Plasma Membrane.ppt

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The Plasma Membrane

-Gateway to the Cell

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Photograph of a Cell

Membrane

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Cell Membrane

The cell

membrane is

flexible

flexible and

allows a

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Homeostasis

•

Balanced

internal condition of

cells

•

Also called

equilibrium

•

Maintained by plasma membrane

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Functions of Plasma

Membrane

 Protective barrier_{Protective barrier}

 Regulate transport in & out of cell _{Regulate transport in & out of cell}

(selectively permeable)

 Allow cell recognition_{Allow cell recognition}

 Provide anchoring sites for filaments _{Provide anchoring sites for filaments}

of cytoskeleton

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Functions of Plasma

Membrane

 Provide a binding site for enzymes_{Provide a binding site for enzymes}

 Interlocking surfaces bind cells _{Interlocking surfaces bind cells}

together (junctions)

together (junctions)

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Structure of the Cell

Membrane

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Phospholipids

Phospholipids

Cholesterol

Proteins

(peripheral and integral)

Carbohydrates (glucose)

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Phospholipids

Make up the cell membrane

Contains 2 fatty acid chains that are nonpolar

Head is polar & contains a –PO₄ group &

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FLUID

FLUID- because individual phospholipids and proteins can - because individual phospholipids and proteins can

move side-to-side within the layer, like it’s a liquid.

MOSAIC

MOSAIC- because of the pattern produced by the - because of the pattern produced by the scattered protein molecules when the membrane is

scattered protein molecules when the membrane is

viewed from above

viewed from above..

FLUID MOSAIC MODEL

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Polar heads are hydrophilichydrophilic “water loving”

Nonpolar tails are hydrophobic_hydrophobic “water fearing”

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Cell Membrane

Hydrophobic

molecules pass

easily; hydrophilic

DO NOT

The cell membrane is made of 2 layers of

phospholipid

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Solubility

•

Materials that

are soluble in

lipids

can pass

through the

cell membrane

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Small molecules and larger hydrophobic

molecules move through easily.

e.g. O₂, CO₂, H₂O

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Ions, hydrophilic molecules larger than

water, and large molecules such as proteins do not move through the membrane on their own.

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Types of Transport

Across Cell

Membranes

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Simple Diffusion

•

Requires

NO

energy

•

Molecules

move from

area of

HIGH

to LOW

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DIFFUSION

Diffusion is a

PASSIVE

PASSIVE process which means no

energy is used to make the

molecules move, they have a

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Diffusion through a

Membrane

Cell membrane

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Osmosis

• Diffusion of water_{Diffusion of water}

across a across a

membrane membrane

• Moves from Moves from HIGH HIGH water potential

water potential

(low solute) to (low solute) to

LOW water

potential

potential (high (high solute)

solute)

Diffusion across a membrane

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Diffusion of H

₂₂

O Across A

Membrane

High H2O potential

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Aquaporins

• Water Channels

• Protein pores used during

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Cell in Isotonic Solution

CELL CELL

10% NaCL 90% H2O

10% NaCL 90% H₂O

What is the direction of water movement?

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Cell in Hypotonic Solution

CELL CELL

10% NaCL 90% H2O

20% NaCL 80% H₂O

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Cell in Hypertonic Solution

CELL CELL

15% NaCL 85% H2O

5% NaCL 95% H₂O

What is the direction of water movement?

ENVIRONMENT

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Isotonic Solution

NO NET

MOVEMENT OF H₂O (equal amounts

entering & leaving)

Hypotonic Solution

CYTOLYSIS

Hypertonic Solution

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Cytolysis & Plasmolysis

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Osmosis in Red Blood Cells

Isotonic

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hypotonic hypertonic isotonic

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Three Forms of Transport Across the Membrane

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Passive Transport

Simple Diffusion



Doesn’t

require energy



Moves

high to low

concentration



Example:

Oxygen

or

water

diffusing into a

cell and

carbon dioxide

diffusing out

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Passive Transport

Facilitated diffusion



Doesn’t

require energy



Uses

transport

proteins

to move

high to

low

concentration

Examples:

Glucose

or

amino acids

moving from

blood into a cell.

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Proteins Are Critical to

Membrane Function

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Types of Transport Proteins

•

Channel proteins

are embedded

in the cell membrane & have a

pore

for materials to cross

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Facilitated Diffusion

Molecules will randomly move through

Molecules will randomly move through

the

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Facilitated Diffusion

• SomeSome Carrier Carrier

proteins

proteins do not _{do not}

extend through the

membrane.

• They They bond and drag bond and drag molecules

molecules through through

the lipid bilayer and

release them on the

opposite side.

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Carrier Proteins

•

Other carrier

proteins

change shape

to move

materials

across the cell

membrane

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Active Transport



Requires energy or

ATP



Moves materials from

LOW to HIGH

concentration



AGAINST

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Active transport



Examples: Pumping

Na

+

(sodium ions)

out and

K

+

(potassium ions) in

against

strong

concentration

gradients

.

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Sodium-Potassium Pump

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Moving the “Big Stuff”

Molecules are

Molecules are moved outmoved out of the cell by of the cell by vesiclesvesicles that that fusefuse with the plasma membrane.

with the plasma membrane.

Exocytosis

- moving

things out.

This is how many

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Moving the “Big Stuff”

Large molecules move materials into the cell by

Large molecules move materials into the cell by

one of

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Pinocytosis

Most

Most commoncommon form of endocytosis form of endocytosis.

Takes in

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Pinocytosis

• Cell forms an Cell forms an

invagination

invagination

• Materials Materials dissolve in

dissolve in

water

water to be _{to be}

brought into cell

• Called Called “Cell “Cell Drinking”

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Example of Pinocytosis

pinocytic vesicles forming mature transport vesicle

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Receptor-Mediated Endocytosis

Some

Some integral proteinsintegral proteins have have receptorsreceptors

on their surface to recognize & take in

hormones, cholesterol

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Receptor-Mediated Endocytosis

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Endocytosis – Phagocytosis

Used to

Used to engulf large particles_{engulf large particles} such as _{such as}

food,

food, bacteriabacteria, etc. into vesicles, etc. into vesicles Called

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Phagocytosis

- Capture

of a

Yeast

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Exocytosis

Exocytosis

The opposite of endocytosis is exocytosis.

The opposite of endocytosis is exocytosis. Large Large molecules

molecules that are manufactured in the cell are _{that are manufactured in the cell are}

released

released through the cell membrane through the cell membrane..

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