Membranes and Transport

Question 1

What are the functions of the plasma membrane?

Answer 1

1. Barrier to polar molecules, charged molecules, and large molecules
2. Maintains ion gradients
3. Involved in signaling

Question 2

How many layers is the plasma membrane made up of?

Answer 2

One phospholipid bilayer

Question 3

The plasma membrane is amphipathic, what does that mean?

Answer 3

Consists of hydrophilic and hydrophobic parts

Question 4

What is the general structure of a phospholipid?

Answer 4

Polar head (glycerol and phosphate)

Non polar tail (fatty acid tails)

Question 5

What is meant by the asymmetry of membranes? Why is this important?

Answer 5

The types of phospholipids differ between the two mono layers

Different phospholipids do different jobs

Question 6

Name 3 characteristics of membranes?

Answer 6

Flexible (change shape)

Repairable (move to reform continuous surface)

Expandable (increases surface area by adding new lipids)

Question 7

Why is the membrane able to repair, expand, and change shape?

Answer 7

Membrane fluidity

Question 8

How do phospholipids typically move?

Answer 8

Constant lateral motion but rarely flip to other side of bilayer

Question 9

What are some factors that affect membrane fluidity?

Answer 9

Ratio of unsaturated vs saturated fatty acids

Chain length of fatty acid tails

Temperature

Cholesterol

Question 10

What is the difference between saturated and unsaturated fatty acid tails?

Answer 10

Saturated are a straight chain with no double bonds

Unsaturated have double bonds which causes a bend

Question 11

A higher amount of unsaturated fatty acids means?

Answer 11

The double bond pushes other phospholipids away making it is less packed and therefore more fluid and permeable

Question 12

A higher amount of saturated fatty acids means?

Answer 12

The phospholipids can pack closely and it’s less fluid and permeable

Question 13

Something with a higher ratio of unsaturated fats would be what at room temperature?

Answer 13

Liquid

Question 14

Will a bilayer with short and unsaturated tails be more fluid at a higher temperature than a bilayer with long and saturated hydrocarbon tails? Why?

Answer 14

Yes

Molecules are already spaced out and the heat will cause them to space out more

Question 15

Will a bilayer with short and unsaturated tails solidify before a bilayer with long and saturated tails?

Answer 15

No

Already closely packed molecules will get closer

Question 16

If the fatty acid tails are longer than the membrane is? Why?

Answer 16

Less fluid

Link together and restrict movement

Question 17

Why is cholesterol important?

Answer 17

Maintains fluidity/permeability at lower and higher temperatures

Question 18

How does cholesterol help maintain fluidity?

Answer 18

At lower temperatures by reducing the packing opportunities

At higher temperatures by acting as a buffer to prevent them from separating too much

Question 19

What does the mosaic part of the fluid mosaic model mean?

Answer 19

Membranes contain many different proteins, carbohydrates, and lipids

Question 20

What can and cannot diffuse through the membrane?

Answer 20

Ions, large molecules, and polar molecules can’t

Small non polar molecule can

Question 21

What are the types of transport across the membrane?

Answer 21

Passive simple diffusion
Passive facilitated difffusion
Osmosis
Active transport

Question 22

What is simple diffusion? What uses it?

Answer 22

Movement of substances from high to low concentrations (increases entropy)

Spontaneous

No transporter or energy required

Small non polar molecules

Question 23

What is passive facilitated diffusion?

Answer 23

Movement from high to low concentration that doesn’t require energy but requires transport protein

Question 24

What types of proteins help with facilitated diffusion?

Answer 24

Integral/transmembrane protein

Peripheral protein

Question 25

What are some functions of membrane proteins?

Answer 25

Transport Enzyme activity Signal transduction Cell recognition

Question 26

What are integral/transmembrane proteins?

Answer 26

Integral are inserted into membrane and are amphipathic, difficult to remove Transmembrane proteins are the most common integral proteins are they cross the entire membrane once or multiple times

Question 27

Where do the hydrophilic/hydrophobic parts of transmembrane proteins go?

Answer 27

Hydrophobic are embedded in the membrane Hydrophilic are inside or outside the cell

Question 28

What are peripheral proteins?

