Cell Transport- Homeostasis

- Cell Membrane- Vocabulary

- Diffusion and Osmosis- Active vs. Passive Transport

Homeostasis Homeostasis means maintaining a

balance internally (inside a cell or organism) despite what is going on externally (outside the cell or organism).

Organisms must adjust to changes in the environment in order to survive or they could die!

Homeostasis For example, when you need to drink

water, your brain tells your kidneys to use less water in making urine so you can keep your blood flowing nicely (and then your brain tells you that you’re thirsty!)

Homeostasis Another example, if it is

below freezing outside, you must put on a heavy coat, gloves, double socks, a warm hat, ear muffs, and lots and lots of layers to maintain a healthy INTERNAL body temperature despite the EXTERNAL temperature

Homeostasis What structure maintains homeostasis

in our cells? How does it maintain homeostasis?

How?

The Cell Membrane

By controlling the passage of molecules, such as water, salts (ions), amino acids, carbohydrates, etc in and out of the cell.(it regulates what enters and leaves)

-through passive transport, & active transport -cell to cell communication!

The Cell MembraneThe Cell Membrane is: A phospholipid bilayer

Two layers made of proteins and lipidsPhospholipid Structure:

Polar Head (hydrophilic—”water loving”) Nonpolar Tails—(hydrophobic—”water

fearing”)Draw:

The Cell Membrane proteins embedded in the phospholipid

layers› some go all the way through both layers

(integral)› some are just on the inside of the membrane

or just on the outside of the membrane (peripheral)

cholesterol is a second lipid that’s also found inbedded in the phospholipid bilayer› helps keep the membrane fluid

The Cell Membrane Bilayer arrangement Draw:

The Cell Membrane There are 3 types of membrane proteins

imbedded or “floating” in the lipid bilayer, each with a different function:› transport—help molecules enter or leave the

cell› marker—identify the cell› receptor—allow cells to communicate (send

and receive messages)

The Cell Membrane1. Transport Proteins function as “gates/passageway” allow sugars, salts (ions), amino acids and

carbohydrates to cross the membrane channel proteins

› gated ion channels—gates that open/close in response to charged particles these are important in nerve cell

function, but we will not study them in detail

› carrier proteins—change shape to allow specific molecule to pass through the membrane when it binds to the carrier protein; some require energy (ATP), others do not require energy carrier proteins are important in

getting glucose into the cells http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm

The Cell MembraneMarker Proteins Cell’s “Name Tag” Protein sticks out of phospholipid

layer Often has carbohydrates attached

to outside end Functions in cell identification to

identify the cell to other cells and molecules

Important in › immunity—so various white

blood cells in your body do not mistake your cells for foreign cells

- blood typing – so you can’t receive just any ol’ type of blood

Blood Typing Continued each blood type is based on the

glycoproteins (protein-carbohydrate molecule) that stick up from the cell membrane. › type A – has a glycoprotein named antigen A› type B – has a glycoprotein named antigen B› type AB – has both antigen A and antigen B› type O – has no marker proteins (no

glycoproteins/antigens)

The Cell MembraneReceptor Proteins- primary

molecules involved in cell communication

Function as messengers Receive information from

the environment (extracellular fluid, blood, interstitial fluid) and transmit that info to the inside of the cell

Protein has specific shape/charge to only allow certain molecules (like hormones) to bond

Triggers a response in cell

http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm

http://www.d.umn.edu/~sdowning/Membranes/signalinganim.html

Click, hold, and drag slider to move forward, bckword, or slow down

Cell Membrane in step 1 a signal molecule (sometimes called a ligand) binds

to a receptor protein in the cell membrane› examples of signal molecules include insulin and testosterone

in step 2 the receptor protein has changed shape as a result of the signal molecule binding, which can cause additional changes or reactions inside the cell

after step 2, there are 2 possibilities: › step 3 says “cellular response” – an example of a cellular response is an

enzyme being activated to make a reaction happen for example, insulin binding to a receptor in a liver or muscle cell membrane

would tell the cell to start hooking together glucose into glycogen for storage› step 4 says “change in gene expression” – this means that a gene in the

DNA is going to be “read” and mRNA made (transcription will occur); this will ultimately result in the cell producing a particular protein for example, testosterone binding to a receptor protein in a skin cell could

tell the cell to begin producing hair and a male would then begin growing a beard

Cell Membrane it’s important to note that the binding of the signal

molecule (like insulin or testosterone) to the receptor is temporary; when it unbinds, the signal stops and the cell response (enzyme reaction or gene expression) stops; this is another way organisms maintain homeostasis (you don’t always want to store sugar, sometimes you want to break it down, so insulin is not always bound to your cells but is only released into the blood from the pancreas when blood sugar levels are high; when they’re low, another molecule called glucagon is released and would tell the cells to break down glycogen and release the glucose)

The Cell MembraneThe Cell Membrane is: Selectively permeable/semipermeable

permeable means particles, like molecules, can travel through

selectively or semi permeable means it only allows SOME things through and not others

The Cell Membrane This represents a selectively permeable

membrane. It allows (selects) certain things to pass

through it.

