From Genes to Proteins
Your traits are determined by proteins that are
built according to instructions in DNA.
These sections of DNA are your genes.
The first step in decoding the DNA instructions is
to copy part of the DNA into RNA.
Like DNA, RNA consists of a long chain of
3 main differences between DNA and RNA:
The sugar in RNA is ribose, not deoxyribose.
RNA is single – stranded, while DNA is double –
RNA contains uracil instead of thymine.
3 Types of RNA:
1. Messenger RNA (mRNA) –
serves as “messengers” from
DNA to the rest of the cell.
2. Ribosomal RNA (rRNA) –
make up ribosomes
3. Transfer RNA (tRNA) – transfers
each amino acid to the ribosome.
Met Amino Acid
RNA Synthesis: Transcription
Occurs in the nucleus
Copying part of DNA into a complementary
sequence in RNA.
Requires an enzyme known as RNA
RNA polymerase binds to DNA and separates the
It uses one strand of DNA as a template to make a
strand of mRNA.
How does RNA polymerase
know where to start?
Promoters – have specific base sequences
where RNA polymerase will bind to begin
DNA Template strand:
Write the corresponding mRNA sequence:
In eukaryotes, many genes are
interrupted by introns, which have no
Exons are the portions of a gene that
After transcription the introns in the
mRNA are cut out by spliceosomes.
13.2 Ribosomes and
The sequence of bases in mRNA serve as
instructions for the order of amino acids to
produce proteins (polypeptides).
Steps of Translation:
1. mRNA transcribed
from DNA moves to
2. mRNA attaches to a
3. As mRNA moves
acid is attached
to the growing
This is the job
4. A peptide bond
forms between the
until the ribosome
reaches a stop
releases the amino
The Genetic Code
RNA contains 4 bases: adenine, uracil, cytosine,
These 4 letters code for 20 amino acids.
The code is read 3 letters at a time.
Each group of 3 letters is known as a codon.
Separate the following mRNA
sequence into codons:
The codon AUG can serve as a “start” codon for
protein synthesis (Methionine).
There are also 3 “stop” codons which act like a
period at the end of a sentence.