DNA and Protein Synthesis
• DNA contains the genetic information to
make amino acids
• Amino acids combine to make proteins
• These proteins determine the physical traits
of an organism and control cellular functions.
• Proteins do everything,
and DNA gets all the
credit!
• Think of them as tiny minions
who do all the work
DNA and Protein Synthesis
DNA and Protein Synthesis
• Codon: three bases code for a specific protein:
ex: AAA = Lysine
• The codons code for 20 amino acids
• Just like the alphabet has 26 letters to make all
the words we know, the 20 amino acids make
all the different proteins found in living
organisms
• The codons are the template for protein synthesis,
which takes place on the ribosomes (rRNA) in the
cytoplasm
DNA and Protein Synthesis – Codons and amino acids
Name the
Amino
Acid:
UAU
Tyrosine
CCG
Proline
AGU
Serine
GCA
Alanine
DNA and Protein Synthesis
But… How does the
information get from the DNA
to the cytoplasm?
mRNA
Messenger RNA (mRNA) carries the DNA message out
into the cytoplasm where protein synthesis takes place.
DNA and Protein Synthesis - Transcription
Transcription:
1) DNA unzips
2) mRNA (messenger ribonucleic acid) copies info
from DNA using base pairings
•
RNA is different from DNA
a) Single stranded, not double stranded
b) Instead of deoxyribose, it has ribose
c) instead of Thymine, it uses Uracil
3) Carries the genetic code from the nucleus to the
ribosome in the cytoplasm
DNA and Protein Synthesis - Translation
Translation:
1) rRNA (ribosomal RNA) attaches to mRNA and
starts reading the codons
2) tRNA (transfer RNA) – carries amino acids and
attaches them to the growing protein chain
3) When protein production is complete, the
ribosome releases the protein chain
DNA and Protein Synthesis - Summary
DNA and Protein Synthesis
Practice making mRNA using the DNA template
A T T A C A
C U A A U G U
mRNA
DNA and Protein Synthesis
• Amino acids are linked together in the same
order as the codons , creating a protein chain
• Just like linking letters to make words, linking
amino acids makes proteins
mRNA
CUA AUG UGC
Amino
Acid
Amino
Acid
Amino
Acid
Translation
Translation begins when a
ribosome attaches to an
mRNA molecule in the
cytoplasm.
As the ribosome reads each
codon of mRNA, it directs
tRNA to bring the specified
amino acid into the ribosome.
One at a time, the ribosome
then attaches each amino acid
to the growing chain.
Translation
Each tRNA molecule carries just
one kind of amino acid.
In addition, each tRNA molecule
has three unpaired bases,
collectively called the
anticodon—which is
complementary to one mRNA
codon.
The tRNA molecule for
methionine has the anticodon
UAC, which pairs with the
methionine codon, AUG.
Translation
The ribosome has a second
binding site for a tRNA molecule
for the next codon.
If that next codon is UUC, a
tRNA molecule with an AAG
anticodon brings the amino acid
phenylalanine into the
ribosome.
Translation
The ribosome helps form a
peptide bond between the first
and second amino acids—
methionine and phenylalanine.
At the same time, the bond
holding the first tRNA molecule
to its amino acid is broken.
Translation
That tRNA then moves into a
third binding site, from which it
exits the ribosome.
The ribosome then moves to
the third codon, where tRNA
brings it the amino acid
specified by the third codon.
Translation
The polypeptide chain
continues to grow until the
ribosome reaches a “stop”
codon on the mRNA
molecule.
When the ribosome reaches
a stop codon, it releases both
the newly formed polypeptide
and the mRNA molecule,
completing the process of
translation.
DNA and Mutations
Mutations are any changes that take place in DNA:
• Can be spontaneous or caused by mutagens
• ex: Chemicals, high temperatures, UV light,
radiation
• Can change the genetic code, and be replicated
when forming new body cells.
• In sex cells, can be passed on to offspring.
• Mutations can be neutral, beneficial, or harmful
• ex: Blue eyes – a mutation that occurred 610,000 years ago, can be traced back to one
ancestor
• what kind of mutation is that?
DNA and Mutations – Lets looks at different mutations
THE DOG BIT THE CAT
DNA and Mutations - Substitution
THE DOG BIT THE CAT
• Substitution - Replace just one letter:
THE DOG BIT THE CAR
DNA and Mutations - Deletion
THE DOG BIT THE CAT
• Deletion: Delete just one letter (T):
THE DOG BIT HEC AT
DNA and Mutations-Insertions
THE DOG BIT THE CAT
• Insertion - Add just one letter (E):
THE DOE GBI TTH ECA T
Cells have “proof reading” proteins that constantly
check the DNA and fix errors, so most are corrected