Presentation on theme: "Protein Targetting Prokaryotes vs. Eukaryotes Mutations"— Presentation transcript:
1 Protein Targetting Prokaryotes vs. Eukaryotes Mutations AP BiologyUnit 2
2 Protein TargettingSecretory proteins have molecular tags that help direct them to the ER = signal peptideSignal peptide = sequence of amino acids at beginning of protein that binds to the SRP (signal recognition particle)
3 Protein TargettingRibosome begins translating protein and the amino acids of the signal peptide.Signal peptide is recognized by SRP and bound by it.The SRP and ribosome bind to the receptor on ER.The protein is fed into the ER as it is made.Signal sequence is removed by enzyme inside the ER.Binding the SRP temporarily stops protein synthesis until the ribosome attaches to the ER.Binding the SRP to the complex converts the receptor into a channel protein that feeds into the ER.
4 Protein Synthesis in Eukaryotes Between transcription and translation there is an extra step = RNA ProcessingRNA is modified before it is translatedPre mRNA = the RNA before RNA processing
5 RNA Processing 3 main things happen in RNA processing: Step 1: 5’ (G) cap is addedPoly A tail addedIntrons removedStep 1:Modified G nucleotide is added to the 5’ end of the pre mRNAHelps mRNA bind to ribosomePrevents RNA from being broken down by enzymes
6 RNA ProcessingStep 2:Poly A tail is added to the 3’ end of the pre mRNA ( A nucleotides)NOT the same thing as the termination sequenceHelps direct the mRNA out of the nucleusMakes the RNA more stable
7 RNA Processing Step 3: RNA splicing Introns are noncoding regions (“junk” DNA)Exons are sections that code for part of proteinIntrons are cut out of the pre mRNA and exons are joined together.
8 Question…What kind of molecules are doing all of these tasks (adding poly A tail, cutting out introns, etc.)?Accomplished by many different enzymes
9 Protein Synthesis in Prokaryotes In prokaryotes, translation can start even as transcription is still occurring.What characteristic of prokaryotic cells allows this to happen?Absence of a nucleus– it can all happen in “one room”Prokaryotes and eukaryotes also have slightly different ribosomes
10 Mutations A change in the DNA sequence Could be due to a substitution, insertion or deletion of nucleotide(s)Wildtype = “normal” sequenceNOT a mutation!
11 Point Mutation When a nucleotide is substituted for another one. a variety of things can occur depending on the specific substitution
12 Point Mutation: Silent Mutation DNA sequence changes RNA sequence changes still codes for the same amino acidNo effect on the amino acid sequenceGly
13 Point Mutation: Missense Mutation DNA sequence changes RNA sequence changes codes for a different amino acidCould affect the functioning of the proteinUnder what conditions might the protein not be affected much by a missense mutation?If the amino acid has similar properties as the wild type amino acid (+ charged + charged)Ser
14 Point Mutation: Nonsense DNA sequence changes RNA sequence changes early stop codon introducedTranslation stops Protein is incomplete
15 Frameshift MutationsCaused by the insertion or deletion of nucleotide(s)Can cause nonsense, extensive missense, or the insertion/deletion of single amino acidsWhy would a frameshift mutation cause a protein to lose its function?If primary sequence is wrong, then sequence will also be wrong shape changes function lostNote: book doesn’t call all of these frameshifts, but just make sure the students know the concept of inserting/deleting bases and the effects. Not crucial for them to know the name as much as what is happening.Leu AlaPhe Gly