Cell Membrane Notes

A polar hydrophilic head and nonpolar hydrophobic tails

What are the two parts of phospholipids?

The heads contact water inside and outside the cell. The tails are hidden in the middle forming a nonpolar, hydrophobic barrier

How do phospholipids arrange themselves?

They are designed to stay in place

What are proteins in cell membranes designed to do?

Transport Proteins

Act as channels, gates, or pumps that allow materials into and out of the cell

Receptor Proteins

Act as receptors for cell messengers such as hormones or changes in the environment

Marker proteins

Act as identification badges for the cell which is useful for cell sorting and the immune system

Passive Transport

A process that moves molecules from a high to low concentration without using energy. It is based on diffusion

Diffusion

Movement of molecules from a high to low concentration

Small molecules such as O2 and CO2

What kinds of molecules does simple diffusion allow to go through the membrane?

Equilibrium

Changes in concentrations of a substance will stop when they are equivalent on both sides of the membrane

Nonpolar and small molecules can pass through the cell membarane

What molecules can pass through the membrane?

Polar molecules and ions do not pass through the cell membrane

What molecules cannot pass through the cell membrane?

Osmosis

Diffusion of water

Hypotonic Solution

Less concentrated solution: lower concentration of water in the cell than outside the cell; water enters the cell causing it to enlarge and burst

Hypertonic Solution

Very concentrated solution: higher concentration of water in the cell than outside the cell; water leaves the cell causing it to shrink

Isotonic Solution

Same concentration of water inside and outside the cell. The cell maintains its size as water enters and leaves at the same rate

They have a strong outer cell wall

How do plant cells protect themselves?

They pump water out

How do unicellular organisms protect themselves?

They surround themselves with isotonic fluid (blood)

How do animal cells protect themselves?

Facilitated Diffusion

Protein channels assist the diffusion process passive transport (no energy is required)

Active Transport

A process that moves molecules from a low to a high concentration which requires energy. Refers to process where cell membrane proteins act as pumps