The Cell MembraneMs. NapolitanoHonors Biology

12/10 – Do Now Please get your clickers! Turn in your webquest if you did not

hand it in last class. Think about the following question:

Why are cells small?

The Cell Membrane Selectively permeable – allows some

substances to cross more easily than others 8 nm thick Fluid mosaic model

Fluid structure of phospholipids with a mosaic of various proteins embedded in it

Cholesterol maintains fluidity – acts as a temperature buffer less fluid as temp increases (restricts

movement) More fluid as temp decreases (maintains space)

The Structure of the Cell Membrane

Membrane Proteins Different types of cells contain different

types of membrane proteins

Integral proteins – embedded into the hydrophobic core of the lipid bilayer Can go all the way through the membrane

Peripheral proteins – on the surface of the membrane

Types of Membrane Proteins Transport

Channel/carrier proteins allow polar molecules & ions to pass through hydrophobic layer

Channel & carrier proteins are substance specific Enzymatic Signal Transduction (chemical messages)

Receptor proteins transmit information from outside of the cell to inside of the cell

Cell Recognition ID tags – glycolipids or glycoproteins

Intercellular Joining Join together adjacent cells

Cell Support Attach to cytoskeleton or extracellular matrix for stability

What type of membrane protein is this?

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1. Integral2. Peripheral

A cell that has been frozen will have a more fluid membrane than a cell at room temperature.

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1. True2. False

What would happen to a cell that lacks cholesterol in the membrane?

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1. It would not be able to transport materials into/out of the cell

2. The membrane would change drastically with temperature

3. It would not be able to use enzymes effectively

4. Chemical messages would not be able to get into the cell

What is the function of membrane carbohydrates?

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1. Transport2. Signal

transduction3. Cell recognition4. Intercellular

joining

Passive Transport Passive Transport – movement across the cell

membrane that does not require energy Diffusion – movement of particles from an area of

high concentration to an area of low concentration until an equilibrium is reached Said to go with/down its concentration gradient

Concentration gradient – the difference in the concentration of a substance across a space

Equilibrium – concentration of a substance is equal throughout a space

Doesn’t stop moving

OsmosisOsmosis – the diffusion of free water

across a selectively permeable membrane

Water diffuses across the cell membrane from a region of low solute concentration

to that of a higher solute concentration until it reaches equilibrium

Really cool video!http://www.youtube.com/watch?v=EsJ73x4ycp0

Osmoregulation in Cells without Cell Walls

Osmoregulation – control of water balance Tonicity – ability of a solution to cause a cell to

gain/lose water Isotonic solution – no net movement of water

across the cell membrane Hypertonic solution – more free water inside the

cell Cell loses water to environment and shrivels

Hypotonic solution – less free water inside the cell Water will enter the cell and swell (and maybe lyse) Some cells have a contractile vacuole to pump water

out of the cell

Animal Cells

Osmoregulation of Cells with Cell Walls

Plant cells are healthiest in a hypotonic solution, osmotic pressure keeps cell walls turgid (very firm)

Plant cells are flaccid (limp) in an isotonic solution

In a hypertonic solution, the cell membrane will shrink and pull away from the cell wall Called plasmolysis (wilting)

Plant Cell

U – Tube (not YouTube!)

Which of the following can readily diffuse across a lipid bilayer?

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1. Glucose2. Oxygen3. Carbon dioxide4. Both 2 & 3

If you immerse a living cell in a hypotonic solution, water will…

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1. Diffuse into the cell

2. Diffuse out of the cell

3. Show no net movement

Plant 1 is in better shape than plant 2 because the cells of plant 1 are…

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1. Turgid2. Flaccid3. Undergoing

plasmolysis4. The same as

plant 2Plant 1Plant 2

The image below is a U-Tube with a semi-permeable membrane. How will water flow?

