membrane transport

Question 1

key qualities of cellular membranes

Answer 1

1) semi-permeable (only certain materials can freely cross)
2) selective (membrane proteins regulate the passage)

Question 2

passive transport

Answer 2

Passive transport involves the movement of material along a concentration gradient (high to low)
does not require energy (ATP) since it moves down a concentration gradient

Question 3

3 main types of passive transport

Answer 3

1) Simple diffusion (movement of small or lipophilic molecules)
2) Osmosis (movement of water molecules)
3) Facilitated diffusion (movement of large or charged molecules via membrane proteins)

Question 4

active transpot

Answer 4

active transport involves the movement of materials against a concentration gradient (low to high)
requires energy (ATP) since it moves up the concentration gradient

Question 5

2 main types of active transport

Answer 5

1) Primary (direct) - involves the direct use of ATP to mediate transport
2) secondary (indirect) - involves coupling the molecule with another moving along an electrochemical gradient

Question 6

Diffusion

Answer 6

Diffusion is the net movement of molecules from a region of high conentration to a hregion of low concentration. This is passive movement and continued till a balanced equilibrium is achieved. Small and non polar molecules diffuse across membrane easily.

Question 7

factors influencing rate of diffusion

Answer 7

1) temperature (affects kinetic energy of particles in solution)
2) Molecular size (larger particles create larger resistance)
3) Steepness of gradient (rate of diffisuin increases with higher concentration gradient)

Question 8

Osmosis

Answer 8

Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration.

Question 9

what role does water play?

Answer 9

Water is considered the universal solvent (associate or dissolve; polar or charged molecules)
Water will move to equalise two solutions aiding them crossing the membrane
Osmosis is essentially the diffusion of free water molecules and occurs from low solute regions concentration

Question 10

Osmolarity

Answer 10

Osmolarity is a measure of solute concentration as defined by the number of osmoses of a solute per litre of solution

Question 11

Hypertonic

Answer 11

Solutions with a relatively higher osmolarity are categorised as hypertonic (high solutes = gains water)

Question 12

Hypotonic

Answer 12

solutions with a relatively lower osmolarity are categorised as hypotonic (low solute = looses water)

Question 13

Isotonic

Answer 13

solutions that have the same osmolarity are categorised as isotonic (same solute = no net water)

Question 14

Osmolarity

Answer 14

the osmolarity of a tissue may be interpolated by bathing the sample in solutions with known osmolarities

Question 15

tissues reacting to osmolarity

Answer 15

The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions.
Water loss or gain can be determined with weighing before and after water gain when placed in solution.

Question 16

Negative effects of uncontrolled osmosis

Answer 16

1) Hypertonic: water will leave the cell causing it to shrivel
2) Hypotonic: water will enter the cell causing it to swell and burst

Question 17

How to control osmosis

Answer 17

1) Hypertonic: cytoplasm will shrink the the cell wall maintains structure
2) Hypotonic: cytoplasm will expand but be unable to rupture

Question 18

Facilitated diffusion

Answer 18

facilitated diffusion is the passive movement of molecules across the cell membrane via the aid of a membrane protein
- used by molecules that can’t cross the phospholipid bilayer freely
- aided by two transport proteins: Channel and carrier proteins

Question 19

Carrier Proteins

Answer 19

1) Integral glycoproteins which bind a solute and undergo a conformational change to translocate the solute across the membrane
2) Only bind a specific molecule via an attachement similar to an enzyme substrate interaction
3) Carrier proteins may move molecules against concentration gradients in the precedes of ATP
4) Carrier proteins have a much slower transportation rate then channel proteins

Question 20

Channel Proteins

Answer 20

1) Integral lipoproteins which contain a pore via which ions may cross from one side of the membrane to the other
2) Channel proteins are ion selective and may be gated to regulate the passage of ions in response to stimuli
3) Channel proteins only move molecules along a concentration gradient
4) Channel proteins have a much faster rate of transportation then carrier proteins

Question 21

Axons of nerve cells

Answer 21

The axons of nerve cells transmit electrical impulses by translocation ions to create a voltage difference between membranes

