Membranes + Simple diffusion

Cell membrane

A barrier that separates a cell from the external environment

What are cell membranes composed of?

2 phospholipid layers (Bilayer)

2 Major functions of the cell membrane:

1. Forms a boundary between inside and outside of the cell.

2. Controls passage of materials.

Receptors bind with ___ and change shape.

Ligands

2 types of receptors:

1. Intracellular receptor

2. Membrane receptor

2 parts of a phospholipid:

1. Hydrophillic head.

2. Hydrophobic fatty acid tails.

Why is it called a fluid mosaic model?

The cell membrane is flexible. If it is disturbed, the phospholipids making up the membrane go back into place. The collection of phospholipids make up the “mosaic”

Selectively Permeable

Only small and non polar molecules can pass through the membrane. Large and polar molecules cannot pass through and need a protein channel in order to do so.

How can materials move across membranes?

Concentration differences.

Solution

Homogeneous mixture (liquid + dissolved solutes)

Solvent

Dissolving agent

Solute

agent being dissolved

Universal solvent

water

Passive transport

Molecules can move across the cell membrane. It does NOT require energy input from a cell.

2 types of passive transport:

1. diffusion

2. osmosis

Diffusion

net passive movement of particles from regions of higher concentration to regions of lower concentration. AKA a concentration gradient; diffuse down.

Diffusion through transport proteins

For molecules that cannot easily diffuse across a cell membrane. This is facilitated diffusion.

Osmosis

The diffusion of water molecules across a semipermeable membrane.

3 types of solutions:

1. Isotonic: equal concentrations.

2. Hypotonic: Low concentration of solutes.

3. Hypertonic: High concentration of solutes.

Can water pass through the cell membrane?

yes

Can inorganic ions pass through the cell membrane?

no

Can sugar pass through the cell membrane?

no

can nucleic acids pass through the cell membrane?

no

can starch pass through the cell membrane?

no

can lipids pass through the cell membrane?

yes