Central Dogma

Question 1

Which are the sense strand and the antisense strand?

Answer 1

Sense strand = Coding DNA strand
Antisense strand = Template DNA strand

Coding DNA strand: 5’-3’ direction
Template DNA strand: 3’-5’ direction
RNA: 5’-3’ direction

Question 2

Role of RNA polymerase

Answer 2

• Unwind the portion of DNA, the gene that it needs to transcribe from
• Add RNA nucleotides, complementary to the template strand of DNA
• Winds back the DNA behind that has been transcribed

Question 3

What are the promoter region, coding sequence, and terminator region?

Answer 3

Promoter region: non-coding sequence of nitrogenous bases
Role: initiate the transcription process

Coding sequence: sequence of nitrogenous bases that code for the protein to be synthesized

Terminator region: sequence of nitrogenous bases that do not code for proteins
Role: termination of mRNA synthesis

Question 4

What are the START codons?

Answer 4

AUG - codes for amino acid methionine

Role: marks the start of translation

Question 5

Prokaryotes vs Eukaryotes

Answer 5

• Eukaryotes have a larger cell size and genome than prokaryotes

Eukaryotes:
- transcription occurs in the nucleus 
- translation occurs in the cytoplasm 
Prokaryotes: 
- transcription and translation occur simultaneously in the cytoplasm

Eukaryotes:
- undergo post-transcriptional mRNA processing
Prokaryotes
- do not undergo post-transcriptional mRNA processing

Eukaryotes:
- mRNA has both introns and exons
Prokaryotes:
- mRNA only have introns, no exons

Question 6

Post-transcriptional mRNA processing in eukaryotes

Answer 6

• Addition of 5’ cap and 3’ poly(A) tail to pre-mRNA
• This is to improve the stability of the mRNA, allowing its transport from the nucleus to the cytoplasm
• RNA splicing, to produce functional mRNA by intron excision

Question 7

What are the STOP codons?

Answer 7

UAG, UAA, UGA

• signal the stop of translation process
• they do not code for amino acids
• aka nonsense codon/termination codon

Question 8

What does the term “degeneracy” mean?

Answer 8

Many codons coding for one amino acid

- e.g. CGU & AGA code for the amino acid Arg

Question 9

What is the function of tRNA

Answer 9

Decode the mRNA sequence into protein