Cellular & Molecular Biology - Chapter 11

What is another term for the lipid bilayer?

Fluid mosaic model

Why is the lipid bilayer called the fluid mosaic model?

made up of a lot of individual pieces and when it comes together it’s functional

Cell membranes act as _________.

Selective barriers

Has a plasma membrane enclosing cell

Bacterial cell

Has a plasma membrane enclosing cell and internal membrane enclosing intracellular compartment (tons of membrane inside of cell that makes up organelles)

Eukaryotic cell

What prevents molecules on one side of the membrane from mixing with those on the other?

Membrane

What are the three things the membrane is involved in?

Communication, import/export, and growth/movement

Membranes allow cell compartments: _______

Organelles

• Allows chemical reactions to be separated from each other.

• Protects vital structure (DNA)

Membrane

Does the lipid bilayer exist alone?

No, it does not exist alone

There are a number of proteins underneath the _______ that are important as far as getting its shape and structure.

Lipid bilayer

Both hydrophilic and hydrophobic properties

Amphipathic

Everything that’s going to make up the basic structure of the membrane is ________.

Amphipathic

What is the structure of membrane lipids?

Hydrophilic head and hydrophobic tail

Most abundant = ______.

Phospholipids

Hydrophilic head is water ______.

Loving

Hydrophobic tail is water ______.

Fearing

Dissolve readily in water - charged atoms or polar groups

Hydrophilic

Water lovers

Hydrophilic

Insoluble in water - uncharged and nonpolar

Hydrophobic

Water haters

Hydrophobic

These properties are important for molecular organization:

• The lipid membrane (inside) is _______.

• ______ of amino-acids affects protein folding (3-D).

Hydrophobic, polarity

Is the lipid membrane (inside) hydrophobic or hydrophilic?

Hydrophobic

What affects protein folding (3-D)?

Polarity of amino-acids

What is the structure of a water molecule?

Bent

Water is bent molecule that’s covered in charge. Anything else that’s charged can ______ bond with it.

Hydrogen

What is the most common phospholipid in cell membranes?

Phosphatidylcholine

What is the structure of phosphatidylcholine?

Hydrophilic (polar) head and hydrophobic (nonpolar) tail

Polar, loves water, hydrogen bond, has a charge

Hydrophilic head

Nonpolar, hates water, no charge

Hydrophobic tails

Are all lipids amphipathic?

NO

Are all membrane lipids amphipathic?

YES

Two layers of lipids

Lipid bilayer

What is fundamental to creation of living cell?

Phospholipid bilayer

Do you need energy/enzymes/proteins to form a lipid bilayer?

No

Lipid membranes can form _______.

On their own

Why is all life in water?

Membranes make themselves spontaneously and putting lipids in water creates things on their own that looks like cells

What are liposomes important for?

Drug delivery

Pure phospholipids added to water

Liposomes

Artificial bilayers can be created in lab

Liposomes

Used in pharmacy for nano drug delivery systems (delivering mRNA in vaccines)

Liposomes

Phospholipids can ___ within the plane of the membrane.

Move

Lipids ____ around in the membrane.

Move

Proteins are required to allow ______ to occur.

Flip-flop

Moving around and passing each other (“Walking” around)

Lateral diffusion

Does lateral diffusion require energy/enzymes?

No

Goes from one side of membrane to another

Flip-flop

Rarely occurs, does not happen naturally

Flip-flop

Does flip-flop require enzymes/energy?

Yes

Spinning in one place

Rotation

Does rotation require energy/enzymes?

No

Moving the tails/legs (hydrocarbon tails)

Flexion

Does flexion require energy/enzymes?

No

What three things happen at the same time in the membrane?

Lateral diffusion, flexion, and rotation

Groups of lipids travelling together; have very similar functions and help with cell signaling

Lipid rafts

more or less fluid

Fluidity

Water, gas, acetone

Very fluid

Syrups (honey)

Less fluid

What 2 properties of hydrocarbon tails affect how tightly they pack in the bilayer?

Length and number of double bonds they contain

For length in hydrocarbon tails, what happens when it’s shorter?

Decreases interactions of tails and increases fluidity

Describe what long legs do in hydrocarbon tails.

Less fluid, creates drag, solid and rigid

Describe what shorter legs do in hydrocarbon tails. (WE PREFER THIS!)

More fluid, doesn’t drag, things move around

More double bonds = more _____

Fluid

Are double bonds flexible?

No

What property do double bonds possess?

Kink in tail

Double bonds are more ____ to pack against one another.

Difficult

Double bonds: More unsaturated hydrocarbon tails = ____ fluid

More

Double bond has kink in legs and takes up more physical space, which means what?

You can move around easier

Single bonds (packed in) makes it ______ to move around.

Harder

Cholesterol ____ the membrane.

Stiffens

Does cholesterol increase or decrease fluidity in normal conditions?

decreases fluidity

Cholesterol constitutes about ____ of the lipids in the membrane by weight.

20%

Cholesterol _____ the bilayer in animals at room temp. = more rigid and less permeable.

Stiffens

Describe cholesterol structure.

Rigid planar steroid ring structure

Lipid bilayer is _______.

Asymmetrical

Different on both sides

Asymmetrical

Lipids on one side are _______ as the other side.

Not the same

Two halves of bilayer have different sets of ________ and _________.

Phospholipids and glycolipids

Mainly structural found on outside

Phosphatidylcholine

Myelin sheathing, mostly outside, signaling

Sphingomyelin

Maintain fluidity and structure of the membrane

Cholesterol

New membrane synthesis - occurs in the ER

Bilayer synthesis

New membrane exported to other membranes by budding and fusion

Bilayer synthesis

In bilayer synthesis, bilayer pinches off from ER to form vesicles which can then be incorporated into another ________ by fusing with it.

Membrane

Explain bilayer synthesis.

We make all of our membrane inside the cell, and as we make it, we’re going to make sure the two sides are different. As that membrane is traveling to other places of the cell to be a part of other destinations, the fact that the two sides are different always remains the same.

Bilayer synthesis: Two sides face ________ environments, have ______ functions.

Different, different

_______ is maintained throughout bilayer synthesis.

Asymmetry

Catalyze the transfer of specific phospholipid molecules to opposite / cytosolic monolayer.

Flippases

Enzyme that does flip-flop (flips lipids from one side to another)

Flippases

What are proteins made up of?

Amino acids

What determines protein function?

Shape

50% of the mass of most plasma membranes

Proteins

Are proteins rare?

No, proteins are not rare and are doing tons of different function

What membrane proteins are associated with the lipid bilayer?

transmembrane proteins, monolayer-associated alpha helix proteins, lipid-linked proteins, and protein-attached proteins

Transmembrane proteins are ________.

Amphipathic

Transmembrane Proteins: Hydrophobic - ______

Interior

Transmembrane Proteins: Hydrophilic - ______

Exposed to aqueous environment

Going from one side through middle to come out other side

Transmembrane proteins

If you’re going through hydrophobic interior of lipid membrane, what do you have to be?

Hydrophobic

Amphipathic alpha-helix exposed on the surface of the protein

Monolayer-associated proteins