Unit 6: Biological Membranes

Question 1

What is the enzyme scramblase and where is it located?

Answer 1

Transfers phospholipids across the leaflet to the extracellular side to even distribution. The beginning of membrane synthesis occurs in the ER

Question 2

What is flippase and where is it located?

Answer 2

Enzyme in the Golgi that transfers P.E. and P.S. lipids to the cytosolic leaflet causing membrane asymmetry

Question 3

What tonic solution do animal cells prefer and what tonic solution do plant cells prefer

Answer 3

Animal cells prefer isotonic solution

Plant cells prefer hypotonic solutions to produce tutor pressure within their cells to provide support

Question 4

How easily do ions transfer through cell membranes

Answer 4

Ions are not able to pass through the membrane unaided by a transporter

Question 5

Ion Channels

Answer 5

electrochemical gradient
high volume
bidirectional

Question 6

Carrier Protein

Answer 6

Facilitated diffusion - passive
very specific
saturable and inhibitable

Question 7

Following transporters with or against concentration gradient?

a) ion channels
b) carrier proteins
c) pumps

Answer 7

a) with
b) with
c) against

Question 8

Describe symport coupled transport

Answer 8

Moving an ion with gradient concentration along with another ion tagging along going against concentration gradient
Secondary active transport

Question 9

How are concentration gradients maintained?

Answer 9

Na-K pumps keeps K inside the cell by pumping Na out of the cell and maintaining a negative environment inside the cell

Question 10

The fluidity of membranes in a plant cell during cold weather could be maintained by increasing the:

a) proportion of peripheral proteins
b) proportion of long chain hydrocarbon tails
c) cholesterol content in the membrane
d) proportion of phospholipids with unsaturated hydrocarbon tails
e) proportion of phospholipids with saturated hydrocarbon tails

Answer 10

d)

Question 11

A major factor in generating the asymmetrical distribution of phospholipids observed in the leaflets of the plasma membrane is:

a) selective placement of (PS, PE) in the cytosolic leaflet during membrane assembly in the ER
b) the tendency for certain phospholipids to be attracted to the plasma membrane leaflet facing the extracellular space
c) the action of scramblase in the ER, catalyzing transfer of (PS, PE) to the opposite leaflet
d) the action of flippase in the ER, catalyzing transfer of (PS, PE) to the opposite leaflet
e) the action of flippase in the Golgi, catalyzing transfer of (PS, PE) to the opposite leaflet

Answer 11

e) flippase responsible for transferring specific lipids across the leaflet in the Golgi

Question 12

An animal cell placed in the hypertonic environment will:

a) swell
b) become turgid
c) lyse
d) be unaffected
e) shrink

Answer 12

e)

Question 13

Where would you expect to find the R-groups of hydrophobic amino acids of a transmembrane protein?

a) hydrophobic R-grous would clump together in the proteins interior, avoiding contact with the phospholipid bilayer
b) because they are charged at physiological pH, proteins are found only on the membrane surface. The hydrophilic regions would be attracted to the phosphate groups of membrane phospholipids through ionic bonds
c) hydrophobic R-groups in the transmembrane part of the molecule would be oriented toward the part of the protein, which is in contact with the hydrocarbon tails of the membrane phospholipids
d) integral membrane proteins are oriented such that none of their amino acid R-groups come into contact with the membrane interior

Answer 13

c)

Question 14

Which of the following is NOT true of carrier proteins involved in facilitated diffusion?

a) they increase the rate of transport of their cargo molecule across the membrane
b) through their transport activities, they can concentrate solute molecules on the opposite side of the membrane
c) they have specific binding sites for the molecules that they transport
d) they undergo a change in conformation upon binding of the solute
e) they do not require energy from the cell to operate

Answer 14

b)

Question 15

GLUT-1 is an example of:

a) a membrane-associated pump that moves glucose against its gradient by using ATP
b) a symport that co-transports Na+ and glucose into intestinal epithelial cells
c) a membrane transport protein that transports hexoses across animal cell membranes
d) a membrane transport protein that facilities the diffusion of D-glucose down its concentration gradient
e) a membrane transport protein that facilitates the diffusion of monosaccharides across animal cell membranes

Answer 15

d)

Question 16

Which of the following describes co-transport?

a) active transport of two solutes via a membrane protein
b) two hydrophobic molecules of the same type that dimerize and diffuse together through the lipid bilayer
c) ions diffusing against an electrochemical gradient created by a pump
d) a pump such as the Na-K pump that moves two ions in opposite directions
e) transport of one solute that is coupled with transport of an ion moving down its concentration gradient

Answer 16

e)

Question 17

Which of the following statements is/are true concerning the transport of glucose from the gut lumen across the intestinal epithelium?

