Ch 5 cell membrane and transport
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CH. 5 CELL MEMBRANE AND TRANSPORT. A Closer Look at Cell Membranes. BOZEMAN VIDEO—CELL MEMBRANES. http://www.youtube.com/watch?v=y31DlJ6uGgE http://www.youtube.com/watch?v=S7CJ7xZOjm0. http://www.youtube.com/watch?v=y31DlJ6uGgE http://www.youtube.com/watch?v=S7CJ7xZOjm0. Lipid Bilayer.

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CH. 5 CELL MEMBRANE AND TRANSPORT

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Ch 5 cell membrane and transport

CH. 5 CELL MEMBRANE AND TRANSPORT

A Closer Look at Cell Membranes


Bozeman video cell membranes

BOZEMAN VIDEO—CELL MEMBRANES

http://www.youtube.com/watch?v=y31DlJ6uGgE

http://www.youtube.com/watch?v=S7CJ7xZOjm0


Ch 5 cell membrane and transport

http://www.youtube.com/watch?v=y31DlJ6uGgE

http://www.youtube.com/watch?v=S7CJ7xZOjm0


Lipid bilayer

Lipid Bilayer

  • Cell membranes consist of a lipid bilayer containing different proteins

  • Membrane is a continuous boundary layer that selectively controls the flow of substances across it


Ch 5 cell membrane and transport

hydrophilic

parts

hydrophobic

parts

fluid

fluid

one layer of lipids

one layer of lipids

b

cross-section

through lipid bilayer

a

Fig. 5.3, pg. 76


Fluid mosaic model

Fluid Mosaic Model

  • Every cell membrane has a mixed composition of phospholipids, glycolipids, sterols, and proteins

  • KNOW THE CAMPBELL DIAGRAM “CELL MEMBRANE MOSAIC”


Fluid mosaic model1

Fluid Mosaic Model

passive

transporter

recognition

protein

phospholipid

adhesion

protein

cholesterol

receptor

Lipid bilayer

active transporter

(ATPase pump)

active transporter

(calcium pump)

Cytoplasm

Plasma

Membrane

cytoskeletal proteins just beneath the plasma membrane

Fig. 5.4, pg. 77


Studying membranes

Studying Membranes

Stepped Art

Fig. 5.5a, pg. 77


Overview of membrane proteins

Overview of Membrane Proteins

Adhesion

Proteins

Communication

Proteins

Fig. 5.6, p.78


Overview of membrane proteins1

Overview of Membrane Proteins

Receptor

Proteins

Recognition

Proteins

Passive

Transporters

Active

Transporters

Fig. 5.6, p.79


Transport proteins

Transport Proteins

  • Span the lipid bilayer

  • Interior is able to open to both sides

  • Change shape when they interact with solute

  • Play roles in active and passive transport


Concentration gradient

Concentration Gradient

  • Means the number of molecules or ions in one region is different than the number in another region

  • In the absence of other forces, a substance moves from a region where it is more concentrated to one one where it’s less concentrated - “down” gradient


Diffusion

Diffusion

  • The net movement of like molecules or ions down a concentration gradient

  • Although molecules collide randomly, the net movement is away from the place with the most collisions (down gradient)


Diffusion1

Diffusion

Stepped Art

Fig. 5.7a, p.80


Factors affecting diffusion rate

Factors Affecting Diffusion Rate

  • Steepness of concentration gradient

    • Steeper gradient, faster diffusion

  • Molecular size

    • Smaller molecules, faster diffusion

  • Temperature

    • Higher temperature, faster diffusion

  • Electrical or pressure gradients


Membrane crossing mechanisms

Membrane Crossing Mechanisms

Diffusion across lipid bilayer

Passive transport

Active transport

Endocytosis

Exocytosis


Cell membranes show selective permeability

Cell Membranes Show Selective Permeability

oxygen, carbon

dioxide, and other

small, nonpolar

molecules; some

water molecules

glucose and other large,

polar, water-soluble

molecules; ions (e.g.,

H+, Na+, K+, Ca++,

Cl–); water molecules

Fig. 5-8, p.80


Membrane crossing overview i

Membrane Crossing: Overview I

High

Concentration

gradient across

cell membrane

ATP

Low

Diffusion of

lipid-soluble

Substances

across bilayer

Passive transport of water-

soluble substances

through channel protein;

no energy input needed

Active transport

through ATPase;

requires energy

input from ATP

Fig. 5-9, p.81


Passive transport

Passive Transport

  • Flow of solutes through the interior of passive transport proteins down their concentration gradients

