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module two biology > biological membranes > Flashcards

biological membranes Flashcards

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1
Q

What do plasma membranes do? ( surface of cells)

A

• barrier between a cell and its environment
• partially permeable
• allow cell recognition
• allow cell communication/cell signalling)

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2
Q

What do membranes within cells do?

A

• organise organelles into compartments (compartmentalisation)
• act as a barrier between the organelle and the cytoplasm
• control what substances enter and leave the organelle (partially permeable).
• can form vesicles to transport substances
• site of chemical reactions

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3
Q

What structure do cell membranes have?

A

a fluid mosaic structure

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4
Q

What are cell membranes composed of?

A

• lipids
• proteins
• carbohydrates

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5
Q

Describe the fluid mosaic structure

A

Phospholipids form a continuous double bilayer which is fluid. This is because they are constantly moving. Protein molecules are scattered through the bilayer like tiles in a mosaic

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6
Q

What is a glycoprotein?

A

a carbohydrate attached to a protein in the phospholipid bilayer

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7
Q

What’s a glycolipid?

A

a carbohydrate attached to a lipid in the phospholipid bilayer

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8
Q

Describe phospholipid molecules in cell membranes

A

They have a head (hydrophilic) and a tail (hydrophobic) which automatically arrange into a bilayer. The centre is hydrophobic so water soluble substances like ions can’t pass through but vitamins and fat soluble substances can dissolve through.

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9
Q

Describe cholesterol in the phospholipid bilayer

A

Cholesterol is a type of lipid which fits in between the phospholipids, binding to the hydrophobic tails causing them to pack more closely together, making it less fluid and more rigid.

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10
Q

What is the function of proteins in a phospholipid bilayer?

A

Proteins form channels in the membrane allowing small or charged particles through. Carrier proteins transport molecules and ions across the membrane by active transport and facilitated diffusion. They also act as receptor molecules in cell signalling, as when a molecule binds to a protein, a chemical reaction is triggered inside of the cell.

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11
Q

Describe the function of glycolipids and glycoproteins

A

They stabilise the membrane by forming hydrogen bonds with surrounding water molecules, and are also sites where drugs hormones and antibodies bind. They act as receptors in cell signalling, and are also antigens involved in the immune response.

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12
Q

How do cells communicate with each other?

A

Cell signalling
• one cell releases a messenger molecule such as a hormone
• this molecule travels in the blood to another cell
• this messenger molecule is detected by the cell because it binds to a receptor on its cell membrane

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13
Q

Describe proteins as receptors

A

They are referred to as membrane bound receptors, and they have specific shapes, only messenger molecules with a complementary shape can bind to it. Different cells have different receptors, a cell that responds to a particular receptor molecule is called a target cell.

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14
Q

What’s an example of a messenger molecule?

A

Glucagon
• glucagon is a hormone releases when there isn’t enough glucose in the blood. It binds to receptors on liver cells causing them to break down glycogen stores into glucose.

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15
Q

Other than messenger molecules, what can bind to cell membrane receptors?

A

Drugs
• many drugs work by binding to receptors in cell membranes, they either trigger a response in the cell or block the receptor and prevent it from working

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16
Q

What’s an example of a drug that binds to cell membrane receptors?

A

Antihistamines
• cell damage causes the release of histamine, this binds to receptors in the surface of other cells and causes inflammation, anti histamines work by blocking histamine receptors on cell surfaces which prevents histamine from binding and causing inflammation

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17
Q

How can you investigate the permeability of the cell membrane in the lab?

A
  1. Cut five equal sized pieces of beetroot and rinse them to remove any pigment released during cutting
  2. Place the five equal pieces in five different test tubes with 5 cm of water
  3. Place each test tube in a water bath at a different temperature e.g 10, 20, 30 etc
  4. Remove the pieces of beetroot leaving just the coloured liquid
  5. Now use a colorimeter, the higher the permeability of the membrane the more pigment is released, so the higher the absorbable of the liquid
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18
Q

What is the permeability of the cell membrane affected by?

A

• temperature
• solvent type
• solvent concentration

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19
Q

What does increasing the temperature do to membrane permeability?

A

Increase the permeability

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20
Q

What happens to the cell membrane at temperatures below 0?

A

The phospholipid don’t have much energy so they can’t move very much. They’re packed closely together and the membrane is rigid. Channel proteins and carrier proteins in the membrane deform and this increases the permeability. Ice crystals may form which causes the membrane to become pierced which makes it highly permeable when it thaws

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21
Q

What happens to the cell membrane at temperatures between 0 and 40°?

A

The phospholipids can move around and aren’t packed as tightly together - the membrane is partially permeable. As the temperature increases the phospholipids move more because they have more energy, increasing permeability

22
Q

What happens to the cell membrane at temperatures above 45°?

A

The phospholipid bilayer starts to melt and the membrane becomes more permeable. Water inside the cell expands putting more pressure on the membrane. Chanel proteins and carrier proteins deform so they can’t control what enters and leaves a cell - increasing the permeability.

