Studied by 15 people
G proteins are an example of multi-domain proteins. (T or F)
False
In signaling through G proteins and GPCRs, which one of the following is true:
The GPCR is very rigid and cannot change its shape -all of these are correct -the extracellular signal molecule passes through the plasma membrane to activate the G protein -the GDP is part of the chemical structure of the G protein -none of these are correct
none of these are correct
Put the following steps regarding GPCR/G-protein signaling in the correct sequence: (1) The G protein dissociates into an alpha subunit and a beta gamma complex (2) The GTP molecule binds the G a subunit (3) The GPCR undergoes a conformational shape change (4) A signal molecule binds the GPCR (5) The GDP leaves the G a subunit 4 - 5 - 3 - 1 - 2 2 - 4 - 5 - 3 - 1 4 - 3 - 2 - 5 - 1 1 - 2 - 3 - 4 - 5 none of the above
none of the above
Secondary structure is stabilized primarily by hydrogen bonds between the amino acid side groups (True or False)
False
Protein domain is the term used to describe structurally stable independent regions within one polypeptide chain, which are usually connected to each other by relatively short and unstructured polypeptide segments. (True or False)
True
The alpha helix and beta sheet are two examples of regular folding patterns that are often found in parts of proteins. These patterns result from hydrogen-bonding between the N-H and C=O groups in the polypeptide backbone and do not involve the side groups. (True or False)
True
Protein secondary structure elements such as α helices and β sheets constitute the major regular folding patterns in proteins. With regard to these elements, -the folding patterns result from hydrogen-bonding between the N-H and C=O groups in the polypeptide backbone -only a few specific amino acid sequences can adopt these repetitive structures. -hydrogen-bonding between the amino acid side chains defines the type of secondary structure. -a certain short amino acid sequence always adopts the same secondary structure. -All of the above.
the folding patterns result from hydrogen-bonding between the N-H and C=O groups in the polypeptide backbone
Which of the following is NOT true regarding the members of a protein family in general? -Over evolutionary time scales, the family has expanded mainly through gene duplication events. -They have similar three-dimensional conformations. -They can functionally replace each other. -Their gene sequence is less well conserved than their structure. -They share an ancestry; i.e. they are homologs.
They can functionally replace each other.
Many viruses have large capsids in the form of a hollow sphere, made of hundreds of identical protein subunits. What are the advantages of having coats made of several copies of only a few subunits? -It requires a smaller amount of genetic information. -The effect of mistakes in protein synthesis on the overall assembly is minimized. -Disassembly can be readily regulated. -All of the above. -Assembly can be readily regulated.
All of the above.
Stable β-sheet aggregates can form from many proteins, forming intertwined cross-beta strands that have the potential to kill cells or damaged tissues. Which of the following is NOT true regarding these aggregates? -Different types of such aggregates can form from the same protein. -Some healthy cells form these aggregates to store their secretory proteins. -Their formation is associated with conditions such as Parkinson's disease -They form almost exclusively in the cells of the nervous system. -They can form spontaneously, but also can be triggered to form by an infection with the same aggregate.
They form almost exclusively in the cells of the nervous system.
The enzyme lysozyme catalyzes the cutting of a polysaccharide chain through hydrolysis. Which of the following is NOT true regarding the catalytic cycle for this enzyme?
It involves base catalysis.
It involves acid catalysis.
It involves strain catalysis.
It involves covalent catalysis.
It involves metal ion catalysis.
It involves metal ion catalysis.
Phosphorylation of a protein by a protein kinase ...
can create a binding site for other proteins.
requires the hydrolysis of two molecules of ATP per phosphorylated residue.
deactivates the protein.
adds two positive charges to the protein.
activates the protein.
can create a binding site for other proteins.
Many macromolecular complexes in the cell contain scaffold proteins. What do these proteins do that benefit the cell?
They can hold the many subunits of a large complex together.
They can confine and concentrate a specific set of interacting proteins to a particular cellular location.
They can enhance the rate of critical cellular reactions.
They can provide a large macromolecular complex with either flexibility or rigidity.
All of the above
All of the above.
which group of organic compounds includes the enzymes?
Starches
Proteins
Lipids
Carbohydrates
Proteins
Enzymes influence chemical reactions in living systems by:
combining with excess hydrogen to form gaseous wastes
absorbing water released when polymers are formed
providing the substrate required for the retain to occur
affecting the rate at which reactions occur
affecting the rate at which reactions occur
Which chemical is classified as an enzyme?
Manganese dioxide
Galactose
Lipid
Protease
Protease
In enzyme regulation, phosphorylation is an example of Covalent modification Product inhibition All of the above Allosteric regulation
Covalent modification
Enzymes that are allosterically regulated have multiple active sites. When an allosteric inhibitor binds to an enzyme, all active sites on the protein subunits are changed and work less well. (True or False)
True
Vitamins are essential to the survival of organisms because vitamins usually function as:
Substrates
Coenzymes
Nucleotides
Nucleic acids
Coenzymes
Enzymes can catalyze cellular reactions through various mechanisms. Which of the following statements is NOT true regarding enzymes?
