Transcript

Only 1 DNA strand, called template strand, is used as the template for transcription.

• True

• False

Answer explanation

Explanation: The DNA strand is used as the template for transcription, thus its name, template strand.

 

Extra:

In exam questions, the term “template strand” or “non template strand” usually used.

However, if the term “non-coding strand” or “coding strand” is used instead of “template strand” or “non-template strand”, look for clues in the question stem (as there is different definition under British or USA system).  See Pg 28 of lecture note.

i.e non-coding / coding strand è depend on question’s clues, no fixed definition.

The product of transcription is always mRNA.

• True

• False

Answer explanation

Correct ans:

The product of transcription is always RNA, which can be tRNA, rRNA or mRNA.

 

Explanation: Transcription refers to using DNA as template to make RNA. This includes mRNA, tRNA and rRNA etc. Just that only mRNA undergo translation as the mRNA sequence is read by ribosome, while non-mRNA ie tRNA and rRNA do not undergo translation but are involved in translation process e.g tRNA is involved in amino acid activation (amino acid attached to tRNA) to carry amino acids to ribosomes for translation process.  rRNA is a component of ribosomes (composed of rRNA & proteins)

In one round of transcription, the entire chromosome gets transcribed.

• True

• False

Answer explanation

Correct ans: for each round of transcription, a gene gets transcribed instead of the entire chromosome.

For initiation of transcription in Eukaryotes, RNA polymerase cannot bind to promoter, if transcription factors are absent.

• True

• False

Answer explanation

Explanation: Unlike prokaryotes, eukaryotic RNA polymerase requires general transcription factors (proteins) to aid RNA polymerase to bind to the promoter of the gene for initiation of transcription.  

In Prokaryotes, RNA polymerase has the sigma factor that recognises the promoter directly without the help of transcription factors.

• True

• False

RNA polymerase and DNA polymerase both synthesise their products in the same direction [5’ to 3’].

• True

• False

Answer explanation

Explanation: Both indeed synthesise product in 5’ to 3’ direction, due to the 3’OH group needed for condensation reaction to form phosphodiester bonds.

 

RNA polymerase is involved in transcription and DNA polymerase is involved in DNA replication.

RNA polymerase and DNA polymerase both read their DNA template in the same direction [3’ to 5’].

• True

• False

Answer explanation

Explanation: Both indeed use DNA as template & both indeed read template in 3’ to 5’ direction. This is to comply with anti-parallel rule. If product strand is made 5’ to 3’ direction, the template is read 3’ to 5’.

During transcription, hydrogen bonds were broken, and some were formed.

• True

• False

Answer explanation

Explanation:

 

H bond breakage:

- H bonds were first broken when the 2 strands of DNA molecule are separated to allow RNA polymerase to access the template strand;

- H bonds were also broken between product (RNA) strand and DNA template strand to allow RNA product to be released.

 

H bond formation:

- occurs during complementary base pairing between RNA nucleotides and the DNA template

- re-annealing of both DNA strands after transcription is done

Eukaryotes:

During post-transcriptional modification, exons are excised (= cut out) and introns are ligated (=joined) together in the mRNA.

• True

• False

Answer explanation

Correct ans: Exons (coding) are ligated/joined together while introns (non-coding) are excised/removed.

In Eukaryotes during pre-mRNA processing, a 5’ cap is always formed first.

• True

• False

Answer explanation

Explanation:  The moment 5’ end of mRNA is formed, enzymes will catalyse the formation of the 5’cap immediately [in post-transcriptional modification process].