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H2 Biology > Cell Membrane and Transport Across Membrane > Flashcards

Cell Membrane and Transport Across Membrane Flashcards

1
Q

Functions of a biological membrane (5)

A

1) Defines cell’s boundaries
2) Organisation and localisation of function
3) Regulates cell contents
4) Signal Transduction
5) Mediates cell-to-cell communication and adhesion

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2
Q

How does the membrane’s selective permeability help in its function?

A

It allows desirable substances to be kept within and undesirable substances to be kept out of the cell

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3
Q

S->F: Definition of cell’s boundaries

A

The hydrophobic core of the membrane keeps cell interior physically separated from the surrounding environment

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4
Q

S->F: organisation and localisation of function

A

Molecules or structures with specific functions are embedded in membranes or localised within organelles

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5
Q

S->F: Regulation of cell’s contents

A

Proteins and other components like cholesterol embedded in the membrane help to regulate transport of substances into and out of the cell and organelles

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6
Q

S->F: Signal Transduction

A

Specific protein receptors on the outer surface of the cell membrane are crucial in detecting specific signals and triggering specific responses within the cell

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7
Q

S->F: Cell-to-cell communication and adhesion

A

Membrane proteins bind to the extracellular matrix or cell surface constituents to mediate adhesion and communication between adjacent cells

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8
Q

‘Fluid’ in Fluid Mosaic Model (FMM) (3)

A

1) * the membrane is composed of two layers, consisting of mainly phospholipids
2) Phospholipids, cholesterol and some proteins are free to move about laterally within the membrane, within (laterally) or between (flip transversely) layers

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9
Q

‘Mosaic’ in Fluid Mosaic Model (FMM)

A

proteins are randomly distributed and attached to the phospholipid bilayer, which is asymmetrical on the two lipid layers

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10
Q

In the FMM, the membrane is viewed as _____

A

a collage of proteins randomly distributed and attached to the fluid phospholipid bilayer which is free to move about laterally

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11
Q

Characteristics of FMM (4)

A

1) bilayer is asymmetrical
2) bilayer is fluid
3) unit membrane is dynamic
4) membranes are amphipathic

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12
Q

Asymmetry of phospholipid bilayer: Two lipid layers may differ in
(__________ __ _____ & ____)

A

composition/arrangement of proteins and lipids

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13
Q

Dynamism of membranes: Embedded proteins can float, some (________) while others are
(_________) by (_____________)

A

some moving freely; fixed in positions; microfilaments on the cytoplasmic face

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14
Q

Amphipathicity of membranes

A

Phospholipids have a hydrophilic phosphate head and hydrophobic hydrocarbon tail

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15
Q

Where do the head and tail of phospholipids face?

A

1) p. head face outwards into aqueous environment both inside and outside the cell
3) Hydrocarbon tails face inwards and create a hydrophobic core

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16
Q

Three types of lipids

A

1) Phospholipids
2) *Cholesterol
3) Glycolipids

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17
Q

Why can phospholipids move about laterally?

A

Hydrophobic interactions between hydrophobic fatty acid tails are weak

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18
Q

Why is it rare for phospholipids to flip transversely across the membrane?

A

Hydrophilic head must cross the hydrophobic core of the membrane to do so

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19
Q

Factors affecting membrane fluidity (and their relationship) (4)

A

1) Temperature (Temp. ↓ , MF ▼)
2) Length of fatty acid chains (length 🠕, MF ▼)
3) Degree of saturation of fatty acid chains (degree of saturation 🠕, MF ▼)
4) Amt. of cholesterol (effect on MF depends on temp.)

