Question

protein synthesis
protein synthesis is a complex process. you will trace the steps that are involved in the protein synthesis of a part of a molecule of oxytocin. oxytocin is the pituitary hormone that helps regulate blood - pressure, stimulates the uterus to contract during childbirth, and stimulates the production of milk after childbirth.
a. protein synthesis begins with dna in the nucleus. below is a dna sequence that could code for part of a molecule of oxytocin.

• write the sequence of messenger rna (mrna) codons that would result from the transcription of this portion of dna. the arrow marks the starting point.

(nucleus) dna→aca - ata - tag - ctt - ttg - acg - ggg - aac - ccc - att
1 2 3 4 5 6 7 8 9 10
transcription:
mrna: (codon) ugu - uau - auc - gaa - aac - ugc - ccc - uug - ggg - uaa
start: initiator codon (aug)
b. after transcription (in nucleus), mrna attaches to a ribosome where translation (in cytoplasm) takes place. each codon of mrna bonds with an anticodon of a transfer rna (trna) and each trna molecule bonds with a specific amino acid. the table below shows the mrna codons and the amino acids for which they code. for example, if you were given the codon aga, you can see from the table that these bases code for the amino acid arginine.
stop: terminator codon (uaa,uag,uga)
second base in code
a g u c
first base in code
a lysine arginine isoleucine threonine
lysine arginine methionine threonine
asparagine serine isoleucine threonine
asparagine serine isoleucine threonine
g glutamic acid glycine valine alanine
glutamic acid glycine valine alanine
aspartic acid glycine valine alanine
aspartic acid glycine valine alanine
u stop stop leucine serine
stop tryptophan leucine serine
tyrosine cysteine phenylalanine serine
tyrosine cysteine phenylalanine serine
c glutamine arginine leucine proline
glutamine arginine leucine proline
histidine arginine leucine proline
histidine arginine leucine proline
third base in code
a g u c
aug: methionine (start)

• use the mrna sequence from a to write the sequence (1 - 10) of amino acids in this part of the oxytocin molecule.

translation (cytoplasm) on ribosomes
1 - 2 - 3
cysteine - tyrosine -

1. how many amino acids make up this portion of the oxytocin molecule?
2. what is the purpose of the uaa codon?

Explanation:

Step1: Count amino - acids

The mRNA sequence has 10 codons listed. Each codon codes for an amino - acid (except stop codons). Since there are 10 codons, there are 10 amino - acids in this portion of the oxytocin molecule.

Step2: Identify UAA function

From the information given, UAA is a stop (terminator) codon. It signals the end of translation.

Answer:

1. 10
2. It is a stop (terminator) codon that signals the end of translation.