Chapter 7.3Chapter 7.3Cell BoundariesCell Boundaries

Passive TransportPassive Transport The movement of a substance across a The movement of a substance across a

cell membrane without the use of energy cell membrane without the use of energy is called is called passive transportpassive transport..

Why would a cell need to move Why would a cell need to move substances?substances? Hint: One of the Characteristics of Life!Hint: One of the Characteristics of Life!

Passive Transport cont.Passive Transport cont.

The difference in the The difference in the amount of material amount of material between two areas is between two areas is called a called a concentration concentration gradientgradient.. The difference in the The difference in the

concentration of a concentration of a substance across a substance across a space.space.

Movement of SubstancesMovement of Substances Moving from a room with a lot Moving from a room with a lot

of people to a room with less of people to a room with less people is an example of people is an example of moving with the concentration moving with the concentration gradient.gradient.

When the amount of people is When the amount of people is equal in the two rooms you equal in the two rooms you have reached have reached equilibriumequilibrium this this is when the concentration of a is when the concentration of a substance is equal throughout substance is equal throughout a space.a space.

DiffusionDiffusion DiffusionDiffusion – The movement of a substance from an – The movement of a substance from an

area of high concentration to an area of lower area of high concentration to an area of lower concentrationconcentration

Some particles move very easily across the Some particles move very easily across the membrane others need help.membrane others need help.

Small particles can fit right between the Small particles can fit right between the phospholipids in a membrane, larger molecules phospholipids in a membrane, larger molecules like proteins need help in getting across.like proteins need help in getting across.

Non-polar molecules move across the cell Non-polar molecules move across the cell membrane much easier than polar. Why?membrane much easier than polar. Why?

OsmosisOsmosis

OsmosisOsmosis – The movement of – The movement of waterwater through the cell membrane.through the cell membrane.

If there is more water on the inside of a If there is more water on the inside of a cell than on the outside the water will cell than on the outside the water will move out.move out.

The cell membrane it is said to be The cell membrane it is said to be

Semi-permeable- Semi-permeable- only certain materials can only certain materials can move acrossmove across

Osmosis cont.Osmosis cont. Sometimes the movement of water will be Sometimes the movement of water will be

too great in one direction.too great in one direction. If there is too much of a substance, for If there is too much of a substance, for

instance sugar or salt, inside a cell which instance sugar or salt, inside a cell which direction do you think water will move to direction do you think water will move to stabilize the concentration?stabilize the concentration?

Think about a water balloon. If you fill a Think about a water balloon. If you fill a balloon with water what happens to it? balloon with water what happens to it? What happens when you squeeze the What happens when you squeeze the water out?water out?

Moving WaterMoving Water

In which way will water move if there is In which way will water move if there is less water outside of a cell than inside?less water outside of a cell than inside?

Hypertonic SolutionHypertonic Solution – Water moves out of – Water moves out of the cell. Cell shrinks.the cell. Cell shrinks.

Hypotonic SolutionHypotonic Solution – Water moves into the – Water moves into the cell. Cell swells.cell. Cell swells.

If the amount of water is equal outside and If the amount of water is equal outside and inside the cell, the solution is inside the cell, the solution is isotonicisotonic. .

Hypertonic means “Lots of stuff”Hypertonic means “Lots of stuff”

Hypertonic and Hypotonic SolutionsHypertonic and Hypotonic Solutions

Hypertonic SolutionHypertonic Solution

Red blood cells in a Red blood cells in a hypertonic solutionhypertonic solution

Plant cells in a Plant cells in a hypertonic solutionhypertonic solution

Hypotonic SolutionHypotonic Solution

Red blood cells in a Red blood cells in a hypotonic solutionhypotonic solution

Plant cells in a Plant cells in a hypotonic solutionhypotonic solution

You tell me!You tell me!

Aren’t fish made of cells? Why don’t the cells Aren’t fish made of cells? Why don’t the cells of salt water fish shrivel up to nothing? What of salt water fish shrivel up to nothing? What happens to humans in salt water? Why can’t happens to humans in salt water? Why can’t a fresh water fish live in salt water?a fresh water fish live in salt water?

Red blood cell Red blood cell in a hypotonic in a hypotonic

solution.solution.

OsmosisOsmosis

The Cell MembraneThe Cell Membrane Larger molecules need a protein embedded in a Larger molecules need a protein embedded in a

cell membrane to move across.cell membrane to move across.

