Transcription Credit for the original presentation is given to Mrs. Boyd, Westlake High School

Choose 3 to discuss with your partner Conversation Starters Choose 3 to discuss with your partner What organelle makes proteins? What are the monomers of proteins? What elements make up proteins? What are the 3 parts of a nucleotide of RNA? In RNA, adenine base pairs with _________. Enzyme names have what ending? Free floating ribosomes make proteins that go where? Bound ribosomes? What are ribosomes made out of?

I. Review: RNA vs. DNA DNA RNA mRNA, tRNA, rRNA, siRNA… transcription Key Differences: ribose sugar N-bases uracil instead of thymine U : A C : G single stranded lots of RNAs mRNA, tRNA, rRNA, siRNA… transcription DNA RNA

A. Central Dogma

A. Central Dogma DNA RNA PROTEIN The CENTRAL DOGMA of molecular biology says that genetic information only goes from DNA in the nucleus to RNA and then to make PROTEINS in the ribosomes.

A. Central Dogma - Part 1: DNA RNA PROTEIN Transcription Genetic information is passed from DNA to RNA by a process called TRANSCRIPTION.

B. Overview of Transcription The process by which genetic information is copied from DNA to mRNA. mRNA carries genetic information from DNA in the nucleus to the ribosomes in the cytosol.

B. Overview of Transcription RNA polymerase: makes mRNA using one strand of DNA. coding strand 3 A G C A T C G T 5 A G A A G C A T T T T C T C A A C G DNA T 3 C G T A A T 5 G G C A U C G U T 3 C unwinding G T A G C A rewinding mRNA RNA polymerase template strand build RNA 53 5

Transcription: making a copy Step 1: RNA Polymerase unwinds DNA A G C T 3’ 5’ RNA polymerase T A T A A G C T A T A T 5’ 3’

Transcription: making a copy Exception to base-pair rule: U instead of T!! Step 2: RNA Polymerase adds nucleotides to mRNA A G C T 3’ 5’ RNA polymerase T A T A U C G A A T A T T C G A mRNA 5’ 3’

Transcription: making a copy Step 3: mRNA leaves the nucleus and DNA returns to double helix A G C T 3’ 5’ T A T A A G C T U C G A mRNA A T A T T C G A 5’ 3’

C. Transcription Practice (Write it down!) DNA: ACTGCGTAA RNA: DNA: CCTGGATAA

QUICK CHECK: Review What is the enzyme called that makes mRNA from DNA? What do you call the process of making mRNA from DNA? ____________

II. Stages of Transcription Bacterial chromosome 2007-2008 Transcription mRNA Psssst… no nucleus! Cell membrane Cell wall

A. Prokaryote vs. Eukaryote genes 1. Prokaryotes DNA in cytoplasm circular chromosome naked DNA no introns 2. Eukaryotes DNA in nucleus linear chromosomes DNA wound on histone proteins introns vs. exons Walter Gilbert hypothesis: Maybe exons are functional units and introns make it easier for them to recombine, so as to produce new proteins with new properties through new combinations of domains. Introns give a large area for cutting genes and joining together the pieces without damaging the coding region of the gene…. patching genes together does not have to be so precise. introns come out! intron = noncoding (inbetween) sequence eukaryotic mRNA exon = coding (expressed) sequence

II. Stages of Transcription STEP 1: INITIATION -RNA polymerase starts making mRNA by binding to specific regions of DNA called promoters. Role of promoter Starting point where to start reading start of gene Template strand which strand to read Direction on DNA always read DNA 35 build RNA 53

II. Stages of Transcription C: STEP 2: Elongation RNA polymerase copies DNA as it unwinds ~20 base pairs at a time 300-500 bases in gene builds RNA 53 reads DNA 35

II. Transcription in Prokaryotes D. STEP 3: Termination RNA polymerase stops at termination sequence

III. Transcription in Eukaryotes: Pre-mRNA The initial mRNA that is made from DNA has segments of introns and exons. When mRNA has both introns and exons, it is called pre-mRNA. Introns: sections of pre-mRNA that do not code for amino acids and are not translated into proteins. Exons: sections of pre-mRNA that code for amino acids and are translated into proteins. Pre-mRNA

While still in the nucleus, the introns that do not code for proteins, are cut out, and the exons are connected. (splicing) Final mRNA strand made of only exons. Finished mRNA leaves the nucleus through the nuclear pores.

