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Biology > 5- Plasma Membranes > Flashcards

5- Plasma Membranes Flashcards

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1
Q

What are 4 functions of plasma membranes?

A

-recognition of other cells
-separated cell contents from the outside (barrier between cells and its environment
-controls the passage of materials in and out
-allows cell communication
-phagocytosis
-cell to cell attachment
-site of chemical reactions

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2
Q

What are 4 functions of membranes inside cells?

A

-isolates DNA
-act as an intercellular transport system
-compartmentalises reactions
-site of chemical reactions
-ribosomes attach
-protection from lysosomes
-forms vesicles

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3
Q

What is compartmentalisation?

A

The formation of separate membrane-bound areas

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4
Q

Why is compartmentalisation important in cells?

A

-incompatible reactions occur within cell
-isolates reactions making them more efficient
-allows reaction conditions to be maintained
-protects vital cell components

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5
Q

What does partially permeable mean?

A

A membrane that allows some substances to cross but not others

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6
Q

What is cell signalling?

A

A complex system of intercellular communication

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7
Q

What is a phospholipid bilayer

A

-arrangement of phospholipids found in cell membranes
-the hydrophilic phosphate heads from both the inner and outer surface of a membrane
-sandwiching the fatty acid tails to for a hydrophobic core inside the membrane

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8
Q

Why are membranes referred to as having a “fluid-mosaic” structure?

A

-the phospholipids are able to move freely relative to each other (relative)
-the proteins embedded in the bilayer vary in shape, size and position (mosaic)

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9
Q

What is a glycoprotein?

A

Extrinsic membrane proteins with attached carbohydrate molecules of varying lengths and shapes

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10
Q

What is a glycolipid?

A

Cell-surface membrane lipids with attached carbohydrate molecules of varying lengths and shapes

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11
Q

What is a phospholipid?

A

Modified triglycerides, where one fatty acid has been replaced with a phosphate group

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12
Q

What are channel proteins?

A

Intrinsic membrane proteins that provide a hydrophilic channel through a membrane. Allow the passive movement of polar and ions down a concentration gradient.

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13
Q

What are receptor proteins?

A

Extrinsic glycoproteins that bind chemical signals, triggering a response by the cell

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14
Q

What are carrier proteins?

A

Intrinsic membrane proteins that play a part in the transport of substances through a membrane. Important told in passive and active transport into cells. Often involves the shape of the protein changing

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15
Q

What is the appropriate width of an animal cell plasma membrane?

A

7nm

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16
Q

What are the functions of cholesterol in cell surface membranes?

A

-regulates fluidity and adds stability to membranes without making them too rigid
-prevents phospholipids from crystallising

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17
Q

What are the functions of phospholipids in cell surface membranes?

A

-forms a basic structure
-acts as a partially permeable barrier
-allows the passage of lipid soluble molecules
-prevents water soluble molecules from moving across the membranes

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18
Q

What is the function of glycoproteins in cell surface membranes?

A

-receptors for chemical signals
-cell adhesion
-when chemical bonds to the receptor, events inside the cell are set off
-binding sites for chemical eg. hormones
-hydrogen bonds to water to stabilise movement

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19
Q

What are examples of cell communication and cell signalling in glycoproteins?

A
  • receptors for neurotransmitters such as acetylcholine at nerve cell synapses. Binding of neurotransmitters triggers or prevents an impulse into the next neurone
    -receptors for peptide hormones, including inside and glucagon which affect the uptake and storage of glucose by cells
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20
Q

What are the function of glycolipids in cell surface membranes?

A

-act as antigens that can be recognised by the immune system
-form hydrogen bond with water molecules to stabilise membrane

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21
Q

What are the functions of carrier proteins in cell surface membranes?

A

-have an important role in both passive movement of polar molecules and ions down a concentration gradient and have a role in active transport
-this involves the shape of the protein changing

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22
Q

What is the function of channel proteins in cell surface membranes?

A

-provide a hydrophilic channel that allows passive movement of polar molecules and ions down a concentration gradient

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23
Q

What are the functions of extrinsic proteins in cell surface membranes?

A

-can attach to the cytoskeleton

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24
Q

Describe 2 ways in which cholesterol regulates membrane fluidity?

A

-hydrophilic end of cholesterol interact with phosphate heads
-hydrophobic end of cholesterol interacts with fatty acid tails
-pull the phospholipids together
-prevents membranes from becoming too solid and crystallising by preventing the phospholipids from getting too close together

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25
Q

What are the 3 factors that affect membrane structure?

A

Temperature
Solvents
Cholesterol

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26
Q

How does an increase in temperature affect cell membranes?

A

-increases membrane fluidity, phospholipids have increased kinetic energy and move more
-increases membrane permeability, easier for particles to cross it
-carrier and channel proteins are dentures at higher temperatures
-membrane looses its structure

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27
Q

Why does an increase in temperature increase membrane permeability?

