cell membranes and transport

Question 1

what does fluid mosaic model explain

Answer 1

explains how biological molecules are arranged to form cell membranes

Passive and active movement between cells and their surroundings
Cell-to-cell interactions
Cell signalling

Question 2

phospholipid regions

Answer 2

phosphate head
lipid tail

Question 3

phosphate head

Answer 3

phospholipid is polar (hydrophilic) and therefore soluble in water

Question 4

lipid tail

Answer 4

non-polar (hydrophobic) and insoluble in water

Question 5

phospholipid monolayer

Answer 5

phospholipids are spread over the surface of water they form a single layer with the hydrophilic phosphate heads in the water and the hydrophobic fatty acid tails sticking up away from the water

Question 6

micelle

Answer 6

phospholipids are mixed/shaken with water they form spheres with the hydrophilic phosphate heads facing out towards the water and the hydrophobic fatty acid tails facing in towards each other

Question 7

phospholipid bilayers

Answer 7

two-layered structures may form in sheets
These are called phospholipid bilayers – this is the basic structure of the cell membrane

Question 8

An example of a membrane-bound organelle

Answer 8

each containing many hydrolytic enzymes that can break down many different kinds of biomolecule

Question 9

two protein types

Answer 9

intrinsic
extrinsic

Question 10

intrinsic

Answer 10

embedded in the membrane with their arrangement determined by their hydrophilic and hydrophobic regions

Question 11

extrinsic

Answer 11

found on the outer or inner surface of the membrane

Question 12

why fluid mosaci is described as fluid

Answer 12

phospholipids and proteins can move around via diffusion
move sideways, within their own layers
proteins interspersed throughout the bilayer move about within it

Question 13

The fluid mosaic model describes cell membranes as ‘mosaics’ because:

Answer 13

The scattered pattern produced by the proteins within the phospholipid bilayer looks somewhat like a mosaic when viewed from above

Question 14

three types of lipid

Answer 14

Phospholipids
Cholesterol
Glycolipids

Question 15

two types of proteins

Answer 15

Glycoproteins (also containing carbohydrates)
Other proteins
eg. transport proteins)

Question 16

Phospholipids:

Answer 16

Form a bilayer
Hydrophobic tails
Hydrophilic heads
Individual phospholipid molecules can move around within their own monolayers by diffusion

Question 17

Cholesterol:

Answer 17

Cholesterol molecules also have hydrophobic tails and hydrophilic heads

Fit between phospholipid molecules and orientated the same way (head out, tail in)

Are absent in prokaryotes membranes

Question 18

Glycolipids

Answer 18

These are lipids with carbohydrate chains attached
These carbohydrate chains project out into whatever fluid is surrounding the cell

Question 19

Glycoproteins

Answer 19

These are proteins with carbohydrate chains attached
These carbohydrate chains also project out into whatever fluid is surrounding the cell

Question 20

Proteins:

Answer 20

embedded within the membrane are known as intrinsic proteins
inner or outer phospholipid monolayer

Question 21

Transport proteins

Answer 21

transmembrane proteins as they cross the whole membrane

Question 22

Phospholipids

Answer 22

Act as a barrier to most water-soluble substances (the non-polar fatty acid tails prevent polar molecules or ions from passing across the membrane)

ensures water-soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell

Question 23

Cholesterol function

Answer 23

regulates the fluidity of the membrane
Cholesterol molecules sit in between the phospholipids, preventing them from packing too closely together
prevents membranes from freezing and fracturing.

Question 24

Interaction between cholesterol and phospholipid tail

Answer 24

stabilises the cell membrane at higher temperatures by stopping the membrane from becoming too fluid
Cholesterol molecules bind to the hydrophobic tails of phospholipids, stabilising them and causing phospholipids to pack more closely together

Question 25

Glycolipids & glycoproteins function

Answer 25

carbohydrate chains that exist on the surface
enables them to act as receptor molecules
allows glycolipids and glycoproteins to bind with certain substances at the cell’s surface

Question 26

three main receptor types:

Answer 26

signalling receptors for hormones and neurotransmitters
receptors involved in endocytosis
receptors involved in cell adhesion and stabilisation (as the carbohydrate part can form hydrogen bonds with water molecules surrounding the cell

Question 27

Proteins functions

Answer 27

channel (pore) proteins
carrier proteins
Each transport protein is specific to a particular ion or molecule
Transport proteins allow the cell to control which substances enter or leave

Question 28

transport prtein functions

Answer 28

create hydrophilic channels to allow ions and polar molecules to travel through the membrane.

