Essentials of Anatomy and Physiology

57

Cell nucleus

Nuclear pore

Nuclear membrane

A

A Codon

A

DNA

Amino acids

Peptide bonds

mRNA

tRNA

Ribosome

Anticodon

A

A

G C

A U

A A A G U C U

U U

G

U A

U

U U

Figure 3–4. Protein synthesis. The mRNA is formed as a copy of a portion of the DNA in
the nucleus of a cell. In the cytoplasm, the mRNA becomes attached to ribosomes. See text
for further description.
QUESTION:A tRNA molecule has two attachment sites; what is each for?