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biosci > Structure and Function of the Cell Membrane > Flashcards

Structure and Function of the Cell Membrane Flashcards

1
Q

What are the two main consitutients of the cell membrane

A

Phospholipids and proteins

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2
Q

What is the structure of the membrane

A

A think, 8nm flexible and sturdy barrier that surrounds the cytoplasm of a cell.

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3
Q

Describe the fluid mosaic modle of the membrane

A
  • “sea of lipids in which proteins float like icebergs”
  • membrane is 50% lipid and 50% protein
  • lipid is barrier to entry and exit of polar substances
  • proteins are “gatekeepers”
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4
Q

What type of bonds hold the membrane together

A

Hydrogen bonds

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5
Q

What is the lipid bilayer of the cell membrane

A

Two back-to-back layers of 3 types of lipid molecules

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6
Q

What are scattered among a double row of phospholipid molecules

A

Cholestrol and glycolipids

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7
Q

What are phospholipids

A

A lipid consisting of a phosphate molecule

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8
Q

What is the phospholipid bilayer

A

In water, most phospholipds form a lipid bilayer structure with polar head groups at the surface in contact with water and the fatty acid chains in the core screened from water contact.

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9
Q

What percentage of lipids are phospholipids

A

75%

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10
Q

What is an important feature of the hydrophobic core

A

Provides a highly impermeable barrier to the passage of charged ions.

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11
Q

What does the cell membrane control

A

The passages of substances in and out of the cells

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12
Q

By having the cell membrane control the passages of substances in and out of the cell, what does this allow

A
  • maintain concentration gradients
  • spatial organsiaton of chemical and physical processes within the cell
  • controlled uptake of nutrietns and discharge of waste products and secretion of molecules
  • developement of membrane potential
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13
Q

What does it mean by membrane fluidity

A

Membranes are fluid structures and lipids can move around within the plane of the membrane leaflet

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14
Q

How is the lipid composition of the leaflets assymetric

A

Lipids rarely flip-flop between membrane leaflets

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15
Q

What is membrane fluidity determined by

A
  • lipid tail length: longer the tail, the less fluid the membrane
  • Number of double bones: more increases fluidity
  • amount of cholestrol: more decreases fluidity
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16
Q

What are the two basic classes of membrane proteins

A

Integral and peripheral

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17
Q

What are integral membrane proteins

A

They extend into or completly across teh cell membrane (transmembrane protein)

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17
Q

Are integral membrane proteins amphiphatic or not

A

They are amphiphatic - they have hydrophobic regions that span the hydrophobic core of the lipid bilayer. These regions usually consist of non polar amino acids coiled into helices. The hydrophilic ends of the proteins interact with the aqueous solution.

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18
Q

What do the hydrophobic regions on integram membranes consist of

A

These regions consists of non-polar amino acids coiled into helices. The hydrophobic ends of the proteins interact with the aqueous solution

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19
Q

What are peripheral membrane proteins

A

They are attatched to either the inner of outer surface of the cell membrane and can be easily removed from it as well.

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20
Q

6

What can membrane proteins act as

A
  • receptors
  • cell identity markers
  • linkers
  • enzymes
  • channels
  • transporters
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21
Q

What are two common transport functions of membrane proteins

A

Ion channel and carrier.

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22
Q

What is an ion channel (integral)

A

Forms a pore through which a specific ion can flow to get across membrane. Most plasma membranes include specific channels for several common ions.

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23
Q

What is a carrier/transporter (integral)

A

Transports a specific substances across membrane by undergoing a change in shape. Also known as a transporter

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24
Q

What is an example of the use of a carrier (integral)

A

Amino acids needed to synthesise new proteins, enter body cells via carriers.

25
Q

What is permeability

A

Ability of a particular molecule to cross a cell membrane

26
Q

What does the permeability of a molecule depend on

A

The molecule’s size, charge and lipid solubility.

27
Q

The lipid bilayer is permeable to what

A
  • Non-polar uncharge molecules (O2, N2, benzne)
  • lipid soluble molecules (steroids, fatty acids, vitamins
  • small uncharged polar molcules: water, urea, glycerol, CO2
28
Q

What is the lipid bilayer impermeable to

A
  • large uncharged poalar molecules: glucose, amino acids
  • ions: Na+, K+, Cl-, Ca2+, H+
29
Q

Membrane proteins mediate the transport of substances across the membrane that can not permeate what

A

the hydrophobic core of the lipid bilayer

30
Q

Diffusion

A

The random mixing of particles in a solution as a result of the particle’s kinetic energy. More molecules move away from an area of high concentraion to an area of low concentration.

31
Q

For diffusion, is the rate of diffusion faster or slower when there is a higher temperature.

A

Faster

32
Q

For diffusion, is the rate of diffusion faster or slower when there is a larger size of the diffusion substance

A

Slower

33
Q

For diffusion, is the rate of diffusion faster or slower when there is an increase in surface area

A

Faster

34
Q

For diffusion, is the rate of diffusion faster or slower when increasing the diffusion distance

A

Slower

35
Q

What is diffusion

A

Random mixing of particles in a solution as a result of a particle’s kinetic energy.

36
Q

To increase diffusion, a cell can increase the ___

A

Membrane area available for exchange (diffusion) of a substance.

37
Q

How does membrane thickness affect diffusion

A

The thicker the membrane, the slower the rate of diffusion

38
Q

What are the two gradients across the cell membrane

A

Concentration and electrical gradient

39
Q

Concentration gradient

A

When non-charged molecules diffuse down their concentration gradients

40
Q

Electrical gradient

A

Ions will be influenced by membrane potential in addition to their concentration gradient.

41
Q

Movement of ions are influenced by what

A

Electrochemical gradient

42
Q

The selective permeability of the membrane enables a difference in what

A

Concentration or concentration gradient

43
Q

How is an electrochemical gradient established

A

Cells can maintain a difference in charged ions between the inside and outside of membrane, establishing an electrochemical gradient.

44
Q

Cells use what to maintain concentration and electrochemical gradients

A

~30% of resting energy

45
Q

What is osmosis

A

Net movement of water through a selectively permeable membrane from an area of high concentration to an area of lower water concentration.

46
Q

Osmosis occurs if what

A

Membrane is permable to water but not to certain solutes.

47
Q

Osmotic water can be prevented by what

A

An opposing force

48
Q

Pf is mediated by what

A

Aquaporins (isoforms)

49
Q

Properties of Pd

A
  • small
  • mercury insensitive
  • temp dependent (liquid fluidity)
50
Q

Properties of Pf

A
  • large
  • mercury sensitive
  • temp independent
51
Q

What is osmotic pressure

A

Pressure applied to a solution to prvent the inward flow of water across a semi-permeable membrane.

52
Q

if the solution has the same osmolarity, it is what?

A

Isosmotic

53
Q

If the solution has lower osmolarity, it is what?

A

Hyposmotic

54
Q

If the solution has a higher osmolarity, it is what

A

Hyperosmotic

55
Q

What is tonicity

A

The effect a solution has on cell volume.

56
Q

What is tonicity dependent on

A

The membrane permeability of the solute. Hence the osmolarity of a solution does not alwas indicate the effect it will have on cell volume.

57
Q

What is an isotonic solution

A

No change in cell volume

58
Q

What is hypotonic solution

A

Cause cell swelling and eventually cell lysis

59
Q

What is hypertonic solution

A

Causes cell shrinkage

biosci (28 decks)

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