B2.1: Membranes and Membrane Transport Flashcards
1
Q
State that phospholipids naturally form continuous sheet-like bilayers in water.
A
A bilayer of phospholipids and other amphipathic molecules forms a continuous sheet that controls the passage of substances despite being 10nm or less across
2
Q
What term refers to a property of fatty acid chains of a phospholipid
A
- Hydrophobic
3
Q
List locations of lipid bilayers in cells.
A
- Nucleus
- Mitochondria
- Chloroplasts
4
Q
State the primary function of the cell membrane and list 2 key qualtiies of the cell membrane that function to promote homeostatic regulation.
A
- The cell membrane acts as a barrier controlling the exchange of materials between the internal and external environment
- Composed of lipids, proteins and small amounts of carbs.
2 key qualities:
- Semi-permeability: Only certain materials are able to freely cross the cell membrane
- Selectivity: The cell can control the passage of any material that can’t freely cross the membrane
5
Q
What could selective permeability change
A
Selective Permeability may involve a change in permeability
6
Q
Outline the location of aqueous solutions in relation to the lipid bilayer.
A
- Hydrophilic phosphate heads of the inner layer of the phospholipid bilayer face the internal aqueous environment of the cell whereas heads of the outer layer face the external aqueous environment
- In an aqueous environment, phospholipid molecules spontaneously organise themselves in a way that their hydrophobic hydrocarbon tails are shielded from water.
7
Q
Explain why the hydrophobic core of a lipid bilayer has low permeability to large molecules and hydrophobic particles.
A
- The 2 hydrocarbon “tails” of the phospholipid bilayer are hydrophobic and interact with each other to form the core of biological membranes hence, the biological membranes have a low permeability to all hydrophilic particles (including ions) and polar charged molecules like glucose which allows for charged particles to be kept in or out of a cell.
(The larger the molecule, the lower the permeability)
8
Q
What proteins / transporters are involved in active transport
A
- Sodium Potassium pumps
- Sodium dependent glucose cotransporters
9
Q
What proteins / transporters are involved in passive transport
A
- Channel proteins
- Pump proteins
10
Q
Describe simple diffusion.
A
The movement of molecules of a subsatnce down a concentration gradient i.e. a region of where its concentration is higher to a region where its concentration is lower.
- It is a passive process meaning it doesn’t involve expenditure of energy by cells
11
Q
What is simple diffusion controlled by
A
Controlled by the solutes involved and not the membrane
12
Q
Outline the impact of concentration gradient, particle size and polarity or charge of molecules on the rate of diffusion across a lipid membrane.
A
- Concentration Gradient: A steeper concentration gradient results in a faster rate of diffusion. Higher concentration differences lead to more frequent collisions between molecules, increasing the rate of diffusion.
- Particle Size: Larger molecules (molecules with smaller SA:V ratio) experience greater resistance when moving through the lipid bilayer and have slower diffusion rate
- Polarity of molecules: Polar and charged molecules have a harder time diffusing across a lipid membrane compared to nonpolar molecules.
vice versa
13
Q
Explain two examples of simple diffusion of molecules into and out of cells.
A
Into cells:
- O2 diffuses from O2-rich air into alveoli down the concentration gradient and to the blood in capillaries that surround the alveoli and this O2 is carried to tissues.
Out Cells:
- CO2 diffuses from the cells, where its concentration is higher, to blood, where its concentration is lower, where its then carried to Lungs. In Lungs, CO2 diffuses from blood to alveoli down the concentration gradient
14
Q
Compare the location of integral and peripheral proteins in the membrane.
A
Integral Proteins:
- They are embedded in the lipid bilayer and are therefore difficult to isolate as extraction techniques disrupt the bilayer
- They are amphipathic molecules - the hydrophobic regions of integral proteins interact with the hydrophobic interior of the lipid bilayer hence, causing them to be embedded into the bilayer.
- Most integral proteins are transmembrane proteins (extend across the protein)
Peripheral Proteins:
- They are found on the surface of the membrane and interact only with the hydrophilic regions of the internal proteins hence, this means that these molecules are easier to remove from biological membranes
15
Q
What is Glycocalyx
A
Eukaryotic cells have this
- This is protein and polysaccharide amtrix covering the surface of a cell
- Used for cell recognition and adhesion of cells together
e.g: Cells lining the intestine have a glycocalyx to protect them from physical stress of food flowing through them
16
Q
List at least four functions (with example) of membrane bound proteins [JETRAT]
A
JETRAT
- Junctions - serve to connect and join 2 cells together
- Enzymes - fixing to membranes localises metabolic pathways
- Transport - responsible for facilitated diffusion and active transport
- Recognition - May function as markers for cellular identification
- Anchorage - Attachment points for cytoskeleton and extracellular matrix
- Transduction - Function as receptors for peptide hormones
17
Q
Define osmosis.
