Unit 3: Membrane Structures and Transport

Question 1

Generally speaking, what is a membrane structure composed of?

Answer 1

a. Lipids (usually phospholipids)
b. sterol lipids
c. proteins

Question 2

Describe phospholipids.

Answer 2

Phospholipids form a bilayer due to their construction. They have a hydrophilic head and a hydrophobic tail (composed of fatty acids).

Question 3

True or False: Lipid membranes are stationary.

Answer 3

False. They move constantly in the same plane.

Question 4

What is cholesterol?

Answer 4

A sterol lipid found between fatty acid chains. They keep membranes fluid and stabilize them.

Question 5

What is cholesterol’s equivalent in plants?

Answer 5

Phytosterols.

Question 6

What is the approximate ratio of proteins in the cell? Why?

Answer 6

Approximately 50 lipid molecules to 1 protein. This is due to the larger size of a protein.

Question 7

What are two main points about proteins with regards to the cell membrane?

Answer 7

a. There are many different types.

b. They are specific to each cell type.

Question 8

What are the 7 membrane functions?

Answer 8

1. Define the cell–contains and separates.
2. Selective transport.
3. Enzyme activity.
4. Signal transduction–protein receptors
5. Cell adhesion– cell-to-cell link
6. Cell recognition
7. Attachment to cytoskeleton

Question 9

What do protein receptors do?

Answer 9

They transfer messages from the outside of the cell to the inside of the cell. The reverse is also possible.

Question 10

What allows cell membranes to have their 7 functions?

Answer 10

Membrane Proteins.

Question 11

Where is most of our cholesterol used?

Answer 11

To make bile.

Question 12

What re the 3 types of membrane proteins?

Answer 12

Peripheral membrane proteins, integral membrane proteins, trans-membrane proteins.

Question 13

What is diffusion?

Answer 13

The movement of particles down concentration gradient examples of molecules that can diffuse thru membrane.

Question 14

What can diffuse thru a membrane?

Answer 14

Water, EtOH, oxygen, carbon dioxide, nitrogen gas, hydrophobic molecules and lipid-soluble molecules.

Question 15

What is osmosis?

Answer 15

The passive transport of water through aquaporin channels ad through membranes.

Question 16

What are the three “main types” of solutions?

Answer 16

Hypotonic, isotonic and hypertonic.

Question 17

What are some examples of osmosis?

Answer 17

Turgor pressure (plants), using salt or sugar as preservatives, water moving into the stomach after the addition of H and Cl ions, and contractile vacuoles (some protists).

Question 18

What is facilitated diffusion?

Answer 18

The transport of solutes across membrane down concentration gradient via specific transport proteins (channel proteins).

Question 19

What does down concentration gradient mean?

Answer 19

To move from an area of high concentration to one of low concentration.

Question 20

What are two examples of facilitated diffusion?

Answer 20

Glucose transporter and gated ion channels in membranes of neurons.

Question 21

What is active transport?

Answer 21

It is transport against concentration gradient. It requires energy and transmembrane proteins.

Question 22

What are other terms for transmembrane proteins?

Answer 22

Pumps or exchangers.

Question 23

What are the 4 types of active transport?

Answer 23

a. Ion pumps
b. Co-transport
c. Exocytosis
d. Endocytosis

Question 24

What are ion pumps?

Answer 24

They move ions across the membrane against their concentration gradient.

Question 25

What are the two purposes of ion pumps?

Answer 25

a. maintain membrane pressure

b. help maintain osmotic pressure

Question 26

What are 4 examples of ion pumps?

Answer 26

a. Na+/K+ ion pump
b. Ca++ pump in sarcoplasmic reticulum
c. proton pump (transports H+)
d. H+/K+ ATPase (H+/K+ exchanger)

Question 27

In what eukaryotes are proton pumps common?

Answer 27

Fungi, plants and some protists.

Question 28

Where are Ca++ pumps found?

Answer 28

In the muscles.

Question 29

What is co-transport?

Answer 29

The movement of an ion down its concentration gradient. This is coupled with the movement of “transported” molecule against its gradient. Both molecules move through the same transport protein.

Question 30

What are 2 examples of co-transport?

Answer 30

Symport and antiport.

Question 31

What is symport?

Answer 31

coupled molecules move in the same direction. Ex. plant cell uptake of sucrose coupled with H+ diffusion.

Question 32

What is antiport?

Answer 32

Coupled molecules move in opposite directions. E. In cardiac muscle cells, Na+ diffusion into cell, coupled to Ca++ export out of cell.

Question 33

What is exocytosis?

Answer 33

The secretion of macromolecules by fusion of vesicles with plasma membrane.

Question 34

How does exocytosis work?

Answer 34

A vesicle is a ball of membrane. The vesicle fuses with the membrane and its inside contents are released. ATP is used to move the vesicles.

Question 35

What are 6 examples of exocytosis?

Answer 35

a. neuron secretion of neurotransmitters
b. secretion of hormones and enzymes by glandular cells
c. insertion of plasma membranes
d. insertion of transmembrane proteins and external surface proteins
e. antigen presentation–immune response
f. make more cell membrane