Gene Expression: Prokaryotic Transcription

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which strand of DNA is used as the template for transcription?

The non-template strand

The coding strand

The promoter strand

The template strand (correct)

What is the main function of the promoter in the transcription unit?

To serve as a coding sequence

To initiate RNA synthesis (correct)

To enhance RNA stability

To terminate transcription

During transcription, which nucleotide base is replaced with uracil in RNA synthesis?

Adenine

Cytosine

Thymine (correct)

Guanine

What is the primary role of transfer RNA (tRNA) in protein synthesis?

tRNA attaches to amino acids and incorporates them into a polypeptide chain. Signup and view all the answers

Which of the following regions is NOT a part of a transcription unit?

Replication origin Signup and view all the answers

Which class of small RNA molecules participates in the conversion of pre-mRNA into mRNA?

Small nuclear RNAs (snRNAs) Signup and view all the answers

How does transcription differ from DNA replication in the context of strands used?

Only one strand is transcribed while the other is not Signup and view all the answers

How do microRNAs (miRNAs) primarily function within eukaryotic cells?

They assist in the degradation of specific mRNA targets. Signup and view all the answers

What is the result of transcription in terms of nucleic acid sequences?

An RNA molecule with a base sequence identical to the coding strand Signup and view all the answers

What is the main difference between small nuclear RNAs (snRNAs) and small interfering RNAs (siRNAs)?

snRNAs are involved in RNA processing, while siRNAs are primarily involved in gene silencing. Signup and view all the answers

Which of the following statements about transcription units is correct?

Each transcription unit encodes a single RNA molecule Signup and view all the answers

Where are small nuclear RNAs (snRNAs) typically located within the cell?

In the nucleolus Signup and view all the answers

What is the primary role of the terminator in the transcription unit?

It signals where transcription is to end. Signup and view all the answers

In which direction does the transcription apparatus move during transcription?

Downstream toward the terminator. Signup and view all the answers

How are nucleotides numbered around the transcription start site?

Nucleotides downstream are assigned positive numbers. Signup and view all the answers

Which statement accurately describes the transcription of RNA in relation to the DNA template strand?

RNA synthesis is complementary and antiparallel to the DNA template. Signup and view all the answers

Which of the following best defines a transcription unit?

A set of sequences defining where transcription begins and ends. Signup and view all the answers

What distinguishes the non-template (coding) strand in relation to the RNA produced?

It has the same sequence as the RNA with U in place of T. Signup and view all the answers

Which feature is unique to RNA synthesis compared to DNA synthesis?

RNA synthesis does not require a primer to begin. Signup and view all the answers

What component is primarily responsible for executing the steps of transcription?

RNA polymerase. Signup and view all the answers

What is the orientation of the coding strand when represented in nucleotide sequences?

5’ end on the right and 3’ end on the left. Signup and view all the answers

Which statement about bacterial RNA polymerase is true?

It forms a holoenzyme only in the presence of the sigma factor. Signup and view all the answers

What is the primary function of RNA polymerase II in eukaryotic cells?

Transcribes pre-mRNAs and some small RNA types. Signup and view all the answers

How is transcription initiated in bacterial cells?

Through stable binding of RNA polymerase and sigma factor to the promoter. Signup and view all the answers

Which RNA polymerase in eukaryotes is responsible for transcribing tRNAs?

RNA polymerase III Signup and view all the answers

What is the general role of accessory proteins in RNA polymerase function?

To enhance the enzyme's action at different stages. Signup and view all the answers

Which of the following statements correctly describes eukaryotic RNA polymerases?

All eukaryotic RNA polymerases consist of at least a dozen subunits. Signup and view all the answers

What type of RNA is primarily transcribed by RNA polymerase I?

large rRNA Signup and view all the answers

Which option correctly pairs eukaryotic RNA polymerases with their functions?

RNA polymerase III - transcribes tRNAs and small rRNA Signup and view all the answers

What role does the sigma factor play in bacterial transcription?

It enhances RNA polymerase's ability to recognize and bind to the promoter. Signup and view all the answers

Study Notes

Gene Expression: Transcription in Prokaryotes

RNA is a polymer of nucleotides joined by phosphodiester bonds
RNA contains ribose sugar, uracil instead of thymine, and a hydroxyl group on the 2' carbon
DNA nucleotides contain deoxyribose sugars, lack a free hydroxyl group on the 2' carbon, and are more stable
RNA is less stable than DNA under alkaline conditions due to the free hydroxyl group
RNA can have secondary structures due to hydrogen bonding between complementary bases
RNA molecules perform various functions in cells such as ribosomal RNA (rRNA) that makes up the ribosome for protein assembly, messenger RNA (mRNA) carrying the coding instructions from DNA to ribosomes for protein synthesis, and transfer RNA (tRNA) that links mRNA codons to amino acids

