RNA and Protein Synthesis
Protein Synthesis
Protein Synthesis is the process that cells use to produce
protein.
- it involves 2 distinct phases
Transcription – occurs in the nucleus
involves the creation of mRNA
Translation – occurs in the cytoplasm
at a ribosome – the protein recipe is “read” and the
correct protein is made

Proteins are chains of amino acids
amino acid + amino acid + amino acid = protein
The order of amino acids determines protein
shape
Shape determines function
DNA recipe consists of the order of amino acids
for each protein
- the recipes are known as genes
Recipe has to get from DNA to the
ribosome which builds the protein
Transcription: makes a copy of the protein
recipe
This is necessary because:
 DNA cannot leave the nucleus!!!
 Proteins are made on ribosomes in the
cytoplasm.
mRNA provides the solution


Messenger ribonucleic acid
mRNA is a copy of the protein recipe that can leave
the nucleus
Knowledge Check
• How do transcription and translation work
together to produce proteins?
• What is necessary for protein synthesis to
occur?
• CRITICAL THINKING: What is the one time
when DNA does leave the nucleus? (It is not in
strands that can be copied at this time)
• The Structure of RNA
– There are three main differences between RNA
and DNA:
• The sugar in RNA is ribose instead of deoxyribose.
• RNA is generally single-stranded.
• RNA contains uracil in place of thymine.
Types of RNA
• There are three main types of RNA:
– messenger RNA
– ribosomal RNA
– transfer RNA
Messenger RNA (mRNA) carries copies of
instructions for assembling amino acids into
proteins, leaving the nucleus and traveling to
the ribosome
Ribosomes are made up of proteins
and ribosomal RNA (rRNA).
During protein construction, transfer RNA
(tRNA) transfers each amino acid to the
ribosome.
Critical Thinking
• Based on their descriptions, hypothesize why
you think each type of RNA is required for
proteins synthesis to occur.
Transcription: Initiation
The Process Begins


The enzyme RNA polymerase finds the
beginning of a protein recipe called the
promoter
- promotor = a series of nucleotides that
indicate the start of a protein recipe
The RNA polymerase opens the DNA
molecule at the promoter
Transcription: Initiation
 The
RNA polymerase uses one DNA strand as
a template to build the mRNA
- only one of the DNA strands contains the
protein recipe
- the strand with the recipe is the
template strand
- the strand without the recipe is
the non-template strand
- it is not copied
Ho
Transcription: Elongation
Building the mRNA Molecule
• RNA polymerase brings RNA nucleotides to
the template strand
-pairs them with their complements on
the original DNA molecule
-this follows the base pairing rules
except that uracil replaces thymine
- Adenine on DNA is paired with Uracil (U)
on the new mRNA
Transcription: Termination
The Process Ends
the RNA polymerase continues to add new
nucleotides until it reaches the terminator
- the terminator is a sequence of nucleotides
that indicates the end of the recipe
 the mRNA drops off the DNA
-this is pre-mRNA it needs further

processing before it can be translated
Knowledge Check
• How does RNA polymerase assist in
transcription?
• What role does the promoter play?
• Summarize the major steps of transcription
(you should have at least 3)
RNA Editing
• Introns – segments of nucleotides not
involved in coding for proteins
• Exons – DNA sequences that code for proteins
• Introns get cut out and exons get spliced
(added) together
Transcription
Genetic Code
• The genetic code is the “language” of mRNA
instructions.
• The code is written using four “letters” (the
bases: A, U, C, and G).
• A codon consists of three consecutive
nucleotides on mRNA that specify a particular
amino acid.
The Genetic Code
• “Start” codon – AUG (methionine)
• 3 “stop” codons – do not code for amino
acids; signify the end of a protein molecule
Knowledge Check
• What is the amino acid for AUC?
• What is the amino acid for CUG?
• Explain (in words) how you determine the
amino corresponding to each codon.
Translation Overview
Translation
• Translation is the decoding of an mRNA
message into a polypeptide chain (protein).
• Translation takes place on ribosomes.
• During translation, the cell uses information
from messenger RNA to produce proteins.
Translation
1. mRNA molecule attaches to a ribosome
2. As each codon of the mRNA molecule moves
through the ribosome, the proper amino acid
is brought to the ribosome by the tRNA
3. In the ribosome, the amino acid is
transferred to the growing protein molecule
Translation
• Each tRNA molecule carries only one kind of
amino acid
• Each tRNA has 3 unpaired bases
– Anticodon – complementary to the one mRNA
codon
Knowledge Check
• Where does translation occur?
• Summarize the major steps of translation (you
should have at least 3).
• Critical Thinking: How does the anti-codon
relate to the original DNA template strand?
The ribosome binds new tRNA molecules and
amino acids as it moves along the mRNA,
beginning with the “start” codon
The process continues until the ribosome reaches a
stop codon.
DNA
mRNA
Protein