a8) Transport Across the Membrane

8/11/2019 a8) Transport Across the Membrane

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PRESCRIBED LEARNING OUTCOMES(Chapter 4, pp. 65-76)

G1. Apply knowledge of organic molecules to explain the structure and

function of the fluid-mosaic model

G2. Explain why the cell membrane is described as selectively

permeable

G3. Compare and contrast the following: diffusion, facilitated transport,

osmosis, and active transport.

G4. Explain factors that affect the rate of diffusion across a cell

membrane.

G5. Describe endocytosis, including phagocytosis and pinocytosis, and

contrast it with exocytosis.

G6. Predict the effects of hypertonic, isotonic, and hypotonic

environments on animal cells

G7. Demonstrate an understanding of the relationship and significance

of surface area to volume, with reference to cell size.


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_____ Active transport

_____ ATP energy

_____ Blood antigen

_____ Concentration gradient

_____ Crenate

_____ Diffusion_____ Endocytosis

_____ Exocytosis

_____ Facilitated transport

_____ Glycolipid

_____ Glycoprotein

_____ Hemolysis_____ Hypertonic

_____ Hypotonic

_____ Isotonic

_____ Na/K pump

_____ Neuron

_____ Osmosis

_____ Osmotic pressure

_____ Phagocytosis

_____ Phospholipid

_____ Pinocytosis

_____ Polarity

_____ Protein channels

_____ Receptor sites

_____ Selectively permeable

_____ Solubility

_____ Solute

_____ Solvent

_____ Surface area/volume ratio_____ Thyroid gland

_____ Thyroxin

_____ Tonicity

_____ Turgor pressure

_____ Villi

_____ Viscosity


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SELECTIVELY PERMEABLE: Controls what comes in and outof the cell. Does not letlarge, chargedor polarthings through

without help.


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FLUID MOSAIC MODEL: The phospholipids move, thus

allowing small non-polar molecules to slip through.


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GLYCOLIPIDS and GLYCOPROTEINS: Act as

receptorsreceive info. from body to tell cell

what to do.


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INTEGRAL PROTEINS: assistsspecific larger and charged

molecules to move in and outof the cell. Can act as tunnels

or will change shape.


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CHOLESTEROL: Reducesmembrane fluidityby reducingphospholipid movement. Also stops the membrane from

becoming solidat room temperatures.


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CYTOSKELETON: A cytoskeleton acts as a framework thatgives the cell it's shape. It also serves as a monorail to

transportorganelles around the cell.


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1. Passive transportmoves

molecules from a [high]to[low]in order to establish

equilibrium.

The molecules may or maynot need to use aprotein

channel or carrier.

Everything that is transported across the cell membranetakes place by one of two fundamental processes:


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2. Active transportmoves molecules from [low]to [high],

AGAINSTthe concentration gradient and this process

requiresenergyin the form of ATP.


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Simple Diffusionis a passiveprocess ( noenergy required).

Some substances will diffuse through

membranes as if the membranes

werent even there.

Molecules diffuse until they are

evenlydistributed.

The molecules move from an area of [high] to [low].

EXAMPLES of moleculesthat easily cross cell membranes

by simple diffusion are: oxygen, carbon dio xide, alcoho ls,

fatty acids, gly cerol, and urea.
http://www.schoolscience.co.uk/content/3/chemistry/materials/images/diffusion3.gif


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Alcohol Urea

Fatty Acids, Glycerol,


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The rate of diffusion will be increased when there is :

1. Concen trat ion: the difference in [ ] between two areas

(the [ ] gradient) causes diffusion. The greater the

difference in concentration,the fasterthe diffusion.

2. Mo lecu lar s ize: smaller substances diffuse more quickly.

Large molecules (such as starches and proteins) simply

cannot diffuse through.

3. Shape of Ion /Molecule: a substances shape may prevent

it from diffusing rapidly, where others may have a shape

that aids their diffusion.


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4. Visco sity o f the Medium: the lower the viscosity, the moreslowlymolecules can move through it.

5. Movement of the Medium: currents will aid diffusion. Like

the wind in air, cytop lasm ic steaming(constant movement

of the cytoplasm) will aid diffusion in the cell.

6. So lu bi l i ty : lipid- soluble molecules will dissolve through

the phospholipid bilayer easily,as will gases like CO2and

O2.

7. Polarity: waterwill diffuse, but because of its polarity, it will

notpass through the non-polar phospholipids. Instead,

water passes though specialized protein ionchannels.


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Osmosisis the diffusionof wateracross a selectively

permeable membranedriven by a difference in the

concentration of soluteson the two sides of the membrane.

A selectively permeable

membrane is one that

allows unrestricted

passage of water, but not

solute molecules or ions.

So it is the WATER THAT

MOVESto create

equilibrium!!!


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Osmosis requires NOENERGY.

Osmosis is the net movement of

WATERmolecules from the area

of [high]of water to the area of

[low]of water until it is equally

distributed.