Question 29

Diffusion

Answer 29

The net movement, as a result of the random motion of its molecules or ions, of a substance from a region of its higher concentration to a region of its lower concentration.down a concentration gradient

Question 30

result of diffusion

Answer 30

molecules or ions tend to reach an equilibrium situation (given sufficient time), where they are evenly spread within a given volume of space
The rate at which a substance diffuses across a membrane depends on several factors

Question 31

factors affecting diffusion

Answer 31

1)Steepness of conc gradient
2)temperature
3)sa
4)properties of molecules or ions

Question 32

steepness of conc gradient

Answer 32

greater difference in the conc means a greater difference in the number of molecules passisng in the 2 directions and therefore a faster rate of diffusion

Question 33

temperasture and diffusuin

Answer 33

-molecules more kinetic energy at higher temps
move faster greater rate of diffusion

Question 34

preoperties of molecules an ions affecting diffusuin

Answer 34

-large moleculews diffuse more slowly that smallee aa they require more energy
-non polar diffuse directly across bilayer
-soluble in the bialyer

Question 35

Facilitated diffusion

Answer 35

Large polar molecules such as glucose and amino acids
Ions such as sodium ions (Na+) and chloride ions (Cl-)
only cross the phospholipid bilayer with the help of certain proteins
highly specific

Question 36

Channel proteins

Answer 36

highly specific
water-filled pores
allow charged substances to diffuse through the cell membrane
part of the channel protein on the inside surface of the membrane can move in order to close or open the pore
This allows the channel protein to control the exchange of ions

Question 37

Carrier proteins

Answer 37

can switch between two shapes
binding site of the carrier protein to be open to one side of the membrane first, and then open to the other side of the membrane when the carrier protein switches shape
The direction of movement of molecules diffusing across the membrane depends on their relative concentration on each side of the membrane
Net diffusion of molecules or ions into or out of a cell will occur down a concentration gradient (from an area containing many of that specific molecule to an area containing less of that molecule)

Question 38

Osmosis

Answer 38

net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane

Question 39

Water potential

Answer 39

tendency of water to move out of a solution.

Question 40

dilute solution

Answer 40

high water potential (the right-hand side of the diagram below) and a concentrated solution has a low water potential

Question 41

plant cell is placed in pure water or a dilute solution,

Answer 41

water will enter the plant cell through its partially permeable cell surface membrane by osmosis, as the pure water or dilute solution has a higher water potential than the plant cell
volume of the plant cell increases
pressure builds up inside the cell – the inelastic cell wall prevents the cell from bursting
turgid

Question 42

animal cell is placed in a concentrated sucrose solution

Answer 42

water will leave the cell through its partially permeable cell surface membrane by osmosis and the cell will shrink and shrivel up
hypertonic environment

Question 43

hypertonic environment

Answer 43

the solution outside of the cell has a higher solute concentration than the inside of the cell)

Question 44

animal cell is placed in pure water or a dilute solution,

Answer 44

water will enter the cell through its partially permeable cell surface membrane by osmosis, as the pure water or dilute solution has a higher water potential. The cell will continue to gain water by osmosis until the cell membrane is stretched too far and the cell bursts (cytolysis), as it has no cell wall to withstand the increased pressure created
hypotonic environment

Question 45

hypotonic environment

Answer 45

(the solution outside of the cell has a lower solute concentration than the inside of the cell)

Question 46

isotonic environment

Answer 46

(the solution outside of the cell has the same solute concentration as the inside of the cel

Question 47

active transport

Answer 47

is the movement of a substance against the concentration gradient across a membrane by a protein carrier using energy
energy supplied by atp
proteins highly specific

Question 48

co transport

Answer 48

-carrier proteins can sometimes transport two particles at once
-both must be present for transport to take place
-often with an active and passive process as one particle is moved with the concentration gradient and the other is moved against it
-subsrances can be moved in the same (symport)or opposite (anti port)direction o ;:::