  • Passive transport proteins allow solutes to move both ways

  • Does not require any energy input


Types of passive transport

TYPES OF PASSIVE TRANSPORT

  • DIFFUSION

  • FACILITATED DIFFUSION—diffusion that is “helped out” by membrane transport proteins (such as helping larger molecules pass)


Passive transport1

Passive Transport

glucosetransporter

solute (glucose)

high

low

Stepped Art

Fig. 5.10, p.80


Active transport

Active Transport

  • Net diffusion of solute is against concentration gradient

  • Transport protein must be activated (requires an integral membrane protein)

  • ATP gives up phosphate to activate protein

  • Binding of ATP changes protein shape and affinity for solute


Types of active transport

TYPES OF ACTIVE TRANSPORT

  • SODIUM-POTASSIUM PUMP—3 Na move out and allow 2 K to enter; needs net 1 ATP molecule to dothis

  • PROTON PUMP– pushes H ions out of the membrane allowing them to eventually diffuse back in; generates ATP for the cell; used in cell respiration

    This uses ATP synthase enzyme

  • COTRANSPORT– when molecules travel together across the membrane


Types of active transport continued

Types of active transport Continued

  • Endocytosis—”engulfing “things into cell membrane; difficult for plants to do

    Ex: white blood cells engulfing bacteria—to fight infections

    phagocytosis (large food)

    pinocytosis (small things)

    Receptor-mediated endocytosis—use of receptor proteins to help pull things into cell

    Exocytosis—”spitting” things out of cell


Osmosis

Osmosis

  • Diffusion of water molecules across a selectively permeable membrane

  • Direction of net flow is determined by water concentration gradient

  • Side with the most solute molecules has the lowest water concentration


Ch 5 cell membrane and transport

Osmosis

p.84


Tonicity

Tonicity

Refers to relative solute concentration of two fluids

Hypotonic - having fewer solutes

Hypertonic - having more solutes

Isotonic - having same amount


Ch 5 cell membrane and transport

Tonicity and Osmosis

2% sucrose solution

1 liter of

10% sucrose solution

1 liter of

2% sucrose solution

1 liter of distilled water

Hypotonic

Conditions

Hypertonic

Conditions

Isotonic

Conditions

Fig. 5-13, p.85


Dialysis bag mass change

DIALYSIS BAG % MASS CHANGE


Pressure and osmosis

Pressure and Osmosis

  • Hydrostatic pressure

    • Pressure exerted by fluid on the walls that contain it

    • The greater the solute concentration of the fluid, the greater the hydrostatic pressure

  • Osmotic pressure

    • Amount of pressure necessary to prevent further increase of a solution’s volume


Increase in fluid volume

Increase in Fluid Volume

first compartment

second compartment

hypotonic

solution

hypertonic

solution

membrane permeable to

water but not to solutes

fluid volume rises in second compartment

Fig. 5.14, p.85


Endocytosis and exocytosis video

ENDOCYTOSIS AND EXOCYTOSIS VIDEO

http://www.youtube.com/watch?v=DuDmvlbpjHQ


Endocytosis and exocytosis

Endocytosis and Exocytosis

  • Exocytosis: A cytoplasmic vesicle fuses with the plasma membrane and contents are released outside the cell

    3 types: phagocytosis—engulfs large molecules; difficult for plant cells to do (WHY??)

    pinocytosis—engulfs small molecules

    receptor-mediated—uses receptor membrane proteins to pull things in

  • Endocytosis: A small patch of plasma membrane sinks inward and seals back on itself, forming a vesicle inside the cytoplasm – membrane receptors often mediate this process


Macrophage engulfing leishmania mexicana

Macrophage engulfing Leishmaniamexicana

parasite

macrophage

Fig 5.17, p.87


Ch 5 cell membrane and transport

Phagocytosis

bacterium

phagocytic vesicle

Fig. 5-17b, p.87


Contractile vacuole

Contractile Vacuole

contractile vacuole filled

contractile vacuole emptied

Fig. 5.21, pg. 89


Plasmolysis

Plasmolysis

Plasmolysis


Ch 5 cell membrane and transport

adhesion protein

passive transporter

recognition

protein

receptor protein

lipid bilayer

cytoskeletal

proteins

cytoplasm

active transporter (calcium pump)

active transporter (ATPase pump)

Fig. 5-19, p.88


Bozeman video cell transport across membranes and animation

BOZEMAN VIDEO—CELL TRANSPORT ACROSS MEMBRANES AND ANIMATION

http://www.youtube.com/watch?v=RPAZvs4hvGA

http://www.youtube.com/watch?v=RPAZvs4hvGA


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