23
Q

What happens when a cell membrane is surrounded in a solvent?

A

The permeability increases as solvents dissolve the lipids in a cell membrane causing it to loose its structure

24
Q

Define diffusion

A

The net movement of particles from an area of higher concentration to lower concentration.

25
Q

Is diffusion active or passive?

A

Passive - no energy is needed

26
Q

What is the concentration gradient? And which way do particles dissolve?

A

The path from an area of high concentration to lower concentration. Particles diffuse down a concentration gradient

27
Q

What molecules can get through phospholipids in the cell membrane?

A

Small, non polar molecules such as oxygen and carbon dioxide. Water is also small enough to fit between phospholipids so it’s able to diffuse across plasma membranes even though its polar

28
Q

What does the rate of diffusion depend on?

A

• the concentration gradient
• the thickness of the exchange surface
• the surface area
• the temperature

29
Q

How can you investigate diffusion?

A
  1. Make up some agar jelly with phenolphthalein and dilute sodium hydroxide
  2. Fill a beaker with some dilute HCl and using a scalpel cut out a few cubes from the jelly and put them in the beaker of acid
  3. If you leave the cubes for a while they will eventually turn colourless as the acid diffuses into the agar jelly and neutralises the sodium hydroxide
30
Q

How do larger molecules such as ions glucose and amino acids diffuse into the phospholipid bilayer?

A

Through carrier proteins and channel proteins, via facilitated diffusion, this moves down a concentration gradient and doesn’t require energy - it’s passive.

31
Q

How do carrier proteins move large molecules into the phospholipid bilayer?

A

A large molecule attaches to a carrier protein in the membrane and then the protein changes shape. This releases the molecule in the opposite side of the membrane

32
Q

How to channel proteins move substances through the phospholipid bilayer?

A

Channel proteins form pores in the membrane for charged particles to diffuse down through. Different channel proteins facilitate the diffusion of different charged particles

33
Q

Describe how active transport moves substances into the phospholipid bilayer

A

• an active process (requiring energy)
• similar to facilitated diffusion and involves a carrier protein
• a molecule attaches to a carrier protein and changes shape and this moves the molecule across the membrane releasing it on the other side.
• the only difference is that energy is used from ATP to move the solute against its concentration gradient.

34
Q

How do cells take in substances?

A

Endocytosis

35
Q

Describe endocytosis

A

When molecules are too large to be taken in by carrier proteins, a cell can surround a substance with a section of its plasma membrane. This then pinches off to form a vesicle inside the cell containing the ingested substance. Some cells take in larger objects to destroy them, for example white blood cells

36
Q

Is endocytoisis active or passive?

A

Active

37
Q

How do cells secrete substances?

A

Exocytosis
• some substances produced by the cell such as digestive enzymes need to be released from the cell

38
Q

How do cells secrete substances by exocytosis?

A

Vesicles containing these substances pinch off from the sacs of the golgi apparatus and move toward the plasma membrane, these fuse with the plasma membrane and release their contents outside of the cell

39
Q

Is exocytosis active or passive?

A

Active - requires ATP

40
Q

Describe osmosis

A

The diffusion of water molecules across a partially permeable membrane down a water potential gradient . This means water molecules move from an area of higher water potential to an area of lower water potential.

41
Q

What is water potential?

A

The potential of water molecules to diffuse out of or into a solution

42
Q

What has the highest water potential?

A

Pure water

43
Q

What is a solution with a higher water potential than the cell called?

A

Hypotonic solution.

44
Q

What might a hypertonic solution do in an animal cell?

A

Cause the cell to burst

45
Q

What is a solution with the same water potential as the cell called?

A

Isotonic solution

46
Q

What happens in an isotonic solution in animal cells?

A

Water molecules pass into and out of the cell in equal amounts, the cell stays the same

47
Q

What are solutions with a lower water potential than the cell called?

A

Hypertonic solutions

48
Q

What may hypertonic cells do in animal cells?

A

Cause the cell to shrink due to net movement out of it

49
Q

What do hypertonic solutions do in plant cells?

A

They cause the cell to become flaccid and the cytoplasm and membrane to pull away from the cell wall (plasmolysis) due to net movement of water out of the cell

50
Q

What do hypotonic solutions cause in plant cells?

A

They cause the vacuole to swell and the vacuole and cytoplasm to push against the cell wall (turgid), due to net moment into the cell

51
Q

How can you investigate water potential?

A

By using potato cylinders
1. Prepare sucrose solutions from 0.0 to 1.0M ( going up by 2 each time)
2. Use a cork to cut potato cylinders into the same size pieces, roughly 1 cm in diameter
3. Use a mass balance to weigh the potato cylinders individually
4. Place one potato in each solution
5. Leave the potatoes in the solution for 20 minutes
6. Remove the potatoes and blot with a tissue
7. Weigh each potato again individually
8. Calculate the percentage change in mass and plot on a graph

module two biology (7 decks)

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