15.2

Question 1

Explain transcription, including a description of important molecules involved in the process.

Answer 1

o The template strand provides a template for ordering the sequence of complementary nucleotides in an RNA transcript
o The first stage of gene expression
o RNA synthesis is catalyzed by the RNA polymerase
• Follows the same base-paring rules as DNA except U substitutes T

Question 2

illustrate initiation of transcription in eukaryotes (transcription factors)

Answer 2

 Necessary to get the RNA polymerase II enzyme to the promoter and initiate gene expression
 Recognize and bind to the TATA box sequence in the promoter
 Interact with RNA polymerase to form an initiation complex at the promoter

Question 3

illustrate initiation of transcription in eukaryotes (promoter)

Answer 3

 Forms the recognition and binding site for RNA polymerase
 Found upstream of the start site

Question 4

illustrate initiation of transcription in eukaryotes (TATA box)

Answer 4

specifies to other molecules where transcription begins, indicates where a genetic sequence can be read and decoded

Question 5

illustrate initiation of transcription in eukaryotes (RNA polymerase)

Answer 5

 Pries DNA strands apart and joins together RNA nucleotides
• Produces RNA that’s complementary to the DNA template strand and does not need a primer

Question 6

RNA polymerase I

Answer 6

transcribe rRNA

Question 7

RNA polymerase II

Answer 7

transcribes mRNA and snRNA

Question 8

RNA polymerase III

Answer 8

transcribes tRNA and some other small RNAs

Question 9

Describe the role of the RNA polymerase and sigma-factor in prokaryotic transcription initiation.

Answer 9

o Sigma factor binds to promoter sequence in DNA upstream of start site
o RNA polymerase opens the double helix
o Once transcription begins the sigma factor dissociates

Question 10

Bacterial elongation of transcript

Answer 10

• Grows in the 5’ to 3’ direction as ribonucleotides are added
• Transcription bubble: Contains RNA polymerase, DNA template, and growing RNA transcript
• Passes after transcription allowing the now-transcribed DNA to be rewound as it leaves the bubble

Question 11

Eukaryotic elongation of transcript

Answer 11

• as RNA polymerase moves along the DNA, it untwists the double helix
• a gene can be transcribe simultaneously by several RNA polymerases
• nucleotide are added to the 3’ end of growing RNA molecules

Question 12

Bacterial termination of transcript

Answer 12

• terminator sequences signal “stop” to polymerase: RNA dissociates from template and DNA rewinds (mRNA can be translated without further modification)
• simplest terminator sequence: series of C-G base-pairs followed by a series of A-T base- pairs & forms a hairpin which causes RNA polymerase to pause

Question 13

Eukaryotic termination of transcript

Answer 13

• RNA polymerase II transcribes the polyadenylation signal sequence and the RNA transcript is released 10-35 nucleotides past this sequence
• after transcription & RNA processing, the mRNA is transported out of the nucleus into the cytoplasm where it is translated

Question 14

Trace the steps involved in eukaryotic RNA processing: 5’ cap, poly-A-tail, and RNA splicing.

Answer 14

o Addition of a 5; cap protects from degradation and is involved in translation initiation
o Addition of a 3’ poly-A tail: created by poly-A polymerase and protects from degradation
Removal of introns (splicing)

Question 15

contrast introns and exons

Answer 15

introns: no coding sequences
exons: sequences that will be translated

Question 16

Explain the functional importance of alternative splicing.

Answer 16

Explains how 20000 genes of the human genome can encode the estimated 93000 protein-coding transcripts

Question 17

Transcribe a template DNA sequence into mRNA.

3’ AUGCCCGUAAGCUAA 5’ –>

Answer 17

3’ AUGCCCGUAAGCUAA 5’ –> 5’ UACGGGCAUUCGAUU 3’