Classes of RNA

Ribosomal RNA (rRNA) forms the ribosome, the site of protein synthesis, and is found in both bacterial and eukaryotic cells
Messenger RNA (mRNA) carries the coding sequence from DNA to the ribosome in both bacterial and eukaryotic cells
Transfer RNA (tRNA) links codons in mRNA to specific amino acids in both bacterial and eukaryotic cells
Small nuclear RNAs (snRNAs) are involved in processing pre-mRNA into mRNA in eukaryotic cells
Small nucleolar RNAs (snoRNAs) are involved in processing rRNA in eukaryotic cells
MicroRNAs (miRNAs) and small interfering RNAs (siRNAs) are involved in RNA interference (RNAi) in eukaryotic cells. RNA interference regulates gene expression by degrading mRNA or inhibiting translation

The Concept of Transcription

All cellular RNAs are synthesized from DNA templates during transcription
During replication, all nucleotides in DNA are copied
During transcription, only small parts (single genes or a few genes) of the DNA molecule are transcribed into RNA.
Transcription is a highly selective process; individual genes are transcribed only as needed or when their products are needed
Transcription requires DNA template, raw materials (substrates) to build RNA molecules, and the transcription apparatus

The Template for Transcription

The template for RNA synthesis is a single strand of the DNA double helix
The transcription of a gene takes place on one of the two DNA nucleotide strands
The nucleotide strand used for transcription is called the template strand.
The non-template strand is not ordinarily transcribed and is also referred to as the coding strand, which has the same sequence as the RNA molecule, except that it replaces thymine (T) with uracil (U)

The Transcription Unit

A transcription unit is a DNA segment that encodes an RNA molecule.
Each transcription unit contains a promoter, RNA-coding region, and a terminator.
The promoter is a DNA sequence that the transcription apparatus recognizes and binds.
The RNA-coding region is a DNA sequence that is copied into an RNA molecule.
The terminator is a DNA sequence that signals where transcription ends.
The sequence of the non-template strand is written with the 5' end on the left and 3'end on the right, while the sequence of the RNA transcript proceeds in the 5'-3' direction.

The Transcription Apparatus

The RNA polymerase carries out all the required steps of transcription.
RNA polymerase is enhanced by various accessory proteins during transcription
Bacterial cells typically possess one type of RNA polymerase responsible for all classes of bacterial RNA (mRNA, tRNA, and rRNA).
RNA polymerase is a large multimeric enzyme containing polypeptide chains
The core enzyme binds with a sigma factor to form a holoenzyme during transcription.
The sigma factor controls RNA polymerase binding to the promoter, and initiates transcription at a proper start site.
Eukaryotic RNA polymerase are large multimeric enzymes, consisting of more than a dozen subunits.
Eukaryotic cells have three distinct types of RNA polymerases.
- RNA polymerase I transcribes large rRNA (ribosomal RNA).
- RNA polymerase II transcribes pre-mRNAs (pre-messenger RNA) along with some snoRNAs, miRNAs, and snRNAs.
- RNA polymerase III transcribes tRNAs and small rRNAs along with some miRNAs, and snRNAs
RNA polymerase IV transcribes some siRNAs in plants

The Process of Bacterial Transcription

Transcription occurs in three stages:
- Initiation: Transcription apparatus assembles and begins RNA synthesis on the promoter
- Elongation: RNA polymerase unwinds the DNA, adding nucleotides to the 3' end of the growing RNA
- Termination: Recognition of the end of the transcription unit, ending RNA separation from the DNA template

Initiation

A consensus sequence is stretches of nucleotides within the DNA found in the promoter region.
The common consensus sequence in bacterial promoters is centered about 10 bp upstream of the start site, and is called the -10 or Pribnow box.
The -35 consensus sequence is located ~35 bp upstream of the start site.
A promoter is a DNA sequence adjacent to a gene and required for transcription

Elongation

RNA polymerase moves along the template DNA from 3' to 5', producing the RNA transcript by adding nucleotides to the 3' end of the growing RNA.
Transcription takes place within a short stretch of DNA (~18 nucleotides) called the transcription bubble.

Termination

RNA polymerase transcribes a specific terminator sequence
Transcription stops after the terminator has been transcribed
RNA polymerase stops synthesizing the RNA molecule , detachs from the DNA template and releases the RNA transcript.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the intricate process of transcription in prokaryotes with this quiz. Learn about the structures and functions of different types of RNA, including rRNA, mRNA, and tRNA. Test your knowledge on RNA's stability, roles in protein synthesis, and key differences from DNA.