Post on 30-May-2018
transcript
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 1/36
Copyright 2009 John Wiley & Sons, Inc.
Cell membrane physiology
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 2/36
Copyright 2009 John Wiley & Sons, Inc.
A Generalized Cell
1. Plasma membrane
- forms the cell¶s outer boundary
- separates the cell¶s internal environmentfrom the outside environment
- is a selective barrier
- plays a role in cellular communication
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 3/36
Copyright 2009 John Wiley & Sons, Inc.
A Generalized Cell
2. Cytoplasm
- all the cellular contents between the plasma
membrane and the nucleus- cytosol - the fluid portion, mostly water
- organelles - subcellular structures having
characteristic shapes and specific functions
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 4/36
Copyright 2009 John Wiley & Sons, Inc.
A Generalized Cell
3. Nucleus
- large organelle that contains DNA
- contains chromosomes, each of whichconsists of a single molecule of DNA and
associated proteins
- a chromosome contains thousands of hereditary units called genes
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 5/36
Copyright 2009 John Wiley & Sons, Inc.
Fig. 3.1 Generalized Body Cell
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 6/36
Copyright 2009 John Wiley & Sons, Inc.
Plasma Membrane
Flexible yet sturdy barrier
The fluid mosaic model - the arrangement of
molecules within the membrane resembles asea of lipids containing many types of
proteins
The lipids act as a barrier to certain
substances The proteins act as ³gatekeepers´ to certain
molecules and ions
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 7/36
Copyright 2009 John Wiley & Sons, Inc.
Structure of a Membrane
Consists of a lipid bilayer - made up of
phospholipids, cholesterol and glycolipids
Arrangement of membrane proteins Integral proteins - extend into or through the lipid
bilayer
Transmembrane proteins - most integral
proteins, span the entire lipid bilayer Peripheral proteins - attached to the inner or
outer surface of the membrane, do not extend
through it
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 8/36
Copyright 2009 John Wiley & Sons, Inc.
Structure of the Plasma Membrane
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 9/36
Copyright 2009 John Wiley & Sons, Inc.
Structure of a Membrane
Many membrane proteins are glycoproteins
Glycoproteins - membrane proteins with a
carbohydrate group attached that protrudes
into the extracellular fluid
Glycocalyx - the ³sugary coating´
surrounding the membrane made up of the
carbohydrate portions of the glycolipids andglycoproteins
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 10/36
Copyright 2009 John Wiley & Sons, Inc.
Structure of the Plasma Membrane
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 11/36
Copyright 2009 John Wiley & Sons, Inc.
Functions of Membrane Proteins
Ion channels ± pores or holes ± through which specific
ions such as K+ can flow to get in/out of the cell
Transporters - selectively move substances through the
membrane
Receptors - for cellular recognition; a ligand is a moleculethat binds with a receptor
Linkers ± which anchor proteins in the plasma membranes
of neighbouring cells to one another or to protein filaments
inside and outside the cell Enzymes - catalyze chemical reactions
Others act as cell-identity markers (e.g. glycoproteins or
glycolipids)
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 12/36
Copyright 2009 John Wiley & Sons, Inc.
Figure 3.3
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 13/36
Copyright 2009 John Wiley & Sons, Inc.
Membrane Permeability
The cell is either permeable or impermeable
to certain substances
The lipid bilayer is permeable to oxygen,
carbon dioxide, water and steroids, but
im permeable to glucose
Transmembrane proteins act as channels
and transporters to assist the entrance of certain substances, for example, glucose and
ions
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 14/36
Copyright 2009 John Wiley & Sons, Inc.
Passive vs. Active Processes
Passive processes - substances move across
cell membranes without the input of any
energy; use the k inetic energy of individual
molecules or ions i.e. down a concentration
or electrical gradient
Active processes - a cell uses energy,
primarily from the breakdown of ATP, tomove a substance across the membrane, i.e.,
against a concentration gradient
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 15/36
Copyright 2009 John Wiley & Sons, Inc.
