Biological membranes 2.5

Question 1

What does a cell membrane consist of?

Answer 1

Phospholipids, carrier proteins, channel proteins, glycoproteins, glycolipids and cholesterol

Question 2

What two structures can phospholipids form?

Answer 2

Bilayer and micelle

Question 3

What are the functions of membranes?

Answer 3

• sites of cell communication
• sites of chemical reactions
• allow selected molecules to move in and out the cell
• allows a cell to change shape
• allows cellular components to have separate conditions
• isolating organelles from the rest of the cytoplasm

Question 4

Which substances can pass through the phospholipid bilayer?

Answer 4

• small polar molecules diffuse slowly (H20)
• fat soluble substances
• small non-polar molecules diffuse rapidly (O2 and CO2)

Question 5

What is the membrane structure called?

Answer 5

Fluid mosaic model

Question 6

Why is the membrane structure called the fluid mosaic model?

Answer 6

The proteins, glycolipid, glycoproteins and cholesterol floating around in the bilayer form a mosaic pattern and the phospholipids can move making the membrane fluid

Question 7

What are the components of the phospholipid bilayer?

Answer 7

• phospholipids
• proteins
• cholesterol
• glycoproteins
• glycolipids

Question 8

What is the difference between extrinsic and intrinsic proteins?

Answer 8

Intrinsic proteins penetrate 2 layers of the bilayer and extrinsic only penetrates 1

Question 9

What is a glycoprotein?

Answer 9

A lipid attached to a protein

Question 10

What is a glycolipid?

Answer 10

A lipid attached to a phospholipid

Question 11

How does a phospholipid form a bilayer?

Answer 11

The hydrophobic tails of the phospholipid turn in to face eachother and the hydrophilic heads face outwards to form hydrogen bonds with the water forming a bilayer

Question 12

What does an intrinsic protein do?

Answer 12

• consists of channel proteins that have pores and act as channels to allow ions to pass through the membrane
• also contains carrier proteins which change their shape to carry specific (bigger) molecules across the membrane

Question 13

What does an extrinsic protein do?

Answer 13

• provide structural support
• act as enzymes, antigens or receptor sites

Question 14

What do glycolipids do?

Answer 14

Act as antigens for cell recognition

Question 15

What do glycoproteins do?

Answer 15

• act as receptors for chemical signals
• has a role in cell adhesion sometimes

Question 16

what does cholesterol do?

Answer 16

• regulates the fluidity of the membrane
• provides mechanical support

Question 17

What happens if a membrane contains less cholesterol?

Answer 17

It becomes less fluid and less permeable

Question 18

What are the three ways that substances can get in and out of a cell using no energy? (passive transport, no ATP)

Answer 18

• osmosis
• diffusion
• facilitated diffusion

Question 19

What are the three ways that substances can get in and out of a cell using energy?

Answer 19

• active transport
• exocytosis
• endocytosis

Question 20

How do substances cross a membrane without using energy from respiration?

Answer 20

They use the kinetic energy from a higher body temperature to cross the membrane

Question 21

What affects the rate of diffusion?

Answer 21

• Temperature
• concentration gradient
• diffusion distance
• surface area

Question 22

What does facilitated diffusion transport?

Answer 22

• polar molecules
• charged molecules
• large molecules

Question 23

What does it mean when a substance is insoluble?

Answer 23

The substance forms no hydrogen bonds with water

Question 24

Define water potential and what is it measured in?

Answer 24

• the tendancy of water molecules in a system to move
• Kilo Pascals (KPa)

Question 25

What is the water potential of pure water?

Answer 25

0 KPa

Question 26

Where do water molecules move?

Answer 26

Water molecues always move from an area of high water potential to an area of low water potential

Question 27

What happens if a solution is added to pure water?

Answer 27

Even if the volume of water stays the same, the WP decreases as there is less water that is free to move and more water is making hydrogen bonds

Question 28

What does crenated mean?

Answer 28

Shrivelled

Question 29

What is osmotic concentration?

Answer 29

It is the amount of dissolved solutes in a solution

Question 30

Do insoluble molecules affect water potential or osmotic concentration?

Answer 30

No

Question 31

What are the characteristic of a solution with a high volume of water and a low volume of solute?

Answer 31

- low osmotic concentration - high water potential - dilute solution

Question 32

What are the characteristic of a solution with a low volume of water and a high volume of solute?

Answer 32

- high osmotic concentration - low water potential - concentrated solution

Question 33

What do hypertonic and hypotonic relate to?

Answer 33

The solute

Question 34

What is isotonic?

Answer 34

- when the WP outside the cell is the same as the WP of the cell cytoplasm - no net movement

Question 35

What is hypertonic?

Answer 35

- when the WP of the outside of the cell is less than the WP of the cell cytoplasm - when the OC of the outside of the cell is higher than the OC of the cell cytoplasm - net movement of water out of the cell - animal cells crenate (flacid) - plant cells undergo plasmolysis

Question 36

What is hypotonic?

Answer 36

- when the WP of the outside of the cell is more than the WP of the cell cytoplasm - when the OC outside the cell is lower than the OC of the cell cytoplasm - net movement of water into the cell - cells undergo lysis (turgid)

Question 37

When is active transport used?

Answer 37

- to move substance up their concentration gradient - if diffusion isn't fast enough for what the body needs - to set up a concentration gradient

Question 38

How does active transport work?

Answer 38

A molecule binds itself to a carrier protein, then ATP attaches to the protein on the inside of the cell causing it to change shape and allowing the molecule to pass through

Question 39

What are endocytosis and exocytosis examples of?

Answer 39

Bulk transport

Question 40

What is bulk transport?

Answer 40

When extremely large substances need to be moved across a cell membrane

Question 41

How does the cell membrane move?

Answer 41

The cytoskeleton moves it

Question 42

What is endocytosis?

Answer 42

The bulk movement of substances into the cell and consists of phagocytosis and pinocytosis

Question 43

What is exocytosis?

Answer 43

The bulk movement of substances out of the cell

Question 44

What is phagocytosis?

Answer 44

The bulk movement of solid substances into the cell

Question 45

What is pinocytosis?

Answer 45

The bulk movement of liquid substances into the cell

Question 46

What are the three factors that affect membrane structure?

Answer 46

- heat - cholesterol - solvents

Question 47

Why do membranes need to be fluid?

Answer 47

- to allow diffusion of substances across the membrane - to allow the membrane to fuse with vesicles in endo/excocytosis - to enable the cell to move

Question 48

How does heat affect the membrane structure?

Answer 48

- it increases kinetic energy, which creates gaps in the bilayer allowing molecules to pass through - proteins denature

Question 49

How does the cold affect the membrane structure?

Answer 49

Since water expands into ice in temperatures below freezing, the ice shards penetrate the membrane and push the phospholipids apart, increasing permeability

Question 50

How do solvents affect membrane structure?

Answer 50

- Water is polar and creates membrane stability with the phospholipids - non-polar molecules can move into the bilayer and disrupt the structure by dissolving phospholipids

Question 51

How does cholesterol affect membrane structure?

Answer 51

- it controls membrane fluidity - it increases mechanical strength and stability of membranes

Question 52

How does cholesterol affect membrane structure if the temperature is too high?

Answer 52

- it decreases the fluidity - it binds to the phospholipid tails due to a chemical attraction which causes them to pack closer together, stabalising them

Question 53

How does cholesterol affect membrane structure if the temperature is too low?

Answer 53

- it increases fluidity - it stops the phospholipid tails from packing too closely together by being in between the phospholipids