Facilitated DiffusionFacilitated Diffusion Facilitated DiffusionFacilitated Diffusion – is the use of a – is the use of a

carrier protein to move molecules across a carrier protein to move molecules across a cell membrane. cell membrane.

Carrier ProteinCarrier Protein – is a transport protein that – is a transport protein that carries a specific substance across a cell carries a specific substance across a cell membrane.membrane.

When a carrier protein is used to transport When a carrier protein is used to transport a specific substance, for instance, amino a specific substance, for instance, amino acids, proteins or sugars, the process is acids, proteins or sugars, the process is called facilitated diffusion.called facilitated diffusion.

Carrier ProteinCarrier Protein

Facilitated Diffusion cont.Facilitated Diffusion cont. The following are the steps of moving a substance The following are the steps of moving a substance

across a cell membrane using facilitated diffusion:across a cell membrane using facilitated diffusion: Step 1:Step 1: Molecule binds to a protein on one Molecule binds to a protein on one

side of the cell membrane, causing the side of the cell membrane, causing the protein to change its shape.protein to change its shape.

Step 2:Step 2: The change in shape sends the The change in shape sends the molecule across the phospholipid molecule across the phospholipid bilayer.bilayer.

Step 3:Step 3: The once open side of the protein, now The once open side of the protein, now closes, and the molecule is then closes, and the molecule is then released on the other side of the released on the other side of the membrane.membrane.

Passive Transport in a nutshell. Passive Transport in a nutshell.

Protein

Movement of SubstancesMovement of Substances

These channels allow for proteins, ions These channels allow for proteins, ions and other large molecules to cross. and other large molecules to cross.

NaNa++, , KK++,, CaCa2+2+ and and ClCl--

These ions are very important for nerve These ions are very important for nerve impulses and muscle movement.impulses and muscle movement.

In order for these ions to work they need In order for these ions to work they need to be able to move in and out of the cell to be able to move in and out of the cell but they are too large to fit between the but they are too large to fit between the phospholipids and they can not move phospholipids and they can not move

across the non-polar tails.across the non-polar tails.

Movement of IonsMovement of Ions

Ions have a charge, do you think that they Ions have a charge, do you think that they can move across the non-polar part of the can move across the non-polar part of the cell membrane?cell membrane?

The ions need the help of a protein called The ions need the help of a protein called an ion channel to move across the cell an ion channel to move across the cell membrane.membrane.

Ion ChannelIon Channel – protein with a polar pore – protein with a polar pore through which ions pass.through which ions pass.

Movement of Ions cont.Movement of Ions cont. Some ion channels are always open while Some ion channels are always open while

others are gated. others are gated. The gated proteins can open with the stretching The gated proteins can open with the stretching

of a cell, change in electrical charge or by of a cell, change in electrical charge or by binding a specific molecule.binding a specific molecule.

Ion channels do not require energy that means Ion channels do not require energy that means the movement of an ion is a form of the movement of an ion is a form of passive passive transporttransport..

The interior of a cell has a slight negative charge The interior of a cell has a slight negative charge so would a negatively charged ion move in or so would a negatively charged ion move in or out of a cell? What about a positively charged out of a cell? What about a positively charged ion?ion?

Active TransportActive Transport So far we have talked about movement of So far we have talked about movement of

molecules in and out of a cell without the use of molecules in and out of a cell without the use of energy. What is this called?energy. What is this called?

Passive transport usually occurs when a Passive transport usually occurs when a molecule is moving from a high to low molecule is moving from a high to low concentration or with the concentration gradient.concentration or with the concentration gradient.

Active TransportActive Transport – When a substance is – When a substance is transported from an area of low to high transported from an area of low to high concentration or against the concentration concentration or against the concentration gradient with the use of energy.gradient with the use of energy.

The energy that is used in active transport is The energy that is used in active transport is supplied by .supplied by .

How Active Transport WorksHow Active Transport Works

Just like during facilitated diffusion Just like during facilitated diffusion sometimes active transport requires a sometimes active transport requires a protein to move a substance across the protein to move a substance across the membrane.membrane.

Instead of being called a carrier protein Instead of being called a carrier protein these proteins are called “these proteins are called “pumpspumps” because ” because they pump substances across the they pump substances across the concentration gradient.concentration gradient.

