RNA nucleotides are added and linked via covalent bonds. Behind the RNA pol. the DNA close, reforming the double helix.
• Instructions for proteins are inGene Expression nucleotide sequence of genes • (2) different types of RNA• What differences / molecules read instructionssimilarities can you and put together amino acidsobserve in the that make up the proteinpictures below? • Process by which proteins are• Why are theredifferences? made is based on information in DNA = Gene Expression
Transcription: DNA to RNA• RNA polymerase adds complementary nucleotides starting at the gene’s promoter region (start signal) during Transcription• 1. RNA pol. binds to the promoter• 2. RNA pol. unwinds and separates the double helix• 3. RNA pol. Moves along the nucleotides of DNA adding complementary bases, AU and CG• RNA pol. continues until it reaches (stop signal)• RNA pol. Is released along with RNA molecule
Transcription vs. Replication Features RNA DNA• Uses (1) strand of DNA as a • Uses (2) strands of DNA as a template for making RNA template during DNA during Transcription Replication• Transcription occurs in • Replication occurs in cytoplasm of prokaryotic cytoplasm of prokaryotic cells cells• Transcriptions occurs in • Replication occurs in nucleus of eukaryotic cells nucleus of eukaryotic cells• Many RNA molecules are • (2) Identical DNA copies made from a (1) gene made from (1) DNA
REVIEW• 1. Outline the steps for the process of going from DNA to proteins.• 2. What are three features of DNA and RNA?• 3. What are proteins made of?• 4. What biochemical structures within the body enable you to have unique features?• 5. What is the Central Dogma of DNA?• 6. List the steps of Transcription.• 7. What are two features of replication of DNA and transcription of RNA?
Genetic Code In Three-Nucleotide Words• Different types of RNA are made during Transcription• mRNA is made when a cell needs a particular protein• Messenger RNA (mRNA) carries instructions for making a protein and delivers it to the site of Translation• Question: When is mRNA made and what is its function?______________________________
INSTRUCTIONS• RNA instructions are written as series of (3) nucleotide sequences on the mRNA called codons ex. UAA, UGA, AUG• Each codon in mRNA corresponds to an a.acid or codes for a start or stop signal for translation• Nirenberg deciphered the first codon, UUU.• UUU in mRNA = the a.acid phenylalanine• Question: What are codons and who discovered them?_______________________
Genetic Code• Sequence of nucleotides that specifies the a.acid sequence of proteins and the start and stop signals in mRNA.• There are 64 mRNA codons• Many of the codons code for the same a. acids.• Question: What is the genetic code and how many codons does it contain? _____________
• 1. Transfer RNA (tRNA):Many RNAS Are Used toMake a Protein Single strands of RNA that temporarily carries a specific a.acid at one end and an anticodon (3 nucleotide sequence that binds to complementary codon in mRNA) at the other end. • Question: What (2) structures do tRNA molecules carry? _______ and _________
tRNA molecule and Ribosomal RNA moleculeAnticodon (UAC) on tRNA binds to codon (AUG) onmRNAAmino acid Methionine (Met) is carried on top oftRNA
Review• 1. What is the first step in Transcription?• 2. If there was a mutation in the promoter sequence, what would happen to protein production?• 3. What is the codon sequence for the amino acid sequence:• Isoleucine-Valine-Glycine-Serine-Alanine ?• 4. What is the a.acid sequence for the codon sequence: AUG- CCA-CAA-AAG-UUA ?• 5. What structures are carried by tRNA?• Who diciphered the first codon and what a.acid did it contain the instructions for?
Ribosomal RNA and Translation• RNA molecules that contain RNA and are part of the structures of Ribosomes = Ribosomal RNA (rRNA)• Cytoplasm contains thousands of ribosomes composed of (2) subunits; large and small• Each one can temporarily hold (1) mRNA and (2) tRNA
Assembling Proteins• 1. Ribosome subunits, mRNA and tRNA carrying the a.acid Methionine bind together at P site of ribosome• 2. tRNA with the a.acid specified by the codon in the A site arrives• 3. Peptide bonds forms between adjacent a.acids.• 4. tRNA in the P site detaches and leaves the a.acid behind• 5. The tRNA in the A site moves to the P site. The tRNA carrying the a.acid specified by the mRNA codon arrives to the A site• A peptide bond forms between adjacent a.acids repeat steps 4-5 until stop codons of: UAG, UAA or UGA is reached
• http://www.brookscole.co Translation m/chemistry_d/templates/• Animation of the student_resources/shared_Translation resources/animations/protProcess. ein_synthesis/protein_synt hesis.html • http://www.hippocampus.org/Biolo gy;jsessionid=00CCE1F5BD67C4889D BB76E3C3A0C27D
Bell Ringer04/01/20091.What is the total number ofmRNA codons? pg.2092.What is the commonfeatures among all RNAmolecules?3.RNA instructions are writtenin a series of 3 nucleotidesequences called__________pg. 2094.What molecules do tRNAcarry? pg. 210
Prokaryotic Gene Regulation• There are several thousand genes for prokaryotic organisms• There are more than 100,000 genes for eukaryotic organisms.• Not all genes are Transcribed and Translated at the same time.• Organisms are able to regulate (control) which genes are expressed based on the needs of the cell.
Gene Regulation in E.coli• When you eat or drink dairy products, the disaccharide lactose (milk sugar) becomes available to E.coli.• E.coli can break down lactose into (2) sugars, glucose and galactose.• This requires (3) different enzymes which are coded by different genes.
Turning Genes on and off• Lactose metabolizing genes are located next to each other and are controlled by the same promoter site. Fig. 10-6 pg. 213• A control switch (operator) activates transcription when lactose is available and deactivates transcription when it is not available.• The operator is a piece of DNA that overlaps the promoter site (on/off switch)
Lac Operon and Repressors• Operon: Groups of genes that code for enzymes involved in the same function, their promoter site and the operator that controls them.• Repressor proteins bind to an operator and blocks RNA pol. from binding to a promoter site. Fig. 10-6 pg. 213.
Lactose and Repressor Proteins• When lactose is present, it binds to the repressor and causes it to be released from the operator: Transcription occurs• When lactose is not present, repressor remains attached to operator: Transcription does not occur