A
Osmosis is the diffusion of water molecules across a partially permeable membrane from high water potential to low water potential
- Highest water potential is 0.
- Low water potentials are negative
18
Q
Predict the direction of water movement based upon differences in solute concentration.
A
Water diffuses from an area of higher water potential to an area of lower water potential through the selectively permeable membrane.
This continues until the concentration becomes the same on both sides of the membrane. Once this happens, although the random movement of water molecules continues, there is no net movement of water.
19
Q
Outline the structure and function of aquaporin proteins.
A
Structure:
- Aquaporins are integral proteins composed of 4 monomeric subunits (this protein is called a tetrameric protein) where each
subunit has a water channel hence, an aquaporin molecule has 4 identical water channels.
Function:
- They have water channels linked with specific hydrophilic chains (of which are amino acid residues) which allows the passage
of water molecules but not of ions.
- Aquaporins permit the rapid movement of water in and out of the cell by forming hydrophilic channels that span across
the membrane - The volume of water that needs to be transported across the cell membranes determines the # of aquaporins
20
Q
Describe the structure and function of channel proteins.
A
Structure:
- Channel proteins are tubular shaped, acting as a passageway for the molecules to pass from one side of the membrane to the other. They are composed of multiple amino acid subunits that are identical to each other
Function:
- assemble to form channels for the passage of polar molecules
21
Q
What are carrier proteins
A
carrier proteins are transmembrane transport proteins that play an important role in facilitated diffusion. They are highly specific meaning they can be involved in both facilitated diffusion or active transport
22
Q
Most channels open or close in response to what specific stimuli?
A
- Changes in voltage across the membrane or voltage-gated channels
- Binding of small molecules to the channel proteins or ligand-gated channels
- Mechanical Forces like pressure
23
Q
Define facilitated diffusion.
A
The movement of a molecule’s particles down its concentration gradient with the help of specialised transport proteins – carrier and channel proteins – across the cell membrane
24
Q
What are channel proteins
A
Form pores or channels in the cell membrane, allowing specific molecules or ions to pass through - facilitated diffusion occurs
25
What are carrier proteins
Bind to large molecules and then change shape to move them across the membrane (they are also specific for a particular molecule)
26
Outline the specificity of channel proteins for ions.
Selectivity of the ion channels is due to:
- The binding sites of the hydrophilic amino acid side chains lining the channel being highly ion-specific
- The size of the pore acting as a size filter
27
List types of gates on channel proteins.
- Voltage-gated channels
- Ligand-gated channels
28
Describe one example of facilitated diffusion through a protein channel.
Ion channels, the tiny pores of which act as pathways for ions like Na+ and K+.
- When the gates open, the ions pass through the pore down the concentration gradient.
- When the gates close, the pore's plugged which prevents the passage of the ion.
29
Define Active transport
- When molecules are transported against the concentration gradient i.e. from a region of their lower concentration to a region of their higher concentration
- Requires ATP of which is generated by mitochondria during cellular respiration
30
What is the main function of membrane pumps
To move substances against the concentration gradient
31
Describe the structure and function of pump proteins, including the role of specificity, conformational change and ATP.
- ATP: During the transport cycle, ATP is hydrolysed to provide the necessary energy for ion transport. The energy released from ATP is used to pump ions against their concentration gradients allowing it to actively transport ions or molecules
- Conformational Change: When specific ions or molecules bind to the pump's active sites, it changes shape to allow the ions to move across the membrane.
- Specificity: Pump proteins are highly specific for the ions or molecules they transport
32
Where is the sodium potassium pump found
- In the neurons
33
Whats the role of sodium potassium pumps
They use indirect active transport to have a high concentration of Na+ outside the cell and high concentration of K+ inside the cell
34
How is the sodium potassium pump functioned
It will pump out 3 Na+ ions and pump into the cell 2 K+ ions hence, creating an electronegative gradient (outside is more positive than the inside although the inside still stays positive)
- 3 Na+ ions bind to intracellular sites on the sodium-potassium pump
- A phosphate group is transferred to the pump via the hydrolysis of ATP
- The pump undergoes a conformational change, translocating sodium across the membrane
- The conformational change exposes 2 K+ binding sites on the extracellular surface of the pump
- The phosphate group is released which causes the pump to return to its original conformation
- This translocates the K+ ions across the membrane, completing the ion exchange
35
Compare active transport using a pump protein to facilitate diffusion using a channel protein.