A

-more temperature means phospholipids move more
-becuase they have higher kinetic energy
-make it easier for particles to mass through

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28
Q

Why are polar solvents such as water essential in the plasma membrane structure?

A

-To keep the heads and tails of phospholipids arranged correctly and keep them intact

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29
Q

Why do organic solvents dissolve membranes?

A

-Many are less polar then water (eg. alcohol) and some are non-polar (eg. benzene)
-can enter the cell membrane and disrupt the membrane
-membrane becomes more fluid and more permeable
-can also denature proteins by disrupting bonds

30
Q

Why is alcohol used in antiseptics?

A

-less polar then water
-dissolve the plasma membranes of bacteria

31
Q

Why are alcoholic drinks harmful to cells?

A

-they do not dissolve the plasma membranes like strong or pure alcohols
-But still damage membranes as nonpolar alcohol molecules disrupt the membrane, making it more permeable and fluid

32
Q

What is diffusion?

A

-Passive process, does not require energy
-The net movement of particles from an area of high concentration to an area of low concentration
-Continues until equilibrium is reached

33
Q

What are the factors affecting simple diffusion?

A

-concentration gradient
-membrane thickness
-surface area
-temperature

34
Q

How does the concentration gradient affect the rate of simple diffusion?

A

-the greater the concentration gradient difference the faster the rate of diffusion
-overall movement from the high conc to the low conc is larger

35
Q

How does the membrane thickness affect the rate of simple diffusion?

A

-the thinner the membrane the faster the rate of diffusion
-thin membranes reduce the distance the particles have to travel

36
Q

How does the surface area affect the rate of simple diffusion?

A

-the larger the surface area the faster the rate of diffusion
-increasing the SA of a membrane means more particles can be exchanged in the same amount of time

37
Q

How does the temperature affect the rate of simple diffusion?

A

-the higher the temperature the faster the rate of diffusion
-at higher temperatures particles will have more kinetic energy so they will be able to move around faster

38
Q

What is facilitated diffusion?

A

-diffusion of larger, charge molecules through specialised carrier or channel proteins
-moving down their concentration gradient from high to low concentrations
-passive process, no energy involved

39
Q

How do carrier proteins assist facilitated diffusion?

A

-move large molecules across a membrane
-large molecules attach to carrier proteins and then the protein changes shape, releasing the molecule on the other side

40
Q

How do channel proteins assist facilitated diffusion?

A

-form pores for charged particles to diffuse through
-different channel facilitate the diffusion of different charged particles
-simple tunnel which allows particles to cross the membrane

41
Q

What are the factors affecting the rate of facilitated diffusion?

A

-concentration gradient
-number of channel and carrier proteins

42
Q

How does the concentration gradient affect the rate of facilitated diffusion?

A

-the greater the concentration gradient, the faster the rate of diffusion
-until all the proteins are in use/ equilibrium is reached then rate will level off/slow down

43
Q

How does the number of channel and carrier proteins affect the rate of facilitated diffusion?

A

-the greater the number of channel or carrier proteins the faster the rate of facilitated diffusion

44
Q

What is osmosis?

A

-diffusion of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane
-passive process, no energy required

45
Q

What is water potential?

A

-the potential or likelihood of water molecules to diffuse out of a solution
-symbol ψ
-unit kilopascal (kPa)
-the more negative the water potential = the more concentrated the solution is

46
Q

What is the water potential of pure water like?

A

-zero (0 ψ)
-becuase no water will diffuse into this solution, high chance it will leave
-highest possible water potential, highest possible concentration of water molecules

47
Q

What is hydrostatic pressure?

A

-the diffusion of water = increased volume of solution
-if a solution is in a closed system this results in an increase in pressure
eg.cells
-units kPa
-at the cellular level this pressure is relatively large, potentially damaging

48
Q

What would happen if an animal cel is placed in a solution with a higher water potential than that of its cytoplasm?

A

-water will move into the cell by osmosis
-hydrostatic pressure inside cell increases
-the cell membrane is thin and not very strong, cannot withstand pressure and cannot stretch
-cell membrane breaks, cell bursts
-cytolysis

eg. pure water, dilute solution

49
Q

What would happen if an animal cel is placed in a solution with a lower water potential than that of its cytoplasm?

A

-cell will loose water by osmosis
-reduction in the volume of the cell
-cell will shrivel/shrink
-crenation

50
Q

How is water potential controlled to prevent cytolysis and crenation in animal cells?

A

-have control mechanisms
-make sure cells are constantly surrounded by aqueous solutions with an equal water potential (isotonic)

51
Q

What would happen if a plant cell is placed in a solution with a lower water potential than that of its own?

A

-water is lost from the cells by osmosis
-reduction in the volume of water
-vacuoles shrink
-eventually the cell membranes pull from cell walls
-plasmolysis

52
Q

What would happen if a plant cell is placed in a solution with a higher water potential than that of its own?

A

-water enters cell by osmosis
-hydrostatic pressure inside cell increases
-does not burst as cell wall protects them
-vacuole expands
-become turgid as cell membrane pushes on the cell wall

53
Q

What happens to a cell when it is turgid?

