Final Exam Review Flashcards
1
Q
What are the 3 building blocks of dna
A
Phosphate, sugar and base
2
Q
What are the Pyrimidines
A
C and T
3
Q
What are the purines
A
G and A
4
Q
What type of bonds hold together are nucleotide subunits
within a DNA
strand are
held
together by
A
phosphodiester
bonds
5
Q
how many hydrogen bonds are between a and t
A
2
6
Q
how many hydrogen bonds are between c and g
A
3
7
Q
how much dna does a human cell contain
A
about 2 meters of DNA
8
Q
What is the basic unit of units
of eukaryotic
chromosome
structure
A
nucleosomes
9
Q
heterochromatin
A
makes up about 40% of typical chromosome
10
Q
euchromatin
A
60% of typical chromosome
11
Q
When was the first draft of the human genome completed
A
1999
12
Q
When was the human genome sequenced
A
2021
13
Q
how many nucleotide pairs are needed
to encode an average size protein
A
1300
14
Q
what percentage of the human genome is exons
A
less than 1%
15
Q
What are the 2 dna sequencing methods
A
Maxam-Gilbert method
* chemical cleavage of DNA at specific nt
* Sanger method
* enzymatic extension of DNA strand to a
defined terminating base
16
Q
how many reading frames are there
A
3
17
Q
what is the start codon
A
MET
18
Q
What is the DNA replication mechanism
A
semiconservative
19
Q
how was semi conservative dna replication discovered
A
using heavy and light nitrogen
20
Q
how many replication forks are there
A
2
21
Q
what is the rate of replication of bacteria and humans
A
- 100 nt/s humans
1,000 nt/s bacteria
22
Q
What direction is dna synthesis
A
5’-to-3’direction
23
Q
DNA helicase
A
unwinding of the parent DNA double helix
ATP dependent
24
Q
Single-strand DNA binding proteins
A
prevent reforming of double helix and
keeping them in elongated form
25
sliding clamp
keeps
DNA pol
attached to
DNA template
26
DNA Topoisomerases
enzymes that relieve the tension that builds
up in front of a replication fork
27
What is depurination
removal of A nucleotide
28
What is deamination
conversion of cytosine to uracil
29
What is a thymine dimers
covalent linkages between two adjacent
pyrimidine bases
30
What type of mutation does Deamination lead to
* produce permanent mutations
* can lead to substitution
31
What type of mutation does Depurination lead to
can lead to deletion
32
What are the 3 steps in repairing dna damage
1. DNA damage is recognized
and removed by a variety of
nucleases
2. a repair DNA polymerase binds
to the 3’-OH end of the cut
DNA strand
3. DNA ligase seals the break
left in the sugar-phosphate
backbone
33
What can cause double-stranded DNA breaks
* radiation
* mishaps at the replication fork
* various chemical assaults
34
How can cells to repair dsDNA breaks
nonhomologous end joining and homologous recombination
35
* nonhomologous end joining
* quickly stick the broken ends together
* before the DNA fragments drift apart and
get lost
36
* homologous recombination
* shortly after DNA
replication
* specialized enzymes
* recA bacteria
* repair DNA polymerase
* uses complementary
undamaged strand
as a template
37
how many hydrogen bonds are between a and u
2
38
What is a gene
* a segment of DNA that directs the production
of a particular protein or functional RNA
molecule
39
What is transcription
gene to RNA
40
what is translation
rna to protein
41
* RNA polymerase
* catalyzes
formation of
phosphodiester
bond
* moves stepwise
along the DNA
42
* ribosomal RNAs (rRNAs)
* form the structural and catalytic core
of the ribosome
43
* transfer RNAs (tRNAs)
* serve as adaptors between mRNA and
aa during protein synthesis
44
microRNAs (miRNAs)
regulate gene expression
45
* small interfering RNAs (siRNAs)
* provide protection from viruses and
proliferating transposable elements
46
* long noncoding RNAs (lncRNAs)
* act as scaffolds and serve other diverse
functions, many of which are still being
discovered
47
what is the sigma factor
recognizes the promoter
48
RNA polymerase 1
most rRna genes
48
RNA polymerase 2
all protein coding genes
49
RNA polymerase 3
tRna genes
50
What RNA polymerase is used for mRNA
RNA polymerase 2
51
* RNA capping
* modifies the 5’ end
of the RNA transcript
* introduces atypical nt
52
* polyadenylation
* special structure
at the 3’ end
* series of repeated
adenines
53
How many nucleotides are there
20
54
how many triplet possibilies are there
64
55
What are the 3 stop codons
UAA
UAG
UGA
56
What is a tRNA molecule
* specific adaptor molecules serve as intermediaries
between the codons of mRNA and aa
* ~ 80nt long
* 4 short segments form
double helical structures
57
What is a anticodon
* form by a set of three consecutive nt
that bind, through base-pairing, to the
complementary codon in an mRNA
molecule
58
What is a ribosome
* large complex
* ribosomal proteins
* ribosomal RNA (rRNA)
* composed of
* one large subunit
* one small subunit
59
* ribosome
by weight:
* 2/3 RNA
* 1/3 protein
60
* small ribosomal subunit
* matches the tRNA to the codon of the mRNA
61
* large ribosomal subunit
* catalyzes the formation of the peptide bonds
that covalently link the aa together into
a polypeptide chain
62
What are the 3 binding sites of the ribosome
* A site - aminoacyl-tRNA
* P site - peptidyl-tRNA
* E site - exit
63
What is the first step of translation
* a charged tRNA enters
at the A site by base-
pairing with the
complementary codon
on the mRNA molecule
64
What is the second step of translation
* C-term of the polypeptide
chain is uncoupled from
the tRNA at the P site and
joined to the free aa
linked to tRNA in A site
Alberts, et. al, Essential Cell Biology, 6th edition, Figure 7-39 (partial), p. 263
