Alternative transcript:

to P site, all others bind to A site first P- contains growing polypeptide chain as the amino acids link and form peptide bonds E- site where the tRNA exits once it has delivered its amino acid P site (Peptidyl-tRNA binding site) E site (Exit site) EPA mRNA binding site (b) Schematic model showing binding sites A site (Aminoacyl- tRNA binding site) Large subunit Small subunit 7 Nucleol Base helix sugar-pho: Ribonucleic Acid (RNA) RNA Single Stranded Molecule O Can be in different shapes and lengths! Found in: Nucleus and Cytoplasm (depending on type) Made up of Nucleotides (like DNA!) o Sugar (Ribose) O o Phosphate o Nitrogen Base (Uracil) Golgi apparatus Cytoplasm Ribosome Phosphate group O O=P-O O Nucleus -CH₂ www H HC H H Mitochondrion H Lysosome Nitrogenous base (A,G,C, or U) H OH Sugar (ribose) Centrosome Rough endoplasmic reticulum H Uracil (U) mRNA Processing Before pre-mRNA leaves the nucleus, introns are removed and exons are spliced together. Introns= non-coded sections (a.k.a “Junk” DNA) Exons = Coded sections for a protein They can splice in different ways to produce different proteins! - splicing translation pre-mRNA alternatively spliced mRNAs protein isoforms Protein Synthesis (10.6-10.16) K Elongation RNA Polymerase II unwinds the DNA and breaks the hydrogen bonds to separate the DNA strands. Base pairing occurs between incoming RNA nucleotides and DNA nucleotides of the gene (template strand). RNA polymerase II moves in a 5' to 3' direction! 5% 5'1111 3' RNA AACTGC... A DNA TTGACG... TATAAT I I I I T + CA C G C A C T C A T O id G I A direction of synthesis promoter 1 AAGTGCGTG I I I ÚČAUGUG AGTACA RNA polymerase nontemplate strand 3' 1 ⠀⠀⠀⠀3' TACCACGTA ATGTGCAT template strand 5' What is a gene? Gene- a section of DNA that codes for one specific protein. One Gene = One protein! Fun Fact: Humans have about 30,000 protein-coding genes!! GENE key G с amino acid amino acid Thousands of units are in this middle section but are not shown. amino acid amino acid amino acid Chain of amino acids from which a PROTEIN is made. 1. Initiation Steps to Translation The two ribosomal subunits come together at the 5' end of the mRNA Ribosome will read the mRNA in a 5' to 3' direction to find the start codon (AUG). This is the ONLY tRNA that will attach to the P site first (skipping the A site) First amino acid is always methionine (MET) Large subunit AOMME ΕΙΡΙΑ SMPDOOMMMM AUG What is a Codon? Codon: group of 3 nucleotides on the mRNA that specifies one amino acid. There are 64 different codons (Only 61 code for amino acids) A AC AUGA Codon Codon 7 Termination RNA Polymerase II continues until it gets to a termination sequence. Termination sequence is a special sequence that signals the end of the gene creating a hairpin loop. Termination: intrinsic mechanism Anana 3' 5' 5' RNA being released UUU AAA 3' L'5' Hairpin loop 0 T Messenger RNA Elongation stage polymerase links nucleotides to the 3' end of the growing RNA molecule. Once the RNA polymerase reaches the Steps to Translation 2. Codon Recognition Next tRNA anticodon will hydrogen bond to the mRNA codon in the A site. ΕΙΡ COMMMOMO! IMMM. www.dnalc.org Steps to Translation Termination The release factor recognizes the stop codon, attaches to the mRNA strand in the A site, and releases the polypeptide strand. All factors detach from one another and can be reused again. 5' Release factor 3' Stop codon (UAG, UAA, or UGA) 5' Free polypeptide 3' 5' x11xxxxxx 31 ANSWER DNA is too BIG (double stranded) to fit through the nuclear pores of the nucleus RNA can fit through the pores (single stranded) to get the genetic code out to the ribosomes in cytoplasm! Ribosome Nuclear pore 01230F Nuclear envelope Cell's Nucleus Nuclear lamin 123 -Nucleoplasm Chromatin - Nucleolus I tRNA Structure tRNA has an anticodon: 3 unpaired nucleotides that are complementary to the codon on the mRNA strand. Attach to mRNA strand with hydrogen bonds Amino Acid Hydrogen bonds Anticodon 2000 University of Nebraska, Board of Regents ㅁ Location: Nucleus Transcription First step in making proteins DNA mRNA DNA CONNOTA Base pair Pre-mRNA Takes one gene in DNA and converts it into a mRNA strand mRNA Transcription Codon Cell nucleus Cytoplasm mRNA Processing A 5' cap and Poly-A tail is added to the ends of the sequence 5' cap - (single G nucleotide) helps mRNA bind to ribosome — - Poly-A tail- (50-250 adenine nucleotides) Keeps mRNA from degradation from exonuclease enzymes **These are NOT translated as part of the protein!! - Mature mRNA will leave the nucleus through the nuclear pores, and travel to ribosome Cap Exon Intron Exon Intron Poly(A) tail Pre-mRNA mRNA 5' 5'UTR 5' Exon RNA splicing: introns removed Protein-coding sequence AAAAAAA...3' 3'UTR AAAAAAA...3' 3 Types of RNA 1. Messenger RNA (mRNA) ▪ A long strand of RNA nucleotides that are formed complementary to ONE strand of DNA o Carries genetic information from DNA in the nucleus to ribosome in cytoplasm mRNA Proteins The order of amino acids can change how a protein folds! How a protein folds, determines its structure Different structures = different proteins!! Primary Structure Secondary Structure S Polypeptide Chains Tertiary Structure Aggregation of two or more polypeptides Amino Acid Helix Quaternary Structure polypeptide tRNA anticodon UCA CGUGACAGU ribosome GCA CGU peptide bond UG C ACG amino acid UCA codon GAU C mRNA 1. Initiation Steps of Transcription 2. Elongation 3. Termination DNA duplex SUNNU 3' 5' Template DNA strand RNA 5' Figure 15-1 Molecular Biology: Principles and Practice © 2012 W. H. Freeman and Company Nontemplate DNA strand IMNIN' 3' 3' *Similar to replication although less enzymes are required -5' Direction of transcription transcription Pol II m'G ♡ ♡ RNA processing (5'-capping, 3'-polyadenylation, splicing) m'G AAAAAA translation B 88 protein coding gene (DNA) transcription machinery pre-mRNA mRNA AAAAAA translation machinery ribosome protein nucleus cytoplasm P Ribosome 3 Types of RNA 2. Ribosomal RNA (rRNA): Associates with protein to form ribosomes Ribosomes read the mRNA strand to make the proteins! o Found in cytoplasm of cell Large subunit Small subunit mRNA maitze www.dnale.org 3 Types of RNA 3. Transfer RNA (tRNA): Smaller segments of RNA nucleotides that transport amino acids to the ribosome Located in the cytoplasm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amino acid complementary base pairing GG anticodon a. tRNA-amino acid Recall... Amino acids are the monomers of protein A chain of bonded amino acids is called a Polypeptide (another name for protein) Proteins are made of one or more polypeptides Each circle in the diagram represents an amino acid. The entire chain is called a polypeptide! Gln Gly Ile Gln Arg Arg Gly Met Arg Arg Phe Gly Thr Gly Thr mRNA Processing (a.k.a Splicing) Pre-mRNA - the original sequence of RNA created from transcription. Pre-mRNA will go through mRNA Processing: edited to have correct protein sequence BEFORE leaving the nucleus. Creates mature mRNA that reaches the ribosome. Occurs in the nucleus of eukaryotic cells ONLY How do we get protein now?? Part 2 of the central dogma: The RNA strand is decoded and produces specific proteins by translation Involves all three types of RNA! DNA RNA Protein Translation Translation Translation - Production protein by the ribosomes reading the mRNA strand in the cytoplasm Three main stages: 1. Initiation 2. Elongation 3. Termination 5' TRANSCRIPTION AN RNA transcript RNA PROCESSING y Ca CYTOPLASM 2011 Pearson Education, Inc. Exon an NUCLEUS RNA polymerase mRNA Ribosomal subunits DNA Cap 5 RNA transcript (pre-mRNA) Intron ACC Poly-A Poly-A acid tRNA Growing polypeptide UGGUUUAUG Codon Ribosome Aminoacyl- tRNA synthetase -Aminoacyl (charged) tRNA AMINO ACID TIVATION TRANSLATION Anticodon Poly-A DNA Pre-mRNA mRNA Polypeptide 2010 Pearson Education, Inc. Promoter Cap Exon 5' 5'UTR 5' RNA-coding sequence Transcription by RNA polymerase II. Addition of 5' cap when 20-30 nucleotides of pre-mRNA made. Addition of 3' poly(A) tail. Intron Exon Intron RNA splicing: introns removed Protein-coding sequence Translation Exon is Poly(A) tail AAAAAAA...3' 3'UTR AAAAAAA...3' Steps to Translation Termination tRNA's will continue delivering amino acids until a stop codon is reached Stop codons do NOT code for amino acids - Three stop codons: - UAG - UGA - UAA - [5' Release factor 3' Y Stop codon (UAG, UAA, or UGA) Recall... Proteins are polymers made from amino acids (monomers) connected by peptide bonds Amino acids bond to form polypeptide chains Only 20 different amino acids But there are hundreds of thousands of different proteins! 20 — Peptide bond Amino acid Eukaryotes vs. Prokaryotes Eukaryotes: Transcription occurs in the nucleus and translation occurs in the cytoplasm Prokaryotes: Transcription and translation occur simultaneously in the cytoplasm DNA mRNA Direction of transcription Ribosome mRNA RNA polymerase DNA Polyribosome Polypeptide 0.25 μm RNA polymerase > Polyribosome ooo How do we get a protein from a gene sequence? The Central Dogma of Biology: DNA Transcription RNA Protein Translation