MOLECULAR BIOLOGY EXAM: LATEST A+ QUESTIONS
AND ANSWERS BREAKDOWN
What is the Central Dogma of Microbiology?
DNA undergoes replication, then undergoes transcription to become RNA. The RNA goes
through translation to become a protein
DNA > RNA > Protein
What sugar is used in RNA?
Ribose
In RNA, what replaces Thymine?
Uracil
What are the three types of RNA?
tRNA, mRNA, and rRNA
What is special about siRNA?
Small Interfering RNA is double stranded, which is significant because RNA is normally single
stranded. It's job is to interfere or silence the expression of a gene. When mRNA is produced,
siRNA can produce a complementary strand to the mRNA that blocks the translation of the
gene.
Where does the synthesis of the complementary RNA strand occur?
Transcription bubble
What enzyme makes RNA?
RNA polymerase
What are repressor proteins (lac operon)?
A high amount of tryptophan acts as a key that enters a lock (repressor protein) and does not
allow for the RNA polymerase to transcribe genes. If there is a low amount of tryptophan, the
repressor proteins are inactive; therefore, they do not get in the way of RNA polymerase. Gene
transcription can continue. ***mainly in prokaryotes!!!! sometimes in eukaryotes.
What are the three steps of transcription?
1. Initiation
2. Elongation
3. Termination
, What happens in initiation?
RNA polymerase binds to the promoter sequence on DNA.
What is the role of the promoter?
1. Shows where to start reading = the start point.
2. Shows which strand to read = template strand
3. Direction of DNA = it runs across from DNA 3' to 5', and writes RNA from 5' to 3' (antiparallel)
What happens in Elongation?
The RNA polymerase unwinds DNA (20 base pairs at a time). It moves across DNA 3' to 5' and
builds RNA 5' to 3'. There's no proofreading because it has a short life and it makes many
copies.
What happens in termination?
RNA polymerase stops at termination sequence. The hairpin turn dislodges the RNA
Polymerase. **** in prokaryotes: mRNA leaves DNA but doesn't have a nucleus to exit
What does is prokaryotic DNA like?
Prokaryotic DNA:
- circular in shape
- in the cytoplasm
- not wrapped around proteins
- no introns
- no 5' cap or 3' poly-a tail
- fewer average base pairs
What is eukaryotic DNA like?
Eukaryotic DNA:
- linear in shape
- in the NUCLEUS
- wrapped around proteins
- introns and eons
- 5' cap and 3' poly-a tail
- more base pairs
What's an intron?
non-coding (in-between) sequence in DNA
What's an exon?
coding (expressed) sequence in DNA
AND ANSWERS BREAKDOWN
What is the Central Dogma of Microbiology?
DNA undergoes replication, then undergoes transcription to become RNA. The RNA goes
through translation to become a protein
DNA > RNA > Protein
What sugar is used in RNA?
Ribose
In RNA, what replaces Thymine?
Uracil
What are the three types of RNA?
tRNA, mRNA, and rRNA
What is special about siRNA?
Small Interfering RNA is double stranded, which is significant because RNA is normally single
stranded. It's job is to interfere or silence the expression of a gene. When mRNA is produced,
siRNA can produce a complementary strand to the mRNA that blocks the translation of the
gene.
Where does the synthesis of the complementary RNA strand occur?
Transcription bubble
What enzyme makes RNA?
RNA polymerase
What are repressor proteins (lac operon)?
A high amount of tryptophan acts as a key that enters a lock (repressor protein) and does not
allow for the RNA polymerase to transcribe genes. If there is a low amount of tryptophan, the
repressor proteins are inactive; therefore, they do not get in the way of RNA polymerase. Gene
transcription can continue. ***mainly in prokaryotes!!!! sometimes in eukaryotes.
What are the three steps of transcription?
1. Initiation
2. Elongation
3. Termination
, What happens in initiation?
RNA polymerase binds to the promoter sequence on DNA.
What is the role of the promoter?
1. Shows where to start reading = the start point.
2. Shows which strand to read = template strand
3. Direction of DNA = it runs across from DNA 3' to 5', and writes RNA from 5' to 3' (antiparallel)
What happens in Elongation?
The RNA polymerase unwinds DNA (20 base pairs at a time). It moves across DNA 3' to 5' and
builds RNA 5' to 3'. There's no proofreading because it has a short life and it makes many
copies.
What happens in termination?
RNA polymerase stops at termination sequence. The hairpin turn dislodges the RNA
Polymerase. **** in prokaryotes: mRNA leaves DNA but doesn't have a nucleus to exit
What does is prokaryotic DNA like?
Prokaryotic DNA:
- circular in shape
- in the cytoplasm
- not wrapped around proteins
- no introns
- no 5' cap or 3' poly-a tail
- fewer average base pairs
What is eukaryotic DNA like?
Eukaryotic DNA:
- linear in shape
- in the NUCLEUS
- wrapped around proteins
- introns and eons
- 5' cap and 3' poly-a tail
- more base pairs
What's an intron?
non-coding (in-between) sequence in DNA
What's an exon?
coding (expressed) sequence in DNA
