Membrane Structure and Transport Flashcards
1
Q
All membranes of bacteria and eukaryotes are constructed of what?
A
Phospholipid bilayer
2
Q
Membranes also contain various….
A
Proteins
3
Q
Where are the proteins found in membranes
A
Inner surface, outer surface, some span the entire membrane
4
Q
Where are the proteins in the membranes made
A
Made along cytosolic side of endoplasmic reticulum in eukaryotes
5
Q
What are the most abundant membrane lipids
A
Phospholipids
6
Q
Phospholipids are
A
Amphipathic
7
Q
What are that characteristics of phospholipids
A
have a polar, hydrophilic head that contains a phosphate group, and have two nonpolar, hydrophobic hydrocarbon tails
8
Q
Cholesterol and other types of what are common
A
lipids
9
Q
Cholesterol and lipids lack what but have other charged groups
A
phosphate
10
Q
Cholesterol and lipids alter membrane fluidity for organisms but particularly those living where
A
In extreme temperatures
11
Q
All membranes are what
A
Selective barriers
12
Q
plasma membranes surround the what of all cells
A
the cytoplasm
13
Q
Eukaryotes have additional what around their organelles
A
cell membranes
14
Q
with a “sheet” orientation, the edges of the lipids would interact with
A
the water
15
Q
What is the most energetically favorable shape for the bilayer to form
A
a sphere
16
Q
In water, pure phospholipids spontaneously form a….
A
Liposome
17
Q
Phospholipids rapidly spin and laterally traverse their monolayers, but mostly need what to switch sides
A
Enzymes
18
Q
What two things switch phospholipids across monolayers
A
Scramblase (ER) and flippase (Golgi)
19
Q
The fluidity of a membrane depends on what
A
The types of lipids present
20
Q
Saturated fats have no what
A
No double bonds (pack together better)
21
Q
Unsaturated fats have what
A
At least 1 double bond that causes a kink (don’t pack together well)
22
Q
Regions of a membrane can be made more or less fluid based on
A
The types of lipids present
23
Q
Higher amounts of saturated fatty acids decrease what
A
Membrane fluidity and create “lipid rafts”
24
Q
Higher amounts of what correlate with high temperature adaptation/plasticity in certain animals
A
Cholesterol
25
Protein structure allows part of the protein to interact with lipids with the other part is what
Hydrophilic and forms a path for polar molecules to move through
26
hydrophilic residues are indicated by what
red center, left
27
hydrophobic residues are indicated by what
green edges, left
28
Transmembrane proteins provide what in the membrane
"Gates"
29
Type "D" membrane proteins can be separated by what
Mild detergents
30
What is the cell cortex
The cell cortex in a meshwork of filamentous proteins that provide structure and support to animal cells
31
Proteins that are inserted into the membrane attach to what
They attach to proteins that span the inner surface of the membrane to provide structural support
32
Do plant cells need a cell cortex?
No
33
Proteins embedded in lipid membranes using what type of domain
Alpha - helical
34
Hydrophobic amino acids on the outside of the helix interact with what
Lipids
35
The polar backbone of a polypeptide makes up the inner portion of what
the helix
36
Cell surfaces are frequently coated with what?
Carbohydrates
37
What is it called when carbohydrates link to proteins
Glycoproteins
38
What is it called when long polysaccharides link to proteins
Proteoglycans
39
What is it called when carbohydrates are on lipids
Glycolipids
40
Glycocalyx =
all CHO's on a cell
41
What is glycocalyx dependent on
Flippase dependent in the case of glycolipids
42
Membrane carbohydrates are related to many functions including...
Protection, Adhesion, Cellular identity (ABO blood type)
43
What is permeability
The ability to allow solids or gasses to cross the membrane
44
Lipid bilayers are
Semipermeable
45
The smaller and more hydrophobic the molecule, the easier what
it moves across it
46
The lipid membrane may restrict movement of what
Nutrients or wastes
47
Lipid membrane permeability allows concentrations gradients to form and can set up what
Stored energy for later conversion
48
A cell must balance water levels to maintain what
Concentrations of solutes
49
Water movement across a membrane occurs through what?
