Mimg 101 Midterm 2 Questions with
All Correct Answers 2026 Updated.
Summarize Griffith's experiments on transformation - Answer Griffith's experiments allowed
him to observe the change of nonvirulent organisms into virulent ones. This means that living
bacteria could transfer some component to dead bacteria.
- to do this, he injected mice with a live smooth strain of Streptococcus pneumoniae, which
killed them
- he then injected them with a live rough strain of the same bacteria, which did not harm the
mouse
- then, he injected mice with a heat-killed S-strain, which also left the mouse unharmed
- finally, he injected the mice with a mixture of heat-killed S-strain and live R strain. this resulted
in the mice dying, and when isolated, live S and live R strains were BOTH recovered from the
mouse
Relate how the contributions of Avery, MacLeod, McCarty, Hershey, and Chase confirmed that
DNA stores genetic material. - Answer - Avery, MacLeod, and McCarty showed that the
transforming principle was DNA based on the results from Griffith's experiments
- they found that transformation was blocked if DNase was treated
- They used the same bacteria and plated them--testing different conditions: R cells = no DNA
so no transformation. R and S leads to DNA transformation, When R and S+DNase is added, the
DNA is destroyed. Type R and S + RNase leads to DNA but no RNA transformation, and R and S +
Protease leads to DNA but no proteins transformation
- Additionally, Hershey and Chase in 1952 used Bacteriophage T2 infection as a model
- the DNA labeled with 32P and the protein coat was labeled with 35S. ONLY DNA entered the
cell, biut both DNA and protein coats were able to synthesize in new viruses, which showed that
DNA had genetic information for BOTH components.
Compare and contrast the structure of DNA and RNA - Answer - both use nucleotides and
have sugar phosphate helixes, and they are linked together by phosphodiester bonds
- they are different because they have different nitrogenous bases (adenine, guanine, and
cytosine are same but thymine for dna and uracil for rna)
- DNA contains deoxyribose as its sugar whereas RNA contains ribose
- DNA is double stranded, whereas RNA is single stranded
Identify the covalent bonds that link nucleotides together to form a nucleic acid and amino
acids together to form a polypeptide. - Answer - In DNA, there are covalent bonds between
the 3' hydroxyl of one sugar and 5' phosphate attached to an adjacent sugar
- nucleotides are linked by phosphodiester bonds
,- in polypeptides, there are peptide bonds, which are covalent bonds that link amino acids
together to form the chain
- the peptide bond is formed between the carboxyl (-COOH) group of one amino acid and amino
group (-NH2) of an adjacent amino acid
Describe the contribution of DNA supercoiling to DNA structure. - Answer - DNA supercoiling
makes it more compact and stable, and it allows for gene expression to be limited
- the process involves the coiling of the DNA double helix upon itself to create a higher order
structure
- DNA packaging condenses the length of DNA to fit inside cells
- Negative supercoiling facilitates replication and transcription (strand separation)
- positive supercoiling (can help protect DNA from thermal denaturation)
- DNA replication and repair: allows for decatenation, which disentangles replicated DNA
molecules by using topiosomerases
Describe a bacterial replicon - Answer - DNA molecule or a region of DNA that can be
independently replicated from a single origin of replication sequence and initiator protein
- DnaA boxes and AT-rich region can be used as origin of replication
- initiator protein binds to origin of rep to start the replication
- initiator protein recruits other factors to open the double helix
Summarize the events that occur during the three phases of DNA replication: initiation,
elongation, termination - Answer initiation
- DNA helicase unwinds double helix at origin of replication
- proteins bind to origin of replication to mark where process will start
- enzyme helicase unwinds DNA double helix
- creates 2 Y-shaped structures called replication forks, which move in opposite directions from
a replication bubble
elongation:
- RNA primer is added to each template stran to serve as a starting point for DNA polymerase
- DNA polymerase then adds new, complementary nucleotides to the 3' end of the growing
strand
- energy for this reaction is provided by incoming nucleotide triphosphates
