ESSENTIAL CELL BIOLOGY EXAM #1
QUESTIONS WITH COMPLETE
SOLUTIONS
proteasome - ANSWER-Large protein complex in the cytosol that is responsible for
degrading cytosolic proteins that have been marked for destruction by ubiquiylation or
by some other means.
reading frame - ANSWER-The set of successive triplets in which a string of nucleotides
is translated into protein. An mRNA molecule is read in one of three possible reading
frames, depending on the starting point.
ribosomal RNA
(rRNA) - ANSWER-Any one of a number of specific RNA molecules that form part of the
structure of a ribosome and participate in the synthesis of proteins. Often distinguished
by their sedimentation coefficient.
ribosome - ANSWER-Particle composed of ribosomal RNAs and ribosomal proteins that
associates with messenger RNA and catalyzes the synthesis of protein.
ribozyme - ANSWER-An RNA molecule possessing catalytic properties.
RNA polymerase - ANSWER-Enzyme that catalyzes the synthesis of an RNA molecule
on a DNA template from nucleoside triphosphate precursors.
RNA processing - ANSWER-The modifications that an RNA undergoes as it reaches its
mature form. For a eucaryotic mRNA, processing typically includes capping, splicing,
and polyadenylation.
RNA splicing - ANSWER-Process to which intron sequences are excised from RNA
molecules in the nucleus during the formation of messenger RNA.
small nuclear RNA
(snRNA) - ANSWER-RNA molecules of around 200 nucleotides involved in RNA
splicing.
spliceosome - ANSWER-Large assembly of RNA and protein molecules that splices
introns out of pre-mRNA in eucaryotic cells.
transcription - ANSWER-A process that uses one strand of DNA as the template to
synthesize a complementary RNA sequence, sometimes termed the primary transcript,
catalyzed by the enzyme RNA polymerase.
,transfer RNA
(tRNA) - ANSWER-Set of small RNA molecules used in protein synthesis as an
interface (adaptor) between mRNA and amino acids. Each type of tRNA molecule is
covalently linked to a particular amino acid.
translation - ANSWER-Process by which the sequence of nucleotides in a messenger
RNA molecule directs the incorporation of amino acids into protein; occurs on a
ribosome.
translation initiation factor - ANSWER-Protein that promotes the proper association of
ribosomes with mRNA and is required for the initiation of protein synthesis.
DNA polymerase - ANSWER-Enzyme that catalyzes the addition of nucleotide subunits
to make DNA.
DNA repair - ANSWER-Collective term for the enzymatic processes that correct
deleterious changes affecting the continuity or sequence of a DNA molecule
DNA replication - ANSWER-The process by which a copy of a DNA molecule is made.
homologous recombination - ANSWER-Genetic exchange between a pair of identical or
very similar DNA sequences, typically located on a pair of homologous chromosomes. A
similar process is used to repair double-stranded breaks in DNA.
lagging strand - ANSWER-One of the two newly made strands of DNA found at a
replication fork. The lagging strand is made in discontinuous lengths that are later joined
covalently.
leading strand - ANSWER-One of two newly made strands of DNA found as a
replication fork. The leading strand is made by continuous synthesis in the 5'-to-3'
direction.
mobile genetic element - ANSWER-Short segment of DNA that can move, sometimes
through an RNA intermediate, from one location in a genome to another. They are an
important source of genetic variation in most genomes.
mutation - ANSWER-A randomly produced, heritable change in the nucleotide
sequence of a chromosome.
nonhomologous end-joining - ANSWER-Mechanism for repairing double-strand breaks
in DNA in which the two broken ends are brought together and rejoined without
requiring sequence homology.
Okazaki fragment - ANSWER-Short length of DNA produced on the lagging strand
during DNA replication. Adjacent fragments are rapidly joined together by DNA ligase to
form a continuous DNA strand.
