cell membranes + internal membranes (1.2)

Cell membrane stuff

What does every cellular membrane have? What is different about this that helps them have different activities?

Same: Basic structure, phospholipid bilayer

Different: Proteins, allow for distinctive activities

What are the 5 general functions of all cell membranes?

1) barrier: they separate an internal environment from some external environment

2) transport: they can move specific molecules/ions/compounds through the membrane

3) Localization of function: they keep certain things where they need to be, either inside the cell/organelle or outside eg; compartmentalization: helps with efficiency → stuff happens independently

4) Signaling: membranes have proteins that allow them to make a response to external signals

5) Cell to cell communication: provide contacts between cells to facilitate direct cell-to-cell communication

image: gap junctions

What are cell membranes?

• surround the cell, separating the outside environment from the inner volume of the cell

What kind of organelles have internal membranes? (4)

• nucleus

• mitochondria

• vacuole

• golgi apparatus

What does an internal membrane do?

• separates the outside environment from the inner environment/volume of the cell

What do all membranes have in common?

they all have the SAME GENERAL STRUCTURE + SAME GENERAL FUNCTION (creates a semipermeable barrier around the cell/organelle)

What are the 2 components of membranes? What are the 3 types in one of the components?

2 components: PROTEINS and LIPIDS

Lipids

1) phospholipids → mostly phosphoglycerides (glycerol backbone)

2) phospholipid sphingomyelin (NO GLYCEROL)

3) steroid: cholesterol

What do phospholipids contain? Which part is polar, which is non polar? and interacts with water?

• glycerol

• 2 fatty acids (NON POLAR PART, do NOT interact with water)

• phosphate group (POLAR PART, INTERACTS WITH WATER)

What does amphipathic mean?

molecules with both hydrophilic and hydrophobic regions

How does water interact with amphipathic molecules? What does this form and what interaction stabilizes this?

Interaction:

• they associate with the hydrophilic region and exclude the hydrophobic region

Formation:

• form bilayered sheets where the polar groups face the water

Stabilization: Hydrophobic bonds/forces → arranged that way b/c water excludes the hydrophobic groups (hydrophobic effect)

How do phospholipids make a bilayer in water?

• they arrange themselves so that the polar heads are oriented toward the water

• the fatty acid tails are oriented toward the inside of the bilayer

this enables the fatty acid (hydrophobic) tails to remain together and avoid water

polar phosphate groups are oriented toward water

What does cholesterol do in the membrane?

• effects membrane FLUIDITY

low temps: keeps phospholipids APART and prevents a solid forming

High temps: cholesterol attracts phospholipids and stabilizes the membrane, prevents too much FLUIDITY

Where are proteins embedded into the membrane?

• inner surface

• outer surface

• embedded in bilayer

scattered throughout, capable of moving around in the bilayer

what is localization of function

Specific parts of a cell or structure have specific jobs

DIFF PARTS = DIFF JOBS

What are the 3 types of proteins in membranes + locations?

1) glycoprotein: surface

2) integral protein: middle (globular protein; compact/globeshaped)

3) Peripheral protein

What is the importance of proteins in membranes?

they give membranes their SPECIFIC FUNCTIONS

What is the difference in membranes of all membrane organelles and cell membranes? How does this make each unique?

they all have different COMPOSITION of proteins

• even though membranes all have the same general structure, their unique functions come from the proteins embedded in them

What are 2 examples of the different functions proteins have in membranes?

1) Special carriers or transport channels: molecules that are too LARGE or HYDROPHILIC to pass through the phospholipid bilayer

2) Glycoproteins: carb and protein combination act as ATTACHMENT SITES for molecules that need to enter or carry a message to the cell

What is the fluid mosaic model?

• describes the structure of the cell membrane

• explains why the membrane is flexible and made of different types of molecules

What does the fluid in “fluid mosaic” model stand for?

• describes the structure of a membrane b/c the phospholipid molecules and proteins that make up the membrane are FREE TO DRIFT AROUND

• THEY ARE NOT LOCKED IN POSITION, FREE TO MOVE

What does the term mosaic mean in the fluid mosaic model?

• describe the fact that membranes are embedded with protein molecules

• the molecules are placed RANDOMLY, there is NO SET PATTERN

What does selectively permeable mean?

Cells are selectively permeable because they control WHAT PASSES THROUGH THEM

What is a ligand?

molecule that binds to a large protein (receptor) and triggers action/chemical messgae