Diffusion
µA passive process in which the random mixing of particles in a solution occurs because of the particle¶sk inetic energy¶
Steepness of concentration
gradient
Temperature
Mass of diffusing substance
Surface area
Diffusion distance
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 16/36
Simple diffusion
A passive process in which substances move
freely through the li pid bilayer of the plasma
membrane of cells, without the hel p of membrane
trans port proteins.
Non-polar, hydrophobic molecules move across
the lipid bilayer through the process of simple
dffusion e.g. Oxygen, carbon dioxide and nitrogen
gases; fatty acids, steroids, and fat soluble
vitamins A, D, E and K
Copyright 2009, John Wiley & Sons, Inc.
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 17/36
Simple diffusion
Small, uncharged polar molecules such as water,
urea and small alcohols also pass through the lipid
bilayer by simple diffusion
This type of diffusion is the route for movement of
oxygen and carbon dioxide between blood and
body cells, an between blood and air within the
lungs during breathing
Copyright 2009, John Wiley & Sons, Inc.
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 18/36
Copyright 2009 John Wiley & Sons, Inc.
Simple Diffusion, Channel-mediated
Facilitated Diffusion, and Carrier-mediatedFacilitated Diffusion
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 19/36
Facilitated diffusion
Solutes that are too polar or highly charged to
move through the lipid bilayer by simple
diffusion can cross the plasma membrane by a
passive process called facilitated diffusion
In this process an integral membrane protein
(channel or carrier) assists a specific substanceacross the membrane (e.g. K+, Cl-, Na+ and
Ca2+ )
Copyright 2009, John Wiley & Sons, Inc.
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 20/36
Copyright 2009 John Wiley & Sons, Inc.
Channel-mediated Facilitated Diffusion of
Potassium ions through a Gated K + Channel
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 21/36
Glucose
transporter
Glucose
gradient
Glucose
Glucose
Extracellular fluid Plasma membrane Cytosol
1
2
3
Carrier-mediated Facilitated Diffusion of Glucose
across a Plasma Membrane
Examples include glucose
and some vitamins
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 22/36
Copyright 2009 John Wiley & Sons, Inc.
Osmosis
Net movement of water through aselectively permeable membrane from anarea of high concentration of water (lower concentration of solutes) to one of lower
concentration of water Water can pass through plasma membrane
in 2 ways:
1. through lipid bilayer by simple diffusion
2. through aquaporins, integral membraneproteins
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 23/36
Copyright 2009 John Wiley & Sons, Inc.
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 24/36
Copyright 2009 John Wiley & Sons, Inc.
Osmosis
The cell (or plasma) membrane is selectively permeable.Normally the osmotic pressure on both sides of the
membrane is the same and so cell volume is relatively
constant.
When cells are placed in a solution having a different osmoticpressure than the cytosol, water moves in or out of the cell
leading to a change in shape and volume.
A solution¶s tonicity (tonic=tension) is a measure of thesolution¶s ability to change the volume of cells by altering
water content.
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 25/36
Copyright 2009 John Wiley & Sons, Inc.
Tonicity and its effect on RBCS
Any solution in which acell maintains its
normal shape and
volume is µisotonic¶. In
this case the
concentration of
solutes that cannotcross the plasma
membrane are the
same on both sides of
the solution. For
example normalphysiological saline
(0.9% NaCl solution).
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 26/36
Copyright 2009 John Wiley & Sons, Inc.
Tonicity and its effect on RBCS
If cells are placed in asolution having a
lower concentration
of solutes than the
cytosol (i.e.
Hypotoni
csolution),the water molecules
enter the cell faster
than they leave and
the cell swells
eventually bursting(i.e. Lysis)
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 27/36
Copyright 2009 John Wiley & Sons, Inc.
Tonicity and its effect on RBCS
If cells are placed in asolution having a
higher concentration of
solutes than the
cytosol (i.e.