IV. Post-Transcription Processing mRNA processing (making mature mRNA) mRNA splicing = edit out introns add methylated G cap add polyA tail 3' poly-A tail 3' A A A A A 5' cap mRNA 50-250 A’s P P P 5' G eukaryotic RNA is about 10% of eukaryotic gene. intron = noncoding (inbetween) sequence ~10,000 bases eukaryotic DNA exon = coding (expressed) sequence pre-mRNA primary mRNA transcript ~1,000 bases mature mRNA transcript spliced mRNA

Functions of poly A tail and 5’ Cap protect mRNA from enzymes in cytoplasm Helps mRNA leave nucleus Helps it bind to ribosome

QUICK CHECK: Review Non coding regions of mRNA that are cut out are called _______________ Regions of mRNA that code for proteins are called _________________

Looking Forward… After the mRNA is made from DNA in the nucleus, where does it go? What are the monomers of proteins called? What organelle makes proteins?

Learning Log: What enzyme is used to make mRNA from DNA? On what region of DNA does it land to begin transcription? in prokaryotes? In eukaryotes? Contrast introns and exons. Why is mRNA necessary for transcription to occur? (why can’t DNA be used)

Translation Credit for the original presentation is given to Mrs. Boyd, Westlake High School

Central Dogma

Central Dogma - Part 2: DNA RNA PROTEIN Genetic information is passed from RNA to PROTEINS made by the ribosomes by a process called TRANSLATION.

A. Translation Overview Using mRNA to make a protein by connecting amino acids together. Occurs at ribosomes outside of the nucleus.

Translation: making a protein But why do we need to translate RNA? The language of DNA and RNA (nucleotides) needs to be translated into the language of proteins (amino acids). PROTEIN A,U,G,C (nucleotides) Pro, met, ser, val, leu, met… (amino acids)

B. Protein Structure Proteins are made up of monomers of amino acids. There are 20 different amino acids that can make up a protein. The sequence of the amino acids determines its shape and function.

C. Codons The genetic information for making proteins encoded in series of three mRNA nucleotides Codons code for a specific amino acid.

QUICK CHECK Codons are found on what type of RNA? Which nucleotide can vary and still code for the correct amino acid? (1st, 2nd, 3rd)

D. Elements of Translation: Start and Stop Codons The start codon (AUG), which also codes for the amino acid methionine (Met), tells a ribosome to start translating an mRNA molecule. Stop codons (UAA, UAG, UGA) cause the ribosome to stop translating the mRNA. An release factor binds to the polypeptide chain and releases it from the ribosome.

E. Steps of Translation 1. Step 1: mRNA leaves the nucleus and goes to the ribosome Ribosome

E. Steps of Translation 2. Step 2: Ribosome looks for sequence that tells it to start translating = AUG ribosome START U C G A

E. Steps of Translation 3. Step 3: Ribosome reads the mRNA strand in triplets called CODONS ribosome START U C G A

E. Steps of Translation 4. Step 4: tRNA leu E. Steps of Translation 4. Step 4: RNAs called tRNAs match codons to AMINO ACIDS and transfers it to growing protein. ribosome START U C G A

QUICK CHECK: Name the three nucleotide sequence that codes for a start codon on mRNA. What type of RNA carries amino acids?

4. tRNA and Anticodons Each tRNA molecule binds to 1 amino acid. Anticodon--a sequence of three nucleotides on tRNA on the end opposite from the amino acid attachment site that pairs with a complementary codon on mRNA

QUICK CHECK: Codons are on what kind of RNA? Anti-codons are on what kind of RNA? Codon: AUG What is the anti codon? Codon: UUU What is the anti codon?

ribosome Met mRNA Do you know what amino acid comes next?

Always use this code with mRNA codons!

Met Ala mRNA

5. Extending the Polypeptide: Ribosomes Ribosomes are composed of (2/3) rRNA and proteins. Ribosomes have three binding sites that are used in translation.

5. Extending the Polypeptide A site: where incoming tRNA’s with amino acids land. P site: where amino acids are joined and polypeptide grows. E site: where tRNA “exits” ribosome and leaves.

Embedded or Secreted proteins All proteins start growing in a free floating ribosome. Signal peptide: (zip code) tells the ribosome to go to the ER, nucleus, chloroplast, mitochondria Recognized by SRP RNA: RNA protein complex that directs ribosome to where it needs to go. Docks to ER SRP (signal recognition particle) Protein can be embedded into ER, signal peptide cleaved

Learning Log: Where does transcription occur? Translation? On which type of RNA do you find codons? Anticodons? Which type of RNA carries amino acids to ribosomes? How many a.acids does each carry? To use the genetic code (codon dictionary), you look at codons found on what type of RNA?