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biological membranes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Three ways molecules pass in/out of cell membranes

A
  • Small molecules diffuse between structural molecules
  • Dissolve in lipid layers and pass through
  • protein channels or carrier proteins
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2
Q

Roles of the cell surface membrane (6)

A
  • separates from external environment
  • regulates transport of materials in/out
  • contains enzymes for metabolic pathways and chemical reactions
  • antigens, so not attacked by immune system
  • release signalling chemicals
  • receptors for chemical signals like hormones or drugs
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3
Q

Example of reaction occurring in membranes in chloroplasts

A

thylakoids and thylakoid membrane site of photosynthesis, contain chlorophyll

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4
Q

Example of reaction occurring in membranes in small intestine

A

membranes of epithelial cells, digestive enzymes help break down sugars

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5
Q

Example of reaction occurring in membranes in mitochondria

A

membrane cristae, large sa, site of aerobic respiration

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6
Q

Three examples of reactions which occur in membranes

A

photosynthesis at thylakoid membrane, respiration in cristae, digestion in epithelial cells

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7
Q

Explain the fluid mosaic model

A

Phospholipid bilayer, with floating proteins, no regular pattern, creates mosaic style. Lipids can move and change places giving fluidity

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8
Q

Who proposed the fluid mosaic model?

A

1972, Singer and Nicolson

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9
Q

What does the fluid mosaic model allow?

A

passage of molecules through the membrane, more dynamic and more interaction with environment

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10
Q

Describe the phospholipid bilayer

A

Phospholipids with hydrophillic phosphate heads pointing towards water and hydrophobic tails tucked inside in two layers.

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11
Q

Name components of cell surface membrane (10)

A
  • glycoprotein
  • protein receptor site
  • phospholipid
  • carrier protein
  • cholesterol
  • glycolipid
  • channel protein
  • cytoskeleton filaments
  • peripheral protein
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12
Q

Name proteins found in plasma membrane (7)

A
  • glycoproteins
  • protein receptor sites
  • proteins
  • carrier proteins
  • channel proteins
  • peripheral proteins
  • cytoskeleton filaments
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13
Q

Name lipids found in the plasma membrane

A
  • phospholipids
  • glycolipid
  • cholesterol
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14
Q

Three roles of cholesterol

A
  • regulates fluidity of the membrane
  • maintain mechanical stability
  • resists effects of temperature on structure of the membrane
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15
Q

What is glycoalyx?

A

combination of glycolipids and glycoproteins formed by carbohydrates on the outside of the membrane

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16
Q

What does glycoalyx do?

A

hydrophilic helps cell interact with watery environment and attract dissolved substances

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17
Q

What do protein channels do?

A

allow charged ions to pass across the membrane

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18
Q

What do carrier proteins do?

A

change shape to carry specific molecules across the membrane

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19
Q

Roles of proteins attached to carrier proteins

A

could be antigens, enzymes or receptor sites, various functions

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20
Q

How are the axon membranes of neurones adapted?

A

channels and carriers cover axon, allow entry/exit of ions, conduct action potentials

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21
Q

How are the myelin membranes of neurones adapted?

A

flattened cells wrapped around neurone several times, numerous membranes with about 20% protein 76% lipid

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22
Q

How are the plasma membranes of white blood cells adapted?

A

special protein receptors to recognise foreign antigens of pathogens or tissues (e.g, organ transplant)

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23
Q

Adaptation of root hair cells and their membrane

A

Many carrier proteins to actively transport nitrate ions into cell

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24
Q

Adaptations of membrane of mitochondria

A

many electron carriers and hydrogen ion channels associated with ATP synthase enzymes for respiration

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25
Q

What are passive processes in cell membranes?

A

Substances which pass through the cell membrane without using metabolic energy or ATP, only kinetic energy

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26
Q

What do cells need to export?

A

waste - carbon dioxide
molecules - enzymes, hormones, signalling molecules

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27
Q

What do cells need to import?

A

raw materials - oxygen, glucose

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28
Q

Describe simple diffusion (3)

A
  • passive movement of small, non polar lipid soluble molecules
  • from area of high concentration to an area of low concentration
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29
Q

Molecules which can cross the membrane through diffusion (3)

A

oxygen, water, carbon dioxide, fat-soluble molecules

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30
Q

How do fat-soluble molecules pass through the lipid bilayer?

A

dissolve in the phospholipid bilayer (fatty acid tails) and diffuse through

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31
Q

What kind of molecules can dissolve in the lipid bilayer?

A

non-polar molecules, as fatty acid tails of phospholipids are non-polar

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32
Q

Why can water diffuse through the phospholipid bilayer?

A

although water is polar, it is a small molecule so it can diffuse between phospholipids or through channels called aquaporins

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33
Q

What are aquaporins?

A

channel proteins for water

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34
Q

Which molecules cannot dissolve in the lipid bilayer?

A

polar molecules (fat-soluble molecules)

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35
Q

Define osmosis

A
  • diffusion of water molecules from are of low solute concentration to area of high solute concentration through partially permeable membrane
36
Q

How does dissociation of solute molecules lower water potential?

A

when solutes dissociate, split into two ions - doubles number of molecules in the solution, lowering water potential

37
Q

What is a solvent?

A

liquid medium in which the solvent is dissolved

38
Q

What is a solute?

A

substance which is dissolved in the solvent

39
Q

What is an aqueous solution?

A

a solution in which water is the solvent

40
Q

How does water diffuse through the plasma membrane?

A

osmosis - straight through pores or channels called aquaporins

41
Q

What is water potential?

A
  • measure of tendency of water molecules to diffuse from one region to another
42
Q

How is water potential measured?

