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What is the job of p53? What does a cell need to build p53? Or any other protein? The central dogma of biology is… DNA RNA Protein What do think this means? Using the Information Stored in DNA to Build Proteins • • • • • Genetic code is… Sequence of bases impt b/c… A gene is … Proteins are made on…. How do we get the code for making proteins out of the nucleus and into the cytoplasm? Protein Synthesis: Transcription and Translation DNA vs RNA Transcription • Process by which the genetic code is copied from DNA into messenger RNA Transcription occurs in nucleus before translation RNA nucleotides RNA polymerase Direction of transcription Newly made RNA Template strand of DNA Stages of Transcription Initiation: RNA polymerase binds to a promoter, where the helix unwinds and transcription starts Elongation: RNA nucleotides are added to the chain Termination: RNA polymerase reaches a terminator sequence and detaches from the template http://ramsey.schoolwires.com/114 620810131521263/lib/114620810 131521263/Transcription_2.mov RNA polymerase DNA of gene Promoter DNA Terminator DNA 1 Initiation 2 Elongation 3 Termination Completed RNA Area shown in Figure 10.9A Growing RNA RNA polymerase Exon Intron Exon Intron Exon DNA Cap RNA transcript with cap and tail Transcription Addition of cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm RNA Splicing – Eukaryotic mRNA has non-coding sequences called introns, separating the coding regions called exons – Eukaryotic mRNA undergoes processing before leaving the nucleus – Cap added to 5’ end: single guanine nucleotide – Tail added to 3’ end: Poly-A tail of 50–250 adenines – RNA splicing: removal of introns and joining of exons to produce a continuous coding sequence Copyright © 2009 Pearson Education, Inc. 10.8 The genetic code is the Rosetta stone of life – Characteristics of the genetic code – Triplet: Three nucleotides specify one amino acid – 61 codons correspond to amino acids – AUG codes for methionine and signals the start of transcription – 3 “stop” codons signal the end of translation Copyright © 2009 Pearson Education, Inc. Translation Translation • Process of decoding mRNA into a polypeptide sequence. Codon to Amino Acid Translation • Involves: 1. mRNA- carries codon 2. ribosome- rRNA, part of ribosome 3. tRNA- carries aa and anticodon 4. enzymes- help aa bond to tRNA 5. chemical energy, ATP tRNA molecules Growing polypeptide Large subunit mRNA Small subunit tRNA-binding sites Large subunit mRNA binding site Small subunit Amino acid Polypeptide A site P site Anticodon mRNA Codons 1 Codon recognition Amino acid Polypeptide A site P site Anticodon mRNA Codons 1 Codon recognition 2 Peptide bond formation Amino acid Polypeptide A site P site Anticodon mRNA Codons 1 Codon recognition 2 Peptide bond formation New peptide bond 3 Translocation Amino acid Polypeptide A site P site Anticodon mRNA Codons 1 Codon recognition mRNA movement Stop codon 2 Peptide bond formation New peptide bond 3 Translocation Translation: Start Translation: Elongation Translation: Termination Protein Synthesis Protein Synthesis: Key Points • DNA “directs” synthesis of proteins • Proteins made on ribosomes • Transcription: - RNA polymerase unzips DNA - occurs in nucleus • Translation: DNARNAProtein - occurs in cytoplasm - mRNA(codon) and tRNA(anticodon) • Genetic Code is UNIVERSAL!!!!!!! Proteins • • • • Composed of aa Chain of aa called polypeptide Peptide bonds hold aa together 1 or more polypeptide chains can link and fold together to form a 3-dimensional protein • Proteins differ in number and sequence of aa • Protein structure determines their function Protein Folding and Function As the amino acid chain grows, it folds into a three-dimensional (3-D) structure, which depends on both the chemical nature and order of the different amino acids. The 3-D structure determines the function of the protein. When there is a change in one or more amino acids, then the ability of the protein to function may be affected. The protein's function may be unchanged or it may become sluggish, hyperactive, or inactive. Proteome: collection of all proteins in a species