BCHM 4360 ACTUAL EXAM 2 2025 VERIFIED RATIONALES WITH COMPLETE
SOLUTIONS GRADED A
What is the information stored in DNA used for?
to make a functional protein or RNA molecule
Transcription
the copying of one strand of DNA (coding strand) into an RNA molecule (transcript)
transcript
RNA
translation
reading of the mRNA sequence by the ribosome to produce a protein from the RNA
molecule
RNA polymerase
-large multi-subunit enzyme
-transcribes DNA
-copies the coding strand of DNA by using the complementary strand (the template or non-
coding strand) as a template
-separates the DNA strands and allows nucleoside triphosphate to base-pair with the
template strand
,coding vs template strand
coding = identical to mRNA
template = noncoding/complementary to mRNA
transcription can be divided into...
initiation, elongation, termination
initiation of transcription (overview)
-starts when RNA polymerase binds to the DNA sequence just preceding the gene (the
promoter) = promoter recognition
-TSS = +1
-RNA polymerase separates the DNA strands to make a transcription bubble, and the first
few ribonucleoside triphosphates are added while the RNA polymerase is at the promoter
-when the RNA is a sufficient size, the RNA polymerase moves past the promoter and
changes conformation to be more stably associated with the DNA (allows higher
processivity) = promoter clearance
When does transcription start?
when RNA polymerase binds to the DNA sequence just preceding the gene (the promoter) =
promoter recognition
,transcription start site
+1
the first base to be transcribed
direction of transcription
5' to 3' (template read 3' to 5')
Upstream vs. Downstream
upstream = bases 5' of site on RNA
downstream = bases 3' of site on RNA
promoter clearance
when the RNA is a sufficient size, the RNA polymerase moves past the promoter and
changes conformation to be more stably associated with the DNA (allows higher
processivity)
RNA polymerase undergoes a conformational change that associates it very stably with
DNA, and loosens its grip on initiation factors
-phosphorylated as it converts to the elongating complex (Cdk)
elongation of transcription (overview)
, -after promoter clearance, the RNA polymerase moves along the DNA, adding
ribonucleotides and elongating the RNA transcript
-the RNA polymerase unwinds the DNA ahead of it, and the DNA re-pairs behind the
enzyme, maintaining the transcription bubble along the DNA
-in the bubble, a short region of the transcript is paired with the DNA while the rest of the
RNA is extruded from the polymerase
-elongation continues until the polymerase meets a DNA sequence called a terminator that
signals RNA synthesis to cease (RNA polymerase then dissociates from DNA)
transcription bubble
-much smaller than replication bubble
-contained within RNA polymerase
-maintained along DNA by RNA polymerase unwinding the DNA ahead of it, and the DNA
re-pairing behind the enzyme
-has a short region of the transcript is paired with the DNA while the rest of the RNA is
extruded from the polymerase
How long does elongation continue (transcription)?
until the polymerase meets a DNA sequence called a terminator that signals RNA synthesis
to cease (RNA polymerase then dissociates from DNA)
heavy regulation of transcription
-so only the required RNA is produced at the right times
-usually controlled by chromatin packing
SOLUTIONS GRADED A
What is the information stored in DNA used for?
to make a functional protein or RNA molecule
Transcription
the copying of one strand of DNA (coding strand) into an RNA molecule (transcript)
transcript
RNA
translation
reading of the mRNA sequence by the ribosome to produce a protein from the RNA
molecule
RNA polymerase
-large multi-subunit enzyme
-transcribes DNA
-copies the coding strand of DNA by using the complementary strand (the template or non-
coding strand) as a template
-separates the DNA strands and allows nucleoside triphosphate to base-pair with the
template strand
,coding vs template strand
coding = identical to mRNA
template = noncoding/complementary to mRNA
transcription can be divided into...
initiation, elongation, termination
initiation of transcription (overview)
-starts when RNA polymerase binds to the DNA sequence just preceding the gene (the
promoter) = promoter recognition
-TSS = +1
-RNA polymerase separates the DNA strands to make a transcription bubble, and the first
few ribonucleoside triphosphates are added while the RNA polymerase is at the promoter
-when the RNA is a sufficient size, the RNA polymerase moves past the promoter and
changes conformation to be more stably associated with the DNA (allows higher
processivity) = promoter clearance
When does transcription start?
when RNA polymerase binds to the DNA sequence just preceding the gene (the promoter) =
promoter recognition
,transcription start site
+1
the first base to be transcribed
direction of transcription
5' to 3' (template read 3' to 5')
Upstream vs. Downstream
upstream = bases 5' of site on RNA
downstream = bases 3' of site on RNA
promoter clearance
when the RNA is a sufficient size, the RNA polymerase moves past the promoter and
changes conformation to be more stably associated with the DNA (allows higher
processivity)
RNA polymerase undergoes a conformational change that associates it very stably with
DNA, and loosens its grip on initiation factors
-phosphorylated as it converts to the elongating complex (Cdk)
elongation of transcription (overview)
, -after promoter clearance, the RNA polymerase moves along the DNA, adding
ribonucleotides and elongating the RNA transcript
-the RNA polymerase unwinds the DNA ahead of it, and the DNA re-pairs behind the
enzyme, maintaining the transcription bubble along the DNA
-in the bubble, a short region of the transcript is paired with the DNA while the rest of the
RNA is extruded from the polymerase
-elongation continues until the polymerase meets a DNA sequence called a terminator that
signals RNA synthesis to cease (RNA polymerase then dissociates from DNA)
transcription bubble
-much smaller than replication bubble
-contained within RNA polymerase
-maintained along DNA by RNA polymerase unwinding the DNA ahead of it, and the DNA
re-pairing behind the enzyme
-has a short region of the transcript is paired with the DNA while the rest of the RNA is
extruded from the polymerase
How long does elongation continue (transcription)?
until the polymerase meets a DNA sequence called a terminator that signals RNA synthesis
to cease (RNA polymerase then dissociates from DNA)
heavy regulation of transcription
-so only the required RNA is produced at the right times
-usually controlled by chromatin packing