Answer 28

Attached to one hydrophilic side and don’t interact with hydrophobic core Primarily found on intracellular (cytosolic) side Attach via non covalent bonds (easy to detach)

Question 29

What are some major proteins involved in facilitated diffusion?

Answer 29

Hydrophilic channel proteins Gated channels Carrier proteins

Question 30

What are channel proteins? What does the rate of diffusion depend on?

Answer 30

Always open (don’t change shape) Provide easier route across membrane for a specific molecule Concentration gradient (stronger gradient means faster diffusion) and number of channel proteins (more channels means faster movement)

Question 31

What are gated channels? What does the rate of diffusion depend on?

Answer 31

Only open via stimulus (molecules bind to protein which causes shape change to open protein) Whether it’s open or closed, concentration gradient, number of gated channels

Question 32

What are carrier proteins?

Answer 32

Transport specific molecules across the membrane Molecule attaches to binding site, causes shape change, transporter opens to other side

Question 33

What are lipids?

Answer 33

carbon-containing compounds that are nonpolar and hydrophobic

Question 34

What are the three naturally occurring fatty acids in our food?

Answer 34

polyunsaturated fatty acids monounsaturated fatty acids saturated fatty acids

Question 35

What are steroids?

Answer 35

family of lipids that have a four-ring structure ex. estrogen, cholesterol, testosterone

Question 36

What are fats?

Answer 36

nonpolar molecules composed of three fatty acids linked to a glycerol (triglycerides/triglycerols)

Question 37

How is glycerol and fatty acids linked?

Answer 37

ester linkage

Question 38

What are phospholipids?

Answer 38

glycerol that is linked to phosphate and two fatty acid chains

Question 38

What are phospholipids?

Answer 38

glycerol that is linked to phosphate and two fatty acid chains

Question 39

What is a lipid micelle?

Answer 39

tiny cluster created when the hydrophilic heads of a set of lipids face the water and form hydrogen bonds and the hydrophobic tails interact with each other

Question 40

What is a lipid bilayer?

Answer 40

lipid molecules align in paired sheets where the hydrophilic heads face the surrounding and the hydrophobic tails interact with each other

Question 41

What lipids form micelles vs bilayers?

Answer 41

micelles: fatty acids or other single amphipathic lipids with single hydrocarbon chains bilayer: phospholipids which have bulkier two-hydrocarbon tails

Question 42

What does selective permeability mean?

Answer 42

some substances cross a membrane easier than others

Question 43

What happens when equilibrium is reached during diffusion?

Answer 43

solutes continue to move but at equal rates

Question 44

What is a hypertonic solution? What happens to a vesicle?

Answer 44

solution outside the membrane has a higher concentration of solutes than the interior, water will move out of the vesicle causing the vesicle to shrink and the membrane to shrivel

Question 45

What is a hypotonic solution? What happens to a vesicle?

Answer 45

solution outside the membrane has a lower concentration of solutes than the interior, water will move into the vesicle causing it to swell or burst

Question 46

What is an isotonic solution? What happens to a vesicle?

Answer 46

solute concentrations are equal inside and outside the membrane, does not affect the membranes shape

Question 47

Can proteins be amphipathic? How?

Answer 47

yes amino acids have side chains that can be either nonpolar, polar, or charged

Question 48

What is aquaporin?

Answer 48

channel proteins that allow water to cross but nothing else, water can pass without aquaporin but its 10 times faster

Question 49

Which are faster, channel proteins or carrier proteins? Why do they use these then if they are slower?

Answer 49

channel proteins because they don't have to change shape use carrier proteins b/c of the need for specificity (can transport large molecules and be specific)

Question 50

What is transport against a concentration called?

Answer 50

active transport

Question 51

How can transport proteins use ATP?

Answer 51

channel proteins can be gated by ATP pumps are powered by ATP

Question 52

What is a coupled transporter?

Answer 52

transmembrane carrier protein that facilitates diffusion of an ion down its gradient and uses the energy from that process to transport some other substance

Question 53

What is a cotransporter/symporter?

Answer 53

cotransport protein that allows an ion to diffuse down its gradient, using the energy of that transport a different substance in the same direction against its concentration gradient

Question 54

What is an antiporter?

Answer 54

cotransport protein that allows an ion to diffuse down its gradient, using the energy of that transport a different substance in the opposite direction against its concentration gradient