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Biology Miss Negus > Biological Membranes > Flashcards

Biological Membranes Flashcards

1
Q

What is the fluid mosaic model?

A

Theory of cell membrane structure with proteins embedded in sea of phospholipids

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2
Q

What is a glycolipid?

A

Lipid/phospholipid with a chain of carbohydrate molecules attached

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3
Q

What is a glycoprotein?

A

Protein with a chain of carbohydrate molecules attached

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4
Q

What is a plasma membrane?

A

A cell surface membrane

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5
Q

Why are cell membranes described as partially permeable?

A

They don’t let all types of molecules pass through them

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6
Q

What does permeable mean?

A

Refers to the ability to let substances pass through

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7
Q

What are the roles of the plasma membrane?

A
  • separates the cells components from its external environment
  • regulates transport of materials into and out of the cell
  • may contain enzymes involved in specific metabolic pathways
  • has antigens
  • may release chemicals which signal other cells
  • contains receptors
  • may be the site of chemical reactions
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8
Q

What is the roles of membranes within the cell?

A
  • mitochondria have folded inner membranes (cristae) this gives a large surface area for some reactions of aerobic respiration
  • the inner membrane of chloroplasts called thylakoid membranes, house chlorophyll. This is where some reactions of photosynthesis happen
  • some digestive enzymes on the plasma membranes of epithelial cells that line the small intestine
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9
Q

Describe what the fluid mosaic model is like:

A

It is the plasma membrane where the fabric of the membrane is the lipid blister made up of two layers of phospholipid molecules. Their hydrophilic heads are in contact with the cytoplasm. The hydrophobic rail regions are in the centre of the membrane away from water. There are proteins floating it in making up a mosaic pattern. There are glycoproteins and glycolipids on the outside of it acing as receptors

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10
Q

What do the proteins do in the fluid mosaic model plasma membrane?

A
  • some of them have pores and act as channels to allow ions which have an electrical charge and are surrounded by water molecules to pass through
  • some proteins are carriers and by changing their shape carry specific molecules across the membrane
  • other proteins may be attached to the carrier proteins and function as enzymes, antigens or receptor sites for complementary shaped signalling chemicals such as hormones
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11
Q

What is the glycocalyx?

A

It is formed from the carbohydrate chains attached to either lipids (glycolipids) or proteins (glycoproteins) in the membrane

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12
Q

Why do not all cell membranes have the composition?

A

Their membranes have particular distributions of proteins in order to enable them to carry out their specific functions

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13
Q

What is an example of a composition of a cell membrane?

A

In neurones (nerve cells), the protein channels and carriers in the plasma membrane covering the long axon allow entry and exit of ions to bring about the conduction of electrical impulses along their length

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14
Q

What is diffusion?

A

The movement of molecules from an area of high concentration of that molecule to an area of low concentration; it may or may not be across a membrane; it does not involve metabolic energy (ATP)

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15
Q

What is facilitated diffusion?

A

Movement of molecules from an area of high concentration of that molecule to an area of low concentration, across a partially permeable membrane via protein channels or carriers; it does not involve metabolic energy (ATP)

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16
Q

What is simple diffusion?

A

Where some molecules have kinetic energy and move randomly within gas or liquids. The molecules bump into each other in the area with high concentration and spread further from each other l. More move to an area of low concentration until they are equally dispersed (equilibrium). They then move randomly but there is no net diffusion

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17
Q

What molecules can diffuse via simple diffusion?

A
  • Some molecules such as oxygen and carbon dioxide which are small
  • Fat soluble molecules such as steroid hormones even though they are larger they dissolve in the lipid bolster
  • Only if water is present in such great concentrations there may be specific water channel proteins (aquaporins)
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18
Q

How is the concentration gradient maintained?

A

Many molecules entering cells then pass into organelles and are used for metabolic reactions which maintains the concentration gradient and keeps more of the molecules entering the cell

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19
Q

What factors affect the rate of simple diffusion?

A
  • Temperature
  • Diffusion distance
  • Surface area
  • Size of diffusing molecule
  • Concentration gradient
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20
Q

How does temperature affect the rate of simple diffusion?

A

As the temperature increases, molecules have more kinetic energy so their rate of diffusion will increase. Conversely as they lose heat their rate of diffusion will slow down

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21
Q

How does diffusion distance affect the rate of simple diffusion?

