Honors Biology
Protein Synthesis Study Guide ANSWERS
1. What are the 3 steps in Protein Synthesis (in order)?
Transcription, RNA splicing, translation
2. Transcription takes place in the nucleus.
3. What are the 3 main types of RNA? Describe what each type is used for.
mRNA- messenger RNA, contains codons that code for amino acids
tRNA – transfer RNA, brings amino acid to ribosome during translation; has anticodons that are complementary to mRNA codons
rRNA – ribosomal RNA, combine with proteins to make ribosomes
4. What are introns and exons?
Introns- sequences of mRNA that do not contain the code for protein
Exons- sequences of mRNA that contain the code for protein
5. What is mRNA splicing and when does it occur?
Introns are removed and exons are spliced together; occurs in the nucleus after
transcription takes place
6. What is a codon? What is an anti-codon?
Codons are 3 nucleotides of mRNA that code for a specific amino acid
Anti-codons are 3 nucleotides of tRNA that are complementary to a codon on
the mRNA
7. DNA and RNA are polymers called nucleic acids made up of monomers
called nucleotides.
8. Explain the difference between the 3 sites on the ribosome (E, P, and A)?
Peptidyl (P) site – site on the ribosome where the polypeptide chain is built
(amino acids link together)
Acceptor (A) site – site on the ribosome where tRNAs initially bind to the
ribosome, matching their anti-codon to codons on mRNA, and bring the correct
amino acid
Exit (E) site – site on the ribosome where empty tRNAs (without their amino acid)
exit the ribosome
9. Where does translation occur?
Ribosomes floating in the cytoplasm or ribosomes on the rough ER
10. During translation, the first tRNA molecule carrying methionine, enters the
ribosome at the P site.
11. What is the base sequence on DNA that signals RNA polymerase to bind in
the promoter region? TATAAAA
12. What structure is responsible for translating mRNA?
Ribosomes
13. How are proteins that are going to be exported outside of the cell sent to a
ribosome on the rough ER to finish their synthesis?
A signal sequence on the mRNA will direct their synthesis
14. Differentiate between the following mutations. Which are point mutations?
Silent
point
substitution…
codes for the
same amino
acid… no
effect
Nonsense
Missense
Frameshift
point
substitution…
codes for a
stop codon…
amino acid
chain
incomplete
and protein
not functional
point
substitution..
codes for a
different
amino acid..
could
potentially
cause a
different
shape in
protein
structure and
a not fully
functioning
protein
insertion or
deletion
causes a shift
in the reading
of the mRNA
codons…
many
mistakes in
amino acid
chain and
protein not
functional
15. Give a detailed explanation of translation. Discuss what happens during
initiation, elongation, and termination. Be sure to include ALL molecules that
play an important role in this process.
Initiation – small and large ribosomal subunits, mRNA, and the first tRNA carrying
the amino acid methionine all come together to form a complex
Elongation – codons are read and tRNAs bring the correct amino acids in the
order layed out by the codons. A polypeptide chain is built by peptide bonds
forming between amino acids.
Termination – a stop codon is reached on the mRNA and the polypeptide chain
breaks away
16. The following is a single strand of DNA: 3’ TACACACAAACGGGG 5’. Write
the following in the space provided.
a. Complementary DNA strand:
5’ ATG TGT GTT TGC CCC 3’
b. mRNA: (transcribe the gene in bold letters)
5’ AUG
UGU GUU UGC CCC 3’
c. amino acid sequence:
methionine, cysteine, valine, cysteine, proline
24. The DNA sequence undergoes the following change:
TAC ACA CAA ACG GGG → TAC ACC CAA ACG GGG
a. How would the sequence of amino acids be changed as a result of this
mutation? Different amino acid (UGU= cysteine and UGG = trytophan)
b. What type of mutation is this? Point mutation resulting in missense