how transport across the membrane is regulated

Question 1

The cell membrane is selectively permeable. what molecules is it permeable to?

Answer 1

The lipid bilayer is permeable to non-polar molecules such as O2, CO2 and hormones

Question 2

what is the cell membrane impermeable to?

Answer 2

It is impermeable to ions and large molecules such as Na+ and glucose. They need trans-membrane channel and carrier proteins

Question 3

is it permeable to water?

Answer 3

It is slightly permeable to small uncharged polar molecules such as water

Question 4

Membrane permeability: Gradients

why is selective permeability important in terms of gradient

Answer 4

Selective permeability allows cells to build concentration gradients

pH can be regulated

Electrical gradients are built (the inside of a cell is more –ve) creating membrane potentials

Question 5

give an example of concentration gradient.

Answer 5

E.g. O2and Na+ are more concentrated in the extracellular fluid: the opposite is true for K+ & CO2

Question 6

transport can occur in 3 different ways . what are they ?

Answer 6

passive
active
vesicular

Question 7

what processes does passive transport carry out?

Answer 7

diffusion,
osmosis
facilitated diffusion

Question 8

what processes does active transport carry out?

Answer 8

primary active transport

secondary active transport

Question 9

what processes does vesicular transport carry out?

Answer 9

endocytosis
phagocytosis
pinocytosis
trancytosis

Question 10

what is passive transport

Answer 10

No cellular energy is used as substances move down their own concentration gradient.
• It is of the following types
– 1. Diffusion through lipid bilayer
– 2. Channel mediated facilitated diffusion
– 3. Carrier mediated facilitated diffusion

Question 11

How Is diffusion affected by:
Temperature
Concentration gradient
Mass
Surface area
Diffusion distance

Answer 11

temp: increase will increase rate of diffusion
increase in conc will increase diffusion
mass increase will decrease rate of diffusion
surfave area depends
diffusion distance will decrease diffusion rate

Question 12

what are the two types of facilitated diffusion?

Answer 12

Channel mediated

• Can be gated
• Can be timed or signal regulated

Carrier mediated
Subject to transport maximum and saturation

Question 13

how is faciltated diffusion regulated? give an example

Answer 13

The selective permeability can be regulated to maintain homeostasis
E.g. the hormone insulin, via its receptor, up-regulates

Question 14

give an example of a disease which is due to malfunction in facilitated diffusion .

Answer 14

Diabetic patients can lack the ability to up regulate GluT

Question 15

what is osmosis?

what transmembrane protein is used to transport water?

Answer 15

• It is the diffusion of water through a semi-permeable membrane.
– diffusion through the lipid bilayer occurs through specific transmembrane protein channels called aquaporins

Question 16

what does the following words mean?
Hypertonic
Isotonic
Hypotonic

Answer 16

hypertonic causes water to move out of a cell causing cell to shrivel up.
isotonic is when there is a balance in water potential inside and outside the cell causing the cell not to be affected by osmosis.
hypotonic causes water to move into the cell due to unbalanced water potential.

Question 17

give an example of Osmosis & tonicty

Answer 17

RBC’s for transfusion are destroyed by hypertonic and hypotonic solutions
Most intravenous solutions are isotonic (0.9% saline or 5% dextrose)

Question 18

give a medical use for hypertonic solutions

Answer 18

Infusion of hypertonic solution to relieve cerebral edema

Question 19

what is active transport ?

Answer 19

• It involves expenditure of energy from hydrolysis of ATP.
• It is used to transport essential ions against their concentration gradient. (Helps maintain tonicity, volume and charge)

Question 20

what are the two types of active transport?

Answer 20

Primary active transport (uses energy from the hydrolysis of ATP)

– Secondary active transport (uses energy stored by an ionic concentration gradient)

Question 21

what is primary active transport?

Answer 21

Movement against a concentration gradient (mainly ions)

ATP changes the shape of the carrier protein, pumping the substance across

Cells typically use 40% of their generated ATP this way

Must work non-stop due to passive leaking

Question 22

give an example of primary active transport.

Answer 22

sodium-potassium pump
removes 3 Na+ by binding from cytosol. ATP is hydrolysed by ATPase.
2K+ is gained via carrier protein.

Question 23

what is secondary active transport (co-transport )

Answer 23

Secondary active transportis a form ofactive transportacross a biological membrane in which a transporter protein couples the movement of an ion (typically Na+or H+) down its electrochemical gradient (this gradient has been made by primary active transport) to the uphill movement of another molecule or ion against a concentration/electrochemical gradient.

Question 24

what is symport and antiport ?

Answer 24

Symport is where the molecules travel in the same direction (used for Ca2+ regulation and H+ regulation)

Antiport is where they go in opposite directions

Question 25

explain how glucose is transported into a kidney or small intestine cell.

Answer 25

• low conc of glucose in the lumen compared to the epithelial cell.
• high conc of Na+ in the lumen
• Na+ and glucose go together due to diffusion gradient and are co-transported into epithelial
• this occurs as Na+ is at low conc in epithelial due to the primary active transport of Na+ by a sodium-potassium pump into the blood stream.
• glucose travels into the blood stream as there is a lower concentration of glucose in the blood stream compared to the epithelial.

