Gene Expression in Prokaryotes: Transcription

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Questions and Answers

Which statement accurately describes the structure of RNA compared to DNA?

RNA has ribose sugars, while DNA contains deoxyribose sugars. (correct)

RNA contains thymine, while DNA contains uracil.

RNA is usually double stranded, whereas DNA is single stranded.

RNA is more stable than DNA due to its two-stranded structure.

What leads to the rapid degradation of RNA under alkaline conditions?

The absence of mitosis in prokaryotic cells.

The presence of a 2’-hydroxyl group in ribose. (correct)

The phosphorylation of specific nucleotides.

The formation of double-stranded structures.

What distinguishes ribozymes from other types of RNA?

They are non-catalytic and primarily structural.

They catalyze specific biochemical reactions. (correct)

They can serve as templates for DNA synthesis.

They contain a unique sugar not found in other RNA.

How does the stability of RNA compare to that of DNA?

RNA degrades more readily than DNA due to its structure. Signup and view all the answers

Which of the following is true regarding the pairing of RNA nucleotides?

RNA can pair and form secondary structures. Signup and view all the answers

What is the primary role of ribosomal RNA (rRNA) in the cell?

Structural and functional components of the ribosome Signup and view all the answers

Which component is directly involved in the inhibition of mRNA translation?

MicroRNA (miRNA) Signup and view all the answers

During transcription, what is the primary source of the RNA molecule synthesized?

DNA templates Signup and view all the answers

What distinguishes small nucleolar RNA (snoRNA) from small nuclear RNA (snRNA)?

snoRNA is involved in processing and assembly of rRNA Signup and view all the answers

In the transcription process, which of the following statements is true regarding its selectivity?

Only specific genes are transcribed as needed Signup and view all the answers

Which of the following statements is true regarding the transcription process?

Only one strand of the DNA double helix serves as the template for transcription. Signup and view all the answers

What is the role of the promoter in a transcription unit?

It serves as the binding site for the transcription apparatus. Signup and view all the answers

What is the result of transcription in terms of nucleotide sequencing?

The RNA transcript matches the coding strand, replacing thymine with uracil. Signup and view all the answers

What distinguishes a transcription unit from other segments of DNA?

It includes a promoter, RNA-coding region, and terminator. Signup and view all the answers

Which statement correctly describes the template strand used during transcription?

It is complementary and antiparallel to the synthesized RNA. Signup and view all the answers

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

tRNA serves as the link between mRNA and specific amino acids. Signup and view all the answers

Which class of RNA molecules is known to combine with proteins to form small nuclear ribonucleoproteins (snRNPs)?

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

What is a shared characteristic of microRNAs (miRNAs) and small interfering RNAs (siRNAs)?

Both classes of RNA are very small and found in eukaryotic cells. Signup and view all the answers

What distinguishes small nuclear RNAs (snRNAs) from microRNAs (miRNAs)?

snRNAs participate in RNA processing while miRNAs regulate gene expression. Signup and view all the answers

Which statement about the location and function of different classes of RNA is accurate?

Different classes of RNA perform distinct functions within eukaryotic cells. Signup and view all the answers

Study Notes

Gene Expression in Prokaryotes: Transcription

RNA molecules are synthesized from DNA during transcription
Transcription copies only specific parts of DNA, such as a gene or a few genes, into RNA
Transcription is a selective process: individual genes only get transcribed when needed
Transcription requires DNA template, raw materials (substrates), and a transcription apparatus.
The template used for transcription is a single strand of the DNA double helix
The nucleotide strand used is called the template strand. The opposite strand is called the non-template or coding strand.
RNA synthesis is complementary and antiparallel to the template DNA strand.
RNA is usually single-stranded, unlike DNA which consists of two polynucleotide strands.
RNA synthesis always proceeds in the 5' to 3' direction.

RNA Structure

Ribosomes are catalytic RNA molecules (ribozymes) and might have been the first carriers of genetic information
RNA is a polymer of nucleotides bound together with phosphodiester bonds
RNA has ribose sugar
RNA contains uracil instead of thymine
RNA usually consists of one strand; under specific conditions, RNA segments can be paired, creating a secondary structure and forming regions that can be paired.

Classes of RNA

Ribosomal RNA (rRNA): combines with ribosomal proteins to form ribosomes.
Messenger RNA (mRNA): carries the genetic code from the DNA to the ribosome, specifying the order of amino acids to synthesize proteins.
Transfer RNA(tRNA): acts as a link between the genetic code in mRNA and the amino acid sequence in the protein.
rRNA, tRNA and mRNA molecules perform specific functions inside the cell
Pre-mRNAs or primary transcripts are modified before becoming mRNA and exiting the nucleus for translation into protein
Additional RNA classes exist in eukaryotic cells: small nuclear RNA (snRNA); small nucleolar RNA (snoRNA), microRNA (miRNA) and small interfering RNA (siRNA)

The Transcription Unit

A transcription unit is a segment of DNA that encodes an RNA molecule.
It typically consists of three regions: promoter, RNA-coding region, and terminator.
Promoter: a DNA sequence where the transcription apparatus binds. It indicates which strand is the template for transcription and the direction.
RNA-coding region: segment of DNA that contains the sequence of nucleotides that is copied into an RNA molecule.
Terminator: a sequence of nucleotides that signals the end of transcription.
Transcription apparatus, including RNA polymerase, plays a critical role

The Transcription Apparatus

RNA polymerase: the enzyme that catalyzes the transcription process, synthesizing RNA using a DNA template.
Bacterial RNA polymerase usually consist of one type that synthesizes all kinds of bacterial RNA, mRNA, tRNA, rRNA.
Eukaryotic cells have three different types of RNA polymerase
RNA polymerase I: synthesizes rRNA
RNA polymerase II: synthesizes mRNAs and some snRNAs, snoRNAs, and miRNAs
RNA polymerase III: synthesizes tRNAs, the small rRNAs, some snRNAs, and some other small RNAs
The sigma factor is involved in binding with bacterial RNA polymerase to the promoter

The Process of Bacterial Transcription

Transcription, including initiation, elongation, and termination stages
Initiation: the process of assembling the transcription apparatus at the promoter and initiating RNA synthesis
Elongation: the process of adding nucleotides to the 3' end of the elongating RNA.
Termination: the recognition of and separation of RNA from the DNA template

Initiation of Transcription

Consensus sequences are short stretches of nucleotides and play role in initiation of transcription sequences within the DNA.
Promoters in bacterial DNA contain short consensus sequences, which are important in initiation of transcription.
The sigma factor plays a role in binding RNA polymerase with promoter
Sigma factor leaves after transcription initiated.

Elongation of Transcription

RNA polymerase undergoes conformational changes in elongation.
The sigma subunit is released.
The RNA transcripts are synthesized from the DNA template.

Termination of Transcription

Transcription stops when the polymerase transcribes a terminator.
Bacterial cells: utilize either rho-dependent or Rho-independent terminators.
Rho-dependent terminators require specific proteins called rho factor.

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Description

This quiz explores the fundamental processes of transcription in prokaryotes. Learn how RNA is synthesized from DNA, the role of template strands, and the specifics of RNA structure. Test your knowledge on the selective nature of gene transcription and the requirements for RNA synthesis.