1.4 membrane transport

Question 1

phospholipid bilayer is

Answer 1

a selectively permeable membrane

Question 2

what can pass through the phospholipid bilayer

Answer 2

some molecule can pass through the bilayer easily (diffusion), some molecules pass through a tunnel (facilitated diffusion), and some require energy/atp (active transport

Some large molecules can use their own membrane for endocytosis and exocytosis

Question 3

why cant all molecules just pass through the membrane

Answer 3

• phosphate head attracts polar molecules, but lipid tails repel positively charged ions and therefore most molecules can not just pass through the membrane.

Question 4

How to maximize rate of diffusion

Answer 4

• larger concentration gradient
• shorter path of diffusion
• higher surface area to volume ratio

Question 5

Examples of high surface area to volume ratios

Answer 5

• root hairs to absorb mineral ions
• Alveioli a thin membrane in lungs increases surface area for gas exchange
• micro villi in small intestines helps with the absorption of ingested food particles
• intestines folded over to maximize surface area
• membrane of mitochondria is folded, cristae

Question 6

shorter path of diffusion does what

Answer 6

• When membranes fold over they have a higher surface area/volume ratio and are able to absorb things better
• smaller distance for molecules to diffuse
• membrane is incredibly thin 7-10nm

Question 7

Diffusion

Answer 7

Diffusion is the passive net movement of molecules from an area of high concentration to low concentration. this is through a partially permeable membrane.
-passive: doesn’t require energy

Question 8

Osmosis

Answer 8

Osmosis is the movement of water across selectively permeable membranes

• water moves from an area with low solute concentration to an area of high solute concentration
• aquaporin - integral proteins in the membrane that act as pores and help water move faster

Question 9

Facilitated diffusion - what it is and why its neccesary

Answer 9

Facilitated diffusion is necessary because ions and large molecules can not travel across membranes through simple diffusion

• transmembrane polytopic proteins help molecules travel across the membrane
• does not require energy/atp
• the direction of movement depends on the concentration gradient

Question 10

active transport

Answer 10

• requires the use of energy/atp
• integral proteins pumps use the energy from the hydrolisis of atp to move large molecules across the membrane
• molecules move against their concentration gradient

Question 11

Sodium potassium pump

Answer 11

• an example of sodium potassium pumps is seen in nuerons (nerve cells) on the membrane of the axon
• sodium potassium pump in the axon are voltage gated
• potassium pump allows potassium to have facilitated diffusion out of the axon
• the sodium potassium pump works in a cycle, in which 3 sodiums exit the axon and 2 potassiums enter. The entire cycle takes one ATP

Question 12

3 types of possible transport

Answer 12

uniport - one molecule is moved
symport- two molecules are moved in the same direction
antiport - two molecules are moved in opposite directions

Question 13

All the steps of a sodium potassium pump

Answer 13

1) The pump is open to the interior of the axon, and 3 sodiums enter the pump and attach to their binding sites
2) An atp releases a phosphate group attached to the pump, which induces a conformational change closing the pump
3) the pump then opens to the exterior of the cell and the 3 sodium ions are released
4) 2 potasium ions enter the pump and bind to their binding site
5) this binding causes the phosphate group to be released from pump
6) the pump changes shape and opens up to the inside of the axon again, and the 2 potassiums are released, and the cycle starts again

Question 14

Exocytosis

Answer 14

the release of substances from a cell (secretion) through the binding of a vesicle to the plasma membrane

Question 15

constituitive secretion

Answer 15

happen continuously in a cell (depending on its function)

Question 16

regulated secretion -exocytosis

Answer 16

happens in response to a trigger (like the release of a neurotransmitter)

Question 17

endocystosis

Answer 17

external substances getting taken in by a pinched off layer of the plasma membrane, which then becomes a vesicle

Question 18

3 times of endocytosis

Answer 18

phagocytosis, penocytosis, receptor mediated endocytosis.

cell eating, cell drinking

Question 19

what is a vesicle and how does it work with other organelles

Answer 19

a vesicle is a small sphericle package that buds of the rer and golgi apparatus
it recieves proteins from the ribosomes on the rer and carries them to the golgi apparatus, which then repackages them in a new vesicle to be transported outside the cell.

Question 20

3 implications of osmodic balance

Answer 20

hypertonic: to little water (plasmolyzed)
isotonic: osmodic balance (flaccid)
hypotonic: too much water (turgid)

Question 21

functions of osmodic balance in the medical field

Answer 21

• used in iv saline drips (to restore cell hydration)
• eye drops/wash
• cleaning wounds or open scrapes

Question 22

happens in a cell constantly (depending on its function)

Answer 22

constitutive secretion

Question 23

Describe with examples the proccess of exocytosis

Answer 23

• transport of large or bulk or material out of a cell
• is enabled by membrane fluidity
• example: digestive enzymes
• protiens made by ribosomes on rer are carried by vesicle to the golgi where they are repacked into a new vacoule
• the new vacoule travels across the cytoplasm to membrane
• fuses with plasma membrane and materials are released outside the cell

Question 24

By using the terms hypertonic, isotonic, and hypotonic, outline the medical application of osmosis with reference to a red blood cell.

Answer 24

Hypertonic - a solution with higher osmolarity than the other
Hypotonic - a solution with lower osmolarity than the other.
Isotonic - a solution with the same osmolarity as the other
- red blood cells have no cell wall
- Red blood cells explode in hyotopinc situation, and shrivel in hypertonic situations
- organs have to be kept in isotonic solutions before transplants.