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CellMembrane;Cytoskeleton

2017-09-29 11:11:22   0  举报

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molecular cell biology - cell membrane and cytoskeleton

biology

medical

Biomedical

biochemistry

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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

<br>

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

<p>allow non-polar, hydrophobic molecules (e.g. O2, CO2, steroids)</p><div><p>don't allow polar, hydrophilic substances (e.g. water, ions, carbohydrates)</p></div>

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

<font color="#c41230">diffusion of water</font>

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 <b>cytoplasm</b>

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: <i><b><font color="rgba(0, 0, 0, 0)">dynamic instability model</font></b></i><br>

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<div>(recurrent respiratory infections)</div>

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

<font color="#c41230">actin</font>

structure

<font color="#c41230">twisted double chain</font> 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<div>because actin monomers tend to add to plus end and leave from minus end</div>

<br>

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)

<span style="font-family: 'Comic Sans MS';">α-helical rods - assemble into ropelike filaments</span>

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)<div>mutation of human Keratin 14 gene</div>

cells

prokaryotic<div>(no nucleus)</div>

unicellular

e.g. bacteria

eukaryotic<div>(has nucleus)</div>

unicellular

e.g. amoeba

multicellular

e.g. human

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