CELL MEMBRANE

How the cell membrane helps to maintain homeostasis

HOMEOSTASIS

Definition:The maintenance of a stable environment.• In cells this happens by monitoring what goes

in and out of the cell.

Cell Membrane

Cell Membrane

PROTEINS IN THE MEMBRANE Proteins - are involved in the passage of molecules through the membrane.

A. Channel proteins - a protein that allows a particular molecule or ion to freely cross the membrane as it enters or leaves the cell.B. Carrier proteins (Transport)- a protein that selectively interacts with a specific molecule or ion so that it can cross the cell membrane to enter or exit the cell. C. Receptor proteins - A protein that has a specific shape so that specific molecules can bind to them. The binding of a molecule, such as a hormone, can influence the metabolism of the cell. D. Enzyme proteins - An enzyme that catalyzes a specific reaction.E. Cell-recognition proteins (Cell surface marker) - Glycoprotein's that identify the cell. They make up the cellular fingerprint by which cells can recognize each other.

How Cells Maintain Homeostasis

Passive Transport1) Movement of any substance

across a membrane without the use of chemical energy (ATP).

2) Movement of molecules will go with the concentration gradient(High to Low)

3) Kinetic Energy

Active Transport1) Movement of any substance

across the membrane using chemical energy – ATP

2) Movement of the molecule will go across/against the concentration gradient(opposite-low to high)

PASSIVE DIFFUSION

FOUR TYPES• Diffusion• Osmosis• Facilitated Diffusion• Diffusion with Ion Channels

DEFINITION OF DIFFUSION

The process that molecules or ions spread from an area of high concentration to an area of low concentration

Examples: Air freshener, food coloring in water, sugar cube dissolving

Diffusion

What causes Diffusion?

The KINETIC ENERGY of the molecules

• Diffusion is driven by the molecules’ kinetic energy.• Kinetic Energy – the energy of motion. • Molecules are in constant motion because they have

kinetic energy, they will move in a random motion. • If they are concentrated in a small area they will keep

rebounding until they spread out

Which way will the molecules move?

Particles will move down(go with) the CONCENTRATION GRADIENT

Definition: Difference in concentration of molecules across a distance

What do the particles want to reach?

EQUILIBRIUM

Definition:When all the molecules are spread out equally

in a given area

Note: This can be reached in the absence of other influences

Diffusion across the Cell Membrane

Cell Membrane is Semi-permeable- It will let some molecules through

• Diffusion of a molecule across a membrane depends on the size of the molecule and the solubility (polar, nonpolar)

• Small molecules like water are small enough to get through the pores in the membrane and will pass through by Osmosis

Molecules that can diffuse through the membrane by Simple Diffusion

Yes!Oxygen (nonpolar)Carbon Dioxide (nonpolar)Water (Osmosis, small

enough)

No!Large ParticlesStarchIons (Charged Particles)Glucose(Hydrophilic)

OSMOSIS

The process by which WATER molecules diffuse through a cell membrane from an area of high concentration to an area of lesser concentration

Direction of OSMOSIS

Depends on relative concentration of solute molecules on both sides of the cell membrane

• Water will either enter the cell or exit the cell

CHEMISTRY REVIEW- What is a solution?

• Solute - Item that is dissolvedEx: Sugar

• Solvent - Item that does the dissolvingEx: Water

• In a cell, Water is the solvent and Organic and Inorganic molecules are the solutes.

Give examples of solutes in the cell?

Direction of water if cell is placed in a Hypotonic Solution

Hypotonic Solution –When the concentration of solute molecules outside the cell is lower than the concentration of the solute molecules inside the cytosol of the cell.

• The outside solution is said to be hypotonic compared to the cytosol inside the cell

Direction of Water: Into the cellCondition: Cytolysis

Direction of the water if a cell is placed in a Hypertonic Solution

Hypertonic Solution- When the concentration of solute molecules outside the cell is Higher than the concentration of the solute molecules inside the cytosol of the cell.

