Biology Chapter on Transcription and RNA Types

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Questions and Answers

What function does a gene primarily serve?

To produce special functional RNA (correct)

To code for structural proteins only

To act as a spacer between proteins

To exclusively code for DNA replication

Which strand of DNA is directly transcribed during the transcription process?

The sense strand

The non-coding region

The antisense strand (correct)

The coding strand

What percentage of RNA is typically r-RNA in a cell?

30%

10%

80% (correct)

50%

What is a primary transcript?

The original RNA molecule synthesized during transcription Signup and view all the answers

What process involves removing introns and stitching together exons in RNA?

Splicing Signup and view all the answers

Which type of RNA is characterized by the presence of a CCA sequence at its 3' end?

t-RNA Signup and view all the answers

What modification is made to m-RNA at its 5' end?

Guanine capping Signup and view all the answers

Which of the following r-RNA types is found in prokaryotes?

5S Signup and view all the answers

What happens during terminal addition to m-RNA?

A methylated guanine cap is added Signup and view all the answers

Which of these RNA types is present only in eukaryotes?

s-n-RNA Signup and view all the answers

Which unit of the prokaryotic RNA polymerase primarily stabilizes the shape of the core enzyme?

ω unit Signup and view all the answers

What is the significance of the σ factor in the formation of the RNA holoenzyme?

It recognizes the promoter region and facilitates attachment. Signup and view all the answers

Where is the promoter box typically located in relation to the transcribable portion of a gene?

On the 5' end (upstream) of the transcribable portion Signup and view all the answers

What are the subunits that perform the catalytic function in prokaryotic RNA polymerase primarily responsible for?

Making phosphodiester bonds between RNA nucleotides Signup and view all the answers

What designation is given to the first nucleotide that is transcribed after the RNA polymerase begins to function?

+1 Signup and view all the answers

Which sequence is commonly found in the Pribnow box of a prokaryotic promoter?

TATAAT Signup and view all the answers

How are the nucleotides prior to the +1 designation numbered?

As negative numbers Signup and view all the answers

What is the core enzyme of prokaryotic RNA polymerase composed of?

1 ω unit and 2 β units Signup and view all the answers

What is a characteristic of the holoenzyme once it has attached to the promoter box?

The σ factor dissociates after attachment. Signup and view all the answers

Which of the following statements is true regarding RNAP's entry into the promoter region?

It enters through either the Pribnow box or the -35 sequence. Signup and view all the answers

Study Notes

Transcription

A gene is a specific nucleotide sequence in DNA, responsible for producing functional RNA
DNA contains sequences between genes that don't code for RNA, called spacer DNA
During transcription, only one DNA strand is transcribed, acting as a template. This is called the antisense strand
The resulting RNA is complementary to the antisense strand (and identical to the other DNA strand). This other strand is the sense strand
RNA polymerase synthesizes RNA

Types of RNA

There are four major types of RNA
- rRNA (ribosomal RNA): most abundant, 80%
- mRNA (messenger RNA): most massive
- tRNA (transfer RNA): smallest
- snRNA (small nuclear RNA): found only in eukaryotes, small
When RNA is first produced during transcription, it's called the primary transcript
Primary transcripts undergo post-transcriptional modifications
- Terminal trimming
- Terminal addition
- Internal segment removal (removal of introns)
- Splicing (joining of exons)
- Base modifications (mostly in mRNA). Some bases can be modified

Prokaryotic rRNA Types

Prokaryotic cells have three types of rRNA: 5S, 16S, and 23S (Svedberg units)

Eukaryotic rRNA Types

Eukaryotic cells have four types of rRNA: 5S, 5.8S, 18S, and 28S

tRNA Structure

Every tRNA has a CCA sequence on the 3' end
This sequence attaches and carries amino acids

mRNA Modifications

Examples of terminal additions to primary mRNA transcripts include:
- Guanine capping (methylated guanine triphosphate added to 5' end)
- Poly-A tail (adenine nucleotides added to 3' end)

Transcription in Prokaryotic Genes

Prokaryotic RNA polymerase (RNAP) is made of multiple subunits. The core enzyme consists of 5 subunits (2 α, β, β', and ω). The complete holoenzyme includes a 6th subunit (σ factor)
The sigma factor (σ subunit) is crucial for recognizing a gene's promoter region and attaching the holoenzyme to the promoter. After binding, the sigma factor detaches and moves downstream, unzipping the DNA. The ω subunit plays a structural role.
RNA nucleotides stabilize RNAP on the DNA after sigma factor dissociates

Transcription Initiation

RNAP holoenzyme attaches to a gene at a specific place called a promoter box which is typically located upstream from the gene (on the 5' end)
The promoter box commonly has two regions:
- −35 region (sequence: TTGACA)
- −10 region (Pribnow box; sequence: TATAAT).
RNAP holoenzyme can bind either or both promoter regions
The first transcribed nucleotide is assigned the +1 designation. The nucleotides before +1 are given negative numbers.

Promoter Box Location & Role

The location of the promoter box is conventionally determined by the sense strand, not the template strand.
Modifications in the promoter box sequence can affect the rate of transcription

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Description

This quiz covers the process of transcription in DNA and the different types of RNA involved. Learn about the roles of rRNA, mRNA, tRNA, and snRNA, as well as the modifications that primary transcripts undergo after transcription. Test your knowledge on this essential biological process.