6 Biological Membranes Flashcards
1
Q
Lipids are compounds that are primarily:
- ______
- ______
- _______ (beh in water)
A
Compounds that are primarily:
- Non-polar (or amphipathic)
- Hydrophobic
- Insoluble in water
2
Q
What are four types of lipids?
A
- Fatty acids
- Triacylglycerol
- Membrane lipids
- Cholesterol
3
Q
What are Fatty acids?
A
- Long chain hydrocarbon carboxylic acid
- up to 24 carbons long (16 & 18) most common
- General formula (for a saturated Fatty Acid) CH3(CH2)NCOO-
- Amphipathic (Amphiphilic)
- Polar and non-polar portions
- May be saturated or unsaturated
- Saturated = no double bonds
- Unsaturated = double bonds
- Mono- or polyunsaturated (1+ DB’s)
- usually cis (z) double bonds
4
Q
FATTY ACIDS are:
- Long-chain _____________\_
- up to __\_carbons long (__\_ & __\_ most common)
- General formula (for a saturated Fatty Acid) ________\_
-
_____\_(_____\_)
- Polar and non-polar portions
- May be _____\_or _____\_
- _____\_ = no double bonds
-
_____\_ = double bonds
- Mono- or polyunsaturated (1+ DB’s)
- usually _____\_ conformation double bonds
A
FATTY ACIDS are:
- Long-chain hydrocarbon carboxylic acid
- up to 24 carbons long (16 & 18 most common)
- General formula (for a saturated Fatty Acid) CH3(CH2)NCOO-
-
Amphipathic (Amphiphilic)
- Polar and non-polar portions
- May be saturated or unsaturated
- Saturated = no double bonds
-
Unsaturated = double bonds
- Mono- or polyunsaturated (1+ DB’s)
- usually cis (z) conformation double bonds
5
Q
What type of molecules are shown in the image?
A
Fatty acids (Lipids)
(a) is saturated
(b) is monounsaturated (1 double bond between C9 and C10)
(c) is polyunsaturated (>1 double bond)
* ALL in Z or CIS configuration
6
Q
Would CIS or TRANS conformation of Fatty acids be more favourable? Why?
A
- TRANS appears more energetically favourable
- HOWEVER impact of of CIS = Creates a kink in the structure
- affects melting point (lowers mp) = liquid at room temperature
- Most naturally occurring db’s are in the cis conformation
7
Q
- Most naturally occurring double bonds are in the ___\_ conformation
- impact of __\_ = Creates a kink in the structure
- affects _______\_ = liquid at room temperature
A
- Most naturally occurring double bonds are in the cis conformation
- impact of CIS = Creates a kink in the structure
- affects melting point (lowers mp) = liquid at room temperature
8
Q
What is the shorthand notation of fatty acids and what does it identify about the structure?
A
- Shorthand notation identifies: (#C):(#double bonds)Δ(locations of the double bonds)
- eg:
- CH3CH2CH2CH2CH2COOH is 6:0 (5 carbons, no double bonds)
- carbon 1 is associated with the -OOH (carboxyl group)
9
Q
In a fatty acid, what Carbons would be designated alpha α, beta β, and omega ω?
A
Alpha: Carbon 2 (the carbon attached to the carboxyl group (COOH))
Beta: Carbon 3 - follows alpha
Omega: The last carbon in the chain
10
Q
Give the shorthand notation for the fatty acid in the image
- Is it a cis or trans double bond?
A
16:1 Δ7
Cis double bond
11
Q
Provide the shorthand notation for the fatty acid in the image:
A
16:1 trans Δ7
12
Q
If a shorthand notation for a fatty acid doesn’t indicate cis or trans explicitly, what can you assume it’s configuration is?
A
CIS
13
Q
How do double bonds affect fatty acids?
A
Double bonds alter the shape of fatty acids
14
Q
As length of the fatty acid chain increases, what happens to the Melting Point?
A
Melting point increases with length
15
Q
How does melting point change with increased degrees of unsaturation?
A
Melting point decreases with increased degrees of unsaturation (more double bonds)
16
Q
What two properties affect the fatty acid melting points and how?
