Cell Membrane & Cell Transport

What does the cell membrane look like?

• It consists of 2 layers of lipids with their tails pointed inward. These lipids are called phospholipids. Their heads are hydrophilic (attracted to water) and tails are hydrophobic (repel water).

Photograph of a Cell Photograph of a Cell MembraneMembrane

What does the cell membrane look like?

• It also contains several different types of proteins, carbohydrate markers, and cholesterol.

Types of Cell Transport

• Passive Transport- this type of transport requires NO energy because particles travel from where they are highly concentrated to a low concentrated area. They travel DOWN the concentration gradient.

HI

LO

Types of Cell Transport

• Active Transport- this type of transport does require energy. Particles travel from low concentration to high concentration. In other words, they move AGAINST or UP the concentration gradient.

HI

LO

Simple DiffusionSimple Diffusion

• Requires NONO energy

• Molecules move from area of HIGH to LOWHIGH to LOW concentration

DIFFUSIONDIFFUSION

Diffusion is a PASSIVEPASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY

Diffusion of LiquidsDiffusion of Liquids

Diffusion through a MembraneDiffusion through a Membrane

Cell membrane

Solute moves DOWN concentration gradient (HIGH to LOW)

OsmosisOsmosis• Diffusion of waterDiffusion of water

across a membraneacross a membrane• Moves from Moves from HIGH HIGH

water potentialwater potential (low (low solute) to solute) to LOW LOW water potentialwater potential (high (high solute)solute)

Diffusion across a membrane

Semipermeable

membrane

Diffusion of HDiffusion of H22O Across A O Across A

MembraneMembrane

High H2O potentialLow solute concentration

Low H2O potentialHigh solute concentration

Cell in Isotonic SolutionCell in Isotonic Solution

CELLCELL

10% NaCL90% H2O

10% NaCL

90% H2O

What is the direction of water movement?The cell is at _______________.equilibrium

ENVIRONMENTENVIRONMENT

NO NET NO NET MOVEMENMOVEMENTT

Cell in Hypotonic SolutionCell in Hypotonic Solution

CELLCELL

10% NaCL90% H2O

20% NaCL

80% H2O

What is the direction of water movement?

Cell in Hypertonic SolutionCell in Hypertonic Solution

CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

Cells in SolutionsCells in Solutions

Isotonic Solution

NO NET MOVEMENT OF

H2O (equal amounts entering

& leaving)

Hypotonic Solution

CYTOLYSIS

Hypertonic Solution

PLASMOLYSIS

Cytolysis & PlasmolysisCytolysis & Plasmolysis

Cytolysis Plasmolysis

Osmosis in Red Blood CellsOsmosis in Red Blood Cells

IsotonicIsotonic Hypotonic

Hypertonic

hypotonic hypertonic isotonic

hypertonic isotonic hypotonic

Three Forms of Transport Across the MembraneThree Forms of Transport Across the Membrane

Passive Passive TransportTransport

Simple DiffusionSimple Diffusion

Doesn’tDoesn’t require require energyenergy

Moves Moves high to lowhigh to low concentrationconcentration Example: Example: OxygenOxygen or or waterwater diffusing into a diffusing into a cell and cell and carbon carbon dioxidedioxide diffusing out diffusing out.

Passive Passive TransportTransport

Facilitated diffusion

Doesn’t require energy

Uses transport proteins to move high to low concentrationExamples: Examples: GlucoseGlucose or or amino acidsamino acids moving moving from blood into a from blood into a cell.cell.

Proteins Are Critical to Proteins Are Critical to Membrane FunctionMembrane Function

Types of Transport ProteinsTypes of Transport Proteins• Channel proteins are embedded in

the cell membrane & have a pore for materials to cross

• Carrier proteins can change shape to move material from one side of the membrane to the other

Facilitated DiffusionFacilitated Diffusion

Molecules will randomly move Molecules will randomly move through the through the porespores in in Channel Channel ProteinsProteins..

Facilitated DiffusionFacilitated Diffusion

• SomeSome Carrier Carrier proteinsproteins do not do not extend through the extend through the membrane.membrane.

• They They bond and drag bond and drag moleculesmolecules through through the lipid bilayer and the lipid bilayer and release them on the release them on the opposite side.opposite side.

Carrier ProteinsCarrier Proteins

• Other carrier Other carrier proteins proteins change shapechange shape to move to move materials materials across the cell across the cell membranemembrane

Active TransportActive Transport

Requires energy or ATP

Moves materials from LOW to HIGH concentration

AGAINST concentration gradient

Active transportActive transport

Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.

Called Na+-K+ Pump

Sodium-Potassium Sodium-Potassium PumpPump

3 Na+ pumped in for every 2 K+ pumped out; creates a membrane

potential

Moving the “Big Stuff”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.

ExocytosExocytosisis-

moving things out.

This is how many This is how many hormoneshormones are secreted and how are secreted and how nerve cellsnerve cells communicate with one another communicate with one another.

ExocytosisExocytosisExocytic Exocytic vesicle vesicle immediately immediately after fusion after fusion with plasma with plasma membrane.membrane.

Moving the “Big Moving the “Big Stuff”Stuff”Large molecules move materials into the Large molecules move materials into the

cell by one of cell by one of three forms of endocytosisthree forms of endocytosis.

PinocytosisPinocytosis

Most Most commoncommon form of endocytosis form of endocytosis. Takes in Takes in dissolveddissolved molecules as a molecules as a vesiclevesicle.

PinocytosisPinocytosis

• Cell forms an Cell forms an invaginationinvagination

• Materials Materials dissolve dissolve in waterin water to be to be brought into cellbrought into cell

• Called Called “Cell “Cell Drinking”Drinking”

Example of Example of PinocytosisPinocytosispinocytic vesicles forming mature transport vesicle

Transport across a capillary cell (blue).

Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis

Some Some integral proteinsintegral proteins have have receptorsreceptors on their surface to on their surface to recognize & take in recognize & take in hormones, hormones, cholesterolcholesterol, etc., etc.

Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis

Endocytosis – Phagocytosis Endocytosis – Phagocytosis

Used to Used to engulf large particlesengulf large particles such such as food, as food, bacteriabacteria, etc. into vesicles, etc. into vesicles

Called Called “Cell Eating”“Cell Eating”

Phagocytosis About to OccurPhagocytosis About to Occur

PhagocytoPhagocytosissis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)

ExocytosisExocytosis The opposite of endocytosis is exocytosis. The opposite of endocytosis is exocytosis. Large moleculesLarge molecules that are manufactured in that are manufactured in

the cell are the cell are releasedreleased through the cell through the cell membranemembrane..

Inside Cell Cell environment