65
What is the third step of translation
* large ribosomal subunit
shifts relative to small subunit
* moves the two bound tRNAs
* P site → E site
* A site → P site
66
What is the first fourth of translation
* small ribosomal subunit moves
exactly three nt along the mRNA
* ejects the spent tRNA
* resets the A site for new
incoming charged tRNA
67
What direction is mRNA translated in
5’-to-3’ direction
* N-terminal end of the protein is made first,
aa are added to the C-terminal end of the
polypeptide chain
68
What is the rates of ribosomes
* eukaryotic ribosome:
* adds about 6 amino acids to
a polypeptide chain each second
* bacterial ribosome:
* adds about 20 amino acids to
a polypeptide chain each second
69
how does the end of translation occur
* proteins known as
release factors bind
to any stop codon
that reaches the A site
on the ribosome
* this binding alters
the activity of peptidyl
transferase in the ribosome
70
What is an antibiotic
* inhibitors of prokaryotic protein synthesis
71
* proteases
* enzymes responsible for degrading proteins
* hydrolyze the peptide bond between aa
72
* proteosomes
large protein machines responsible for
breaking down proteins
73
* chaperone proteins
* steer growing
polypeptide along
productive folding
pathways while
preventing
proteins from
aggregating
74
* gene expression
is the complex process by which cells
selectively direct the synthesis of the many
thousands of proteins and RNAs encoded
in their genome
75
What are some common proteins to all cells
* RNA polymerases
* DNA repair enzymes
* ribosomal proteins
* enzymes involved in glycolysis and
other metabolic processes
* proteins that form cytoskeleton
76
* specialized proteins
* responsible for cell’s distinctive properties
77
what cells respond to cortisol
* liver cells
* fat cells
78
* nucleosome
* a beadlike structural unit of a eukaryotic
chromosome composed of a short length
of DNA wrapped around an octamer core
of histone proteins
79
What are the 4 peices that make up a histone
h3, h2A, H2b, H4
80
What is illumina sequencing
using fluorescent on each nt. Dna polymerase adds nt to the sequence, terminates the fluorescence and repeats
81
Ribosome profiling
* which mRNA are being actively translated
to produce proteins
82
What is one of the best methods to study the function of a gene
to see what happens to an organism
When the gene is inactivated
83
What is a conditional knockout
* conditional knockouts are useful if the gene
under study is critical during embryonic
development
84
What is CRISPR System
method to turn
selected genes
on and off
85
What enzyme is used in CRISPR
Cas 9
86
DNA cloning
* allows production of recombinant protein
in large quantities
87
What is Vector/plasmids
* circular recombinant dsDNA
* modified bacterial plasmids. bacteria plasmid is cleaved and dna is addded in
88
Where are restriction enzymes expected to occur
256 nt
(1 in 44) purely by chance
89
what type of bonds hold together aa
covalent peptide bonds
90
What end of the protein is positive and negative
positive N terminus
Negative C terminus
91
What are the 5 aspects of an amino acid
Central carbon
hydrogen
Carboxyl group
amino group
R group
92
How are amino acids bonded together
H2O is removed when C terminus and N terminus is bonded together
93
hydrophobic force
occurs during protein folding when polar side chains are on the outside while nonpolar sidechains in the middle
94
What is the most diverse macro molecule
protein
95
How does alpha helix and beta sheets form
result from hydrogen bonds that form between
the N-H and C=O groups in the polypeptide
backbone
96
what is a coiled coil protein shape
2-3 alpha helices
wrap around
to form a stable
structure
97
What is a parallel beta sheet
all C terminus on the same side
98
what is an antiparallel beta sheet
what C terminus are on other ends
99
What is the primary structure of a protein
aa sequence
100
* secondary
structure
* stable conformation
101
* tertiary
structure
* protein domain
102
* quaternary
structure
* complex* subunit
103
What is a protein binding site
* any region on a protein surface that interacts
with another molecule through set of
noncovalent bonds
104
What is a protein dimer
two polypeptide chains form a symmetrical
complex of protein subunits
105
What are 2 common ECM proteins
* collagen, elastin
106
How are extracellular proteins stabilized
covalent disulfide bonds
107
what is a Ligand
any substance that is bound to protein by covalent bounds
108
What is Biotin
found in enzymes that transfer a
carboxyl group from one molecule
to another
109
What is feedback inhibition
* an enzyme acting early in a reaction pathway
is inhibited by a molecule produced later in
that pathway
110
What type of regulation is feedback inhibition
* negative regulation
111
What aa controls the regulation of the bacterial biosynthetic pathway
aa controls the 1st enzyme
112
What is an allosteric enzyme
* many enzymes contain at least two different
binding sites
* active site
* regulatory molecules binding site
113
What is Reversible Phosphorylation
common mechanism for regulating
protein activity
common mechanism for regulating
protein activity
114
Regulatory GTP-binding proteins
switched on and off by the gain and loss
of a P group
* active protein can shut itself off by hydrolyzing
its bound GTP → GDP + phosphate
115
What is a scaffold protein
* large molecules that contain binding sites
recognized by multiple proteins
* can greatly enhance a rate of particular
chemical reaction or cell process
116
What is an antibodie
