Membranes

Question 1

What are the lipids that compose membrane bilayers?

Answer 1

Triglycerides, sterals, and phospholipids

Question 2

What are some characteristics of lipids?

Answer 2

Water insoluble (hydrophobic) molecules made mostly of carbon and hydrogen atoms (hydrocarbons)

Question 3

What are fatty acids?

Answer 3

Hydrocarbons with a carboxyl group at one end. Each fatty acid molecule varies in number of carbon atoms in a hydrocarbon chain (14 - 24), as well as presence and number of carbon-carbon double bonds

Question 4

What is the difference between saturated and unsaturated fatty acids?

Answer 4

• Saturated fatty acids have no carbon-carbon double bond IN THE HYDROCARBON CHAIN
• Unsaturated fatty acids have 1 or more carbon-carbon double bonds (creates a curve in structure)

Question 5

What are the characteristics of triglycerides?

Answer 5

Long term energy storage molecules, 3 fatty acid tails bound to a glycerol “anchor”

Question 6

What are the characteristics of phospholipids?

Answer 6

A polar head made of phosphate and glycerol (hydrophilic) and 2 fatty acid tails (hydrophobic). Spotaneously form bilayers in water to protect their hydrophobic parts

Question 7

What are the 3 types of phospholipid membranes?

Answer 7

Liposome/sphere, micelle (single layer sphere), and phospholipid bilayer sheet

Question 8

What do biological membranes do?

Answer 8

Compartmentalize the cell: the plasma membrane separates “out” from “in” and the internal membranes create additional cellular regions .
They are also scaffolds for communication and chemical reactions

Question 9

What does “fluid mosaic” mean in respect to the bilayer?

Answer 9

Lipids, proteins, and many other molecules co-exist in the membrane (not just the phospholipids)

Question 10

What are integral and peripheral proteins?

Answer 10

Integral proteins are part of the membrane, peripheral proteins are located on the edges of the bilayer

Question 11

What are trans proteins?

Answer 11

They can pass through the bilayer

Question 12

What is the state of the lipid bilayer?

Answer 12

It is fluid which means that its components are constantly in motion

Question 13

What is the movement of phospholipids in the bilayer?

Answer 13

They are not attached to one another, so they freely roam around the plane of the membrane

Question 14

What is the tendency of dissolved molecules to evenly distribute in a solution?

Answer 14

Diffusion; goes from high to low concentration to dilute, this is also known as the concentration gradient

Question 15

What increases membrane fluidity?

Answer 15

• Temperature (more molecular motion –> more fluid)
• Unsaturated fatty acid tails (the bend pushes other phospholipids away creating an open space and decreases interaction, so it increases fluidity)
• Shorter fatty acid tails (less intermolecular interaction so there is more fluidity)

Question 16

What regulates membrane fluidity?

Answer 16

Sterols

Question 17

How do sterols regulate membrane fluidity?

Answer 17

Animal cells insert cholesterol into the bilayer (acts as a buffer)
- Cholesterol prevents excess viscosity by stopping phospholipids from packing together

• Cholesterol prevents excess fluidity by filling in gaps between phospholipids

Question 18

What does membrane fluidity affect?

Answer 18

Membrane permeability. Fluid membranes are too “leaky” (solutes that don’t normally diffuse leak out).
Viscous membranes stop solutes that normally diffuse across the membrane.
Membranes need a balance between fluid and viscous

Question 19

What can and can’t diffuse through the lipid bilayer?

Answer 19

• Non-polar molecules always can because they interact with the similarly hydrophobic insides
• Small uncharged polar molecules can slowly go through
• Large uncharged polar molecules only sometimes diffuse
• Ions can never diffuse through

Question 20

How does water diffuse through the membrane if it is polar?

Answer 20

Through protein channels that have a hydrophobic exterior and a hydrophilic interior

Question 21

What happens when equilibrium is eventually reached via diffusion?

Answer 21

• Concentration gradient will be eliminated
• Lower energy state (equilibrium is the lowest energy state but that does not mean diffusion stops here)

Question 22

In what case does diffusion actually work?

Answer 22

It only works across membranes if the solute itself is free to pass through the bilayer

Question 23

What is tonicity?

Answer 23

The relative solute concentration difference across a bilayer

Question 24

What are the three categories of tonicity?

Answer 24

Isotonic: net movement of water is the same in both directions; concentration is the same

Hypotonic: net movement of water inside the cell (swelling); one has less concentration than the other

Hypertonic: net movement of water outside the cell (shrivelling); one has more concentration than the other

Question 25

What are the types of passive transport?

Answer 25

Simple diffusion and facilitated diffusion. This does not require cellular energy and is instead powered by the concentration gradient.

Question 26

What is simple diffusion?

Answer 26

Small hydrophobic and polar solutes diffuse directly across the phospholipid bilayer down with the concentration gradient. These molecules are permeable.

Question 27

What is facilitated diffusion?

Answer 27

Most important molecules are large/charged/polar and cannot diffuse across without help. transport protein tunnels cross the membrane and facilitate (help) solutes diffuse down with the concentration gradient

Question 28

What are the two types of transport proteins in facilitated diffusion?

Answer 28

Channel proteins: transport specific molecules like ions and water

Carrier proteins: transport everything else (binds to molecule and changes conformation to allow passage)

Question 29

Distinguish simple and facilitated transport on a graph.

Answer 29

Facilitated transport has a higher rate of transport, approaches maximum when all transporters are occupied (asymptote). Simple diffusion has a lower and linear rate of reaction.

Question 30

Why do cells actively generate concentration gradients?

Answer 30

They live in dilute environments and need to concentrate molecules inside

Question 31

How do cells establish a concentration gradient?

Answer 31

Must move solutes away (up) their gradient, and this requires a cellular energy source

Question 32

What is primary active transport?

Answer 32

There are substrate-specific protein pumps across the membrane that move solutes up (against) the gradient, the transport pump uses ATP directly. This generates a chemical or electrochemical gradient

Question 33

What is secondary active transport?

Answer 33

Substrate specific carrier proteins move solutes against (up) the gradient. “Powered” by the previous energy release that moves down the gradient with it

Question 34

What are symporters?

Answer 34

Both solutes move in the same physical direction

Question 35

What are antiporters?

Answer 35

The solutes move in opposite physical directions