What makes up the protein component of a nucleosome?
One tetramer of histone proteins
Two tetramers of histone
proteins
Eight different histone proteins
Histone H1 protein
Two tetramers of histone proteins
(The protein
component of a nucleosome is composed of two tetramers of histone
proteins. One tetramer is composed of two units each of histones H2A
and H2B, and the other is composed of two units each of histones H3
and H4.)
What is the first order of chromatin packing?
Formation of a
solenoid
Formation of a 300‑nm fiber
Looping of 300‑nm
fibers
Coiling around nucleosomes
Coiling around nucleosomes
(The first order of
chromatin packing occurs when DNA coils around nucleosomes, whereby
DNA is reduced to about one‑third its original length.)
The second order of chromatin packing occurs when nucleosomes coil
together to form a fiber that is 300 nm in diameter.
True
False
False
(The second order of chromatin packing occurs
when nucleosomes coil together to form a solenoid fiber that is 30 nm
in diameter.)
Eukaryotic chromosomes contain two general domains that relate to the
degree of condensation. These two regions are ________.
uniform in the genetic information they contain
separated by
large stretches of repetitive DNA
each void of typical
protein-coding sequences of DNA
called heterochromatin and
euchromatin
void of introns
called heterochromatin and euchromatin
Chromatin of eukaryotes is organized into repeating interactions with
protein octomers called nucleosomes. Nucleosomes are composed of which
class of molecules?
histones
lipids
nonhistone chromosomal proteins
H1 histones
glycoproteins
histones
In contrast with euchromatin, heterochromatin contains more genes and
is earlier replicating.
True
False
False
Telomerase is an enzyme involved in the replication of the ends of
eukaryotic chromosomes.
True
False
True
The genetic code is degenerate, meaning that a codon can specify more
than one amino acid.
True
False
False
(The degeneracy of the genetic code means that an
amino acid may be coded for by more than one codon. However, a single
codon can only ever specify one amino acid.)
A DNA sequence produces a mutant protein in which several amino acids
in the middle of the protein differ from the normal protein. What kind
of mutation could have occurred?
An addition and a
deletion mutation
A nonsense mutation
An addition or
deletion mutation
No mutation
An addition and a deletion mutation
(A single addition
or deletion would change the reading frame of the protein, but if
another mutation occurred to cancel the effects of the first
mutation, only those amino acids between the mutations would change.)
Which of the following statements about eukaryotic transcription is
false?
Transcription initiation occurs when RNA
polymerase binds to a complex of transcription factors at the TATA
box.
The transcripts produced contain both exons and introns.
A polycistronic mRNA may be transcribed if the gene products
are used in the same pathway or needed at the same time.
Eukaryotic promoter regions contain a TATA box and a CAAT box.
A polycistronic mRNA may be transcribed if the gene products are used
in the same pathway or needed at the same time.
(This
statement is false. Polycistronic mRNAs are produced only in
prokaryotes. In eukaryotes, a single gene is transcribed at a time.)
What is the initiator triplet in both prokaryotes and eukaryotes?
What amino acid is recruited by this triplet?
AUG;
methionine
AUG; arginine
UAA or UGA; arginine
UAA, methionine
UAA; no amino acid called in
AUG; methionine
Introns are known to contain termination codons (UAA, UGA, or UAG),
yet these codons do not interrupt the coding of a particular protein.
Why?
These triplets cause frameshift mutations, but not
termination.
Exons are spliced out of mRNA before translation.
UAA, UGA, and UAG are initiator codons, not termination
codons.
Introns are removed from mRNA before translation.
More than one termination codon is needed to stop translation.
Introns are removed from mRNA before translation.
When considering the initiation of transcription, one often finds
consensus sequences located in the region of the DNA where RNA
polymerase(s) binds. Which of the following is a common consensus
sequence?
any trinucleotide repeat
GGTTC
TATA
satellite DNAs
TTTTAAAA
TATA
Promoter recognition
RNA polymerase is a holoenzyme composed of a five-subunit core enzyme and a sigma (σ) subunit. Different types of σ subunits aid in the recognition of different forms of bacterial promoters. The bacterial promoter is located immediately upstream of the starting point of transcription (identified as the +1 nucleotide of the gene). The promoter includes two short sequences, the –10 and –35 consensus sequences, which are recognized by the σ subunit.
Chain initiation
The RNA polymerase holoenzyme first binds loosely to the promoter sequence and then binds tightly to it to form the closed promoter complex. An open promoter complex is formed once approximately 18 bp of DNA around the –10 consensus sequence are unwound. The holoenzyme then initiates RNA synthesis at the +1 nucleotide of the template strand.
Chain elongation
The RNA-coding region is the portion of the gene that is transcribed into RNA. RNA polymerase synthesizes RNA in the 5′ → 3′ direction as it moves along the template strand of DNA. The nucleotide sequence of the RNA transcript is complementary to that of the template strand and the same as that of the coding (nontemplate) strand, except that the transcript contains U instead of T.
Chain termination
Most bacterial genes have a pair of inverted repeats and a polyadenine sequence located downstream of the RNA-coding region. Transcription of the inverted repeats produces an RNA transcript that folds into a stem-loop structure. Transcription of the polyadenine sequence produces a poly-U sequence in the RNA transcript, which facilitates release of the transcript from the DNA.