AP Biology Crosby High School From Gene to Protein AP Biology Crosby High School

George Beadle and Edward Tatum Neurospora Crassa Exposed to radioactive X-rays Created mutations in enzymatic pathways Exposed to specific nutrients Would not grow in absence of some nutrients

Beadle and Tatum Experiment

Transcription and Translation DNA  RNA Nucleic acid to nucleic acid Template produces primary transcript Modified to mRNA and exported to ribosome RNA  Protein Nucleic acid to amino acid Occurs at ribosome Creates primary structure of protein

DNA  RNA  PROTEIN

Genetic Code Based on Triplet code Allows for 64 combinations Only 20 amino acids Three nucleotide bases makes a codon Codons complementary to template strand Some redundancy in third base Must be in the proper reading frame

The Genetic Code

Cracking Genetic Code Poly U placed in tube with ribosomes AUG Stop Produced only Phenylalanine (UUU) AUG Start Methionine Stop UAA UAG UGA

Universal Genetic Code Almost Identical in all life Differences Paramecium Mitochondria

Transcription Three steps Binding and Initiation Elongation RNA Polymerase II attaches at promoter Elongation RNA Polymerase II adds nucleotide bases creating mRNA Termination RNA Polymerase detaches at terminator

Binding and Initiation Transcription factors Recognize the promoter Bind before RNA Polymerase Transcription Initiation Complex RNA Polymerase TATA box Promoter sequence 25 nucleotides upstream

Elongation Adds to 3’ end of RNA strand 60 nucleotides / second Multiple transcriptions

Termination Prokaryotic Eukaryotic Recognizes a STOP codon and terminates transcription Eukaryotic Recognizes a STOP codon and continues downstream AAUAAA sequence terminates transcription

Eukaryotic Cells Modify RNA Alteration of mRNA ends 5’ cap: modified GTP Protects mRNA from degradation “Attach Here” poly (A) tail: 50-250 adenine nucleotides Prevent degradation

RNA Splicing Genetic “Cut and Paste” 8k nucleotides copied for 400 a.a. Introns and Exons Introns Noncoding segments (Intervening sequences) Regulatory roles Allows for crossing over w/o affecting coding sequence Exons Expressed segments

RNA Splicing (cont.) snRNPs: Spliceosome snRNA of snRNP recognizes splice site Spliceosome snRNP and other proteins Cut out Introns Fuse Exons

Transfer RNA Ends: Structure fits Function Specific amino acid Anticodon Structure fits Function 80 nucleotides long U can bind with A or G (wobble) Inosine binds with U,C, or A Aminoacyl-tRNA: bonds a.a. to correct tRNA

Ribosomes Consist of proteins and rRNA Large and Small subunits Structure Binding site for mRNA 3 sites for tRNA E: Exit site P: Peptidyl –tRNA site (Peptide) A: Aminoacyl – tRNA site (Acceptor)

Initiation Small ribo. subunit binds to mRNA Bacteria: rRNA subunit binds to AUG Euk.: rRNA subunit binds to 5’cap Translation begins at AUG Large ribo. Subunit attaches to complete translation Initiation complex Initiator sits in P site

Elongation Codon Recognition: Peptide bond formation: Translocation: Codon of mRNA H-bonds to tRNA anticodon Attaches to the A site Peptide bond formation: rRNA of Large ribo. Subunit forms peptide bond between P and A site Translocation: Each tRNA moves to the next site E site exits

Termination Encounters a STOP codon Binds a release factor

Mutations Changes in genetic material of the cell Point mutations: chemical changes to just one base pair Sickle-cell results from a point mutation in gene for Hemoglobin Mutagens: Create mutations Physical: Mutagenic radiation Chemical

Types of Point Mutations Substitution: replace one pair w/ another Silent mutations: no affect Missense mutations: Makes sense but codes incorrectly Nonsense mutations: results in a STOP codon Insertion and Deletion Usually result in a frameshift mutation

Point Mutations