1 CELL MEMBRANES and TRANSPORT. 2 The Cell 3 Cell Membrane All living things are surrounded by a membrane. A cell membrane is also known as plasma.

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CELL MEMBRANESCELL MEMBRANESandand

TRANSPORTTRANSPORT

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The CellThe Cell

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Cell MembraneCell Membrane All living things are surrounded by a membrane.All living things are surrounded by a membrane.

A cell membrane is also known as plasma A cell membrane is also known as plasma membrane.membrane. Controls exchange of materials such as Controls exchange of materials such as nutrients and waste between cells and nutrients and waste between cells and their environment.their environment. Has other important functions Has other important functions

for example to enable cells to receive for example to enable cells to receive hormones.hormones.

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Cell MembraneCell Membrane

Fluid Mosaic Model - proteins Fluid Mosaic Model - proteins embedded in a phospholipid bilayer.embedded in a phospholipid bilayer.

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Fluid mosaic modelFluid mosaic model

FLUID- because individual phospholipids and FLUID- because individual phospholipids and proteins can move around freely within the layer, proteins can move around freely within the layer, like it’s a liquid.like it’s a liquid.

MOSAIC- because of the pattern produced by the MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane scattered protein molecules when the membrane is viewed from above.is viewed from above.

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HYDROPHILIC heads HYDROPHILIC heads (water liking)(water liking)-Attracted to the -Attracted to the water water

HYDROPHOBIC tails HYDROPHOBIC tails (water fearing)(water fearing)-repel water-repel water

Cell membranes are made Cell membranes are made of PHOSPHOLIPIDSof PHOSPHOLIPIDS

A PhospholipidA Phospholipid

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A Phospholipid BilayerA Phospholipid BilayerPhospholipids can form: Phospholipids can form:

BILAYERSBILAYERS

-2 layers of -2 layers of phospholipids with phospholipids with hydrophobic tails hydrophobic tails protected inside by protected inside by the hydrophilic heads.the hydrophilic heads.

The PHOSPHOLIPIDThe PHOSPHOLIPIDBILAYER is the basicBILAYER is the basicstructure of membranes.structure of membranes.

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Bilayer: 2 layers of phospholipidsBilayer: 2 layers of phospholipids The heads stay on the outside and the The heads stay on the outside and the

tails stay on the inside.tails stay on the inside.

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Cell MembraneCell Membrane

Cell surface proteinsCell surface proteins a. Channel proteins - transport food and a. Channel proteins - transport food and

other molecules into the cell and other molecules into the cell and transport wastes out of the cells.transport wastes out of the cells.

b. Receptor proteins - gather information b. Receptor proteins - gather information about the cell’s surroundings.about the cell’s surroundings.

c. Cell surface markers - identify the type c. Cell surface markers - identify the type of cell, important for cell recognition. of cell, important for cell recognition.

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Movement of selected Movement of selected molecules across the cell molecules across the cell

membrane membrane

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Cell MembraneCell Membrane

Permeability of the cell membranePermeability of the cell membrane 1. Semi permeable/selectively 1. Semi permeable/selectively

permeable - only certain substances can permeable - only certain substances can pass across the membrane.pass across the membrane.

2. Factors that determine whether a 2. Factors that determine whether a molecule can pass through a membrane molecule can pass through a membrane or not:or not:• a. size a. size • b. typeb. type

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Transport MechanismsTransport Mechanisms

Transport Mechanisms - moving material in Transport Mechanisms - moving material in and out of the celland out of the cell

Concentration gradient - the difference in the Concentration gradient - the difference in the amount of a substance inside and outside of amount of a substance inside and outside of the cellthe cell 1. Going “with the gradient”-moving from high to 1. Going “with the gradient”-moving from high to

low concentrationlow concentration 2. Going “against the gradient”-moving from low 2. Going “against the gradient”-moving from low

to high concentrationto high concentration 3. Equilibrium exists when the concentration of 3. Equilibrium exists when the concentration of

molecules is the same throughout a space (inside molecules is the same throughout a space (inside and outside the cell)and outside the cell)

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Transport MechanismsTransport Mechanisms

Two categories of transport based on Two categories of transport based on concentration gradient and the need for concentration gradient and the need for energyenergy 1. Passive transport does not require 1. Passive transport does not require

energy energy • goes with the gradient.goes with the gradient.

2. Active transport requires energy 2. Active transport requires energy • goes against the gradient.goes against the gradient.

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Methods of Transport Methods of Transport Across MembranesAcross Membranes

1. Diffusion1. Diffusion

2. Osmosis2. Osmosis

3. Facilitated Diffusion3. Facilitated Diffusion

4. Active Transport4. Active Transport

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Methods of Transport Methods of Transport Across MembranesAcross Membranes

1.1. Diffusion -passive transport - no Diffusion -passive transport - no energy expendedenergy expended2. Osmosis - Passive transport of water2. Osmosis - Passive transport of water

across membrane across membrane3.3. Facilitated Diffusion - Use of proteins to Facilitated Diffusion - Use of proteins to carry molecules or ions acrosscarry molecules or ions across4.4. Active Transport- requires energy to Active Transport- requires energy to transport molecules against a transport molecules against a concentration gradient – energy is concentration gradient – energy is in the form of ATPin the form of ATP

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Types of Transport

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Passive Transport Passive Transport MechanismsMechanisms Diffusion Diffusion

Movement of molecules from an area of Movement of molecules from an area of high concentration to an area of low high concentration to an area of low concentration.concentration.