immunoglobulin proteins produced by the
immune system in response to foreign
molecules
* each Ab binds to a particular target molecule,
an antigen, with remarkable specificity
117
What is the shape of an antibody
are Y-shaped molecules with two identical
antigen-binding site
118
* facilitated transport
* passage across cell membrane must be
accelerated by specialized membrane
transport proteins
119
* channels
* discriminate mainly on the basis
of size and electric charge
120
* transporters
* transfers only those specific molecules that
fit into specific binding sites on the protein
* binding specificity =
transporter selectivity
121
What is the highest intracellular concentraion
k @ 140
122
What is the highest extracellular concentration
na @ 145
123
What is passive transport
solute from high concentration to low concentration with ATP
124
What is active transport
movement of a solute against concentration
gradient
* active transport
* requires an input of energy
125
What are aquaporins
proteins that allow diffusion of water
126
* osmolarity
total concentration of solute particles
inside of the cell
127
What are the 3 conformation states of transporters
* outward-open
state
* inward-open
state
occluded state
128
What are the 3 types of active transports
Light driven pump
atp driven pump
gradient driven pump
129
What is the Na pump
* transports Na+ out of the cell as it carries K+ in
* uses energy derived from ATP
130
What is the CA pump
* move of Ca2+ ion across membrane is crucial
131
What is symport transport
2 molecules move in the same direction
132
what is antiport transport
2 molecules move in opposite directions
133
what is uniport
one molecule involved
134
What are the 2 names of the relatively large channels
porins and gap junctions
135
how are ion channels selective
permit some inorganic ions to pass but
not others
* depends on
* diameter and shape of the ion channel
* distribution of charged aa
135
What is the cytosol
contains many metabolic pathways
136
what is the nucleus
contains main genome, dna and rna synthesis
136
What is the ER
synthesis of most lipids, synthesis of proteins
137
What is the golgi apparatus
modifications, sorting and packaging of proteins and lipids
138
What is the endosomes
sorting of endocytosed materials
138
what is a lysosome
intercellular degration
138
what is a peroxisomes
oxidative breakdown of toxic materials
138
What type of membrane surronds the nucleus
double membrane
* nuclear envelope
139
what type of membrane surronds the mitochondira
surrounded by double membrane
139
What takes up the largest volume within a cell
cytosol the mitochondira
140
what organelle has the largest number per cell
mitochondira
141
Living systems are incredibly diverse in size, shape, environment, and behavior. It is
estimated that there are between 10 million and 100 million different species. Despite this
wide variety of organisms, it remains difficult to define what it means to say something is
alive. Which of the following can be described as the smallest living unit?
(a) DNA
(b) cell
(c) organelle
(d) protein
B
142
The flow of genetic information is controlled by a series of biochemical reactions that
result in the production of proteins, each with its own specific order of amino acids.
Choose the correct series of biochemical reactions from the options presented here.
(a) replication, transcription, translation
(b) replication, translation, transcription
(c) translation, transcription, replication
(d) translation, replication, transcription
A
142
Proteins are important architectural and catalytic components within the cell, helping to
determine its chemistry, its shape, and its ability to respond to changes in the
environment. Remarkably, all of the different proteins in a cell are made from the same
20 __________. By linking them in different sequences, the cell can make protein
molecules with different conformations and surface chemistries, and therefore different
functions.
(a) nucleotides.
(b) sugars.
(c) amino acids.
(d) fatty acids.
c
143
Which statement is NOT true about mutations?
(a) A mutation is a change in the DNA that can generate offspring less fit for survival
than their parents.
(b) A mutation can be a result of imperfect DNA duplication.
(c) A mutation is a result of sexual reproduction.
(d) A mutation is a change in the DNA that can generate offspring that are as fit for
survival as their parents are.
c
143
Changes in DNA sequence from one generation to the next may result in offspring that
are altered in fitness compared with their parents. The process of change and selection
over the course of many generations is the basis of __________.
(a) mutation.
(b) evolution.
(c) heredity.
(d) reproduction.
b
144
The __________ __________ is made up of two concentric membranes and is continuous
with the membrane of the endoplasmic reticulum.
(a) plasma membrane
(b) Golgi network
(c) mitochondrial membrane
(d) nuclear envelope
D
145
The nucleus, an organelle found in eukaryotic cells, confines the __________, keeping
them separated from other components of the cell.
(a) lysosomes
(b) chromosomes
(c) peroxisomes
(d) ribosomes
b
145
Which of the following organelles has both an outer and an inner membrane?
(a) endoplasmic reticulum
(b) mitochondrion
(c) lysosome
(d) peroxisome
b
146
The cell constantly exchanges materials by bringing nutrients in from the external
environment and shuttling unwanted by-products back out. Which term describes the
process by which external materials are captured inside vesicles and brought into the
cell?