Aquaporins
50
All cells have aquaporins to allow what
The movement of water across membranes
51
What is diffusion
The movement of a substance across a membrane from high to low concentration
52
What is diffusion related to?
Entropy and random distribution
53
Movement across ions is what type of energy
Kinetic energy
54
Having a concentration gradient is what type of energy
Potential
55
What is osmosis?
The movement of water across a membrane from high to low concentration OF THE WATER
56
In osmosis, water moves from an area of low solute concentration to what
An area of high solute concentration
57
Osmosis is related to what
Entropy and random distribution
58
In uncharged molecules what determines the movement direction
Concentration gradient
59
What determines the movement direction in ions (charged molecules)
concentration gradient and electrochemical gradient
60
Organic compounds including DNA, RNA and amino acids have what charge
Negative charge
61
Most cations are at higher concentrations where
Outside the cell
62
Also high concentrations of phosphates and what in cells
Phosphates and phospholipids
63
Na + may leak back into the cell, but K+ usually does or doesn't?
K+ usually doesn't leak out of cells
64
What is membrane potential measured in?
Millivolts
65
Polar and charged substances that do not readily cross a lipid bilayer are transported by what?
Membrane proteins
66
What do channels do?
Allow movement based on size and charge; may allow movement of more than one chemical
67
Movement across a membrane can be
passive (diffusion) or active (energy required)
68
What is passive transport
movement of a substance down a gradient
69
Passive transport is what type of movement
Energetically favorable (releases energy)
70
What is active transport
Uses energy to move solutes against a gradient
71
Active transport is what type of movement
Energetically unfavorable because it needs energy put in / needs to be coupled
72
What are the two types of active transport?
Primary and secondary
73
What is primary active transport
Uses ATP or light directly
74
What is secondary transport
Converts stored energy (ATP was needed previously) by exploiting gradient concentrations
75
Transporters mostly move small organic compounds, but also some what?
Inorganic ions
76
Are transporters specific?
Yes, highly specific
77
Different membranes in a cell have the same or different transporters present?
Different
78
Are transporters active or passive?
Both
79
Na+/K+ ATPase Pump
Uses ATP directly, 3 Na+ are pumped out, and 2K+ are pumped in, keeps [Na+] high outside and [K+] high inside
80
Na+ Glucose Symporter
Couple movement of a solute in the same direction as the Na+ concentration gradient
81
Na+ Glucose Symporter is important for what
Digestive function
82
Glucose always moves into what type of cells, even if the cell has higher concentration than the __________.
Gut cells
83
Na+/H+ Antiporter
Couple movement of H+ in the opposite direction as the Na+ and is regulated by hormones in distal kidneys
84
Proton H+ gradients
H+ gradients are used as an energy source for ATP synthesis and symports
85
Cells use multiple gradients as energy sources which means what
ATP and activated carriers (NADH, etc.) are not the only sources of energy
86
Both types of transport are. mediated by what
Proteins
87
Active transporters are commonly called what?
Pumps
88
Some ion channels are selective where some ions can pass but others cannot, what is that dependent on?
Shape, size, and charge
89
Some channels are gated and only do what
Open/close
90
Gated channels can be opened or closed based on what?
Signals that affect proteins conformation
91
Voltage-gated
Responds to a change in resting membrane potential (-70millivolts), many examples from neurons to muscles
92
Ligand-gated
Direct specific binding, taste
93
Mechanically-gated
"touch receptors", hearing and balance, venus flytrap prey capture, mimosa pudica leaf closing response
94
Ca2+ ATP-Driven Pump
Cells also regulate Ca2+ balance; low the cytosol, higher outside the cell and in the ER
95
Ca2+ have multiple roles in cells related to regulating protein activity which includes
Muscle contraction, nerve signaling, fertilization
96
Action potentials in nerve cell signaling
Neurons receive and transmit signals
97
What is an action potential
The wave of signaling
98
The signal results from changes in what
Membrane potential (voltage) across the neurons plasma membrane
99
Neuron dendrites receive signals from other cells and then what happens to the signals?