Movement from one side of a Movement from one side of a membrane to anothermembrane to another Example: smoke across a room, food Example: smoke across a room, food

coloring dropped into water, oxygen coloring dropped into water, oxygen in lungsin lungs

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Diffusion

Diffusion in action

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Passive Transport MechanismsPassive Transport MechanismsOsmosisOsmosis

Diffusion of waterDiffusion of water Direction of osmosis-the direction of water Direction of osmosis-the direction of water

flow depends upon the concentration of flow depends upon the concentration of solute and solvent (water)solute and solvent (water)

Tonicity-term used to compare 2 solutions Tonicity-term used to compare 2 solutions (usually the inside and the outside of the (usually the inside and the outside of the cell)cell)• a. Hypotonic - less solute (more water)a. Hypotonic - less solute (more water)• b. Hypertonic - more solute (less water)b. Hypertonic - more solute (less water)• c. Isotonic - equal amounts of solute and waterc. Isotonic - equal amounts of solute and water

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Passive Transport MechanismsPassive Transport MechanismsOsmosisOsmosis

Water will flow from a hypotonic Water will flow from a hypotonic solution to a hypertonic solutionsolution to a hypertonic solution

Will water move in an isotonic Will water move in an isotonic solution?solution? •Yes, but it won’t be noticeable-Yes, but it won’t be noticeable-

equilibrium is establishedequilibrium is established

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Osmosis

How Osmosis works

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SolutionsSolutions Solutions are made of solute and a Solutions are made of solute and a

solventsolvent Solvent - the liquid into which the Solvent - the liquid into which the

solute is poured and dissolved. solute is poured and dissolved. Solute - substance that is dissolved Solute - substance that is dissolved

or put into the solvent. or put into the solvent. Salt and sucrose are solutes.Salt and sucrose are solutes.

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Passive Transport Passive Transport MechanismsMechanisms

Turgor pressure/osmotic pressure-Turgor pressure/osmotic pressure-pressure due to water in cell.pressure due to water in cell.•Analogy: air pressure in a tire.Analogy: air pressure in a tire.

When a cell has high turgor pressure, it is When a cell has high turgor pressure, it is bigger and stiffer. bigger and stiffer.

When a cell has low turgor pressure, it is When a cell has low turgor pressure, it is smaller and flimsy.smaller and flimsy.

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Passive Transport Passive Transport MechanismsMechanisms

Plasmolysis - wilting of a cell due to Plasmolysis - wilting of a cell due to loss of turgor pressureloss of turgor pressure

Cytolysis - bursting of a cell due to an Cytolysis - bursting of a cell due to an increase in turgor pressure.increase in turgor pressure. How do plant cells avoid cytolysis? Cell How do plant cells avoid cytolysis? Cell

wallswalls How do unicellular freshwater organisms How do unicellular freshwater organisms

avoid bursting? Contractile vacuoles.avoid bursting? Contractile vacuoles.

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Plant and Animal Cells put into various solutions

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Passive Transport Passive Transport MechanismsMechanisms

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Passive Transport Passive Transport MechanismsMechanisms

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Passive Transport Passive Transport MechanismsMechanisms

Facilitated diffusion - transport of Facilitated diffusion - transport of specific molecules across a specific molecules across a membrane with the help of a channel membrane with the help of a channel proteinprotein An example of a molecule that is often An example of a molecule that is often

transported in this manner is glucosetransported in this manner is glucoseHow Facilitated Diffusion Works

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Active Transport MechanismActive Transport Mechanism

Active Transport MechanismActive Transport Mechanism(requires energy in the form of ATP)(requires energy in the form of ATP)

Ex. Ex. Sodium-potassium pump Sodium-potassium pump - pumps sodium - pumps sodium

ions out and forces potassium ions in. ions out and forces potassium ions in. • Important for conducting nerve impulses and Important for conducting nerve impulses and

muscle contraction.muscle contraction. Proton pump-transport protons through Proton pump-transport protons through

membranes of chloroplasts and membranes of chloroplasts and mitochondriamitochondria

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Active Transport MechanismActive Transport Mechanism Endocytosis - process of bringing Endocytosis - process of bringing

larger molecules into the cell by larger molecules into the cell by engulfing them.engulfing them. 1. Pinocytosis – liquids1. Pinocytosis – liquids 2. 2. PhagocytosisPhagocytosis - solids - solids

• amoebas eat this way amoebas eat this way • white blood cell engulf bacteriawhite blood cell engulf bacteria