transport across the membrane

Question 1

the plasma membrane contains what kinds of proteins?

Answer 1

• they include enzymes, receptors, binding sites for anchoring cell, transport proteins
• most are involved in transport functions, protein channels and carrier proteins
• some are glycoproteins, proteins which bind with one or more sugar groups.

Question 2

what is passive transport?

Answer 2

• w/o any energy (ATP) input from the cell
• solutes move down a conc gradient from area of high to low solute conc
• occurs via membrane pores, protein channels or carrier proteins

Question 3

what is simple diffusion?

Answer 3

• some molecules are able to diffuse freely through the plasma membrane
• a molecule simple dissolves in the phospholipid bilayer and diffuses across it. no membrane proteins are involved and the direction of transport is determined simply by the relative concentrations of the molecule inside and outside of the cells.

Question 4

what is facilitated diffusion?

Answer 4

• large polar molecules such as glucose and amino acids cannot diffuse through the phospholipid bilayer, nor can ions like Na+
• these can only cross the membrane by passing through channels created by protein molecules and carrier proteins

Question 5

what are carrier and channel proteins?

Answer 5

carrier:
- serve as channels for water soluble substances such as glucose and electrolytes
- carrier proteins bind to the solute on one side of a membrane, undergo conformational changes, and release them on the other side of the membrane.
channel:
serve as channels through which ions can pass, only pass water soluble molecules
( transport by carriers can be either active or passive, transport through channel proteins is always passive )

Question 6

what is active transport?

Answer 6

• ATP produced within the cell drives the process
• this can move molecules against the concentration gradient from low to high areas of concentration
• involves carrier proteins specifically
• endocytosis, exocytosis

Question 7

what is osmosis?

Answer 7

• involves the movement of water
• water passes through special pores called aquaporins created by proteins in the membrane
• water moves down a concentration gradient

Question 8

what is exocytosis and endocytosis?

Answer 8

exocytosis
- secretion of hormones, mucus, eject certain wastes
- moves material out of the cell
endocytosis
- moves material into the cell

Question 9

what are the 3 types of endocytosis?

Answer 9

1. pinocytosis
   - fluid is taken up by the cell
2. phagocytosis
   - large particles such as bacteria or dead cells
3. receptor mediated endocytosis
   - involves membrane receptors
   - targets molecules attached to receptors
   - cell engulfs receptor-target molecule complex
   - e.g, enzymes, hormones, cholesterol and iron

Question 10

what are the similarities and differences between active transport and facilitated diffusion?

Answer 10

facilitated diffusion
1. needs a carrier protein and they are named as channels
2. highly specific in nature
3. inhibited by competitive inhibitors
4. solutes are transported from high conc to low conc
5. no energy is needed
active transport
1. needs a carrier protein and they are named as pumps
2. highly specific in nature
3. inhibited by competitive inhibitors
4. solutes are transported from low conc, to high conc
5. energy is needed

Question 11

what is tonicity?

Answer 11

• ability of an extracellular solution to influence osmosis in a cell
  1. hypertonic solutions
• higher conc of dissolved solute than inside the cell
• lower water conc than inside the cell
• net osmosis out of the cell
  2. hypotonic solutions
• lower conc of dissolved solute than inside the cell
• higher water conc than inside the cell
• net osmosis into the cell
  3. isotonic solutions
• same solute conc inside than outside of the cell
• same water conc inside than outside the cell
• no net movement of water

Question 12

what is the sodium-potassium pump?

Answer 12

in animal cells, high conc of Na ions outside the cell and high conc of K ions inside the cell. uses energy in the form of ATP, to move Na+ out of the cell and K+ into the cell
after ions have been used, they return to their original side of the membrane via a channel protein, the return movement is by facilitated diffusion because the ions are moving back down their concentration gradients.

Question 13

what is bulk transport?

Answer 13

proteins and polysaccharides are too large to pass through the cell membrane or to move through transport proteins, instead, the cell uses energy to form new vesicles to package the substance