A

kPa (kilaPascals)
Pure water is 0 kPa and highest water potential

43
Q

How would you describe water potential in cells?

A

lowered due to solutes in cytoplasm/vacuole

44
Q

What causes a lower water potential?

A

solutes in solution,

45
Q

What is cytolysis?

A

water moves in and the cell swells and eventually bursts

46
Q

What is turgidity?

A

water moves into plant cell by osmosis and cell swells, exerts pressure on cell wall, which prevents cell from bursting

47
Q

What is a plasmolysed cell?

A

plant cell loses water until cell membrane pulls completely away from cell wall

48
Q

What happens when animal cell placed in solution of lower water potential?

A

water leaves by osmosis, cell shrivels and becomes crenated

49
Q

What does crenated mean?

A

animal cell has lost water, becomes shrivelled and wrinkled

50
Q

What happens when plant cells are placed in solution of lower water potential?

A

water leaves cell by osmosis, cytoplasm shrinks and pulls away from cell wall
cell described as plasmolysed and flaccid
cannot continue metabolism

51
Q

What is a flaccid cell?

A

plant cell has lost water by osmosis, cell membrane does not exert pressure on the cell wall, vacuole smaller/shrunken

52
Q

What is active transport?

A
  • movement of molecules from area of low concentration to an are of high concentration
  • requires energy from ATP
53
Q

When does active transport occur?

A

when more substance is required than could be gained by diffusion alone

54
Q

Example of active transport

A

mineral ions into root hair cells

55
Q

Describe the structure and action of carrier proteins

A

have region which binds with molecule/ion and region acts as enzyme, binds and allows hydrolysis ATP to release energy, helps change conformational shape, carries molecule to other side of protein

56
Q

What is bulk transportation?

A

Transport of large molecules through plasma membrane using energy from ATP

57
Q

What are two bulk transportation processes?

A

endocytosis and exocytosis

58
Q

What is endocytosis?

A

large molecules entering cell, uses ATP

59
Q

Describe endocytosis

A
  • particles enclosed in vesicles from plasma membrane
  • transported into cell
  • uses ATP
60
Q

What is phagocytosis?

A

form of endocytosis, intake of solid matter into cell

61
Q

What is pinocytosis?

A

form of endocytosis, intake of liquid matter into cell

62
Q

What is exocytosis?

A

large molecules exported from cell using ATP

63
Q

Describe the process of exocytosis

A
  • vesicles containing large molecules moves to and fuses with plasma membrane
64
Q

Give an example of exocytosis

A

chemical neurotransmitters in vesicles are released into the synapse from the presynaptic membrane. motor proteins and cytoskeleton threads move vesicle, and fuses with the membrane.

65
Q

When is ATP needed in endo/exocytosis?

A

to move vesicles, and to fuse membranes

66
Q

Effect on phospholipids when temperature drops

A

fatty acids compress, unsaturated fats push adjacent phospholipids apart due to kinks in tails, maintains fluidity

67
Q

What is ATP?

A

energy store -
‘ - used by all cells to release energy for metabolic processes

68
Q

Where are fatty acids found in membrane?

A

inside, away from aqueous solution (hydrophobic), part of phospholipid

69
Q

Difference between saturated and unsaturated fatty acids

A

unsaturated have a double bond, a kink in chain, which pushes atoms apart - more fluid

70
Q

How do fatty acids determine the fluidity of the plasma membrane?

A

unsaturated fatty acids make more fluid due to the kinks in the chains

71
Q

Role of cholesterol when temperature changes

A

Buffers effects of temperature, prevents phospholipids packing too closely becoming rigid, or from becoming too fluid

72
Q

Effect on phospholipids when temperature increases

A

move , increasing fluidity;
permeability increases;
affects protein positions, if proteins drift can alter rate of reactions;
may affect cell signalling and phagocytosis

73
Q

How does temperature increase affect proteins in the plasma membrane?

A

as becomes more fluid proteins may drift altering rate of reactions/transport. Also may damage enzymes at high temperatures, lowering rate of reactions

74
Q

Which processes in the plasma membrane are affected by increasing the temperature?

A

enzyme catalysed reactions, phagocytosis, cell signalling

75
Q

How does increase temperature affect phagocytosis?

A

affects infolding of the plasma membrane during process

76
Q

How is cell signalling affected by increase in temperature?

A

change ability of cells to release chemicals by exocytosis due to effects on the plasma membrane

77
Q

Structural effects of high temperature on membrane proteins

A

atoms vibrate and hydrogen/ionic bonds break, tertiary structure unfolds;
shape changes irreversibly, denatured

78
Q

What happens if the membrane proteins and the cytoskeleton threads denature?

A

Plasma membrane begins to fall apart, becomes more permeable/porous

79
Q

Effect of non-polar solvents on phospholipids

A

organic solvents like acetone and ethanol damage cell membranes as they dissolve lipids (alcohols)

80
Q

Two solvents which can damage the cell membrane

A

acetone and ethanol

81
Q

What is a cell membrane?

A

partially permeable barrier

82
Q

What are integral/intrinsic proteins?

A

proteins within the membrane - carrier and channel proteins

83
Q

What are extrinsic proteins?

A

peripheral proteins

84
Q

How do channel proteins attract water/solutes?

A

lined with hydrophillic amino acids

85
Q

How does ice affect phospholipid membrane at low temperatures?

A

ice crystals can pierce the membrane, causing increased fluidity

86
Q

Describe facilitated diffusion

A
  • needs channel protein in cell membrane to transport polar molecules and water soluble molecules across membrane
  • can use carrier proteins
87
Q

is facilitative diffusion an active or passive process

A

passive, does need energy from ATP

Biology (18 decks)

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