Question 22

Sodium potassium cell at rest

Answer 22

At rest the sodium potassium cell expels sodium ions from the nerve cell, while potassium ions are accumulated within

When the neutron fires these ions swap locations via facilitated diffusion through sodium and potassium channels

Question 23

Potassium Channels

Answer 23

1) integral proteins with a hydrophilic inner pore with which potassium ions may be transported
2) the channel is compromised of four trans membrane subunits, while the inner pore contains a selectivity filter at its narrowest region that restricts passage of alternative ions
3) Potassium channels are typically voltage gated and cycle between an open and closed conformation depending on the transmembrane voltage

Question 24

Active transport

Answer 24

Active transport uses energy to move molecules against a concentration gradient.
This can be generates by:
1) the direct hydrolysis of ATP (primary)
2) indirectly coupling transport with another molecule (secondary)

Question 25

Usage of carrier proteins for active transport:

Answer 25

1) a specific solute will bind to the protein pump on one side of the membrane
2) the hydrolysis of the ATP causes a conformational change in the protein pump
3) the solute molecule is consequently translocated across the membrane and released

Question 26

Sodium-potassium pump process

Answer 26

An integral protein that exchanges 3 sodium ions with 2 potassium ions. It is energy dependant
1) 3 sodium ions bind to intracellular sites on the pump
2) a phosphate group is transferred to the pump via the hydrolysis of ATP
3) the pump undergoes a conformational change translocating the sodium across the membrane
4) the conformational change exposes 2 potassium binding sites on the extracellular surface of the pump
5) the phosphate group is released, letting the pump return to its original conformation
6) potassium is translocated across the membrane, completing the ion exchange

Question 27

vesicles

Answer 27

Materials destined for secretion are carried around the cell in membranous containers called vesicles

Question 28

Endoplasmic Reticulum

Answer 28

the endoplasmic reticulum is a membraneous network in charge of synthesising secretory materials

Question 29

different ER types (rough and smooth)

Answer 29

1) rough ER is embedded with ribosomes and synthesises proteins destines for extracellular use
2) smooth ER is involved in lipid synthesis and also plays a role in carbohydrate metabolism

Question 30

Link of ER and vesicles

Answer 30

Materials are transported from the ER when the membrane bulges and then budges to create vesicles surrounding the material

Question 31

Golgi apparatus

Answer 31

The vesicle is then transported to the Golgi apparatus and fuses to the internal (cis) face of the complex
1) Materials move (via vesicles) from the internal face to the externally orientated trans face of the Golgi
2) While within the Golgi apparatus, materials may be structurally modified (ex. glycosylated)
Materials stored within the Golgi may either be secreted externally or transported to the lysosome

Question 32

Plasma membrane

Answer 32

vesicles containing materials destines for extracellular use will be transported to the plasma membrane.
the vesicle will fuse with the cell membrane and its materials will be expelled into the extracellular fluid

Question 33

after effect of materials sorted by Golgi apparatus:

Answer 33

1) released immediately into the extracellular fluid
2) stored within a intracellular vesicle for a delayed release in response to a cellular signal

Question 34

membrane fluidity

Answer 34

the membrane is held together due to the hydrophobic associations between the fatty acid tails of phospholipids. This weak association allows membrane fluidity as the phospholipids can move to some extend. This allows the bilayer to break and reform allowing larger and smaller materials to enter and leave.

Question 35

Endocytosis

Answer 35

the process in which large substances (in bulk smaller substances) enter the cell without crossing the membrane.
1) Invagination of membrane formes a depression enveloping the extracellular material
2) sealed of to form intracellular vesicle with material

Question 36

two types of endocytosis

Answer 36

1) Phagocytosis - solid substances ingested
2) Pinocytosis - liquids/dissolved substances ingested

Question 37

Exocytosis

Answer 37

the process by which bigger substances (bulk of smaller substances) leave or exit the cell without crossing the membrane
1) vesicle fuse with plasma membrane expelling their contents into extracellular environment
2) adds vesicular phospholipids to the cell membrane replacing the ones lost when vesicles were formed by endocytosis