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Unit 6: DNA & Protein Synthesis Ch. 9: Chemistry of the Gene Ch. 10: From Genes to Proteins DNA = Deoxyribonucleic Acid 300 Video PPT: Lies, Thieves, & DNA • How did each of the following scientists contribute to our knowledge of DNA and the genetic code? – – – – – – – – Friedrich Miescher Frederick Griffith Oswald Avery, Colin MacLeod, & Maclyn McCarty Alfred Hershey & Martha Chase P.A. Levene Erwin Chargaff Rosalind Franklin & Maurice Wilkins James Watson & Francis Crick Describing DNA • Who first described the true shape of DNA? – James Watson & Francis Crick • What shape did they use to describe DNA? – double helix DNA is a Polymer… • What is the monomer that repeats to make DNA? –nucleotide What are the parts of a nucleotide? • phosphate group • sugar (deoxyribose) • nitrogenous base – 4 kinds: • Adenine (A) • Thymine (T) • Guanine (G) • Cytosine (C) – base gives name to nucleotide adenine, thymine, guanine, cytosine What are the parts of a nucleotide? • 4 kinds of nitrogen bases: – Purines (2 rings) • Adenine • Guanine – Pyrimidines (1 ring) • Thymine • Cytosine • Always pair –A – T –G – C DNA Structure Video A Model of DNA • Is DNA single or double stranded? – double-stranded • 2 chains of nucleotides bonded together – shape = “double helix” (spiral staircase) Purines 1 2 nucleotide Pyrimidines 3 4 DNA Structure Video A Model of DNA • What parts make up the strands? – “backbone”/sides • alternating sugars (deoxyribose) & phosphates – “rungs”/steps (attached to sugar) • complementary nitrogenous base pairs –A - T –G - C » held by hydrogen bond nucleotide Purines Pyrimidines 1 3 2 4 • Strands are complementary (A-T & G-C) & antiparallel (opposite directions/upside down) Where is DNA found in eukaryotic cells? • DNA is contained in chromosomes (chromatin) within the nucleus. sugar-phosphate “backbone” & nitrogenous base “rungs” DNA Replication • What is another word for replication? – copying • Why must DNA replicate? – so when cell divides, each new cell gets a copy of DNA http://www.stolaf.edu/peo ple/giannini/flashanimat/m olgenetics/dna-rna2.swf DNA Replication • When does DNA replicate? – before the cell divides (before mitosis or meiosis) • Where does DNA replicate? – inside the nucleus What are the steps in DNA replication? • 1. “Helicase” enzyme unzips DNA molecule along H bonds (between bases) forming two “parent strands”. What are the steps in DNA replication? • 2. “Parent” strands act as templates… – “parent” strand’s base is paired up with complementary “new” nucleotide with help of “DNA Polymerase” enzyme • forming complementary daughter strand – ex. “G” on “parent” DNA polymerase brings “C” T C What are the steps in DNA replication? • 3. Sections of nucleotides (Okazaki Fragments) are joined by enzyme DNA ligase. – Now, have 2 exact copies of original DNA molecule. • & when cell divides, each “new” daughter cell gets a copy What are the steps in DNA replication? T C DNA Replication Video Let’s Practice… Predict the next base… Let’s Practice… Finish the replications… Let’s Practice… Finish the replications… Deoxyribonucleic Acid vs. Ribonucleic Acid DNA RNA • sugar = deoxyribose • sugar = ribose • double stranded • single stranded •CANNOT •Can move leave nucleus between nucleus & cytoplasm • N bases = • N bases = adenine, adenine, thymine, uracil, guanine, guanine, cytosine cytosine The DNA Code & Protein Synthesis • What is a gene? – section of DNA that codes for synthesis of a specific protein • Which part of DNA carries the code for a protein? – the nitrogen bases • & their order – change sequence amino acid (usually) changes & protein made (usually) changes The DNA Code & Protein Synthesis • So, the big question is… – How does the DNA code in a cell’s nucleus get to the ribosomes where proteins are synthesized? • transcription & translation The Central Dogma of Biology Transcription • What is transcription? – DNA code is “transcribed”/copied into mRNA codons • When does transcription happen? – when a protein is needed Transcription • Where does transcription happen? – in the nucleus • What does transcription make? – A single-stranded messenger RNA (mRNA) • made from instructions/order of the bases in the DNA http://www.stolaf.edu /people/giannini/flash animat/molgenetics/t ranscription.swf Steps of Transcription • When a protein is needed: – 1. DNA near needed gene gives signal (“start codon”) – 2. DNA unzips (w/ help of RNA polymerase) Steps of Transcription http://www.stolaf.edu /people/giannini/flash animat/molgenetics/t ranscription.swf • 3. RNA polymerase pairs complementary RNA nucleotides with unzipped DNA strand – until reaches a “stop codon” • 4. Nucleotides bond to form single RNA strand of mRNA (messenger RNA) • 5. The 2 DNA strands rejoin & mRNA moves out of nucleus into cytoplasm mRNA Carries DNA’s Code Using “Codons” • What is a codon? – 3 consecutive bases on mRNA that codes for a particular amino acid • 64 possible combos – Some amino acids have more than one codon. mRNA Carries DNA’s Code Using “Codons” • How can we figure out the amino acid coded for by a codon? – a codon chart What amino acid does the AUG codon code for? mRNA Codons & Amino Acids • What amino acid does the AUG codon code for? It must be in this row It must be It must be in this in this square amino acid mRNA Codons & Amino Acids Translation • What is translation? – process of reading mRNA codons to synthesize proteins • with help of tRNA (transfer RNA) & ribosomes • When and where does translation occur? – when mRNA from the nucleus joins with ribosomes in the cytoplasm http://www.stolaf.edu/ people/giannini/flash animat/molgenetics/tr anslation.swf Steps of Translation 1. mRNA comes from the nucleus & joins with ribosome in cytoplasm 2. Ribosome “reads” the codon until it finds the start codon (AUG) 3. tRNA (with complementary anticodon) joins to the mRNA codon – tRNA carries the amino acid specified by the mRNA codon http://www.stolaf.edu/ people/giannini/flash animat/molgenetics/tr anslation.swf Steps of Translation 4. Ribosome moves along mRNA reading each codon until “stop” codon is reached – tRNA transfers each amino acid to ribosome 5. Amino acids line up & bond to form polypeptide 6. Polypeptide chain forms protein (3-D) – Shape of protein is related to its function transcription translation DNA codon tRNA anticodon mRNA codon mRNA codon Let’s Practice… What would the mRNA strand made during transcription look like? What amino acids would be coded for using this mRNA? What would the anticodons on the tRNA be for each amino acid? Let’s Practice… • Given the DNA sequence below, determine the: 1. mRNA codon sequence 2. amino acids that would be coded for by each codon 3. anticodons on each tRNA which allowed it to “bring” that amino acid (using the mRNA codons) • • • • DNA = TAC mRNA codon = AUG amino acid = Met/start tRNA anticodon = UAC CCA TTG GAT CCG ACT GGU AAC CUA GGC UGA Gly Asn Leu Gly stop CCA UUG GAU CCG ACU Mutations • What are mutations? – mistakes/changes in a gene on a chromosome • can occur spontaneously during replication • can be caused by mutagens (such as radiation, high temperatures, or chemicals) • often corrected, but not always – once occurs, copied as if correct – can cause different protein Types of Mutations • What are the 3 types of mutations? 1. deletion • What happens in a deletion mutation? – a nucleotide (base) is left out » causes “frame shift” ~moves nucleotides after the deletion to the left causing a different protein to be formed Types of Mutations 2. insertion • What happens in an insertion mutation? –a nucleotide (base) is added in » causes “frame shift” ~moves nucleotides after the insertion to the right causing a different protein to be formed Types of Mutations 3. point (base substitution) • What happens in a point mutation? –one nucleotide (base) is replaced by another » affects only 1 amino acid & does not cause “frame shift” » sometimes amino acid & protein can be the same (“silent mutation”) » protein may be able to function normally or nearly normally Sickle Cell Mutation • What does the sickle cell mutation do? – affects hemoglobin (protein in blood carries O2) • What type of mutation causes sickle cell? – point mutation • changes one amino acid – changes the protein “Silent” mutation (no change in polypeptide) (point mutation)