Exam I | Membrane Transport

Question 1

State (in one sentence) what the sodium-potassium pump does.

Answer 1

moves 2 K+ ions into cell and 3 Na+ ions out of cell

Question 2

List the 5 steps of how the sodium-potassium pump works.

Answer 2

1) ATP positions itself into ATPase
2) hydrolysis releases PO4-, which binds to exterior, causing conformational change
3) 3 Na+ ions are released
4) 2 K+ position themselves into ATPase, causing conformational change while PO4- gets released
5) K+ ions are expelled into interior and protein resumes original shape

Question 3

What are the consequences of sodium-potassium pump activity?

Answer 3

• alters cell membrane osmotic balance

- alters membrane charge gradient

Question 4

The sodium-potassium pump is essential to what 2 processes?

Answer 4

• generation of nerve impulses (use electrochemical gradient)
• metabolism

Question 5

Will sodium-potassium pump activity cause water to move into or out of the cell?

Answer 5

out of the cell

Question 6

What is another name for secondary active transport?

Answer 6

Sodium-dependent transport

Question 7

What is secondary active transport?

Answer 7

the process of molecules moving into the cell against their concentration gradient using the electrochemical gradient caused by primary active transporters (usually sodium-potassium pump)

Question 8

What is an antiporter?

Answer 8

• active transport protein that transports two molecules in OPPOSITE directions against their concentration gradient
• are also ATPases, using ATP to drive the transport

Question 9

Where does sodium move in secondary active transport?

Answer 9

into the cell

Question 10

What is a uniporter?

Answer 10

• active transport protein that moves molecule or a group of molecules in the same direction against concentration gradient
• are also ATPases, using ATP to drive transport

Question 11

What is a symporter?

Answer 11

active transport protein that transports TWO DIFFERENT molecules across the cell membrane at the SAME time

Question 12

What is SGLUT?

Answer 12

a transporter that moves glucose into the cell by secondary active transport (activity of sodium-potassium pump)

Question 13

In what two ways can glucose move into the cell?

Answer 13

• secondary active transport

- passive transport

Question 14

How many passive glucose transporters exist?

Answer 14

at least 4

Question 15

Where is the GLUT2 protein found?

Answer 15

• liver
• pancreas
• small intestine

Question 16

Where is GLUT4 protein found?

Answer 16

• skeletal (striated) muscle
• adipose tissue
• heart

Question 17

what is the difference between GLUT 2 and GLUT 4 protein?

Answer 17

• GLUT2 is insulin-independent, GLUT4 is not

- GLUT4 requires binding of ligand

Question 18

What is the charge inside the cell after Na-K pump activity?

Answer 18

negative

Question 19

To what 2 processes is the calcium pump essential?

Answer 19

• neurotransmission

- contractile cells of the skeletal muscle, smooth muscle, and of the heart

Question 20

is SGLUT a symporter or antiporter?

Answer 20

symporter

Question 21

How do transport vesicles travel in the cell?

Answer 21

along microtubules by motor proteins( such as dyneins or kinesins)

Question 22

Why might vesicular packaging be necessary?

Answer 22

• to maintain osmotic gradients
• to regulate intracellular concentrations
• to make sure contents are secreted and do not diffuse around the inside of the cell

Question 23

How are vesicles generally formed?

Answer 23

through interactions with the ER, Golgi, and perhaps lysosomes

Question 24

What are the 3 forms of endocytosis?

Answer 24

1) phagocytosis
2) pinocytosis
3) receptor-mediated endocytosis

Question 25

What happens in phagocytosis?

Answer 25

cells use plasma membrane to engulf relatively large portions of material in ECF (such as bacterial cells) and takes them into the cell

Question 26

What happens in pinocytosis?

Answer 26

the cell takes in fluid containing small particles

Question 27

What happens in receptor-mediated endocytosis?

Answer 27

ligand-dependent incorporation of ECF (along with ligand)

Question 28

What is the difference between basic endocytosis and phagocytosis?

Answer 28

• in basic endocytosis, the cell membrane INVAGINATES (incorporates vesicle into the membrane), rather than EXTRUDES (using the plasma membrane to package material) as in phagocytosis
• volume of membrane is decreased in phagocytosis

Question 29

What is basic endocytosis?

Answer 29

a constitutive process in which plasma membrane surrounds macromolecules or fluid and then buds off inside the cells to form a vesicle with the ingested material inside

Question 30

What is an example of receptor-mediated endocytosis?

Answer 30

cholesterol entering cells through LDL receptors

Question 31

What are clathrins? What do they do?

Answer 31

• in receptor-mediated endocytosis, binds to inner cell membrane receptors following binding of the substrate to the membrane receptors, causing membrane to invaginate substrate
• coats intracellular vesicle which may be subsequently digested by lysosomes

Question 32

Give 2 examples of cells that perform phagocytosis.

Answer 32

• paramecium

- white blood cells

Question 33

What is the difference between constitutive and regulated secretion (exocytosis)?

Answer 33

• Constitutive secretion is ongoing. It does not stop. Substances are not stored after synthesis
• Regulated secretion requires binding of a ligand for it to happen. Substances are stored prior to release.

Question 34

Give 3 examples of regulated secretion (exocytosis)

Answer 34

• release of insulin by beta cells
• release of neurotransmitters by neurons
• release of hormones by pituitary gland

Question 35

Describe characteristics of transcytosis.

Answer 35

• transepithelial transport
• requires DIFFERENT types of transporter on the apical and basal surfaces
• important for virtually all tissues

Question 36

What does it mean if a substance has a high partition coefficient?

Answer 36

can passively diffuse through plasma membrane