the cell membrane & movement of materials in & out of...

The Cell Membrane &

Movement of Materials In &

Out of CellsPACKET #11

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ay, March

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Introduction I

Biological membranes are phospholipid bilayers with associated proteins.

Current data support a fluid mosaic model of the cell membrane.

In 1935, Davson and Daniellastated that phospholipids form a membrane two molecules thick.

Singer and Nicholson developed the fluid mosaic model in 1972.

Furthermore, the membrane is only 10nm thick.

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Introduction II

Biological membranes

fuse and form closed

vesicles.

Endocytosis and

exocytosis are products of

membrane fusion.

More later.

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Cell Membrane

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Properties of

Phospholipids

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Phospholipids are Amphipathic

Molecules with both

hydrophilic and hydrophobic

properties are termed

amphipathic

Other examples

Sterols

Cholesterol

Glycolipids

Hydrophilic (sugar) head

The aqueous environment

inside and outside the cell

prevent membrane lipids from

escaping the bilayer Tuesday, March

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Fluidity of the Membrane

Depends on Two Main Features

Saturated vs. Unsaturated Fatty

Acid tails (phopsholipids)

Unsaturated more fluid

Kinks prevent molecules from

packing together

Cholesterol

Absent in plants, yeast and bacteria

Fill the holes produced by kinks

Stiffens bilayer and makes it less

fluid and permeable.

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Fluidity of the Cell Membrane II

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Check Point 1

LEARNING GOALSSTUDENT EVIDENCE

{Student developed Questions}

4In addition to level 3, …

• Describe the relationship between the cell membrane, homeostasis and

sweating (Packet #9).

3The student will (target learning goal)

• Identify and describe the basic unit of the cell membrane (phospholipid).

• Explain how the relation of phospholipids to water.

2

The student will understand/perform basic processes, such as:

Relate the structure phospholipids to water (a polar molecule).

Identify reactants, products, and basic functions of photosynthesis,

anaerobic, and aerobic cellular respiration.

The student will recognize or recall specific vocabulary, such as:

Phospholipid; hydrophilic; hydrophobic; amphipathic; saturated; unsaturated

1With help, I have a partial understanding of some of the simpler details and

processes at level 2.

I can describe the basic structure of the cell membrane.

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Proteins of the

Cell Membrane


Functions of Membrane Proteins

• Cell Membrane

Proteins

• Six different

functions

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Functions of Proteins

Transport

Enzyme Activity

Signal Transduction

Cell to cell Recognition

Intercellular Joining

Attachment to Cytoskeleton

Integral vs. Peripheral Proteins

Integral Proteins

A protein that is firmly

anchored in the plasma

membrane via interactions

between its hydrophobic

domains and the membrane

phospholipids

Directly attached to the

membrane

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Integral vs. Peripheral Proteins

Peripheral Proteins

Not embedded in the lipid

bilayer

Can be released from the

membrane by relatively

gentle extraction

procedures

Possible key player in cell

communication.

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Transmembrane Protein

Protein that spans the entire

membrane

Have both hydrophobic and

hydrophilic regions

Alpha helical secondary

structure is normally the

hydrophobic regions of the

protein

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Check Point 2




• Describe the relationship between proteins of the cell membrane, classes of

proteins and enzymes (Packet #6 & 7).


• Explain the roles of proteins within the cell membrane

2


Describe the functions of proteins within the cell membrane


Integral protein; Peripheral protein



I can list the types of proteins within the cell membrane.

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Diffusion

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Introduction

Atoms and molecules,

above absolute zero,

exhibit motion.

This random motion

allows particles to move

from an area of higher

concentration to an area

of lower concentration in

an attempt to reach

equilibrium.Tuesday, March

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Introduction

There are 5 ways of transporting materials across the cell

membrane

Diffusion

Regular & Facilitated

Passive Transport

Active transport

Osmosis

Phagocytosis

Pinocytosis

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Categories of Diffusion I

Regular Diffusion

Movement of molecules down the

concentration gradient

High to low

Facilitated Diffusion

Movement of molecules down the

concentration gradient via a channel

In cells, these channels are found in

proteins

More to come later

Active transport

Movement of molecules against the

concentration gradient via channels and

with the use of energy.

