Cell Membranes And Membrane Transport 2.2-2.4 and CP3 Flashcards

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1
Q

Describe the fluid mosaic model

A
  • Phospholipid belayer is constantly moving, therefore it’s fluid
  • Protein molecules are scattered through the bilayer , like tiles in a mosaic, which can also move
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2
Q

Describe a phospholipid molecule

A
  • Phosphate head is hydrophilic so attracts water

- Fatty acid (x2) tail is hydrophobic

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3
Q

How is the bilayer orientated and what does this prevent?

A
  • The hydrophilic heads face outwards towards the water

- The hydrophobic tails face the centre which prevents water-soluble substances, such as ions, from passing through

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4
Q

What does it mean that the membrane is ‘partially permeable’?

A
  • Small molecules move through gaps between the phospholipids
  • Large molecules and ions can only pass through channel proteins and carrier proteins
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5
Q

What did scientists think of the cell membrane pre-1970s?

A

Originally thought there were two protein layers with a phospholipid layer in the middle = 3 layers

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6
Q

What experiment did scientists do to prove the model is ‘fluid’?

A

Fused a mouse cell with a human cell = membrane proteins of both organisms had intermixed throughout the cell membrane

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7
Q

What types of molecule are found in a membrane?

A
  • Glycoproteins
  • Glycolipids
  • Cholesterol
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8
Q

What are glycoproteins?

A

Proteins with a polysaccharide chain

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9
Q

What are glycolipids?

A

Lipids with a polysaccharide chain attached

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10
Q

Where does cholesterol attach? What does it provide?

A

Fits in between the phospholipids to form bonds with them
It allows the membrane to be more rigid
At lower temperatures cholesterol makes the membrane more fluid

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11
Q

What is osmosis?

A

The net movement of water molecules across a partially permeable membrane from an area of high water potential to low water potential.
(Water molecules diffuse both ways)

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12
Q

What kind of process is osmosis, diffusion and facilitated diffusion?

A

Passive process

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13
Q

When would facilitated diffusion be used?

A

When large molecules or ions that can’t diffuse through the phospholipid bilayer want to get across the membrane

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14
Q

What is facilitated diffusion?

A

The movement of molecules down a concentration gradient using carrier or channel proteins and not requiring energy

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15
Q

What size molecules do carrier proteins transport?

A

Large molecules

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16
Q

How do carrier proteins work in facilitated diffusion?

A

1) A large molecules attached to the carrier protein
2) The protein changes shape
3) The molecules is release on the opposite side of the membrane

17
Q

What type of molecules do channel proteins allow through?

A

Charged particles

18
Q

How do channel proteins work in facilitated diffusion?

A

They form pores in the membrane

19
Q

What is active transport?

A

Uses energy and carrier proteins to move molecules and ions against a concentration gradient

20
Q

What’s the difference between active transport and facilitated diffusion?

A
  • Active transport requires energy from the hydrolysis of ATP
  • Active transport only uses carrier proteins, not channel proteins
21
Q

What size of molecules are transported by endocytosis?

A

Very large molecules eg. Proteins , lipids and carbohydrates

22
Q

How does endocytosis work?

A
  • Cell membrane surrounds the molecule(s)

- The membrane pinched off to form a vesicle containing the ingested substance

23
Q

Do endocytosis and exocytosis require energy?

A

Yes, through the hydrolysis of ATP

24
Q

Give an example of a cell that uses endocytosis

A

White blood cell (phagocytes) inject microorganisms and dead cells

25
Q

What type of substances are removed by exocytosis?

A

Digestive enzymes, hormones, lipids

26
Q

How does exocytosis work?

A
  • Vesicles which contain the substance pinch off from the sacs of Golgi apparatus and move towards cell membrane
  • Vesicle fuses with csm and release contents out of cell
27
Q

Describe an experiment to investigate how temperature affects beetroot membrane permeability:

A

1) use a scalpel to cut 5 equal sized pieces of beetroot and rinse to remove any pigment released during cutting
2) Use a pipette to measure 5cm ³ of water into 5 different test tubes
3) Place the test tubes into water baths at different temperatures (10, 20, 30, 40, 50) and leave for 5 mins to acclimatise
4) Place the pieces of beetroot into the test tubes and record for a period of time
5) Remove pieces of beetroot from tubes to leave behind coloured liquid
6) Measure absorbency of coloured liquid with a colorimeter (see separate card)

28
Q

How does a colorimeter work?

A

Machine passes light of a specific wavelength through a liquid and measures how much light is absorbed

29
Q

Describe the steps in taking a colorimeter reading?

A

1) Switch on and allow colorimeter to stabilise for 5 mins
2) Select blue filter (wavelength 470nm) and use pure water to calibrate machine to zero
3) Use a pipette to transfer sample of beetroot liquid to cuvette until it’s three-quarters full
4) Put cuvette in colorimeter and record absorbance
5) Repeat for remaining 4 test tubes

30
Q

What’s the relationship between the absorbance and permeability?

A

The higher the absorbance the less light is passing through the solution which means more pigment has been released so the higher the permeability of the membrane

31
Q

Describe membrane permeability at temperatures below 0 degrees Celsius:

A
  • Phospholipids have limited energy so can’t move as much
  • Membrane is rigid as packed close together
  • HOWEVER Channel proteins and carrier proteins in membrane deform increasing the permeability
  • Ice crystals pierce membrane making it highly permeable when it thaws
32
Q

Describe membrane permeability at temperatures between 0-45 degrees Celsius:

A
  • Phospholipids can move around and aren’t as tightly packed together (partially permeable)
  • As temp increases the phospholipids move as they have more energy which increases permeability
33
Q

Describe membrane permeability at temperatures above 45 degrees Celsius:

A
  • Phospholipid bilayer starts to melt and membrane becomes more permeable
  • Water inside the cell expands putting pressure on the membrane
  • Channel and carrier proteins deform so can’t control what enters or leaves the cell
34
Q

Describe relationship between alcohol concentration and membrane permeability + why:

A

As alcohol concentration increases, the permeability go through cell membrane increases because alcohol dissolves the lipids in the cell membrane so loses its structure