Transcription and TranslationTranscription and Translation

DNA’s destiny!DNA’s destiny!

What does DNA really do?What does DNA really do? The DNA code must code for something The DNA code must code for something

right??? So what IS IT????right??? So what IS IT???? The DNA alphabet essentially codes for amino The DNA alphabet essentially codes for amino

acidsacids Which are the building blocks for…….Which are the building blocks for…….

PROTEINS!!!!!!!!!!PROTEINS!!!!!!!!!! This occurs in several organized steps IN 2 This occurs in several organized steps IN 2

PHASESPHASES

What is RNA?What is RNA?

From DNA to Protein: the 2 From DNA to Protein: the 2 phasesphases PHASE 1:PHASE 1:

TranscriptionTranscription DNA IS TRANSCRIBED INTO READABLE DNA IS TRANSCRIBED INTO READABLE

FORM (mRNA)FORM (mRNA)

PHASE 2:PHASE 2: TranslationTranslation

mRNA IS TRANSLATED (tRNA) TO CODE mRNA IS TRANSLATED (tRNA) TO CODE FOR AMINO ACIDSFOR AMINO ACIDS

Transcription: The Video ClipTranscription: The Video Clip

Phase 1: TranscriptionPhase 1: Transcription Occurs Occurs INSIDE THE NUCLEUSINSIDE THE NUCLEUS1.1. DNA strands separateDNA strands separate2.2. ComplimentaryComplimentary RNA bases take their RNA bases take their

places along DNA with the help of places along DNA with the help of enzymesenzymes RNA bases are A, C, G, and U (uracil)RNA bases are A, C, G, and U (uracil) U instead of T!U instead of T! This creates an mRNA strandThis creates an mRNA strand

Let’s see this in action!

Phase 1: TranscriptionPhase 1: Transcription Let’s practice making a complimentary mRNA

from a DNA strand!

DNA mRNAC

G

A

T

T

A

G

A

T

G

C

U

A

A

U

C

U

A

Proteins…the ultimate resultProteins…the ultimate result Long chains formed by 20 different Long chains formed by 20 different

amino acidsamino acids Protein shape is determined by DNA Protein shape is determined by DNA

sequence!sequence! DNA transcribed to mRNADNA transcribed to mRNA mRNA is eventually translated by tRNA mRNA is eventually translated by tRNA

(transfer RNA) and codes for amino (transfer RNA) and codes for amino acids!acids!

Protein Synthesis: The Video ClipProtein Synthesis: The Video Clip

Proteins…the ultimate resultProteins…the ultimate result 3 mRNA bases will code for a specific 3 mRNA bases will code for a specific

amino acid.amino acid. Ex. GCU codes for AlanineEx. GCU codes for Alanine This is called a This is called a CODONCODON

Each amino acid has more than one Each amino acid has more than one codon!codon!

Polypeptide: String of amino acids

Let’s look at the mRNA we transcribed Let’s look at the mRNA we transcribed earlier!earlier!

Proteins…the ultimate resultProteins…the ultimate result The strand we made earlier is:The strand we made earlier is: G C U A A U C U A If 3 bases code for an amino acid, how many If 3 bases code for an amino acid, how many

amino acids are coded in our strand?amino acids are coded in our strand?3 of course!3 of course!

G C U | A A U | C U A

Alanine | Asparagine | Leucine

Coding and stringing amino acids together is called TRANSLATION!

The Genetic Code!

Phase 2: TranslationPhase 2: Translation mRNA is shipped out of nucleus for mRNA is shipped out of nucleus for

translationtranslation **Review** Which organelle is in **Review** Which organelle is in

charge of protein synthesis?? (Hint: very charge of protein synthesis?? (Hint: very tiny little buggers)tiny little buggers)

RIBOSOMES!RIBOSOMES! mRNA binds to a ribosome for mRNA binds to a ribosome for

translation!translation!

Phase 2: TranslationPhase 2: Translation1. mRNA binds to ribosome

2. Ribosome translates the codons on the mRNA

3. This signals a tRNA to bring the correct amino acid

4. tRNA drops off the amino acid

Phase 2: TranslationPhase 2: Translation5. Ribosome moves to next

codon6. Another tRNA comes

with next amino acid7. Amino acids are

connected by PEPTIDE BONDS

This continues until all of This continues until all of the mRNA has been read the mRNA has been read and a STOP codon is and a STOP codon is reached.reached.

End result: a End result: a protein!!!!!!!!!protein!!!!!!!!!

Let’s return to the transcription/translation site!