Cell Membrane Cell Membranes Phospholipid bilayer The main

Cell Membrane

Cell Membranes Phospholipid bi-layer The main portion of the cell membrane is constructed of a phospholipid bi-layer. There are two layers that are mirror images of each other.

Phospholipids • Each phospholipid is made of two parts: • The head is a PHOSPHATE molecule (PO 4) – The Phosphate is polar which makes it HYDROPHILLIC (attracted to water). • The tails are made of FATTY ACIDS. – The Fatty Acid tails are non-polar which make it HYDROPHOBIC (repelled by water)

Cell Membranes - Proteins Receptor proteins: enables cell to sense surroundings by binding to substances. Transport proteins: moves substances through the bi-layer that cannot do so themselves.

Cell Membranes - Carbs Surface markers: chains of carbohydrates that identify what type of cell it is.

Homeostasis • The Cell Membrane plays an important role in homeostasis by managing the amount of water is in the cell.

Selectively Permeable • The Cell Membrane SELECTIVELY PERMEABLE. This means that only some items are able to pass through the membrane.

SELECTIVELY PERMEABLE (Semi-permeable)

Passive Transport • Passive transport is when a cell transports things across the membrane without energy. • Things always move from high concentration to low concentration when no energy is used.

Diffusion Across a Space • Type of passive transport Molecules move automatically down the concentration gradient from an area of higher concentration (more particles) to an area of lower concentration (less particles). Examples: Blue dye in a beaker demo someone making popcorn or grilling (smell) strong perfume bad smell in room

Concentration Gradient • A difference in the concentration of a substance across a distance

Diffusion Through a Cell Membrane The particles move until they are evenly distributed, which is called “equilibrium” semipermeable

Osmosis • The diffusion of water molecules across a selectively permeable membrane is known as osmosis

Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential High solute concentration

Osmosis • If a cell has more particles (like sugar) inside the cell than outside, this means that there is a higher concentration of water outside than inside – Remember that osmosis is the movement of WATER across a membrane – Also remember that in diffusion, particles move from areas of HIGHER CONCENTRATION TO LOWER CONCENTRATION

Osmosis • Therefore the water is going to move INSIDE the cell until equilibrium is reached • This cell is said to be in a hypotonic solution. Hypotonic solution has less particles outside than inside the cell. • As water moves in, the cell will get bigger.

Cell in Hypotonic Solution 10% Na. CL 90% H 2 O CELL 20% Na. CL 80% H 2 O What is the direction of water movement?

Osmosis • If the concentration of particles is higher outside of a cell than inside, then the concentration of water is higher inside and the water will move out of the cell until equilibrium is reached. – This cell is said to be in a hypertonic solution where there is more particles outside of the cell. – As water moves out of the cell, the cell will shrink.

Cell in Hypertonic Solution 15% Na. CL 85% H 2 O ENVIRONMENT CELL 5% Na. CL 95% H 2 O What is the direction of water movement?

Osmosis • If the concentration of particles outside the cell are the same as inside of the cell, water will not move in or out. – A cell in this case is said to be in an isotonic solution where the concentration of particles is the same on both sides of the cell membrane.

Cell in Isotonic Solution 10% Na. CL 90% H 2 O ENVIRONMENT CELL 10% Na. CL 90% H 2 O NO NET MOVEMENT What is the direction of water movement? equilibrium The cell is at ________.

Osmosis Type of Solution Hypotonic Hypertonic Isotonic Particle concentration in solution Particle concentration in cytoplasm Where is there more water? Which way will water move?

Passive Transport Simple & Facilitated Diffusion v Doesn’t require energy v Moves high to low concentration Example: Simple-O 2. H 2 O, CO 2 Facilitated- amino acids, glucose v

Active Transport v. Requires energy or ATP v. Moves materials from LOW to HIGH concentration v. AGAINST concentration gradient

Moving the “Big Stuff” Exocytosis - moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another

Exocytosis Exocytic vesicle immediately after fusion with plasma membrane.

Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis

Moving Ions through pumps - The Sodium/Potassium Pump