Eukaryotic Gene Expression: RNA Processing

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Questions and Answers

What is the function of tryptophan in the trp operon?

Activator

Corepressor (correct)

Inducer

Repressor

What type of operon is the trp operon?

Constitutive operon

Regulatory operon

Repressible operon (correct)

Inducible operon

What is the role of the trpR gene?

To regulate the trp operon

To code for the trp repressor protein (correct)

To synthesize tryptophan

To activate the lac operon

What type of enzymes are involved in the trp operon?

Anabolic enzymes Signup and view all the answers

What is the function of allolactose in the lac operon?

Inducer Signup and view all the answers

What type of operon is the lac operon?

Inducible operon Signup and view all the answers

What is the role of regulatory genes?

To regulate the expression of operons Signup and view all the answers

What occurs to the RNA molecule after it is cut free from the polymerase?

It is digested by an enzyme that moves along the RNA Signup and view all the answers

What is the primary function of the 5′ cap and poly-A tail in eukaryotic mRNA?

To protect the mRNA from hydrolytic enzymes and aid in export from the nucleus Signup and view all the answers

What is the function of inducible enzymes?

To respond to a chemical signal Signup and view all the answers

What is the average length of a transcription unit along a human DNA molecule?

27,000 base pairs Signup and view all the answers

What is the purpose of RNA splicing?

To remove large portions of the RNA molecule Signup and view all the answers

What happens to the RNA produced by continued transcription after the RNA is cut free from the polymerase?

It is digested by an enzyme that moves along the RNA Signup and view all the answers

What is the function of the enzyme that moves along the RNA during transcription termination?

To digest the RNA produced by continued transcription Signup and view all the answers

What is the approximate number of nucleotides required to code for an average-sized protein of 400 amino acids?

1,200 nucleotides Signup and view all the answers

Why do eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides?

To separate coding segments of the gene Signup and view all the answers

What is the role of siRNAs produced by yeast cells in chromosome formation?

They are crucial for the formation of heterochromatin at the centromeres of chromosomes. Signup and view all the answers

What is the process by which cells become specialized in structure and function?

Cell differentiation Signup and view all the answers

What determines the path of a particular cell in a developing organism?

The specific genes expressed in the cell Signup and view all the answers

What is the term for the physical processes that give an organism its shape?

Morphogenesis Signup and view all the answers

What is the term for the maternal substances in the egg that influence the development of the future embryo?

Cytoplasmic determinates Signup and view all the answers

What is the process in which signals cause changes in target cells?

Induction Signup and view all the answers

What is the other major source of developmental information, which becomes increasingly important as the number of embryonic cells increases?

The environment around a particular cell Signup and view all the answers

What is characteristic of the unfertilized egg's cytoplasm?

It is heterogeneous Signup and view all the answers

What is the main function of chromatin structural organization?

To regulate gene expression Signup and view all the answers

What happens to the positive charges of lysines when they are acetylated?

They are neutralized Signup and view all the answers

What is the effect of adding a phosphate group to an amino acid next to a methylated amino acid?

It has the opposite effect of condensation Signup and view all the answers

How do activators promote transcription?

By recruiting proteins that acetylate histones Signup and view all the answers

What is the typical methylation state of inactive DNA?

Hypermethylated Signup and view all the answers

What is the effect of DNA methylation on gene expression?

It silences gene expression Signup and view all the answers

What happens to methylated genes after cell division?

They stay methylated Signup and view all the answers

What is the typical state of histone tails when lysines are acetylated?

They no longer bind to neighboring nucleosomes Signup and view all the answers

What was the main goal of Christiane Nüsslein-Volhard and Eric Wieschaus's research in the 1970s?

To identify the genes affecting segment formation in Drosophila Signup and view all the answers

What was the first major difficulty faced by Nüsslein-Volhard and Wieschaus in their research?

The large number of genes in Drosophila Signup and view all the answers

What is a characteristic of a maternal effect gene?

When mutant in the mother, it results in a mutant phenotype in the offspring Signup and view all the answers

Why did Nüsslein-Volhard and Wieschaus study the mother's genes in addition to those of the embryo?

Because maternal effect genes can cause embryonic lethals Signup and view all the answers

What was the method used by Nüsslein-Volhard and Wieschaus to induce mutations in Drosophila?

Exposing flies to a mutagenic chemical Signup and view all the answers

What did Nüsslein-Volhard and Wieschaus screen for in the descendants of mutagenized flies?

Flies with abnormal segmentation or other defects Signup and view all the answers

What is the role of maternal effect genes in Drosophila?

They control the orientation of the egg Signup and view all the answers

What was the third major difficulty faced by Nüsslein-Volhard and Wieschaus in their research?

The fact that mutations affecting segmentation would be embryonic lethals Signup and view all the answers

Study Notes

Transcription Termination

In eukaryotic cells, transcription is terminated when an enzyme reaches the polymerase, cutting the RNA free from the polymerase.
Continued transcription produces RNA that is digested by an enzyme that moves along the RNA.
This process occurs hundreds of nucleotides downstream from the AAUAAA signal.

RNA Processing

5' end receives a 5' cap, a modified form of a guanine nucleotide with three phosphate groups.
3' end receives a poly-A tail, adding 50-250 adenine (A) nucleotides.
These modifications facilitate mRNA export from the nucleus, protect mRNA from hydrolytic enzymes, and help ribosomes attach to the 5' end.

RNA Splicing

Removal of large portions of the RNA molecule, mostly noncoding sequences, occurs through RNA splicing.
Average length of a transcription unit in human DNA is 27,000 base pairs, but only 1,200 nucleotides are needed for an average-sized protein of 400 amino acids.

Gene Regulation

Repressible operons, like the trp operon, are usually on but can be inhibited when a specific small molecule binds allosterically to a regulatory protein.
Inducible operons, like the lac operon, are usually off but can be stimulated when a specific small molecule interacts with a regulatory protein.
Structural organization of chromatin regulates gene expression by compacting DNA into a nucleus-friendly form.

Chromatin Regulation

Genes within heterochromatin, a highly condensed form, are usually not expressed.
Histone acetylation, methylation, and phosphorylation can promote or repress gene transcription.
siRNAs produced by yeast cells are crucial for the formation of heterochromatin at centromeres of chromosomes.

Cell Differentiation and Development

Cell differentiation is the process by which cells become specialized in structure and function.
Morphogenesis is the process by which an organism's shape is formed.
Cytoplasmic determinates, maternal substances in the egg, influence the course of early development.
Induction, signals from the environment, cause changes in target cells during development.
Maternal effect genes, when mutant in the mother, result in a mutant phenotype in the offspring, regardless of the offspring's own genotype.

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Description

This quiz covers the process of RNA processing in eukaryotic gene expression, including the role of the AAUAAA signal and the cleavage of RNA from the polymerase.