Cell Membrane

The cell membrane or plasma membrane completely surrounds the cell and serves as a barrier between the cell and its environment.

Allows entrance of needed substances (glucose, amino acids, lipids, etc.) and prevents entrance of other substances.

Allows waste products (CO2) to exit the cell

The cell membrane allows some molecules to enter the cell but prevents entrance of other molecules.

The cell membrane retains certain molecules inside the cell but allows other molecules to exit.

Therefore, the cell membrane is said to be selectively permeable to molecules.

Lipid molecule = 1 glycerol + 3 fatty acids

Phospholipid molecule = 1 glycerol + 1 phosphate group + 2 fatty acids

The head region of the phospholipid is also called the polar region and is hydrophilic (water loving)

The tail region of the phospholipid is also called the nonpolar region and is hydrophobic (water hating)

The cell membrane is composed of a phospholipid bilayer.

The cell membrane is composed of a phospholipid bilayer.

The heads of the bilayer can interact with water because they are polar.

The tails of the bilayer cannot interact with water because they are nonpolar.

Therefore, water soluble molecules cannot move through the bilayer easily.

Transporting across the cell membrane

- Passive Transport

- Active Transport

Passive Transport

- does not require energy

- moves from an area of high concentration to an area of low

concentration ( a downhill flow)

There are two types of cellular transport that occurs across the cell membrane.

Passive Transport (con’t)

Passive transport includes- diffusion

- facilitated diffusion - osmosis Diffusion- occurs when molecules move

randomly away from each other in a liquid or gas. Example: sugar/water

salt/watersmoke/air

Passive Diffusion

moves from an area of high concentration to an area of low concentration ( a downhill flow)

Diffusion (con’t)

Diffusion is the continual moving about and bumping of particles into each other. This continues until all the particles of a substance are equally distributed throughout the container. However, the bumping never stops!

Facilitated Diffusion

Passive TransportPassive Transport

Osmosis

Osmosis is the diffusion of WATER across a semi-permeable membrane

osmosis occurs in response to the concentration of solutes dissolved in water.

Water moves low solutes to high solutes

A simple rule to remember is:Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty.

Osmosis in a Isotonic solution

If the concentration of a solute (salt) is equal of on both sides, the water will move back in forth but it won't have any result on the overall amount of water on either side. "ISO" means the same

Animation of Osmosis (Cell in an Isotonic Environment)

Outside of Cell

Inside of Cell

Equal number of solutes inside and outside of cell

Cell will remain same

Osmosis in a Hypertonic solution

The word "HYPER" means more, in this case there are more solute (salt) molecules outside the cell, which causes the water to be sucked in that direction.In plant cells, the central vacuole loses water and the cells shrink, causing wilting.

Osmosis Animation (Cell in Hypertonic Environment)

Outside of Cell

Inside of Cell

Higher percent of solutes outside of cell

Cell willshrivel

Osmosis in a Hypotonic Solution

The word "HYPO" means less, in this case there are less solute (salt) molecules outside the cell, since salt sucks, water will move into the cell. The cell will gain water and grow larger. In plant cells, the vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting

Osmosis Animation (Cell in Hypotonic Environment)

Inside of Cell

Outside of CellLower percent of solutes outside of cell

Cell will swell

Osmosis in actionOsmosis in action

Facilitated Diffusion

a process whereby a large substance passes through a membrane with a aid of a facilitator.

The facilitator is an integral membrane protein that spans the width of the membrane.

The force that drives the molecule from one side of the membrane to the other is the force of diffusion.

Active Transport

Energy is needed in active transport Active transport is the movement from

an area of low concentration to an area of high concentration (uphill flow)

Active transport use carrier proteins that act as pumps.

Active Transport

Active transport is the movement from an area of low concentration to an area of high concentration (uphill flow)

Active Transport (con’t)

Active transport include: Bulk Transport Bulk Transport is for solutes to large to cross a cell membrane. Examples: endocytosis

exocytosis

Endocytosis

During endocytosis the cell membrane Folds into a pouch that encloses the particles. The pouch pinches off INSIDE the Cell to form VESICLE (membrane-wrapped bubbles). The VESICLE can then fuse with other Organelles (LYSOSOMES) or Release its contents into the Cytoplasm.

Endocytosis con’t(Pinocytosis & Phagocytosis) Pinocytosis and

Phagocytosis are two types of endocytosis. Pinocytosis is sometimes referred to as “cell drinking”

Solutes or Fluids outside the Cell Membrane can be brought into the Cytoplasm by pinocytosis.

Pinocytosis takes in liquids

Pinocytosis

Pinocytosis is the ingestion of dissolved materials by endocytosis. The cytoplasmic membrane folds in and pinches off placing small droplets of fluid in a pinocytic vesicle. The liquid contents of the vesicle is then slowly transferred to the cytosol.

Phagocytosis

Phagocytosis is like pinocytosis except the cell engulfs a food particle or other cells instead of a drop of liquid.

"CELL EATING"

Phagocytosis takes in solid particles

Phagocytosis

Phagocytosis is the ingestion of solid particles by endocytosis. The cytoplasmic membrane folds in and pinches off placing the particle in a phagocytic vacuole. The phagocytic vacuole then fuses with lysosomes and the material is degraded.

Exocytosis

During exocytosis waste and cell products leave the cell. Products made in the cell are packaged in golgi vesicles, which then fuse with the cell membrane and secrete material out of the cell.

Exocytosis

During exocytosis, a cell releases waste products or specific secretion products by the fusion of a vesicle with the cytoplasmic membrane.

How active transport occursHow active transport occurs