(a) degradation
(b) exocytosis
(c) phagocytosis
(d) endocytosis
d
146
Eukaryotic cells are able to trigger the release of material from secretory vesicles to the
extracellular space using a process called exocytosis. An example of materials
commonly released this way is _____________.
(a) hormones.
(b) nucleic acids.
(c) sugars.
(d) cytosolic proteins.
a
147
__________ are fairly small organelles that provide a safe place within the cell to carry
out certain biochemical reactions that generate harmful, highly reactive oxygen species.
These chemicals are both generated and broken down in the same location.
(a) Nucleosomes
(b) Lysosomes
(c) Peroxisomes
(d) Endosomes
c
147
The cytoskeleton provides support, structure, motility, and organization, and it forms
tracks to direct organelle and vesicle transport. Which of the cytoskeletal elements listed
below is the thickest?
(a) actin filaments
(b) microtubules
(c) intermediate filaments
(d) none of the above (all the same thickness)
b
147
Which pair of values best fills in the blanks in this statement: On average, eukaryotic
cells are __________ times longer and have _________ times more volume than
prokaryotic cells.
(a) 5, 100
(b) 10, 200
(c) 10, 100
(d) 10, 1000
d
148
Caenorhabditis elegans is a nematode. During its development, it produces more than
1000 cells. However, the adult worm has only 959 somatic cells. The process by which
131 cells are specifically targeted for destruction is called ______________.
(a) directed cell pruning.
(b) programmed cell death.
(c) autophagy.
(d) necrosis
b
148
Chemical reactions carried out by living systems depend on the ability of some organisms
to capture and use atoms from nonliving sources in the environment. The specific subset
of these reactions that break down nutrients in food can be described as _____________.
(a) metabolic.
(b) catabolic.
(c) anabolic.
(d) biosynthetic.
b
149
Polypeptides are synthesized from amino acid building blocks. The condensation reaction
between the growing polypeptide chain and the next amino acid to be added involves the
loss of ________________.
(a) a water molecule.
(b) an amino group.
(c) a carbon atom.
(d) a carboxylic acid group
a
149
The variations in the physical characteristics between different proteins are influenced by
the overall amino acid compositions, but even more important is the unique amino acid
______________.
(a) number.
(b) sequence.
(c) bond.
(d) orientation.
b
150
Protein folding can be studied using a solution of purified protein and a denaturant (urea),
a solvent that interferes with noncovalent interactions. Which of the following is
observed after the denaturant is removed from the protein solution?
(a) The polypeptide returns to its original conformation.
(b) The polypeptide remains denatured.
(c) The polypeptide forms solid aggregates and precipitates out of solution.
(d) The polypeptide adopts a new, stable conformation.
a
151
Which of the following is not true of molecular chaperones?
(a) They assist polypeptide folding by helping the folding process follow the most
energetically favorable pathway
(b) They can isolate proteins from other components of the cells until folding is
complete.
(c) They can interact with unfolded polypeptides in a way that changes the final fold
of the protein.
(d) They help streamline the protein-folding process by making it a more efficient
and reliable process inside the cell.
c
152
Molecular chaperones can work by creating an “isolation chamber.” What is the purpose
of this chamber?
(a) The chamber acts as a garbage disposal, degrading improperly folded proteins so
that they do not interact with properly folded proteins.
(b) This chamber is used to increase the local protein concentration, which will help
speed up the folding process.
(c) This chamber serves to transport unfolded proteins out of the cell.
(d) This chamber serves to protect unfolded proteins from interacting with other
proteins in the cytosol, until protein folding is completed
d
152
Which of the following is not a feature commonly observed in α helices?
(a) left-handedness
(b) one helical turn every 3.6 amino acids
(c) cylindrical shape
(d) amino acid side chains that point outward
a
152
Which of the following is not a feature commonly observed in β sheets?
(a) antiparallel regions
(b) coiled-coil patterns
(c) extended polypeptide backbone
(d) parallel regions
b
153
Two or three α helices can sometimes wrap around each other to form coiled-coils. The
stable wrapping of one helix around another is typically driven by ________________
interactions.
(a) hydrophilic
(b) hydrophobic
(c) van der Waals
(d) ionic
b
154
Protein structures have several different levels of organization. The primary structure of a
protein is its amino acid sequence. The secondary and tertiary structures are more
complicated. Consider the definitions below and select the one that best fits the term
“protein domain.”
(a) a small cluster of α helices and β sheets
(b) the tertiary structure of a substrate-binding pocket
(c) a complex of more than one polypeptide chain
(d) a protein segment that folds independently
d
154
Proteins bind selectively to small-molecule targets called ligands. The selection of one
ligand out of a mixture of possible ligands depends on the number of weak, noncovalent
interactions in the protein’s ligand-binding site. Where is the binding site typically
located in the protein structure?
(a) on the surface of the protein
(b) inside a cavity on the protein surface
(c) buried in the interior of the protein
(d) forms on the surface of the protein in the presence of ligand
b
154
Cyclic AMP (cAMP) is a small molecule that associates with its binding site with a high
degree of specificity. Which types of noncovalent interactions are the most important for
providing the “hand in a glove” binding of cAMP?
