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Cell Membranes Chapt 4

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Cell Membranes Chapt 4 www.cellsalive.com/ The Cell Membrane Fluid Mosaic Membrane Cell Membrane: Fluid Mosaic Model Membrane Structure Flash movie too.. – PowerPoint PPT presentation

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Title: Cell Membranes Chapt 4


1
Cell Membranes Chapt 4
www.cellsalive.com/
2
The Cell Membrane
3
Fluid Mosaic Membrane
Text pg 80
4
Cell Membrane Fluid Mosaic Model
At Very High Magnification in color
5
Membrane Structure Flash movie too..
CLICK ON THE PICTURE TO SEE AN ANIMATION OF THE
CELL MEMBRANE
6
Cell Membrane
  • Every cell is encircled by a membrane
  • Membranes fence off the cell's interior from its
    surroundings. Membranes let in water, certain
    ions and substrates and they excrete waste
    substances. They act to protect the cell.
  • Without a membrane the cell contents would pass
    into the surroundings
  • Allows the cell to maintain
  • HOMEOSTASIS a constant internal environment
  • kind of like the cells happy place ?

7
Cell Membranes
  • Fluid-like structurelike soap bubbles
  • Structure
  • Lipids in a bilayer
  • Protein-coated pores extend through membrane
    (MOSAIC)
  • Pores are very small and give the membrane polar
    properties
  • H2O penetrates membrane easily
  • Large polar molecules do not
  • Proteins embedded in lipid layer
  • Some proteins floating within the lipid sea
    (called integral proteins)
  • Some proteins associated outside the lipid
    bilayer (peripheral)

8
Membrane Lipids
  • Composed largely of phospholipids
  • Phospholipids composed of.glycerol and two fatty
    acids PO4 group
  • P-Lipids are polar molecules

P-Lipids are represented like this
9
Membrane Lipids form a Bilayer
Outside layer
Inside Layer
10
Quiz
  • If Phospholipids are polar, which end seeks out
    water and which avoids water?

11
Phospholipid Molecule Model

phosphate (hydrophilic)
glycerol fatty acids (hydrophobic)
12
Fluid Mosaic Membrane
Text pg 80
13
Functional Parts of the Cell Membrane
  • Cell Recognition Proteins unique markers that
    identify cells
  • Channel Proteins allows molecules and ions to
    move across
  • Carrier Proteins combine with substrate to move
    across membrane
  • Receptor Proteins bind to specific molecules (ex.
    hormone receptors)
  • Enzymatic Proteins proteins that run specific
    metabolic reactions

14
  • Cell membrane contains carbohydrate (CHOs)
    attached to proteins or lipids ( makes
    Glycoproteins and Glycolipids)
  • Found on outside of cell functioning as markers
    to identify cells to the immune system

15
Auto-Immune Disease
  • Inflamed body cells in the joints or colon
    respectively being recognized by white blood
    cells as non-self.
  • Result is an immune response that causes injury
    to the bodys cells in this case, the cartilege
    at the joints

16
Membrane Proteins
  • Integral embedded within bilayer
  • Peripheral reside outside hydrophobic region of
    lipids

17
Membrane Proteins
18
Integral membrane proteins
19
Peripheral membrane proteins
Integral
20
Membrane Models
  • Fluid Mosaic Model - lipids arranged in bilayer
    with proteins embedded or associated with the
    lipids.

21
Evidence for the Fluid Mosaic Model (Cell Fusion)
22
More Evidence for the Fluid Mosaic Model
23
Membrane Permeability
  • Biological membranes are physical barriers..but
    which allow small uncharged molecules to pass
  • And, lipid soluble molecules pass through
  • Big molecules and charged ones do NOT pass
    through

24
How to get other molecules across membranes??
  • There are three ways that the molecules typically
    move through the membrane
  • Facilitated transport
  • Passive transport
  • Active transport
  • Active transport requires that the cell use
    energy that it has obtained from food to move the
    molecules (or larger particles) through the cell
    membrane.
  • Facilitated and Passive transport does not
    require such an energy expenditure, and occur
    spontaneously.

25
Membrane Transport Mechanisms I. Passive Transport
  • Diffusion- simple movement from regions of high
    concentration to low concentration
  • Osmosis- diffusion of water across a
    semi-permeable membrane
  • Facilitated diffusion- protein transporters which
    assist in diffusion

26
Membrane Transport Mechanisms II. Active Transport
  • Active transport- proteins which transport
    against concentration gradient.
  • Requires energy input

27
Diffusion
  • Movement generated by random motion of
    particles.
  • Applies to any molecule/requires NO ENERGY!!
  • Movement always from region of high concentration
    to low concentration

28
Diffusion continued
  • Lipid soluble molecules (alcohols) and gases (O2
    and CO2) pass easily thru the membrane
  • H2O passes through protein channels
  • Large molecules and charged ions have difficulty
    passing thru (charge on membrane polarity)

29
Osmosis
  • Movement of water across a semi-permeable
    barrier.
  • Example
  • Salt in water, cell membrane is barrier
  • Salt will NOT move across membrane, water will.