Is the membrane permeable to ? Is the membrane permeable to ?

The Cell Membrane Molecules pass through the cell

membrane in one of two general ways:› Passive Transport

Diffusion Facilitated Diffusion Osmosis

› Active Transport Vesicles Pumps

Cell Transport Vocabulary Molecule- the smallest unit

of a compound/substance› Cannot be seen with the

naked eye› 1 drop of water has

16,700,000,000,000,000,000,000 molecules of H20

› 1 grain of salt has 120,000,000,000,000,000 molecules of salt

Cell Transport Vocabulary

Concentration Gradient- an area of high concentration next to an area of low concentration

Low Concentration of Molecules

High Concentration of Molecules

Cell Transport Vocabulary Equilibrium is when there is an EQUAL amount of molecules on each side of the membrane

There is no net movementof molecules (you won’t SEE a change) but there is continuous movement of molecules back and forth through the membrane.

Passive Transport Passive Transport is when molecules

move from an area of HIGH concentration to an area of LOW concentration until equilibrium is reached.

Requires NO ENERGY! Examples:

› Diffusion› Osmosis› Facilitated Diffusion

Passive Transport Diffusion- the process by which molecules (“stuff”) spread

from areas of high concentration, to areas of low concentration

Molecules are said to go “down” or “with” the concentration gradient.

Requires no energy

Air Freshener Diffusion in a Classroom

Where is the greatest concentration of cows? Where is the least concentration of cows? What will happen when the gate is opened?

This process is called…diffusion

Passive Transport Facilitated Diffusion

› What does facilitate mean?› When substances move from high to

low concentration (down the concentration gradient) using channel/carrier proteins located in membrane

› Does not require energy

Facilitated Diffusion Animation

http://www.d.umn.edu/~sdowning/Membranes/diffusionanimation.htmlClick, hold, and drag slider to move forward, bckword, or slow down

Passive Transport Osmosis- a special type of diffusion the process by which WATER

molecules move from an area with a high concentration of water to an area of low concentration of water across a membrane› the “diffusion of water”

Requires no energy

Passive TransportOsmosis- may be the passing of water through pores (spaces between the molecules of) in the

membrane -may be the passing of water through

special channel proteins called aquaporins (2003

Nobel Prize to Agre & McKinnon for this discovery)

Osmosis in biological systems, water is often the

only substance that can pass through a membrane

water moves INTO a solution with a HIGHER concentration of SOLUTE (molecules/particles)

water moves OUT OF a solution with a LOWER concentration of SOLUTE

Passive Transport water will move in where there is a low

concentration of SOLVENT (water), and a high concentration of SOLUTE (water)

› A solute = “stuff” (ions, glucose)› A solvent = “water” (you’ll learn about

different solvents in chemistry, but in biology the solvent is almost always water)

Osmosis

Semi-

Click to open web page with interactive animation

How osmosis works (click here or picture to go to video)

Passive Transport Animation

http://sites.sinauer.com/cooper5e/animation0202.html

Passive Transport There are three words use

to compare and describe solutions:› Hypotonic- water moves

INTO a cell and the cell swells (gets bigger)

› Hypertonic – water moves OUT of a cell and the cell shrinks (gets smaller)

› Isotonic- water moves into AND out of a cell at an equal rate (remember- molecules are constantly moving)

Passive TransportHypotonic- describes a solution that is

less CONCENTRATED (has less solute, more water)

when a cell is placed in a hypotonic solution, the cell will swell as water moves INTO the cell

there is more solvent/less solute on the outside of the cell than the inside

the solvent (water) moves to an area of low solvent (water) concentration

the cell could burst (lyse)

Passive TransportHypertonic- describes a solution that is

more CONCENTRATED (has more solute, less water)

when a cell is placed in a hypertonic solution, water moves OUT of a cell and the cell shrinks(gets smaller)

there is less solvent/more solute on the outside of the cell than the outside

the solvent (water) moves to an area of low solvent (water) concentration

Passive TransportIsotonic: describes a solution that is of

equal concentration to another

water moves into AND out of a cell at an equal rate (remember- molecules are constantly moving)

No change in the size of the cell will be observed

the concentration of solvent and solute on the inside of the cell is equal to the concentration of solvent and solute on the outside of the cell

Practice Draw arrows to show the flow of water Label at the top if the solution is

isotonic, hypotonic or hypertonic

selectively permeable membrane

Where is the greatest concentration of solvent? Outside of the bag

What type of solution is this?Hypotonic

Which way does the water move?

