B2.1 Membranes and Membrane Transport Flashcards
1
Q
What is the primary function of cell membranes?
A
To enclose the contents of the cell and separate intracellular components from the external environment
This allows for the control of internal conditions within the cell and the maintenance of homeostasis.
2
Q
What are the two key qualities of cell membranes that promote homeostatic regulation?
A
- Semi-permeability
- Selectivity
Semi-permeability allows only certain materials to cross, while selectivity enables the cell to control the passage of materials.
3
Q
What are the main components of cell membranes?
A
- Phospholipids
- Proteins
These components work together to form the structure and function of the membrane.
4
Q
What is the role of the phospholipid bilayer in cell membranes?
A
Acts as a barrier to certain materials and is semi-permeable
The bilayer structure restricts the passage of large and charged substances.
5
Q
What characteristic of hydrocarbon chains in the phospholipid bilayer affects permeability?
A
They are hydrophobic and have low permeability to large and charged substances
This means that large compounds and hydrophilic particles cannot cross the bilayer.
6
Q
What is the function of membrane proteins in cell membranes?
A
They act as points of transport for large and charged substances
This enables the selective transport of hydrophilic materials according to cellular needs.
7
Q
What type of molecules cannot cross the phospholipid bilayer?
A
- Large compounds
- Hydrophilic particles (ions and polar molecules)
Their size and polarity prevent them from freely crossing the bilayer.
8
Q
What are the components of the polar head of phospholipids?
A
A glycerol and a phosphate molecule
9
Q
What do the non-polar tails of phospholipids consist of?
A
Fatty acid (hydrocarbon) chains
10
Q
What classification do phospholipids fall under due to their structure?
A
Amphipathic
11
Q
What is the arrangement of phospholipids in membranes?
A
They spontaneously arrange into a bilayer
12
Q
Which regions of the phospholipid bilayer face inwards?
A
The hydrophobic tail regions
13
Q
What do the hydrophilic head regions of the phospholipid bilayer associate with?
A
The cytosolic and extracellular fluids
14
Q
What type of interactions hold the phospholipid bilayer together?
A
Weak hydrophobic interactions
15
Q
What does the presence of hydrophilic and hydrophobic layers in the bilayer do?
A
Restricts the passage of many substances
16
Q
What allows for membrane fluidity and flexibility?
A
The movement of individual phospholipids within the bilayer
17
Q
What processes are facilitated by the fluidity of the phospholipid bilayer?
A
Endocytosis and exocytosis
18
Q
What are phospholipid bilayers embedded with?
A
Proteins, which may be either permanently or temporarily attached to the membrane
These proteins play various roles in cell function.
19
Q
What are integral proteins?
A
Proteins that penetrate the phospholipid bilayer to remain permanently attached to the membrane
Integral proteins include glycoproteins, ion channels, carrier proteins, and protein pumps.
20
Q
What happens to transmembrane proteins if the bilayer is disrupted?
A
They cannot be readily isolated without disrupting the bilayer
Disruption can occur using detergents.
21
Q
What are peripheral proteins?
A
Proteins that are only temporarily associated with one side of a membrane
They can be removed by polar solvents.
22
Q
How are peripheral proteins typically attached?
A
They are attached to integral proteins, linked to the polar heads of the bilayer, or held in place by the cytoskeleton or extracellular matrix
Examples include receptor complexes involved in cell signaling.
23
Q
What determines the composition of a membrane protein?
A
Its function within the cell
This affects how the protein interacts with the membrane.
24
Q
What type of amino acids associate with the lipid bilayer?
A
Non polar amino acids (hydrophobic)
These help anchor the protein within the membrane.
25
What type of amino acids face the aqueous solutions?
Polar amino acids (hydrophilic)
## Footnote
This orientation helps in interactions with the surrounding environment.
26
What lines the inner surface of a protein channel?
Polar amino acids
## Footnote
This facilitates the passage of specific polar or charged molecules.
27
What are the functions of membrane proteins? List them.
* Junctions
* Enzymes
* Transport
* Recognition
* Anchorage
* Transduction
## Footnote
Each function plays a critical role in cellular processes.
28
What is the function of junctions in membrane proteins?
To connect and join two cells together
## Footnote
This is essential for tissue formation and communication.
29
What role do enzymes play when fixed to membranes?
They localize metabolic pathways
## Footnote
This enhances the efficiency of biochemical reactions.
30
What is facilitated diffusion?
