Exam 2 Flashcards
(116 cards)
1
Q
Do Euk and Prok cells both have membranes that separate internal contents from the external environment?
A
Yes both share this characteristic
2
Q
Membranes serve as?
A
selective barrier “selectively permeable”
3
Q
General Structure of Membrane
A
-Framework is a phospholipid bilayer
-proteins associated with membranes
-additional amphipathic lipid in the membrane( eg. cholesterol and glycolipids)
4
Q
Phospholipid bilayer
A
form into a sphere automatically to avoid a “free edge” where hydrophobic fatty acid would be exposed to water (tears)
5
Q
membrane fluidity
A
-lateral motion of individual phospholipids within one leaflet
-rotation in place of phospholipids
-flexion of fatty acids
-flipflop from our leaflet to the next rarely occurs spontaneously
6
Q
Factors that affect fluidity
A
- Saturated(favors viscosity) and Unsaturated fatty acids(favors fluidity)
- fatty acid length: Shorter favors fluidity, and longer favors viscosity
- Temperature higher temp favors fluidity and lower temp favors viscosity
7
Q
What role does cholesterol have in membranes?
A
helps maintain proper fluidity of the membrane by interacting with fatty acids and phospholipids
8
Q
cytosolic leaflet
A
faces the cytosol
9
Q
non-cytosolic leaflet
A
faces the EXF or the internal compartments of an organelle
10
Q
true or false, all membranes have cytosolic and non-cytosolic leaflets?
A
TRUE
11
Q
Where does the membrane assembly occur?
A
In the ER, enzymes bound to the cytosolic surface of the ER membrane assemble the phospholipids using fatty acids as substrates
new phospholipids are then added to the cytosolic leaflet of the ER membrane
12
Q
Scarmblase
A
Enzymes that will randomly remove phospholipids and flip them to another resulting is that the ER membrane being a symmetric mixture of both lengths have approximately equal numbers of different phospholipids.
13
Q
Where can newly formed phospholipids go?
A
some of the newly assembled membranes will stay at the ER the rest will leave (through vesicle formation) and supply new membranes to other organelles or PM
14
Q
are the other membranes symmetrical ( besides ER)?
A
no, they are asymmetrical
15
Q
What does it mean when a membrane is asymmetrical?
A
one leaflet has a different proportion of specific phospholipids than the other, eg. the Golgi apparatus has phosphatidylcholine and sphingomyelin concentrated in the non-cytosolic layer.
16
Q
Flipasse
A
specifically slip one or two types of phospholipids from one leaflet to the other resulting in asymmetrical membranes
17
Q
Where do carbohydrates face when substituting glycolipids and phospholipids?
A
they are concentrated in the non-cytosolic surface and end up facing the ECF and PM
18
Q
Homoviscous adaptation
A
maintaining optimal fluidity of the membrane
19
Q
What are the functions of membrane proteins?
A
Channels, transporters
anchors
receptors
enzymes
20
Q
What are the types of membrane protein classifications?
A
Integral membrane proteins
peripheral membrane proteins
21
Q
Integral Membrane protein
A
directly attached to the lipid bilayer
22
Q
Peripheral membrane protein
A
bond to integral membrane proteins face one side of the membrane or the other
23
Q
What are the types of integral membrane proteins
A
Transmembrane proteins
monolayer associated
lipid-linked
24
Q
transmembrane proteins
A
span entier bilayer with regions exposed at ECF and ICF (amphipathic)
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monolayer associated
anchored to the cytosolic leaflet of the bilayer by an amphipathic alpha helix
26
lipid linked
linked to either side of the membrane by covalently attached lipid molecule
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Transmembrane Protein Structure
-portions exposed to ECF and ICF ten to be hydrophilic a.a
-the portion that spans the hydrophobic core of the membrane tends to have hydrophobic a.a
-the majority of bilayers spanning the region are alpha helices and occasionally Beta Barrels
28
alpha helix region
spans the membrane can occur as a single pass or multipass alpha helices
29
What function do multipass alpha helices serve?