Question 26

what is endocytosis and exocytosis?

Answer 26

Used for endocytosis (bringing substances into the cell) and exocytosis (expelling from the cell)
Used for inter-organelle transport
Both use ATP

Question 27

Endocytosis is further classified into:

Answer 27

Receptor mediated endocytosis
Phagocytosis and
Pinocytosis

Question 28

what is the use of Receptor mediated endocytosis?

Answer 28

Typically used for transporting LDL or some vitamins and hormones

Question 29

what is clathrin?

Answer 29

Clathrin is a protein for enriching membrane domains

Question 30

describe the steps that occur in Receptor mediated endocytosis

Answer 30

Binding
lateral diffusion
invagination
Vesicle formation
Unseating(uncoating)
Fusion with endosome
either 
transcytosis
Recycling of receptor
Degradadtion in lysosomes

Question 31

example of Receptor mediated endocytosis

Answer 31

CD4 Receptor mediated endocytosis in a T helper cell

Question 32

what is pahgocytosis

Answer 32

Engulf large particles such as worn out cells and bacteria

Is carried out by macrophages and neutrophils

Question 33

describe the process of phagocytes

Answer 33

1. Chemotaxis and adherence of microbe to phagocyte
2. Ingestion of microbe to phagocyte
3. Formation of phagosome
4. Fusion of the phagosome with a lysosome to form a phagolysosome
5. Digestion of ingested microbe by enzymes
6. Formation of residual body containing indigestible materials
7. Discharge of waste materials

Question 34

what is Bulk phase endocytosis (pinocytosis = to drink)

Answer 34

Small droplets of extracellular fluid are taken in
No receptors are needed
All solutes in the extracellular fluid are brought in (non-selective)

Question 35

where does pinocytosis occur the most?

Answer 35

Occurs in most cells but especially absorptive cells in the intestines and kidney

Question 36

what is Exocytosis

Answer 36

It is used to transport material out of the Cell.

Question 37

which cells exhibit exocytosis?

Answer 37

It is exhibited by all cells but very important in
– Secretory cells (digestive enzymes and hormones)
– Nerve cells (neurotransmitters)

Question 38

what is trancytosis ?

Answer 38

Combination of endo and exocytosis

Substances are passed through a cell

Question 39

where is trancytosis expressed?

Answer 39

Is common in endothelial cells which line the blood vessels

Question 40

How are gap junctions formed?
where are they found? give two examples.
how do they work? i.e: talk about the type of molecules they allow to pass through. and anything else you know about how they function.

Answer 40

Gap junctions are formed between adjacent cells which are connected by hollow cylinders known as connexons. They are found in electrically excitable tissues such as heart and smooth muscles.
They directly connect the cytoplasm of two cells together enabling small molecules/ ions and electrical impulses to pass through. These channels act like tunnels although not with a big opening but large enough for movement of molecules from cytoplasm of one cell to the next.

Question 41

What is the role of tight junctions?
How are they formed?
Where can they be found?

Answer 41

Tight junctions prevent movement of substances.They prevent anything passing through extracellular space between them
Tight junctions are formed by the fusion of integral proteins of adjacent cells.
They can be found in cells lining the digestive tract.

Question 42

How are tight junctions formed?

Where is it common?

Answer 42

Tight junctions are formed when two membrane bond into one, making a strong barrier between two cells. they form solid walls.
It is common where one area needs to protected from the contents of other areas, sealing epithelial cells together.

Question 43

Is there any intra-cellular space where tight junctions are found and explain your answer?

Answer 43

There is no intra-cellular space found where there is a tight junction, because there re long rows of tight junction proteins that form a complex mesh-work.

Question 44

where are adherens junctions found?

Answer 44

Found at sites where cell-to-cell interactions occur of epithelial cells, which are subject to stretching and pulling, yet require tight contact between them so they can function as one unit.

Question 45

what is the function of adherens junction?

Give an example.

Answer 45

To maintain cellular position. For example they resist separation in contractile movements such as peristalsis.

Question 46

Describe the structure of adherens junction.

Answer 46

PLAQUE which attaches to membrane proteins and the microfilaments of the cytoskeleton.
Often form adhesion belts
They connect actin filaments in neighbouring cells.

Question 47

how does a hemidesmosome differ from a desmosome?

Answer 47

hemisdesmosome athough has a similar structure to desmosome yet it JOINS a cell to its BASILAR membrane (basement membrane) rather than to another cell.

Question 48

describe the structure of desmosome/ hemisdesmosome.

Answer 48

they are anchoring junctions held together by linker protein filaments called cadherins or integrins extending from button like thickenings called plaques, this distributes tension and prevents tearing e.g: skin and heat muscle.

Question 49

what is the role of desmosomes?

Answer 49

they physically connect cells like the gap junction but no opening is created. proteins that bond the membrane of one cell to its neighbour creates desmosomes: cell-to-cell adhesion.