The Plasma Membrane

What is the cytoplasm?◦ Cyto = “cell”◦ Plasma= “liquid substance of the cell”

Cytoplasm?◦ Clear, gelatinous fluid inside the cell

Let’s Recall

What contains it?◦ Plasma Membrane

Do all cells have this?◦ YES!

Putting it together

Cells need an inside & an outside…◦ separate cell from its environment

◦cell membrane is the boundary

4

Cell (plasma) membrane

INfood- sugars- proteins- fats

saltsO2

H2O

OUTwaste- ammonia- salts- CO2

- H2O products- proteins

cell needs materials in & products or waste out

Why have a plasma membrane?◦ Allow nutrients to move in and out of the cell

How does it control how much goes in and out?◦ Selective permeability

Per= “through” Meare= “ to glide”

Therefore, what does it mean?

Plasma Membrane

What’s the point for allowing materials in and out of the cell?

HOMEOSTASIS!!!!!

Recap

How do you build a barrier that keeps the watery contents of the cell separate from the watery environment?

7

Building a membrane

What substance do you know that doesn’t mix with water?

FATS

LIPIDS

Remember: oil & water don’t mix!!

Membrane is made of special kind of lipid ◦ phospholipids◦ “split personality”

Membrane is a double layer ◦ phospholipid bilayer

8

Lipids of cell membrane

inside cell

outside cell

lipid

“repelled by water”

“attracted to water”

phosphate

Cell membrane controls what gets in or out Need to allow some materials — but not all

— to pass through the membrane ◦ semi-permeable

only some material can get in or out

9

Semi-permeable membrane

aa H2Osugar lipids salt waste

So what needs to get across the membrane?

O2

What molecules can get through the cell membrane directly?◦ fats and oils can pass directly through

10

Crossing the cell membrane

inside cell

outside cell

lipid

salt

aa H2Osugar

waste

but…what about other stuff?

Need to make “doors” through membrane ◦ protein channels allow substances in & out

specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc.

11

Cell membrane channels

inside cell

outside cell

sugaraaH2O

saltwaste

Channels are made of proteins◦ proteins both “like” water & “like” lipids

12

How do you build a semi-permeable cell membrane?

bi-lipidmembrane

protein channelsin bi-lipid membrane

Proteins act as doors in the membrane◦ channels to move specific molecules through cell

membrane

13

Protein channels

HIGH

LOW

Protein Channels

Integral Proteins Peripheral Proteins

Embedded all the way through the bilayer

Allow ions to pass through the membrane

Bond to only one side of the membrane

Attach to or near integral proteins

Help with ion identification

Other Key Players

Cholesterol Glycolipid and Glycoprotein

Cell signaling Maintains membrane

fluidity Secures Proteins

Lipid or Protein with a carbohydrate attached

Provide energy Cellular recognition

Why do molecules move through membrane if you give them a channel?

16

Movement through the channel

?

?

HIGH

LOW

Diffusion◦ move from HIGH to LOW concentration

17

Molecules move from high to low