They pass through the bilayer multiple times, which can be commonly seen in membrane proteins that create hydropholic pores (e.g., channels, or transporters), creating passages for hydrophilic substances across the membrane. The a.a. on the outer end interacts with the phospholipid layer, while the a.a. in the center creates a pore.
30
Beta barrels
A possible transmembrane spanning regions,
-multiple Beta sheets rolled into a cylinder
-hydrophobic a.a facing surrounding lipids and a.a that faces the inside being hydrophilic
-common bacterial membrane and outer membrane of mitochondria( form large water-filled pored)
31
Bacteriorhodopsin
-Proton Pump
-Transmembrane protein that is covalently linked to retinal
-retinal absorbs light that allows it to change shape which can lead to protons being pumped againts its gradient
-establishes and maintains a gradient of protons across a membrane often used to create ATP
32
What reinforces PM?
protein interactions
33
Give some examples of PM being reinforced by protein interactions.
Cell wall and Cell cortex
34
Cell wall
present in plant, yeast, and some bacteria
-composed of cellulose and protein other sugars and macro molecules maintaining cell shape and mechanical properties
35
Cell Cortex
a network of proteins attached to the cytosolic leaflet of the membrane
-stabilizes the PM in animal cells
composed of actin and myosin( cytoskeleton proteins)
eg. In RBC actin interacts with transmembrane anchoring protein and attaches to spectrin
36
True or False in general membrane proteins are fluid and allow proteins to migrate.
True but they're exceptions
37
What are examples of proteins having to remain in certain domains known as tethering?
a) membrane proteins can be bound to proteins within the cytosol, cell cortex
b) can be bound to protein or extracellular matrix
c) bound to membrane protein or another cell
d)tight junctions between adjacent cells can prevent lateral movement and restrict protein to a specific domain
38
Carbohydrates at the cell surface are known as
Glycocalyx
39
What are the types of glycocalyx?
a) most protein in PM have short chains or sugars "oligosaccharides" linked to them( glycoproteins)
b) proteins with longer chains of polysaccharides linked to them ( proteoglycan)
c) lipids in membrane with attached carb groups (glycolipids)
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glycoproteins + proteoglycans + glycolipids
glycocalyx
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Glycocalyx
the carbohydrate groups are hydrophilic and attract a layer of H2O just outside the cell ( lubricant)
-protects from mechanical damage
-Cell-to-cell recognition ( 2x sperm recognize the egg, immune system - infection puts lectin to bind glycocalyx to make neutrophils)
-everyone has a different glycocalyx so transplant resection can occur
42
Phospholipids have what type of core?
hydrophobic
43
what substance can dissolve into a membrane bilayer?
nonpolar/hydrophobic ( don't need assistance)
44
what are the majority of physiological revenant substances that must get across the membrane?
hydrophilic ( need assistance)
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what allows hydrophilic substances to cross the membrane?
1)transporters/carries
2)channels
46
What other major factors play a role in the rate of substances crossing the phospholipid bilayer?
size and solubility
47
describe some examples of substances that may need to transport proteins
2. small polar molecules have some ability to cross the bilayer ( grey area) like water ethanol and glycerol
3. Larger polar hydrophilic can not pass at a time frame that would be necessary for the cell to use
4. ion with a full charge can not cross
48
Membrane transport protein
assist hydrophilic molecules to cross the membrane
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What are the 3 cases of substances being able to cross the membrane with assistance?
a) membrane proteins- allows the membrane to be selectively permeable because the transport proteins are specific for 1 type of molecule
b)channels- allow for small hydrophilic substances mostly specific ions to cross by forming a hydrophilic pore
c) transports/carriers-large specific polar substances (ex. glucose) by specifically binding the substance, changing shape, and releasing the substance on the other side of the membrane-like 2-door elevator
50
Passive transport
-Substance moves across a membrane down the chemical concentration gradient
-toward equilibrium
-does not require additional energy
51
What are the types of passive transport?
