Transcription & Translation
WARM UP…
What are the differences between DNA & RNA?
November 21 - 25, 2012
Transcription & Translation
November 21 - 25, 2012
Transcription & Translation
November 21 - 25, 2012
Why is RNA almost always Single Stranded?
What is the benefit gained from RNA being
Single Stranded?
Transcription & Translation
November 21 - 25, 2012
• Genes are the functional unit of Chromosomes
• Each Chromosome is made of Genes, and
Each Gene is made of Nucleotides
• Gene = Genotype (code); Protein = Phenotype (observable outcome)
Transcription & Translation
November 21 - 25, 2012
How do we go from DNA (information) to Proteins
(outcome)?
• Transcription is the synthesis of RNA, using DNA as a
template
• The RNA strand is the same as one of the DNA strands but has
Uracil instead of Thymine
• The RNA strand that is formed is called messenger RNA (mRNA)
• Translation is the synthesis of Protein (polypeptide),
using RNA as a template
• The mRNA that serves as the template for the new polypeptide
• The RNA strand that forms the new polypeptide is called
messenger transfer RNA (tRNA)
Transcription & Translation
*Baking a Cake Analogy
November 21 - 25, 2012
Transcription & Translation
November 21 - 25, 2012
What are the three types of RNA?
• transfer RNA (tRNA) has a major role in
translation
• ribosomal RNA (rRNA) is a structural and
functional component of ribosomes
• messenger RNA (mRNA) is the “Genetic Code”
that delivers the DNA genetic message to the
Ribosome
Transcription & Translation
Transcription
November 21 - 25, 2012
Transcription & Translation
November 21 - 25, 2012
Transcription
How do we make mRNA from DNA?
• The DNA to be transcribed is separated by Helicase in
the region of the gene to be transcribed
• The enzyme RNA polymerase binds to a site called
the Promoter on the DNA
• RNA nucleotides pair with their complementary bases
on 1 strand of DNA only
• There is NO Thymine in RNA, so Uracil pairs with Adenine
• RNA polymerase forms covalent bonds between the
nucleotides
• The RNA separates from the DNA and the DNA double
helix reforms
Transcription & Translation
November 21 - 25, 2012
Transcription & Translation
November 21 - 25, 2012
Which two processes involve the unwinding
(uncoiling) of the DNA double helix and its separation
into two strands of nucleotides?
A concept map involves drawing lines between
associated concepts, and labeling the lines to show the
relationships between the connected concepts. Create
a concept map that links the following terms:
DNA, nucleotide, mRNA, tRNA, rRNA, protein, amino
acid, ribosome.
Transcription & Translation
November 21 - 25, 2012
The Genetic Code
What is the Genetic Code?
The “translation dictionary” that enables the cellular
machinery to convert the base sequence on the mRNA into
an amino acid sequence is called the genetic code.
What is a Codon and what is an Anti-Codon?
• A sequence of three bases on mRNA is called a codon
• A sequence of three bases on tRNA is called an anti-codon
• Each codon (except for 3) corresponds to a specific tRNA
• Each codon (except for 3) codes for a specific amino acid
• Each amino acid has more than one codon that codes for it
Transcription & Translation
November 21 - 25, 2012
What is meant by the degeneracy of the Genetic Code?
• There are 64 possible codons (4 x 4 x 4)
• Different codons can code for the same amino acid
• For example, the codons GUU and GUC both
code for the amino acid Valine
This is the “degenerate” nature of the Genetic Code…
64 codons = 20 Amino Acids and 3 Stops
So… 64 codons, but only 61 anti-codons (tRNA molecules)
Transcription & Translation
November 21 - 25, 2012
Transcription & Translation
November 21 - 25, 2012
Transcription & Translation
November 21 - 25, 2012
Translation
What is Translation?
The last major step in protein synthesis, wherein the
genetic code (carried by mRNA) is decoded to produce the
specific sequence of amino acids (peptides) that make up a
polypeptide chain
Where does translation take place?
• Translation takes place on organelles called ribosomes
• Each ribosome comprises a small and a large subunit
• Each ribosome is made of rRNA and Proteins
Transcription & Translation
November 21 - 25, 2012
What translates mRNA into Protein?
tRNA is the molecule that translates mRNA’s genetic code into Protein
DNA polymerase replicates new DNA from old DNA
RNA polymerase transcribes DNA into mRNA
tRNA translates mRNA into Protein
Transcription & Translation
November 21 - 25, 2012
How are Proteins translated from mRNA’s genetic code?
INITIATION
• mRNA binds to the small subunit of the ribosome
• tRNA molecules are present
o Each
tRNA has a specific anti-codon on one end, and a specific
amino acid on the other end
• First tRNA binds to the ribosome at the site where its anticodon matches the AUG codon on the mRNA
So… first mRNA codon translated is AUG;
first tRNA anti-codon matched is UAC;
first amino acid on protein is Met (methionine)
Transcription & Translation
November 21 - 25, 2012
ELONGATION
• Second tRNA binds to ribosome (two tRNAs are bound at once)
• The first tRNA transfers its amino acid to the second tRNA
• The ribosome moves along the mRNA, releasing the first tRNA
These steps are then repeated, elongating the polypeptide chain
o 3rd tRNA attaches to ribosome → 2nd tRNA transfers amino acids
to 3rd tRNA→ 2nd tRNA leaves…
o
4th tRNA attaches to ribosome → 3rd tRNA transfers amino acids
to 4th tRNA → 3rd tRNA then leaves…
o
5th tRNA attaches to ribosome → 4th tRNA transfers amino acids
to 5th tRNA → 4th tRNA then leaves… and so on…
Transcription & Translation
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TERMINATION
• The elongation process continues until a stop codon is
reached, then the completed protein (polypeptide) is
released from the ribosome
How can we illustrate the process of Translation?
Transcription & Translation
November 21 - 25, 2012
Transcription & Translation
K.I.S.S. it!!!
November 21 - 25, 2012