Neurospora crassa Experiment on Gene Function

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Questions and Answers

What structure facilitates the binding of RNA to initiate transcription?

TATA box (correct)

RNA polymerase II

Promoter region (correct)

Ribosome

At what rate does transcription progress in eukaryotes?

40 nucleotides per second (correct)

60 nucleotides per second

100 nucleotides per second

20 nucleotides per second

During transcription elongation, which end of the RNA strand do nucleotides get added to?

3' end (correct)

5' end

Middle of the strand

Both ends

How many RNA polymerases can transcribe a gene simultaneously?

Several Signup and view all the answers

What happens to the DNA helix during the elongation phase of transcription?

It opens and untwists Signup and view all the answers

Which of the following components is NOT part of the transcription initiation complex?

Ribosomal RNA Signup and view all the answers

What is the primary function of transcription factors in the transcription process?

To bind to the DNA and facilitate transcription initiation Signup and view all the answers

What is the sequence orientation of the non-template strand of DNA during transcription?

5' to 3' Signup and view all the answers

Which class of Neurospora crassa mutants can grow with ornithine but cannot grow with citrulline or arginine?

Class I mutants Signup and view all the answers

What is the correct restatement of Beadle and Tatum's hypothesis regarding gene expression?

One gene codes for one polypeptide. Signup and view all the answers

Which of the following statements about feedback inhibition is true?

Stopping at the end may allow for the production of some byproducts. Signup and view all the answers

Which class of mutants requires arginine to grow?

Class III mutants Signup and view all the answers

Which amino acid is related to the precursor in all classes of Neurospora crassa mutants?

Ornithine Signup and view all the answers

What is the role of ribozymes in RNA processing?

They serve as catalysts to splice RNA. Signup and view all the answers

Which of these proteins is not an enzyme?

All proteins are enzymes Signup and view all the answers

What property of RNA enables it to function as an enzyme?

Its capacity to form secondary structures. Signup and view all the answers

What type of medium was used as a control in the experiment?

Minimal medium without supplements Signup and view all the answers

What is alternative RNA splicing?

The capability of a gene to encode multiple polypeptides by splicing different exons. Signup and view all the answers

How do introns contribute to gene expression regulation?

They may contain sequences that regulate gene expression. Signup and view all the answers

Which class of mutants cannot grow at all in minimal medium?

Mutant cells Signup and view all the answers

Which type of mutation causes Class II mutants not to grow on citrulline?

Mutation in gene B Signup and view all the answers

What was a significant implication of the discovery of ribozymes?

The understanding of RNA's role in catalysis was expanded. Signup and view all the answers

What is a key difference between enzymes and proteins based on the revised hypothesis?

Enzymes are a type of protein, but not all proteins are enzymes. Signup and view all the answers

What is the function of the spliceosome in RNA processing?

To facilitate the splicing of introns from pre-mRNA. Signup and view all the answers

Which of the following correctly describes the relationship between genes and proteins?

One gene can code for multiple proteins through alternative splicing. Signup and view all the answers

Which of the following aspects is NOT a property of RNA that allows it to function catalytically?

It can only bind to RNA molecules. Signup and view all the answers

What type of mutation involves a change in just one base pair of a gene?

Point mutation Signup and view all the answers

Which of the following is true about nucleotide-pair substitutions?

They can lead to a change in amino acid sequence. Signup and view all the answers

What is the result of a mutation that changes a single nucleotide in a DNA template strand?

It causes the production of an abnormal protein. Signup and view all the answers

Which of the following accurately describes the function of the signal recognition particle (SRP)?

It helps to transport proteins across the ER membrane. Signup and view all the answers

What distinguishes sickle-cell hemoglobin from wild-type hemoglobin?

A point mutation in the gene Signup and view all the answers

Which of the following is NOT a type of small-scale mutation?

Chromosomal inversion Signup and view all the answers

The normal amino acid sequence in hemoglobin is altered in sickle-cell disease due to which of the following changes?

A substitution of a nucleotide Signup and view all the answers

What is the effect of a frame shift mutation compared to other mutation types?

It alters the reading frame of the gene. Signup and view all the answers

How many codons function as stop signals during translation?

3 Signup and view all the answers

What does it mean that the genetic code is redundant?

More than one codon can specify the same amino acid. Signup and view all the answers

What is the correct reading frame for codons?

Codons must be read in the appropriate groupings. Signup and view all the answers

Which of the following amino acids is encoded by the codon AUG?

Methionine Signup and view all the answers

Which statement about the genetic code is false?

Each codon can specify more than one amino acid. Signup and view all the answers

What is the significance of the three stop codons?

They signal the termination of protein synthesis. Signup and view all the answers

In the context of mRNA, what does transcription refer to?

The production of mRNA from a DNA template. Signup and view all the answers

How many amino acids do the 61 codons code for?

20 Signup and view all the answers

What role do codons play in protein synthesis?

They specify the sequential order of amino acids in a protein. Signup and view all the answers

What can be inferred about the evolutionary origin of the genetic code?

It has evolved to allow genes to interchange empirically between species. Signup and view all the answers

What is the function of the start codon?

It marks the beginning of the coding sequence for protein. Signup and view all the answers

Which of the following is true regarding the relationship between DNA and mRNA?

mRNA is derived from DNA through transcription. Signup and view all the answers

Study Notes

Transcription

The promoter facilitates the binding of RNA polymerase to initiate transcription.
Transcription progresses at a rate of approximately 40 nucleotides per second in eukaryotes.
Nucleotides are added to the 3' end of the RNA strand during transcription elongation.
Multiple RNA polymerases can transcribe a gene simultaneously, allowing for efficient protein synthesis.
During elongation, the DNA helix unwinds to expose the template strand for transcription.
Transcription factors are NOT part of the transcription initiation complex.
Transcription factors facilitate the binding of RNA polymerase to the promoter, thereby regulating gene expression.
The non-template strand of DNA has the same sequence as the mRNA transcript, except for thymine being replaced by uracil.

Gene Expression and Mutations

Class I Neurospora crassa mutants require arginine to grow.
Class II mutants can grow with ornithine but not with citrulline or arginine.
Beadle and Tatum's hypothesis states that one gene codes for one enzyme.
Feedback inhibition occurs when the end product of a metabolic pathway inhibits an enzyme involved in its synthesis.
Class III Neurospora crassa mutants cannot grow at all in minimal medium.
The precursor amino acid related to all classes of Neurospora crassa mutants is ornithine.

RNA Processing and Function

Ribozymes are catalytic RNA molecules involved in RNA processing.
Proteins are not enzymes.
The ability of RNA to form complex three-dimensional structures allows it to function as an enzyme.
The minimal medium was used as a control in the experiment.
Alternative RNA splicing allows for the production of multiple proteins from a single gene.
Introns contribute to gene expression regulation by affecting RNA splicing and stability.
Class II mutants have a mutation that prevents them from converting citrulline to arginine.

Implications of Ribozymes

The discovery of ribozymes challenged the dogma that only proteins can catalyze biological reactions.
The revised hypothesis states that some RNA molecules can act as enzymes, whereas proteins function as enzymes and other cellular roles.
The spliceosome is a complex of RNA and proteins that removes introns from pre-mRNA.

Genes, Proteins and Mutations

Genes code for proteins.
The ability of RNA to base-pair with itself is not a property that enables it to function catalytically.
A point mutation involves a change in a single base pair.
Nucleotide-pair substitutions can result in silent, missense, or nonsense mutations.
A mutation altering a single nucleotide in a DNA template strand can lead to a change in the amino acid sequence of a protein.
The signal recognition particle (SRP) guides ribosomes synthesizing proteins destined for secretion to the ER.
Sickle-cell hemoglobin differs from wild-type hemoglobin due to a single amino acid substitution.
Insertions and deletions are not small-scale mutations.
The substitution of valine for glutamic acid at position 6 in the beta globin chain leads to sickle-cell disease.
A frameshift mutation can alter the reading frame of a gene and lead to a non-functional protein.

The Genetic Code

Three codons function as stop signals during translation.
The genetic code is redundant because multiple codons can code for the same amino acid.
The reading frame is the set of three nucleotides that defines the codons.
The codon AUG codes for methionine.
The genetic code is not universal across all organisms.
Stop codons signal the termination of protein synthesis.

Transcription and Translation

Transcription refers to the process of synthesizing mRNA from DNA.
There are 61 codons that code for amino acids.
Codons dictate the order of amino acids in a polypeptide chain.
The evolutionary origin of the genetic code suggests it is ancient and universal, indicating a common ancestor for all life.
The start codon initiates protein synthesis.
DNA contains the genetic information while mRNA transmits it to the ribosomes for protein synthesis.

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Description

Explore the experiment conducted on Neurospora crassa focusing on the growth of mutant cells in minimal media. This quiz covers the classification of mutants based on their ability to grow with various supplements and the corresponding gene functions involved in arginine biosynthesis. Test your understanding of the one gene – one polypeptide hypothesis as it relates to enzyme production.