A) simple diffusion
B) facilitated passive transport
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Simple Diffusion
-small nonpolar molecules ( hydrophobic) are capable of dissolving the phospholipid bilayer
-high to low eg. O2, CO2 , steroid hormones and fatty acids
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Facilitated passive transport
-transporter or channel allows specific hydrophilic substances to cross membranes
-high to low eg. glucose, amino acids, ions
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Active transport
-moving a solute against its gradient, the solute becomes more concentrated on one side of the membrane
-moving away from equilibrium( requires energy)
-low to high
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Ions and Membranes.
-the bulk of the ECF and ICF in electrically neutral
-each ion can be at different concentrations inside and outside the cell
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What are the Mamalian Cells Na+ and K+ membrane concentration
ECF Na+ = 145 mM
ICF Na+ = 14.5 mM
ICF K+ = 140-150mM
ECF K+ = 5mM
57
Membrane potential ( Vm)
-separation of opposite charge across the membrane
-measured in mV
58
What influences the movement of ions in a cell ?
-must consider both electrical properties and chemical concentration
-opposite attracts and like repels
58
What is the membrane potential of animal cells?
-Typically varies from -20 to -200 mV (depending on species and cell type)
eg. human neuron has resting membrane potential -70mV
58
What is the overall charge on animal cells?
-Have a slight excess negative charge inside the cell
-these negative charges attract positive charges in ECF
59
At a resting Vm of a human cell (70mV), what happens when you open a Na+ channel?
both chemical concentration and electrical properties for movement into the cell
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At a resting Vm of a human cell (70mV), what happens when you open a K+ channel?
the chemical concentrations are greater than the electrical so K+ leaves the cell through an open channel
61
Osmosis
-the diffusion of water across a selectively permeable membrane
-some water movement across the membrane is through simple diffusion but most occurs through aquaporins
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aquaporins
membrane proteins => water channel
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What happens if unequal concentrations of nonpenetrating solutes on either side of the membrane?
-water will move down its concentration gradient
- high water -> low water
-low solute -> high solute
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osmolarity
total solution concentration
#mol of solution/ 1L
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Transports/Carriers
responsible for transport of small hydrophilic organic molecules (monosaccharides, amino acids, nucleotides)
66
What are some characteristics of transporters and carriers
-specific transport of only one type of solute
-solute binds in specific binding pockets; transporter undergoes a conformational change; solute is released to the other side of the membrane
-saturable
-each membrane will have a characteristic site of transport present in the membrane regulating which specific solutes can cross that membrane.
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saturable
fine number of transporters in the membrane ( can reach a max rate of transport)
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passive transport
allow for facilitated diffusion
-the movement of hydrophilic substances down their electrochemical gradient
-no additional energy made
-eg. passive glucose transporters( glucose moving across membrane down the gradient) high to low
69
active transport
often called pumps
membrane proteins that move solute against the electrochemical gradient
-responsible for maintaining gradient across membranes
-requires energy 3 different sources
70
What are the 3 sources of energy in active transport
ATP driven
gradient driven
light-driven
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ATP driven
Molecule of ATP transfers a phosphate group to the pump
-providing energy to move a solute against it electrochemical gradient
eg. Na/K ATPase pump
3Na out for every 2K in (both ions moving against electrochemical gradient
72
describe the Ca2+ ATPase pump example
↳ maintain the low cytosolic concentration of Ca ions
↳ located in the plasma membrane and membrane of ER
↳ constantly pumping Ca ions out of the cell or sequestering
Ca+ in the ER
↳ as a result Ca+ concentration in ECF ~ 10^4 more
concentrated than in the cytosol
↳ low cytosolic Ca+ concentrations are important in cell
Signaling
73
gradient-driven pumps/ "secondary active transport"
↳ A gradient in any solute across a membrane can be
used to drive the active transport of a second molecule
↳ the movement of the driving solute down its gradient
Provides the Energy to move the second solute
against its gradient
In animal cells, Na+ is often the driving ion
In Plant cells, H+ is often the driving ion
74
co-transport/symport
both the driving ion and the actively transported substance move in the same direction
75
counter-transport/ antiport
the driving ion and actively transported substances move across the membrane in opposite directions
76
light-driven pump
↳ a photon of light provides energy for the membrane
to move a solute from an area of low concentration
too high concentration (against a gradient
eg. Bacteriorhodopsin: retinal responds to photons and
causes conformational change. Changes in Pump
moves It against a gradient.
