Cellular Processes Flashcards
(65 cards)
1
Q
Membrane made of _____ and held together by ___?
A
Made of 50% lipid and 50% protein held together by hydrogen bonds
2
Q
Integral proteins
A
Embedded into or across cell membrane (transmembrane)
3
Q
Peripheral protein
A
Attached to inner or outer surface of membrane, easily removed
4
Q
Membrane fluidity determined by?
A
- Lipid tail length: longer tail, less fluidity
- # of double bonds: more = increase fluidity
- Amount of cholesterol: more = decrease fluidity
5
Q
Integral protein properties
A
- Amphiphatic.
- Hydrophobic regions spanning hydrophobic core.
- Hydrophilic ends interacting with aqueous solution.
6
Q
What do hydrophobic regions of intergral proteins consist of?
A
Non-polar amino acids coiled into helices
7
Q
Functions of membrane proteins
A
- Receptor proteins
- Cell identity markers
- Linkers
- Enzymes
- Ion channels
- Transporter proteins
8
Q
Selectively permeable
A
Allow certain substances in and out but not others.
9
Q
Lipid bilayer permeable to ___
A
- Non-polar, uncharged molecules
- Lipid soluble molecules
- Small uncharged polar molecules
10
Q
Lipid bilayer impermeable to ___
A
- Large uncharged polar molecules
- Ions
11
Q
Membrane protein function for permeability
A
Mediate transport of substances across membrane that are unable to permeate the hydrophobic core of bilayer.
12
Q
Diffusion
A
- High conc. To low conc.
- Equilibrium when evenly distributed.
13
Q
Factors influencing rate of diffusion
A
- Greater difference in concentration, faster.
- Higher temp, faster.
- Larger size of diffusing substance, slower.
- Increase surface area for diffusion, faster.
- Increasing diffusion distance, slower.
14
Q
Concentration gradient
A
Non-charge molecules diffusing down their concentration gradients. (Eg. oxygen, carbon dioxide)
15
Q
Electrochemical gradient
A
Movement of ions are influenced by electrical and concentration gradients.
16
Q
Gradients
A
- Selective permeable membrane enables a concentration gradient across the the membrane to be established.
- Cells maintain difference in ions between in and out of membrane, establishing electrical gradient.
- Mimics capacitors, separate and store charge.
17
Q
Do maintaining gradients require energy?
A
- Cells use ~30% of resting energy to maintain conc.and electrical gradients.
- Gradients represent stored energy.
18
Q
Osmosis
A
High water conc. to low water conc.
19
Q
When does osmosis occur?
A
- Occurs if membrane is permeable to water but not to certain solutes.
- Osmotic gradient exists, water will move to eliminate it.
20
Q
Membrane permeability to water
A
- Pw = Pd + Pf
- Pd - permeability through lipid bilayer.
- Pf - permeability through water channel.
21
Q
Pd
A
- Small
- Mercury insensitive
- Temperature dependent
22
Q
Pf
A
- Large
- Mercury
- Temperature independent
- Most water movement
- Mediated by aquaporins
23
Q
Why do cells have different Pw?
A
Because they express different aquaporin isoforms.
24
Q
Osmotic pressure
A
Pressure applied to a solution to prevent inward flow of water across semi-permeable membrane.
25
Non-mediated transport
Does not directly use a transport protein.
26
Mediated transport
Moves substances with assistance of a transport protein.
27
Passive transport
Moves substances down their conc. or electrochemical gradients using only their kinetic energy.
28
Active transport
Uses energy to move substances against their conc. or electrochemical gradients.
29
Vesicular transport
Move materials across membranes in small vesicles by exocytosis or endocytosis.
30
Non-mediated transport, what gets diffused and importance?
- Important for absorption of nutrients and excretion of waste products.
- Nonpolar, hydrophobic molecules diffused.
31
How does diffusion through ion channels occur?
Channel forms water filled pore that has hydrophilic amino acids lining it to form a pathway for ions to diffuse down electrochemical gradient.
32
Why is diffusion through ion channels rapid?
Ions do not bind to channel pore therefore transport is rapid.
33
What is ion selectivity filter?
