Cell biology Chapter 4

chichi's version from 2015-07-21 22:41

Part One

Question Answer
Generally, the total number of nonpolar amino acids has a greater effect on protein structure than the exact order of amino acids in a polypeptide chainFalse, The order in which amino acids are linked unique for each protein and is the most important factor in determining overall protein structure
The "polypeptide backbone" refers to all atoms in a polypeptide chain, except for those that form the peptide bonds.False, Peptide bonds are planar amide bonds that are central to the polypeptide backbone formation. The atoms in the amino acid side chains are not considered to be part of the backbone
The chemical properties of amino acid side chains include charged, uncharged polar, and nonpolar.True
The relative distribution of polar and nonpolar amino acids in a folded protein is determined largely by hydrophobic interactions, which favor the clustering of nonpolar side chains in the interior.True
Although all protein structures are unique, there are common structural building blocks that are referred to as regular secondary structures. Some have α helices, some have β sheets, and still others have a combination of both. What makes it possible for proteins to have these common structural elements?hydrogen bonds along the protein backbone.
Which of the following statements is true?Disulfide bonds stabilize but do not change a protein's final conformation
Lysozyme is an enzyme that specifically recognizes bacterial polysaccharides, which renders it an effective antibacterial agent. Into what classification of enzymes does lysozyme fall?hydrolase
For some proteins, small molecules are integral to their structure and function. Enzymes can synthesize some of these small molecules, whereas others, called vitamins, must be ingested in the food we eat. Which of the following molecules is not classified as a vitamin but does require the ingestion of a vitamin for its production?retinal
Feedback inhibition is defined as a mechanism of down-regulating enzyme activity by the accumulation of a product earlier in the pathwayFalse. Feedback inhibition occurs when an enzyme acting early in a pathway is inhibited by the accumulation of a product late in the pathway
If an enzyme's allosteric binding site is occupied, the enzyme may adopt an alternative conformation that is not optimal for catalysisTrue

Part Two

Question Answer
Protein phosphorylation is another way to alter the conformation of an enzyme and serves exclusively as a mechanism to increase enzyme activityFalse. Phosphorylation of a protein can change its conformation, this act can either increase or decrease the activity of the enzyme.
GTP binding proteins typically have GTPase activity and the hydrolysis of GTP transforms them to the off conformationTrue
Where does most new membrane synthesis take place in a eucaryotic cell?in the endoplasmic reticulum
There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)?15 carbons with 2 double bonds
Motor proteins use the energy in ATP to transport organelles, rearrange elements of the cytoskeleton during cell migration, and move chromosomes during cell division. Which of the following mechanisms is sufficient to ensure the unidirectional movement of a motor protein along its substrate?A conformational change is linked to ATP hydrolysis.
Which of the following membrane lipids does not contain a fatty acid tail?cholesterol
Although cholesterol is a hydrophobic molecule, it has a hydrophilic head group like all other membrane lipidsTrue
Phosphatidylserine is the most abundant type of phospholipid found in cell membranesFalse, Phophcholine is the most abundant type
Glycolipids lack the glycerol component found in phospholipidsTrue
The highly ordered structure of the lipid bilayer makes its generation and maintenance energetically unfavorableFalse, makes it FAVORABLE

Part Three

Question Answer
Which of the following statements is true?Membrane lipids diffuse within the plane of the membrane.
Cholesterol serves several essential functions in mammalian cells. Which of the following is not influenced by cholesterol?membrane thickness
A protein that relies on protein-protein interactions to stabilize its membrane association is classified as a peripheral membrane proteinTrue
Lipid-linked proteins are classified as peripheral membrane proteins because the polypeptide chain does not pass through the bilayer.False, Lipid-linked proteins are classified as integral membrane proteins because although they are not transmembrane proteins, they are covalently bound to membrane lipids and cannot be dissociated without disrupting the membrane's integrity
A protein can be embedded on the cytosolic side of the membrane bilayer by employing a hydrophobic α helix.False, An embedded protein employs an amphipathic helix. The hydrophobic side interacts with the fatty acid tails of the membrane lipids and the hydrophilic portion interacts with the aqueous components of the cytosol
Membrane proteins that pump ions in and out of the cell are classified as enzymes.False, Membrane proteins that pump ions in either direction across the membrane are in the functional class of transporters
Which of the following statements about the carbohydrate coating of the cell surface is false?The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain.
We can estimate the relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area. What is this method called? What does the abbreviation stand for?FRAP, Fluorescent recovery after photobleaching
CO2 and O2 are water-soluble molecules that diffuse freely across cell membranes.True
The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content.False. The primary difference between cell membranes and artificial membranes is that cell membranes have proteins responsible for creating a selective permeability, which varies with the location and function of the membrane.

