topic 5 plasma membranes

Question 1

why was the fluid mosaic model proposed to describe the structure of cell membranes?

Answer 1

Fluid – phospholipids form a bilayer, which the phospholipid molecules are constantly moving ,its flexible and can change shape
mosaic – there are proteins of different sizes and shapes embedded in the phospholipid bilayer so it looks like a mosaic

Question 2

Phospholipid bilayer

Answer 2

-phosphophlip molecule has hydrophilic head and hydrophobic tail so they arrange themselves in a bilayer
- creates hydrophobic centre so water soluble substances cant pass thru but lipid soluble substances can dissolve in the bilayer and pass directly thru
- hydrophilic water soluble molecules are prevented from easily passing thru bcs they are polar
-water can pass bcs its small but takes place at slow rate

Question 3

cholesterol

Answer 3

-provide stability
-consist of hydrophilic polar group that attracts phophsolipid heads rest of cholesterol is hydrophobic and binds to phospholipids fatty acid tails causing them to pack more
- increases strength of cell surface membrane and reduces sideways movement (fluidity)
- helps reduce the movement of water soluble chemicals to cross
- prevents membrane becoming too fluid under warm conditions and too rigid under cool

Question 4

intrinsic proteins

Answer 4

-embedded through both sides of the phospholipid bilayer. have hydrophobic amino acids on outside, interact with hydrophobic fatty acid tail

Question 5

protein channels

Answer 5

-intrinsic
-contain channel running thru the centre
- channel is lines w hydrophilic amino acids filled w water molecules. allow water soluble molecules and ions to diffuse thru

Question 6

carrier proteins

Answer 6

intrinsic
can change their shape or position to transfer molecules or ions from one side of the membrane to the other

Question 7

extrinsic proteins

Answer 7

present only one side of the phospholipid bilayer. these provide support to the membrane or may be involved in cell signaling and might have structural roles or roles as enzymes and receptors

Question 8

glycoproteins

Answer 8

-consist of intrinsic proteins attached to carbohydrates
- allow cells to attch to eachother to form tissues
-play a role in the immune system by presenting antigens to T cells and act as receptors for hormones

Question 9

glycolipids

Answer 9

• consist of carbohydrates attached to phospholipids
• used to contact each other and act as antigens

Question 10

glycolipids and glycoproteins are involved in the following

Answer 10

-cell adhesion
-cell signalling
-cell recognition

Question 11

roles of cell membrane

Answer 11

• used as a location for chemical recation
• cell signaling
• barrier cytoplasm external envirnoment

Question 12

how temp affects cell membranes

Answer 12

• at low temp (below 0)- phospholipids don’t have much kinetic energy so packed closely and form rigid cell membrane and decrease permeability
• at medium temp (0-40)- as temp increases phospholipids have more kinetic energy so move faster and arnt packed as closly increasing the permeability
• at high temp ( above 40)- phospholipd bilayer breaks down.channel and carrier proteins denature meaning they cannot control what enter or leaves this increases the permeability

Question 13

what will happen if cells are placed in a solvent like ethanol

Answer 13

phospholipids dissolve causing membrane to become more fluid

Question 14

diffusion

Answer 14

net movement of particles from a region of higher concentration to a region of lower concentration down the concentration gradient

Question 15

is diffusion a passive or active process

Answer 15

passive

Question 16

two types of diffusion

Answer 16

simple diffusion
facilitated diffusion

Question 17

what two types of proteins are involved in facilitated diffusion

Answer 17

carrier proteins
channel proteins

Question 18

carrier proteins

Answer 18

have a binding site for specific molecules
when the molecule binds the tertiary structure of the protein changes and this changes brings the molecule across the membrane
they mainly transport large molecules

Question 19

channel proteins

Answer 19

proteins with a central pore lined w hydrophilic amino acids and contain water.
these proteins form pores in the cell membrane which ions can travel through
-they are selective for the chemical that can pass through
-some are always open, some only open in response to a triggerfa