- DNA polymerase also proofreads strand
termination
- process ends when replication forks meet or when replication is complete
- RNA primers are removed and replaced with DNA nucleotides
- enzyme DNA ligase seals the nicks in DNA backbone joining the new DNA fragments
,- final result is two identical DNA molecules with one original and one new strand (semi-
conservative)
List the enzymatic and structural elements needed by DNA polymerases for DNA synthesis -
Answer - DNA polymerase III: holoenzyme---complex of 3 core enxzymes and several other
proteins used for proofreading
- helicases ---unwind DNA strands by disrupting H-bonds and provides force to move the
replisome
- single-stranded DNA binding proteins (SSBs) ---coat single stranded DNA to protect it from
damage
- topoisomerases---relieve twist generated by rapid unwinding of double helix to prevent
supercoiling
- primase --- synthesizes short complementary strands of RNA primers needed by DNA
polymerase
Outline the major events that occur at the replication fork - Answer - the lagging strand is
synthesized in Okazaki fragments (short fragments)
- new primer is needed for synthesis of each Okazaki fragment. Primase synthesizes RNA primer
- DNA polymerase I removes RNA primers, fills gap with DNA
- DNA ligase forms phosphodiester bond between 3'-OH of growing strand and 5' -phosphate of
Okazaki fragment
Describe the structure of a typical bacterial RNA polymerase holoenzyme - Answer the RNA
polymerase holoenzyme consists of a core enzyme and sigma factor
Outline the events that occur during the three phases of transcription - Answer initiation
- RNA polymerase binds to specific DNA sequence called the promoter, which signals the start of
a gene
- the DNA double helix unwinds, creating a bubble that separates the two strands so that they
can be accessed
elongation
- the trasncription bubble
- moves with polymerase as it synthesizes mRNA
- within bubble, temporary RNA DNA hybrid is formed
- ATP GTP CTP and UTP incorporated into RNA complementary to DNA template
-RNA synthesized in 5' to 3' direction
- RNA polymerase moves along the template strand of the DNA
- it adds complementary RNA nucleotides to build a new mRNA strand following A & U and G&C
- process continues and mRNA strand grows longer
, termination
- the process stops when RNA polymerase reaches a specific DNA sequence known as the
terminator sequence
- DNA double helix reforms
- core RNA polymerase dissociates from template DNA
- intrinsic termination or factor dependent
0 intrinsic is AU rich and has a stem loop
- factor dependent uses rho(p) factor to rut site
Discuss the role of bacterial promoters and sigma factors in transcription initiation - Answer -
promoters are DNA sequences that signal the start of a gene, while sigma factors are proteins
that help the RNA polymerase core enzyme recognize and bind to these promoters to initiate
transcription
sigma factors
- holenzyme formation: a sigma factor binds to the core RNA polymerase enzyme, forming the
holoezyme necessary for transcription initiation
- promoter recognition: sigma factor is subunit responsible for recognizing and binding to the
promoter sequences on DNA
- DNA unwinding: after binding, the sigma factor helps melt or unwind the DNA double helix at
the promoter region to create a bubble
- initiation and promoter escape: the sigma factor stimulates the initial steps of RNA synthesis
and helps facilitate "promoter escape," where the sigma factor dissociates from the core
enzyme so that elongation can occur
- gene regulation: bacteria have different types of sigma factors that bind to different sets of
promoters, which allow cell to control which genes are expressed under various conditions
Distinguish factor-independent termination of transcription from rhodependent termination of
transcription - Answer factor-independent
- no protein factor is required bc it is intrinsic to RNA sequence
- formation of a hairpin loop structure in mRNA followed by a sequence of uracil residues
- the hairpin loop causes the RNA polymerase to stall, and the weak AU bonds at the end of
loop allow RNA transcript to detach from DNA template
- the hairpin loop causes the RNA polymerase to stall, and weak AU bonds at end of loop allow
RNA transcript to detach from DNA template
- does not use ATP
- a specific DNA sequence that results in GC rich hairpin followed by a U-rich tail in RNA
transcript
Rho-dependent
- requires Rho protein
All Correct Answers 2026 Updated.