A

The thicker the membrane across which molecules have to diffuse the slower the rate of diffusion

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22
Q

How does surface area affect the rate of simple diffusion?

A

More diffusion can take place across a larger surface area. Cells specialised for absorption have extensions to their cell surface membranes, called microvilli. These increase the surface area

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23
Q

How does the size of a diffusing molecule affect the rate of simple diffusion?

A

Smaller ions or molecules diffuse more rapidly than larger molecules

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24
Q

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

A

The steeper this gradient (the more molecules there are on one side of the membrane compared with the other side), the faster the diffusion to the side where there are fewer molecules, down the gradient

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25
Q

What molecule use facilitated diffusion?

A
  • small molecules that have polarity as they are insoluble in lipids as they can’t interact with the hydrophobic tails of the lipid bilayer
  • large molecules e.g. glucose
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26
Q

Why do different molecules have different carrier proteins?

A

Because there are specific carrier profiles for different types of molecules. Different cells types have membranes with differing proportions of transmembrane protein channels and transmembrane proteins carriers. This allows cels to control the types of molecule that pass in or out

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27
Q

What is an example of a molecules type of protein carrier or channel?

A

The plasma membrane of epithelial cells that line the airways have chloride ion channels and these play a crucial role in regulating the composition of mucus to trap particles and pathogens

28
Q

What is osmosis?

A

The net diffusion from a region with a high concentration of free water molecules to an area with a low concentration of water molecules, down their water potential gradient, across a partially permeable membrane

29
Q

What is water potential?

A

The measure of the tendency of water molecules to diffuse from one region to another

30
Q

What has the highest possible water potential?

A

Pure water as when solute molecules are added they lower the water potential of the solutionp

31
Q

What is the water potential of cells?

A
  • The water potential inside cells is lower than pure water as there are solutes in solution in the cytoplasm and inside the large vacuole of plant cells
  • When cells are placed in a solution of higher water potential then water molecules move by osmosis down the water potential gradient across the plasma membrane into the cell
32
Q

What is cytolysis?

A

In animal cells if a lot of water molecules enter, the cell will swell and bust as the plasma membrane breaks. When a cell is placed in water with a high water potential so water enters the cell via osmosis across a partially permeable membrane

33
Q

What does turgid mean?

A

When the plant cell swells up to a certain size when it’s contents push against the cell wall. This happens when the fell is placed in a solution of high water potential so water moves into the cell via osmosis across a partially permeable membrane

34
Q

What does cremates mean?

A

When an animal cell shrivels died to being placed in a solution of lower water potential so water leaves the cells by osmosis across the partially permeable membrane

35
Q

What does plasmolysed mean?

A

When the cytoplasm of plant cells shrink and the membrane pulls away from the cellulose cells walk when the cell is placed in a solution of lower water potential so water leaves the cell by osmosis across the partially permeable membrane

36
Q

What is active transport?

A

The movement of substances against their concentration gradient (from low to high concentration of that substance) across a cell membrane, using ATP and protein carriers

37
Q

What is endocytosis?

A

Bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins into a cell

38
Q

What is exocytosis?

A

Bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins out of a cell

39
Q

Why do carrier proteins need ATP?

A

They have specific regions, or sites that combine feverishly with only certain solute molecules or ions. They also have a region which allows the hydrolysis of ATP. The energy helps the carrier protein change its conformation (shape) so it can carry the ion from one side of the cell membrane to another

40
Q

What happens in endocytosis?

A

A segment of the plasma membrane surrounds and enclosed the particle and brings it into the cell, enclosed in a vesicle

41
Q

What are the different types of endocytosis?

A
  • Phagocytosis

* Pino(endocytosis)cytosis

42
Q

What is phagocytosis?

A

A type of endocytosis which means ‘eating by cells’ and refers to this type of intake of solid matter

43
Q

What is pino(endo)cytosis?

A

A type of endocytosis where cells ingests liquids by endocytosis

44
Q

Why is ATP needed in endocytosis?

A

It is needed to provide energy to from the vesicles and move them using molecular motor proteins along cytoskeleton threads into the cell interior

45
Q

What happens in exocytosis?

A

A vesicle containing the molecules is moved towards and then fuses with the plasma membrane. The fuses site opens releasing the contents of the secretory vesicle

46
Q

Why is ATP needed for exocytosis?

A

It is needed to fuse the membranes together as wells as for moving the vesicles. A molecule of ATP is hydrolysed for every step that a motor protein takes along the cytoskeleton thread as it drags the vesicle

47
Q

What happens to phospholipids when the temperature drops?

