oday DN RN rotein utorial 1 he entral Dogma of molecular biology Information flow in genetics:» ranscription» ranslation» Making sense of genomic information Information content in DN - Information content is in the sequence of bases along a DN molecule - Redundancy in the code rules of base pairing each strand of the double helix has all the info needed to recreate the other strand DN and the flow of information he genetic material: DN - Four kinds of subunits (bases,,, ) coding problem His Val lu la lu rg ln er la rg la sn ly la ln ro ys yr Lys ln ro ly la His hr ly Val ly ln yr ys sn la he ly ly Val Val he ly lu he lu H rg ly 3 N + ly ctivities within the cell performed by proteins - wenty kinds of subunits (amino acids) la yr ln lu er ly ys lu ro Ile sn ro er yr ln hr ys Lys ys rg ys sn OO - ly ln Ile Val lu enome 371 utorial 1-1
Francis rick and ydney Brenner: 1957 OH olved the coding problem and proposed the entral Dogma of molecular biology DN RN rotein OH he entral Dogma genes and transcription enes specific segments along the DN that code for some function?? ranscription: copy gene into RN to make a specific protein ranscription (cont d) ranscription: copy gene into RN to make a specific protein ribonucleic acid uses uracil (U) in place of thymine () gene coding or sense strand w c mrn template strand Where s the end of the mrn? Which way is RN polymerase moving? RN polymerase enome 371 utorial 1-2
ene structure ranscription in vivo Eukaryotic genes are interrupted by introns (non-coding information). hey must be removed from the RN before translation in a process called splicing. ene exons pre-mrn introns DN nascent RN transcripts mature mrn ORF = open reading frame RN polymerases ranscription ractice questions ractice questions 1. How many genes are being transcribed in this picture? Four genes, or one gene with 3 introns? What s your reasoning? w c 2. Which way (to the right or left) are RN polymerases moving? enome 371 utorial 1-3
Francis rick and ydney Brenner: 1957 olved the coding problem and proposed the entral Dogma of molecular biology w c DN RN rotein 3. Where is the promoter? o the right or the left of the transcribed region? 4. Which strand (W or ) is the template strand? ranslation solution to the coding problem DN and the flow of information he genetic material: DN - Four kinds of subunits (bases,,, ) coding problem His Val lu la lu rg ln er la rg la sn ly la ln ro ys yr Lys ln ro ly la His hr ly Val ly ln yr ys sn la he ly ly Val Val he ly lu he lu H rg ly 3 N + ly ctivities within the cell performed by proteins - wenty kinds of subunits (amino acids) la yr ln lu er ly ys lu ro Ile sn ro er yr ln hr ys Lys ys rg ys sn OO - ly ln Ile Val lu enome 371 utorial 1-4
ranslation ranslating the nucleic acid code to a peptide code ossible coding systems: 1 base per amino acid 2 bases per amino acid 3 bases per amino acid he triplet code 3 bases = 1 amino acid More than 1 triplet can code for the same amino acid codon U U U U U mrn U Met hr er V al hr he NH + 3 OO - ranslation: read the information in RN to order the amino acids in a protein protein unctuation: start: stop: he enetic ode: Who is the interpreter? Where s the dictionary? What are the rules of grammar? trn = transfer RN Met Met U U U U U U Met hr er V al hr he NH + 3 OO - mrn protein synthetase U trn U anticodon enome 371 utorial 1-5
he ribosome: mediates translation Met hr the ribosome breaks the Met-tRN bond; Met is instead joined to the second amino acid Met hr ribosome...u U UUUUUUU ribosome UU... UUUUUUU released Met hr and the Met-tRN is and the next trn can bind, and the process repeats Met hr er ribosome U U... UUUUUUU U... U... UUUUUUU then ribosome moves over by 1 codon in the direction enome 371 utorial 1-6
Met hr er Met hr er U U... UUUUUUU U... UUUUUUU When the ribosome reaches the top codon termination he finished peptide! Met hr er Val hr he NH 3 + Met hr er Val hr he OO - O U... UUUUUUU UUUUUUU enome 371 utorial 1-7
Reading Frame: the ribosome uses the first U it encounters to establish the grouping of nucleotides that correspond to codons. tart counting triplets from this base UUUUUUU Open Reading Frame: ORF: from the first U to the first in-frame stop. he ORF is the information for the protein. Finding genes in DN sequence iven a chunk of DN sequence...... How do you find out if it contains a gene? How do you identify the gene? Finding genes in DN sequence (cont d) Identifying ORFs in DN sequence What features of genes might you look for in DN sequence? O UUUUUUU O mrn enome 371 utorial 1-8
ractice questions protein-coding portion of ene 1 protein-coding portion of ene 2 Neither gene has an intron 5'--3' transcription 5'-UUUUUUUUUUUUUUUUUUUU-3' 1. Which strand on the DN sequence is the coding (sense) strand? How can you tell? (ssume that there are no introns in this gene.) 2. On the DN sequence, circle the nucleotides that correspond to the start codon. 3. How many amino acids are encoded by this gene? enome 371 utorial 1-9
ractice questions (cont d) protein-coding portion of ene 1 protein-coding portion of ene 2 Neither gene has an intron 5'--3' Now considering ene 2 4. Which strand is the template strand? What is the direction of transcription (left!right vs. right!left)? ssume that there are no introns in this gene. enome 371 utorial 1-10
ractice question (homework) enome 371 utorial 1-11
nd lastly, a challenge Here is the chunk of sequence again from a few slides back (p.8):...... and here is one representation of its protein-coding information content: Looking at how each axis is labeled, and thinking about what we ve been discussing, can you puzzle out how this representation is derived? We ll be discussing such representations in more detail, so don t worry if you don t get it just yet but see if you can at least get a general sense of what is represented here. enome 371 utorial 1-12
enome 371 utorial 1-13