A
- Length
- longer fatty acids melt at higher temperatures
- shorter fatty acids melt at lower temperatures
- Unsaturation
- Saturated fatty acids melt at higher temperatures
- Unsaturated fatty acids melt at lower temperatures
- Has a greater effect on melting point than length
17
Q
Does length or unsaturation have a greater effect on melting point (fatty acids)
A
Unsaturation has a greater effect
18
Q
Why does unsaturation have such a dramatic effect on melting point of fatty acids?
A
- Saturated fatty acids can align closely to maximize van der waal’s interactions
- Unsaturated fatty acids are bent = interferes with close packing
- Trans fatty acids are able to pack better than Cis ones
19
Q
What is triacylglycerol (TAG)?
A
Molecule that contains fatty acids as part of its structure; also contains glycerol
- Very hydrophobic (NOT amphipathic)
- way of storing fatty acids
- Three (ester-linked) acyl chains attached to glycerol
20
Q
Three acyl chains attached to glycerol make up what molecule?
A
Triacylglycerol
- Acyl chains from fatty acids (ester linked)
21
Q
What is the molecule in the image?
A
Triacylglycerol
- 3 acyl chains attached to glycerol
- acyl chains from fatty acids (ester-linked)
22
Q
TAG (triacylglycerol) is extremely ________ (not amphipathic). Why?
A
TAG (triacylglycerol) is extremely Hydrophobic (not amphipathic). Why?
- This is due to the Ester-linkage between the polar hydroxyls of glycerol and the polar carboxylates of the fatty acids.
- TAG (triglycerides) are hydrophobic, non-polar, and insoluble in water
Forms droplets in aqueous environment.
23
Q
Melting points for triacylglycerols will be lower for those containing ________ or ________
A
Melting points for triacylglycerols will be lower for those containing unsaturated fatty acids or Shorter chains
24
Q
What are the three lipids found in the membrane (ie membrane lipids)?
A
- Glycerophospholipids
- Sphingolipids
- Cholesterol
Glycerophospholipids and sphingolipids contain fatty acids as part of their structure and are structurally similar
25
Compare glycerophospholipids and triacylglycerol
* Like triacylglycerol, glycerolphospholipids have glycerol with _fatty acyl_ groups covalently attached
* Unlike triacylglycerol, the presence of a large polar group (phosphate) makes these molecules **amphipathic**
**\***variations exist in both polar head groups and acyl chains, affecting size and melting points
26
What is the molecule shown?
Cholesterol
27
Describe cholesterol
* Weakly amphipathic (because has single OH group - 3 h-bond interactions 2 accept 1 donor)
* Rigid, non-polar structure
* hydrocarbon/ring structure
* Accounts for ~35% of mammalian membranes
28
Cholesterol is mostly ______ (weakly amphipathic because of \_\_\_\_)
* ____ carbons and 1 \_\_\_
* Maintains _____ and _____ of membrane
Cholesterol is mostly _hydrophobic_ (weakly amphipathic because of _OH_)
* _27_ carbons and 1 _OH_
* Maintains _fluidity_ and _rigidity_ of membrane
29
How does cholesterol associate with the membrane?
Does not form membranes alone:
OH associates with polar headgroups of other lipids
* non-polar portion found in the membrane
30
Amphipathic molecules form _____ or ______ in water
Amphipathic molecules form _micelles_ or _bilayers_ in water
31
Membrane lipids form a ______ when mixed in water;
Fatty acids form _____ when mixed in water
Membrane lipids for a _bilayer_ when mixed in water;
Fatty acids form _micelles_ when mixed in water
32
What is the goal for Bilayer sheets, micelles and liposomes?
to eliminate unfavourable contact between H2O and hydrophobic tails while still permitting solvation of polar head groups
33
Why do fatty acids form micelle's instead of bilayers or liposomes?
The geometry is different:
* Fatty acids are more conical in shape - favours micelle formation
* Membrane lipids are more cylindrical - favours bilayers/liposomes
34
What are liposomes?
Simplified lipid membrane bilayer structures
- spherical vesicles
- allow for separation of different environments
- Isolates core from exterior environment
35
The structure and physical characteristics of bilayers depends on ________ which includes
* \_\_\_\_\_\_
* \_\_\_\_\_\_
The structure and physical characteristics of bilayers depends on _lipid composition_ which includes
* _acyl chain_
* _polar head group_
36
How are bilayers capable of being both fluid and stable?
