bern & levy Flashcards
cytoskeleton filaments
actin filament
intermediate filament
microtubule
actin filament in muscle cells and other cells
muscle cell: critical component of contractile apparatus
other cells: involved in locomotion..eg. macrophages
Actin makes up core of, and links what?
Microvilli, and links interior of cell to adjacent cells through cell junctions.. eg. zonula adherens and zonula occludens
Intermediate filament types …. simple examples
Several diff types varying by cell. eg. Keratin filament found on epithelial cells, neurofiliaments found in neurons
intermediate filament function
Primarily structural in function.
can link interior of cell to adjacent cells via desmosomes
can link interior of cell to to surrounding extracellular matrix via hemidesmosomes
Microtubule function
Many functions with IN the cell:
- IC transport of vesicles e.g. neurotransmitters
- Chromosome movement during mitosis and meiosis
- Movement of cilia and flagella e.g. tail of spermatozoa
Microtubule formed from
alpha and beta tubulin dimers
microtubule formation
its organizing center exists near the cell’s nucleus, microtubles grow out from this center toward periphery
Microtubules use what motor proteins and how do they work
Kinesin: drives transport from center toward periphery
Dynein: opposite
Dynein is the motor protein that drives the movement of both cilia and flagella.
Plasma membrane important functions… 6
- Selective transport of molecules in and out ( a function carried out by membrane transport proteins)
- cell recognition via surface antigens
- cell communication through NT and hormone receptors and signal transduction pathways
- tissue organization, temporary or permanent cell junctions, as well as interaction with EC matrix
- enzymatic activity
- determination of cell shape by linking cytoskeleton to plasma membrane
lipids and proteins can diffuse withIN
the plane of the membrane
the major lipids of the plasma membrane are
Phospholipids and phosphoglycerides
majority of membrane phospholipids have what backbone
glycerol
except sphingomyelin
Common alcohols are ?
Choline ethanolamine serine inositol glycerol
sphingomyelin ( an important phospholipid ) has what as its backbone
it has the amino alcohol sphingosine as its back bone instead of glycerol
phospholipids that are predominantly in the outer leaflet
phosphatidylcholine
sphingomyelin
phospholipids that are predominantly in the inner leaflet
Phosphatidylethanolamine
phosphatidylserine
phosphatidylinositol
Cholesterol- critical lipid component of bilayer
Found in both leaflets, stabilizes membrane at normal body temp ( 37c)
-it can represent as much as 50% of lipids found in membrane
Glycolipid- minor component of bilayer
GPI plays an important role in anchoring proteins to the outer leaflet of the membrane
Cholesterol, glycolipids, phospholipids are
amphipathic
The presence of unsaturated fatty acyl chains in phospholipids and glycolipids will do what to membrane fluidity
increase
lipids that aggregate e.g sphingomyelin and cholesterol form what
lipid raft
Lipid rafts function
different functions, important one being to segregate signaling mechanisms and molecules.
Remember, lipid rafts often have specific proteins associated with them and diffuse in the plane of the membrane as a discrete unit
membrane proteins
As much as 50% of the membrane is composed of proteins
membrane proteins classified into 3 types
integral
lipid anchored
peripheral
Integral membrane protein
Besides the obvious that they are embedded in the lipid bi layer.
they are embedded where hydrophobic amino acid residues are associated with the hydrophobic fatty acyl chains of the membrane lipids
integral membrane protein info
many span the bilayer and are termed Transmembrane proteins, Thus they (transmembrane proteins) must have hydrophilic and hydrophobic region
Transmembrane proteins hydrophobic/philic regions
hydrophobic region often in form of alpha helix with hydrophobic A.A. facing out and spaning the membrane
hydrophilic A.A. residues are then exposed to aqueous environment on either side of the membrane
Proteins can also be attached to the membrane via lipid anchors
Protein is covalently attached to a lipid molecule which is then embedded in one leaflet of the bilayer
Proteins can be attached to outter leaflet e.g. GPI and inner leaflet by?