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1. It won’t2. Left to right 3. Right to left

12/ 16 Do Now: Get Your Clicker! Compare/Contrast Active & Passive

Transport Compare/Contrast Diffusion & Osmosis

Facilitated Diffusion Facilitated diffusion: passive transport aided

by proteins Channel proteins – hydrophilic passageways

Some always open for diffusion Rate of movement is determined by concentration

gradient (+) charged ions more likely to diffuse into the cell (-) charged ions more likely to diffuse out of the cell Some ion channels have gates and can be opened

by: Stretching of the cell membrane Change in electrical charge Binding of specific molecules

Voltage Gated ChannelsNerve cells transmit electrical signals by

opening a series of Na+ gated channels1. Channel is closed2. Area changes voltage3. Channel opens briefly4. Na+ flood into cell – voltage changes5. Channel closes and electrical signal passes

on to the next voltage channel

Chemically (Ligand) Gated Channels Nerve cells send out a neurotransmitter called

acetylcholine (ACh) to nearby muscle cells to signal muscles to contract1. ACh binds to ACh receptor proteins2. Receptor gate opens for a microsecond to allow

Na+ in3. Na+ sets off muscle contraction

Facilitated Diffusion Carrier Proteins1. Specific substance

binds to carrier protein2. Protein changes shape

and transports substances across cell membrane

3. Molecule is released into the cell, and carrier protein returns to its original shape

Which image best represents facilitated diffusion?

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1. 12. 23. 34. 4

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____are transported by a particular carrier or pass through a particular channel.

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1. All water soluble ions or molecules

2. Certain water soluble molecules or ions

3. All insoluble molecules or ions

4. Certain insoluble ions or molecules

5. Only the smallest molecules or ions

Active TransportActive Transport – uses energy to move

solutes against the concentration gradient

Carrier proteins act as “pumps” powered by ATP

Examples: Sodium Potassium Pump Proton Pump Cotransport

Sodium Potassium Pump Pumps 3 Na+ out of the cell and 2 K+ into the cell Actively transports both ions against their

concentration gradient, powered by ATP Prevents Na+ from accumulating in the cell Steps:

1. 3 Na+ and a P (from ATP) bind to inside protein pump

2. Pump changes shape transporting 3 Na+ across membrane and out

3. 2 K+ bind to pump and are transported across membrane

4. 2 K+ and P are released inside of cell

Sodium Potassium Pump

The sodium-potassium pump passes

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1. More Na+ out than K+ in

2. K+ out and Na+ in on a one-for-one basis

3. Na+ out and K+ in on a one-for-one basis

4. K+ and Na+ in the same direction

Proton PumpActively transports protons (H+) through

the internal membranes of mitochondria and chloroplasts

Cotransport (Coupled Transport) Cotransport – an ATP-powered pump that

transports a specific solute Can indirectly drive the active transport of

several other solutes Ex: as proton pumps pump H+ out, H+ diffuse back into the cell pulling sucrose molecules into the cell with it

By a mechanism called cotransport

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1. sugar moves down (with) its concentration gradient while sodium moves up (against) its concentration gradient

2. sodium moves outward against is concentration gradient while sugar moves inward down its concentration gradient

3. sugar and sodium move inward down their concentration gradient

4. sodium moves inward down its concentration gradient while sugar moves inward up its concentration gradient

5. sodium and sugar move outward against their concentration gradient

Bulk Transport Substances that are too large to be transported by

carrier proteins Exocytosis (export)

Secretion of macromolecules by fusion of vesicles with membranes, releasing the contents outside of the cell

Endocytosis (import) Cell membrane engulfs particles and pinches off to

form vesicles inside the cell. Vesicle may fuse with lysosomes or other organelles

3 Types: Phagocytosis – engulf another organism Pinocytosis – engulf fluid Receptor-mediated - specific

Exocytosis (top)/Endocytosis (bottom)

A cell engaged in phagocytosis must be

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1. engulfing a live organism

2. acquiring a liquid 3. engulfing a dead

organism4. transporting bulk

dissolved nutrients

5. transporting bulk solid material

Substances transported by facilitated diffusion

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1. move passively through specific channels from an area of greater concentration to one of lower concentration

2. are limited to solvents3. must have movements coupled to

those of other substances4. may flow to a region of higher

concentration by the expenditure of energy

5. are restricted to only one direction through the membrane

A contractile vacuole is an organelle that pumps excess water out of many freshwater protozoan cells. A freshwater protozoan was placed in solution A and observed to form contractile vacuoles at a rate of 11 per minute. The same protozoan was then placed in solution B and observed to form contractile vacuoles at a rate of 4 per minute. Based on this information, which of the following statements is correct?

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1. Solution A is hyperosmotic to solution B.

2. Solutions A and B are isosmotic.

3. Solution B is hyperosmotic to solution A.

4. Solutions A and B are isosmotic to the protozoan cell.

5. Both a and b

The methods of membrane transport that don't require protein channels or carriers are

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1. osmosis 2. Diffusion3. Phagocytosis4. Exocytosis5. all of the above