Signals are transmitted along the axon, including membrane potentials, pumps, and voltage-gated channels
100
Nerve terminals interact with dendrites of another neuron to send the signal where?
Send the signal to new neurons or a target like skeletal muscle cells
101
What percent of the body's energy is used by the nervous system, mostly in Na+/K+ pump activity
20%
102
Voltage-gated (VG) Na+ channels
Activation gate and inactivation gate, at rest activation gate is closed and inactivation gate open, transient influx of Na+ causes the membrane to depolarize
103
Voltage-gated (VG) K+ channels
Single activation gate that is closed in the resting state, K+ channel opens slowly, Efflux of K+ repolarizes the membrane
104
At the resting potential, the membranes permeability is determined by what?
Its open ion channels
105
Resting phase
Equilibrium between diffusion of K+ out of cell and voltage pulling K+ into cell, at rest this is usually -70mV, and K+ leak channels allow a slow leak of K+ in both directions
106
A stimulus generates an electrical signal at or above threshold which is?
-55mV
107
Rising phase
Stimulus causes a change in voltage at or above the threshold (-55 mV), positively charged ions rush into the cell, charge inside becomes less negative (depolarization), voltage-gated K+ channels are also triggered but are SLOW
108
After a delay, voltage gated K+ channel slow gates open and what happens as a result??
Voltage gated Na+ channel inactivation gates close
109
At the top of the curve what is reached
Maximum voltage is reached
110
At the top of the curve, there is a rapid shift of what
High Na+ permeability and low K+ permeability to high K+ permeability and low Na+ permeability
111
With the voltage-gated K+ channels open, what happens
Positive ions rush out of the cell
112
Falling phase
Undershoot occurs as excess K+ diffuses out before (VG) K+ channel closes and the charge inside becomes more negative again (hyperpolarizes)
113
Before a new action potential can begin, all voltage-gated channels must reset
No new action potentials can occur until this happens (absolute refractory period)
114
Refractory period
VG K+ channel slow gate closes
VG Na+ channel activation gate closes
VG Na+ channel inactivation gate opens
115
Once channels are reset, a greater or less then normal depolarization can result a new action potential (relative refractory period)
GREATER
116
What do Na+/K+/ATP pumps must do in the refractory period
Restore ion gradients
117
APs are self-propagating (change in potential triggers) and also what
Undirectional
118
What are the two ways of speeding up electrical propagation?
1) Myelination
2) Large diameter
119
Myelination
Cellular insulation, "jumps segments", and saltatory conduction
120
Large diameter
Reduces electrical resistance, giant squid "fight or flight" axons
121
Transmitting signals between neurons
Electrical signals do not jump from neuron neuron
122
Transmitting signals between neurons
There is a synapse (a gap) between the nerve terminal and the dendrites of the next neuron
123
To transmit the signal, neurotransmitters are released from the nerve terminal
Ex. acetylcholine
124
Electrical signals help bind to what
They bind receptors on the dendrites of the next neuron
125
At the nerve terminal, the action potential causes what to open
voltage-gated Ca2+ channels to open
126
After voltage gated Ca2+ channels open, what happens
Ca2+ moves into the cell, Higher [Ca2+] causes vesicles containing neurotransmitters to fuse
with the plasma membrane, Neurotransmitters are released into the synapse
127
What are neurotransmitters
igands that bind ligand-gated Na+ channels
on dendrites neurons, or similar channels on skeletal muscles
128
The ligand-gated Na+ channels open and allow Na+ to enter the cell, causing what
An action potential in that cell, or electrical trigger for contraction.