(a) hydrogen bonds
(b) electrostatic interactions
(c) van der Waals interactions
(d) hydrophobic interactions
a
154
The process of generating monoclonal antibodies is labor-intensive and expensive. An
alternative is to use polyclonal antibodies. A subpopulation of purified polyclonal
antibodies that recognize a particular antigen can be isolated by chromatography. Which
type of chromatography is used for this purpose?
(a) affinity
(b) ion-exchange
(c) gel-filtration
(d) any of the above
a
155
Antibody production is an indispensible part of our immune response, but it is not the
only defense our bodies have. Which of the following is observed during an infection that
is not a result of antibody–antigen interactions?
(a) B cell proliferation
(b) aggregation of viral particles
(c) systemic temperature increase
(d) antibody secretion
c
156
Lysozyme is an enzyme that specifically recognizes bacterial polysaccharides, which
renders it an effective antibacterial agent. Into what classification of enzymes does
lysozyme fall?
(a) isomerase
(b) protease
(c) nuclease
(d) hydrolase
d
157
Which of the following statements about allostery is true?
(a) Allosteric regulators are often products of other chemical reactions in the same
biochemical pathway.
(b) Allosteric regulation is always used for negative regulation of enzyme activity.
(c) Enzymes are the only types of proteins that are subject to allosteric regulation.
(d) Binding of allosteric molecules usually locks an enzyme in its current
conformation, such that the enzyme cannot adopt a different conformation
a
157
The process of DNA replication requires that each of the parental DNA strands be
used as a ___________________ to produce a duplicate of the opposing strand.
(a) catalyst
(b) competitor
(c) template
c
158
The chromatin structure in eukaryotic cells is much more complicated than that
observed in prokaryotic cells. This is thought to be the reason that DNA replication
occurs much faster in prokaryotes. How much faster is it?
(a) 2×
(b) 5×
(c) 10×
(d) 100×
C
158
Which of the following statements is false?
(a) A new RNA molecule can begin to be synthesized from a gene before the
previous RNA molecule’s synthesis is completed.
(b) If two genes are to be expressed in a cell, these two genes can be transcribed with
different efficiencies.
(c) RNA polymerase is responsible for both unwinding the DNA helix and catalyzing
the formation of the phosphodiester bonds between nucleotides.
(d) Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.
d
159
Unlike DNA, which typically forms a helical structure, different molecules of RNA can
fold into a variety of three-dimensional shapes. This is largely because
___________________.
(a) RNA contains uracil and uses ribose as the sugar.
(b) RNA bases cannot form hydrogen bonds with each other.
(c) RNA nucleotides use a different chemical linkage between nucleotides compared
to DNA.
(d) RNA is single-stranded
d
159
Which of the following molecules of RNA would you predict to be the most likely to fold
into a specific structure as a result of intramolecular base-pairing?
(a) 5′-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′
(b) 5′-UGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUG-3′
(c) 5′-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-3′
(d) 5′-GGAAAAGGAGAUGGGCAAGGGGAAAAGGAGAUGGGCAAGG-3′
a
160
The sigma subunit of bacterial RNA polymerase ___________________.
(a) contains the catalytic activity of the polymerase.
(b) remains part of the polymerase throughout transcription.
(c) recognizes promoter sites in the DNA.
(d) recognizes transcription termination sites in the DNA
c
160
Which of the following might decrease the transcription of only one specific gene in a
bacterial cell?
(a) a decrease in the amount of sigma factor
(b) a decrease in the amount of RNA polymerase
(c) a mutation that introduced a stop codon into the DNA that precedes the gene’s
coding sequence
(d) a mutation that introduced extensive sequence changes into the DNA that
precedes the gene’s transcription start site
d
160
There are several reasons why the primase used to make the RNA primer for DNA
replication is not suitable for gene transcription. Which of the statements below is not one
of those reasons?
(a) Primase initiates RNA synthesis on a single-stranded DNA template.
(b) Primase can initiate RNA synthesis without the need for a base-paired primer.
(c) Primase synthesizes only RNAs of about 5–20 nucleotides in length.
(d) The RNA synthesized by primase remains base-paired to the DNA template.
b
161
Transcription in bacteria differs from transcription in a eukaryotic cell because
__________________________.
(a) RNA polymerase (along with its sigma subunit) can initiate transcription on its
own.
(b) RNA polymerase (along with its sigma subunit) requires the general transcription
factors to assemble at the promoter before polymerase can begin transcription.
(c) the sigma subunit must associate with the appropriate type of RNA polymerase to
produce mRNAs.
(d) RNA polymerase must be phosphorylated at its C-terminal tail for transcription to
proceed.
a
162
Which of the following does not occur before a eukaryotic mRNA is exported from the
nucleus?
(a) The ribosome binds to the mRNA.
(b) The mRNA is polyadenylated at its 3′ end.
(c) 7-methylguanosine is added in a 5′-to-5′ linkage to the mRNA.
(d) RNA polymerase dissociates.
a
163
Which of the following statements about the genetic code is correct?
(a) All codons specify more than one amino acid.
(b) The genetic code is redundant.
(c) All amino acids are specified by more than one codon.
(d) All codons specify an amino acid
b
163
Which of the following statements is true?
(a) Ribosomes are large RNA structures composed solely of rRNA.
(b) Ribosomes are synthesized entirely in the cytoplasm.
