CellMembrane;Cytoskeleton
2017-09-29 11:11:22 0 举报AI智能生成
molecular cell biology - cell membrane and cytoskeleton
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cell membrane
semi-permeable
functions
support, hold the shape
protect the cell
organize the chemical activities of cells
structure & composition
membrane lipid
composition
phospholipid
one phosphate group: hydrophilic/polar
head
glycerol: backbone
two fatty acids: hydrophobic/non-polar tail
non-polar interior zone: true barrier that separates the cell from its surroundings
structure
bilayer, fluid-like, planar would close like a bubble spontaneously
cholesterol
inside the lipid bilayer
functions
prevents the hydrocarbon chains from comming together, prevent phospholipids from sticking together
helps maintain membrane fluidity (decrease)
decreases the permeability
holds the membrane together
adds strength to the membrane
membrane protein
structure & composition
integral proteins
permanently embedded in lipid bilayer
transmembrane proteins
integral monotopic/anchored proteins
peripheral proteins
not embedded, temporarily attached either to the lipid bilayer or to integral proteins
functions
transport
enzymatic activity
signal transduction
cell-cell recognition
intercellular joining
attachment to the cytoskeleton and extracellular matrix (ECM)
carbohydrate
functions
recognition of cells
covalently bone
Fluid Mosaic Model
phospholipids in the plasma membrane can move within the bilayer
some proteins in the plasma membrane can drift within the bilayer
proteins move slower than lipids
Membrane Transport
classification
passive transport
simple diffusion
from high concentration to low concentration
no energy required
no transport proteins required
allow non-polar, hydrophobic molecules (e.g. O2, CO2, steroids)
don't allow polar, hydrophilic substances (e.g. water, ions, carbohydrates)
factors
steepness of concentration gradient
steeper, faster
molecular size
smaller, faster
temperature
higher, faster
surface area
larger, faster
faciliated diffusion
from high concentration to low concentration
no energy required
require transport protein
osmosis
diffusion of water
only factor: total solute concentration
from low concentration to high concentration
osmosis terms
tonicity
the ability of a solution to cause a cell to gain or lose water
hypertonic solution
more solute, less water
hypotonic solution
less solute, more water
isotonic solution
equal solute, equal water
active transport
against concentration gradient, from low concentration to high concentration
require energy
require transport protein (highly selective)
bulk flow
types
endocytosis
phagocytosis
"cell eating"
solid particles
not selective
pinocytosis
"cell drinking"
receptor-mediated
highly selective, only bind specific substance (vitamin, hormones...)
exocytosis
export products
put out garbage
transport large particles
require energy
membrane permeability
semi-permeable/selectively permeable
lipid soluble molecules
membrane allows
small uncharged/nonpolar molecules to pass through (macromolecules and charged/polar ones can NOT)
lipid soluble molecules
cytoskeleton
definition (narrow sense): a complex network consisting of interconnected fibrous proteins that extends through the cytoplasm
types
microtubules (MTs)
functions
cell shape maintenance (compression resistance)
directionally intracellular transport
cell division
movement of mitotic spindle and chromosomes
cell mobility
cilia and flagella
fix the position of cell organelles
intracellular signal transduction
structure
hollow tube made of a- and b-tubulin which form heterodimer
microtubule assembly: dynamic instability model
initiated from microtubule-organizing centers (MTOCs)
search and capture during cell polarization and mitosis
phases
nucleation phase
elongation/polymerization phase
steady/equilibrium phase
drugs affect the assembly of MTs (anti-mitotic drugs)
colchicine, vinblastine/vincristin
binding to tubulin dimers, inhibit MTs polymerization
block mitosis
taxol
binding to MTs and stabilize MTs, preventing disassembly
blocks cell division
arrangement
"9+0" arrangement
centrosome
defects & disease
deregulation of centrosome numbers
genome instability
tumor formation
mutations in centrosomal proteins
microcephaly
dwarfism
"9+2" arrangement
cilia
back-and-forth motion
defects & diseases
Kartagener's syndrome
(recurrent respiratory infections)
inability of cilia in the respiratory tract to clear away bacteria or other materials
flagella
snakelike motion
defects & diseases
male sterility
inability of sperm cells to propel themselves via flagella
microfilaments (MFs)
basic unit
actin
structure
twisted double chain of actin protein that forms a solid rod
tension resistent
microfilaments assembly
dynamic equilibrium between the G-actin and polymeric forms
regulated by ATP hydrolysis rate and G-actin concentration
three phases
nucleation phase
elongation phase
steady phase
both ends of the MF grow, but the plus end faster than the minus
because actin monomers tend to add to plus end and leave from minus end
specific drugs affect polymer dynamics
cytochalasin
prevent addition of new monomers to existing MFs, eventually depolymerize
phalloidin
a cyclic peptide from the death cap fungus, blocks the depolymerization of MF
actin-binding proteins
actin polymerization related protein
proflin
promote actin polymerization
thymosin
inhibits actin assembly
microfilament structure related protein
fragmin
filamin
microfilament contraction related protein
myosin
tropomyosin
troponin
microfilament assembly related protein
Arp2/Arp3
initiate assembly of microfilaments
formin
promote assembly
cofilin/ADP
actin depolymerizing factor
functions
maintain cell's shape and enforce plasma membrane
cell migration: amoeboid movement
intracellular transport
cytokinesis
muscle contraction
fertilization
signal transduction
intermediate filaments (IFs)
most abundant, complex and stable component of cytoskeleton
structure
extremely stable (hair, nails, wool)
α-helical rods - assemble into ropelike filaments
assemble from different IF proteins
assemble through several intermediate structures
functions
help create the supportive structure of cell
enhance tension resistance of cell
fix the position of organelles
involved in cell differentiation
involved in intracellular signal transduction
diseases
desminopathy
malfunctions in keratin (skin diseases)
epidermolysis bullosa simplex (EBS)
mutation of human Keratin 14 gene
cells
prokaryotic
(no nucleus)
unicellular
e.g. bacteria
eukaryotic
(has nucleus)
unicellular
e.g. amoeba
multicellular
e.g. human
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