Hypertoni
csolution),the water molecules
leave the cell faster
than they enter and the
cell shrink (i.e.
crenation)
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 28/36
Osmosis, osmolarity and osmolality
The osmolarity of a solution is a measure of
the total number of dissolved particles per
litre of solution.
The osmolality of a solution is the number of
particles per kilogram of solution.
The term osmolarity is more commonly used
than osmolality.
Copyright 2009, John Wiley & Sons, Inc.
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 29/36
Osmosis, osmolarity and osmolality
Normally, osmolality is about the same as
osmolarity.
The normal osmolality value for plasma is
280-295 mOsmo/kg. At this value, there is no
net water movement in/out of the cell.
Copyright 2009, John Wiley & Sons, Inc.
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 30/36
Copyright 2009 John Wiley & Sons, Inc.
Active TransportSolutes are transported across plasma membranes with the use of energy, from an area
of lower concentration to an area of higher Concentration Sodium-potassium pump
1
3 Na+
K+
gradient
Na+
gradientNa+ /K+ ATPase
Extracellular fluid
Cytosol
1
3 Na+ expelled
3 Na+
ADP
P
K+
gradient
Na+
gradientNa+ /K+ ATPase
Extracellular fluid
CytosolATP
21
3 Na+ expelled
3 Na+
ADPP
P
K+
gradient
Na+
gradientNa+ /K+ ATPase
Extracellular fluid
Cytosol
2K+
ATP2 31
3 Na+ expelled
3 Na+
ADPP
P
2 K+
imported
K+
gradient
Na+
gradientNa+ /K+ ATPase
Extracellular fluid
Cytosol
2K+
ATP2 3 4
Sodium-potassium pump
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 31/36
Copyright 2009 John Wiley & Sons, Inc.
Cytoplasm - 2 components
1. Cytosol - intracellular fluid, surrounds the organelles
- the site of many chemical reactions
- energy is usually released by these reactions
- reactions provide the building blocks for cell maintenance,
structure, function and growth
2. Organelles
Specialized structures within the cell
The cytoskeleton - network of protein filaments throughout the
cytosol-provides structural support for the cell
-three types according to increasing size: microfilaments,intermediate filaments, and microtubules
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 32/36
Copyright 2009 John Wiley & Sons, Inc.
Organelles
Ribosomes - sites of protein synthesis
Endoplasmic reticulum - network of membranes in
the shape of flattened sacs or tubules
- R ough E R - connected to the nuclear envelope, aseries of flattened sacs, surface is studded with
ribosomes, produces various proteins
-Smooth E R - a network of membrane tubules, does
not have ribosomes, synthesizes fatty acids andsteroids, detoxifies certain drugs
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 33/36
Copyright 2009 John Wiley & Sons, Inc.
Endoplasmic Reticulum
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 34/36
Copyright 2009 John Wiley & Sons, Inc.
Organelles
Mitochondria - the ³powerhouses´ of the cell
Generate ATP
More prevalent in physiologically active cells: muscles, liver
and kidneys Inner and outer mitochondrial membranes
C ristae - the series of folds of the inner membrane
M atrix - the large central fluid-filled cavity
Self-replicate during times of increased cellular demand or
before cell division
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 35/36
Copyright 2009 John Wiley & Sons, Inc.
Mitochondria
8/9/2019 PHTH 211 Cell Membrane Physiology
http://slidepdf.com/reader/full/phth-211-cell-membrane-physiology 36/36
Copyright 2009 John Wiley & Sons, Inc.
End of Chapter 3
Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond thatpermitted in section 117 of the 1976 United States Copyright Act withoutexpress permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley& Sons, Inc. The purchaser may make back-up copies for his/her own useonly and not for distribution or resale. The Publishers assumes noresponsibility for errors, omissions, or damages caused by the use of thesesprograms or from the use of the information herein.