, proofreading - ANSWER-The process by which DNA polymerase corrects its own errors
as it moves along DNA.
replication fork - ANSWER-Y-shaped region of a replicating DNA molecule at which the
two daughter strands are formed and seperate.
retrotransposon - ANSWER-Type of mobile genetic element that moves by being first
transcribed into an RNA copy that is reconverted to DNA by reverse transcriptase and
inserted elsewhere in the chromosomes.
retrovirus - ANSWER-RNA-containing virus that replicates in a cell by first making a
double-stranded DNA intermediate. This DNA is inserted into the cell's chromosome,
where it can be maintained for a long time and its transcribed to produce new viral
genomes and mRNAs that encode viral proteins.
reverse transcriptase - ANSWER-Enzyme that makes a double-stranded DNA copy
from a single-stranded RNA template molecule. Present in retroviruses and as part of
the transposition machinery of retrotransposons.
telomerase - ANSWER-Enzyme that elongates telomeres, the repetitive nucleotide
sequences found at the ends of eucaryotic chromosomes.
template - ANSWER-A molecular structure that serves as a pattern for the production of
other molecules. Thus, a specific sequence of nucleotides in DNA can act as a template
to direct the synthesis of a new strand of complementary DNA.
transposon - ANSWER-Short segments of DNA that can move from one location to
another in the genome. Also known as mobile genetic element.
virus - ANSWER-Particle consisting of nucleic acid (RNA to DNA) enclosed in a protein
coat and capable of replicating within a host cell and spreading from cell to cell. OFten
the cause of disease.
base pair - ANSWER-Two nucleotides in an RNA or DNA molecule that are specifically
paired with hydrogen bonds--for example G with C, and A with T or U.
cell cycle - ANSWER-Reproductive cycle of the cell: the orderly sequence of events by
which a cell duplicates its contents and divides in two.
centromere - ANSWER-Constricted region of a mitotic chromosome that holds sister
chromatids together; also the site on the DNA where the kinetochore forms and then
captures microtubules from the mitotic spindle.
chromatin - ANSWER-Complex of DNA, histones, and nonhistone proteins found in the
nucleus of a eucaryotic cell. The material of which chromosomes are made.
QUESTIONS WITH COMPLETE
SOLUTIONS
proteasome - ANSWER-Large protein complex in the cytosol that is responsible for
degrading cytosolic proteins that have been marked for destruction by ubiquiylation or
by some other means.
reading frame - ANSWER-The set of successive triplets in which a string of nucleotides
is translated into protein. An mRNA molecule is read in one of three possible reading
frames, depending on the starting point.
ribosomal RNA
(rRNA) - ANSWER-Any one of a number of specific RNA molecules that form part of the
structure of a ribosome and participate in the synthesis of proteins. Often distinguished
by their sedimentation coefficient.
ribosome - ANSWER-Particle composed of ribosomal RNAs and ribosomal proteins that
associates with messenger RNA and catalyzes the synthesis of protein.
ribozyme - ANSWER-An RNA molecule possessing catalytic properties.
RNA polymerase - ANSWER-Enzyme that catalyzes the synthesis of an RNA molecule
on a DNA template from nucleoside triphosphate precursors.
RNA processing - ANSWER-The modifications that an RNA undergoes as it reaches its
mature form. For a eucaryotic mRNA, processing typically includes capping, splicing,
and polyadenylation.
RNA splicing - ANSWER-Process to which intron sequences are excised from RNA
molecules in the nucleus during the formation of messenger RNA.
small nuclear RNA
(snRNA) - ANSWER-RNA molecules of around 200 nucleotides involved in RNA
splicing.
spliceosome - ANSWER-Large assembly of RNA and protein molecules that splices
introns out of pre-mRNA in eucaryotic cells.
transcription - ANSWER-A process that uses one strand of DNA as the template to
synthesize a complementary RNA sequence, sometimes termed the primary transcript,
catalyzed by the enzyme RNA polymerase.
