Bio 2100: Exam 4 Questions With Complete Solutions
Alteration of mRNA ends after transcription Correct Answers
(1) 5' end of mRNA, which is synthesized first, receives a 5' cap,
a modified form of a guanine nucleotide added onto the 5' end
after transcription of the first 20-40 nucleotides
(2) 3' end of the pre-mRNA molecule receives 50-250 more
adenine nucleotides, forming a poly-A tail
Functions of the 5' cap and poly-A tail: (1) facilitate the export
of the mature mRNA from the nucleus, (2) help protect the
mRNA from degradation by hydrolytic enzymes, and (3) help
ribosomes attach to the 5' end of the mRNA once the mRNA
reaches the cytoplasm
Alternative RNA Splicing Correct Answers genes that give rise
to two or more different polypeptides, depending on which
segments are treated as exons during RNA processing; because
of this, the number of different protein products an organism
produces can be much greater than its number of genes
Aminoacyl-tRNA Synthetases Correct Answers catalyzes the
covalent attachment of the amino acid to its tRNA in a process
driven by the hydrolysis of ATP --> produces charged tRNA;
ensures that a given amino acid is bound to its appropriate
tRNA; 20 synthetases exist (one for each amino acid)
Anticodon Correct Answers the particular nucelotide triplet that
base-pairs to a specific mRNA codon; conventionally written in
the 3' --> 5' direction to align properly with codons written 5' -->
3'
,Bacteriophages Correct Answers viruses that infect bacteria
Based on his previous results (living S cells result in dead
mouse, living R cells result in healthy mouse, and heat-killed S
cells result in healthy mouse), what result was Griffith expecting
when mixing the heat-killed S cells with the living R cells?
Correct Answers He was expecting the mouse to remain healthy
because neither type of cell alone would kill the mouse
Because it is identical in sequence to the mRNA, except for
having T instead of U, the nontemplate DNA strand is often
called the __________ strand Correct Answers coding
Chargaff Correct Answers analyzed the base composition of
DNA from a number of different organisms and found that it
varies from one species to another; found that in each species,
the number of adenines approximately equaled the number of
thymines and the number of guanines approximately equaled the
number of cytosines
Chargaff's Rules Correct Answers (1) DNA base composition
varies between species
(2) For each species, the percentages of A and T bases are
roughly equal, as are those of G and C bases
Chromatin Packing in a Eukaryotic Chromosome (DETAILED)
Correct Answers (1) Starts off as a DNA double helix, which
has negatively charged backbones due to phosphate
(2) Proteins called histones (4 main types) bind tightly to the
negatively charged DNA
, (3) Unfolded chromatin is 10nm in diameter and resembles
beads on a string; each "bead" is a nucleosome, the basic unit of
DNA packing (consists of DNA wound twice around a core of 8
histones --> amino end of of each histone extends outward from
nucleosome, forming histone tail) and the "string" between
beads is called linker DNA
(4)Histone tails of one nucleosome and the linker DNA and
nucleosomes on the other side interact; interactions cause the
extended 10 nm fiber to coil, forming a 30 nm fiber; requires 5th
type of histone
(5) 30 nm fiber forms loops called looped domains attached to a
chromosome scaffold composed of proteins, thus making up a
300 nm fiber
(6) Looped domains coil and fold, producing the characteristic
metaphase chromosome
Chromatin Packing in Eukaryotic Chromosomes (OVERVIEW)
Correct Answers DNA double helix --> histones -->
nucleosomes (10nm fiber) --> 30nm fiber --> looped domains
(300nm fiber) --> metaphase chromosome
Compare/Contrast DNA Replication in Bacteria and Eukaryotes
Correct Answers Bacteria: circular; have a single origin of
replication; have two major DNA polymerases (DNA
polymerase III and DNA polymerase I); shortening of DNA
does NOT occur because there are no ends; DNA is packaged
into the nucleoid
Eukaryotes: linear; have hundreds of origins of replication and
multiple replication bubbles; have several DNA polymerases;
shortening of DNA occurs because 5' ends cannot be completed;