They can provide the chemical groups necessary for simultaneous acid and base catalysis.
They accelerate a cellular reaction by destabilizing the transition state.
They can form covalent bonds with the substrate during catalysis.
They can strain a substrate to force it toward a specific transition state.
They have a higher affinity for the transition state of the substrate than for its stable form
They accelerate a cellular reaction by destabilizing the transition state.
Which of the following enzymes would digest fat?
lipase
nuclease
sucrase
protease
lipase
Competitive inhibitors:
bind to the active site of an substrate and compete with the enzyme
none of the above
bind to another part (NOT the active site) of an enzyme, causing enzyme shape to change
bind to the active site of an enzyme, competing with the substrate
bind to the active site of an enzyme, competing with the substrate
noncompetitive inhibitors:
none of the above
bind to another part (NOT the active site) of an enzyme, causing enzyme shape to change
bind to the active site of an enzyme, competing with the substrate
bind to the active site of an substrate and compete with the enzy
bind to another part (NOT the active site) of an enzyme, causing enzyme shape to change
Allosteric regulation
occurs when a regulatory molecule binds to a protein at one site and affects protein's function at another site
may inhibit enzyme activity
may stimulate enzyme activity
all of the above
all of the above
What do antibodies look like?
Each antibody structure consists of two heavy chains and two light chains
antibody forms a Y-shaped molecule
each antibody is shaped differently
antibody has a different amino acid sequence at the tips of the "Y"
All of the above
All of the above
A carbohydrate layer is present on the inner leaflet of cell membranes. (True or False)
True
The actions of a protein kinase to modify a protein can be reversed by a:
protein phosphatase
protein dephosphorylase
protein kinase
protein GTPase
protein phosphatase
Because the lipid bilayer is thicker and the lipid composition is specialized in lipid rafts, specific membrane proteins can accumulate there. This enables membrane proteins, which are normally highly mobile, to function together. (True or False)
True
Which of the following is not true of the plasma membrane.
The lipid layer is fluid
The plasma membrane is a continuous double layer of lipid molecules
Phospholipids in the lipid bilayer are free to flip back and forth from one layer to there other.
Lipid bilayer fluidity depends upon the layer's composition
Phospholipids in the lipid bilayer are free to flip back and forth from one layer to there other.
Which of the following is not a class of membrane lipid molecules:
Proteins
Cholesterol
Glycolipids
Phospholipids
Proteins
What do all β-barrel transmembrane proteins have in common?
The number of β strands.
The diameter of the barrel.
The general function, i.e. membrane transport.
The structural rigidity compared to α-helical transmembrane proteins.
The structural rigidity compared to α-helical transmembrane proteins.
Transmembrane proteins:
can be released from the membrane by a gentle extraction procedure such as salt treatment.
are sometimes covalently attached to a fatty acid chain that inserts into the membrane.
cannot contain β sheets in the part of their structure that interacts with the membrane interior.
are often further attached to the membrane via a GPI anchor. are typically exposed only to one side of the membrane.
are sometimes covalently attached to a fatty acid chain that inserts into the membrane.
For each membrane protein in the following schematic drawings, indicate whether the cytoplasmic side of the membrane is more likely to be on the left (L) or on the right (R). Your answer would be a four-letter string composed of letters L and R only, e.g. RRRR.
LRLR
RRLR
LLRL
RLLR
LLRL
While examining the crystal structure of a membrane protein, you find several phospholipid molecules bound to the protein. You know that these lipids ...
are thought to help stabilize many membrane proteins.
may enhance the crystallization of the bound membrane proteins.
All of the above.
can have head groups of various sizes and charges depending on the protein.
interact specifically with the protein.
All of the above.
Glycolipids such as gangliosides ...
are found in the extracellular leaflet (facing away from the cytosol) in the cellular membranes.
All of the above
are found to constitute about 10% of the total lipid mass in the plasma membrane of neurons. affect the electrical environment of the membrane.
may contain oligosaccharide chains with negatively charged residues.
All of the above
The motion of lipid molecules in a synthetic bilayer can be studied by various techniques. Which of the following has been observed in these systems?
The flip-flops are very rare for phospholipids but cholesterol molecules flip-flop more often.
Within a bilayer, lipid molecules rarely rotate about their long axis, but diffuse laterally at very high rates.
All of the above.
Phospholipids diffuse rapidly within and between the two leaflets of a bilayer.
The flip-flops are very rare for phospholipids but cholesterol molecules flip-flop more often.
