Transcription

Question 1

the antisense strand is the …
the sense strand is the ….

Answer 1

DNA template strand
DNA coding strand

Question 2

describe the second step of transcription (3 main points)

why is the coding strand called the coding strand

Answer 2

RNA polymerase directs the sequential binding of ribonucleotides
to the growing RNA chain in the 5’ to 3’ direction after the promoter.

RNA polymerase forms phosphodiester bonds in the RNA chain

Once the RNA polymerase machinery passes, the two DNA strands reform back together

key notes

The template strand is the strand being read

the other strand is called the DNA coding strand and is not transcribed

its called the coding strand as its sequence is the same as the RNA sequence that is produced, with the exception of U replacing T

task before quiz: find out why these strands have those names.

Question 3

Describe the first step of transcription (2 main points)

Answer 3

enzyme RNA polymerase recognizes a promoter region, which lies “upstream” from the gene(usually repeating A and T)

The RNA polymerase binds tightly to the promoter causing the DNA strands to pull apart within the promoter region

• A and T have 2 bonds so easier to pull apart

Question 4

Describe the third step of transcription (3 main points)

Answer 4

• regions at the end of genes signal termination and are named “terminator sequence”, work with RNA polymerase to loosen the association between the mRNA strand and the DNA template

-mRNA falls off the transcription complex and is modified in nucleus

 RNA polymerase can bind to another promoter site on DNA

Question 5

Posttranscriptional Modifications

Answer 5

1. Capping: Addition of a 5’ cap to start end
    Protects it from digestion by nucleases and phosphatases as it exits
   the nucleus
    Helps to initiate translation
2. Tailing: Addition of the poly-A tail by poly-A polymerase
    200-300 adenine bases added to the end of mRNA transcript
    Helps end translation
3. Introns are cut out by spliceosomes
    Eukaryotic DNA has exons (coding regions) and introns (non-coding
   regions).
    Introns are interspersed among the exons, therefore sections of the
   primary transcript do not code for part of the protein
   Won’t make proper amino acid sequence so the protein won’t
   fold properly

Question 6

what is the primary transcript

what is Modified primary transcript

Answer 6

RNA just transcribed = primary transcript

Modified primary transcript = mRNA

Question 7

what connects Poly-A tail to enzyme to mRNA strand

Answer 7

poly-A polymerase

Question 8

what is DNA gyrase reffereed to as

Answer 8

topoisomerase

Question 9

what is RNA polymerase

Answer 9

an enzyme because of the ase ending