They are non-covalently assembled
* no bonding between the individual lipid molecules and the surrounding aqueous environment
* relatively weak interaction
* individual components within bilayer are relatively mobile
37
Examine the image:
In what ways are the dimensions of a lipid bilayers variable?
* The lipid head groups have significantly different dimensions
* The acyl tails vary between 16-20 carbon atoms in **length** and degree of **unsaturation**
* Cholesterol is almost entirely buried in the bilayer
38
\_\_\_\_\_\_ is about the same size as a 16:0 fatty acid. What does this imply?
_Cholesterol_ is about the same size as a 16:0 fatty acid. What does this imply?
* If we have a 16:0 fatty acid and cholesterol nearby they are on the same scale which is important when looking at interactions within the membrane
39
What is the "ordered gel phase" of lipid bilayers?
**Below** the transition temperature (ie below melting point), acyl chains are packed together in van der Waals contact in a gel-like solid state
* Freeze membranes
* become fragile
* membranes can fracture
40
What is the disordered liquid crystalline phase of lipid bilayers?
Above the transition temperature (melting point), the lipid molecules and their acyl chains move freely and rapidly
41
What is the melting temperature (transition temperature) of a lipid bilayer?
The temperature of its transition from an ordered crystalline to a more fluid state
* Depends on acyl-chain unsaturation and length
42
A sharp transition of a short range is associated with a relatively _____ sample.
Biological membranes typically do not have a sharp transition temperature, why?
A sharp transition of a short range is associated with a relatively _pure_ sample.
* Biological membranes are a mixture of compounds (various lipids/proteins)
* must operate above gel temperature but not be completed disordered
43
How can a membrane maintain its fluidity with decreasing temperature?
* Add more unsaturated fatty acids
* Shorter fatty acids
44
How can a membrane maintain (in this case reduce) its fluidity with increasing temperatures?
* More **saturated** fatty acids (fewer double bonds)
* Longer fatty acids
45
How does cholesterol reduce the dynamic ability of fatty acids that are adjacent to it?
Cholesterol is rigid and planar = limits the rotational movement of neighbouring acyl tails thereby increasing van der Waals interactions
46
What is the effect of cholesterol on membrane rigidity at each temperature extreme (Low temperature and high temperature)
* Low temperature
* Prevents close packing between acyl chains = increases fluidity (decreases rigidity)
* High temperature
* decreases motion/disorder of acyl chains = increases rigidity
47
What is the overall effect of cholesterol?
To increase the membrane fluidity for a larger effective temperature range
48
What type of individual lipid movement happens freely and rapidly within the bilayer?
* Lateral movement happens freely and rapidly (within leaflet)
* Transverse movement (flip-flop) does not happen freely (from one leaflet to another)
* requires flipases and other enzymes
49
What types of proteins allow for differences in lipid composition in the leaflets?
Flipases and other enzymes that increase the rate of transverse diffusion
- requires significant amount of energy to move the polar head group through the hydrophobic core
50
Why doesn't transverse diffusion happen freely?
There is a significant energy barrier associated with desolvating a polar head group to move it through a hydrophobic bilayer
- requires flipases and other enzymes
51
\_\_\_\_\_\_ carry out most membrane processes
_Proteins_ carry out most membrane processes
52
What are the three types of membrane protein?
1. Integral membrane protein
2. Peripheral membrane protein
3. Lipid-linked protein
53
Which of the three types of membrane proteins has a hydrophobic surface and a hydrophilic surface (is amphipathic)?
Integral membrane protein
54
Peripheral membrane proteins are joined to the _______ of the membrane lipids via \_\_\_\_\_\_\_,\_\_\_\_\_\_\_\_,\_\_\_\_\_\_\_\_ interactions and can be easily disrupted (eg by changing \_\_\_\_\_\_\_\_)
Peripheral membrane proteins are joined to the _polar heads_ of the membrane lipids via _polar/ionic/electrostatic_ interactions and can be easily disrupted (eg by changing _[Salt]_)
55
Lipid-linked proteins associate with the membrane through __________ interactions via \_\_\_\_\_\_\_\_\_\_\_
Lipid-linked proteins associate with the membrane through _hydrophobic_ interactions via _lipid prosthetic group (hydrophobic)_
56
The portion of an integral membrane protein that is in contact with the **acyl** tails of the bilayer must have __________ on its surface
The portion of an integral membrane protein that is in contact with the **acyl** tails of the bilayer must have _hydrophobic amino acid side chains_ on its surface
57
What is the most important non-covalent force leading to the stabilization of the membrane proteins and lipids?
