Plasma membrane structure and

functionAugust 27-28, 2014

Selectively permeable barrier between the cell and the environment.

Plasma Membrane

Selectively permeable barrier between the cell and the environment.

What does ‘selectively permeable’ mean?

Plasma Membrane

Selectively permeable barrier between the cell and the environment.

What does ‘selectively permeable’ mean? Only some materials can cross the membrane

Selective permeability is necessary for the cell to maintain the correct internal environment for physiological functions.

Plasma Membrane

Plasma Membrane Structure

Phospholipids◦ Make up the majority of

the membrane

◦ Arranged in a bilayer, with hydrophilic heads outside, and hydrophobic tails inside

Plasma Membrane components

Phospholipids◦ Make up the majority of

the membrane

◦ Arranged in a bilayer, with hydrophilic heads outside, and hydrophobic tails inside

Plasma Membrane components

Hydrophilic = ___________Hydrophilic molecules are __________ like water.

Hydrophobic = ____________Hydrophobic molecules are __________ like oil.

Phospholipids◦ Make up the majority of

the membrane

◦ Arranged in a bilayer, with hydrophilic heads outside, and hydrophobic tails inside

Plasma Membrane components

Hydrophilic = water lovingHydrophilic molecules are polar like water.

Hydrophobic = water fearingHydrophobic molecules are nonpolar like oil.

Phospholipids

The structure of phospholipids is the key to their function!

Plasma Membrane components

Hydrophilic heads can interact with watery external environment and watery cytoplasm.

Hydrophobic tails reduce the diffusion of water and other charged or polar substances across the membrane.

Cholesterol◦ Makes the cell membrane more rigid and less permeable to water

Proteins◦ Act as enzymes, pores, carriers, and hormone

receptors, and structural elements

Plasma membrane components

Glycoproteins and Glycolipids◦ Glyco = sugar!◦ Influence cell interactions (e.g. identifying cell as

‘self’) and molecule transport

Plasma membrane components

Talk with a partner then share as a class

Scholar on the left answers …◦ What are the 4 membrane components?◦ Which component has most functions? Why?

Scholar on the right answers …◦ Name 4 functions of membrane proteins◦ Which two components are primarily responsible

for reducing fluid loss through the cell? What do those components have in common?

Quick Review: Plasma Membrane Structure

____________ a dissolving agent (water, usually)

____________ substances dissolved in a solution

____________ watery environment outside cells

____________ lower solute concentration

____________ higher solute concentration

____________ equal solute concentration

Cell Transport Vocabulary

Solution: a dissolving agent (water, usually)

Solute: substances dissolved in a solution

Interstitial fluid: watery environment outside cells

Hypotonic: lower solute concentration

Hypertonic: higher solute concentration

Isotonic: equal solute concentration

Cell Transport Vocabulary

Transport of materials across the cell membrane can be characterized as passive or active.

Transport mechanisms

Transport of materials across the cell membrane can be characterized as passive or active.

Passive mechanisms require NO ENERGY from the cell. ALL passive mechanisms transport molecules down their concentration gradient.

Active mechanisms require energy from the cell.

Transport mechanisms

Diffusion is the net movement of molecules down their concentration gradient. Results from the random movement of molecules.

Diffusion animation

Passsive Transport - Diffusion

Simple Diffusion – diffusion directly across the cell membrane or through membrane pores. Only works for tiny OR non-polar molecules.

Examples:

Passsive Transport - Diffusion

Simple Diffusion – diffusion directly across the cell membrane or through membrane pores. Only works for tiny OR non-polar molecules.

Examples: fats, fat-soluble vitamins, O2, CO2, Cl-

Passsive Transport - Diffusion

Simple Diffusion – diffusion directly across the cell membrane or through membrane pores. Only works for tiny OR non-polar molecules.

Examples: fats, fat-soluble vitamins, O2, CO2, Cl-

Osmosis is simple diffusion of water.

Passsive Transport - Diffusion

Facilitated diffusion - diffusion using a protein carrier; used for large polar molecules◦ Example: glucose

Passsive Transport - Diffusion

Filtration occurs when water and solutes are pushed through a membrane by hydrostatic (fluid) pressure.

Water and solutes move down pressure gradient.

Process by which blood is filtered in the kidney.

Passsive Transport - Filtration

Wait 30 sec, then show answer with your fingers

What 2 things do all passive transport mechanisms have in common?1) Membrane proteins are always involved and no

energy is required2) Membrane proteins are always involved and energy is

required3) Molecules move down a gradient and no energy is

required4) Molecules move down a gradient and energy is

required

Quick Review: Passive Transport

Wait 30 sec, then show answer with your fingers

What 2 things do simple and facilitated diffusion have in common?1) Membrane proteins are always involved and no

energy is needed2) Membrane proteins are always involved and energy is

required3) Molecules move down their concentration gradient

and no energy is needed4) Molecules move down their concentration gradient

and energy is required

Quick Review: Passive Transport

How is each molecule transported? Show1) Simple diffusion through lipids2) Simple diffusion through protein pores3) Facilitated diffusion using carrier proteins

a) Waterb) CO2

c) Glucosed) Cl-

Quick Review: Passive Transport

How is each molecule transported? Show1) Simple diffusion through lipids2) Simple diffusion through protein pores3) Facilitated diffusion using carrier proteins

a) Water - 2b) CO2 - 1

c) Glucose - 3d) Cl- - 2

Quick Review: Passive Transport

Use the picture to answer.

In which direction will ions diffuse?1) into the cell2) out of the cell

In which direction will osmosis occur?

1) into the cell2) out of the cell

Quick Review: Passive Transport

Use the picture to answer.

In which direction will ions diffuse?1) into the cell2) out of the cell

In which direction will osmosis occur?

1) into the cell2) out of the cell

Quick Review: Passive Transport

Active transport requires the use of energy (ATP) to transport material across the cell.

Active transport is used for◦ Solutes moving against the concentration gradient - or - ◦ Very large substances

Active Transport

Solute Pumping (aka active transport) Membrane proteins (called solute pumps) use ATP to carry solutes against their concentration gradient.

Examples: amino acids and most ions

Active Transport

Exocytosis - movement of materials out of the cell by vesicle

Examples: hormones, neurotransmitters, mucus, some wastes

Active Transport

Endocytosis – movement of materials into the cell by vesicle

Active Transport

Endocytosis – movement of materials into the cell by vesicle◦ Phagocytosis (cell eating) – white blood cells engulf bacteria, dead cells, and foreign debris◦ Pinocytosis (cell drinking) – used to take up droplets of fats and dissolved proteins

Animation

Active Transport

Many diseases are caused by malfunctions in cell membrane transport.

Examples: Cystic Fibrosis: a Cl- channel is missing,

causing Cl- to build up within the cell Familial hypercholesterolemia – cholesterol

receptors on cell membrane missing, so cholestrol builds up in the blood

Burned tissue ‘weeps’ fluids, proteins, ions, etc.

Homeostatic Imbalance

Draw a detailed picture of the cell membrane.

Include, and label: The structural components

Phospholipids, cholesterol, membrane proteins, glycoproteins, glycolipids

The transport mechanisms Simple diffusion, osmosis, facilitated diffusion, solute

pumping, exocytosis, pinocytosis, phagocytosis

When done, compare with a neighbor, but don’t add to it.

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