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A Level Biology > Cell Membranes > Flashcards

Cell Membranes Flashcards

1
Q

Which model describes the structure of cell membrane?

A

Fluid Mosaic Model

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2
Q

Why is cell membranes structure described as fluid mosaic?

A

Fluid - phospholipids can move freely past each other (within a particular layer)
Mosaic - proteins embedded in the membrane are various shapes, sizes and patterns

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3
Q

Name the molecules involved in cell membranes?

A

Phospholipids
Channel protein (intrinsic)
Carrier protein (intrinsic)
Extrinsic Proteins
Glycolipid
Glycoprotein
Cholesterol

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4
Q

What are the roles of cell membranes?

A
  • Boundary separating cell contents from cytoplasm/outside world
  • Cell recognition and signalling
  • Holding components for some metabolic pathways
  • Regulation of cells in/out of
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5
Q

What can pass through the phospholipid bilayer?

A

LIPID SOLUBLE (non-polar) molecules can diffuse through

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6
Q

What is the purpose of the phospholipids in the bilayer?

A

They make the cell membrane flexible and self-sealing

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7
Q

What are extrinsic proteins?

A

Proteins found on the surface of either side of the membrane bilayer

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8
Q

What are intrinsic proteins?

A

Extends across/through both layers of the membrane (bilayer)

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9
Q

What are two types of intrinsic proteins?

A

Carrier Proteins
Channel Proteins

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10
Q

What is the function of channel proteins?

A

Allow water soluble molecules (polar/ionic) to pass through

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11
Q

What is the purpose of carrier proteins?

A

They bind to solute/molecules which fit into the binding site this causes a conformational (shape) change transferring the molecule from one side to of the membrane to the other

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12
Q

What is a glycoprotein?

A

A protein with a carbohydrate group/chain attached to it

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13
Q

What is a glycolipid?

A

A lipid molecule with a carbohydrate chain (made from monosaccharides) attached to it

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14
Q

What is the function of a glycolipid?

A
  • Act as cell surface receptors for specific chemicals ( basis of ABO blood system)
  • Helps maintain stability of membrane and attach cells to one another to form tissue
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15
Q

What is the function of a glycoprotein?

A
  • Acts as cell surface receptors (eg. For hormones)
  • Helps attach cells to one another to form tissues
  • Allows cells to recognise each other (eg. Lymphocytes recognise organisms body cells)
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16
Q

Where is Cholesterol found?

A

Between phospholipid tails

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17
Q

What is cholesterol?

A

It’s a molecule made from 4 hydrocarbon rings
Has a polar head (due to OH group) so can associate with phospholipid heads

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18
Q

What type of molecule is cholesterol?

A

STEROID

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19
Q

What is the purpose of Cholesterol?

A

Adds strength and rigidity to the membrane by pulling fatty acid tails closer together
Prevents loss of water and dissolved ions from the cell (stops leaking)

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20
Q

What are the two types of transport across membranes?

A

Passive
Active Transport

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21
Q

What does passive transport across a membrane refer to?

A

Does not require any external energy (ATP)

22
Q

What does active transport across a membrane refer to?

A

Requires energy in the form of ATP (to move molecules against the concentration gradient)

23
Q

What are the two types of passive transport across membranes?

A

Simple diffusion
Facilitated diffusion

24
Q

Define diffusion?

A

The net movement of particles from a region of high concentration to a region of low concentration down the concentration gradient until equilibrium is reached

25
Q

What is simple diffusion?

A

Diffusion directly across the phospholipid bilayer (small, lipid soluble, uncharged molecules like oxygen)

26
Q

What type of molecules move by simple diffusion?

A

Small
Lipid Soluble
Uncharged molecules

27
Q

What is facilitated diffusion?

A

Diffusion using channel and carrier proteins (water soluble molecules -mainly ions/polar)

28
Q

What type of molecules are transported across membranes using channel proteins (by facilitated diffusion)?

A

Small, water-soluble molecules (mainly ions/polar)
Eg. Na+, H+ ions

29
Q

What type of molecules are transported across membranes using carrier proteins (by facilitated diffusion)?

A

Larger, water-soluble molecules like glucose and amino acids

30
Q

Why does the transport rate plateau when facilitated diffusion occurs?

