Cell MembraneCell Membrane

Cell MembraneCell Membrane -Thin flexible layer around -Thin flexible layer around

cellcell -Controls what goes in or -Controls what goes in or

out of cellout of cell -Provides protection and -Provides protection and

supportsupport -Made of a -Made of a phospholipid phospholipid

bilayerbilayer—two layers of —two layers of lipidslipids

-Proteins are embedded in -Proteins are embedded in bilayerbilayer

-These help move materials -These help move materials across the cell membraneacross the cell membrane

Phospholipids in cell membrane are Phospholipids in cell membrane are arranged in two layers with arranged in two layers with nonpolar fatty acid “tails” together. nonpolar fatty acid “tails” together. The polar “heads” face the watery The polar “heads” face the watery environments found inside and environments found inside and outside the cell.outside the cell.

This structureThis structure

creates a barriercreates a barrier

that helps the cellthat helps the cell

maintain homeostasismaintain homeostasis

Cell Membrane ClipCell Membrane Clip

http://www.youtube.com/watch?http://www.youtube.com/watch?v=GW0lqf4Fqpgv=GW0lqf4Fqpg

The cell membrane can be The cell membrane can be described as a described as a Fluid Mosaic ModelFluid Mosaic Model. . – The phospholipids in the bilayer float The phospholipids in the bilayer float

together like beach-balls on water. The together like beach-balls on water. The lipids are in constant motion, and can lipids are in constant motion, and can slide past each other, and other slide past each other, and other molecules, like proteins can move in molecules, like proteins can move in between them.between them.

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Section 7-3

Figure 7-12 The Structure of the Cell Membrane

Movement across Cell Movement across Cell BoundariesBoundaries

Passive TransportPassive Transport Does not require energyDoes not require energy Materials move from area of high Materials move from area of high

concentration to area of low concentration to area of low concentration until concentration until equilibriumequilibrium * is * is reachedreached

Three types of passive transportThree types of passive transport

1.1. DiffusionDiffusion is the movement of particles is the movement of particles from where they are more from where they are more concentrated* to where they are less concentrated* to where they are less concentrated. concentrated.

It occurs due to the random movement It occurs due to the random movement of particles.of particles.

It continues until a It continues until a dynamic equilibriumdynamic equilibrium is reached—the concentration is the is reached—the concentration is the same on both sides of the membrane.same on both sides of the membrane.

Particles still move in both directions Particles still move in both directions across membrane, but there is no across membrane, but there is no further change in concentration.further change in concentration.

2.2. OsmosisOsmosis is the movement of water is the movement of water through a through a selectively permeableselectively permeable membrane.membrane.

This means that some substances can This means that some substances can pass through the membrane, and others pass through the membrane, and others can’t due to their size or charge.can’t due to their size or charge.

Isotonic: Isotonic: concentrations of the water are the same both inside concentrations of the water are the same both inside and outside the cell; water enters and leaves cell at same rate; and outside the cell; water enters and leaves cell at same rate; cell size doesn’t changecell size doesn’t change

Hypotonic:Hypotonic: lower water concentration inside the cell than lower water concentration inside the cell than outside; water enters the cell; cell swellsoutside; water enters the cell; cell swells

Hypertonic:Hypertonic: lower water concentration outside the cell than lower water concentration outside the cell than inside; water moves out of the cell; cell shrinksinside; water moves out of the cell; cell shrinks

3. 3. Facilitated DiffusionFacilitated Diffusion is when large is when large molecules like glucose move across the molecules like glucose move across the cell membrane through cell membrane through protein protein channels: channels: protein molecules embedded protein molecules embedded in the lipid bilayer.in the lipid bilayer.

They are specific to different substances They are specific to different substances and have and have carbohydrate marker chainscarbohydrate marker chains on them that act as identification cards.on them that act as identification cards.

The protein channels act like an open The protein channels act like an open gate for the substance they are marked gate for the substance they are marked for.for.

Proteinchannel

Section 7-3

Passive Transport ClipPassive Transport Clip

http://www.youtube.com/watch?http://www.youtube.com/watch?v=2UPqLm-uDnIv=2UPqLm-uDnI

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Section 7-3

Figure 7-12 The Structure of the Cell Membrane

Active TransportActive Transport Requires energy from the cellRequires energy from the cell Materials move from an area of Materials move from an area of

lower concentration to an area of lower concentration to an area of higher concentration.higher concentration.

It is usually done by transport It is usually done by transport proteins or “pumps” found in the proteins or “pumps” found in the cell membranecell membrane

Three types of active transportThree types of active transport

Sodium/Potassium Sodium/Potassium PumpPump

In animal cell In animal cell membranesmembranes

Uses energy to Uses energy to move Namove Na++ out of out of cell and Kcell and K++ into into cellcell

Endocytosis:Endocytosis: Process of moving large molecules Process of moving large molecules

intointo a cell a cell Materials enter the cell by making Materials enter the cell by making

folds in the cell membrane.folds in the cell membrane. Requires energyRequires energy

Exocytosis:Exocytosis: Process of Process of

moving large moving large materials out of materials out of the cell.the cell.

Materials leave Materials leave the cell by fusing the cell by fusing vesicles with the vesicles with the cell membrane.cell membrane.

Requires energyRequires energy

Video CLipVideo CLip

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