Hydrophobic effect
58
What can we ascertain about the sidechain type and distribution of integral membrane proteins from looking at the image of a K+ channel?
\*What four side chains could be indicated by the red? (very polar/charged)
* Nonpolar side chains (green) make up most of the helix surfaces that face the lipid tails
* Polar side chains (yellow) are more prominent in the loops, interacting with the lipid head groups and solvent
* Very polar (charged) side chains (Asp, Glu, Lys, and Arg) (red) often flank these regions interacting with solvent
59
What issue arises when we have a transmembrane structure found within a very hydrophobic portion of the bilayer? (similar to what happens in the core of soluble globular proteins)
If we are in a very hydrophobic environment, and we have a polypeptide chaine, present, then the preferred structure that would be adopted by those pp chains would be a regular secondary structure (alpha helices and beta sheets/barrels)
* Regular structures satisfy the hydrogen bond potential of the polypeptide backbone
60
\_\_\_\_\_\_\_\_\_ and ______ predominate as the portions of these protein structures that are assoc with these transmembrane regions
_Regular alpha-helices_ and _beta-sheets/barrels_ predominate as the portions of these protein structures that are assoc with these transmembrane regions
61
What type of residues would we expect to predominate on the surface of the alpha-helices around the region associated with the transmembrane structure?
Hydrophobic residues - need to associate with the non-polar tails of the lipid membranes
62
In regular beta sheets/barrels, the portion exposed to the hydrophobic portion of the bilayer will be \_\_\_\_\_\_
In regular beta sheets/barrels, the portion exposed to the hydrophobic portion of the bilayer will be _hydrophobic_
* Forms hydrophobic interactions with the lipid core of the bilayer
63
Amino acids that form a transmembrane alpha-helix are generally __________ (hydrophobic or hydrophilic)
Amino acids that form a transmembrane alpha-helix are generally _hydrophobic **along entire length of that portion of the polypeptide chain**_ (hydrophobic or hydrophilic)
64
It takes approx _______ amino acids to cross a membrane/bilayer. What is the significance of this?
It takes approx _20_ amino acids to cross a membrane/bilayer. What is the significance of this?
* If we find 20 hydrophobic aa in a row when looking at a protein structure, it is a clue that we may be dealing with something that has an integral membrane aspect to it (at least one integral membrane alpha-helix as part of its structure)
65
Both lipids and proteins can easily move ______ but cannot easily undergo ________ movement
Both lipids and proteins can easily move _laterally_ but cannot easily undergo _transverse_ movement
66
The "fluid" part of "Fluid Mosaic Model" stems from what concept?
That the bilayer is formed from a NON-COVALENT, dynamic, complex assembly of lipids and proteins (and carbohydrates)
67
Movement of proteins (within the bilayer environment) may be limited by the \_\_\_\_\_\_\_\_
Movement of proteins (within the bilayer environment) may be limited by the _cytoskeleton_
- fixed proteins
68
Carbohydrate chains are attached to the _______ surface of some proteins and lipids
Carbohydrate chains are attached to the _extracellular_ surface of some proteins and lipids
69
What type of molecules can freely cross the lipid bilayer via simple diffusion?
Small, non-polar molecules
70
\_\_\_\_\_\_/\_\_\_\_\_\_\_ molecules require assistance to cross the bilayer
_large_/_polar_ molecules require assistance to cross the bilayer
71
The rate of simple, unmediated diffusion depends on what three characteristics?
1. Size
* smaller = faster
2. Concentration gradient
* determines kinetics
* Larger gradient = faster rate of diffusion
3. Lipid solubility \*\*\*\*\*Most important\*\*\*\*\*
* Greater solubility (non-polar) increases diffusion rate
72
What are the two major types of **transport** across biological membranes?