(c) rRNA contains the catalytic activity that joins amino acids together.
(d) A ribosome binds one tRNA at a time
c
163
4 Ribozymes catalyze which of the following reactions?
(a) DNA synthesis
(b) transcription
(c) RNA splicing
(d) protein hydrolysis
c
164
A neuron and a white blood cell have very different functions. For example, a neuron can
receive and respond to electrical signals while a white blood cell defends the body against
infection. This is because ______.
(a) the proteins found in a neuron are completely different from the proteins found in
a white blood cell.
(b) the neuron and the white blood cell within an individual have the same genome.
(c) the neuron expresses some mRNAs that the white blood cell does not.
(d) neurons and white blood cells are differentiated cells and thus no longer need to
transcribe and translate genes.
c
165
The distinct characteristics of different cell types in a multicellular organism result
mainly from the differential regulation of the _________________.
(a) replication of specific genes.
(b) transcription of genes transcribed by RNA polymerase II.
(c) transcription of housekeeping genes.
(d) proteins that directly bind the TATA box of eukaryotic genes
b
166
Which of the following statements about differentiated cells is true?
(a) Cells of distinct types express nonoverlapping sets of transcription factors.
(b) Once a cell has differentiated, it can no longer change its gene expression.
(c) Once a cell has differentiated, it will no longer need to transcribe RNA.
(d) Some of the proteins found in differentiated cells are found in all cells of a
multicellular organism.
d
166
Which of the following statements about transcriptional regulators is false?
(a) Transcriptional regulators usually interact with the sugar–phosphate backbone on
the outside of the double helix to determine where to bind on the DNA helix.
(b) Transcriptional regulators will form hydrogen bonds, ionic bonds, and
hydrophobic interactions with DNA.
(c) The DNA-binding motifs of transcriptional regulators usually bind in the major
groove of the DNA helix.
(d) The binding of transcriptional regulators generally does not disrupt the hydrogen
bonds that hold the double helix together
a
166
Operons ___________________________.
(a) are commonly found in eukaryotic cells.
(b) are transcribed by RNA polymerase II.
(c) contain a cluster of genes transcribed as a single mRNA.
(d) can only be regulated by gene activator proteins.
c
167
Which of the following statements about the Lac operon is false?
(a) The Lac repressor binds when lactose is present in the cell.
(b) Even when the CAP activator is bound to DNA, if lactose is not present, the Lac
operon will not be transcribed.
(c) The CAP activator can only bind DNA when it is bound to cAMP.
(d) The Lac operon only produces RNA when lactose is present and glucose is
absent.
a
168
.Which of the following channels would not be expected to generate a change in voltage
by movement of its substrate across the membrane where it is found?
(a) an aquaporin
(b) a sodium channel
(c) a calcium channel
(d) a proton channel
a
168
Cells use membranes to help maintain set ranges of ion concentrations inside and outside
the cell. Which of the following ions is the most abundant inside a typical mammalian
cell?
(a) Na+
(b) K+
(c) Ca2+
(d) Cl–
b
168
Cells use membranes to help maintain set ranges of ion concentrations inside and outside
the cell. Which of the following ions is the most abundant outside a typical mammalian
cell?
(a) Na+
(b) K+
(c) Ca2+
(d) Cl–
a
169
Cells use membranes to help maintain set ranges of ion concentrations inside and outside
the cell. Which of the following negatively charged ions is not primarily used to buffer
positive charges inside the cell?
(a) PO4
3–
(b) OH–
(c) Cl–
(d) HCO3
–
c
170
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.
(a) Mg2+
(b) H+
(c) K+
(d) Cl–
b
171
Some cells have aquaporins—channels that facilitate the flow of water molecules through
the plasma membrane. For these cells, what regulates the rate and direction of water
diffusion across the membrane?
(a) aquaporin conformation
(b) resting membrane potential
(c) solute concentrations on either side of the membrane
(d) availability of ATP
c
172
Transporters, in contrast to channels, work by ________________.
(a) specific binding to solutes.
(b) a gating mechanism.
(c) filtering solutes by charge.
(d) filtering solutes by size.
a
172
Active transport requires the input of energy into a system so as to move solutes against
their electrochemical and concentration gradients. Which of the following is not one of
the common ways to perform active transport?
(a) Na+-coupled
(b) K+-coupled
(c) ATP-driven
(d) light-driven
b
172
Cells make use of H+ electrochemical gradients in many ways. Which of the following
proton transporters is used to regulate pH in animal cells?
(a) light-driven pump
(b) H+ ATPase
(c) H+ symporter
(d) Na+-H+ exchanger
d
172
Ca2+-pumps in the plasma membrane and endoplasmic reticulum are important for
_____________.
(a) maintaining osmotic balance.
(b) preventing Ca2+ from altering the activity of molecules in the cytosol.
(c) providing enzymes in the endoplasmic reticulum with Ca2+ ions that are necessary
for their catalytic activity.
(d) maintaining a negative membrane potential
b
173
Which of the following best describes the behavior of a gated channel?
(a) It stays open continuously when stimulated.
(b) It opens more frequently in response to a given stimulus.
(c) It opens more widely as the stimulus becomes stronger.
(d) It remains closed if unstimulated.
b
173
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?