In diffusion a substance moves down its concentration gradient - from an area of high concentration to a low concentration (no energy required)
In active transport, a substance moves against its concentration gradient - from an area of low concentration to a high concentration (energy required)
36
Explain one example of active transport of molecules into and out of cells through a protein pump.
- Active transport functions to maintain the right concentrations of ions in the cells; active transport helping RBC maintain their internal sodium levels
37
Define selective permeability.
The property of a biological membrane that allows certain substances to pass through while restricting the passage of others, based on factors such as particle size, polarity, and chemical properties.
38
Outline how channels and pumps in the membrane allow for selective permeability.
- Gated ion channels like Cl- channels only bind to Cl- ions
- Carrier proteins are highly specific. For example, GLUT (glucose transporter) recognises and binds only to glucose and a few other monosaccharide molecules.
39
How is simple diffusion not selective?
Simple diffusion depends only on the concentration gradient, particle size and polarity molecules.
40
Outline the structure of glycoproteins and glycolipids.
Glycoproteins:
- Covalent bonding of oligosaccharides (short carb chains) to the protein molecules reuslts in glycoproteins
- Carb groups often stick out into the extracellular environment
Glycolipids:
- Covalent bonding of carbs to lipids results in glycolipids
- Amphipathic molecules; Carb groups are polar whereas non-polar lipid component lies embedded in the bilayer
- contribute to stability of membrane as they form H-bonds with water molecules surrounding the cell
41
Describe the role of glycoproteins and glycolipids in cell adhesion and cell recognition.
Cell adhesion:
- They both help cells attach and bind to other cells to form tissues.
Cell recognition:
- They both act as markers on the cell surface and help cells of the body recognise one another. Also help cells of the immune system to recognise foreign cells
42
"fluid" meaning in Fluid-Mosaic model
- The phospholipid bilayer is viscous and individual phospholipids can move position
43
"mosaic" meaning in Fluid-Mosaic model
- The phospholipid bilayer is embedded with proteins, resulting in a mosaic of components
44
Draw and label a two-dimensional representation of the fluid mosaic model of membrane structure. Include:
* Phospholipid bilayer with hydrophobic tails facing inward and hydrophilic heads facing outwards
* Integral proteins shown embedded the membrane
* Peripheral proteins on membrane surface or anchored to an integral protein
* A transmembrane protein channel with a pore
* Glycoproteins with a carbohydrate side chain facing the outside of the cell
* Glycolipid with a carbohydrate side chain facing the outside of the cell
* Cholesterol embedded between phospholipids in the hydrophobic region
* An indication of thickness (8-10nm)
pk
45
Compare and contrast the structure, melting point and relative fluidity of saturated and unsaturated fatty acids in lipid bilayers.
Saturated fatty acids:
- Structure: Fatty acid chain lies parallel to each other
- Melting point: Higher due to no double bonds disrupting the layers
- Relative fluidity: Provide stability to membrane
Unsaturated fatty acids:
- Fatty acid chain is kinked hence preventing membrane lipids with unsaturated fatty acids from packing together closely therefore maintaining fluidity.
- Structure: - Melting point: Lower due to double bonds causing kinks
- Relative fluidity: Ensure fluidity of the membrane
46
What is the connection between saturated / unsaturated acids and melting points
Unsaturated fatty acids have lower melting points
47
At higher temperatures, what is the connection between stability and unsaturated/saturated fatty acids
At higher temperatures, unsaturated fatty acids make membranes less stable
48
Outline an example of adaptation in membrane composition in relation to habitat.
- Cold blooded organisms adapt to lower temperatures by increasing the proportion of unsaturated fatty acids in their membranes hence, regulating fluidity
- Additionally, in hibernating animals, the body temperature of the mammal drops hence, the proportion of unsaturated fatty acids in the membrane phospholipids increases.