a) glucose travels passively down its concentration gradient via carrier proteins, out the basolateral surfaces of intestinal epithelial cells
b) Na/K pumps which are highly expressed on the baso-lateral surfaces of intestinal epithelial cells, play an indirect role in glucose import from the intestinal lumen
c) the movement of sodium down its concentration gradient drives the import of glucose from the gut lumen across the apical membranes of intestinal epithelial cells
d) a and b
e) a, b and c

Answer 17

e)

Question 18

Proton pumps in plant cells are functionally similar to an animal cells

a) carrier proteins that mediate co-transport
b) Na+/K+ pumps
c) contractile vacuoles
d) aquajets
e) ligand-gated ion channels

Answer 18

b)

Question 19

Fluidity of membranes refers to

a) diffusion of lipids within each leaflet
b) diffusion of lipids between membrane leaflets
c) diffusion of proteins within each leaflet
d) a and c
e) a, b and c

Answer 19

d) diffusion of proteins and lipids within each leaflet

Question 20

Compared to the cytosolic leaflet, the extracellular leaflet of the plasma membrane of mammalian cells

a) consists of the same types of phospholipids
b) consists of different phospholipids, but has a similar cholesterol content
c) higher cholesterol content
d) higher carbohydrate content
e) both b and d

Answer 20

e)

Question 21

You have just discovered an aquatic plant that lives in extremely cold environments. Compared to related plants living in warmer regions, you would predict that the cold-adapted plants will have membranes with

a) longer fatty acid chains
b) higher proportion of unsaturated fatty acids
c) higher proportion of saturated fatty acids
d) modified cholesterol content
e) b and d

Answer 21

b) as plans don’t have cholesterol

Question 22

Integral membrane proteins stay embedded in membranes because of:

a) osmotic pressure from proteins outside the cell
b) diffusion of proteins from the cytoplasm to the membrane
c) the locations of their polar and nonpolar amino acids
d) their large size, which does not allow them to pass through the membrane

Answer 22

c)

Question 23

The solutions in the arms of the U-tube are separated by a semi-permeable membrane. The membrane is permeable to water but not sugar. What will happen? 1M of glucose in A side and 0.2 M fructose & 0.7 M sucrose in B side

a) the three sugars will cross the membrane until they are at equal concentrations on both sides
b) nothing, because sugars can’t cross the membrane
c) there will be a net movement of water from B to A
d) there will be a net movement of water from A to B
e) both a and c

Answer 23

c)

Question 24

The solutions in the arms of the U-tube are separated by a semi-permeable membrane contain 1 M glucose in side A and 0.2 M fructose & 0.7 M sucrose. The membrane is permeable to monosaccharides but not disaccharides

a) The three sugars will cross the membrane until they are at equal concentration
b) Glucose and fructose will cross the membrane until their concentrations are equal on both sides
c) There will be a net movement of water from B to A
d) There will be a net movement of water from A to B
e) both b and d

Answer 24

e)

Question 25

Rank the following according to their ability to diffusion directly through a lipid bilayer, beginning with the one that crosses most readily:

1) Ca2+ 2) CO2 3) ethanol 4) glucose 5) H2O
a) 5-2-3-4-1
b) 5-2-1-3-4
c) 2-5-4-3-1
d) 2-5-3-4-1
e) 1-5-2-3-4

Answer 25

d)

Question 26

Membrane carrier proteins are distinguished from ion channels by the following feature:

a) Carrier proteins move solutes down a gradient, whereas ion channels can move ions down or against a gradient
b) Membrane carriers are specific in what they carry, while channels will let anything through that has the correct charge
c) Membrane carrier proteins can become saturated if the concentration of their cargo molecule is high, whereas channels allow passage of ions at very high rates as long as there is a diffusion gardeint
d) Gene mutations can cause dysfunction of ion channels but not carriers
e) Carriers are integral membrane proteins whereas ion channels are merely holes in the lipid bilayer

Answer 26

c)

Question 27

Transport of glucose across the apical surface of intestinal epithelial cells can be referred to as secondary active transport because:

a) the glucose transporter that moves it uses small amounts of ATP
b) all transporter molecules depend on gradients set up by active transport
c) it is co-transported with Na+ via a symport, such that it indirectly depends on the Na+ gradient maintained by the Na+/K+ pump
d) glucose is transported via a Na+-glucose ATPase

Answer 27

c)

Question 28

Why don’t bacterial cells burst in hypotonic solution?

a) Bacteria that survive in hypotonic environments have very low internal solute concentrations
b) The bacteria will gain some water from their surroundings, but expel the additional water through specialized outlets called aquajets
c) Bacteria have an intracellular organelle that enables them to expel excess water
d) Bacteria have a cell wall that prevents lysis

Answer 28

d)