2Unit Objectives (Chapter 12-3) By the end of this unit you will:know what transcription isknow what translation isunderstand how proteins are made.
3TranscriptionTranscribing or copying the coded message of DNA onto a single stranded nucleic acid called mRNADNA’s code is contained in groups of 3 nitrogen bases called DNA tripletsOne side of DNA is considered the coding side, or template, and the other side is considered the complimentary side.Left side – coding sideRight side – complimentary strand
4To begin transcription, Helicase causes the molecule to split or “unzip”. This exposes the nitrogen bases of the coding sideFree floating mRNA nucleotides attach to the coding side of DNAThe whole mRNA strand is removed from the coding side of DNAThe mRNA strand then moves out of the nucleus and heads for a ribosome.The DNA strand then can re-attach with the complementary side of DNA
9Here is how we will “do it”! DNA Coding Triplet:ATA CGAmRNA Codons that would be transcribed:UAU GCUAmino Acids:Tyrosine + Alanine
10Summary Transcription is copying the DNA code onto a mRNA molecule. mRNA leaves the nucleus and moves to the ribosome where the message is translatedAUG is called the “Initiation Codon” . It begins the process and always codes for Methionine“Termination Codons” indicate the end of the process. UAG,UAA, and UGA are termination codons and don’t code for any amino acids
11Let’s try Transcription: Assume the sequence of nitrogen bases below represents the coding side of DNA.ACT CCC CGA TACTranscribe the DNA triplets into mRNA codonsDraw the mRNA molecule that would be produced during Transcription.Translate the mRNA molecule into the amino acids it represents. Use your codon wheel.
13Transcription ReviewDNA contains the genetic code for the production of __________.Each group of 3 nitrogen bases in DNA is called a __________.The genetic code of _____ is trapped inside the nucleus because it is ____________ to fit through the pores in the nuclear envelope.__________ is the process of copying the genetic code of _____ onto a single strand of _____.The single stranded _____ molecule falls on it’s side with it’s nitrogen bases pointing _____ and moves out of the nucleus to find a __________.Each group of 3 nitrogen bases in mRNA is called a __________.AUG is a special codon that is called an ________________. It always codes for the amino acid __________.Check you codon wheel and identify the amino acids that the following codons code for:GGC - __________UUU - __________CAU - __________GUA - __________
14Transcription ReviewAnother special codon found in mRNA stops the chain of amino acids and indicates the protein is complete. These codons are called ________________. There are only 3 of the codons: _______; ________ and _______.We are always going to assume that the coding side of DNA will be the __________ side.Opposite the coding side is called the __________ side.Two enzymes play a role in transcription: ____________ unzips the DNA molecule and __________________ helps attach the free-floating mRNA nucleotides to the coding side of DNA.
15Transcription ReviewDNA contains the genetic code for the production of Protein.Each group of 3 nitrogen bases in DNA is called a DNA triplet.The genetic code of DNA is trapped inside the nucleus because it is too big to fit through the pores in the nuclear envelope.Transcription is the process of copying the genetic code of DNA onto a single strand of mRNA.The single stranded mRNA molecule falls on it’s side with it’s nitrogen bases pointing up and moves out of the nucleus to find a ribosome.Each group of 3 nitrogen bases in mRNA is called a codon.AUG is a special codon that is called an Initiation codon. It always codes for the amino acid Methionine.Check you codon wheel and identify the amino acids that the following codons code for:GGC - GlycineUUU - PhenylalanineCAU - HistidineGUA - Valine
16Transcription ReviewAnother special codon found in mRNA stops the chain of amino acids and indicates the protein is complete. These codons are called Termination codons. There are only 3 of the codons: UGA; UAA and UAG.We are always going to assume that the coding side of DNA will be the left side.Opposite the coding side is called the complimentary side.Two enzymes play a role in transcription: Helicase unzips the DNA molecule and RNA polymerase helps attach the free-floating mRNA nucleotides to the coding side of DNA.
17TranslationThe process where the message of mRNA is translated into sequences of amino acids.Translation happens on the surface of ribosomes.3 codons can fit on the ribosome at one time.Remember tRNA?
18tRNA Serine amino acid (specific to tRNA) tRNA molecule nitrogen bases called anticodonsSerine
19tRNA cont…Each tRNA molecule with one specific anticodon sequence can carry only one specific amino acid.If the anticodon of tRNA is complimentary to the codon of mRNA the amino acid carried by that tRNA is dropped off.Protein Synthesis PHLet’s go back to our mRNA molecule. Draw the respective tRNA molecules that would be involved in Translation.
21Activity Use your codon chart to complete the following table: Codon Amino AcidAnticodonDNA tripletAUG (initiation codon)UCCAAACGU
22A few things we need to know… Gene AGene BExons – translatable segments of a chromosomeIntrons – segments of DNA that do NOT code for proteinsNonsense DNAAUG – intiation codonCodes for methionineUAA, UAG, and UGA are all termination codons
23Ribosome Structure “A” Site “P” Site “E” Site Arrival Site First tRNA arrives“P” SitePeptidyl SiteAmino Acids bond together“E” SiteExit siteNaked tRNA goes to find another amino acid“P”Site“A” Site“E” Site
25Protein SynthesisAnother look at Protein Synthesis
26Quiz: Protein Synthesis Assume the strand of DNA nucleotides below represents the coding side .ACT CCA CGA TACDraw the mRNA molecule that would be transcribed.(Value: 4)Draw the three tRNA molecules that would be complimentary to the mRNA molecule you created. Make sure the appropriate amino acid and anti-codon are positioned on the tRNA drawings. (Value: 3)Using you amino acid chart, draw the polypeptide that would be created. (Value:3)
27Mutations Point Mutation: A change in one nitrogen base in DNA. EX: DNA AAA TCT CGAmRNA UUU AGA GCUAmino Acids Phen-Arg-AlaPoint MutationDNA AAA TGT CGAmRNA UUU ACA GCUAmino Acids Phen-Thre- Ala
28``Lucky`` Point Mutation DNA AAA TCT CGAmRNA UUU AGA GCUA.A. Phen-Arg-AlaDNA AAA TCC CGAmRNA UUU AGG GCUA.A. Phen – Arg - Ala
29Frame shift Mutations- Mutation that deletes or adds a nitrogen base pair.- The result impacts the rest of the amino acids in the chainDNA AAA TCT CGAmRNA UUU AGA GCUA.A. Phen – Arg- Ala(Deletion) AA ATC TCG_mRNAA.A. YIKES!