Alteration of mRNA ends after transcription Correct Answers
(1) 5' end of mRNA, which is synthesized first, receives a 5' cap,
a modified form of a guanine nucleotide added onto the 5' end
after transcription of the first 20-40 nucleotides
(2) 3' end of the pre-mRNA molecule receives 50-250 more
adenine nucleotides, forming a poly-A tail
Functions of the 5' cap and poly-A tail: (1) facilitate the export
of the mature mRNA from the nucleus, (2) help protect the
mRNA from degradation by hydrolytic enzymes, and (3) help
ribosomes attach to the 5' end of the mRNA once the mRNA
reaches the cytoplasm
Alternative RNA Splicing Correct Answers genes that give rise
to two or more different polypeptides, depending on which
segments are treated as exons during RNA processing; because
of this, the number of different protein products an organism
produces can be much greater than its number of genes
Aminoacyl-tRNA Synthetases Correct Answers catalyzes the
covalent attachment of the amino acid to its tRNA in a process
driven by the hydrolysis of ATP --> produces charged tRNA;
ensures that a given amino acid is bound to its appropriate
tRNA; 20 synthetases exist (one for each amino acid)
Anticodon Correct Answers the particular nucelotide triplet that
base-pairs to a specific mRNA codon; conventionally written in
the 3' --> 5' direction to align properly with codons written 5' -->
3'
,Bacteriophages Correct Answers viruses that infect bacteria
Based on his previous results (living S cells result in dead
mouse, living R cells result in healthy mouse, and heat-killed S
cells result in healthy mouse), what result was Griffith expecting
when mixing the heat-killed S cells with the living R cells?
Correct Answers He was expecting the mouse to remain healthy
because neither type of cell alone would kill the mouse
Because it is identical in sequence to the mRNA, except for
having T instead of U, the nontemplate DNA strand is often
called the __________ strand Correct Answers coding
Chargaff Correct Answers analyzed the base composition of
DNA from a number of different organisms and found that it
varies from one species to another; found that in each species,
the number of adenines approximately equaled the number of
thymines and the number of guanines approximately equaled the
number of cytosines
Chargaff's Rules Correct Answers (1) DNA base composition
varies between species
(2) For each species, the percentages of A and T bases are
roughly equal, as are those of G and C bases
Chromatin Packing in a Eukaryotic Chromosome (DETAILED)
Correct Answers (1) Starts off as a DNA double helix, which
has negatively charged backbones due to phosphate
(2) Proteins called histones (4 main types) bind tightly to the
negatively charged DNA
, (3) Unfolded chromatin is 10nm in diameter and resembles
beads on a string; each "bead" is a nucleosome, the basic unit of
DNA packing (consists of DNA wound twice around a core of 8
histones --> amino end of of each histone extends outward from
nucleosome, forming histone tail) and the "string" between
beads is called linker DNA
(4)Histone tails of one nucleosome and the linker DNA and
nucleosomes on the other side interact; interactions cause the
extended 10 nm fiber to coil, forming a 30 nm fiber; requires 5th
type of histone
(5) 30 nm fiber forms loops called looped domains attached to a
chromosome scaffold composed of proteins, thus making up a
300 nm fiber
(6) Looped domains coil and fold, producing the characteristic
metaphase chromosome
Chromatin Packing in Eukaryotic Chromosomes (OVERVIEW)
Correct Answers DNA double helix --> histones -->
nucleosomes (10nm fiber) --> 30nm fiber --> looped domains
(300nm fiber) --> metaphase chromosome
Compare/Contrast DNA Replication in Bacteria and Eukaryotes
Correct Answers Bacteria: circular; have a single origin of
replication; have two major DNA polymerases (DNA
polymerase III and DNA polymerase I); shortening of DNA
does NOT occur because there are no ends; DNA is packaged
into the nucleoid
Eukaryotes: linear; have hundreds of origins of replication and
multiple replication bubbles; have several DNA polymerases;
shortening of DNA occurs because 5' ends cannot be completed;
