Bio 151 Ch 6 (Lipids and Membranes)

The same minerals in thermal vents ____________

1. Catalyze the polymerization of RNA 2. Promote the formation of fatty acid vesicles 3. Incorporate themselves and RNA inside

What are the three types of lipids found in cells?

1. Fats - composed of three fatty acids linked to glycerol (triaglycerols/triglycerides) 2. Steroids - a family of lipids with a distinctive four-ring structure (ex: cholesterol) 3. Phospholipids - consist of a glycerol linked to a phosphate group and to either 2 chains of isoprene or 2 fatty acids

What do phospholipids form upon contact with water?

1. Micelles - the heads face the water, and tails face each other 2. Phospholipid bilayers (lipid bilayers)

What factors influence the behavior of the membrane?

1. The number of double bonds between the carbons in the phospholipid's hydrophobic tail 2. The length of the tail (longer = stronger) 3. The number of cholesterol molecules in the membrane 4. Temperature (direct relationship to permeability and fluidity)

Co-transports 1. Symport 2. Antiport

1. Two different substances are moved in the same direction 2. One substance is moved in one direction, another is moved in the opposite direction

Hypertonic / osmosis of a hypertonic solution

An outside solution with a higher concentration Water moves out of the cell; the cell shrinks

Peripheral proteins

Are often attached to integral proteins, found only on one side of the membrane

One of the roles of plasma membrane proteins is to A. Dissolve the lipids in the membrane B. Allow passage of select molecules that could not otherwise cross the lipid bilayer C. Form one side of the membrane bilayer D. Provide a structure on which the membrane lipids can assemble a bilayer

B. Allow passage of select molecules that could not otherwise cross the lipid bilayer

In a phospholipid bilayer, the polar heads are oriented toward the _______ of the bilayer. A. Hydrocarbons B. Exterior C. Micelle D. Interior

B. Exterior

Which statement most accurately summarizes a feature of passive transport? A. It involves no change in free energy B. It is a spontaneous process C. It makes the cell interior and exterior more different from one another D. No membrane proteins are involved

B. It is a spontaneous process

Decreasing the saturation of the fatty acid chains on a particular type of phospholipid would result in the formation of A. Vescicles B. More fluid bilayers C. Glycerol D. Less fluid bilayers

B. More fluid bilayers

Molecules that are amphipathic contain A. Glycerol B. Regions that are hydrophobic and regions that are hydrophilic C. Carbon rings D. Both carbohydrates and lipids

B. Regions that are hydrophobic and regions that are hydrophilic

What explains why cholesterol and phospholipids are amphipathic but fats are not?

Cholesterol and phospholipids contain both hydrophilic and hydrophobic regions; fats are primarily hydrophobic.

The presence of membrane-bound organelles also allows _________

Compartmentalization of reactions

The movement of molecules through a plasma membrane channel protein is always A. "paid for" by an expenditure of cell energy B. toward the inside of the cell C. against the molecule's concentration gradient D. down the molecule's concentration gradient

D. Down the molecule's concentration gradient

What creates kinks in fatty acids?

Double bonds

Passive transport vs active transport

Passive: Does not require an input of energy Active: Requires energy in the form of ATP; allows cells to transport molecules or ions against an electrochemical gradient

When a phospholipid bilayer in water is agitated by shaking, what is the result?

Small, water-filled vesicles form

What state are saturated lipids more likely to be at room temperature?

Solid; unsaturated lipids are more likely to be liquid

Isotonic / osmosis of an isotonic solution

Solution concentrations are equal No net water movement; the cell is unchanged

Ion channels

Specialized membrane proteins that circumvent the plasma membrane's impermeability to small, charged compounds

How do phospholipid bilayers form?

Spontaneously (no outside input of energy required); two sheets of phospholipid molecules align, and the hydrophilic heads in each layer face a surrounding solution, and the tails face one another in the bilayer

What happens if acetylcholine binds to a receptor?

The channel conformation changes so it opens, and ions can pass through. Without acetylcholine, the ion channel is closed.

Nonpolar molecules that contain only hydrogen and carbon

Hydrocarbons

What most accurately describes how the three types of membrane proteins compare?