Part Four

Question Answer
Transporters are similar to channels, except that they are larger, allowing folded proteins as well as smaller organic molecules to pass through them.False. Transporters work by changing conformation after specific binding of the solute to be transported. Channels exclude molecules on the basis of size and charge, but do not depend on specific recognition of the molecules moving through.
Cells expend energy in the form of ATP hydrolysis so as to maintain ion concentrations that differ from those found outside the cell.True
Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion?Cl-
A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process: C6H12O6 + 2ADP + 2Pi + H+  2CO2 + 2CH3CH2OH + 2ATP + 2H2O Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cell’s demise?inability to import sugar into the cell
Ion channels are classified as membrane transport proteins. Channels discriminate by size and charge. In addition to Na+, which one of the following ions would you expect to be able to freely diffuse through a Na+ channel? Explain your answer.H+, If an ion channel is open, it will allow any ion that is under a certain size and that has the correct charge to pass through. H+ is the only ion listed that is both smaller and has the same charge of +1.
Transporters, in contrast to channels, work by __________________.specific binding to solutes
Facilitated diffusion can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient.False. This describes coupled transport, which is one type of active transport. Facilitated diffusion can also be called passive transport, in which a solute always moves down its concentration gradient.
Transporters undergo transitions between different conformations, depending on whether the substrate-binding pocket is empty or occupied.True
The electrochemical gradient for K+ across the plasma membrane is small. Therefore, any movement of K+ from the inside to the outside of the cell is driven solely by its concentration gradient.True
The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter.False. Glucose is an uncharged molecule, and its import is not directly affected by the voltage difference across the membrane if glucose is being transported alone. If the example given were the Na/glucose symporter, we would have to consider the charge difference across the membrane.

Part Five

Question Answer
Active transport requires the input of energy into a system so as to move solutes against their electro chemical and concentration gradients. Which of the following is not one of the common ways to perform active transport?K+-coupled Because K+ is a positively charged ion and the outside of the plasma membrane is positively charged, K+ has a very small electrochemical gradient across the membrane even though its concentration gradient is large. Because there is little net movement across the membrane for K+, it would not make a good source of energy to drive the transport of other molecules against their respective gradients.
You have generated antibodies that recognize the extracellular domain of the Ca2+ pump. Adding these antibodies to animal cells blocks the active transport of Ca2+ from the cytosol into the extracellular environment. What do you expect to observe with respect to intracellular Ca2+?Ca2+ concentrations in the cytosol INCREASE at a steady rate.
Which of the following statements is true?The Na+-K+ pump helps to keep both Na+ and Cl– ions out of the cell.
Which of the following best describes the behavior of a gated channel?It opens more frequently in response to a given stimulus.
The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. Which type of gating mechanism do these cells use?stress-gated
If Na+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected?It becomes more positive, As Na+ ions move into the cell, the net charge becomes more positive (less negative)and the membrane potential changes to reflect the Co/Ci for both Na+ and K+ ions.

Part Six

Question Answer
Which of the following is required for the secretion of neurotransmitters in response to an action potential?voltage-gated Ca2+ channels, Voltage-gated Ca2+ channels open in response to the depolarization caused as the action potential moves toward the nerve terminal. The influx of calcium from outside the cell causes the synaptic vesicles to fuse with the plasma membrane and release large amounts of neurotransmitter into the synaptic cleft.
The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions?acetylcholine
Fully folded proteins typically have polar side chains on their surfaces, where electrostatic attractions and hydrogen bonds can form between the polar group on the amino acid and the polar molecules in the solvent. In contrast, some proteins have a polar side chain in their hydrophobic interior. Which of following would not occur to help accommodate an internal, polar side chain?A hydrogen bond forms between a polar side chain and an aromatic side
The three-dimensional coordinates of atoms within a folded protein are determined experimentally. After researchers obtain a protein’s structural details, they can use different techniques to highlight particular aspects of the structure. What visual model best displays a protein’s secondary structures (α helices and β sheets)?Ribbon
The amino acids in the interior of a protein do not interact with the ligand and do not play a role in selective bindingFalse,
Antibodies are Y shaped and are composed of six different polypeptide chainsFalse, 4 polypeptide chains
ATPase generate ATP for the cellFalse, ATPase hydrolyze ATP
Hexokinase recognizes and phosphorylates only one of the glucose stereoisomersTrue