Transcription and the Central Dogma of Biology

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Questions and Answers

What is the first step in gene expression?

RNA processing

Translation

Replication

Transcription (correct)

In which organisms does transcription-translation coupling occur?

Viruses

Fungi

Eukaryotes

Prokaryotes (correct)

Which component is NOT a product of transcription?

DNA (correct)

mRNA

rRNA

tRNA

What kind of sequence is found in eukaryotic genes?

Exons and introns Signup and view all the answers

What does hnRNA stand for?

Heterogeneous nuclear RNA Signup and view all the answers

What marks the start of transcription in a gene?

Transcription start site Signup and view all the answers

Which step is NOT involved in the maturation of RNA?

Transcription Signup and view all the answers

What influences cellular function according to gene expression?

RNA nucleotide sequence Signup and view all the answers

What role do enhancers play in gene expression?

They enhance the expression of genes. Signup and view all the answers

Where does RNA synthesis occur?

In the nucleus. Signup and view all the answers

Which of the following is a difference between RNA and DNA?

RNA is single stranded. Signup and view all the answers

What function do regulatory sequences in mRNA serve?

They stabilize the mRNA and impact translation efficiency. Signup and view all the answers

What is the function of transcription starting site contained in the initiator?

It marks the location where transcription begins. Signup and view all the answers

How do enhancers and repressors affect gene expression?

They can either enhance or repress gene expression. Signup and view all the answers

What is the primary role of RNA polymerase?

To synthesize RNA from a DNA template. Signup and view all the answers

In what format can enhancers or repressors affect gene expression?

Up to hundreds or thousands of bps away on the same chromosome. Signup and view all the answers

Which RNA polymerase is primarily responsible for synthesizing mRNA?

RNA polymerase II Signup and view all the answers

What is the primary product of transcription referred to as?

hnRNA Signup and view all the answers

What modification occurs immediately after the initiation of RNA synthesis?

Addition of 5’ cap Signup and view all the answers

What is the role of the polyadenylation signal in hnRNA processing?

Cleavage and addition of the poly-A tail Signup and view all the answers

What do exons represent in the context of pre-mRNA?

Coding sequences Signup and view all the answers

Which of the following does NOT occur during the maturation of hnRNA?

Replication Signup and view all the answers

What is the function of the 5’ cap added to mRNA?

To protect from degradation by exonucleases Signup and view all the answers

Which enzyme is responsible for adding adenine nucleotides at the 3’ end of the hnRNA?

Poly(A) polymerase Signup and view all the answers

What are the two main components of a gene producing mRNA?

Regulatory region and coding region Signup and view all the answers

What is the role of the basal promoter?

Ensure basal expression and initiate transcription Signup and view all the answers

Which of the following is an example of a proximal promoter element?

TATA box Signup and view all the answers

Which direction does RNA polymerase read the DNA template?

3' to 5' Signup and view all the answers

What replaces thymine in the RNA sequence during transcription?

Uracil Signup and view all the answers

The transcription start site is located where in relation to the promoter?

Downstream of the promoter Signup and view all the answers

What is the function of enhancers in gene regulation?

Increase transcription rates Signup and view all the answers

Which protein complex is responsible for basal transcription in eukaryotes?

RNA polymerase II Signup and view all the answers

Study Notes

Transcription Overview

Transcription is the first step in gene expression
It's DNA-directed synthesis of RNA
The process transforms a specific nucleotide sequence (genetic information) into a product influencing cellular function.
RNA is either translated into protein (mRNA) or contributes to translation (rRNA, tRNA) or regulation (microRNA)

Central Dogma

Replication (DNA→DNA): DNA polymerase
Transcription (DNA→RNA): RNA polymerase
Translation (RNA→Protein) Ribosome

Transcription Steps

Initiation: RNA polymerase binds to promoter region, unwinds DNA
Elongation: RNA polymerase moves along the template strand, synthesizing RNA in the 5' to 3' direction, using complementary base pairing.
Termination: RNA polymerase reaches termination sequence, detaches from DNA, and releases newly synthesized RNA.

Gene Structure

Gene: a minimal linear sequence of nucleotides encoding protein or structural RNA.
Sequence is written 5' to 3'
Eukaryotic genes: composed of exons (coding), introns (non-coding), and non-coding consensus (regulatory) sequences.
Nucleotides before transcription start site have -ve numbers
Nucleotides after start site have +ve numbers.

Gene Structure Components

Coding region: transcribed into mRNA, translated into protein
Regulatory region:
- Basal promoters: ensure basal expression, initiate transcription (example: TATA box)
- DNA regulatory elements: regulate gene expression (examples: proximal promoter elements, enhancers, repressors)

Promoter Elements

Located upstream of transcription start site
Crucial for binding RNA polymerase and initiation of transcription
Examples include TATA box, CAAT box, and GC-rich regions

RNA Synthesis

Occurs in the nucleus
Catalyzed by RNA polymerase
RNA polymerase uses DNA as a template
RNA differs from DNA: single-stranded, uracil (U) instead of thymine (T), shorter length.
Genes coding for proteins are transcribed into mRNA in the nucleus, translation in the cytosol

RNA Polymerases

Multiple RNA polymerases in eukaryotes:
- RNA polymerase I (rRNA synthesis)
- RNA polymerase II (mRNA and microRNA synthesis)
- RNA polymerase III (tRNA and 5S rRNA synthesis)
Transcription factors and accessory proteins (pre-initiation complex) essential for proper RNA polymerase positioning on DNA (upstream from start site)

Heterogeneous nuclear RNA (hnRNA)

hnRNA (primary transcript), larger than mRNA in the cytoplasm
Contains exons (coding) and introns (non-coding)
Undergoes modifications to become mature mRNA
Modifications include 5' cap addition, and Poly A tail addition, and intron removal.

5' cap

Added after RNA initiation; a methyl guanosine residue via a 5' to 5' bridge
Protects mRNA from degradation
Aids mRNA binding to ribosomes for translation

Poly A tail

AAUAAA sequence in the DNA( polyadenylation signal)
Signal recognized by endonuclease, cuts RNA
250 adenine nucleotides added by Poly(rA) polymerase to the 3' end
Important for mRNA stability and translation

Splicing

Introns removed; exons joined to form mature mRNA
Performed by small nuclear RNAs (snRNAs) and proteins (snRNPs) forming spliceosome.
Mature mRNA passes through nuclear pores, translation in the cytoplasm

Splice Site Mutations

Mutations at splice sites alter mRNA size/content
Result in aberrant (abnormal) proteins

Summary Table

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Description

This quiz covers the essential processes of transcription in the context of the central dogma of molecular biology. You will explore the steps of transcription, the role of RNA polymerase, and the importance of gene structure. Ideal for students studying genetics or cell biology.