A

There are on,y so many transport proteins that become saturated

31
Q

Define active transport?

A

The movement of particles into or out of a cell from a region of lower concentration to a region of higher concentration (against the concentration gradient) using ATP and carrier proteins

32
Q

Explain the process of active transport?

A
  • The molecule or ion to be transported across the membrane binds to the specific carrier proteins on one side of the membrane (at the binding site)
  • on the inside of the membrane, ATP binds it the carrier protein at the ATP binding site, causing it to hydrolyse into ADP and Pi (releasing the ADP and energy)
  • This causes the carrier protein to change shape and open to the opposite side of the membrane (releasing the molecule/ion to the opposite side)
  • The Pi is released from the carrier protein causing it to revert back to its original shape
  • The process can then be repeated
33
Q

Describe the process of the Sodium-Potassium pump?

A
  • 3 sodium ions bind to the binding site of carrier protein
  • ATP bonds to the ATP binding site and is hydrolysed releasing ADP and energy whilst Pi remains
  • Carrier proteins changes shape (due to energy) and 3 sodium ions are released against the concentration gradient
  • Whilst carrier protein is open to opposite side the 2 potassium ions bind to the specific binding site
  • Inorganic phosphate is released from the binding site causing it to revert back to the original shape
  • 2 potassium ions are released (against the concentration gradient)
34
Q

Describe the process of glucose and amino acid co-transport?

A

The sodium potassium pump moves sodium out of the epithelial cells into the bloodstream by facilitated diffusion whilst potassium is moved into the cell
The sodium concentration inside the epithelial cells decrease whilst the sodium in the ileum is high. This leads to passive diffusion of sodium ions into the epithelial cells ( down the conc. gradient)
There is a low concentration f glucose/amino acids in the ileum and a high concentration in the epithelial cells.
Co-transport proteins move sodium ions (passively diffusing down the concentration gradient) alongside glucose/amino acids against their concentration gradient
Now there is a high concentration of glucose/amino acids in the epithelial cells causing it to diffuse through the phospholipid bilayer by facilitated diffusion into the bloodstream

35
Q

Define osmosis?

A

The passive movement of water from a region of high potential to a region of low water potential through a selectively permeable membrane

36
Q

Which direction does water always move?

A

Down the water potential gradient

37
Q

What does the symbol mean 🔱?

A

Water potential

38
Q

What does water potential mean?

A

It’s a measure of how free water molecules are to move (potential to do osmosis)

39
Q

What is the water potential of pure water.

A

🔱 = 0

40
Q

How does the addition of solute do to the water potential?

A

It reduces it to a negative value

41
Q

Why does adding solvent reduce the water potential?

A

As water is dipolar it is attracted to the solvent charge (so is less able to move)

42
Q

What does it mean when the solution is hypotonic?

A

There is a higher water potential outside the cell due to a lower solute concentration (than on the inside) causing the net movement of water to move into the cell

43
Q

What does it mean when the solution is isotonic?

A

There is the same water potential outside the cell and the solute concentration is the same causing there to be no net movement of water

44
Q

What does it mean when the solution is hypertonic?

A

There is a lower water potential outside the cell due to a higher solute concentration (than on the inside) causing the net movement of water to move out of the cell

45
Q

What happens to animal cells in isotonic conditions?

A

There’s no net movement of water so the cells remain the same

46
Q

What happens to animal cells in hypotonic conditions?

A

Water enters the cell which may cause it to burst (lyses)

47
Q

What happens to animal cells in hypertonic conditions?

A

Water leaves the cell causing it to shrink/shrivel (crenation)

48
Q

What happens to plant cells in isotonic conditions?

A

There is no net movement of water so incipient plasmolysis occurs (cell membrane starts to pull away from the cell wall)

49
Q

What happens to plant cells in hypotonic conditions?

A

Vacuole fills with water, turgid pressure develops and the chloroplasts are seen next to the cell wall

50
Q

What happens to plants cells in hypertonic conditions?

A

Vacuoles lose water and the cytoplasm shrinks (PLASMOLYSIS) and chloroplasts appear at the centre of the cell because the cell membrane has pulled away from the cell wall

51
Q

What are the two types of bulk transport?

A

Endocytosis
Exocytosis

A Level Biology (15 decks)

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