cellular transport notes (text 7.2 p 175-178 & 8.1 p 194-200)

Cellular Transport NotesCellular Transport Notes(Text 7.2 p 175-178 & (Text 7.2 p 175-178 &

8.1 p 194-200)8.1 p 194-200)

DefinitionsDefinitions

Cell membranes are completely permeable to water. The environment the cell is exposed to can

have a dramatic effect on the cell.

Solutions are made of solute and a solvent

Solvent - the liquid (water) into which the solute is poured and dissolved.

DefinitionsDefinitions

Solute: substance that is dissolved or put into the solvent (water). Common cell solutes include salts, sugars,

some minerals (iron ions and calcium ions) and protons (electrons from acids).

Eg. Sodium chloride dissolved in water makes a saline solution. The sodium chloride is the solute. The water is the solvent.

ConcentrationConcentration

amount of solute per unit volume of solution.

expressed in mass/volume (g/100ml - percentage), ppm (parts per million), and moles/volume (molarity).

The greater the mass or moles per unit volume, the more concentrated the solution.

Concentration GradientConcentration Gradient

Difference in concentration between solute molecules from area high concentration to area of low concentration.

The greater the difference the faster the rate of diffusion and vice versa i.e. the steeper the hill

Cellular MembraneCellular MembraneStructure and Structure and

FunctionFunction

All cells have a cell membrane Chiefly responsible for maintaining

homeostasis inside a living cell using different methods to transport molecules in and out of the cell.

TEM picture of a real cell membrane.

Cellular MembraneCellular MembraneStructure and Structure and

FunctionFunction

Too much water can burst the cell Too many wastes can poison the cell The cell cannot tolerate any great variations

in ion conditions.

TEM picture of a real cell membrane.

Jobs of the Cell Jobs of the Cell MembraneMembrane

1. Provides protection and support for the cell2. Regulate the exchange of substances (gases and

ions)

3. Communicates with other cells

4. Identification (proteins and carbohydrates on its surface)

TEM picture of a real cell membrane.

http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf

http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf

Proteins

Membrane movement animation

Polar heads love water & dissolve

Non-polar tails hide from water

Carbohydrate cell markers

Fluid Mosaic Model of the

cell membrane

Lipid Bilayer

- 2 phospholipid layers

a. Phosphate head is polar (hydrophilic – water loving)

b. Fatty acid tails non-polar (hydrophobic – water fearing)

c. Proteins embedded in membrane

Fluid PortionFluid Portion

Phospholipid

Lipid Bilayer

a. Selectively permeable: Allows some molecules in and keeps other molecules out

b. The structure helps it be selective!

Cell Membrane Pores Cell Membrane Pores

Pores

Outside of cell (interstitial)

Inside of cell (cytoplasm)

Proteins

Transport Protein Phospholipids

Carbohydratechains

Lipid Bilayer

Go to Section:

Animations of membrane of membrane

structurestructure

http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf

The different components of a plasma membrane are integral proteins, peripheral proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol, and lipoproteins.

Construction of the Cell Membrane - Learning Activity

detailed cell membrane animation

Proteins Embedded in Membrane Proteins Embedded in Membrane Serve Different FunctionsServe Different Functions

Transport Proteins regulate movement of substance

Channel Proteins form small openings for molecules to diffuse

through like water

Carrier Proteins binding site on protein surface "grabs" certain

molecules and pulls them into the cell animation

Gated ChannelsGated Channels similar to carrier proteins, not always "open"—

eg. Bind and pull in calcium ions when needed. This requires cell energy—active transport.

Receptor ProteinsReceptor Proteins

molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins)

e.g. The junction between nerve cells e.g. The junction between nerve cells requires the transmission of requires the transmission of neurotransmitters between synaptic gapsneurotransmitters between synaptic gaps—these chemicals bind onto receptor —these chemicals bind onto receptor proteins.proteins.

Recognition Proteins - ID tags, to identify cells to the body's immune system (called antigens)

TRANSPORT MECHANISMSTRANSPORT MECHANISMS

1. PASSIVE TRANSPORT

2. ACTIVE TRANSPORT1. ENDOCYTOSIS

2. EXOCYTOSIS

Types of Cellular TransportTypes of Cellular Transport

Passive Transport

doesn’t use energy

1. Diffusion

2. Facilitated Diffusion

3. Osmosis

Active Transport

uses energy

1. Protein Pumps

2. Endocytosis

3. Exocytosis

high

low

This is gonna

be hard

work!!

high

low

Weeee!!!