,transfer RNA
(tRNA) - ANSWER-Set of small RNA molecules used in protein synthesis as an
interface (adaptor) between mRNA and amino acids. Each type of tRNA molecule is
covalently linked to a particular amino acid.
translation - ANSWER-Process by which the sequence of nucleotides in a messenger
RNA molecule directs the incorporation of amino acids into protein; occurs on a
ribosome.
translation initiation factor - ANSWER-Protein that promotes the proper association of
ribosomes with mRNA and is required for the initiation of protein synthesis.
DNA polymerase - ANSWER-Enzyme that catalyzes the addition of nucleotide subunits
to make DNA.
DNA repair - ANSWER-Collective term for the enzymatic processes that correct
deleterious changes affecting the continuity or sequence of a DNA molecule
DNA replication - ANSWER-The process by which a copy of a DNA molecule is made.
homologous recombination - ANSWER-Genetic exchange between a pair of identical or
very similar DNA sequences, typically located on a pair of homologous chromosomes. A
similar process is used to repair double-stranded breaks in DNA.
lagging strand - ANSWER-One of the two newly made strands of DNA found at a
replication fork. The lagging strand is made in discontinuous lengths that are later joined
covalently.
leading strand - ANSWER-One of two newly made strands of DNA found as a
replication fork. The leading strand is made by continuous synthesis in the 5'-to-3'
direction.
mobile genetic element - ANSWER-Short segment of DNA that can move, sometimes
through an RNA intermediate, from one location in a genome to another. They are an
important source of genetic variation in most genomes.
mutation - ANSWER-A randomly produced, heritable change in the nucleotide
sequence of a chromosome.
nonhomologous end-joining - ANSWER-Mechanism for repairing double-strand breaks
in DNA in which the two broken ends are brought together and rejoined without
requiring sequence homology.
Okazaki fragment - ANSWER-Short length of DNA produced on the lagging strand
during DNA replication. Adjacent fragments are rapidly joined together by DNA ligase to
form a continuous DNA strand.
, proofreading - ANSWER-The process by which DNA polymerase corrects its own errors
as it moves along DNA.
replication fork - ANSWER-Y-shaped region of a replicating DNA molecule at which the
two daughter strands are formed and seperate.
retrotransposon - ANSWER-Type of mobile genetic element that moves by being first
transcribed into an RNA copy that is reconverted to DNA by reverse transcriptase and
inserted elsewhere in the chromosomes.
retrovirus - ANSWER-RNA-containing virus that replicates in a cell by first making a
double-stranded DNA intermediate. This DNA is inserted into the cell's chromosome,
where it can be maintained for a long time and its transcribed to produce new viral
genomes and mRNAs that encode viral proteins.
reverse transcriptase - ANSWER-Enzyme that makes a double-stranded DNA copy
from a single-stranded RNA template molecule. Present in retroviruses and as part of
the transposition machinery of retrotransposons.
telomerase - ANSWER-Enzyme that elongates telomeres, the repetitive nucleotide
sequences found at the ends of eucaryotic chromosomes.
template - ANSWER-A molecular structure that serves as a pattern for the production of
other molecules. Thus, a specific sequence of nucleotides in DNA can act as a template
to direct the synthesis of a new strand of complementary DNA.
transposon - ANSWER-Short segments of DNA that can move from one location to
another in the genome. Also known as mobile genetic element.
virus - ANSWER-Particle consisting of nucleic acid (RNA to DNA) enclosed in a protein
coat and capable of replicating within a host cell and spreading from cell to cell. OFten
the cause of disease.
base pair - ANSWER-Two nucleotides in an RNA or DNA molecule that are specifically
paired with hydrogen bonds--for example G with C, and A with T or U.
cell cycle - ANSWER-Reproductive cycle of the cell: the orderly sequence of events by
which a cell duplicates its contents and divides in two.
centromere - ANSWER-Constricted region of a mitotic chromosome that holds sister
chromatids together; also the site on the DNA where the kinetochore forms and then
captures microtubules from the mitotic spindle.
chromatin - ANSWER-Complex of DNA, histones, and nonhistone proteins found in the
nucleus of a eucaryotic cell. The material of which chromosomes are made.