Summarize Griffith's experiments on transformation - Answer Griffith's experiments allowed
him to observe the change of nonvirulent organisms into virulent ones. This means that living
bacteria could transfer some component to dead bacteria.
- to do this, he injected mice with a live smooth strain of Streptococcus pneumoniae, which
killed them
- he then injected them with a live rough strain of the same bacteria, which did not harm the
mouse
- then, he injected mice with a heat-killed S-strain, which also left the mouse unharmed
- finally, he injected the mice with a mixture of heat-killed S-strain and live R strain. this resulted
in the mice dying, and when isolated, live S and live R strains were BOTH recovered from the
mouse
Relate how the contributions of Avery, MacLeod, McCarty, Hershey, and Chase confirmed that
DNA stores genetic material. - Answer - Avery, MacLeod, and McCarty showed that the
transforming principle was DNA based on the results from Griffith's experiments
- they found that transformation was blocked if DNase was treated
- They used the same bacteria and plated them--testing different conditions: R cells = no DNA
so no transformation. R and S leads to DNA transformation, When R and S+DNase is added, the
DNA is destroyed. Type R and S + RNase leads to DNA but no RNA transformation, and R and S +
Protease leads to DNA but no proteins transformation
- Additionally, Hershey and Chase in 1952 used Bacteriophage T2 infection as a model
- the DNA labeled with 32P and the protein coat was labeled with 35S. ONLY DNA entered the
cell, biut both DNA and protein coats were able to synthesize in new viruses, which showed that
DNA had genetic information for BOTH components.
Compare and contrast the structure of DNA and RNA - Answer - both use nucleotides and
have sugar phosphate helixes, and they are linked together by phosphodiester bonds
- they are different because they have different nitrogenous bases (adenine, guanine, and
cytosine are same but thymine for dna and uracil for rna)
- DNA contains deoxyribose as its sugar whereas RNA contains ribose
- DNA is double stranded, whereas RNA is single stranded
Identify the covalent bonds that link nucleotides together to form a nucleic acid and amino
acids together to form a polypeptide. - Answer - In DNA, there are covalent bonds between
the 3' hydroxyl of one sugar and 5' phosphate attached to an adjacent sugar
- nucleotides are linked by phosphodiester bonds
,- in polypeptides, there are peptide bonds, which are covalent bonds that link amino acids
together to form the chain
- the peptide bond is formed between the carboxyl (-COOH) group of one amino acid and amino
group (-NH2) of an adjacent amino acid
Describe the contribution of DNA supercoiling to DNA structure. - Answer - DNA supercoiling
makes it more compact and stable, and it allows for gene expression to be limited
- the process involves the coiling of the DNA double helix upon itself to create a higher order
structure
- DNA packaging condenses the length of DNA to fit inside cells
- Negative supercoiling facilitates replication and transcription (strand separation)
- positive supercoiling (can help protect DNA from thermal denaturation)
- DNA replication and repair: allows for decatenation, which disentangles replicated DNA
molecules by using topiosomerases
Describe a bacterial replicon - Answer - DNA molecule or a region of DNA that can be
independently replicated from a single origin of replication sequence and initiator protein
- DnaA boxes and AT-rich region can be used as origin of replication
- initiator protein binds to origin of rep to start the replication
- initiator protein recruits other factors to open the double helix
Summarize the events that occur during the three phases of DNA replication: initiation,
elongation, termination - Answer initiation
- DNA helicase unwinds double helix at origin of replication
- proteins bind to origin of replication to mark where process will start
- enzyme helicase unwinds DNA double helix
- creates 2 Y-shaped structures called replication forks, which move in opposite directions from
a replication bubble
elongation:
- RNA primer is added to each template stran to serve as a starting point for DNA polymerase
- DNA polymerase then adds new, complementary nucleotides to the 3' end of the growing
strand
- energy for this reaction is provided by incoming nucleotide triphosphates
- DNA polymerase also proofreads strand