49
What is cholesterol and what is its role
- An amphipathic steroid and it plays an important role in the fluidity of biological membranes
- The more cholesterol there is, the less fluid the membrane is
50
How does cholesterol impact fluidity at higher temperatures
- At higher temperatures, cholesterol reduces membrane fluidity because at higher temperatures, the phospholipids in the membrane have too much energy and so move around a lot which increases the fluidity which causes the membrane to become leaky
51
Identify the structure of cholesterol in molecular diagrams.
- connected from the hydrophilic phosphate head and extends closer to the hydrophobic tails of another fatty acid molecule
52
Describe the structural placement of cholesterol within the cell membrane.
- Found in 1 of the 2 layers, the hydrophillic region and hydrophobic regions of a cholesterol molecule interact with the corresponding hydrophilic and hydrophobic regions of adjacent phospholipid molecules which holds the phospholipid molecules together.
53
Outline how temperature affects cell membrane fluidity.
- At low temperatures, phospholipid molecules come closer together hence, decreasing fluidity
- Saturated fatty acids freeze more easily than unsaturated as there isnt space created due to the absence of double bonds, and therefore the kinks, which prevents the molecules from packing too closely together.
54
Describe the function of cholesterol as a modulator of membrane fluidity.
- At low temp, the inserted cholesterol prevents fatty acid chains from phospholipids from fitting closely together hence, preventing tendency of membranes to freeze
- At high temp, the cholesterol stabilises the membrane by packing the phospholipid bilayer more tightly and reduces fluidity
- Cholesterol decreases permeability of the membrane to ions and molecules
55
Define endocytosis
Endocytosis (endo – inside; cytosis – transport mechanism) is a bulk transport mechanism by which particles are moved into the cell.
56
Define exocytosis
Exocytosis (exo – external; cytosis – transport) is the reverse of endocytosis and involves the bulk transport of material (waste or useful) to be secreted or excreted out of the cell
57
Function of exocytosis?
the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell (waste or useful).
58
2 types of secretion in exocytosis
- Constitutive Secretion
- Regulated Secretion
59
Outline similarities and differences between Endocytosis and Exocytosis
- The fluidity of the membrane plays an important role in the formation of vesicles.
- They allow bulk transport.
- Exocytosis returns lipids and proteins to the plasma membrane whereas endocytosis removes them.
60
Events that follow exocytosis [FMFS]
F - Formation of a vesicle by the golgi apparatus
M - Movement of the vesicle towards the plasma membrane
F - Fusion of a vesicle with the plasma membrane
S - Secretion of the vesicle's contents
61
Define phagocytosis
Intake of large particles like pathogens
62
Define pinocytosis
- Ingestion of liquids
63
Describe indirect active transport and what is it's role
- Involves coupling the molecule with another moving along an electrochemical gradient
- Plays an important role in glucose absorption by the intestinal epithelial cells
64
Outline the function of cotransporters in indirect active transport.
- Indirect active transport involves the transport of 2 solutes (ions or molecules)
Steps:
- Sodium ions bind to binding sites on the outer surface of the cotransporter
- Simultaneously, a molecule of glucose also binds to its binding site on the cotransporter.
- This results in a conformational change that transports both the sodium ions and the glucose molecule to the inside of the cell.
65
Example of a ligand gated channel
Nicotinic Acetylcholine
66
Describe the role of glucose cotransport proteins in the kidney nephron.
- Sodium dependent cotransport's used by cells in the walls of the proximal tubule in kidney which reabsorb glucose that's been filtered out to the blood to prevent it being lost in urine using indirect active transport
67
Describe the role of glucose cotransport proteins in the small intestine
- Sodium dependent cotransport's used by epithelial cells which absorb glucose from the gut lumen, transport it across the cell and into the blood to be used for metabolic functions
68
Outline the events taking place in the operation of the Na+/K+ pump
- 3 sodium ions attach to the binding sites of the sodium-potassium pump inside the cell
- ATPase catalyse the hydrolysis of ATP to ADP and phosphate
- This results in a conformational change which translocates the sodium ions to the exterior of the cell and the pump closes
- Immediately after, the pump opens to reveal 2 potassium ions which bind to the pump and the phosphate group detaches from the pump
- This causes the pump to go back to its original conformation and translocates the potassium ions to the interior of the cell and closes
69
Define CAMs
Cell adhesion molecules
70
Outline the role of CAMs in the formation of tissues.
