Central Dogma

Question 1

Define coding and non-coding RNA.

Answer 1

• Coding RNA molecules; contain a sequence that can be decoded to generate a polypeptide sequence (This is messenger RNA (mRNA)).
• Noncoding RNA molecules; do not serve as templates for making polypeptides. Instead, many are involved in regulation of gene expression.

Question 2

Outline/Draw the steps of transcription and translation.

Question 3

List and state the functions of the RNA polymerases (1,2,3)

Answer 3

1. RNA polymerase I transcribes large rRNAs
2. RNA polymerase II pre-mRNA, some snRNAs, snoRNAs, some miRNAs
3. RNA polymerase III tRNAs, small rRNAs, some snRNAs, some miRNAs

*RNA polymerase I, II, and III recognise different promoters. RNA polymerases do not require primers.

Question 4

Define a transcription unit.

Answer 4

• a stretch of DNA that encodes an RNA molecule plus the sequences needed for its transcription.
• Within a transcription unit are three critical regions:

Question 5

What are the three critical regions in transcription units? Outline.

Answer 5

• Promoter: a DNA sequence that transcription apparatus recognises and binds to. Indicates which DNA strand is to be transcribed and the transcription start site.
• RNA-coding region: a sequence of DNA nucleotides copied into an RNA molecule.
• Terminator: a sequence of nucleotides that signals where transcription is to end.

Question 6

What is a consensus sequence?

Answer 6

Consist of most commonly encountered bases at each position in a group of related sequences.

Question 7

List/Outline pre-mRNA processing.

Answer 7

Medications of pre-mRNA before maturing are:
Addition of 5’ end cap; facilitates binding of ribosome to 5’ end of mRNA.
Addition of poly(A) tail and 3’ end cleavage; increases mRNA stability.
Splicing; removes non-coding introns and facilitates export of RNA to cytoplasm.
Editing; alters nucleotide sequence.

Question 8

What is alternative splicing? Why is it useful? It’s importance?

Answer 8

Alternative Splicing; occurs in most human genes. Allows different combinations of exons to be retained in the mRNA and greatly amplifies the number of proteins that can be produced from ~20,000 protein coding genes.

Question 9

Define small nuclear ribnonucleoproteins (snRNPs).

Answer 9

• Most introns have specific sequences at 5’ and 3’ ends which are recognized by small nuclear ribonucleoproteins (snRNPs).
• snRNPs: complexes of proteins and specific RNA molecules

Question 10

Define splicesome.

Answer 10

It’s a combination of pre-mRNA and the snRNPs and is responsible for folding the pre-mRNA into correct configuration.

Question 11

Define exon-junction complex.

Answer 11

After splicing, proteins deposited ~20 nucleotides upstream of exon-exon junctions which promotes export of mRNA into the cytoplasm.

Question 12

What is the donor and acceptor splice site?

Answer 12

The borders between introns and exons are termed as splice sites. The splice site in the upstream part of an intron is called the donor splice site (in the direction 5’ to 3’) and the downstream part is termed as the acceptor splice site (in the direction 3’ to 5’)

Question 13

Define mRNA surveillance.

Answer 13

Cell has several different mechanisms to deal with
errors in mRNAs and to ensure accuracy of information transfer. Can deal with nonsense mutations for example.

Question 14

What is nonsense mediated mRNA decay (NMD)?

Answer 14

It’s a process which results in rapid elimination of mRNA containing premature termination codons.

Question 15

Define Post-translational Modification.

Answer 15

After translation, several further processes are needed to convert the polypeptide into a fully functional protein modifications.