Low to high

Categories of Diffusion

Passive Transport

Regular Diffusion


Active Transport

OsmosisSpecial type of

diffusion

Phagocytosis

Pinocytosis

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Diffusion


Diffusion

The movement of a

substance from an area of

high concentration to an area

of low concentration

The difference in

concentration between the two

regions is known as the

concentration gradient

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Rate of Diffusion

The rate of diffusion depends on

The difference in concentration

The greater the concentration gradient, the faster the process

The distance between the two regions

Smaller distance means faster process

The area

If the total “area” is increased, the faster the process

The size of the molecules

Small and fat-soluble molecules will diffuse faster

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Passive Transport

Regular vs. Facilitated Diffusion

“Regular” Diffusion

Movement of molecules is from high concentration to low concentration

No proteins are used

No energy (ATP) is required


Movement of molecules is from high concentration to low concentration

Proteins are used

No energy (ATP) is required

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Active Transport

Materials are moved against

the concentration gradient

Molecules move from an area

of low concentration to an

area of high concentration

Proteins are used to move

materials across the

membrane

Energy is also used.

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Active Transport II

Cells carry our active transport in

three ways

ATP driven pumps

Couple uphill transport with

hydrolysis of ATP

Coupled transport (co-transport)*

Light driven pumps

Found mainly in bacterial cells

Input of energy from light

Bacteriohodopsin

Active Transport

ATP PumpsCo-

TransportLight Driven

Pumps

Bacteria Cells

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Active Transport ATP DRIVEN PUMPS

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Active Transport—ATP Driven Pumps

Energy is used

Because energy is used, cells

carrying out active transport have

A high respiratory rate

Many mitochondria

A high concentration/reserve of

ATP

Any factor which reduces or stops

cell respiration will stop active

transport

Cyanide

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Co-TransportINVOLVES ACTIVE

TRANSPORT

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Co-Transport I

The Active Transport of H+ ions

Hydrogen gradients are used to

drive membrane transport in

plants, fungi and bacteria

These are not sodium-potassium

pumps

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Co-Transport II

The Active Transport of H+ ions II

Hydrogen pumps, found in the

plasma membrane, pump H+ out

of the cell

This can also be described as

primary active transport

Setting up an electrochemical

gradient

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Co-Transport III

Pump creates an acidic pH in the

medium surrounding the cell

H+ re-enters the cell via a

cotransporter

Usually transports a substance

in addition to the H+

The uptake of sugars and amino

acids, into bacterial cells for

example, are driven by the

presence H+ pumps

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Active

Transport—Light

Driven Pumps

H+ Pumps in

Bacteria

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Active Transport—Light Driven Pumps

H+ Pumps in Bacteria

In some photosynthetic bacteria, the H+ gradient is created by

the activity of light driven H+ pumps such as

bacteriorhodopsin.

In plants and fungi and many other bacteria, the gradient is set up

by ATPases in their plasma membrane

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Types of Ports

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Types of Ports

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Review so far…

Movement of Materials in/out

of Cells

Passive Transport

Regular Diffusion


Active Transport

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Sodium

Potassium Pump


Electrogenic Pump

These pumps are used to move

electrically charged molecules

Small organic or inorganic ions

MOST cell membranes have a

voltage across them and results in

a difference in electric potential on

each side—i.e. the membrane potential.

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Electrogenic Pump

The membrane potential exerts a force on any molecule that carries an electrical charge

Cytoplasmic side is USUALLYat a negative potential relative to the outside

This tends to pull positively charged solutes into the cell and drive negative charged ones outside the cell

Net driving force = electrochemical gradient

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The Sodium Potassium Pump

For some, ions, voltage

and concentration

gradients work in the

same direction

Sodium Potassium Pump

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Movement of

GlucosePUTTING IT ALL

TOGETHER


The Movement of Glucose

The Na+ gradient generated by the sodium-potassium pump can be used to driveactive transport of a 2nd

molecule.

The downhill movement of the first solute down provides the energy to drive the uphill transport of the second.

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Check Point #3




• Describe the relationship between co-transport, the cell, the pancreas,

blood glucose levels and diabetes.


• Describe how glucose is moved in and out of cells with the help of the

sodium potassium pump.

2


Students will understand the different types of diffusion.