•Transport Animations

Passive Transport (p 198)Passive Transport (p 198) cell uses no energy molecules move randomly Molecules spread out from an area of

high concentration to an area of low concentration.

i.e. down a concentration gradient (High Low) Passive Transport Animation

3 Types of Passive Transport3 Types of Passive Transport

1. Diffusion – high conc. to low conc.

2. Facilitative Diffusion – diffusion with the help of transport proteins

3. Osmosis – diffusion of water

1. Diffusion1. Diffusion

random movement of particles from an area of high concentration to an area of low concentration.

(High to Low) Diffusion continues until all

molecules are evenly spaced (equilibrium is reached) Note: molecules will still move around

but stay spread out.

http://bio.winona.edu/berg/Free.htmhttp://bio.winona.edu/berg/Free.htm

Animation

1. Diffusion1. Diffusion

2. Facilitated Diffusion2. Facilitated Diffusion diffusion that is enabled

by proteins (channel or carrier proteins) which bind onto required molecules so that they flow into the cell. Transport Proteins are

specific – they “select” only certain molecules to cross the membrane

Transports larger or charged molecules

Animation: How Facilitated Diffusion Works

Facilitated diffusion (Channel Protein)

Diffusion (Lipid

Bilayer)

Carrier Protein

A B

http://bio.winona.edu/berg/Free.htmhttp://bio.winona.edu/berg/Free.htm

High Concentration

Low Concentration

Cell Membrane

Glucosemolecules

Proteinchannel

2. Facilitated Diffusion

Go to Section:

Transport Protein

Through a

Cellular Transport from an area of High

Low

Channel Proteins animationsanimations

Diffusion of water through a selectively permeable membrane

From high to low concentrations

•Water moves freely through pores.

•Solute (green) too large to move across.

Animations3. Osmosis3. Osmosis

3. Osmosis

Factors Affecting Rate of Diffusion Factors Affecting Rate of Diffusion

1. Size1. Size small molecules can slip through

phospholipids bilayer easier than large molecules

very large molecules may not be able to diffuse at all

2. Concentration2. Concentration

the greater the concentration gradient (bigger range) the quicker a material diffuses (makes the molecules want to move faster) – think of a crowded room

3. Temperature In general as temperature increases – molecules move

faster which translates into faster diffusion

4. Polarity of molecules4. Polarity of molecules

Water-soluble (polar) molecules will not easily move through the membrane because they are stopped by the middle water-insoluble (nonpolar) layer

5. Surface Area5. Surface Area As a cell’s size increases its volume increases much

quicker than it’s surface area. If you double individual lengths (1 cm to 2 cm) the surface

areas increases 4 times, and the volume increases 8 times.

If cell size is doubled, it would require 8 times more nutrients and have 8 times s much waste. SA only increases by a factor of 4 – not enough surface area through which nutrients and wastes could move. Cell would either starve or be poisoned (waste products)

Cells divide before they come too large to function.

Active TransportActive Transport Involves moving molecules "uphill" against

the concentration gradient, which requires energy. Uses carrier protein molecules as receptors.

One may transport calcium ions another glucose molecules.

Hundreds of these types of protein molecules. Each one changes shape to accommodate a

specific molecule.

(Low High)

2. Active Transport2. Active Transport (cont’d) (cont’d)

Their activity can be stopped from transporting molecules with inhibitors (unfortunately, these are usually poisons) which: either destroy the membrane protein or just plug it up (e.g. for your neurons – tetanus &

botulinum-B secrete a poison that

suppress the Na/K pump)

Three types: active transport animation

http://www.biology4kids.com/files/cell2_activetran.html

1. Protein Pumps1. Protein Pumps

•transport proteins that require energy to do work•Example: Na+/K+ pumps are important in nerve responses.

Sodium Potassium Pumps

Protein changes shape to move molecules: this requires energy!

Sodium-Potassium PumpSodium-Potassium Pump Pumps out 3 sodium atoms for ever 2

potassium atoms taken in against gradient in the cell.

