1. Describe how genetic information is transcribed into sequences of bases in RNA molecules and is finally translated into sequences of amino acids in proteins 2. Explain how restriction enzymes cut DNA molecules into smaller fragments and how ligases reassemble them 3. perform simulations to demonstrate the replication of DNA and the transcription and translation of its information

Gene ExpressionTranscription/Translation

Protein Synthesis

Amino Acids● Frederick Sanger 1952:

- proteins consist of sequence of molecules called amino acids - specific sequence of amino acids determines chemical properties of each protein - proteins produced by cell determine structure, function & development of cell

● Sequence of base pairs in DNA makes up genetic code of organism

● Genetic code determines how amino acids strung together (how proteins are made)

Genetic Code● In a gene: each set of 3 bases is a CODON ● Genetic code always interpreted in terms of mRNA codon

rather than original DNA sequence ● Each mRNA codon codes for a specific amino acid ● Only 20 amino acids found in proteins, depend on

combination of bases in codon - 4 bases, 3 in codon = 64 possible different combinations for the 20 different amino acids - therefore some amino acids have more than one codon

● Start and stop codons initiate or terminate protein synthesis

Ex) A U G C U U A A A G C C U G A

Gene Expression● Way information in a gene is converted into a specific trait

through production of a polypeptide (protein)- products of all genes = polypeptides

● RNA utilized to convert genes into proteins - messenger RNA (mRNA)- transfer RNA (tRNA)- ribosomal RNA (rRNA)

● 2 stages of gene expression: transcription and translation ● Transcription: genetic information converted from DNA

sequence into mRNA, carries information from nucleus to cytoplasm

● Translation: genetic information from mRNA used to synthesize polypeptide chains of specific amino acids

Gene Expression● Central Dogma: 2 step process of transferring genetic

information from DNA to RNA (transcription), then from RNA to protein (translation)

Protein Synthesis Rap

Transcription Overview● DNA sequence copied (transcribed) into the sequence of a

single stranded mRNA molecule ● THREE PROCESSES:

1. Initiation: RNA polymerase binds to DNA at specific site near beginning of gene2. Elongation: RNA polymerase uses DNA as template to build mRNA molecule3. Termination: RNA polymerase passes the end of gene and stops

● mRNA then released from template strand ● Carried through nuclear pores, into cytoplasm of cell

Transcription – Initiation ● Only one strand of the double-stranded DNA is transcribed

for each gene- template strand: one that is transcribed - either strand can serve as the template strand for different genes

● RNA polymerase binds to segment of DNA - opens double helix - binds in front of gene to be transcribed, region called the promoter

● Promoter sequence: contains A & T bases, recognition site for RNA polymerase

Transcription - Elongation● DNA strand to be transcribed =

template ● RNA polymerase moves along

template strand of DNA and begins building mRNA in 5’ to 3’ direction

● Promoter not transcribed ● mRNA strand complementary

to DNA template strand EXCEPT thymine is replaced with URACIL

Transcription - Termination● RNA polymerase reaches end of gene ● Termination sequence: RNA polymerase recognizes it as

end ● Transcription stops, mRNA disconnects from DNA

template strand ● RNA polymerase free to bind to another promoter region

- transcribe another gene ● mRNA free and diffuses out of nucleus into cytoplasm

ReviewTranscription

Translation Overview● mRNA now in the cytoplasm needs to

be translated - puts amino acids together according to genetic information and creates proteins

● Ribosomes: site of translation - composed of 2 subunits: clamp together around mRNA, moves along mRNA

● THREE PROCESSES: 1. Initiation 2. Elongation 3. Termination

Translation - Initiation● Occurs when ribosome recognizes specific sequence on mRNA

– binds to it ● Ribosome moves along mRNA in 5’ to 3’ direction

- adds amino acids to polypeptide chain once it reads a codon ● Must start reading in correct spot on mRNA

- START codon (AUG)- ensures ribosome translates code using reading frame of mRNA molecule- results in correct sequence of amino acids

● Transfer RNA (tRNA) carries amino acids back to ribosome ● structure of tRNA contains an ANTICODON

- complementary to codon of mRNA - tells tRNA which amino acid to bind to - amino acid binds to opposite end - tRNA delivers amino acid to ribosome

tRNA Structure

Translation - Elongation● Start codon recognized by ribosome

- codes for methionine ● 2 sites for tRNA to attach

- A (aminoacyl) - P (peptidyl)

● tRNA with anticodon complementary to start codon enters P site

● Next tRNA carrying required amino acid enters the A site- peptide bond formed between both amino acids

● Ribosome shifts over one codon so that SECOND tRNA is now in P site

● Released first tRNA from P site and allowed THIRD tRNA to enter empty A site- like a tickertape!

● Released tRNA’s recycled back into cytoplasm

Translation - Termination● Ribosome reaches one of THREE STOP CODONS

- UGA, UAG, UAA ● Do not code for an amino acid, no corresponding tRNA’s ● Protein release factor recognizes that ribosome has stalled

and helps release polypeptide chain from ribosome ● TERMINATION. ● Translation ● Transcribe & Translate!