Because membranes often

restrict or preventthe movementof some molecules, particularly

large ones, the water (solvent)

must be the one to move.


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To cross the membrane,

water must move througha protein ion channel.

In certain cellular

conditions, these protein

channels can be opened

or closed (ie: in the

kidneys, large

intestines) depending on

how much water isneeded by the body.


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ISOTONIC SOLUTION:

1. the solution concentration is

equalon both s ides of themembrane.

2. There is no net concentration

difference across the cell

membrane

3. Water moves back and forth,

but there is no net gain or

lossof water.

The ton ic i ty o f a solut ion w il l affect the size & shape of cel ls:


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HYPERTONIC SOLUTION:

1. The solution outsidethe cell

is more concentrated than

inside.

2. There is more water inside

the cell and the water will

move outof the cell.

3. This causes the cell toshrink

4. *Memory Trick... Hyper

people get skinny!


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HYPOTONIC SOLUTION:1. The concentration insidethe

cell is more concentrated than

outside.

2. Therefore there is more wateroutside of the cell, and water

will move intothe cell.

3. This will cause the cell toswell.

4. *Memory Trick...Hippos are

FAT!


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In Biology we usually talk about the SOLUTIONS tonicity,

NOT the cells!


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*MEMORY TRICK: If you eat a lot of sugar (ie: solute)

you get HYPER. The solution with a lot of solute is

called HYPEROSMOTIC.


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When we speak of plants, we speak of TURGOR PRESSURE.

Which of these cells is in a hypertonic solution? Hypotonic?


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Facilitated Transport: Some molecules are not

normally able to pass through the lipid membrane,

and need channel or carrierproteinsto help

them move across.

This does notrequire energywhen moving

from [H] to [L] (with the concentration gradient).

Molecules that need help to move through theplasma membrane are either charged, polar,

or too large.


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Each protein

channel or protein

carrier will allowonly ONE TYPE

OF MOLECULEto

pass through it.


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Many channels contain a gatewhich control the channel's

permeability.

When the gate is open, the channel transports, and when thegate is closed, the channel is closed.

These gates are extremely important in the nervecells.
http://bio.winona.msus.edu/berg/ANIMTNS/voltgtan.gif


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http://nutrition.tufts.edu/img/information/matters/muscle.jpg


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Active Transport: the movement of

polar, large, and charged molecules

moving againstthe [ ] gradient

(uphill).

EXAMPLES of moleculesthat

move this way are all of the things

that require protein carriers to move

across the plasma membrane.

ions(like Na+ and K+ in cells, and

iodine) and sugars, amino acids,

nucleotides...


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Example 2: a Na/K pump (mostly in nerve membranes).These function to restore electrical order in a nerve after an

impulse has traveled along it.
http://bio.winona.msus.edu/berg/ANIMTNS/nakan.gif


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Example 3: In order to make ATP in the mitochondria, aproton pump (hydrogen ion) is required.


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http://www.realrunner.com/common/nutrition/energyfuel.gif


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Endocytosis: (Endo means in).

Endocytosis is the taking in of molecules or particles by

invaginationof the cell membrane forming a vesicle.

This requires energy.


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There are two types of endocytosis:

1. pinocytosis(cell drinking): small

molecules are ingested and a vesicle is

immediately formed. This is seen in

small intestinecells (villi)

2. phagocytosis(cell eating): large

particles, (visible with light microscope)

are invaginated into the cell (ie: white

blood cells eat bacteria).


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Exocytosis: (Exo means out.)

Exocytosis is the reverseof

endocytosis.

This is where a cell releases the

contentsof a vesicle outside of the cell.

These contents may be wastes, proteins, hormones, or

some other product for secretion.

This also requires energy.

Example: vesicles from the Golgifuse with the plasma

membrane and the proteins are released outside of the cell.


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Cells exist individually, or in groups

forming tissues, organs, and

eventually organisms.

Their sizeis a very important

factor for their survival.

Cells are the size they are because

that is the size they have to be

in order to functioneffectively.The materials it needs to use, and the wastesit needs to

remove must pass in and out of the cell through the cell

membrane.


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As a cell grows, it suffers the possibility of the volume

increasing fasterthan the surface area.

The bigger the cell, the more it needsand the more it needs

to get rid of.

If the cell gets too big, there will not be enough roomon the

plasma membranefor things to get in and out quickly

enough to maintain the cell.

Why? Its surface area has not kept up to its volume size.

When the volume of a cell increases, the amount of surface

area does not increase in the same proportion.


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When cells grow larger,if they dont want to

die, the only real

solution is to divide.

Once a cell has divided,

the surface area to

volume ratio will

increaseand the

problem is solved.

*When you see questions regarding surface area to

volume ratio think of a water balloon


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volume ratio, think of a water balloon.

(ie: when you squish a water balloon, it has the same

volume, but the surface area is increased!)

a8) Transport Across the Membrane

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