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20
Q

Effect of low temp. on MF (3)

A

1) KE of hydrocarbon chains decreases
2) Hydrocarbon chains are more tightly packed => stronger hydrophobic interactions between phospholipids molecules => restricted motion
3) bilayer exists in semi-solid state (less fluid)

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21
Q

Effect of increased fatty acid chain length on MF

A

Melting point increases due to increased hydrophobic interactions

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22
Q

Effect of saturated lipids on MF (3)

A

1) they have long. straight hydrocarbon chains 2) -> allows for close packing ( 🠕 hydrophobic interactions)
3) enhances membrane solidification

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23
Q

Effect of unsaturated lipids on MF

A

have kinks -> prevent hydrocarbon chains from packing closely tgt => enhances membrane fluidity

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24
Q

Effect of amt of cholesterol on MF (2)

A

it increases stability and regulates membrane fluidity in ANIMAL cells

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25
Q

Effect of high temp. on MF (4)

A

1) KE 🠕, motion of hydrocarbon chains 🠕
2) allows for 🠕 lateral movements of individual molecules => overcoming hydrophobic interactions between phospholipids
3) -> increased space between adjacent phospholipids
4) bilayer exists in fluid state (more fluid)

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26
Q

Cholesterol [definition]

A

steroids commonly found wedged between phospholipid molecules in cell membranes of ANIMAL cells

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27
Q

How does cholesterol decrease membrane fluidity at high temperatures?

A

restrains mvmt of phospholipids by interfering with motions of HC chains

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28
Q

How does cholesterol increase membrane fluidity at low temperatures?

A

prevents HC chains from packing closely together => ▼ tendency of membrane to freeze

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29
Q

How does cholesterol decrease membrane permeability?

A

fills in gaps between HC chains (plugs transient gaps thru which molecules might pass)

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30
Q

Molecules that are prevent from passing thru the membrane by cholesterol

A

Ions and polar molecules

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31
Q

2 broad categories of membrane proteins

A

integral and peripheral proteins

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32
Q

Location of integral proteins

A

deeply embedded in hydrophobic interior of lipid bilayer

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33
Q

Two sub-categories of integral proteins

A

Unilateral and Transmembrane

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34
Q

Diff. in location between 2 sub-categories of integral proteins

A

unilateral: reaches only a monolayer
transmembrane: spans entire bilayer

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35
Q

Location of peripheral proteins

A

loosely bound to membrane surface, often to exposed parts of integral proteins

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36
Q

Why can’t peripheral proteins on cytoplasmic side move far?

A

they are held by microfilaments of cytoskeleton

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37
Q

Peripheral proteins on exterior side are attached to ________

A

fibres of extracellular matrix

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38
Q

Structure of integral proteins

A

contain both hydrophilic and hydrophobic regions (i.e. amphipathic)

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39
Q

What contributes to the hydrophilicity and hydrophobicity of integral proteins?

A

charged and polar aa; non-polar aa

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40
Q

What interactions hold intrinsic proteins in place?

A

EXTENSIVE hydrophobic interactions with HC portions of phospholipids

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41
Q

Structure of peripheral proteins

A

rich in hydrophilic aa (mainly hydrophilic)

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42
Q

Purpose of hydrophilic aa in extrinsic proteins

A

allows for interaction with surrounding water and polar surface of lipid bilayer

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43
Q

Solubility of integral VS peripheral proteins in aqueous media

A

insoluble (int.) ; soluble (peripheral)

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44
Q

What interactions hold extrinsic proteins in place?

A

ionic interactions between hydrophilic portions of integral proteins or polar phosphate heads and the peripheral proteins

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45
Q

How integral proteins are released from membranes

A

Use of detergents/non-polar solvents

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46
Q

How peripheral proteins are released from membranes

A

adjusting ionic strength/pH of suspending medium

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47
Q

Functions of membrane proteins (6)

A

1) Anchorage
2) Transport
3) Enzymatic activity
4) Signal Transduction
5) Cell-to-cell recognition
6) Intercellular joining

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48
Q

Structure of carbohydrates

A

short, branched chains of fewer than 15 sugar units

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49
Q

Structure of glycolipids

A

carbohydrates covalently bonded to glycerol backbone

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50
Q

Bonds in glycolipids

A

glycosidic, ester

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51
Q

Structure of glycoproteins

A

carbohydrates covalently bonded to membrane proteins

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52
Q

Bonds in glycoproteins

A

glycosidic, ionic, hydrogen, peptide,

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53
Q

S->F: Maintenance of orientation of glycoproteins and glipids

A

As carbohydrates highly hydrophilic, carbohydrate chain kept in contact with external aqueous environment and unlikely to flip transversely to face cell interior

