Transcript Chapter 12:
RNA & Protein Synthesis Quick Review A. What are some proteins you are made of? Ex: keratin, hemoglobin, enzymes, antibodies B. What are the building blocks of proteins? Amino acids C. What organelle makes proteins? Ribosomes D. Where are the instructions for making a protein? DNA! E. Where is this molecule located in cell? Nucleus Central Dogma So, if DNA has the instructions for genes, which build proteins, but DNA never leaves the nucleus, then how can these proteins get made at the ribosomes?? Photo credit: http://katiephd.com/wp-content/uploads/2011/01/central-dogma.jpg DNA “master plan” RNA “blueprints” DNA stays in the nucleus RNA goes to ribosomes to build proteins Photo source: http://www.architecturalmodels.com/assets/images/architectural_models_residential_model.jpg Photo source: http://upload.wikimedia.org/wikipedia/en/thumb/f/ff/House_Pl ans_(Blueprints).pdf/page1-1280pxHouse_Plans_(Blueprints).pdf.jpg What is RNA? RNA is a class of molecules RNA vs. DNA 1. Ribose is the sugar in RNA 2. Single-stranded 3. Uracil, not Thymine Structure of RNA 1. Phosphate group 2. 5-carbon sugar- ribose 3. Bases i. Adenine ii. Uracil iii. Cytosine iv. Guanine Three Main Types of RNA 1. Messenger RNA (mRNA) 2. Ribosomal RNA (rRNA) 3. Transfer RNA (tRNA) 1. Messenger RNA - Made in nucleus - Transcribes a single gene in DNA - Contains instructions for making amino acids --> EXITS the nucleus 2. Ribosomal RNA - Actual site where mRNA codons are translated into amino acids - Like the “workbench” Ribosome attaches to mRNA strand As mRNA strand slides through subunits, the codons are ‘read’ mRNA 3. Transfer RNA - RNA with amino acid attached - Carries complementary anti-codon that matches the codon using base pairing About Codons mRNA transcripts are read 3-letters at a time. These are called ‘CODONS’. They are like the words that make up the sentences of a gene. D.START codon: AUG – stimulates beginning of translation D.STOP codons: UGA, UAA, UAG III. Steps for Protein Synthesis A. Transcription • During transcription, RNA polymerase binds to DNA and separates the DNA strands • RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA copyright cmassengale 16 3. Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA 4. Called the TATA box 5. Specific base sequences act as signals to stop and are called the termination signal Transcription- nucleus B. mRNA Processing 1. After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional 2. Introns, nonfunctional segments of DNA are snipped out of the chain 3. Exons, segments of DNA that code for proteins, are then rejoined by the enzyme ligase 4. A cap is added to the 5’ end of the newly copied mRNA 5. A poly-A tail is added to the 3’ end of the RNA Exons Introns 21 copyright cmassengale mRNA Transcript mRNA leaves the nucleus through its pores and goes to the ribosomes 22 copyright cmassengale C. Translation 1. Translation is the process of decoding the mRNA into a polypeptide chain 2. Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins copyright cmassengale 3. mRNA transcript start codon AUG attaches to the ribosome Process continues until a stop codon. End Product –The Protein! 4. The end products of protein synthesis is a primary structure of a protein 5. A sequence of amino acid bonded together by peptide bonds aa2 aa1 aa3 aa4 aa5 aa199 copyright cmassengale 27 aa200 One gene, one polypeptide Translation Second base in codon So how can you tell what amino acid will be carried on the tRNA? Use this chart! Try AUG codonwhat amino acid? (use codon!) First base in codon Third base in codon Name the Amino Acids • • • • • GGG? UCA? CAU? GCA? AAA? copyright cmassengale • Translation guided animation • All of DNA Translation Mutations M u t a t i o n s Ryan Clark of Pittsburgh Steelers Photo source: http://www.dnalc.org/resources/3d/17-sickle-cell.html 438-base sequence. Can’t Carry Oxygen Tay Sachs http://www.pbs.org/wgbh/nova/body/cracking -the-code-of-life.html Time- 17:00-20:00 Inherited genetic mutation HEXA codes for an enzyme that breaks down fatty acids Build up of fatty acids in the brain IV. Mistakes Happen! Gene mutations A. Mutation is any change in the DNA sequence Ex: Lactase mutation for lactose digestion Ex: Sickle cell- no hemoglobin Some mutations are helpful Sickle cell anemia & malaria B. A mutagen is any agent that causes a change in DNA Mutagens can be chemical or physical • Ex: UV rays, nuclear radiation, chemicals (benzene, formaldehyde) Photo credit: http://www.mrwallpaper.com/wallpapers/Plane Photo credit: http://www.realnewsreporter.com/wpcontent/uploads/2011/04/nuclear-429.n.jpg C. Point Mutations Diseases Caused by Point Mutations Colorblindness Hemophilia Cystic Fibrosis Tay Sachs PKU Occur at ONE point in the DNA sequence. It is a change on one nucleotide Cat ate the rat. Car ate the rat. The protein might still be functional. Types of Point Mutations Original Strand RNA: AUG CCA ACA GAU CAG UAG CGC GUA 1. Substitution AUG CCA ACA GAU CAG UAC CGC GUA 2. Insertion into original ACU GCC AAC AGA UCA GUA GCG CGU A 3. Deletion from original AGC CAA CAG AUC AGU AGC GCG UA The cat ate the rat. Substitution The car ate the rat. Insertion The caa tat eth era t. Deletion Tec ata tet her at. D. Frameshift Mutations • Effects of insertions or deletions are more dramatic • Addition or deletion of a nucleotide causes a shift in grouping of codons • Changes like these are called frameshift mutations Some substitutions don’t cause changes in the amino acids GCC, GCA = alanine CGG, AGG = arginine Remember: there are extra amino acid “words”: 20 A.A.’s, 64 codons! BUT, both insertion and deletion cause frameshifts E. Chromosomal Mutations • Change in shape, size, or structure of chromosome • Now you are affecting 1000s of proteins • System deformities can occur Chromosomal Mutations