(a) voltage-gated
(b) extracellular ligand-gated
(c) intracellular ligand-gated
(d) stress-gated
d
173
When the net charge on either side of the plasma membrane is zero, what else is
true?
(a) There is an equal number of K+ ions on each side of the plasma membrane.
(b) The K+ leak channels are open.
(c) The electrochemical potential across the membrane is zero.
(d) The resting membrane potential is between –20 mV and –200 mV.
174
K+ leak channels are found in the plasma membrane. These channels open and close in an
unregulated, random fashion. What do they accomplish in a resting cell?
(a) They set the K+ concentration gradient to zero.
(b) They set the membrane potential to zero.
(c) They disrupt the resting membrane potential.
(d) They keep the electrochemical gradient for K+ at zero.
d
174
If Na+ channels are opened in a cell that was previously at rest, how will the resting
membrane potential be affected?
(a) The membrane potential is not affected by Na+.
(b) It becomes more negative.
(c) It becomes more positive.
(d) It is permanently reset.
c
175
Which of the following is required for the secretion of neurotransmitters in response to an
action potential?
(a) neurotransmitter receptors
(b) Na+-K+ pumps
(c) voltage-gated K+ channels
(d) voltage-gated Ca2+ channels
d
176
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?
(a) acetylcholine
(b) glutamate
(c) GABA
(d) glycine
a
177
Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism
do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action
potential?
(a) by closing Na+ channels
(b) by preventing the secretion of excitatory neurotransmitters
(c) by opening K+ channels
(d) by opening Cl– channels
d
177
Which of the following gated ion channels are involved in inhibitory synaptic signaling?
(a) voltage-gated Na+ channels
(b) voltage-gated Ca2+ channels
(c) glycine-gated Cl– channels
(d) glutamate-gated cation channels
c
177
Which of the following statements about the endoplasmic reticulum (ER) is false?
(a) The ER is the major site for new membrane synthesis in the cell.
(b) Proteins to be delivered to the ER lumen are synthesized on smooth ER.
(c) Steroid hormones are synthesized on the smooth ER.
(d) The ER membrane is contiguous with the outer nuclear membrane.
b
178
Which of the following statements about membrane-enclosed organelles is true?
(a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the
area of plasma membrane.
(b) The nucleus is the only organelle that is surrounded by a double membrane.
(c) Other than the nucleus, most organelles are small and thus, in a typical cell, only
about 10% of a cell’s volume is occupied by membrane-enclosed organelles; the
other 90% of the cell volume is the cytosol.
(d) The nucleus is the only organelle that contains DNA.
a
178
Which of the following organelles is not part of the endomembrane system?
(a) Golgi apparatus
(b) the nucleus
(c) mitochondria
(d) lysosomes
c
179
Which of the following statements is true?
(a) Lysosomes are believed to have originated from the engulfment of bacteria
specialized for digestion.
(b) The nuclear membrane is thought to have arisen from the plasma membrane
invaginating around the DNA.
(c) Because bacteria do not have mitochondria, they cannot produce ATP in a
membrane-dependent fashion.
(d) Chloroplasts and mitochondria share their DNA.
b
180
Where are proteins in the chloroplast synthesized?
(a) in the cytosol
(b) in the chloroplast
(c) on the endoplasmic reticulum
(d) in both the cytosol and the chloroplast
d
180
Proteins that are fully translated in the cytosol do not end up in _______.
(a) the cytosol.
(b) the mitochondria.
(c) the interior of the nucleus.
(d) transport vesicles
d
181
Proteins that are fully translated in the cytosol and lack a sorting signal will end up in
____.
(a) the cytosol.
(b) the mitochondria.
(c) the interior of the nucleus.
(d) the nuclear membrane.
a
181
3 Signal sequences that direct proteins to the correct compartment are _________.
(a) added to proteins through post-translational modification.
(b) added to a protein by a protein translocator.
(c) encoded in the amino acid sequence and sufficient for targeting a protein to its
correct destination.
(d) always removed once a protein is at the correct destination
c
182
3 Signal sequences that direct proteins to the correct compartment are _________.
(a) added to proteins through post-translational modification.
(b) added to a protein by a protein translocator.
(c) encoded in the amino acid sequence and sufficient for targeting a protein to its
correct destination.
(d) always removed once a protein is at the correct destination
a
182
A large protein that passes through the nuclear pore must have an appropriate _________.
(a) sorting sequence, which typically contains the positively charged amino acids
lysine and arginine.
(b) sorting sequence, which typically contains the hydrophobic amino acids leucine
and isoleucine.
(c) sequence to interact with the nuclear fibrils.
(d) Ran-interacting protein domain.
a
183
Most proteins destined to enter the endoplasmic reticulum _________.
(a) are transported across the membrane after their synthesis is complete.
(b) are synthesized on free ribosomes in the cytosol.
(c) begin to cross the membrane while still being synthesized.
(d) remain within the endoplasmic reticulum.
c
184
After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you
purify the RNAs attached to it. Which of the following proteins do you expect the RNA
from the rough endoplasmic reticulum to encode?
(a) soluble secreted proteins
(b) ER membrane proteins
(c) plasma membrane proteins
(d) all of the above
d
184
In which cellular location would you expect to find ribosomes translating mRNAs that
encode ribosomal proteins?