These are glycoproteins (on the surface of cells) that mediate the binding of cells with one another and maintain the structural integrity of tissues
71
What are the role of cell junctions
- They connect cells to each other allowing intracellular transport and communication
72
What are the main types of cell junctions in animals
- Adhesive Junctions [includes adherens junctions and desmosomes]: Facilitate cell-cell adhesion (present in epithelial cells and cardiac cells)
- Tight Junctions [acts as barriers]: Form a tight seal between 2 neighbouring cells (present in epithelial cells)
- Gap junctions [Communicating junctions]: Physically connect neighbouring cells for the movement of molecules (present throughout the body)
73
what are aquaporins
Channel proteins that allow water to move through
74
What cell junction plays a major role in anchoring cells to each other and to the extracellular matrix
- Desmosomes
75
3 Examples of active transport
- Protein pumps (like sodium-potassium pump)
- Endocytosis
- Exocytosis
76
2 examples of membrane protein pumps
-Sodium potassium pump
- Membrane of a liver cell (removes glucose from blood for storage inside liver cells)
77
What is the type of integral protein that can change shape to allow materials to cross the cell membrane
Carrier protein
78
Nictotinic acetylcholine receptors are an example of what channels
Neurotransmitter ion gated channels
79
What integral protein is used in sodium potassium pumps
Carrier proteins
80
Outline the structure and function of vesicles in cells.
Structure
- A small sac of membrane with a droplet of fluid inside in a spherical shape
Function:
- Responsible for transporting substances (waste or useful) out the cell via exocytosis
81
What properties of the cell membrane allows for the formation of vesles
Fluid properties
82
Outline the formation of a vesicle within the cell.
A small region of a membrane's pulled from the rest of the membrane and is pinched off
83
Describe the transport of materials within a cell using vesicles.
- Vesicles move materials around in a cell and when they reach their destination, vesicles fuse with a target membrane and disappear which transfers all the contents of the vesicle across the membrane
84
Describe the formation of a vesicle via endocytosis.
- Membrane turns inside out to form a flask-like depression which envelopes the extracellular material
- The inside-out membrane is sealed off to form an intracellular vesicle that contains the material
85
Outline two examples of materials brought into the cell via endocytosis.
1. In placenta, proteins from mother's blood are absorbed into foetus by Endocytosis
2. Some white blood cells take in pathogens by endocytosis then kill them.
86
Describe the release of materials from cells via exocytosis.
- Vesicles fuse with plasma membrane expelling their contents into extracellular environment
- Exocytosis adds vesicular phospholipids to cell membranes which replaces those lost when vesicles are formed via endocytosis
87
Outline two examples of materials released from a cell via exocytosis.
1. Removal of excess water from the cells of unicellular organisms from the contractile vacuole
2. Production of glycolipids by the ER and modified in the Golgi Apparatus
88
State the effect of endocytosis and exocytosis on the area of the cell membrane.
- Exocytosis: Area of cell membrane increases
- Endocytosis: Area of cell membrane decreases
89
Contrast secretion with excretion.
- Secretion: A process of movement of materials internally
- Excretion: A process of waste removal from the body
90
What ion channel's involved in synaptic transmission
Neurotransmitter ion gated
91
What’s cholesterol’s role at high temperatures
- at high temperatures, phospholipids have lots of energy hence, they move faster which increases fluidity and causes membrane to be leaky thus, cholesterol decreases the fluidity by restraining their movementand packing the phospholipids closely together
92
What’s cholesterol’s role at low temperatures
- at low temperatures, cholesterol interferes with the regular packing of fatty acids hence, preventing the membrane from solidifying therefore maintaining fluidity
93
What is depolarisation and repolarisation
Depolarization is when a cell's charge becomes more positive, often due to an influx of sodium ions, while repolarization is the return to a more negative charge, typically achieved by the exit of potassium ions;
94
Define conformational change
A change in the shape of a macromolecule
95
3 examples of gated ion channels
- Voltage-gated channels
- Ligand-gated channels
- Mechanically-gated channels
96
A common example voltage-gated ion channels are seen in
Nerve signalling
97
What is the resting membrane potential
At rest, there is a potential difference across the cell membrane - in other words, an electrochemical gradient exists (where the outside is more positive than the inside but the inside's still positive)
98
Outline the structure, function and specificity of voltage-gated channels.
Structure:
- Contains the 'activation gate' that remains closed in resting state
- Contains an inactivation gate which blocks the channel pore
- Channel itself embedded into the phospholipid membrane
Function:
- Depolarisation occurs which opens V-G sodium channels causing Sodium ions to diffuse rapidly in which causes interior to be more +vely charged than exterior creating an action potential.
