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biological membranes 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
What are passive processes in cell membranes?
Substances which pass through the cell membrane without using metabolic energy or ATP, only kinetic energy
26
What do cells need to export?
waste - carbon dioxide molecules - enzymes, hormones, signalling molecules
27
What do cells need to import?
raw materials - oxygen, glucose
28
Describe simple diffusion (3)
- passive movement of small, non polar lipid soluble molecules - from area of high concentration to an area of low concentration
29
Molecules which can cross the membrane through diffusion (3)
oxygen, water, carbon dioxide, fat-soluble molecules
30
How do fat-soluble molecules pass through the lipid bilayer?
dissolve in the phospholipid bilayer (fatty acid tails) and diffuse through
31
What kind of molecules can dissolve in the lipid bilayer?
non-polar molecules, as fatty acid tails of phospholipids are non-polar
32
Why can water diffuse through the phospholipid bilayer?
although water is polar, it is a small molecule so it can diffuse between phospholipids or through channels called aquaporins
33
What are aquaporins?
channel proteins for water
34
Which molecules cannot dissolve in the lipid bilayer?
polar molecules (fat-soluble molecules)
35
Define osmosis
- diffusion of water molecules from are of low solute concentration to area of high solute concentration through partially permeable membrane
36
How does dissociation of solute molecules lower water potential?
when solutes dissociate, split into two ions - doubles number of molecules in the solution, lowering water potential
37
What is a solvent?
liquid medium in which the solvent is dissolved
38
What is a solute?
substance which is dissolved in the solvent
39
What is an aqueous solution?
a solution in which water is the solvent
40
How does water diffuse through the plasma membrane?
osmosis - straight through pores or channels called aquaporins
41
What is water potential?
- measure of tendency of water molecules to diffuse from one region to another
42
How is water potential measured?
kPa (kilaPascals) Pure water is 0 kPa and highest water potential
43
How would you describe water potential in cells?
lowered due to solutes in cytoplasm/vacuole
44
What causes a lower water potential?
solutes in solution,
45
What is cytolysis?
water moves in and the cell swells and eventually bursts
46
What is turgidity?
water moves into plant cell by osmosis and cell swells, exerts pressure on cell wall, which prevents cell from bursting
47
What is a plasmolysed cell?
plant cell loses water until cell membrane pulls completely away from cell wall
48
What happens when animal cell placed in solution of lower water potential?
water leaves by osmosis, cell shrivels and becomes crenated
49
What does crenated mean?
animal cell has lost water, becomes shrivelled and wrinkled
50
What happens when plant cells are placed in solution of lower water potential?
water leaves cell by osmosis, cytoplasm shrinks and pulls away from cell wall cell described as plasmolysed and flaccid cannot continue metabolism
51
What is a flaccid cell?
plant cell has lost water by osmosis, cell membrane does not exert pressure on the cell wall, vacuole smaller/shrunken
52
What is active transport?
- movement of molecules from area of low concentration to an are of high concentration - requires energy from ATP
53
When does active transport occur?
when more substance is required than could be gained by diffusion alone
54
Example of active transport
mineral ions into root hair cells
55
Describe the structure and action of carrier proteins
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
What is bulk transportation?
Transport of large molecules through plasma membrane using energy from ATP
57
What are two bulk transportation processes?
endocytosis and exocytosis
58
What is endocytosis?
large molecules entering cell, uses ATP
59
Describe endocytosis
- particles enclosed in vesicles from plasma membrane - transported into cell - uses ATP
60
What is phagocytosis?
form of endocytosis, intake of solid matter into cell
61
What is pinocytosis?
form of endocytosis, intake of liquid matter into cell
62
What is exocytosis?
large molecules exported from cell using ATP
63
Describe the process of exocytosis
- vesicles containing large molecules moves to and fuses with plasma membrane
64
Give an example of exocytosis
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
When is ATP needed in endo/exocytosis?
to move vesicles, and to fuse membranes
66
Effect on phospholipids when temperature drops
fatty acids compress, unsaturated fats push adjacent phospholipids apart due to kinks in tails, maintains fluidity
67
What is ATP?
energy store - ' - used by all cells to release energy for metabolic processes
68
Where are fatty acids found in membrane?
inside, away from aqueous solution (hydrophobic), part of phospholipid
69
Difference between saturated and unsaturated fatty acids
unsaturated have a double bond, a kink in chain, which pushes atoms apart - more fluid
70
How do fatty acids determine the fluidity of the plasma membrane?
unsaturated fatty acids make more fluid due to the kinks in the chains
71
Role of cholesterol when temperature changes
Buffers effects of temperature, prevents phospholipids packing too closely becoming rigid, or from becoming too fluid
72
Effect on phospholipids when temperature increases
move , increasing fluidity; permeability increases; affects protein positions, if proteins drift can alter rate of reactions; may affect cell signalling and phagocytosis
73
How does temperature increase affect proteins in the plasma membrane?
as becomes more fluid proteins may drift altering rate of reactions/transport. Also may damage enzymes at high temperatures, lowering rate of reactions
74
Which processes in the plasma membrane are affected by increasing the temperature?
enzyme catalysed reactions, phagocytosis, cell signalling
75
How does increase temperature affect phagocytosis?
affects infolding of the plasma membrane during process
76
How is cell signalling affected by increase in temperature?
change ability of cells to release chemicals by exocytosis due to effects on the plasma membrane
77
Structural effects of high temperature on membrane proteins
atoms vibrate and hydrogen/ionic bonds break, tertiary structure unfolds; shape changes irreversibly, denatured
78
What happens if the membrane proteins and the cytoskeleton threads denature?
Plasma membrane begins to fall apart, becomes more permeable/porous
79
Effect of non-polar solvents on phospholipids
organic solvents like acetone and ethanol damage cell membranes as they dissolve lipids (alcohols)
80
Two solvents which can damage the cell membrane
acetone and ethanol
81
What is a cell membrane?
partially permeable barrier
82
What are integral/intrinsic proteins?
proteins within the membrane - carrier and channel proteins
83
What are extrinsic proteins?
peripheral proteins
84
How do channel proteins attract water/solutes?
lined with hydrophillic amino acids
85
How does ice affect phospholipid membrane at low temperatures?
ice crystals can pierce the membrane, causing increased fluidity
86
Describe facilitated diffusion
- needs channel protein in cell membrane to transport polar molecules and water soluble molecules across membrane - can use carrier proteins
87
is facilitative diffusion an active or passive process
passive, does need energy from ATP

Biology (18 decks)

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