- Specific amino acids lining the pore to determine the selectivity of the channel to ions.
- Being selective to a particular ion allows the channel to harness the energy stored in different ion gradients.
34
How does ion selectivity filter work?
Negative filter only allows positive ions in while the size of the filter determines the ion passing through the gap based on atomic radius/size.
35
What are channel gates?
Channel gates control opening and closing of the pore through different stimuli.
36
What are some stimuli that can control channel gates?
- Voltage: change in RMP.
- Ligand binding: binding of neurotransmitters or hormones.
- Cell volume: shrinking or swelling of cell.
- Change in pH: linked to metabolism, differnt levels of lactic acid can influence opening or closing.
- Phosphorylation: phosphorylates gate, conformational change of channel, instigated by enzymes.
37
How does voltage stimulate channel gating?
change in RMP.
38
How does ligand binding stimulate channel gating?
binding of neurotransmitters or hormones.
39
How does cell volume stimulate channel gating?
shrinking or swelling of cell.
40
How does pH stimulate channel gating?
linked to metabolism, differnt levels of lactic acid can influence opening or closing.
41
How does phosphorylation stimulate channel gating?
phosphorylates gate, conformational change of channel, instigated by enzymes.
42
How can we measure ion channel function?
Patch clamp technique
43
What do current fluctuations in ion channels represent?
- They represent the opening and closing of single ion channels.
- They represent the conformational changes in channel structure associated with channel gating.
44
Carrier mediated transport, how does it work?
Substrate to be transported directly interacts with transporter protein, binding to it, causing a conformational change to the transporter protein.
Transport rates are slower than channels.
45
What are the properties of carrier mediated transport?
- Can be passive (facilitated) or active.
- Similar properties as enzymes.
- Specificity
- Inhibition
- Competition
- Saturation
46
What is meant by specificity in carrier mediated transport?
Transporter protein is specific for different molecules and isoforms.
47
What is meant by inhibition in carrier mediated transport?
They can be inhibited by something binding to their binding sites so other molecules are unable to bind to it.
48
What is meant by competition in carrier mediated transport?
The competition of different substances for the same binding site causes competitive inhibition.
49
What is meant by saturation in carrier mediated transport?
This means that there are limited binding sites and transport occurs until all binding sites are saturated/occupied.
50
What is the facilitated diffusion of glucose?
The passive diffusion of glucose down its conc. gradient, usually from blood to cell but can be the other way around.
51
How is the concentration of glucose maintained?
The conversion of glucose to glucose-6-phosphate by kinase enzymes maintains the gradient for glucose energy.
52
Which transport protein does glucose bind to?
GLUT
53
What are the 2 types of active transport?
Primary active and secondary active.
54
How is the energy for primary active transport derived from?
Energy is directly derived from the hydrolysis of ATP.
55
What energy does secondary active transport use?
It uses the energy stored in an ionic concentration gradient.
56
Na+/K+ ATPase is an example of which type of transport?
Primary active transport
57
What goes in and out of the cell in Na+/K+ ATPase?
3 Na+ ions removed from cell and 2 K+ ions brought into the cell.
Net shift of one positive charge therefore electrogenic.
58
What is the pump-leak hypothesis?
The continuous working of the Na pump due to the leaking of Na and K ions down their respective gradients.
59
What is the purpose of the Na pump?
Na pump maintains a low conc. of Na ions and high conc. of K ions in the cytosol.
60
What is the Na pump important for?
- Maintaining RMP.
- Electrical excitability.
- Muscle contraction.
- Maintaining steady state cell volume.
- Uptake of nutrients via secondary active transporters.
- Maintenance of intracellular pH by secondary active transporters.
61
What are secondary active transporters powered by?
The Na+ gradient initially established by the Na pump.
62
What are Na+ antiporters or exchangers examples of?
Secondary active transporters.
63
What are Na+ symporters or cotransporters examples of?
Secondary active transporters.
64
What flows and in what direction in Na+ antiporters?
Na ions rush into the cytosol (passive transport) while Ca or H ions get pushed out into extracellular fluid (active transport).
65
What flows and in what direction in Na+ cotransporters?
Glucose and amino acids rush into the cytosol along with Na ions.
