Question

rna editing

1. many rna molecules from eukaryotic genes have sections, called _, edited out of them before they become functional. the remaining pieces, called _, are spliced together.
2. is the following sentence true or false? rna editing occurs in the cytoplasm of the cell.
3. what are two explanations for why some rna molecules are cut and spliced?

a.
b.
the genetic code

1. proteins are made by joining _ into long chains called polypeptides.
2. how can only four bases in rna carry instructions for 20 different amino acids?
3. what is a codon?
4. circle the letter of the number of possible three - base codons.

a. 4
b. 12
c. 64
d. 128

1. is the following sentence true or false? all amino acids are specified by only one codon.
2. circle the letter of the codon that serves as the “start” codon for protein synthesis.

a. uga
b. uaa
c. uag
d. aug
translation

1. what occurs during the process of translation?
2. where does translation take place?

Explanation:

1. Introns are removed from pre - mRNA, and exons are joined together.
2. RNA editing mainly occurs in the nucleus, so the statement is false.
3. a. To remove non - coding sequences (introns). b. To generate different mRNA isoforms (alternative splicing).
4. Amino acids are joined to form polypeptides.
5. The four bases in RNA form codons (groups of three bases), and different combinations of codons can code for 20 amino acids.
6. A codon is a three - base sequence on mRNA that codes for a specific amino acid or serves as a start/stop signal.
7. Since there are 4 bases and codons are three - base sequences, the number of possible codons is $4\times4\times4 = 64$ (c).
8. Most amino acids are specified by more than one codon, so the statement is false.
9. AUG is the start codon for protein synthesis (d).
10. During translation, the sequence of codons on mRNA is used to assemble amino acids into a polypeptide chain.
11. Translation takes place on ribosomes in the cytoplasm.

Answer:

1. Introns; Exons
2. False
3. a. To remove non - coding sequences (introns)

b. To generate different mRNA isoforms (alternative splicing)

1. Amino acids
2. The four bases in RNA form codons (groups of three bases), and different combinations of codons can code for 20 amino acids.
3. A three - base sequence on mRNA that codes for a specific amino acid or serves as a start/stop signal
4. c. 64
5. False
6. d. AUG
7. The sequence of codons on mRNA is used to assemble amino acids into a polypeptide chain
8. On ribosomes in the cytoplasm