The Cell Membrane: How the cell

maintains homeostasis

Cell Homeostasis Cats hate and are afraid of water.

What do you hate or fear? Think of one or two things that you hate.

What do you love and what are you attracted to? Think of one or two things that are attractive to you.

“phobia” means fear. Fear of water is hydrophobia.

Fear of snakes is Ophidiophobia . Fear of spiders?

“phile” means like. If you like water, you are an

hydrophile. If you like snakes you are an ophidiophile. If

you like spiders, you are an arachnophile.

The cell membrane is composed of two layers of

phospholipids. The Outer “heads” of the phospholipid

really like water and are called _________philic. The area

between the membrane layers is made of the

phospholipid “tails”. Tails are “afraid of water” and are

called: ____________phobic.

Hydrophylic head (PO4-) and

hydrophobic tail behavior

Cell membranes are composed of two

phospholipid layers. (bilayer)-draw the all

blue phospholipid model and label the

tails as “fatty acid tails” and label the

circle as the phosphate head:

Cell membranes are composed of two

phospholipid layers. (bilayer) Take a minute

to Label the cell membrane pictured on

your notes:

Think: Why does your cell need hydrophobic

parts of the membrane?

The components move!

The cell membrane has two

major functions.

1. Forms a boundary between

inside and outside of the cell

2. Controls passage of materials

into or out of the cell

cell membrane

outside cell

inside cell

Consult with a partner and come up with

an analogy for something that is like a

membrane in that it is “fatty and

phobic” on the inside, but “likes water”

on the outside (hint-something that

dissolves easily likes water ALOT)

Components move!

The fluid mosaic model describes the

membrane. Think about definitions for the two words and then

we will discuss how this might relate to the cell

membrane:

FLUID –

MOSAIC (puzzle)–

bendable, movable, not solid

composed of many pieces

The fluid mosaic model describes the

membrane because the

molecule/compound components or pieces

are always moving

(http://www.susanahalpine.com/anim/Life/m

emb.htm

cell membrane

There are other compounds embedded in the

membrane: label the matching parts on your diagram:

example—where are the proteins?. https://www.wisc-

online.com/learn/natural-science/life-

science/ap1101/construction-of-the-cell-membrane

protein

cholesterol

protein

carbohydrate

chain

protein channel

carbohydrate

chain

Analogy

• So…what should the membrane proteins really look like?

Cell Homeostasis: Cell Membrane

components/parts

Protein

Channel

Protein

Carbohydrates

Lipids/Fats

Identification, holds cells together, sends and

receives messages

Macromolecule compounds

Function

Proteins Membrane proteins: Identification, holds cells together, sends messages. Channel proteins transport materials into and out of the cell. Membrane receptor proteins: Are located in cell membrane-Receive chemical signals/ligands from outside the cell. Intracellular receptor proteins: Located inside the cell-Receive chemical signals/ligands like hormones.

Carbohydrates Identification, signaling, and “sugary glue” that holds cell membrane together.

Lipids/Fats (nonpolar-no charge)

Do not mix with water-Cholesterol strengthens the cell membrane and phospholipids form the fatty barrier between cell and environment. Controls the passage of materials into and out of the cell.

The cell membrane is selectively permeable.

Allows some, but not all molecules to cross the membrane. Fig. 3.18

THINK: What molecules would you add to this

membrane to make it a more functional and a

complete “mosaic” ?

cell

mem

bra

ne

The cell membrane is selectively permeable.

Predict: Which way will the water molecules move?

Toward the inside or outside the cell? Why? Check this

out:

http://www.pbslearningmedia.org/resource/tdc02.sci.life.cell.membraneweb/cell-membrane-just-passing-

through/

• Chemical signals are transmitted

across the cell membrane-Read page

84

– Receptor proteins bind with ligands

(chemicals) and change shape.

– A ligand is a specific “signaling” molecule

that binds with a receptor protein to

make something happen.

There are two types of

receptor proteins.

• One type: Intracellular

receptor protein

• *THINK: What does Intracellular mean?

• Ligand moves through the

cell membrane to reach

receptor protein on inside of cell.

• Example: hormones:

http://highered.mheducat

ion.com/sites/0072507470/

student_view0/chapter17/

animation__intracellular_re

ceptor_model.html

There are two types of

receptor proteins.

• The 2nd type of receptor

is: membrane protein

receptor (integral

protein)

• Ligand on outside of cell

binds with a receptor

within the cell

membrane.

• Ex: Neurotransmitters,

growth factors

There are two types of receptor proteins.

• The 2nd type of receptor is: membrane protein

receptor

• Label the missing parts:

Ligand

Receptor