A
  • Saturated fatty acids become compressed
  • Unsaturated fatty acids as they become compressed the kinks in their tails push adjacent phospholipid molecules away maintaining the membranes fluidity
  • So the proportions of saturated and unsaturated fatty acids in a cell membrane determine the membranes fluidity at cold temperatures
  • Cholesterol prevents the phospholipid molecules from packing together too closely to prevent a reduction in the membranes fluidity
48
Q

What happens to phospholipids when the temperature increases?

A
  • The phospholipids have more kinetic energy so they move around more in a random way increasing the membranes fluidity
  • Permeability increases
  • Affects the way membrane embedded proteins are positioned and may function
  • Cholesterol reduces the increase in membrane fluidity
49
Q

What does an increase in membrane permeability do?

A
  • May affect the in folding of the plasma membrane during phagocytosis
  • May also change the ability of cells to signal to other cells by releasing chemicals often by exocytosis
50
Q

What happens to proteins when tempers increases?

A

It causes the stomps within their larger molecules to vibrate and this breaks the hydrogen bonds and ionic bonds that hold their structure so they unfold. Their tertiary structure changed and cannot change back again when they cool- they are denatured.

51
Q

What happens if both membrane embedded proteins and the cytoskeleton threads become denatured?

A

The plasma membrane will begin to fall apart. It will become more permeable as holes will appear in it

52
Q

What is the role of cholesterol in a cell surface membrane in the human body?

A

It binds to the phospholipid fatty- acid tails, increasing the packing of the membrane, therefore reducing the fluidity of the membrane

53
Q

What does isotonic mean?

A

Water solution inside the cell is equal to the outside of the cell there is no net movement

54
Q

How does the fluid mosaic model describe the structure of plasma membranes?

A

As phospholipid are able to move around in the membrane so it is fluid. It has a mosaic pattern as it has protein channels and carriers embedded in it

55
Q

Why can’t glucose pass through cell membranes via simple diffusion?

A

Because it is too large to pass through the membrane and it is rejected by the hydrophobic tails

56
Q

Roles of membranes in organisms?

A
  • Prevents them from busting
  • Contains receptors so it is involved in cell signalling
  • Keeps toxic substances out of the cell
57
Q

What is the structure of the cell surface membrane?

A

It is made up of the lipid bilayer which is made up of two layers of phospholipid molecules with the hydrophilic heads on the surface. It has carrier and channel proteins embedded in it making it partially permeable as they are specific to certain molecules. It has cholesterol in it which gives mechanical stability and flexibility and also maintains the membranes fluidity. It also has glycolipids and glycoproteins on the outside of the membrane from carbohydrate chains which act as receptors in cell signalling

58
Q

Why is it good to repeat experiments?

A

It identifies any anomalies and helps to get averages

59
Q

What is a partially permeable membrane?

A

When the membrane doesn’t let all types of molecules pass through them

60
Q

Why is cholesterol good for cell membranes?

A
  • Helps to regulate the fluidity of the membrane
  • Maintain mechanical stability
  • Resist the effects of temperature changed on the structure of the membrane
61
Q

What do various proteins in the cell membrane do?

A
  • Some of them have pores and act as channels to allow ions, which have an electrical charge and are surrounded by water molecules, to pass through
  • Some proteins are carriers and, by changing their shape, carry specific molecules across the membrane
  • Other proteins may be attached to the carrier proteins and function as enzymes, antigens of receptor sites for complementary- shapes signalling chemicals e.g. hormones
62
Q

What is the effect of fluidity?

A
  • Membrane permeability
  • Membrane embedded proteins and the reactions they are involved in. May move around or clump together
  • The folding of the membrane for phagocytosis
  • Cell communication by limiting exocytosis
63
Q

What does cholesterol do in high and low temperatures?

A
  • In high temperatures it blocks the phospholipids up to decrease permeability
  • In low temperatures it acts like the unsaturated tails do by preventing the close packing of the phospholipids
64
Q

What does ethanol and acetone do to cell membranes?

A

They break down cell membranes causing them to become more permeable this is because lipids dissolve in acetone and ethanol so it would break down the phospholipid bilayer

65
Q

What does hypertonic mean?

A

Very concentrated solution, less water

66
Q

What does hypotonic mean?

A

More dilute solution, more water

Biology Miss Negus (4 decks)

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