ATP and the Na/K Pump

Animation: How the Sodium Potassium Pump Works

The H+/K+ ATPaseThe H+/K+ ATPase

The parietal cells of your stomach (lining) use this pump to secrete gastric juice.

These cells transport hydrogen ions (H+) from a concentration of about 4 x 10-8 M within the cell to a concentration of about 0.15 M in the gastric juice (giving it a pH close to 2). Recall: pH – power of the H+ ion

Small wonder that parietal cells are stuffed with mitochondria and use huge amounts of energy as they carry out this three-million fold concentration of protons.

The H+/K+ ATPaseThe H+/K+ ATPase

3. Exocytosis3. Exocytosis

Moves large, complex molecules such as proteins out of the cell membrane.

Large molecules, food, or fluid droplets are packaged in membrane-bound sacs called vesicles. Cell changes shape – requires energy Ex: Hormones or wastes released from cell Transport Animations

Endocytosis & Exocytosis animations

2. Endocytosis2. Endocytosis

taking bulky material into a cell

• Uses energy• Cell membrane in-folds

around food particle• “cell eating”• forms food vacuole &

digests food• This is how white blood

cells eat bacteria!

EndocytosisEndocytosis

Endocytosis moves large particles (huge molecules or molecular conglomerates) into a cell.

endo & exocystosis animations

PhagocytosisPhagocytosis

Phagocytosis is another type of endocytosis used for massive transport.Cell membrane extends out forming pseudopods (fingerlike projections) that surround the particle.

Membrane pouch encloses the material & pinches off inside the cell making a vesicle.

Vesicle can fuse with lysosomes(digestive organelles) or release their contents in the cytoplasm

Animation: Phagocytosis HowStuffWorks "Phagocytosis"

Used by ameba to feed & white blood cells to kill bacteria.Known as “killer cells"

Pinocytosis is another type of endocytosis Cell membrane surrounds fluid droplets Fluids taken into membrane-bound vesicle Known as “cell drinking”

•Exocytosis is used to remove large products from the cell such as wastes, mucus, & cell products such as hormones and antibodies.

•Exocytosis is the process used by our memory cells (white blood cells that produce antibodies to fight infection).

•It is also used by our gland cells to secrete hormones when needed.

•Phagocytosisanimationanimation

In SummaryIn Summary

Essential Biochemistry - Membrane Transport

Transport FlowchartTransport FlowchartTransport of Materials

Across a Membrane

Active

Phagocytosis

Pinocytosis

Ion Pum

p

Facilitated

Diffusion

OsmosisSimple

Diffusion

Passive

Endocytosis

Exocytosis

Osmosis and TonicityOsmosis and Tonicity

Tonicity is a relative term Water molecules are so small, and there is

so much of it, that the cell can’t control it’s movement through the cell membrane.

Hypotonic SolutionHypotonic Solution

Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water)

Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

Osmosis Osmosis Animations for Animations for

isotonic, hypertonic, isotonic, hypertonic, and hypotonic and hypotonic

solutionssolutions

Hypertonic SolutionHypertonic Solution

Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water)

Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

Osmosis Osmosis Animations for Animations for

isotonic, hypertonic, isotonic, hypertonic, and hypotonic and hypotonic

solutionssolutions

shrinks

Isotonic SolutionIsotonic SolutionIsotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell.

Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)

Osmosis Osmosis Animations for Animations for

isotonic, hypertonic, isotonic, hypertonic, and hypotonic and hypotonic

solutionssolutions

What type of solution are these cells in?

A CB

Hypertonic Isotonic Hypotonic

Plant and Animal Cells put into various solutions

How Organisms Deal with How Organisms Deal with Osmotic PressureOsmotic Pressure

Paramecium (protist) removing excess water video

•Salt water fish pump salt out of their specialized gills so they do not dehydrate.

•Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

•Blood brain barrier allows some substances into the brain, but screens out toxins and bacteria

• Allows water, CO2, glucose, AA’s, alcohol, & antihistamines

• HIV and bacterial meningitis can also cross this barrier

How Organisms Deal with How Organisms Deal with Osmotic PressureOsmotic Pressure

Paramecium (protist) removing excess water video

•Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall by the central vacuole is called tugor pressure. (bike tire analogy)

•A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding.