Genetics Chapter 16 Flashcards

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Questions and Answers

What is a mutant?

An organism that cannot grow in minimal medium

An organism with a heritable change in DNA sequence (correct)

An organism that has not been studied

An organism that is easy to grow in a lab

What defines a model organism?

A species that is easy to grow in the lab and lends itself particularly well to the questions being investigated

What happens to an arg mutant lacking arginine protein when grown on minimal medium?

It only grows with arginine (correct)

It grows slower than normal

It shows no growth (correct)

It shows normal growth

What is the precursor to arginine in the metabolic pathway?

Ornithine Signup and view all the answers

What result indicates that enzyme 2 is defective?

It cannot grow on minimal medium because it lacks the ability to make citrulline and eventually arginine. Signup and view all the answers

How does the experiment support the one gene-one enzyme hypothesis?

Different mutants had distinct growth requirements. Signup and view all the answers

What are exceptions to the one gene-one enzyme hypothesis?

Multiple genes code for proteins that are not enzymes; some enzymes are made of many proteins; some genes encode for mRNA that do not serve as templates for translation. Signup and view all the answers

What is the messenger RNA hypothesis?

DNA is in the nucleus and ribosomes are in the cytoplasm; mRNA serves as the intermediate. Signup and view all the answers

How can only 4 base pairs give rise to 20 different amino acids?

A combination of a few bases can make more complex messages. Signup and view all the answers

How many base pairs is the genetic code composed of for a single amino acid?

Three base pairs Signup and view all the answers

What happens when one nucleotide is removed from a gene?

Results in a mutant phenotype Signup and view all the answers

What is redundancy in the genetic code?

Many codons code for the same amino acid, but a codon cannot code for more than one amino acid. Signup and view all the answers

What is a start codon?

AUG Signup and view all the answers

Why is the genetic code considered unambiguous?

It is clear and specific Signup and view all the answers

The genetic code is universal.

True Signup and view all the answers

What does it mean for the genetic code to be conservative?

The first two base pairs of a codon are the same if they code for the same amino acid; only the third one changes. Signup and view all the answers

Match the following types of mutations with their definitions:

Point mutation = Change in a single DNA base nucleotide Silent mutation = Change in one base that does not code for a different amino acid Missense mutation = Substitution that codes for a different amino acid Nonsense mutation = Substitution that codes for a stop codon Frameshift mutation = Addition or deletion that causes a shift in the reading frame Signup and view all the answers

Study Notes

Gene Function Basics

A mutant is an organism with a heritable change in DNA sequence; knockouts are non-functional proteins used to determine the role of normal genes.
Model organisms are species easy to cultivate in laboratory settings, allowing effective investigation of biological questions.

Arginine Synthesis and Mutants

Arg mutant strains lack the arginine protein; show growth differences in minimal medium with and without arginine.
Enzyme pathways involve specific precursors: ornithine → citrulline → arginine. Defective enzymes inhibit growth at various steps.

Experimental Evidence and Hypotheses

A study on arginine synthesis mutants supports the one gene-one enzyme hypothesis with varied growth profiles based on gene mutations.
Mutant results show that supplementing with products allows pathways to continue functioning despite specific defects.

One Gene-One Enzyme Hypothesis

Supported since distinct mutants exhibit unique growth requirements linked to specific enzyme deficiencies.
Exceptions exist where multiple genes code for proteins beyond enzymes or when mRNA does not translate into proteins.

Messenger RNA and Genetic Code

The messenger RNA hypothesis posits that mRNA acts as a medium transferring genetic information from the nucleus to the cytoplasm.
The genetic code comprises sets of base pairs; three base pairs produce 64 codon combinations allowing for encoding of 20 different amino acids.

Codon Redundancy and Specificity

Codon redundancy permits numerous codons to specify the same amino acid while maintaining clarity in translation.
Examples include:
- Start codon: AUG (also signals methionine).
- Stop codons: UAA, UAG, UGA (do not encode for amino acids).

Characteristics of the Genetic Code

The code is unambiguous: each codon corresponds to a single amino acid.
The code is universal, suggesting a shared ancient lineage across species.
The code is conservative, where changes in the third base pair often lead to the same amino acid being coded, maintaining protein functionality.

Types of DNA Mutations

Point mutation: a single base nucleotide change.
Silent mutation: a substitution causing no change in the amino acid sequence; neutral for fitness.
Missense mutation: alters one amino acid, potentially beneficial or detrimental.
Nonsense mutation: creates a stop codon, truncating protein function adversely.
Frameshift mutation: insertion or deletion of nucleotides that shift the reading frame, often leading to significant functional changes in the protein.

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Description

Explore key concepts from Chapter 16 on how genes work with these flashcards. Learn about important terms like 'mutant' and 'model organism,' and understand their significance in genetic research. Perfect for students looking to reinforce their knowledge before exams.