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54
Q

Functions of glipids and gproteins

A

1) Sorting of cells into tissues and organs in animal embryos
2) Binding extracellular signal molecules in antibody-antigen reactions
3) Intercellular adhesion to form tissues
4) Cell-to-cell recognition (usually glycoproteins)

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55
Q

Add. function of glycolipids

A

fluidity and gas diffusion (lipids)

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56
Q

Function of anchoring proteins : attach (______), stabilise (______) , help maintain (_______), coordinate (____________) changes

A

cell membrane to other substances; position of cell membrane; cell shape; extracellular and intracellular (proteins attached to extracellular matrix)

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57
Q

Anchoring proteins are bound to _____ on cytoplasmic site

A

Microfilaments of cytoskeleton

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58
Q

Anchoring proteins are attached to _____ on exterior side

A

Fibres of extracellular matrix

59
Q

Disruptions in cell-cell adhesion can contribute to _____ _____ __ ______.

A

Metastasis stage of cancer

60
Q

Two types of transport proteins

A

Carrier and channel

61
Q

How do carrier proteins transport solutes?

A

They bind solutes and transport them across the membrane

62
Q

Differences between carrier and channel proteins (2)

A

1) Binding site for solutes VS central hydrophilic pore
2) Undergoes conformational change VS does not undergo CC to transport substances across membrane

62
Q

When does conformational change of the transport protein happen?

A

when solute binding occurs

63
Q

When does the carrier protein return to its original form?

A

Solute is released

64
Q

Two processes carrier protein can participate in

A

Facilitated diffusion (no ATP) and Active transport (ATP required)

64
Q

Structure of channel proteins [type of protein, property]

A

integral proteins that contain a water-filled central pore/hydrophilic channel

65
Q

S->F of channel proteins:

A

The hydrophilic channel forms a passage way to permit the mvmt of water, ions and small hydrophilic solutes across the cell membrane

66
Q

Two types of channels

A

1) Leak
2) Gated

67
Q

Leak channels permit the mvmt of _____/_____ at all times

A

Water;ions

67
Q

Gated channels can _____/_____ to ____________

A

Open or close to regulate ion passage

68
Q

Voltage-gated Na+/K+ channels

A

Examples of gated channels

69
Q

Where do the enzymes embedded in the membrane catalyse reactions?(2)

A

In the extracellular fluid/cytosol, depending on location of active site

70
Q

several enzymes can be (______ ________) to carry out (________ ____) in a (_______) pathway.

A

Grouped tgt; sequential steps; metabolic pathway

71
Q

S->F of membrane proteins: Signal transduction

A

Proteins have very specific 3D conformation, thus are ideal as receptor molecules for chemical signalling between cells

72
Q

Mechanism of chemical signalling

A

A ligand binds to the receptor protein, triggering changes in the cell

74
Q

Why do different cell types have diff sensitivities to hormones and neurotransmitters?

A

Cell membranes have different type and number of receptor proteins

74
Q

Recognition proteins are usually

A

Glycoproteins

76
Q

Each cell type has its own (______ ______s), with (__________ ____ ____) of a unique (______).

A

Specific markers ; carbohydrate side chains; shape

77
Q

S->F: recognition proteins as specific markers

A

This allows cells to recognise other cells, and hence allow foreign markers to be recognised and attacked by the immune system

79
Q

Examples of intercellular junctions

A

Gap junctions and tight junctions

80
Q

Main reason why transport across membrane is vital

A

To maintain a suitable pH and ionic conc. within the cell for enzyme activity

81
Q

Intercellular joining: membrane proteins of adjacent cells may (_____) tgt in various kinds of (_________ _______)

A

Adhere, intercellular junctions

82
Q

Differences between passive and active processes (2)

A

Occurs down VS against conc. gradient
No ATP VS ATP required

82
Q

Examples of active transport processes (3)

A

Active transport, endocytosis, exocytosis

84
Q

Diffusion [defintion]

A

Net mvmt of a substance from a region of higher conc. to a region of lower conc., down a conc. gradient, (until dynamic equilibrium is reached)

86
Q

Dynamic equilibrium is reached when

A

conc. of the substance is equal on both sides of membrane

86
Q

Simple diffusion occurs for what molecules?

