Is the process by which a portion of the molecule of

is the process by which a portion of the molecule of DNA is copied into
a complementary strand of RNA. Through the process of transcription, the DNA
code is transferred out of the nucleus to the ribosomes.

Through a series of chemical signals, the gene for a specific protein is turned on.
An enzyme attaches to the specific location on the DNA molecule where the
gene is found, causing the two strands of DNA to separate at that location.

Complementary RNA nucleotide bases bond to the bases on one of the
separated DNA strands.
DNA nucleotide bases
exposed on the separated
strand
RNA nucleotide
which bonds
Adenine (A) Uracil (U)
Thymine (T) Adenine (A)
Cytosine (C) Guanine (G)
Guanine (G) Cytosine (C)

Nucleotides of RNA bond together, forming a single-stranded molecule of RNA
that separates from the DNA strand and the two DNA strands rejoin. This is
called messenger RNA ( mRNA ).

The messenger RNA (mRNA) is formed complementary to one strand of DNA.

The mRNA strand leaves the nucleus and goes through the nuclear membrane
into the cytoplasm of the cell.
Translation is the process of interpreting the genetic message and building the
specified protein. It begins when the mRNA attaches to a ribosome that contains
proteins and ribosomal RNA (rRNA), in the cytoplasm.

The function of ribosomes is to assemble proteins according to the code that the
mRNA brings from the DNA.

Each three-base nucleotide sequence on the mRNA is called a codon . Each
codon specifies a particular amino acid that will be placed in the chain to build
the protein molecule.
o For example, if the DNA sequence was GAC, then the RNA sequence becomes
CUG and the amino acid that is coded is Leucine.*
*Teacher Note: mRNA codons for specific amino acids can be found in tables
in most textbooks.
Content Overview for Module B-4.4 cont.
Unit VI Structure and Function of DNA/RNA
7-1-10 S 3 Curriculum
12

o The sequence of mRNA nucleotides determines the order of the amino acids
in the protein chain which, in turn, distinguishes one protein from another in
structure and function.
○
Another type of RNA, transfer RNA (tRNA) , is vital in assembling amino acids
into the correct sequence for the required protein by transferring amino acids
to the ribosomes when needed. There are twenty common amino acids that
are used to construct specific proteins.
○
An anticodon site , which has the 3-nucleotide bases complementary to the
codon of mRNA, is found at one end of tRNA whereas the other end of the
tRNA molecule has a specific amino acid that is also determined by the
anticodon.

The translation process takes place as follows:
○
The tRNA with its attached amino acid pairs to the codon of the mRNA that is
attached to a ribosome.
○
When a second tRNA with its specific amino acid pairs to the next codon in
sequence, the attached amino acid breaks from the first tRNA and attaches to
the amino acid of the second tRNA.
○
The ribosome forms a peptide bond between the amino acids, and an amino
acid chain begins to form.
○