1. Passive
2. Active
73
If deltaG (ΔG) is negative (-) than motion is \_\_\_\_\_\_\_\_\_\_\_\_
If deltaG (ΔG) is negative (-) than motion is _spontaneous (passive)_
* If concentration ratio is \<1, ln will be (-) and the process will be spontaneous
Where ΔG= RTln(([x]destination)/([x]source))
T= temperature (K)
R = constant
74
If delta-G (ΔG) is positive (+) then _\_\_\_\_\_\__ must be provided to make transport occur (active)
If delta-G (ΔG) is positive (+) then _energy_ must be provided to make transport occur (active)
Overall, ΔG\<0 for transport to occur
75
The free energy (ΔG) must always be _______ in order for a process to occur
The free energy (ΔG) must always be _negative_ in order for a process to occur
76
Transport proteins reduce the __________ for transport
Transport proteins reduce the _activation energy barrier_ for transport
77
\_\_\_\_\_\_\_ and _____ enable **passive** transport via membrane-spanning pores
_Porins_ and _Ion channels_ enable passive transport via membrane-spanning pores
78
Porins contain a relatively \_\_\_\_\_\_, _______ pore in the center of a \_\_\_\_\_\_
Porins contain a relatively _non-specific_, _water-filled_ pore in the center of a **_Beta-barrel_**
79
Most porins exist as ________ (3 subunits)
* each individual subunit forms a ________ structure and contains a \_\_\_\_\_\_
Most porins exist as _Trimers_ (3 subunits)
* each individual subunit forms a _beta-barrel_ structure and contains a _pore_
* regular secondary structure which characterizes most integral membrane proteins is a Regula beta sheet
80
Porins provide free diffusion up to \_\_\_\_\_\_kDa
Porins provide free diffusion up to _1.5kDa_ (150g/mol)
81
In ion channels, the channel is formed between \_\_\_\_\_\_.
\_\_\_\_\_\_ subunits with channel at the core = highly \_\_\_\_\_\_
In ion channels, the channel is formed between _subunits_
_Four_ subunits (**tetramer)** with channel at the core = highly _selective_
82
Selectivity of ion channels depends on the ________ and the \_\_\_\_\_\_\_\_\_
Selectivity of ion channels depends on the _size of the pore_ and the _properties of the side chains/functional groups_ found there
83
Using potassium channels as an example, explain how the properties of the side-chains/functional groups has more control over channel specificity than the size of the pore:
Potassium channel has four carbonyls forming the pore = K+ is capable of interacting with all four of these groups simultaneously.
Na+ (albeit smaller than K+) can only interact with one carbonyl at a time and therefore moves very slowly through the channel
84
What is the major structural difference between transport proteins (eg ion channels and porins) and **Transporter proteins?**
**Transporter proteins** (**Carrier proteins**) change shape (conformation)
* do not contain membrane-spanning pores
* May be passive or active
85
What type of relationship is shown by the kinetics of passive transport by carrier proteins?
Hyperbolic
86
What characteristic of carrier proteins causes them to have a max rate (whereas porins and ion channels do not have a max rate)
* The conformation change that carrier proteins undergo leads to a max rate
87
Label the red boxes
88
What are the three classifications of carrier proteins?
1. Uniport
2. Symport
3. Antiport
89
Two solutes transported in the same direction would be a _______ carrier protein;
Two solutes transported in opposite directions would be a ______ carrier protein;
One solute being transported is a ________ carrier protein
Two solutes transported in the same direction would be a _symport_ carrier protein;
Two solutes transported in opposite directions would be an _antiport_ carrier protein;
One solute being transported is a _uniport_ carrier protein
90
What is the difference between primary (1°) and secondary (2°) active transporters?
* Primary:
* typically uses ATP as the source of free energy
* Secondary
* Uses an ion gradient (eg Na+) as the source of free energy
91
In both primary and secondary active transport, at least one of the solutes will have an associated delta-G that is \_\_\_\_\_\_\_\_
In both primary and secondary active transport, at least one of the solutes will have an associated delta-G that is _greater than 0 (positive)_
= NON-Spontaneous
92
In _________ active transport, the free energy of the reaction is less than zero
ΔGrxn\<0
In _Primary_ active transport, the free energy of the reaction is less than zero
ΔGrxn\<0
* ATP hydrolysis
* Redox rxn
93
In _______ active transport, the free energy of an ion which is less than zero plus the free energy of the reaction will give us a net free energy that is MORE NEGATIVE than the free energy associated with the transport of our solute in order for the process to occur
ΔGT(ion) \<0 + ΔGrxn =
ΔGnet \< 0 (spontaneous)
In _secondary_ active transport, the free energy of an ion which is less than zero plus the free energy of the reaction will give us a net free energy that is MORE NEGATIVE than the free energy associated with the transport of our solute in order for the process to occur
ΔGT(ion) \<0 + ΔGrxn =
ΔGnet \< 0 (spontaneous)
Ie things have to add up to be less than zero in order for secondary active transport to occur
94
Fill in the table
95
How are primary and secondary active transport connected?
