Download The Cell Membrane

The Cell Membrane
*Very thin (7.5-10 nm) *Elastic *Semipermeable
* Dynamic *lipid bilayer *Made of phospholipids,
proteins, CHO& otherlipids
*amphipathic
AP Biology
Phospholipids
Flexibility & selective permeability Phosphate
 Fatty acid tails

hydrophobic
 Phosphate group head

hydrophilic
 Arranged as a bilayer
AP Biology
Fatty acid
Phospholipid bilayer
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
polar
hydrophilic
heads
AP Biology
 Protein:
*Hydrophilic & hydrophobic
*Integral & peripheral
 Cholesterol: permeability & toughness
 CHO: recognition sites & attach cells
Glycoprotein
Glycolipid
together
Cholesterol
Peripheral
protein
AP Biology
Functions of membrane proteins










1- structural ptns
2- passive channels: ungated & gated(voltage / ligand)
3- carriers for facilitated diffusion
4- carriers for active transport (uniport /symport/ antiport)
5- receptors: number & sensitivity change
6- enzymes
7- identity ptns
8-intercellular connections: a. binding j: tight & desmosomes
b. gap j
9- cell adhesion molecules
10- fixation of cytoskeleton
AP Biology
Many Functions of Membrane Proteins
Outside
Plasma
membrane
Inside
AP Biology
Transporter
Enzyme
activity
Cell surface
receptor
Cell surface
identity marker
Cell adhesion
Attachment to the
cytoskeleton
Membrane carbohydrates
 Play a key role in cell-cell recognition

ability of a cell to distinguish one cell
from another
 antigens
important in organ &
tissue development
 basis for rejection of
foreign cells by
immune system

AP Biology
Movement across the
Cell Membrane
AP Biology
2007-2008
Diffusion
 All molecules are in constant motion
 Diffusion

AP Biology
movement from high  low concentration
AP Biology
Facilitated Diffusion
 Diffusion through protein channels


channels move specific molecules across
cell membrane
facilitated = with help
no energy needed
open channel = fast transport
high
low
AP Biology
Facilitated Diffusion
AP Biology
Active Transport
 Against concentration gradient
 Needs carrier protein
 Energy is needed
low
conformational change
ATP
high
AP Biology
“The Doorman”
Active transport
 Many models & mechanisms
ATP
AP Biology
ATP
antiport
symport
Active transport
 1ry active:
*eg Na+/K+ pump
*α &β subunits
*α subunit contains 2 binding sites for K+ on the outside
& 3 binding sites for Na+ on the inside & an ATP
binding site
*β subunit has ATPase activity.
 2ry active:
*eg Glucose transport 2ry to active transport of Na
1st Na pumped out ….creates concentration gradient…
Na & glucose bind a carrier…transports them to inside
AP Biology
Getting through cell membrane
Passive Transport

Simple diffusion
 diffusion of nonpolar, hydrophobic molecules
 lipids
 high  low concentration gradient

Facilitated transport
 diffusion of polar, hydrophilic molecules
 through a protein channel
 high  low concentration gradient
 Active transport

diffusion against concentration gradient
 low  high


uses a protein pump
requires ATP
 Vesicular transport
AP Biology
ATP
Transport summary
simple
diffusion
facilitated
diffusion
active
transport
AP Biology
ATP
How about large molecules?
 Moving large molecules into & out of cell
through vesicles & vacuoles
 endocytosis

 phagocytosis = “cellular eating”
 pinocytosis = “cellular drinking”

AP Biology
exocytosis
exocytosis
Endocytosis
phagocytosis
fuse with
lysosome for
digestion
pinocytosis
non-specific
process
receptor-mediated
endocytosis
triggered by
molecular
signal
AP Biology
Osmosis is diffusion of water
 Diffusion of water from
high concentration of water to
low concentration of water

across a
semi-permeable
membrane

The pressure necessary to stop solvent mol movements=
osmotic pressure
The numbers of particles per unit volume of fluid
Measured in mmHg
Osmole osmolarity osmolality



AP Biology




The osmolarity of ICF=that ECF=300 mosmol
280 mosmol is due to Na, Cl & HCO3
20 mosmol is due to protein
Tonicity: is the osmolality of a solution relative to
the plasma
 Plasma proteins of blood is called oncotic
pressure. It is important for capillary circulation
&regulation of ECF
AP Biology
Concentration of water
 Direction of osmosis is determined by
comparing total solute concentrations

Hypertonic - more solute, less water

Hypotonic - less solute, more water

Isotonic - equal solute, equal water
water
AP Biology
hypotonic
hypertonic
net movement of water
Donnan effect
 The protein anions inside the cells are
non diffusible hinder the diffusion of
diffusible cations
 More osmotically active particles inside
the cell
 The cell tends to swell
 But the Na+/ K+ pump prevents cell
rupture
AP Biology
Any Questions??
AP Biology