A transport mechanism responsible for moving substances across the membrane
## Footnote
It does not require energy.
31
True or False: Membrane proteins can function as markers for cellular identification.
True
## Footnote
This is part of the recognition function of membrane proteins.
32
What is the anchorage function of membrane proteins?
Providing attachment points for the cytoskeleton and extracellular matrix
## Footnote
This supports cell structure and stability.
33
What do membrane proteins transduce?
Peptide hormones
## Footnote
They act as receptors to initiate cellular responses.
34
What is glycosylation?
The process of attaching carbohydrate chains to phospholipids or membrane proteins
## Footnote
'Glyco' means sugar.
35
What is produced when a phospholipid undergoes glycosylation?
A glycolipid
36
What is produced when a membrane protein undergoes glycosylation?
A glycoprotein
37
Where are the carbohydrate chains located in relation to the cell membrane?
On the extracellular side of the membrane
38
What roles do surface carbohydrates play?
Cell adhesion and cell recognition
## Footnote
Examples include sperm binding to an egg and ABO blood group antigens.
39
How do glycoproteins facilitate sperm binding to an egg?
By acting as attachment points on the surface carbohydrates
40
What are the ABO blood group antigens classified as?
Glycolipids
41
What role do glycoproteins and glycolipids play in the extracellular matrix?
Maintaining structural integrity
42
What is the extracellular matrix?
A network for external molecules providing structure and biochemical support to surrounding cells
43
How do carbohydrate chains contribute to the extracellular matrix?
By linking extracellular molecules together to create a cohesive network
44
What model represents cell membranes due to their characteristics?
Fluid-mosaic model
## Footnote
The fluid-mosaic model accounts for the dynamic nature of cell membranes, which contain both fluid and structural components.
45
What does the term 'Fluid' signify in the fluid-mosaic model?
The phospholipid bilayer is viscous and individual phospholipids can move position
## Footnote
This fluidity allows for the flexibility and functionality of cell membranes.
46
What does the term 'Mosaic' signify in the fluid-mosaic model?
The phospholipid bilayer is embedded with proteins, resulting in a mosaic of components
## Footnote
This mosaic includes various types of proteins that perform different functions.
47
How should phospholipids be arranged when drawing the fluid-mosaic model?
In a bilayer, with the polar and non-polar regions identified
## Footnote
This arrangement is crucial for maintaining the integrity of the cell membrane.
48
Where should glycoproteins and glycolipids face in the fluid-mosaic model?
The extracellular side of the membrane
## Footnote
This orientation is important for cell recognition and signaling.
49
How should integral proteins be represented in the fluid-mosaic model?
Embedded within the bilayer
## Footnote
Integral proteins often span the membrane and are involved in transport and communication.
50
Where should peripheral proteins be anchored in the fluid-mosaic model?
To one side of the membrane
## Footnote
Peripheral proteins typically play roles in signaling and maintaining the cell's shape.
51
What role does cholesterol play in animal cell membranes?
Included between the fatty acid tails
## Footnote
Cholesterol helps to stabilize membrane fluidity and integrity.
52
What characteristic do cell membranes exhibit?
Fluidity
## Footnote
Cell membranes are not fixed in position and can adopt amorphous shapes.
53
What affects the fluidity of a membrane?
The composition of fatty acids within the phospholipid bilayer
## Footnote
Different types of fatty acids influence how lipids pack together.
54
What is the effect of unsaturated fatty acids on lipid chains?
They have double bonds resulting in a kinked hydrocarbon tail
## Footnote
This structure makes it harder for lipids to pack together.
55
How do unsaturated fatty acids affect membrane viscosity and fluidity?
Lower viscosity and increased fluidity
## Footnote
The kinked structure allows for more movement within the membrane.
56
What is the melting point of unsaturated fatty acids?
Lower melting points
## Footnote
This characteristic contributes to increased fluidity and flexibility at cellular temperatures.
57
What is the effect of saturated fatty acids on lipid chains?
No double bonds resulting in a straight hydrocarbon tail
## Footnote
This structure allows lipids to pack more tightly.
58
How do saturated fatty acids affect membrane viscosity and fluidity?
Higher viscosity and lower fluidity
## Footnote
The straight structure enables tighter packing of lipids.
59
What is the melting point of saturated fatty acids?
Higher melting points
## Footnote
This contributes to stronger and more stable membranes at elevated temperatures.