77
Ion Channels/ membrane protein
↳ highly selective pores that allow PASSIVE
movement of specific ions down the Electrochemical gradient
discriminate which ions are allowed to pass based
on Size and charge.
↳ Channels Alternate between open and closed configuration
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leak channels
open most of the time regardless of conditions around the channel
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gated channels
open only under specific conditions
80
what are the keys to gated channels
mechanically gated
ligand-gated Extracellular ligand
ligand-gated intracellular ligand
voltage gated
81
mechanically gated
open in response to physical forces that deform the membranes
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ligand gated channels( chemically gated)
opens in response to the specific bind of extracellular/intracellular fluid chemical
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voltage-gated channels
open in response to a change in membrane potential
84
what is the rate of passive transport dependent on?
magnitude of the concentration gradient for that substance across a membrane
85
evolution of a membrane
enclosed organelles like the nuclear envelope and endomembrane system may have evolved through the invagination of PM
86
endomembrane system
membrane of ER, Golgi , peroxisomes, lysosomes , and endosomes
87
endosymbiotic theory of mitochondria and chloroplast
mito- are decedents of aerobic bacterium engulfed by a primitive prokaryotic cell
chloroplast- descendants of photosynthetic prokaryotes engulfed by a primitive cell
Ideas that support this theory include the fact that they contain their DNA and ribosomes.
88
Protein sorting
-signal sequences
-polypeptides without a signal sequence they stay in the cytosol
-often removed from the final functional form of protein
-multiple ways that proteins are transported
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signal sequences
a specific sequence of a.a that directs a protein to other organelles typically 15-60 a.a long
90
which organelles are considered double membrane structures
nuclear envelope, mitochondria , chloroplast
91
What does the inner nuclear membrane bind?
chromosomes and structural proteins internally
92
The outer nuclear membrane is continuous with?
with the membrane of ER
93
what component lets components enter and exit the nucleus
nuclear pores
94
Structure of nuclear pores
-a complex of 30 different proteins
-unstructured regions of pore proteins acting like "kelp forest" facing inside the pore (prevents the passage of large molecules but small hydrophilic can pass through the nucleus and cytosol)
-some larger macromolecules need to get in and out of the nucleus ribosomal subunits, RNA, and Proteins.
95
How do newly made proteins go from the cytosol to nucleus?
-all proteins destined for the nucleus will have nuclear localization signal/signal sequence (NLS)
-proteins with NLS will bind to the nuclear import receptor (NIR)
-the NIR then escorts the protein through the pore into the nucleus (requires energy like GTP hydrolysis)
-NIR and protein disassociate in the nucleus
-protein can now function in the nucleus
96
Do the mitochondria have a membrane structure?
double membrane
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Does the chloroplast have a membrane structure?
