7.2 Transcription [HY]

Question 1

Template strand (or the antisense strand)

Answer 1

• Transcription results in a single strand of mRNA, synthesized from one of the two nucleotide strands of DNA

Question 2

TATA box

Answer 2

• Binding site of RNA polymerase II in the promoter region
• high concentration of thymine and adenine

Question 3

Transcription factors

Answer 3

help the RNA polymerase locate and bind to this promoter region of the DNA, helping to establish where transcription will start.

Question 4

RNA polymerase I

Answer 4

located in the nucleolus and synthesizes rRNA

Question 5

RNA polymerase II

Answer 5

• located in the nucleus and synthesizes hnRNA (pre-processed mRNA) and some small nuclear RNA (snRNA)

Question 6

RNA polymerase III

Answer 6

• located in the nucleus and synthesizes tRNA and some rRNA

Question 7

Coding strand (or sense strand)

Answer 7

• is not used as a template during transcription
• Because the coding strand is also complementary to the template strand, it is identical to the mRNA transcript except that all the thymine nucleotides in DNA have been replaced with uracil in the mRNA molecule.

Question 8

Numbering System

Answer 8

• The first base transcribed from DNA to RNA is defined as the +1 base of that gene region
• Bases to the left of this start point (upstream, or toward the 5′ end) are given negative numbers: −1, −2, −3, and so on.
• The TATA box, where RNA
  polymerase II binds, usually falls around −25

Question 9

Heterogeneous nuclear RNA
(hnRNA)

Answer 9

• synthesized from the DNA template (antisense) strand
• Before the hnRNA can leave the nucleus and be translated to protein, it must undergo three specific processes to allow it to interact with the ribosome and survive the conditions of the cytoplasm
• Maturation of the hnRNA includes splicing of the transcript to remove
  noncoding sequences (introns) and ligate coding sequences (exons)

Question 10

Spliceosome

Answer 10

• In the spliceosome,
  small nuclear RNA (snRNA) molecules couple with proteins known as small nuclear ribonucleoproteins (also known as snRNPs, or “snurps”). The snRNP/snRNA complex recognizes both the 5′ and 3′ splice sites of the introns

Question 11

5′ Cap

Answer 11

• At the 5′ end of the hnRNA molecule, a 7-methylguanylate triphosphate cap is added.
• The cap is actually added during the process of transcription and is recognized by the ribosome as the binding site.
• protects the mRNA from degradation in the cytoplasm

Question 12

Polyadenosyl (poly-A) tail

Answer 12

• added to the 3′ end of the mRNA transcript and protects the message against rapid degradation
• as soon as the mRNA leaves the nucleus, it will start to get
  degraded from its 3′ end.
• The longer the poly-A tail, the more time the mRNA will be able to survive before being digested in the cytoplasm
• The poly-A tail also assists with export of the mature mRNA from the nucleus

Question 13

Alternative splicing

Answer 13

• the primary transcript of
  hnRNA may be spliced together in different ways to produce multiple variants of proteins encoded by the same original gene