A

-as turgor pressure increases it resists the entry of further water into the cell

54
Q

What are the factors affecting the rate of osmosis?

A

-Water potential gradient
-Membrane thickness
-Surface Area

55
Q

How does water potential gradient affect the rate of osmosis?

A

-the higher the water potential gradient the faster the rate of osmosis

56
Q

How does membrane thickness affect the rate of osmosis?

A

-the thinner the membrane the faster the rate of osmosis
-thin membrane reduces the distance the molecules have to travel

57
Q

How does surface area affect the rate of osmosis?

A

-the larger the surface area the faster the rate of osmosis
-increased surface area means more molecules can move across in the same amount of time

58
Q

What is active transport?

A

-the movement of molecules or ions into a cell from a area of low concentration to an area of high concentration
-active process
-requires energy from ATP which is produced by aerobic respiration in the mitochondria
-requires the use of carrier proteins which change shape and move a molecule across a membrane

59
Q

What is co-transport?

A

-active transport using special carrier proteins called co-transporters
-bind two molecules at a time, one moves down its concentration gradient and this is used to move the other molecule across the membrane against its concentration gradient

60
Q

Describe the co-transport of glucose of glucose in the small intestine.

A

Sodium ions move across the membrane down their concentration gradient by binding co-transporters. Glucose binds along with the sodium so it is moved across the membrane too, against its concentration gradient.

  1. Na+ ions are actively transported out of the epithelial cells in the ileum into the blood by the sodium-potassium (Na+/K+) pump. This creates a concentration gradient as there are more sodium ions in the lumen of the ileum that’s inside the epithelial cell
  2. The concentration gradient causes Na+ ions to diffuse from the lumen of the ileum into the epithelial cell down their concentration gradient. They do this through the Na+-glucose cotransporter protein. Glucose enters the cell with the sodium
  3. Their is a higher concentration of glucose inside the epithelial than in the blood so glucose diffuses into the blood down its concentration gradient through a protein channel by facilitated diffusion.
61
Q

How is the general process of active transport described?

A
  1. The molecule or ion to be transported binds to receptors in the channel of the carrier protein on the outside of the cell
  2. On the inside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and a phosphate
  3. Binding of the phosphate molecule to the carrier protein causes the protein to change shape, opening up up the inside of the cell
  4. The molecule or ion is released to the inside of the cell
  5. The phosphate molecule is released from the carrier protein and recombines with ADP to from ATP
  6. The carrier protein returns to its original shape
62
Q

What are the factors affecting the rate of active transport?

A

-speed of carrier proteins
-number of carrier proteins
-rate of respiration

63
Q

How does the speed of carrier proteins affect the rate of active transport?

A

-the faster the carrier proteins work the faster the rate of active transport

64
Q

How does the number of carrier proteins affect the rate of active transport?

A

-the greater the number of carrier proteins in the plasma membrane the faster the rate of active transport

65
Q

How does the rate of respiration affect the rate of active transport?

A

-the greater the rate of respiration the more ATP there will be available for active transport to take place
-ATP is produced by aerobic respiration, the rate of active transport therefore depends on the rate of respiration

66
Q

What is bulk transport?

A

-another form of active transport
-transport of large particles across the cell membrane, that are too big to move through channel or carrier proteins
-lots of ATP is required to move the vesicles
-requires energy

eg. endocytosis and exocytosis

67
Q

What is endocytosis?

A

-bulk transport of material into cells
-by enclosing them in a vesicle made out of plasma membrane
-two types: phagocytosis and pinocytosis

  1. The plasma membrane of the cell invaginates (folds inwards), forming a pocket around the target particles
  2. The pocket pinches off with the help of specialised proteins, leaving the particle trapped in a newley created vesicle inside the cell
68
Q

What is exocytosis?

A

-how cells transport signalling chemicals or waste products from inside the cell to outside the cell in vessicles which fuse with the plasma membrane
-vesicles usually formed by the gogli apparatus move towards and fuse with the cell surface membrane and contents of the vesicle are released outside of the cell

69
Q

What are some examples of endocytosis?

A
  1. Pinocytosis - ‘cell drinking’
    something that cells regulary do to sample their environment by taking in small amounts of extra cellular fluid
  2. Receptor-mediated endocytosis
    uses receptor proteins on the cell surface to capture a specific target molecule. When the receptor binds to target molecule endocytosis is triggered usually to take up large molecules which are low in concentration outside cells but this can be abused by pathogens such as cholera toxins to gain cell entry
70
Q

What are an example of exocytosis?

A

-most vesicles come from the gogli and contain proteins made to be released outside such as signalling molecules or proteins which need to be embedded in the plasma membrane
other vesicles contain waste proteins that cells need to remove
-signalling mole i;es (eg. neurotransmitters) are not constantly released, exocytosis is triggered by chemicals binding to receptors

Biology (11 decks)

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