chapter 16

Question 1

What hypothesis did Beadle and Tatum propose?

Answer 1

The one-gene, one-enzyme hypothesis, suggesting each gene contains the information to produce a specific enzyme.

Question 2

What organism did Beadle and Tatum use in their experiments?

Answer 2

The bread mold Neurospora crassa.

Question 3

What did Srb and Horowitz contribute to the one-gene, one-enzyme hypothesis?

Answer 3

They demonstrated that each gene in a metabolic pathway is responsible for producing one specific enzyme.

Question 4

How has the one-gene, one-enzyme hypothesis been updated?

Answer 4

It is now called the one-gene, one-polypeptide hypothesis, as not all proteins are enzymes, and some proteins consist of multiple polypeptides.

Question 5

What is the central dogma of molecular biology?

Answer 5

The flow of genetic information:
DNA → RNA → Protein.

Question 6

What is transcription?

Answer 6

The process of synthesizing RNA from a DNA template.

Question 7

What is translation?

Answer 7

The process of synthesizing RNA from a DNA template.

Question 8

What is translation?

Answer 8

The process of using the information in mRNA to synthesize proteins by converting nucleotide sequences into amino acid sequences.

Question 9

How do genotype and phenotype relate according to the central dogma?

Answer 9

Genotype: The sequence of DNA.
Phenotype: The physical traits, which result from the proteins produced by the genotype.

Question 10

What are exceptions to the central dogma?

Answer 10

Some genes code for RNAs that are not translated into proteins.
Viruses with reverse transcriptase can flow information from RNA → DNA.

Question 11

What is the genetic code?

Answer 11

A set of rules that define how nucleotide sequences in mRNA specify amino acids in proteins.

Question 12

What is a codon?

Answer 12

A group of three nucleotide bases that codes for a specific amino acid.

Question 13

How many codons are there?

Answer 13

64 codons:

61 code for amino acids.
1 start codon (AUG).
3 stop codons (UAA, UAG, UGA).

Question 14

What are the key properties of the genetic code?

Answer 14

Redundant: Most amino acids are encoded by multiple codons.
Unambiguous: Each codon specifies only one amino acid.
Non-overlapping: Codons are read one at a time.
Nearly universal: Shared by almost all organisms.
*Conservative: Codons for the same amino acid often share the first two bases.

Question 15

How was the genetic code deciphered?

Answer 15

Nirenberg and Matthaei used synthetic RNA sequences in a test tube to identify which amino acids were coded by specific triplets.

Question 16

What is a mutation?

Answer 16

A permanent change in DNA that alters an organism’s genotype and potentially its phenotype.

Question 17

What are the types of point mutations?

Answer 17

Missense mutation: Changes one amino acid in a protein.
Silent mutation: Does not change the amino acid sequence.
Frameshift mutation: Shifts the reading frame, altering all downstream codons.
Nonsense mutation: Converts an amino acid codon into a stop codon.

Question 18

What are the impacts of point mutations on fitness?

Answer 18

Beneficial: Increases fitness.
Neutral: No effect on fitness.
Deleterious: Decreases fitness.

Question 19

What are chromosome-level mutations?

Answer 19

Inversion: A chromosome segment flips and rejoins.
Translocation: A segment attaches to a different chromosome.
Deletion: A segment is lost.
Duplication: A segment is copied.

Question 20

How are chromosome mutations detected?

Answer 20

Through karyotype analysis, which visualizes the complete set of chromosomes.

Question 21

Why are mutations significant in cancer?

Answer 21

Chromosome mutations such as aneuploidy, inversions, and translocations are commonly associated with cancer cells.

Question 22

What is the significance of AUG in protein synthesis?

Answer 22

AUG is the start codon and codes for methionine, signaling the beginning of translation.

Question 23

Why is redundancy in the genetic code beneficial?

Answer 23

It minimizes the impact of mutations by allowing multiple codons to code for the same amino acid.

Question 24

What are null alleles or loss-of-function alleles?

Answer 24

These are defective alleles that do not produce a functional protein, often leading to a mutant phenotype when studied.

Question 25

What happens if the reading frame is altered by adding or removing nucleotides?

Answer 25

Adding or subtracting one or two bases shifts the reading frame, potentially changing the entire sequence of amino acids. However, adding or subtracting multiples of three bases does not disrupt the reading frame.