Proteins can be attached to inner leaflet via their N-terminus by fatty acids e.g. palmitate or via their C terminus by prenyl anchors
Peripheral proteins
May associate with the polar head groups of the membrane lipids or lipid-anchored proteins.
ICF and ECF are composed primarily of ?
H2O in which solutes (e.g. ions, glucose, A.A.) are dissolved.
Amount of H20 that can enter or leave the cell via AQPs can be regulated by ?
Altering the # of AQPs in the membrane, OR by changing the permeability ( i.e. gating).
-changes in pH have been indentifies as one factor that can modulate the permeability of AQPs.
Ion channels
found in all cells, especially important in excitable cells e.g. neurons and muscle cells
Ion channel selectivity
can be highly selective- only letting one specific ion pass
or non selective-allow all or a group of ions pass. e.g. cations or anions
Ion channel conductance
- another way to characterize ion channels
- expressed in picosiemens (pS)
- For some channels conductance varies depending on which direction the ion is moving.
e. g. if the channel has greater conductance when ions are moving into the cell versus out of the cell, the channel is said to be an inward rectifier.
Ion channels can be classified by what 3 ways?
Selectivity
conductance
mechanism of gating `
Ion channels mechanism of gating
the fluctuate between an open or closed state (gating)
Factors that can control gating:
- membrane voltage
- extracellular agonist/antagonist
e. g. acetylcholine is an EC agonist - intracellular messengers
e. g. Ca2+, ATP, cGMP - mechanical stretch of the plasma membrane
Transmembrane ion flux can be regulated by?
Changing # of ion channels in membrane or by gating the channels
Solute carriers
Represent a large number of membrane transporters
They are divided into 3 major functional groups:
- Uniporters e.g. GLUT2
- Symporters (co-transport)
- Antiporter (exchangers, counter transporter)
ATP dependent transporters
ATPase ion transporter
ATP-binding cassette transporters (ABC-transporters)
ATPase transporters sub types
P-type ATPase: being phosphorylated during the transport cycle e.g. N/K ATPase
V-type ATPase: e.g. H+ ATPase is found in the membranes of several intracellular organels ( e.g. endosomes, lysosomes)
ABC trasporters found in
both prokaryotic and eukaryotic cells and share a common feature of having A.A. domains that bind ATP
7 sub groups
transport diverse group of molecules/ ions, including Cl-, Cholesterol, Bile acids, Drugs, Iron, and Organic anions.
Na/K ATPase
has 3 subunits:
- Alpha
- Beta
- Gamma
the 3 types of endocytosis
pinocytosis
phagocytosis
receptor-mediated endocytosis
Endocytosis involves a number of accessory proteins including…
(in order)
adaptin, clathrin, and the GTPase dynamin
Exocytosis can be either
constitutive or regulated
constitutive e.g. plasma cells secreting immunoglobin or fibroblast secreting collagen
regulated occurs in endocrine cells, neurons, exocrine glands (pancreatic acinar cells)
exocrine cells secretory product is
after synthesis and processing is stored in secretory granules until a signal is received to be released
-signal may be hormonal or neural
Fusion of secretory vescile/granule is mediated by
a nummber of accessory proteins
-one important one being SNARE’s (membrane proteins help target the vesicle to the plasma membrane, process of secretion usually triggered by an increase in Ca2+
Receptor mediated endocytosis
- a receptor on the surface of the cell binds to the ligand– clathrin coated pit is formed with adaptin linking the receptor molecules to the clathrin.
- Dynamin a GTPase, assist the separation of the endocytic vesicle from the membrane
Diffusion
a random process driven by the thermal motion of the molecules
Fick’s first law of diffusion
rate at which a molecule diffuses from point A to point B
diffusion coefficient takes into account
The thermal energy of the molecule, size, and viscocity of the medium through which the diffusion is taking place.
diffusion coefficient for spherical molecule
it is approximated with the stokes einstein equation