termination
- process ends when replication forks meet or when replication is complete
- RNA primers are removed and replaced with DNA nucleotides
- enzyme DNA ligase seals the nicks in DNA backbone joining the new DNA fragments
,- final result is two identical DNA molecules with one original and one new strand (semi-
conservative)
List the enzymatic and structural elements needed by DNA polymerases for DNA synthesis -
Answer - DNA polymerase III: holoenzyme---complex of 3 core enxzymes and several other
proteins used for proofreading
- helicases ---unwind DNA strands by disrupting H-bonds and provides force to move the
replisome
- single-stranded DNA binding proteins (SSBs) ---coat single stranded DNA to protect it from
damage
- topoisomerases---relieve twist generated by rapid unwinding of double helix to prevent
supercoiling
- primase --- synthesizes short complementary strands of RNA primers needed by DNA
polymerase
Outline the major events that occur at the replication fork - Answer - the lagging strand is
synthesized in Okazaki fragments (short fragments)
- new primer is needed for synthesis of each Okazaki fragment. Primase synthesizes RNA primer
- DNA polymerase I removes RNA primers, fills gap with DNA
- DNA ligase forms phosphodiester bond between 3'-OH of growing strand and 5' -phosphate of
Okazaki fragment
Describe the structure of a typical bacterial RNA polymerase holoenzyme - Answer the RNA
polymerase holoenzyme consists of a core enzyme and sigma factor
Outline the events that occur during the three phases of transcription - Answer initiation
- RNA polymerase binds to specific DNA sequence called the promoter, which signals the start of
a gene
- the DNA double helix unwinds, creating a bubble that separates the two strands so that they
can be accessed
elongation
- the trasncription bubble
- moves with polymerase as it synthesizes mRNA
- within bubble, temporary RNA DNA hybrid is formed
- ATP GTP CTP and UTP incorporated into RNA complementary to DNA template
-RNA synthesized in 5' to 3' direction
- RNA polymerase moves along the template strand of the DNA
- it adds complementary RNA nucleotides to build a new mRNA strand following A & U and G&C
- process continues and mRNA strand grows longer
, termination
- the process stops when RNA polymerase reaches a specific DNA sequence known as the
terminator sequence
- DNA double helix reforms
- core RNA polymerase dissociates from template DNA
- intrinsic termination or factor dependent
0 intrinsic is AU rich and has a stem loop
- factor dependent uses rho(p) factor to rut site
Discuss the role of bacterial promoters and sigma factors in transcription initiation - Answer -
promoters are DNA sequences that signal the start of a gene, while sigma factors are proteins
that help the RNA polymerase core enzyme recognize and bind to these promoters to initiate
transcription
sigma factors
- holenzyme formation: a sigma factor binds to the core RNA polymerase enzyme, forming the
holoezyme necessary for transcription initiation
- promoter recognition: sigma factor is subunit responsible for recognizing and binding to the
promoter sequences on DNA
- DNA unwinding: after binding, the sigma factor helps melt or unwind the DNA double helix at
the promoter region to create a bubble
- initiation and promoter escape: the sigma factor stimulates the initial steps of RNA synthesis
and helps facilitate "promoter escape," where the sigma factor dissociates from the core
enzyme so that elongation can occur
- gene regulation: bacteria have different types of sigma factors that bind to different sets of
promoters, which allow cell to control which genes are expressed under various conditions
Distinguish factor-independent termination of transcription from rhodependent termination of
transcription - Answer factor-independent
- no protein factor is required bc it is intrinsic to RNA sequence
- formation of a hairpin loop structure in mRNA followed by a sequence of uracil residues
- the hairpin loop causes the RNA polymerase to stall, and the weak AU bonds at the end of
loop allow RNA transcript to detach from DNA template
- the hairpin loop causes the RNA polymerase to stall, and weak AU bonds at end of loop allow
RNA transcript to detach from DNA template
- does not use ATP
- a specific DNA sequence that results in GC rich hairpin followed by a U-rich tail in RNA
transcript
Rho-dependent
- requires Rho protein