Primary active transport often **drives** secondary active transport
96
The sodium potassium pump (Na+K+ ATPase) is an example of a __________ transporter
The sodium-potassium pump (Na+K+ ATPase) is an example of a _primary active_ transporter
97
The Na+K+ ATPase requires ____ to move ions ______ their concentration gradients
The Na+K+ ATPase requires _ATP_ to move ions _against (up)_ their concentration gradients
98
In each cycle of the Na+K+ ATPase, we see:
* export of \_\_\_\_\_\_\_
* import of \_\_\_\_\_\_\_
* via \_\_\_\_\_\_\_
In each cycle of the Na+K+ ATPase, we see:
* export of _3 Na+ ions_
* import of _2 K+ ions_
* via _ATP + H2O -\> ADP + Pi + H+_
**S**odium
**O**ut
**P**otassium
**I**n
**P**ositive
**O**ut
**N**egative
**I**n
99
The two concentration gradients generated across the cell membrane via Na+K+ATPase are used as ?
The two concentration gradients generated across the cell membrane via Na+K+ATPase are _used as the source of energy for a variety of **secondary active transport** processes_
eg Glucose transport
100
Na+K+ is an electrogenic antiport, what does this mean?
Electrogenic= generates a charge differential across the membrane
Creates a **Transmembrane voltage**
Antiport = moving in opposite directions (Na+ out and K+ in)
101
What does it mean that "the activity of the pump (Na+K+ATPase) is determined by the size of the concentration gradient)?
As the gradient increases (ie the difference in ion concentrations) then the action of the pump slows down
102
The Na+ Glucose transporter is a ____________ transporter
The Na+ Glucose transporter is a _secondary active_ transporter
103
How is the import of Na+ related to the Na+K+ATPase?
Na+K+ATPase has created a high concentration of Na outside the cell relative to inside the cell so importing Na+ = moving DOWN concentration gradient = negative free energy change (delta G \<0 =spontaneous)
104
How does Na+K+ATPase provide energy for glucose transport?
Na+K+ATPase creates the concentration gradient for Na and K. When Na+ moves back into the cell (down its gradient) it releases energy (delta G \<0 ).
The concentration of Glucose is higher inside the cell than outside therefore glucose import would be associated with a POSITIVE free energy change (delta G \>0)
* The NET free energy of transport must be less than zero for glucose import
105
How are the primary and secondary active transports for Na+K+ATPase and Na+ Glucose linked?
The primary active antiporter (Na+K+ATPase) creates a concentration gradient;
The secondary active symporter (Na+ Glucose) uses that concentration gradient (of sodium) to drive the import of a third molecule (glucose)
106
What makes Na+ Glucose transporter a Symporter?
Both Na+ and Glucose are being imported (moving in same direction)
107
Which of the following statements about passive and primary active transporter proteins is FALSE?
A. They are both integral membrane proteins.
B. They both show a high degree of selectivity.
C. Both require a concentration gradient to function.
D. They both change conformation during transport
Which of the following statements about passive and primary active transporter proteins is FALSE?
A. They are both integral membrane proteins.
B. They both show a high degree of selectivity.
_C. Both require a concentration gradient to function._
D. They both change conformation during transport
108
Which of the following statements is TRUE for passive transport across a biological membrane?
A. Passive transport is driven by a solute concentration gradient.
B. Passive transport is driven by ATP.
C. Passive transport is irreversible.
D. Passive transport is endergonic (requires an input of energy to occur).
E. Passive transport is not specific with respect to the substrate.
Which of the following statements is TRUE for passive transport across a biological membrane?
_A. Passive transport is driven by a solute concentration gradient._
B. Passive transport is driven by ATP.
C. Passive transport is irreversible.
D. Passive transport is endergonic (requires an input of energy to occur).
E. Passive transport is not specific with respect to the substrate.
109
Which of the following determines the force that "drives" an ion through an ion channel in a membrane?
A. The size and shape of the channel.
B. The size of the ion.
C. The properties of the selectivity filter.
D. The size of the concentration gradient across the membrane.
Which of the following determines the force that "drives" an ion through an ion channel in a membrane?