Into the Bag

10% salt90% water

Where is the greatest concentration of solvent?

In the bag

selectively permeable membrane

Which way does the water move?

Out of the bagWhat type of solution is this?

Hypertonic

What happens to the bag?

selectively permeable membrane

90 % solvent10% salt

What happens to the bag?

selectively permeable membrane

90 % solvent10% salt

What happens to the bag?

selectively permeable membrane

90 % solvent10% salt

What happens to the bag?

The bag shrinks.

selectively permeable membrane

90 % solvent10% salt

Passive Transport Recap! Passive transport:

› requires no energy› moves from high concentrations to low

concentrations› Moves down the concentration gradient› Includes diffusion, facilitated diffusion and

osmosis

Active Transport When molecules are moved from a low

concentration to a high concentration they must use active transport› Cells must transport certain amino acids, sugars,

etc. into their cytoplasm from the surrounding fluid.

› Some of these substances, however, are already in higher concentrations inside versus outside.

Forcing molecules to move against their concentration gradient requires energy (ATP!)

Active Transport Vesicles can transport molecules across

the cell membrane through:› Endocytosis- moving INTO the cell› Exocytosis- moving OUT of the cell

Requires energy

Active Transport Exocytosis can help get rid of wastes or

secrete products like hormones or insulin Requires energy

Types of Endocytosis

Pinocytosis (drinking) Phagocytosis (eating)

Active Transport Pumps force molecules to travel

against their concentration gradient For example, the sodium/potassium

pump actively transports sodium molecules and potassium molecules through the cell membrane

Requires energy

http://www.goldiesroom.org/Note%20Packets/06%20Transport/00%20Transport--WHOLE.htm

Active Transport

Na+ pumped out of a cell K+ pumped into a cell Important because it

prevents cells from bursting by lowering the sodium inside causing less water to enter through osmosis.

Requires energy

Sodium Potassium Pump

http://sites.sinauer.com/cooper5e/animation1302.html

Transport proteins Cell transport involves proteins that

require ATP for energy These carrier proteins change shape to

move molecules across the membrane Another important way to move

glucose into the cell uses transport proteins combined with an ion pump, this is called coupled transport

Active Transport Opposite of Passive Transport Molecules go against the concentration

gradient Energy is provided by the ATP made in

the mitochondria Active transport can involve pumps or

vesicles Requires energy

http://www.goldiesroom.org/Note%20Packets/06%20Transport/00%20Transport--WHOLE.htm

Reviewwith

Animations!

http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm

The Cell MembraneReceptor Proteins- primary

molecules involved in cell communication

Function as messengers Receive information from

the environment (extracellular fluid, blood, interstitial fluid) and transmit that info to the inside of the cell

Protein has specific shape/charge to only allow certain molecules (like hormones) to bond

Triggers a response in cell

http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm

Passive Transport Diffusion- the process by which molecules (“stuff”) spread

from areas of high concentration, to areas of low concentration

Molecules are said to go “down” or “with” the concentration gradient.

Requires no energy

http://www.d.umn.edu/~sdowning/Membranes/signalinganim.html

Click, hold, and drag slider to move forward, bckword, or slow down

Passive Transport Facilitated Diffusion

› What does facilitate mean?› When substances move from high to

low concentration (down the concentration gradient) using channel/carrier proteins located in membrane

› Does not require energy

Facilitated Diffusion Animation

http://www.d.umn.edu/~sdowning/Membranes/diffusionanimation.htmlClick, hold, and drag slider to move forward, bckword, or slow down

Click to open web page with interactive animation

How osmosis works (click here or picture to go to video)

Passive Transport Animation

http://sites.sinauer.com/cooper5e/animation0202.html

http://www.goldiesroom.org/Note%20Packets/06%20Transport/00%20Transport--WHOLE.htm

Sodium Potassium Pump

http://sites.sinauer.com/cooper5e/animation1302.html

Types of Endocytosis

Pinocytosis (drinking) Phagocytosis (eating)

http://www.goldiesroom.org/Note%20Packets/06%20Transport/00%20Transport--WHOLE.htm