(3) Chapter 8: Microbial Genetics

What is transcription?

The process of synthesizing messenger RNA (mRNA) from a DNA template.

What is the purpose of transcription?

To copy the genetic information from DNA into mRNA so it can be used to make proteins.

What enzyme performs transcription?

RNA polymerase.

What molecule is produced during transcription?

Messenger RNA (mRNA).

What serves as the template during transcription?

One strand of DNA.

Which DNA strand is used during transcription?

Only one DNA strand serves as the template for each gene.

How does RNA polymerase determine which RNA nucleotide to add?

By complementary base-pairing with the DNA template.

Which RNA base replaces thymine?

Uracil (U).

What base pairs with adenine during transcription?

Uracil.

What base pairs with thymine during transcription?

Adenine.

What base pairs with cytosine during transcription?

Guanine.

What base pairs with guanine during transcription?

Cytosine.

What is the promoter?

The DNA sequence where RNA polymerase binds to begin transcription.

What is the terminator?

The DNA sequence that signals RNA polymerase to stop transcription.

Where does transcription begin?

At the promoter region.

Where does transcription end?

At the terminator region.

What happens when RNA polymerase reaches the terminator?

The completed mRNA is released from the DNA.

Why is mRNA much shorter than DNA?

It is complementary to only one gene rather than the entire chromosome.

What is the function of mRNA?

It carries genetic information from DNA to the ribosome for protein synthesis.

Where does transcription occur in prokaryotes?

In the cytoplasm.

Why does transcription occur in the cytoplasm of bacteria?

Bacteria do not have a nucleus.

Where does transcription occur in eukaryotic cells?

In the nucleus.

Can transcription and translation occur simultaneously in bacteria?

Yes.

Why can transcription and translation occur at the same time in bacteria?

Because there is no nucleus separating DNA from ribosomes.

Can transcription and translation occur simultaneously in eukaryotes?

No.

Why can't transcription and translation occur simultaneously in eukaryotes?

The mRNA must first leave the nucleus before reaching ribosomes.

What is the major difference between bacterial and eukaryotic transcription?

Bacteria perform transcription in the cytoplasm, while eukaryotes perform it in the nucleus.

What are exons?

The coding regions of genes that remain in mature mRNA.

What are introns?

Noncoding regions that are removed before translation.

Which organisms contain introns?

Eukaryotes.

Do bacteria contain introns?

Generally no.

What is the first RNA produced during transcription in eukaryotes?

The RNA transcript (pre-mRNA).

What does the initial RNA transcript contain?

Both exons and introns.

What must happen before eukaryotic mRNA can leave the nucleus?

The introns must be removed and the exons joined together.

What are snRNPs?

Small nuclear ribonucleoproteins that remove introns and splice exons together.

What is RNA splicing?

The process of removing introns and joining exons together.

What is produced after RNA splicing?

Mature mRNA.

Where does RNA splicing occur?

In the nucleus.

After processing, where does mature mRNA go?

Through nuclear pores into the cytoplasm.

Where are ribosomes located?

In the cytoplasm.

What process occurs after mRNA reaches the ribosomes?

Translation.

What is the major function of mature mRNA?

To direct protein synthesis.

Why are introns removed?

They do not code for functional proteins.

Which portions of DNA actually code for proteins?

Exons.

What is one major difference between bacterial DNA and eukaryotic DNA discussed by your professor?

Eukaryotic DNA contains introns; bacterial DNA generally does not.

Why doesn't bacterial mRNA require RNA splicing?

Bacteria lack introns.

What is the overall flow of genetic information?

DNA → mRNA → Protein.

What is the central dogma of molecular biology?

Genetic information flows from DNA to RNA to protein.

What happens immediately after transcription in bacteria?

Ribosomes begin translating the mRNA immediately.

What did the electron micrograph shown in lecture demonstrate?

Multiple ribosomes translating the same mRNA while it is still being transcribed.

What is a polysome (polyribosome)?

Multiple ribosomes attached to a single mRNA molecule translating it simultaneously.

Why are polysomes beneficial?

They allow many copies of the same protein to be produced quickly.

What advantage do bacteria gain by coupling transcription and translation?

They can produce proteins much faster.

Which molecule carries the genetic code from DNA to ribosomes?

mRNA.

What determines the sequence of nucleotides in mRNA?

The sequence of bases in the DNA template strand.

Does RNA polymerase require a primer like DNA polymerase?

No. RNA polymerase can begin RNA synthesis without a primer.