Random motion; equilibrium; diffusion; facilitated diffusion; active transport; co-

transport; sodium-potassium pump



I can list the ways materials are transported across the cell membrane.

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OsmosisSPECIAL CASE OF

DIFFUSION

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Osmosis

Concise Definition

The diffusion of water (liquid solvent) across a selectively permeable membrane

Detailed Definition

Transfer of a liquid solvent through a semi permeable membrane, that does not allow dissolved solids (solutes) to pass from an area of high concentration to an area of low concentration

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Osmotic Pressure,

Osmotic Potential

& Solute Potential

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Osmotic Pressure

Osmotic Pressure

Is a measure of the tendency of water to move INTO a solution.

The driving force for the water and is the differencein water pressure on both sides of the membrane.

The differences in pressure provides a net pressure that is exerted by the flow of water as it moves through the semi-permeable membrane.

Class Illustration

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Osmotic Potential = Osmotic Pressure

Osmotic Potential

Difference in osmotic pressure that draws water from an area of less osmotic pressure to an area of greater osmotic pressure.

The potential of a solution to pull in water

Value is always negative

The more concentrated the solution, the more negative its osmotic potential

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= Solute Potential

The presence of solutes, in the solutions, impact the direction of the movement of water.

The ability of a solution to pull in water depends on the number of solute particles present.

The higher the amount of solutes in the solution, the lower the solute potential.

The solution is more concentrated.

Remember, from previous slide, the value is always suppose to be negative.

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= Solute Potential

All three terms represent a measure of the ability of a solution to pull in water.

The value is always negative.

The more solutes present, the more negative the value.

Represented by s

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= Solute Potential

When two solutions have the same osmotic potential, they are said to be isotonic.

Where one solution has a greater osmotic potentialcompared to the other, it is described as being hypertonic.

i.e. It is more concentrated.

The solution with the lower osmotic potential is described as being hypotonic.

Less concentrated.

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Pressure Potential

Solutions/Water are also under the influence of external pressures.

These external pressures are measure as pressure potential.

This force (pressure) is not the same as the one caused by the movement of the liquid solvent (water).

Represented by p

Negative or positive depending on conditions.

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Water Potential

Measure of the tendency of water to leave a solution.

Combination of the sumof osmotic potential/solute potential and pressure potential.

= s + p

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Water Potential II

When measuring the

water potential of two

solutions, the solution

with the lower water

potential receives water

from the solution with

higher water potential

Osmosis!

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Cells and Osmosis

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Pressure Potential in Plant Cells

In plant cells, the cell contents

press the plasma membrane

against the cell wall—

producing an external force

called turgor pressure.

Results in a turgid plant cell

Pressure potential is positive

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Pressure Potential in Plant Cells II

Special plant cells that make up

xylem, tissue that conducts

water in plants, undergoes

transpiration.

This transpiration results in a

negative pressure potential.

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Cells & Osmosis

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Cells & Osmosis

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Check Point #4




• Describe the relationship between osmosis, the cell, the kidneys, urination

and dehydration.


• Explain why water can enter and leave cells.

2


Identify osmotic pressure, osmotic potential and solute potential


Osmosis; osmotic pressure; osmotic potential; solute potential



I can define osmosis.

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Phagocytosis,

Pinocytosis,

Endocytosis and

Exocytosis


Phagocytosis

The take up of large particles by cells via vesicles formed

in the plasma membrane

The cell invaginates to form a depression in which

particles are contained

This then pinches off to form a vacuole

White blood cells

Neutrophils

Monocytes

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Pinocytosis

The take up of liquids rather than solids

Vacuoles are smaller than those used during

phagocytosis

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Endocytosis vs. Exocytosis

Both phagocytosis and

pinocytosis involve the

taking of materials into

the cell in bulk.

These are examples of

endocytosis

The removal of materials

from the cell in bulk is

called exocytosis.

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Check Point #5




• Describe the relationship between the immune system, the body fighting

pathogens and phagocytosis/endocytosis.


• Explain and describe the process in which cells can absorb materials in

bulk.

2


Identify ways that cells can absorb (take in) larger substances in bulk.


Phagocytosis; pinocytosis; endocytosis; exocytosis



I can describe how cells take up larger molecules.

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Review

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