Gene ExpressionGene Expression

• Instructions for proteins are in Instructions for proteins are in nucleotidenucleotide sequence of genessequence of genes

• (2) different types of RNA (2) different types of RNA molecules read instructions molecules read instructions and put together and put together amino acids amino acids that make up the that make up the proteinprotein

• Process by which proteins are Process by which proteins are made is based on information made is based on information in DNA = in DNA = Gene ExpressionGene Expression

• What differences / What differences / similarities can you similarities can you observe in the observe in the pictures below?pictures below?• Why are there Why are there differences?differences?

Transcription: DNA to RNATranscription: DNA to RNA

• RNA polymerase RNA polymerase adds complementary nucleotides adds complementary nucleotides starting at the gene’s starting at the gene’s promoterpromoter regionregion (start signal) (start signal) during during TranscriptionTranscription

• 1.1. RNA pol. RNA pol. binds to the promoterbinds to the promoter• 2. 2. RNA polRNA pol. unwinds and separates the double helix. unwinds and separates the double helix• 3. 3. RNA polRNA pol. Moves along the nucleotides of DNA . Moves along the nucleotides of DNA

adding complementary bases,adding complementary bases, AU AU and and CGCG• RNA pol. continues until it reaches (stop signal)RNA pol. continues until it reaches (stop signal)• RNA pol. Is released along with RNA pol. Is released along with RNA moleculeRNA molecule

Transcription vs. Replication Transcription vs. Replication FeaturesFeatures

RNARNA• Uses Uses (1) strand of DNA(1) strand of DNA as a as a

template for making RNA template for making RNA during during TranscriptionTranscription

• TranscriptionTranscription occurs in occurs in cytoplasmcytoplasm of of prokaryotic prokaryotic cellscells

• Transcriptions occurs in Transcriptions occurs in nucleusnucleus of of eukaryotic cellseukaryotic cells

• ManyMany RNA molecules are RNA molecules are made from a made from a (1)(1) gene gene

DNADNA• Uses Uses (2) strands of DNA (2) strands of DNA as a as a

template during template during DNA DNA ReplicationReplication

• ReplicationReplication occurs in occurs in cytoplasmcytoplasm of of prokaryotic prokaryotic cellscells

• Replication occurs in Replication occurs in nucleus nucleus of of eukaryotic cellseukaryotic cells

• (2) Identical (2) Identical DNA copies DNA copies made from made from (1) DNA(1) DNA

REVIEWREVIEW

• 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 Genetic Code In Three-Nucleotide WordsWords

• Different types of RNA are made during Different types of RNA are made during TranscriptionTranscription

• mRNAmRNA is made when a cell needs a particular is made when a cell needs a particular proteinprotein

• Messenger RNA Messenger RNA ((mRNAmRNA) carries instructions for ) carries instructions for making a protein and delivers it to the site of making a protein and delivers it to the site of TranslationTranslation

• QuestionQuestion: When is mRNA made and what is its : When is mRNA made and what is its function?______________________________function?______________________________

INSTRUCTIONSINSTRUCTIONS• RNA instructions RNA instructions are written as series of are written as series of (3)(3)

nucleotide sequences nucleotide sequences on the on the mRNAmRNA called called codons codons exex. . UAAUAA, , UGAUGA, , AUGAUG

• Each codon in mRNA corresponds to an Each codon in mRNA corresponds to an a.acida.acid or codes for aor codes for a start start or or stopstop signal for signal for translationtranslation

• Nirenberg deciphered the first codon, UUU.Nirenberg deciphered the first codon, UUU.• UUUUUU in mRNA = the a.acid in mRNA = the a.acid phenylalaninephenylalanine• QuestionQuestion: : What are codons and who What are codons and who

discovered them?_______________________discovered them?_______________________

Genetic CodeGenetic Code

• Sequence of nucleotides Sequence of nucleotides that specifies the that specifies the a.acid sequence of proteins and thea.acid sequence of proteins and the start start and and stopstop signals in mRNA. signals in mRNA.

• There areThere are 64 64 mRNA codonsmRNA codons• Many of the codons code for the same a. Many of the codons code for the same a.

acids. acids. • QuestionQuestion: : What is the genetic code and how What is the genetic code and how

many codons does it contain? _____________many codons does it contain? _____________

Many RNAS Are Used to Many RNAS Are Used to Make a ProteinMake a Protein

• 1. 1. Transfer RNA Transfer RNA (tRNA): (tRNA): Single strands Single strands of RNA that of RNA that temporarily carries a temporarily carries a specific specific a.acid a.acid at one end at one end and an and an anticodonanticodon ( (3 3 nucleotide sequence that nucleotide sequence that binds to complementary binds to complementary codoncodon in in mRNAmRNA) ) at the at the other end.other end.