Question 20

factors affecting the rate of diffusion

Answer 20

-tempreture
-concentration gradient
-distance (thickness of membrane)
-surface area
-number of carrier or channel proteins
-particle charge/size

Question 21

active transport

Answer 21

the movement of particles from an area of lower concentration to an area of higher concentration

Question 22

what does active transport involve the use of (similarly to facilitated diffusion)

Answer 22

-carrier proteins
-molecule binds to the receptor site and atp binds to carrier protein. the hydrolysis of ATP to ADP and phosphate releases energy which causes the carrier protein to change shape. the phosphate attaches to the protein transporting the molecule to the other side of the membrane.

Question 23

factors affecting the rate of active transport

Answer 23

-tempreture
-thickness of membrane
-number of carrier proteins
-rate of respiration

Question 24

what type of active transport is large molecules such as enzymes and hormones transported by

Answer 24

bulk transport

Question 25

two types of bulk transport

Answer 25

endocytosis exocytosis

Question 26

endocytosis

Answer 26

the process in which large molecules or many molecules at once are transported into cells

Question 27

how does endocytosis take place

Answer 27

-cell membrane folds inwards to form a cavity around the particles (invagination) -membrane completely encircles the particles to form a vesicle -vesicle moves into the cell

Question 28

endocytosis takes two forms

Answer 28

-phagocytosis- uptake of solid materials -pinocytosis- uptake of liquid materials

Question 29

exocytosis

Answer 29

the process in which large molecules or many molecules at once are transported out of cells

Question 30

how exocytosis takes place

Answer 30

the proteins are found in the golgi apparatus and modified before vesicles containing the proteins bud off the golgi apparatus and make their way towards the cell membrane. the vesicles then fuse with the cell membrane and secreted

Question 31

solutions

Answer 31

mixtures made up of a solute dissolved in a solvent

Question 32

water potential

Answer 32

the pressure exterted by water molecules on the membrne surrounding a solution. it is measured in kilopascals

Question 33

high water potential

Answer 33

this means the solution has a high water concentration

Question 34

low water potential

Answer 34

this means the solution has a low water concentration

Question 35

pure water has a water potential of

Answer 35

0kpa the value decreases as more solute is added

Question 36

osmosis

Answer 36

the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially or selectively permeable membrane

Question 37

animal cell in a hypotonic solution

Answer 37

-hypotonic solution has a higher water potential than the cell -water molecules move into the cell this causes pressure in the cell (hydrostatic pressure) - the cell swells and bursts (haemolysis)

Question 38

animal cells inside isotonic solutions

Answer 38

-isotonic solutions has the same water potential as the cell -no net movement of water -cell stays the same size

Question 39

animal cells in hypertonic solutions

Answer 39

-a hypertonic solution has a lower water potential than the cell -water molecules move out of the cell -the cell shrinks and membrane wrinkles (flaccid)

Question 40

why do plant cells not burst

Answer 40

due to the prescence of a cell wall, vacuole and protoplast

Question 41

plant cells in hypotonic solutions

Answer 41

-hypotonic solution has a higher water potential than the cell -water molecules move into the cell -the cell swells and becomes turgid.the internal pressure is called turgor pressure. at a certain point the turgor pressure prevents any more water from entering the cell by osmosis. the cell wall is made of cellulose and is very strong so does not burst

Question 42

plant cells in isotonic solutions

Answer 42

-isotonic solutions has the same water potential as the cell -no net movement of water -cell stays the same size

Question 43

plant cells in a hypertonic solution

Answer 43

-a hypertonic solution has a lower water potential than the cell -water molecules move out of the cell -the cell shrinks and becomes plasmolysed. when plasmolysis occurs the space between the cell membrane and the cell wall is now filled with the solution which surrounds the plant cell. the protoplast pulls away from the cell when the plant cell is plasmolysed

Question 44

factors affecting the rate of osmosis

Answer 44

tempreture water potential gradient thickness of membrane surface area