Among the three types, only pumps can concentrate substances on one side of the membrane

Integral proteins

Amphipathic; can span a membrane, with segments facing both its interior and exterior surface

Electrochemical gradient

A concentration gradient and a charge gradient established with ions build up on one side of a plasma membrane

The first lipid bilayers provide ________

A container for replicating RNA

When do fats form?

A dehydration reaction occurs between a hydroxyl group of glycol and the carboxyl group of a fatty acid - the glycerol and fatty acid molecules become joined by an ester linkage

Concentration gradient

A difference in solute concentrations

Diffusion

A form of passive transport; random movement (towards equilibrium)

Fatty Acid

A hydrocarbon chain bonded to a carboxyl functional group

Uniport

A single substance is moved in a single direction

Hypotonic / osmosis of a hypotonic solution

A solution with a lower concentration Water moves into the cell; the cell swells/bursts

Lipid vesicles are formed so that they contain pure water. If these vesicles are transferred to a solution that contains a rather high concentration of solutes, what would be the net direction of water movement? A. It will move out of the vesicles B. It will not move at all C. It will move into the vesicles D. It depends on what solute is dissolved in the exterior solution

A. It will move out of the vesicles

What is the effect on membrane permeability of cholesterol and/or temperature?

Adding cholesterol reduces permeability; its steroid rings increase the density of the hydrophobic membrane interior

What most accurately describes how the structures of fats, steroids, and phospholipids compare? A. Fats and phospholipids contain a phosphate group; steroids don't B. Fats and steroids contain ring structures; phospholipids don't C. Fats and phospholipids contain glycerol, steroids don't D. Fats and phospholipids contain isporene, steroids don't

C. Fats and phospholipids contain glycerol, steroids don't

The plasma membranes of all known cells are largely composed of what class of macromolecules? A. Proteins B. Enzymes C. Lipids D. Carbohydrates

C. Lipids

The physical property characteristic that distinguishes lipids from most other cellular macromolecules is that A. Lipids are very large molecules B. Lipids contain carbon C. Lipids are largely hydrophobic D. Lipids readily form hydrogen bonds with water and other polar solvents

C. Lipids are largely hydrophobic

Protocells

Simple vesicle-like structures that harbor nucleic acids; they are possible intermediates in the evolution of the cell

What allows for secondary active transport / cotransport?

Electrochemical gradients provide the potential energy required to power the movement of a different molecule against its particular gradient

Building blocks of lipids

Fatty acids and isoprene

"Head" region of a phospholipid vs the "tail" region

Head: Consist of a glycerol, a phosphate, and a charged group; contains highly polar covalent bonds Tail: Compromised of 2 non polar fatty acid or isoprene chains

Transmembrane proteins

Integral proteins that span the membrane; are involved in the transport of selected ions and molecules across the plasma membrane. They can therefore affect membrane permeability

Does adding cholesterol to a membrane affect its permeability?

It decreases the permeability

Carbon-containing compounds found in organisms Largely non polar and hydrophobic

Lipids

Aquaporins

Membrane channels that allow water to cross the cell membrane

Do phospholipids dissolve in water?

No; the water molecules interact with the hydrophilic heads but not the hydrophobic tails, driving the hydrophobic tails together

Permeability and fluidity of short unsaturated hydrocarbon tails vs that of long saturated hydrocarbon tails

Short/unsaturated: higher Long/saturated: lower

Osmosis

The movement of water across lipid bilayers (occurs only across a selectively permeable membrane)

Facilitated diffusion

The passive transport of substances that would not otherwise cross the membrane; occurs through carrier proteins or transporters that change shape during the transport process

Selective permeability

The permeability of a structure; the tendency to allow a given substance to pass across it

What allows lipids to form membranes?

The phospholipid heads interact with water while the tails do not, allowing these lipids to form membranes. The lipids contain both a polar, hydrophilic region and a non polar, hydrophobic region

What is the job of the plasma membrane (aka cell membrane)?

To separate the cell's interior from the external environment, to keep damaging materials outside, allow entry of needed materials, and facilitate the chemical reactions necessary for life