Biological Membranes

Question 1

what is the plasma membrane

Answer 1

• controls the entry and exit of substances
• partially permeable
• barrier between cell and environment

Question 1

what is the structure of the phospholipid membrane

Answer 1

• phospholipid bilayer
• hydrophilic phosphate heads
• hydrophobic fatty acid tails

Question 2

what is the cell membrane theory

Answer 2

• fluid mosaic model
• phospholipids are free to move within the layers giving flexibility
• scattered proteins

Question 3

what are intrinsic proteins

Answer 3

-transmembrane proteins embedded through both membrane layers
- amino acids + hydrophobic R groups on the external surface interacting with internal hydrophobic core to provide stability

Question 4

What are examples of intrinsic proteins

Answer 4

• channel proteins
• carrier proteins
• glycoproteins
• glycolipids

Question 5

what are channel proteins

Answer 5

• hydrophilic channel allowing passive movement of polar molecules and ions

Question 6

what are carrier proteins

Answer 6

• role in passive and active transport into cells
• shape of the protein changes

Question 7

what are glycoproteins

Answer 7

• embedded in cell surface membrane with attached carbohydrate chains
• cell signalling - chemical binds and elicits a response

Question 8

what are glycolipids

Answer 8

• lipid with carbohydrate chains attached
• recognised by cells of the immune system as self or non-self

Question 9

what are extrinsic proteins

Answer 9

• present in one side of the bilayer
• hydrophilic R groups on the outer surface and interact with polar heads
• cholesterol

Question 10

what is cholesterol

Answer 10

• lipid with a hydrophilic and hydrophobic end
• regulates membrane fluidity
• hydrophilic end interacts with heads and hydrophobic with tails
• add stability
• prevents membrane from becoming solid by stopping phospholipid molecules from grouping closely

Question 11

how does temperature effect membrane structure

Answer 11

• increased temperature the phospholipids have more kinetic energy and move more
• membrane becomes more fluid and loses its structure
• if temperature continues to increase the cell breaks down completely
• carrier and channel proteins are denatured

Question 12

how do solvents effect membrane structure

Answer 12

• organic solvents (non-polar) dissolve membrane and disrupt cells
• pure/strong alcohol solutions are toxic
• disrupted membrane becomes more fluid and more permeable

Question 13

what is diffusion

Answer 13

• net movement of particles from a region of higher concentration to a region of lower concentration until it reaches equilibrium

Question 14

how does temperature affect the rate of diffusion

Answer 14

• high temperature = faster diffusion
• particles have more kinetic energy and move faster

Question 15

what is facilitated diffusion

Answer 15

• larger molecules diffuse through carrier or channel proteins

Question 16

How do carrier proteins move substances

Answer 16

• large molecule attaches to a carrier protein
• protein changes shape
• releases molecule on opposite side of the membrane

Question 17

how do channel proteins move substances

Answer 17

• form pores in membrane for charged particles to diffuse through

Question 18

what is active transport

Answer 18

• movement of molecules in or out of a cell from a region of lower concentration to a region of higher concentration
• requires energy and carrier proteins

Question 19

how do carrier proteins use ATP to move substances

Answer 19

• molecule binds to receptor in channel of the protein on the outside of the cell
• on the inside ATP binds to the carrier protein and is hydrolysed to ADP and phosphate
• phosphate binds to protein causing it to change shape
• opens inside the cell
• molecule released inside the cell
• phosphate molecule released from the carrier protein and recombines with ADP to form ATP
• carrier protein returns to its original shape

Question 20

what is bulk transport

Answer 20

• form of active transport
• molecules that are too larger to move through channel or carrier proteins

Question 21

what is endocytosis

Answer 21

• bulk transport of materials into cells
• cell membrane bends inwards when it comes into contact with the material to be transported
• membrane enfolds to form a vesicle
• vesicle move into the cytoplasm
• transfers material for further processing in the cell

Question 22

what is exocytosis

Answer 22

• bulk transport of material out of cells
• vesicle moves towards and fuses with the cell membrane
• contents released outside of the cell

Question 23

what is an isotonic solution

Answer 23

solution with the same water potential as the cell

Question 24

what is a hypertonic solution

Answer 24

solution with a lower water potential than the cell

Question 25

what is a hypotonic solution

Answer 25

solution with a higher water potential than the cell

Question 26

what happens to an animal cell in a isotonic solution

Answer 26

• water molecules pass in and out in equal amounts
• cell stays the same

Question 27

what happens to an animal cell in a hypertonic solution

Answer 27

• net movement of water molecules is out of the cell
• cell shrinks

Question 28

what happens to an animal cell in a hypotonic solutionn

Answer 28

• net movement of water molecules is in the cell
• cell bursts - cytolysis

Question 29

what happens to a plant cell in a hypotonic solution

Answer 29

• vacuole swells
• vacuole + cytoplasm push against the cell wall
• cell becomes turgid

Question 30

what happens to a plant cell in a isotonic solution

Answer 30

• water molecules move in and out of the cell in equal amounts
• cell stays the same

Question 31

what happens to a plant cell in a hypertonic solution

Answer 31

• cell becomes flaccid
• cytoplasm and membrane pull away from the cell wall - plasmolysis