- V-G sodium channels close and V-G potassium channels open immediately causing Potassium ions to diffuse out and down their conc. grad. and interior becomes more -ve
Specificity:
- Only allow specific ions to pass through: The gated channels would only open or close when the voltage reaches a certain minimum value
99
Describe the function of the voltage-gated potassium channel.
- V-G potassium channels open immediately after V-G sodium channels close causing Potassium ions to diffuse out and down their conc. grad. and interior becomes more -ve hence Repolarisation occurs.
- V-G potassium channels close and the resting membrane potential becomes re-established again
100
What is a ligand
A ligand is a substance that can bind to any target protein
101
An example of a ligand-gated channel
- Nicotinic Acetylcholine receptor
102
What are neurotransmitter-gated ion channels
When the ligand on the ligand-gated channels releases a signalling molecule by a neurone (becomes a neurotransmitter) hence, the ion channel is called a neurotransmitter-gated ion channel
103
Outline the structure, function and specificity of ligand-gated channels.
Structure:
- Consists of binding site, ion channel and the gate
Function:
- After a ligand binds, this results in a conformational change that opens the channel. Sodium ions diffuse down the conc. grad. resulting in the interior of the cell becoming more +ve (depolarisation occurs).
- Almost immediately after, an enzyme breaks down the substrate leading to the closure of the ion channels
Specificity:
- Ion channels open when a ligand binds to the transmembrane protein of the ion channel
104
Describe the function of the ligand-gated sodium channel in the postsynaptic cell membrane (AKA the nicotinic acetylcholine receptor).
- nAchR (nicotinic acetylcholine receptors) are ligand-gated ion channels present at skeletal neuromuscular junctions
- The binding of acetylcholine molecules results in a conformational change which opens the channels
- Sodium diffuses down the conc. grad. resulting in the interior of the cell becoming more +ve (depolarisation occurs).
- Almost immediately after, the enzyme Cholinesterase breaks down Acetylcholine which leads to closure of the ion channels.
- Depolarisation is followed by the opening of V-G Potassium channels and exit of potassium ions results in Repolarisation and soon, the V-G Potassium channels close and resting membrane potential's stored.
105
State the function of an exchange-transporter protein.
E.g: Sodium-Potassium Pump
- Function: Actively exchanges 3 Na+ ions out the cell for 2 K+ ions into the cell vital for maintaining the resting membrane potential
106
What transport mechanism does the sodium potassium pump use
Indirect active transport
107
Describe the structure of the sodium-potassium pump
An integral protein that is embedded into the phospholipid bilayer that exchanges 3 sodium ions with 2 potassium ions and when the neurone fires, these ions swap locations via facilitated diffusion through the sodium and potassium channels
108
Which techniques allowed scientists to falsify the Davson–Danielli model?
freeze-etched electron micrographs and fluorescent markers
109
The operation of the sodium potassium pump moves what in and what out
3 Na+ ions out the cell
2 K+ ions in the cell
110
An example of facilitated diffusion
Diffusion of Chloride ions through Chloride channels
111
Compare and Contrast the structure and function of glycoproteins and glycolipids in the plasma membrane (2 similarities and 2 differences)
- Both are contribute to cell adhesion
- Both are involved in cell recognition
- Glycoproteins have hormone receptors whereas Glycolipids don't
- Glycoproteins have enzymatic roles whereas Glycolipids don't
112
What describes the movement of protein channels using passive transport
Net movement that occurs until the concentrations in and out of the cell are equal
113
What size cuboids have the smallest SA:V ratio
- Either largest cube
- Has one really large area on one face and a really small area on the other face on Cuboid
114
Explain the role of vesicles in transportation of materials within cells (8 marks)
- Vesicles are membrane bound packages
- Formed by pinching off from a membrane
- by Endocytosis
- Vesicles can carry proteins
- rER synthesizes proteins
- Proteins enter ER
- Proteins are transported to Golgi Apparatus
- Vesicles fuse with membrane so that the contents of the vesicle join the organelle
- By exocytosis
115
Outline, with an example, the process of exocytosis (5 marks)
- Vesicles carry material to the plasma membrane
- Vesicle fuses with membrane
- Exocytosis is due to the joining of phospholipid bilayers
-Exocytosis is aided by the fluidity of the membrane
- In exocytosis, material gets released
- Example: Neurotransmitter vesicles release their contents into the synapse
