DNA translation and Mutation

Question 1

1. What is a codon?
   A sequence of three mRNA nucleotides that codes for a specific amino acid.

Question 2

2. How many possible codons are there?
   There are 64 possible codons, as the genetic code is based on combinations of three nucleotides (43 = 64).

Question 3

3. How many amino acids are encoded by the genetic code?
   20 amino acids are encoded by the genetic code.

Question 11

What is a mutation?

Answer 11

A change in the nucleotide sequence of DNA.

Question 12

What causes mutations?

Answer 12

They may occur spontaneously or be induced by environmental factors (mutagens).

Question 13

What is a silent mutation?

Answer 13

A mutation that changes a codon but does not alter the amino acid.

Question 14

4. What is a missense mutation?
   A mutation that changes one amino acid in the protein.

Question 15

What is a nonsense mutation?

Answer 15

A mutation that changes an amino acid codon to a stop codon.

Question 16

What is a frameshift mutation?

Answer 16

A mutation caused by the insertion or deletion of nucleotides,
altering the reading frame.

Question 17

How can mutations affect protein function?

Answer 17

They can lead to loss, gain, or change of function depending on
the alteration.

Question 18

Are all mutations harmful?

Answer 18

No, some are neutral or even beneficial.

Question 20

What determines the severity of a mutation?

Answer 20

Its location, type, and effect on protein structure and function.

Question 21

What does tRNA do?

Answer 21

It brings amino acids to the ribosome during translation.

Question 22

What is an anticodon?

Answer 22

A three-nucleotide sequence on tRNA complementary to a codon on mRNA.

Question 23

Where does the amino acid attach on tRNA?

Answer 23

At the 3’ end.

Question 24

What enzyme charges tRNA with an amino acid?

Answer 24

Aminoacyl-tRNA synthetase.

Question 25

How many synthetases exist?

Answer 25

20—one for each amino acid.

Question 26

What is the wobble hypothesis?

Answer 26

The third base of a codon can form non-standard base pairs, allowing some tRNAs to recognize multiple codons.

Question 27

What is an aminoacyl tRNA?

Answer 27

A tRNA molecule that is attached to its specific amino acid.

Question 28

Where are tRNAs synthesized?

Answer 28

In the nucleus.

Question 29

Do tRNAs undergo splicing or translation?

Answer 29

No, they are not translated and are not typically spliced.

Question 30

Why is accurate tRNA charging important?

Answer 30

To ensure the correct amino acid is added during protein synthesis.

Question 31

1. What are the three phases of translation? Initiation, elongation, and termination.

Question 32

Where does translation occur?

Answer 32

In the cytoplasm, on ribosomes.

Question 34

What is the ribosome made of?

Answer 34

Protein and ribosomal RNA (rRNA).

Question 35

What forms the peptide bonds?

Answer 35

The rRNA in the large ribosomal subunit (acts as a ribozyme).

Question 36

What happens during initiation?

Answer 36

The ribosome assembles around the mRNA and start codon.

Question 37

What does the A site do?

Answer 37

Accepts incoming aminoacyl-tRNAs.

Question 38

What happens at the P site?

Answer 38

Peptide bonds form, and the growing polypeptide is held.

Question 39

What does the E site do?

Answer 39

Allows exit of the now uncharged tRNA.

Question 40

10. What triggers termination? A stop codon recruits a release factor.

Question 41

What is proteolysis?

Answer 41

The cleavage of polypeptides into smaller functional units.

Question 42

What is glycosylation?

Answer 42

The addition of sugar chains to proteins.

Question 44

4. Where are secreted proteins processed? In the rough ER and Golgi apparatus.

Question 45

What directs proteins to the ER?

Answer 45

Signal peptides.

Question 46

6. Why do proteins need PTMs? To become fully functional, stable, or targeted correctly.

Question 47

What organelle is involved in sorting proteins?

Answer 47

The Golgi apparatus.

Question 48

What organelle synthesizes membrane-bound proteins?

Answer 48

The rough ER.

Question 50

Are all proteins modified post-translation?

Answer 50

Not all, but many are.