A. The size and shape of the channel.
B. The size of the ion.
C. The properties of the selectivity filter.
**D. The size of the concentration gradient across the membrane.**
110
Which of the following statements about biological membranes is TRUE?
A. The composition of membrane lipid bilayers may be varied slightly, to maintain it in the gel‐crystalline state.
B. The bilayer is stabilized by hydrophobic interactions between the polar lipid head groups and the aqueous environment.
C. Integral membrane proteins penetrate or span the lipid bilayer, interacting with the hydrophobic lipid acyl chains.
D. Peripheral membrane proteins are covalently bound with the polar lipid head groups of the bilayer.
Which of the following statements about biological membranes is TRUE?
A. The composition of membrane lipid bilayers may be varied slightly, to maintain it in the gel‐crystalline state.
B. The bilayer is stabilized by hydrophobic interactions between the polar lipid head groups and the aqueous environment.
**C. Integral membrane proteins penetrate or span the lipid bilayer, interacting with the hydrophobic lipid acyl chains.**
D. Peripheral membrane proteins are covalently bound with the polar lipid head groups of the bilayer.
111
Which of the following is never found in biological membranes?
A. Glycerophospholipids
B. Cholesterol
C. Sphingolipids
D. Triacylglycerols
E. C and D
Which of the following is never found in biological membranes?
A. Glycerophospholipids
B. Cholesterol
C. Sphingolipids
**D. Triacylglycerols**
E. C and D
112
A transporter protein moves substances X and Y as shown in the following diagram. It moves X down its concentration gradient and Y up its concentration gradient. What type of transport is this?
A. Primary active antiport
B. Primary active symport
C. Secondary active antiport
D. Secondary active symport
A transporter protein moves substances X and Y as shown in the following diagram. It moves X down its concentration gradient and Y up its concentration gradient. What type of transport is this?
A. Primary active antiport
B. Primary active symport
**C. Secondary active antiport**
D. Secondary active symport
113
The following are steps that incompletely describe the mechanism by which Na+ and K+ ions are transported by the Na+-K+ ATPase. What is the correct sequence for the events listed, *assuming that Na+ ions have just dissociated*?
1. The phosphate group on the protein is hydrolyzed.
2. ATP binds to the protein.
3. The protein's conformation changes, exposing K+ binding sites to the cell interior.
4. Na+ ions bind.
**1,3,4,2**
1. The phosphate group on the protein is hydrolyzed.
2. ATP binds to the protein.
3. The protein's conformation changes, exposing K+ binding sites to the cell interior.
4. Na+ ions bind.
114
Why are glycerophospholipids capable of spontaneously assembling into the bilayer structure found in biological membranes?
(2)
* Glycerophospholipids are amphipathic.
* Glycerophospholipids have two acyl chains that align easily side‐by‐side to form a bilayer.
115
Which of the following statements most accurately defines the term “symport”?
A. When a membrane protein transports two substances in the same direction.
B. When a membrane protein transports two substances in opposite directions.
C. When a membrane protein transports two substances in the same direction up their concentration gradients.
D. When a membrane protein transports two substances in opposite directions up their concentration gradients.
Which of the following statements most accurately defines the term “symport”?
**A. When a membrane protein transports two substances in the same direction.**
B. When a membrane protein transports two substances in opposite directions.
C. When a membrane protein transports two substances in the same direction up their concentration gradients.
D. When a membrane protein transports two substances in opposite directions up their concentration gradients.
116
Transport of digested glucose across intestinal cells from the intestinal space to the blood requires multiple transporters. Which of the following proteins is NOT required?
A. The Na+-glucose symporter
B. The Na+-K+ ATPase
C. The K+ channel
D. B and C
E. A and C
Transport of digested glucose across intestinal cells from the intestinal space to the blood requires multiple transporters. Which of the following proteins is *NOT* required?
A. The Na+-glucose symporter
B. The Na+-K+ ATPase
**C. The K+ channel**
D. B and C
E. A and C
117
You have discovered a protein that transports Ca2+ ions up a concentration gradient, from the cytoplasm into the endoplasmic reticulum. No other ions move during this transport. Which type of transport protein does this appear to be?