60
What is homeoviscous adaptation?
Regulation of membrane fluidity through lipid composition
## Footnote
Many organisms adjust their membrane lipid types to maintain fluidity.
61
What is the general trend regarding fatty acids and temperature?
Increase in unsaturated fatty acids at lower temperatures and increase in saturated fatty acids at higher temperatures
## Footnote
This trend helps organisms maintain optimal membrane fluidity.
62
Why is regulating membrane fluidity important for poikilothermic organisms?
Their internal body temperatures vary considerably
## Footnote
Examples include Antarctic fish, which need flexible membranes to adapt to cold environments.
63
What is cholesterol?
Cholesterol is a sterol (ringed) lipid that plays an important role in regulating fluidity in animal cell membranes.
## Footnote
Cholesterol is crucial for maintaining the integrity and functionality of cell membranes.
64
Do organisms with cell walls contain cholesterol in their membranes?
No, organisms with cell walls lack cholesterol in their membranes.
## Footnote
However, plants and fungi may contain related compounds that perform comparable functions.
65
What type of molecule is cholesterol?
Cholesterol is an amphipathic molecule.
## Footnote
Amphipathic molecules have both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties.
66
Where is cholesterol located within the plasma membrane?
Cholesterol is located within the phospholipid bilayer.
## Footnote
It interacts with both the hydrophilic phosphate heads and the hydrophobic fatty acid tails.
67
What role does the hydrophilic hydroxyl group of cholesterol play?
The hydrophilic hydroxyl group of cholesterol associates with the phosphate heads.
## Footnote
This interaction helps integrate cholesterol into the membrane structure.
68
What do the hydrophobic carbon rings of cholesterol do?
The hydrophobic carbon rings of cholesterol sit between the fatty acid tails.
## Footnote
This positioning is essential for modulating membrane fluidity.
69
How does cholesterol function at high temperatures?
At high temperatures, cholesterol stabilizes the membrane and raises the melting point (lowering fluidity).
## Footnote
This helps maintain membrane integrity under stress.
70
How does cholesterol function at low temperatures?
At low temperatures, cholesterol intercalates between the phospholipids, preventing stiffening and crystallization (raising fluidity).
## Footnote
This ensures that the membrane remains functional even in cold conditions.
71
What effect does cholesterol have on membrane permeability?
Cholesterol makes the membrane less permeable to very small water-soluble molecules.
## Footnote
This property helps regulate what can cross the membrane.
72
What functional role does cholesterol play in relation to peripheral proteins?
Cholesterol helps secure peripheral proteins by forming high density lipid rafts.
## Footnote
These rafts are capable of anchoring proteins, contributing to membrane organization.
73
What principle holds the membrane together?
Weak hydrophobic associations between the fatty acid tails of phospholipids
74
What allows the spontaneous breaking and reforming of the bilayer?
The movement and rearrangement of phospholipids
75
What is the method of transport that allows materials to enter or leave the cell without crossing the membrane?
The membrane breaks and reforms around the material
76
What process requires the involvement of vesicles and ATP hydrolysis but is not classified as active transport?
Endocytosis
77
Define endocytosis.
The process by which large substances enter the cell without crossing the membrane
78
What forms a flask-like depression to envelope extracellular material during endocytosis?
An invagination of the membrane
79
What are the two main types of endocytosis?
* Phagocytosis
* Pinocytosis
80
What is phagocytosis?
The process by which solid substances are ingested
81
What is pinocytosis?
The process by which liquids/dissolved substances are ingested
82
How does receptor-mediated endocytosis allow the cell to control the type of content entering?
Involves clathrin-coated pits
83
Define exocytosis.
The process by which large substances exit the cell without crossing the membrane
84
What do vesicles typically derived from during exocytosis?
The Golgi
85
What happens to the vesicles during exocytosis?
They fuse with the plasma membrane, expelling their contents
86
What does exocytosis add to the cell membrane?
Vesicular phospholipids
87
Fill in the blank: The process of exocytosis replaces phospholipids lost when vesicles are formed via _______.
endocytosis
88
What are ion channels?
Integral membrane proteins containing a hydrophilic inner pore for ion passage
## Footnote
Ion channels facilitate the movement of ions in and out of cells according to concentration gradients.
89
What process allows ions to enter or exit a cell through ion channels?
Facilitated diffusion
## Footnote
This process occurs according to the concentration gradient.
90
What are the two key characteristics of channel proteins?