One example of this is the Sodium One example of this is the Sodium Potassium Pump.Potassium Pump.

Sodium Potassium PumpSodium Potassium Pump The Sodium Potassium Pump is a type of The Sodium Potassium Pump is a type of

carrier protein that transports 3 Na+ out of carrier protein that transports 3 Na+ out of a cell and 2 K+ into the cell.a cell and 2 K+ into the cell.

The Sodium Potassium Pump is a form of The Sodium Potassium Pump is a form of active transport so that means it requires active transport so that means it requires

If Na+ is transported out of the cell using If Na+ is transported out of the cell using active transport where is the higher active transport where is the higher concentration? concentration?

What about in the case of K+? What about in the case of K+?

Steps of the Sodium Potassium Steps of the Sodium Potassium PumpPump

Step 1:Step 1: 3 Na+ ions inside the cell bind to the 3 Na+ ions inside the cell bind to the protein, along with a phosphate from ATP.protein, along with a phosphate from ATP.

Step 2:Step 2: The protein changes shape releasing the The protein changes shape releasing the three Na+ ions to the outside of the cell.three Na+ ions to the outside of the cell.

Step 3:Step 3: The pump is now exposed to two K+ The pump is now exposed to two K+ ions outside of the cell. The two K+ ions bind to ions outside of the cell. The two K+ ions bind to the protein causing it to change shape and lose the protein causing it to change shape and lose the phosphate.the phosphate.

Step 4:Step 4: The K+ ions are released into the cell The K+ ions are released into the cell and the protein is ready to bind to three Na+ and the protein is ready to bind to three Na+ ions again.ions again.

Sodium-Potassium PumpSodium-Potassium Pump

Passive and Active TransportPassive and Active Transport

More TransportMore Transport

Sometimes a cell needs to take in or Sometimes a cell needs to take in or release a lot of substances at one time. release a lot of substances at one time. The cell uses a vesicle to do so.The cell uses a vesicle to do so.

EndocytosisEndocytosis – The movement of very large – The movement of very large materials into a cell.materials into a cell.

ExocytosisExocytosis - The movement of very large - The movement of very large materials out of a cell.materials out of a cell.

EndocytosisEndocytosis

Step 1Step 1 – A molecule from outside the cell – A molecule from outside the cell meets the cell membrane and pushes the meets the cell membrane and pushes the membrane in.membrane in.

Step 2Step 2 – The membrane is forced to – The membrane is forced to surround the molecule(s).surround the molecule(s).

Step 3Step 3 – The membrane pinches off to – The membrane pinches off to form a vesicle.form a vesicle.

ExocytosisExocytosis

Step 1Step 1 – A vesicle is formed somewhere in – A vesicle is formed somewhere in the cell usually from the golgi or the ER.the cell usually from the golgi or the ER.

Step 2Step 2 – The vesicle then moves to the – The vesicle then moves to the inside of the cell membrane.inside of the cell membrane.

Step 3Step 3 – The membranes attach and open – The membranes attach and open exposing the material inside the vesicle to exposing the material inside the vesicle to the outside of the cell.the outside of the cell.

Endocytosis & ExocytosisEndocytosis & Exocytosis

Receptor ProteinsReceptor Proteins Receptor proteinReceptor protein – – Protein that is able to Protein that is able to

bind to a signal, enabling a cell to respond.bind to a signal, enabling a cell to respond. The signal is usually a molecule like a The signal is usually a molecule like a

hormone that triggers the response.hormone that triggers the response. Example: How do all cells know how to Example: How do all cells know how to

grow at the same time.grow at the same time. Cell “A” gets the instructions from the brain Cell “A” gets the instructions from the brain

to start growing. Cell “A” sends a to start growing. Cell “A” sends a hormone to Cell “B” and so on. hormone to Cell “B” and so on.

How do you think hormones get to the How do you think hormones get to the other cells?other cells?

Functions of Receptor proteinsFunctions of Receptor proteins Some receptor proteins can tell whether or Some receptor proteins can tell whether or

not an ion channel should be working.not an ion channel should be working.

Some can activate a second messenger Some can activate a second messenger which acts as a signal inside the cell.which acts as a signal inside the cell.

Some can activate an enzyme, triggering Some can activate an enzyme, triggering chemical reactions.chemical reactions.