The Genetic Code (Easy)

Which statement BEST explains why organisms with very different GC/AT ratios can still produce similar proteins?
A. The genetic code is degenerate
B. Codons are overlapping
C. Ribosomes correct mutations during translation
D. Codons are read in both directions

A

The wobble hypothesis primarily explains:
A. Why mutations always change amino acids
B. Why fewer tRNAs are needed than codons
C. Why stop codons are not recognized by tRNA
D. Why codons overlap

B

Which of the following base positions is most flexible in codon–anticodon pairing?
A. 1st base of codon
B. 2nd base of codon
C. 3rd base of codon
D. All bases equally

C

Why did poly-G fail to reveal its corresponding amino acid in early experiments?
A. It degraded too quickly
B. It could not be synthesized
C. It encoded multiple amino acids
D. It formed stable triple helices and did not bind ribosomes

D

Which mutation is MOST likely to produce a truncated protein?
A. Missense
B. Nonsense
C. Frameshift
D. Silent

B

Which feature ensures codons are read correctly during translation?
A. Fixed reading frame
B. Wobble base pairing
C. Degeneracy
D. Release factors

A

Which statement about suppressor mutations is TRUE?
A. They always restore the original DNA sequence
B. They occur only within the same gene
C. They eliminate mutations entirely
D. They can act by altering translation

D

Which codon change occurs in mitochondrial genetic code?
A. UAA → Glutamine
B. UGA → Tryptophan
C. AUG → Stop
D. UAG → Leucine

B

What is the function of release factors?
A. Add amino acids to polypeptide
B. Stabilize mRNA
C. Recognize stop codons
D. Initiate translation

C

Which mutation would MOST drastically alter downstream amino acid sequence?
A. Silent mutation
B. Missense mutation
C. Frameshift mutation
D. Back mutation

C

Codons are read in a 3’ → 5’ direction. (True/False)

False

One tRNA can recognize multiple codons due to wobble. (True/False)

True

The genetic code is overlapping. (True/False)

False

Stop codons are recognized by tRNAs. (True/False)

False

Poly-U experiments demonstrated that UUU codes for phenylalanine. (True/False)

True

Degeneracy reduces the impact of mutations. (True/False)

True

Frameshift mutations always involve substitution of a single base. (True/False)

False

Suppressor genes change the DNA sequence of mutated genes. (True/False)

False

The genetic code is identical in all organisms including mitochondria. (True/False)

False

Selenocysteine is one of the standard 20 amino acids. (True/False)

False

Codons are read in the ______ direction.

5’ to 3’

Multiple codons coding for the same amino acid is called ______.

degeneracy

The flexible pairing at the third codon position is called ______.

wobble

The three stop codons are ______, ______, and ______.

UAA, UAG, UGA

A mutation that introduces a stop codon is called a ______ mutation.

nonsense

______ mutations shift the reading frame of the gene.

Frameshift

Synthetic RNA polymers were made using the enzyme ______.

polynucleotide phosphorylase

The amino acid inserted by UUU is ______.

phenylalanine

In mitochondria, UGA codes for ______ instead of stop.

tryptophan

Suppressor mutations can be ______ or ______.

intragenic; intergenic

Match the term with the correct description:

Column A	Column B
1. Missense mutation	A. Inserts stop codon
2. Nonsense mutation	B. Changes amino acid
3. Frameshift mutation	C. Alters reading frame
4. Suppressor mutation	D. Counteracts another mutation
5. Wobble	E. Flexible base pairing

1-B, 2-A, 3-C, 4-D, 5-E

Match the molecule/process:

Column A	Column B
1. Poly-U	A. Lysine
2. Poly-A	B. Phenylalanine
3. Poly-C	C. Proline
4. Poly-G	D. No result due to structure

1-B, 2-A, 3-C, 4-D

Explain why the genetic code is described as “degenerate.”

Multiple codons can encode the same amino acid, reducing the impact of mutations.

Describe the wobble hypothesis and its significance.

The third base of the codon allows flexible pairing with the first base of the anticodon, enabling fewer tRNAs to recognize multiple codons.

Why was poly-U important in cracking the genetic code?

It demonstrated that UUU codes for phenylalanine by producing polypeptides composed entirely of phenylalanine.

Compare missense, nonsense, and frameshift mutations.

Missense changes one amino acid, nonsense introduces a stop codon, and frameshift alters the reading frame, affecting all downstream codons.

Explain how suppressor mutations work.

They counteract the effects of another mutation by altering translation (e.g., mutated tRNA reads stop codon as amino acid).

Why is the genetic code considered universal, and what are its exceptions?

Most organisms use the same codons, but mitochondria and some microbes have variations.

Why is the reading frame critical in translation?

Incorrect reading frames result in entirely different amino acid sequences and nonfunctional proteins.

Explain why poly-G did not function in early experiments.

It formed stable triple helices that prevented ribosome binding.

What is the role of release factors in translation?

They recognize stop codons and terminate protein synthesis.

Describe how a second mutation can restore protein function.

A second mutation may restore the protein’s 3D structure or reading frame, compensating for the original mutation.