A

molecules w small molecular weight/hydrophobic molecules (i.e. can cross the phospholipid bilayer directly)

88
Q

When dynamic equilibrium is reached,

A

No net mvmt of substances occur

89
Q

Facilitated diffusion occurs for what molecules?

A

Larger, hydrophilic substances

90
Q

“Facilitated” in FD

A

Transport proteins are used to enhance/increase rate of transport of substance across membrane (channel/carrier-mediated)

91
Q

Comparison between simple and facilitated diffusion (molecules, mediated, energy)

A

1) Occurs for molecules with simple molecular weight/hydrophobic VS larger, hydrophilic substances
2) Occurs directly across plasma membrane without aid VS mediated by transport (carrier/channel) proteins
3) Both passive processes, no ATP required

92
Q

Comparison between facilitated diffusion and osmosis (molecules, mvmt thru what, driving force)

A

1) mvmt of water molecules VS larger molecules e.g. glucose, aa, ions
2) mvmt of molecules across selectively permeable membrane VS thru transport protein
3) occurs due to water potential gradient VS conc. Gradient

93
Q

Factors affecting rate of diffusion (6)

A

1) Conc. Gradient
2) Distance over which diffusion occurs
3) SA across which diffusion occurs
4) Structure through which diffusion occurs (gaps, proteins)
5) Size of molecule
6) Temperature

94
Q

Effect of thickness of membrane on no. of molecules that can diffuse per unit time

A

Thinner the cell membrane, the greater the no. of molecules that can diffuse per unit time

95
Q

Effect of gaps in the membrane and transport proteins on diffusion rate

A

1) presence of transient gaps in membrane enhance diffusion
2) type and number of transport proteins present per unit surface area of membrane affects diffusion rate

96
Q

Effect of surface area on the rate of diffusion

A

Larger the SA, the greater the no. of molecules that can diffuse across per unit time, hence the faster the diffusion process

97
Q

Water potential ψ [definition]

A

A measure of the tendency for water to move from one region to another

98
Q

Sign of Solute potential Ψ s

A

negative

99
Q

Sign of Pressure potential

A

Positive

100
Q

Water potential in plant cell is ________________

A

The sum of its solute potential and pressure potential

101
Q

The water potential of animal cell is determined primarily by _______

A

Its solute potential

102
Q

Solute potential [definition]

A

The measure of the ability of a solute to make the WP more negative

103
Q

How does dissolving of solute molecules in pure water lower WP?

A

It reduces the number of free water molecules as they bind to water molecules.

104
Q

The more solute molecules present, _______________, and hence ____________.

A

The more neg. the solute potential (greater ability to make WP more negative), the more neg. the WP

105
Q

Pressure potential Ψ p [definition]

A

The measure of the pressure exerted by the cell wall on its contents

106
Q

Why is Ψ p a positive value?

A

It tends to move water out of the cell

107
Q

Why does WP become less negative if pressure if applied to water/solution?

A

It forces water to move from one place to another

108
Q

Ψ p increases as__________________.

A

Plant cell absorbs water and increases in water

109
Q

Implication of less negative water potential: water is (____ ______) to enter the plant cell

A

Less likely

110
Q

Plant cell in solution of less neg. WP (WP of cell, mvmt of water, change to cell)

A

1) WP in cell is more negative than that of the solution
2) Water enters cell by osmosis from the solution
3) Cell swells and become turgid

111
Q

Plant cell in solution of equal WP (WP of cell, mvmt of water, change to cell)

A

1) WP in cell is equal to that of solution
2) No net mvmt of water
3) no change in cell volume

112
Q

Plant cell in solution of more neg. WP (WP of cell, mvmt of water, change to protoplast)

A

1) WP in cell is less negative than that of solution
2) Water leaves cell via osmosis.
3) protoplasm shrinks and eventually pulls away from cell wall