(a) the nucleus
(b) on the rough ER
(c) in the cytosol
(d) in the lumen of the ER
c
184
Which of the following choices reflects the appropriate order of locations through which
a protein destined for the plasma membrane travels?
(a) lysosome → endosome → plasma membrane
(b) ER → lysosome → plasma membrane
(c) Golgi → lysosome → plasma membrane
(d) ER → Golgi → plasma membrane
d
185
Which of the following statements about vesicle budding from the Golgi is false?
(a) Clathrin molecules are important for binding to and selecting cargoes for
transport.
(b) Adaptins interact with clathrin.
(c) Once vesicle budding occurs, clathrin molecules are released from the vesicle.
(d) Clathrin molecules act at the cytosolic surface of the Golgi membrane.
a
186
Molecules to be packaged into vesicles for transport are selected by ________.
(a) clathrin.
(b) adaptins.
(c) dynamin.
(d) SNAREs
b
186
An individual transport vesicle ________.
(a) contains only one type of protein in its lumen.
(b) will fuse with only one type of membrane.
(c) is endocytic if it is traveling toward the plasma membrane.
(d) is enclosed by a membrane with the same lipid and protein composition as the
membrane of the donor organelle.
b
186
Vesicles from the ER enter the Golgi at the ______.
(a) medial cisternae.
(b) trans Golgi network.
(c) cis Golgi network.
(d) trans cisternae.
c
186
When a signal needs to be sent to most cells throughout a multicellular organism, the
signal most suited for this is a ___________.
(a) neurotransmitter.
(b) hormone.
(c) dissolved gas.
(d) scaffold
b
187
Which of the following statements is false?
(a) Nucleotides and amino acids can act as extracellular signal molecules.
(b) Some signal molecules can bind directly to intracellular proteins that bind DNA
and regulate gene transcription.
(c) Some signal molecules are transmembrane proteins.
(d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but
because they cannot interact with proteins they must act by affecting membrane
lipids.
d
188
All members of the steroid hormone receptor family __________________.
(a) are cell-surface receptors.
(b) do not undergo conformational changes.
(c) are found only in the cytoplasm.
(d) interact with signal molecules that diffuse through the plasma membrane.
d
189
Acetylcholine is a signaling molecule that elicits responses from heart muscle cells,
salivary gland cells, and skeletal muscle cells. Which of the following statements is false?
(a) Heart muscle cells decrease their rate and force of contraction when they receive
acetylcholine, whereas skeletal muscle cells contract.
(b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an
acetylcholine receptor that belongs to the transmitter-gated ion channel family.
(c) Active acetylcholine receptors on salivary gland cells and heart muscle cells
activate different intracellular signaling pathways.
(d) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to
acetylcholine within minutes of receiving the signal.
b
189
The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by
________________.
(a) activating a G protein.
(b) activating a receptor tyrosine kinase.
(c) diffusing into cells and stimulating the cyclase directly.
(d) activating an intracellular protein kinase.
c
189
Which of the following statements about molecular switches is false?
(a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning
them off.
(b) Protein kinases transfer the terminal phosphate from ATP onto a protein.
(c) Serine/threonine kinases are the most common types of protein kinase.
(d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.
a
190
The length of time a G protein will signal is determined by _______.
(a) the activity of phosphatases that turn off G proteins by dephosphorylating Gα.
(b) the activity of phosphatases that turn GTP into GDP.
(c) the degradation of the G protein after Gα separates from Gβγ
(d) the GTPase activity of Gα
d
190
The growth factor Superchick stimulates the proliferation of cultured chicken cells. The
receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken
tumor cell lines have mutations in the gene that encodes this receptor. Which of the
following types of mutation would be expected to promote uncontrolled cell
proliferation?
(a) a mutation that prevents dimerization of the receptor
(b) a mutation that destroys the kinase activity of the receptor
(c) a mutation that inactivates the protein tyrosine phosphatase that normally removes
the phosphates from tyrosines on the activated receptor
(d) a mutation that prevents the binding of the normal extracellular signal to the
receptor
c
190
The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that
binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of
alteration would be most likely to prevent receptor dimerization?
(a) a mutation that increases the affinity of RGFR for RGF
(b) a mutation that prevents RGFR from binding to RGF
(c) changing the tyrosines that are normally phosphorylated on RGFR dimerization to
alanines
(d) changing the tyrosines that are normally phosphorylated on RGFR dimerization to
glutamic acid
b
190
A protein kinase can act as an integrating device in signaling if it ___________________.
(a) phosphorylates more than one substrate.
(b) catalyzes its own phosphorylation.
(c) is activated by two or more proteins in different signaling pathways.
(d) initiates a phosphorylation cascade involving two or more protein kinases
c
191
4 Which of the following statements is true?
(a) MAP kinase is important for phosphorylating MAP kinase kinase.
(b) PI 3-kinase phosphorylates a lipid in the plasma membrane.
(c) Ras becomes activated when an RTK phosphorylates its bound GDP to create
GTP.
(d) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and
activate gene transcription.
b
192
The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-
kinase (PI 3-kinase) to _________.
(a) activate the RTK.
(b) create phosphorylated lipids that serve as docking sites that localize Akt to the
plasma membrane.
(c) directly phosphorylate Akt.
(d) to create DAG.
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