* Ion-selective
* Gated
## Footnote
Ion-selective channels allow only specific ions to pass, while gated channels control the timing of ion movement.
91
Why are ion channels essential for nerve cells?
They establish charge differentials across a membrane (membrane potentials)
## Footnote
This is crucial for the function of neurons.
92
What are voltage-gated ion channels?
Channels that cycle between open and closed conformations based on transmembrane voltage
## Footnote
They play a key role in action potentials in neurons.
93
What happens during depolarization in neurons?
Voltage-gated sodium channels transport sodium ions into the neuron
## Footnote
This influx of sodium ions leads to a change in membrane potential.
94
What is the role of voltage-gated potassium channels during repolarization?
They transport potassium ions out of the neuron
## Footnote
This process helps restore the resting membrane potential.
95
What are ligand-gated ion channels?
Channels that change conformation in response to the binding of a specific chemical (ligand)
## Footnote
They are crucial for synaptic transmission in neurons.
96
What neurotransmitter is released from nerve cells to stimulate adjacent cells?
Acetylcholine
## Footnote
Acetylcholine plays a key role in muscle contraction and neuronal communication.
97
What do nicotinic acetylcholine receptors do in muscles?
Trigger the opening of an ion channel when activated
## Footnote
This leads to an influx of ions that initiates muscular contraction.
98
Binding of acetylcholine to nicotinic receptors results in the influx of ions into the muscle, triggering a _______.
[muscular contraction]
## Footnote
This process is part of the neuromuscular junction function.
99
What are carrier proteins?
Transmembrane transporters that undergo a conformational change to translocate a material across the bilayer
100
How do carrier proteins differ from ion channels?
Carrier proteins undergo conformational changes, while ion channels possess an inert inner pore that is hydrophilic
101
What is cotransport?
The simultaneous movement of two substances, either in the same direction (symport) or opposite directions (antiport)
102
What is the role of cotransporters?
They link the movement of an ion along its concentration gradient to the movement of a solute against its concentration gradient
103
What type of transport is cotransport considered?
Secondary active transport
104
What energy source is used in cotransport?
The electrochemical gradient
105
Give an example of cotransport.
Absorption of glucose in the kidneys and small intestine, cotransported with sodium ions
106
What is antiport?
The movement of two molecules in opposite directions across the membrane
107
Provide an example of antiport.
Translocation of sodium and potassium ions by the sodium-potassium pump
108
What is the function of the sodium-potassium pump?
Establishes an electrochemical gradient across the membrane (resting potential) in nerve cells
109
How many sodium ions bind to the sodium-potassium pump?
Three sodium ions bind to intracellular sites
110
What happens to ATP in the sodium-potassium pump process?
A phosphate group is transferred to the pump via the hydrolysis of ATP
111
What occurs after the sodium ions are translocated across the membrane?
The conformational change exposes two potassium binding sites on the extracellular surface of the pump
112
What happens to the phosphate group in the sodium-potassium pump?
It is released, causing the pump to return to its original conformation
113
What is the result of the pump returning to its original conformation?
Translocates potassium across the membrane, completing the ion exchange
114
What is cell adhesion?
The attachment of cells to other surfaces via specialised membrane proteins called cell adhesion molecules (CAMs)
## Footnote
CAMs facilitate various cellular interactions and processes.
115
How can cells be attached in cell adhesion?
Cells can either be directly attached to other cells or indirectly anchored to the extracellular matrix
## Footnote
The extracellular matrix is a gel-like framework that provides structural support.
116
What roles do cell adhesion molecules play?
They play important roles in:
* Growth
* Apoptosis
* Signal transduction
* Migration
* Tissue development
## Footnote
These processes are crucial for normal cellular function and tissue homeostasis.
117
How can targeting specific cell adhesion molecules affect cancer?
It can limit the spread of malignant cancers by inhibiting metastasis
## Footnote
Metastasis is the process by which cancer cells spread from the original site to other parts of the body.
118
What are anchoring junctions?
Junctions that hold cells together to strengthen contact within tissues
## Footnote
They provide mechanical stability to tissues.
119
What do tight (occluding) junctions do?
They create tight seals that result in an impermeable barrier to diffusion
## Footnote
This is essential for maintaining distinct environments on either side of the junction.
120
What are gap junctions?
Junctions that link cells together to allow the movement of material between them
## Footnote
They facilitate intercellular communication and the transfer of ions and small molecules.