A. A Ca2+ ion channel
B. A Ca2+ ion porin
C. A primary active uniporter
D. A secondary active uniporter
You have discovered a protein that transports Ca2+ ions *up* a concentration gradient, from the cytoplasm into the endoplasmic reticulum. No other ions move during this transport. Which type of transport protein does this appear to be?
A. A Ca2+ ion channel
B. A Ca2+ ion porin
**C. A primary active uniporter**
D. A secondary active uniporter
118
Which of the following statements about passive transport across a membrane is TRUE?
A. It can increase the size of a transmembrane concentration gradient of the diffusing solute.
B. A specific membrane protein lowers the activation energy for movement of the solute across the membrane.
C. It is impeded by the solubility of the transported solute in the nonpolar interior of the lipid bilayer.
D. It is responsible for the transport of gases such as O2, N2, and CH4 across biological membranes.
Which of the following statements about *passive* *transport* across a membrane is TRUE?
A. It can increase the size of a transmembrane concentration gradient of the diffusing solute.
_B. A specific membrane protein lowers the activation energy for movement of the solute across the membrane._
C. It is impeded by the solubility of the transported solute in the nonpolar interior of the lipid bilayer.
D. It is responsible for the transport of gases such as O2, N2, and CH4 across biological membranes.
119
Ion channels are selective whereas porins are not. Which of the following statements explains this difference?
A. In porins, the channel is located within a single subunit, whereas in ion channels it is located between subunits.
B. Ion channels transport charged substances, whereas porins transport polar substances.
C. The quaternary structure of ion channels includes amino acids that are positioned to form non‐covalent interactions with the ion.
D. Porins typically cross the lipid bilayer as b‐barrels, whereas the subunits in ion channels cross the lipid bilayer as a‐helices.
Ion channels are selective whereas porins are not. Which of the following statements explains this difference?
A. In porins, the channel is located within a single subunit, whereas in ion channels it is located between subunits.
B. Ion channels transport charged substances, whereas porins transport polar substances.
**C. The quaternary structure of ion channels includes amino acids that are positioned to form non‐covalent interactions with the ion.**
D. Porins typically cross the lipid bilayer as b‐barrels, whereas the subunits in ion channels cross the lipid bilayer as a‐helices.
120
In the figure shown below, which of the labelled carbons is the β‐carbon?
**Z**
121
The diagram below shows the structure of an integral membrane protein. The solid lines indicate the approximate location of the polar head groups of the lipid bilayer.
Which arrow most correctly identifies a region in the protein where you would expect to find amino acid residues such as Leu, Ile, Val and Ala?
**1**
Leu, Ile, Val and Ala are HYDROPHOBIC and would therefore be found in the hydrophobic, non-polar acyl tail groups
122
Which of the following conclusions can be drawn regarding the protein shown below, given ONLY the information in the diagram?
A. This protein is a transporter protein.
B. This protein is an ion channel.
C. This protein is not a porin.
D. This protein is not an active transporter.
A. This protein is a transporter protein.
B. This protein is an ion channel.
**C. This protein is not a porin.**
D. This protein is not an active transporter.
123
Which of the following does NOT correctly describe the picture below?
A. Polyunsaturated
B. Spontaneously forms a bilayer in aqueous solution.
C. 18:2Δ9,12
D. Fatty acid
Which of the following does NOT correctly describe the picture below?
A. Polyunsaturated
**B. Spontaneously forms a bilayer in an aqueous solution.** (*fatty acids form micelles when mixed with water*)
C. 18:2Δ9,12 *(18C:2db's at C9 and C12)*
D. Fatty acid
124
Which of the following is TRUE for both primary and secondary active transporters?
A. They catalyze ATP hydrolysis to pump a substance against its concentration gradient.
B. Transport occurs via proteins that form a channel through the membrane.
C. They require free energy input to move a substance up its concentration gradient.
D. They are not very specific with respect to the substrates they transport.
E. They couple the transport of one substance against its gradient with co-transport of a second substance down its concentration gradient.
Which of the following is TRUE for both primary and secondary active transporters?
A. They catalyze ATP hydrolysis to pump a substance against its concentration gradient.
B. Transport occurs via proteins that form a channel through the membrane.
**C. They require free energy input to move a substance up its concentration gradient.**
D. They are not very specific with respect to the substrates they transport.
E. They couple the transport of one substance against its gradient with co-transport of a second substance down its concentration gradient.