• The outside solution is said to be hypertonic compared to the cytosol inside of the cell

Direction of Water: Out of the cellCondition: Plasmolysis

REMEMBER

Water moves from the hypotonic solution to the hypertonic solution

VOCAB WORDS

• Osmotic Pressure – The ability of osmosis to generate enough pressure to increase a volume of water

• Turgor Pressure - Water pressure within a cell• Plasmolysis- When water leaves the cell and turgor

pressure is lost and the cell shrinks• Cytolysis – When the cell takes in so much water it

bursts caused by an increase in turgor pressure• Contractile Vacuoles – Organelles that remove water

QUESTIONS?

• What type of solutions would a cell have to be in for cytolysis to occur? Plasmolysis to occur?

• If you were to place celery into a glass of water, would you have cytolysis, plasmolysis or neither?

Plant vs. Animal Cell

FACILITATED DIFFUSION

• Used when molecules are too large to pass through membrane or are not soluble in the membrane

• These molecules moves with the concentration gradient

• Do not use cellular energy-Passive Transport

Carrier Proteins (Transport)

Carrier Proteins transport solute molecules through the membrane without expending energy.

Transport molecules that can’t get through the membrane by simple diffusion

Are specific to one Molecule ! Like a Key.

FOUR STEPS

1. Molecule will bind with a carrier protein on the surface of the cell membrane

2. The carrier protein will change shape shielding the molecule from the interior of the cell membrane

3. The Molecule is released on the other side of the membrane

4. The carrier protein then returns to its original shape WATCH!

FACILITATED DIFFUSION

Glucose

Glucose is an excellent example of facilitated diffusion. Cells depend on Glucose to create energy for the cell

Glucose is to large of a molecule to pass through the cell membrane and it is not soluble in the lipid bilayer

When glucose is low in concentration on the inside it will enter the cell by facilitated diffusion, same if concentration is high on the inside of the cell

Ion Channels (Gated/Non Gated)

• Proteins in the membrane form an Ion channel across the lipid membrane.

• Ions that cannot diffuse through the membrane can move through these channels

• Move molecules from high concentration to low w/o use of energy (Passive Transport)

• Moves ions such as sodium, potassium, calcium and chloride.

• They are specific to one ion. ION CHANNELS

Gated Channels Vs. Non Gated

Gated Channels: Open according to external stimuli such as

stretching of the cell membrane, electrical signals, and chemicals.

Non Gated Channels: Always Open

ION CHANNELS

ACTIVE TRANSPORT

• Moves solutes against the concentration gradient (from low to high)

• Particles are moved from areas of LOW concentration to areas of HIGH concentration

• Uses energy in the form of ATP• May use a Carrier Protein - Cell Membrane

“Pump”

PASSIVE VS ACTIVE TRANSPORT

EXAMPLES:

Examples of substances that are transported this way: Sugar, amino acids, Sodium, Potassium, Calcium, and Hydrogen ion

TYPES:

1. Endocytosis

2. Exocytosis

3. Cell Membrane “Pumps”

MOVEMENT IN VESICLES

ENDOCYTOSIS AND EXOCYTOSIS

Large Macromolecules can’t get through the membrane with the use of pumps so they need an alternate method

These methods require the cell to expend energy

ENDOCYTOSIS

The process by which cells engulf substances that are too large to enter the cell by passing through the membrane (using ATP)

Items Engulfed:External Fluids, Macromolecules, Large Particle

and Cells

Process

1.The particle is enclosed by a portion of the cell, called a Vesicle

2.This vesicle then pinches off from the cell membrane and enters the cytoplasm

3.The contents of the vesicle fuse with a Lysosome and are digested by lysosomal enzymes or it can fuse with another membrane-bound organelle WATCH

TWO TYPES OF ENDOCYTOSIS

BASED ON MATERIAL TAKEN IN:Examples: Food Particles, waste materials, proteins

• 1. Pinocytosis – the movements of solutes or fluids into the cell

• 2. Phagocytosis – the movement of large food particles or whole microorganisms into the cell

Example:1. White blood cells engulf and digest bacteria and viruses-

PHAGOCYTES2. Unicellular organisms also feed by endocytosis

EXOCYTOSIS (TO EXIT)

• The passage of large molecules outside the cell• Process is the same as endocytosis but moves the

molecules out of the cell (uses ATP) WATCH

Example: • The Golgi Bodies put the proteins in vesicles to be

transported out of the cell.• Cells also use this to remove waste from the cell

PHAGOCYTOSIS

PINOCYTOSIS

Sodium-Potassium Pump