Transcription & Translation November 21 - 25, 2012

WARM UP…What are the differences between DNA & RNA?

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 November 21 - 25, 2012

*Baking a Cake Analogy

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 November 21 - 25, 2012

Transcription

Transcription & Translation November 21 - 25, 2012

TranscriptionHow 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 CodeWhat 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

TranslationWhat 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 DNARNA 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

oEach 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 anti-codon 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 chaino 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 November 21 - 25, 2012

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 November 21 - 25, 2012

K.I.S.S. it!!!