• QuestionQuestion: What (2) structures : What (2) structures do tRNA molecules carry?do tRNA molecules carry?_______ and ________________ and _________

tRNA molecule and Ribosomal RNA moleculetRNA molecule and Ribosomal RNA moleculeAnticodon (UAC) Anticodon (UAC) on tRNA binds to on tRNA binds to codon (AUG) codon (AUG) on on mRNAmRNAAmino acid Amino acid Methionine (Met) Methionine (Met) is carried on top of is carried on top of tRNAtRNA

ReviewReview• 1. What is the first step in Transcription?. What is the first step in Transcription?• 2. If there was a mutation in the promoter sequence, what 2. If there was a mutation in the promoter sequence, what

would happen to protein production?would happen to protein production?• 3. What is the codon sequence for the amino acid sequence:3. What is the codon sequence for the amino acid sequence:• Isoleucine-Valine-Glycine-Serine-Alanine ?Isoleucine-Valine-Glycine-Serine-Alanine ?• 4. What is the a.acid sequence for the codon sequence: AUG-4. What is the a.acid sequence for the codon sequence: AUG-

CCA-CAA-AAG-UUA ?CCA-CAA-AAG-UUA ?• 5. What structures are carried by tRNA? 5. What structures are carried by tRNA? • Who diciphered the first codon and what a.acid did it contain Who diciphered the first codon and what a.acid did it contain

the instructions for?the instructions for?

Ribosomal RNA and TranslationRibosomal RNA and Translation

• RNA molecules RNA molecules that contain RNA and are part that contain RNA and are part of the structures of of the structures of Ribosomes Ribosomes = = Ribosomal Ribosomal RNA (rRNA)RNA (rRNA)

• CytoplasmCytoplasm contains thousands of contains thousands of ribosomesribosomes composed of (composed of (22) subunits; ) subunits; large large and and smallsmall

• Each one can temporarily hold Each one can temporarily hold (1) mRNA (1) mRNA and and (2) tRNA(2) tRNA

Assembling ProteinsAssembling Proteins• 1. Ribosome subunits, 1. Ribosome subunits, mRNAmRNA and and tRNAtRNA carrying the a.acid carrying the a.acid

MethionineMethionine bind together at P site of ribosome bind together at P site of ribosome• 2. tRNA with the a.acid specified by the codon in the A site 2. tRNA with the a.acid specified by the codon in the A site

arrivesarrives• 3. 3. Peptide bonds Peptide bonds forms between adjacent a.acids.forms between adjacent a.acids.

• 44.. tRNA tRNA in the in the P site P site detaches and leaves the a.acid behinddetaches and leaves the a.acid behind• 5. The 5. The tRNAtRNA in the A site moves to the P site. The tRNA in the A site moves to the P site. The tRNA

carrying the a.acid specified by the mRNA codon arrives to carrying the a.acid specified by the mRNA codon arrives to the the A siteA site

• A peptide bond forms between adjacent a.acids A peptide bond forms between adjacent a.acids repeat steps repeat steps 4-5 until stop codons of: UAG, UAA or UGA is reached4-5 until stop codons of: UAG, UAA or UGA is reached

TranslationTranslation• http://

www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/protein_synthesis/protein_synthesis.html

• http://www.hippocampus.org/Biology;jsessionid=00CCE1F5BD67C4889DBB76E3C3A0C27D

• Animation of the Translation Process.

Bell Ringer Bell Ringer 04/01/200904/01/2009

1.1.What is the total number of What is the total number of mRNA codons? mRNA codons? pg.209pg.2092.2.What is the common What is the common features among all RNA features among all RNA molecules? molecules? 3.3.RNA instructions are written RNA instructions are written in a series of 3 nucleotide in a series of 3 nucleotide sequences called__________ sequences called__________ pg. 209pg. 2094.4.What molecules do tRNA What molecules do tRNA carry? carry? pg. 210pg. 210

Prokaryotic Gene RegulationProkaryotic 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.coliGene 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 offTurning 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

Transcription DiagramTranscription Diagram

Point Mutations and PhysiologyPoint Mutations and Physiology

Mutations ContinuedMutations Continued