Click Picture Above for an Osmosis Demo
30
(No Transcript)
31
Tonicity of Solutions
  • Tonicity the strength of a solution that a
    cell is placed in
  • 3 Tonicity scenarios you must know!!
  • Isotonic
  • equal conc. of particles inside / out of the cell
  • Cells placed in isotonic solutions do not gain or
    lose H2O
  • Hypertonic
  • outside of cell has greater particle conc.
  • Cells placed in hypertonic solutions lose H2O and
    SHRINK
  • Hypotonic
  • inside of cell has greater conc.
  • Cells placed in hypotonic solutioins gain H2O and
    SWELL

32
Osmosis in Hypertonic Medium

Solute outside cell is greater water is drawn
from inside the cell to outside solute


10 NaCl hypertonic to blood cells
(accustomed to 0.9) CELL SHRINKS OR CRENATES
33
  • Hypertonic solutions- shrink cells

34
Osmosis in Hypotonic medium

Solute inside cell is less and attracts water
inside, causing swelling

gt 0.9 NaCl Hypotonic to blood cells CELL
SWELLS
35
  • Hypotonic solutions- swell cells
  • Pressure on cell due to the flow of water is
    called OSMOTIC PRESSURE

Check out the animation ---gt click me
36
Importance of Osmosis
  • Allows for absorption of H2O by the large
    intestine
  • Retention or shedding of H2O by kidneys
  • Uptake of H2O by the blood affects our blood
    pressure
  • Increased blood pressure creates a greater risk
    of heart attack and stroke
  • Watch these Flash Movies ---gt

37
Endocytosis
  • Transports macromolecules and large particles
    into the cell.
  • Part of the membrane engulfs the particle and
    folds inward to bud off.

38
Endocytosis
39
Putting Out the Garbage
  • Vesicles (lysosomes, other secretory vesicles)
    can fuse with the membrane and open up the the
    outside

40
Exocytosis (Cellular Secretion)
41
Movies!
  • A wee flash tour of endocytosis and exocytosis
    just click the image below

42
Membrane Permeability
  1. lipid soluble solutes go through faster
  2. smaller molecules go faster
  3. uncharged weakly charged go faster
  4. Channels or pores may also exist in membrane to
    allow transport

1
2
43
3 Types of Endocytosis
  • Click on active transport, then next a few times
    until the menu shows endocytosis
  • Phagocytosis cell engulfs large amounts
  • Pinocytosis the cell takes in (drinks) a small
    amount
  • Receptor-guided when receptors must first be
    filled before endocytosis is allowed. This often
    happens with hormones.

44
Three Types of Transport
  • Active Transport
  • requires energy ATP
  • Uses a transport protein in the membrane
  • Facilitated Transport Passive
  • NO ATP necessary
  • Like active transport, uses a transport protein
    in the membrane
  • Diffusion and Osmosis Passive
  • no ATP needed

45
Transport Proteins Facilitated Diffusion
Active Transport
  • move solutes faster across membrane
  • highly specific to specific solutes
  • can be inhibited by drugs

ACTIVE
FACILITATED
46
Active Transport
  • Movement of particles low concentration into high
    concentration (against a concentration gradient)
  • Requires energy input from ATP
  • Cells use active transport to build up their
    stores of important particles, such as vitamins,
    minerals, salts, etc.

47
Active Transport Sodium-Potassium Pump
  • Balance of the two ions is done at same time
  • Helps to create a dipole inside and out of the
    cell
  • This is necessary for nerve cells to pass an
    electric impulse

Click here to see a cool Flash Animation
Na low
Na high
K low
K high
ATP required for maintenance of the pump
48
Sodium-Potassium Pump Click image for an animation
49
Types of Protein Transporters Active Transport
  • carrier proteins
  • go against the concentration gradients Low to
    High
  • require Energy to function (ATP)

50
Facilitated Diffusion
  • Proteins in the membrane assists in diffusion
    process
  • Solutes go from High conc to Low conc.
  • Example Glucose transporters

Flash Animation
http//bio.winona.msus.edu/berg/ANIMTNS/FacDiff.ht
m
51
Glucose Transporter How it works..
  • glucose binds to outside of transporter
    (exterior side with higher glucose conc.)
  • glucose binding causes a shape change in protein
  • glucose drops off inside cell
  • protein reverts to original shape

52
Facilitated Diffusion without a Shape Change Ion
Channels
  • Works fast No protein shape changes needed
  • Not simple pores in membrane
  • proteins are specific to different ions (Na, K,
    Ca...)
  • gates control opening
  • Toxins, drugs may affect channels

53
Toxinshow they work They Plug the Ion Channels
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