Question

1. a small segment of dna has the following nitrogen base sequence:

dna = tac cct acc att
a) determine the complementary mrna codons.
aug gga ugg uaa
b) what are the trna anticodons?
c) what amino acids are called for by this sequence?
d) what is the importance of the \start\ and \stop\ codons?

Explanation:

Part (b)

Step 1: Recall tRNA anticodon rules

tRNA anticodons are complementary to mRNA codons. The base - pairing rules are: A (adenine) pairs with U (uracil), U (uracil) pairs with A (adenine), G (guanine) pairs with C (cytosine), and C (cytosine) pairs with G (guanine).

Step 2: Find anticodons for each mRNA codon

• For mRNA codon AUG: The complementary anticodon is UAC (since A - U, U - A, G - C).
• For mRNA codon GGA: The complementary anticodon is CCU (since G - C, G - C, A - U).
• For mRNA codon UGG: The complementary anticodon is ACC (since U - A, G - C, G - C).
• For mRNA codon UAA: The complementary anticodon is AUU (since U - A, A - U, A - U).

Step 1: Recall genetic code table

We use the genetic code table to find the amino acids corresponding to each mRNA codon.

Step 2: Find amino acid for each codon

• mRNA codon AUG: Codes for Methionine (Met) (also the start codon).
• mRNA codon GGA: Codes for Glycine (Gly).
• mRNA codon UGG: Codes for Tryptophan (Trp).
• mRNA codon UAA: Is a stop codon, so it does not code for an amino acid.

• Start codon (e.g., AUG): It signals the start of translation. It is the point at which the ribosome begins to assemble amino acids into a polypeptide chain, and it also codes for the amino acid methionine in eukaryotes (or a modified form in prokaryotes).
• Stop codons (e.g., UAA, UAG, UGA): They signal the end of translation. When a stop codon is reached in the mRNA sequence, the ribosome - mRNA - tRNA complex dissociates, and the newly synthesized polypeptide chain is released.

Answer:

UAC CCU ACC AUU

Part (c)