
- P-type pump: auto-phosphorylation using ATP, conformational change follows
- ABC transporter - pump small molecules (not ions, usually), also use ATP
what kind of transporter pump is Ca2+ ATPase
P (phosphorylation) type pump:
- Ca2+ concentration in ER needs to be re-established after muscle contraction
- Ca2+ binds non-phosphorylated pump
- ATP binds and auto-phosphorylation occurs
- conformational change opens channel to lumen of SR (muscle’s ER)
what kind of pump transporter is Na+/K+ ATPase
P-type (phosphorylation)
both Na+ and K+ go against concentration gradient
- THREE Na+ binds inside cell
- auto phosphorylation and conformational change
- Na+ released outside
- dephosphorylation and another conformational change
- TWO K+ released into cell
mechanism of ABC transport pumps
ATP Binding Cassettes:
- two ATPase domains on each protein, small molecules bind to non-ATP bound state
- ATP binds, dimerization
- confirmation change and release
- ATP hydrolysis for another round
bacterial ABC import, eukaryotic ABC export (euk = export)
multiple drug resistance (MDR) in tumor cells arises from high levels of one type of ____ transporter
ABC
consequence is more hydrophobic drug is cleared from cytoplasm
how does malaria develop chloroquine resistance
amplified levels of ABC transporter pump drug out
what kind of pump transporter is CFTR
ABC transporter - exception example when ABC transports ion, not small molecules
where in the plasma membrane are spingolipids and phosphotidyl choline found
glycolipids found in outer leaflet
what is the most specific transporter, and what is the most rapid?
most specific - pump
most rapid - channel
(carriers are intermediate in both categories)
lipid rafts are composed mostly of ____
cholesterol and sphingomyelin
major digestive organelle
lysosome
