Genetic Code

Question 1

What is Epistasis?

Answer 1

The effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes

Question 2

What was Beadle and Tatum’s Theory on finding mutations? Why was it false?

Answer 2

They argued that if genes make enzymes, then you should be able to find a mutant corresponding to every enzyme in a pathway.

However, if an allele does not produce a functional enzyme, then the pathway will not create another protein, and therefore will not grow.

Question 3

What is an auxotroph?

Answer 3

An auxotroph is a microorganism with a mutation preventing it from producing a compound needed for growth

Question 4

What is a prototroph?

Answer 4

It is a wild type microorganism, it is capable of producing whatever it needs for growth

Question 5

Where are proteins made?

Answer 5

In the cytoplasm with help of Ribosomes

Question 6

2 major differences between RNA and DNA (other than the number of strands)

Answer 6

• RNA has uracil instead of thymine

- RNA has 2’ hydroxyl that DNA is missing

Question 7

How does information get from DNA to RNA? What is this process called?

Answer 7

This is called transcription:
- RNA polymerase “sits” on DNA and unwinds it to start creating an RNA strand.
This creates mRNA

Question 8

Describe the relationship between the DNA sequence and an amino acid sequence. Does one determine the other?

Answer 8

DNA sequence determines amino acid sequence, but amino acid sequence does not determine DNA sequence

Question 9

How is mRNA create an amino acid?

Answer 9

Once the mRNA travels to the cytoplasm, it is attached to a ribosome (small unit)
The big unit then attaches on with a start tRNA codon at the P site (first site in large unit).
tRNA that corresponds to next codon binds to A site, then moves to the P site.

Question 10

Explain the sense strand vs. the antisense strand

Answer 10

The antisense strand is transcribed. This means the mRNA sequence is equivalent to the sense strand (just with U in place of A)

Question 11

What is wobble pairing?

Answer 11

The first two codons in a code match perfectly, but the third one can vary.
G will sometimes match with C or U
U will be A or G
I is A, U, or C

Question 12

How can the steps in information flow vary?

Answer 12

• Many ribosomes can translate a single mRNA
• Ribosomes sometimes begin translation before being done transcription (prokaryotes)
• Proteins sometimes begin function before translation is finished.

Question 13

What is a Polysome?

Answer 13

Many ribosomes bind to the same transcript, starting at the start codon

Question 14

Two types of mutations:

Answer 14

• Point Mutation

- Chromosomal mutation

Question 15

What are types of point mutations?

Answer 15

• Silent: Change in codon sequence but same amino acid/protein
• Missense: Change in one amino acid, encoding a different protein
• Nonsense: Change in amino acid to a stop codon
• Insertion or deletion: Changes reading frame due to one less or one more nucleotide

Question 16

What are types of Chromosomal mutations?

Answer 16

• Deletion
• Duplication: Large chunks of chromosome are duplicated
• Inversion: When a piece of DNA flips, re-entering chromosome in reverse direction
• Translocation: When a piece of DNA jumps from one chromosome to another

Question 17

What is a mutagen?

Answer 17

A mutagen is any agent that causes mutation (virus, radiation, chemicals…)

Question 18

What happens to Somatic vs Germ line mutations?

Answer 18

• A somatic mutation may make a cell cancerous or kill it. It can be transmitted to a daughter cell but not to progeny
• A germ line mutation may be transmitted to progeny, and can become an allele in a population