15. Gene Expression

Eukaryotic RNA Processing and Splicing

Biologists have investigated how fast pre-mRNA splicing occurs by treating cells with a toxin that blocks the production of new pre-mRNAs, then following the rate of splicing of the pre-mRNAs that were transcribed before adding the toxin. Why is addition of a toxin important in this study?

mRNA splicing

Types of RNA: (mRNA, tRNA, rRNA)

mRNA, rRNA and tRNA

Overview of mRNA Processing in Eukaryotes

2) RNA Splicing Creates Mature mRNA

Animation: A Spliceosome

A cap is added to the 5′ end of the mRNA.         

Adenine nucleotides are added to the 5’ end of the mRNA.

RNA polymerase requires tRNA to elongate the molecule.

Which of the following processes occurs in eukaryotic gene expression?

Animation: Adding the 5' Cap and Poly-A Tail

Eukaryotic RNA processing and modifications - Transcription

 Both introns and exons are transcribed, but neither type of transcribed region leaves the nucleus. 

 Both introns and exons are transcribed, but the RNA transcribed from introns does not leave the nucleus. 

Consider the meaning of the "ex" in exon and the "in" in intron.

Which accurately describes the usual process of eukaryotic transcription?

Evaluate the following statements regarding tracheids and vessel elements. Select True or False for each statement.
T/F Both tracheids and vessel elements are specialized for water conduction.
T/F Both tracheids and vessel elements have pits.
T/F Vessel elements have perforation plates but tracheids do not.
T/F Tracheids and vessel elements have to be alive in order to transport water.

Alternative Splicing / Alternative Processing (Eukaryotes)

 No. DNA packaging makes genes more or less available for transcription. 

 No. These modifiers act before transcription, not after. 

 Construction of a transcription initiation complex 

 No. The transcription initiation complex forms before transcription, not after. 

What is the product of transcription?

In eukaryotes, which mechanism operates after transcription, but before translation of mRNA into protein?

Which of the following is true of RNA processing? 
(A) Exons are cut out before mRNA leaves the nucleus. 
(B) Nucleotides are added at both ends of the RNA. 
(C) Ribozymes may function in the addition of a 5′ cap. 
(D) RNA splicing adds a poly-A tail to the mRNA.

What is a sieve-tube element?
a. the sugar-conducting cell found in phloem
b. the widened, perforation-containing, water-conducting cell found only in angiosperms
c. the nutrient- and water-absorbing cell found in root hairs
d. the nucleated and organelle-rich support cell found in phloem

HHMI BioInteractive: Somatic Cell Nuclear Transfer

The regions in DNA &amp; RNA that encode actual gene products are known as:

BioFlix: RNA Processing

What are RNA, mRNA and tRNA?

1) RNA Processing

Animation: Post-Transcriptional Control Mechanisms

5 Prime Capping of mRNA | Eukaryotic mRNA Processing

Which of the following is not true of RNA processing?
a. Exons are cut out before mRNA leaves the nucleus.
b. Nucleotides may be added at both ends of the RNA.
c. Ribozymes may function in RNA splicing.
d. RNA splicing can be catalyzed by spliceosomes.

 Different systems of DNA unpacking could result in two different mRNAs. 

 No. DNA packing does not affect the nucleotide sequence. 

 A point mutation might have altered the gene. 

 No. Though a point mutation may affect the protein product, it will not result in the production of two different mRNAs from the same DNA sequence. 

 Different transcription factors were involved in the transcription of the two mRNAs. 

 No. mRNAs do not change as a function of the transcription factors used to drive their expression. 

 Exons from the same gene could be spliced in different ways to make different mRNAs. 

Think about what happens during processing of mRNA.

Two different proteins with mostly different structures are translated from two different mRNAs. These mRNAs, however, were transcribed from the same gene. Which mechanism could best account for this?

RNA: mRNA & tRNA - Biology

5 Types of RNA: mRNA, tRNA, rRNA, HnRNA, and SnRNA

 In prokaryotes, proteins are assembled directly from DNA. 

 No. Neither prokaryotes nor eukaryotes assemble proteins directly from DNA. 

 RNA polymerases are involved only in initiation of transcription in eukaryotes. 

 No. RNA polymerases are involved in initiation of transcription in both types of cells. 

 In eukaryotic cells, transcribed RNA sequences function as termination signals. 

 In prokaryotic cells, the RNA transcript is immediately available as mRNA without processing. 

Think about differences and similarities between prokaryotic and eukaryotic cells.

What is a key difference between eukaryotic and prokaryotic gene expression?

RNA Processing

DNA Transcription Processing | Exons, Introns, Splicing, 5' Cap, and 3' Poly A Tail

mRNA, tRNA, and rRNA function | Types of RNA

 Exons are cut out of the primary transcript, and the introns are spliced together. 

 No. Introns are cut out of the primary transcript, not exons. 

 Introns are cut out of the primary transcript and spliced together at the end of the transcript. 

 Exons are cut out of the primary transcript and transported to the endoplasmic reticulum. 

 No. Exons are spliced together and exported to the cytoplasm. 

 Introns are cut out of the primary transcript, and the resulting exons are spliced together. 

Keep introns and exons straight.

Which statement correctly describes mRNA processing?

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