The two monolayers of the plasma membrane in a human red blood cell ...
both contain glycolipids.
have the same abundance of phosphatidylinositol.
have different overall electrical charges, with negatively charged phospholipids (e.g. phosphatidylserine) normally enriched in the inner monolayer.
exchange phospholipids only through spontaneous flip-flops.
have different overall electrical charges, with negatively charged phospholipids (e.g. phosphatidylserine) normally enriched in the inner monolayer.
Many cells store lipids in droplets of varying sizes. These droplets ...
are enclosed by a phospholipid monolayer (instead of a bilayer).
are produced by and released from the Golgi apparatus.
have mostly protein-free bilayer membranes.
are composed primarily of charged amphiphilic lipids.
mostly store cholesterol and phospholipids.
are enclosed by a phospholipid monolayer (instead of a bilayer).
In the following schematic drawing of an abundant plasma membrane phosphoglyceride, which part is positively charged?
C
B
A
D
E
A
Which of the following is correct regarding the molecule Cholesterol in cell membrane?
It is a sterol.
All of the above
It is an amphiphilic molecule
It makes the membrane less permeable to small hydrophilic molecules.
It affects the fluidity of the lipid bilayer.
All of the above
In contrast to transporters, the channel proteins in cellular membranes ...
interact strongly with the solute(s) that they transport.
form pores that are always open.
can only mediate passive transport.
undergo a conformational change every time they transport a solute.
can only mediate passive transport.
Which of the following types of proteins do not extend into the bilayer?
Monolayer-associated proteins
Peripheral proteins
Transmembrane proteins
beta-barrels
Peripheral proteins
Which of the following describes membrane protein function?
They transport ions, nutrients and other substances across the membrane
They anchor cells to each other
They transduce external signals to the inside of the cell
All of the above
All of the above
Transmembrane alpha helices have side chains that are:
Charged
Hydrophobic
Hydrophilic Amphipathic
Hydrophobic
Which of the following terms describes transmembrane proteins?
They are amphipathic with both hydrophilic and hydrophobic portions
None of the above
They have alpha helices with hydrophilic side chains
They associate with only one side of the phospholipid bilayer
They are amphipathic with both hydrophilic and hydrophobic portions
Which intermolecular process primarily drives the formation of a bilayer when phospholipids are added to water?
Lipids cause water to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect.
The ordered arrangement of a bilayer is more favorable than the disordered state of individual free-floating phospholipids
Phospholipid self-assemble into a bilayer due to the strong affinity they have for each other
A bilayer arrangement maximizes the strength of Van der waals forces among phospholipids
Lipids cause water to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect.
Why do cells not have membrane transport proteins for O2?
Because oxygen is transported in and out of the cell in special oxygen-carrying proteins such as hemoglobin.
Because oxygen can dissolve in the lipid bilayer and diffuse in and out rapidly without the need for a transporter.
Because oxygen transport across a membrane is energetically unfavorable.
Because they need to keep the oxygen concentration low inside the reducing environment of the cell.
Because oxygen can dissolve in the lipid bilayer and diffuse in and out rapidly without the need for a transporter.
An ion channel ...
always mediates passive transport. is usually gated.
All of the above.
is typically several orders of magnitude faster than a transporter.
is ion-selective.
All of the above.
ATP is required in the transport of
molecules to areas of higher concentrations
all molecules across a membrane
molecules through a protein channel
molecules to areas of lower concentrations
molecules to areas of higher concentrations
The net movement of uncharged, polar molecules across a semipermeable membrane from a low concentration to a high concentration occurs by facilitated diffusion. (True or False)
False
Red blood cells have a characteristic concave shape because of
hemocyanin
hemoglobin
iron
cytoskeletal spectrin
cytoskeletal spectrin
Principal classes of membrane proteins include all of the following except
cell surface markers
Spectrins
receptors
transport proteins
Spectrins
A, B, and O blood groups are marked by surface
glycerol
glycoproteins
glycocarbohydrates
glycolipids
glycolipids
Transmembrane proteins are
none of the above
always abundant
never abundant
always fixed in position
none of the above
In each cycle the sodium-potassium pumps transfer
two potassium ions in and two sodium ions out
one sodium ion out and one potassium ion in
three sodium ions out and two potassium ions in
one potassium ion out and two sodium ions in
three sodium ions out and two potassium ions in
There are several levels of protein structure, the most complex of which is
Primary
Secondary
Tertiary
Quaternary
Qauternb
In the formation of a macromolecule, what type of bond would join two amino acid subunits?
Hydrophobic reaction
Hydrolysis reaction
Dehydration reaction
Denaturation reaction
Dehydration reaction
What happens during a hydrolysis reaction?
Protein coils into a secondary structure
The bond between two subunits of a macromolecule is broken
Saturated fats become unsaturated
A bond is formed between two subunits of a macromolecule
Water breaks ionic bonds
The bond between two subunits of a macromolecule is broken
Proteins are mainly composed of..
Carbon
Hydrogen
Oxygen
Nitrogen
All of the above
All of the above
Note
Flashcard