Protein SynthesisProtein Synthesis

DNA is transcribed into Messenger RNA. Messenger RNA is translated into Protein

GoalsGoals

• Compare the structure of RNA with that of DNA

• Summarize the process of transcription• Relate the role of codons to the

sequence of amino acids after translation

Are Genes and Enzymes Related?Are Genes and Enzymes Related?

• In 1909,Archibald Garrod “suggested” that genes dictate phenotypes through enzymes.Garrod's One Gene-One Enzyme Hypothesis (click the link)

• In 1936 Beadle & Ephrussi supported Archibald’s ideas with research concerning fruit fly eye color. http://www.genetics.org/cgi/reprint/22/1/76.pdf

One Gene – One EnzymeOne Gene – One Enzyme

• 1941 George Beadle and Edward Tatum experimented with the bread mold, Neurospora crasa.

• They showed that a single gene mutation could result in a single enzyme deficiency.Genome News Network - Timeline: 1941. (Click the Link to Learn More.)

Current HypothesisCurrent Hypothesis• One gene directs the synthesis of a

single polypeptide.

ONE GENE = ONE POLYPEPTIDE

Central DogmaCentral Dogma

TranscriptionTranscription

TranscriptionTranscription

• RNA molecules-Nucleic acids made of linked nucleotides

• Different How?• Single stranded, not double• Ribose instead of Deoxyribose• Contain Uracil instead of Thymine

TranscriptionTranscription

• Transcription-When the instructions for making a protein are transferred from a gene to an RNA molecule

• Translation-When instructions on an RNA molecule are read and coded as proteins

The Stages of TranscriptionThe Stages of Transcription

1) RNA polymerase binds to the promoter and unwinds the DNA and begins RNA synthesis.

2) RNA polymerase adds RNA nucleotides to the template strand of DNA in a 5’ to 3’ direction.

3) RNA polymerase transcribes the terminator sequence which signals the process to end. The RNA is then released.

TranscriptionTranscription

• The DNA molecule unzips • One side of the DNA acts as a template

for making RNA• At the end, the RNA is unzipped from the

DNA • Portions called introns are taken out. • Portions called exons are spliced

together

• http://www.youtube.com/watch?v=ztPkv7wc3yU&feature=related&safety_mode=true&persist_safety_mode=1&safe=active

Transcription to translationTranscription to translation

• RNA is transcribed on the DNA in the nucleus

• mRNA is translated in the cytoplasm

RibosomeRibosome

• The ribosome is made of two subparts

• The ribosome becomes attached to the mRNA

• After a tRNA has given up its amino acid it breaks off and goes back into the cytoplasm to find another amino acid

Messenger RNAMessenger RNA

• The long form of RNA is called messenger RNA (mRNA)

• The mRNA leaves the nucleus and goes into the cytoplasm

• The mRNA lies along an endoplasmic reticulum

mRNAmRNA

• mRNA has thousands of nitrogenous bases

• The bases are divided into 3 base words called codons

• The mRNA becomes attached to a ribosome

• The ribosome moves along the mRNA and allows tRNA to join onto the codons

TranslationTranslation

• Process by which the proteins in our body are coded for

TranslationTranslation

• Genetic Code-codes that give us the proteins in our body, this is based on three letters• How many three letter words can be made

from the letters A, R, E, and T

• A tRNA molecule consists of a strand of about 80 nucleotides that folds back on itself to form a three-dimensional structure.• It includes a loop containing the anticodon and

an attachment site at the 3’ end for an amino acid.

Transfer RNA (tRNA)Transfer RNA (tRNA)

• tRNA molecules find a specific amino acid within the cytoplasm

• tRNA molecules have an anticodon on their ends.

• tRNA takes its amino acid to a specific codon on the mRNA

• Each ribosome has a binding site for mRNA and three binding sites for tRNA molecules.• The P site holds the tRNA carrying the

growing polypeptide chain.• The A site carries the tRNA with the next

amino acid.• Discharged tRNAs leave the ribosome at the E

site.

• Initiation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits.• First, a small ribosomal subunit binds with

mRNA and a special initiator tRNA, which carries methionine and attaches to the start codon.

• Initiation factors bring in the large subunit such that the initiator tRNA occupies the P site.

• The three steps of elongation continue codon by codon to add amino acids until the polypeptide chain is completed.

• Termination occurs when one of the three stop codons reaches the A site.

Translation Steps….#1Translation Steps….#1

• mRNA leaves the nucleus and enters cytoplasm

• Methionine is always the first amino acid

• Start codon is AUG• tRNA molecule binds methionine to

AUG codon

Step #2Step #2

• Codon in A site of ribosome is ready to receive the next tRNA

• tRNA with the complementary anticodon arrives and binds to the codon with the right amino acid

Step #3Step #3

• A and P site are holding tRNA molecules

• Enzymes bind the adjacent amino acids together

Step #4Step #4

• tRNA goes to the E site, where it detaches to go get another amino acid

Step #5Step #5

• tRNA in the A site moves over and fills the empty P site

• Because the A site is open another tRNA brings an amino acid and bonds to the growing protein

Step #6Step #6

• tRNA goes to E site and exits

Step #7Step #7

• Steps 2 through 6 are repeated until a stop codon is reached

• Stop codons-UAG, UAA, UGA• Newly made protein is released into the

cell

• http://www.youtube.com/watch?v=-zb6r1MMTkc&NR=1&safety_mode=true&persist_safety_mode=1&safe=active

• http://www.youtube.com/watch?v=41_Ne5mS2ls&safety_mode=true&persist_safety_mode=1&safe=active

Gene Regulation and StructureGene Regulation and StructureGoalsGoals• Describe how the lac operon is turned

on or off• Summarize the role of transcription

factors in regulation eukaryotic gene expression

• Describe how eukaryotic genes are organized

RegulationRegulation

• Both prokaryotic and eukaryotic cells are able to control which genes are expressed and which are not

RegulationRegulation

• Operator-The piece of DNA that overlaps the promoter site and serves as the on-off switch

RegulationRegulation

• In Bacteria• Genes that code for enzymes involved in

the same function, their promoter site and operator is called the OPERON

• Lac Operon-controls the metabolism of lactose

RegulationRegulation

• Repressor-a protein that binds to an operator and physically blocks RNA polymerase from binding to a promoter site