triple membrane stucture
98
Protein entering the mitochondria and chloroplast
-proteins synthesized in the cytosol must cross both membranes
-the precursor proteins are unfolded as they cross membranes
-energy costly: ATP powered
99
Process of proteins entering the mitochondria
-mitochondria signal sequences of the precursor protein are recognized by an import receptor protein in the outer mitochondria membrane( MM)
-the import receptor is. closely associated with the protein translocator in the outer membrane(TOM)
-once the protein is bonded to the receptor it creates a complex of receptor, protein, TOM
-the receptor transfers the protein to the TOM complex which then migrates laterally in the outer MM and begins to thread protein into intermembrane space until the signal sequence encounters a translocator in the inner membrane (TIM)
-the protein is threaded (unfolded) through TOM and TIM and enters the mitochondria matrix
-once in the matrix, the signal sequence is cleaved off ( by peptidase) it gets folded into the final form
100
proteins entering peroxisomes from cytosol
-these proteins have a short signal sequence of 3 a.a
-Cytosolic receptor protein will bind protein with a signal sequence
-receptor, protein complex then associate with translocator that aids in transport across peroxisomes
-poorly understood mechanisms and kinetics
101
Where are most proteins made that enter the nucleus, chloroplast, most peroxisomes, and mitochondria?
ribosomes in cytosol
102
Where are proteins targeted for the ER translated?
being translated at ribosomes initially in cytosol but then the whole complex of ribosome, polypeptide, and mRNA translocated to ER
103
Where do proteins that enter the ER go?
destined for another organelle of the endomembrane system, secretion. out of the cell, or remain in the ER—proteins moved by vesicular transport.
104
Mechanism of release of water-soluble protein to lume of ER ( not membrane proteins.
1.mRNA transcript associates with the ribosome in the cytosol
2. translation begins
3. the N-terminus (start) of a polypeptide is the ER signal sequence
4. A protein in the cytosol called signal recognition particle (SRP) will bind to ER signal sequence and ribosomes, SRP will pull complex toward ER
5. SRP has a complementary side with SRP receptor and will bind
6. SRP is released and ribosomes with polypeptide are transferred to the protein translocator in the ER membrane signal sequence remains bound to the translocator and the rest of the polypeptide is threaded through to the ER lumen as translocation progresses
7. signal peptidase cleaves the signal sequence (remains embedded in ER membrane) rest of the polypeptide is released to lume of ER
105
mechanism of water-insoluble molecules (remains in the membrane) for single-pass membrane proteins
1. The initial ER signal sequence binds to SRP and follows the steps of WS molecules until the threading occurs in step 6
2. polypeptide has a second hydrophobic sequence of a.a that functions as a stop translocation signal. when that sequence enters the translocator the polypeptide is discharged latterly into the ER membrane
3. signal peptidase cleaves off signal sequence-> polypeptide remains embedded in the membrane
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multi-pass membrane protein mechanism?
starting steps all the same as WIS molecule
-at the translocator, the signal sequence to start translocation is not at the N-terminus, it is further into a polypeptide chain
-so signal to start translocation occurs at the downstream location of the polypeptide
-translocation continues until a second hydrophobic sequence signal stops translocating
-polypeptide is discharged laterally into the membrane with multiple areas embedded in the membrane
107
vesicles
they are structures that transport cargo to and from organelles and PM the boundary of the vesicle is a phospholipid bilayer( membrane)
108
Formation of vesicles
vesicles form at membranes that have a protein coat on the cytosolic surface eg. clathrin
109
Vesicle formation
at the membrane, versicles start as a coated pit(clathrin eg.), and molecules assemble to form a basket-like weave-shaped membrane into a budding vesicle. dynamin pinches off the vesicle from the membrane and coat protein generally falls off the new vesicle
110
dynamin
motor protein wraps around the "neck" of vesicles and pinches it off from membrane
111
How do cargo sorting and destination targeting work?
each cargo molecule will have a specific transport signal
112
Transport signal
a specific sequence of a.a that binds to a specific cargo receptor present at the membrane (Golgi)
113
adaptin
proteins that are part of the coat complex bind to specific cargo receptors on the cytosolic side and anchor the coated pit
114
How does the vesicle target the correct membrane
-each vesicle will have a specific RAB protein and specific V-SNARE accosted with the cytosolic side of the vesicle. Rab and SNARE ( are based on cargo and cargo receptors)
-target membrane will have a specific tethering protein to bind rab protein and t-SNARE to bind V-SNARE