113
Q

Order of water leaving the plant cell

A

First: water is lost from cytoplasm thru the cell membrane
Second: from the vacuole thru the tonoplast

114
Q

Plasmolysis [definition]

A

Process where Protoplast shrinks and pulls away from the cell wall

115
Q

Incipient plasmolysis [definition]

A

Point at which plasmolysis begins (when 50% of plant cells are plasmolysed)

116
Q

At incipient plasmolysis: the protoplast had just ______ to _______ any ______ against the ____ ____

A

Ceased; exert; pressure; cell wall

117
Q

State of cell at incipient plasmolysis

A

Flaccid

118
Q

What happens to animal cell in hypotonic solution

A

Cell swells and lyses due to lack of cell wall

119
Q

What happens to animal cell in isotonic solution?

A

No change in cell vol.

120
Q

What happens to animal cell in hypertonic solution?

A

Cell becomes crenated/shriveled

121
Q

Active transport [definition]

A

Mvmt of substances from region of lower conc. To a region of higher conc., against the conc. Gradient

122
Q

Active transport occurs for

A

Ions and small hydrophilic molecules

123
Q

Which type of transport proteins is used for active transport?

A

Carrier proteins

124
Q

Why is conformational change necessary for active transport?

A

To ensure that solutes do not leak back across the membrane down the concentration gradient

125
Q

Step 1 of AT: solutes on the (_________ ____) of the plasma membrane bind to (_______ _______ _____) on the transport protein.

A

Cytoplasmic side, specific binding sites

126
Q

Step 2: ATP transfers a (________ _____) to the transport protein.

A

Phosphate group

127
Q

Step 3: Protein changes its (___________), causing the solute to be (________) on the (_____ ____) of the membrane.

A

Conformation; released; other side

128
Q

Step 4: the phosphate group (______) and the transport proteins returns to its (______ __________).

A

Detaches; original conformation

129
Q

Primary active transport involves

A

The direct use of ATP by a carrier protein to transport solutes

130
Q

Uniport VS symport VS antiport (transport of molecules across membrane)

A

Only 1 substance VS 2 substances tgt in the same direction VS 2 substances tgt in opposite directions

131
Q

Example of antiport

A

Sodium-potassium pump

132
Q

Endocytosis and exocytosis occur for what molecules?

A

Macromolecules such as proteins, polysaccharides, enzyme complexes

133
Q

Exocytosis [definition]

A

A process where the cell secretes macromolecules (into extracellular fluid) by fusion of vesicles with the plasma membrane

134
Q

Where do vesicles for exocytosis come from?

A

Usually bud off from ER or Golgi apparatus

135
Q

Function of exocytosis: used by (_________ ____) for the (_____) of products or the (_________) of waste materials.

A

Secretory cells; export; removal

136
Q

Endocytosis [definition]

A

A process where the cell takes in macromolecules by the folding in of the plasma membrane to form vesicles

137
Q

How do vesicles in endocytosis form?

A

They form from a localised region of the plasma membrane that folds inwards and then pinches off into the cytoplasm

138
Q

Function of endocytosis

A

Used by cells to incorporate extracellular substances

139
Q

Types of endocytosis (refer to Google doc for more)

A

1) Phagocytosis
2) Pinocytosis
3) Receptor mediated endocytosis

140
Q

How are voltage gated channels activated?

A

Changes in voltage (charge) across membranes

141
Q

Explain the importance of active transport in a cell.

A

Enables a cell to maintain internal concentrations of molecules that are much higher or lower in concentration than that in the extracellular environment.

142
Q

Facilitated Diffusion [definition]

A

Transport of solutes down a concentration gradient, with the aid of a transport protein embedded in the membrane

143
Q

Effect of high temp. on membrane permeability (4)

*describe effect on both phospholipids and membrane proteins

A

1) KE of HC chains of phospholipids increases
2) allows for increased lateral movements of individual molecules => overcoming hydrophobic interactions between phospholipids
3) -> more transient pores between adjacent phospholipids
4) membrane proteins denature at high temperatures

H2 Biology (4 decks)

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