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Chapter 12 Molecular Genetics 12.1 Vocabulary • DNA – molecule that contains genetic information that is used in the development and functioning of all living organisms. Found in the nucleus and is the “code of life”. • • • • Nucleotide Double Helix Chromosome Nucleosome Section 1 DNA: The Genetic Material Standards: 2.3, 4.1-4.3, 4.7 Objectives: • Summarize the experiments leading to the discovery of DNA as the genetic material. • Diagram and label the basic structure of DNA. • Describe the basic structure of the Eukaryotic chromosome. Discovery of DNA • Fredrick Griffith (1928) – studied bacteria that causes pneumonia. – Strains can be transformed into other forms. • Oswald Avery (1944) – identified the specific molecule that transformed the R strain S strain. Discovery of DNA • Alfred Hershey & Martha Chase (1952) – studied a bacteriophage (virus that attacks bacteria) by using radioactive labeling. – DNA & not protein is the transforming factor. DNA • Deoxyribonucleic Acid • Genetic material found in nucleus – Also in mitochondria & chloroplasts • Instructions written in a chemical code – Determines all cellular functions (appearance, develop, etc.) Structure of DNA • Building blocks of DNA nucleotides – Nucleotide contains: • 1 nitrogen base (A, T, G, C) • 5 carbon sugar deoxyribose • 1 phosphate group How Many Nucleotides? Structure of DNA • James Watson & Francis Crick (1953) – discovered that DNA is a double helix (two strands of twisted nucleotides twisted ladder or spiral staircase) Structure of DNA • “Railing” alternating phosphates & sugars on outside (backbone) • “Steps” nitrogen base pairs on inside “Railing” 4 Base Pairs –Adenine (A) –Guanine (G) –Thymine (T) –Cytosine (C) Structure of DNA • “Complementary base pairing” – Bases pair up in middle of DNA molecule and held together by H bonds following the BASEPAIR RULE: • A always pairs with T by 2 H bonds • G always pairs with C by 3 H bonds • Purines ALWAYS bind to Pyrimidines There are 4 different nitrogen bases They are categorized into 2 groups: Purines: Double-carbon ring • Adenine • Guanine Pyrimidines: Single-carbon ring • Cytosine • Thymine Base-Pairing Practice • A = _____ • T = _____ • C = _____ • G = _____ • T = _____ • C = _____ DNA Structure • The two sides of DNA are oriented in opposite directions Antiparallel – Like a two-lane road Chromosome Structure • DNA coils around histones (proteins) to form chromatin fibers creating a Nucleosome supercoils for form chromosome X shape DNA packaging HHMI 12.2 Vocabulary • • • Semiconservative Replication DNA Polymerase Okazaki Fragment Section 2 Replication of DNA Standards: 2.3, 4.3 Objectives: • Summarize the role of the enzymes involved in the replication of DNA. • Explain how leading and lagging strands are synthesized differently. DNA Replication • Semiconservative Replication – parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA and one strand of new DNA. – Process of copying DNA – Occurs in 3 Steps Replication - basic Replication - schematic Semiconservative Replication Step 1: Unwinding the Double Helix – DNA Helicase (an enzyme) unwinds and unzips DNA into two separate strands H bonds break leaving single strands of DNA. – Single-stranded binding proteins keeps strands separate during replication. – Primase (an enzyme) adds primer (short segments) on each DNA strand. Step 1: Unwinding the Double Helix Semiconservative Replication Step 2: Add New Base Pairs – DNA Polymerase (an enzyme) – catalyzes the addition of appropriate nucleotides to the new DNA strand. • Adds new nucleotides to the old DNA molecule. • Follows the base-pair rule: (A-T, G-C) Semiconservative Replication Step 2: Add New Base Pairs (cont’d) • Two new strands produced in different ways: – Leading Strand new nucleotides added in a smooth, continuous motion. – Lagging Strand new nucleotides added in small chunks called Okazaki Fragments and in a discontinuous motion. • DNA Ligase (an enzyme) adds more bases to fill in the gaps between the Okazaki Fragments to make a continuous new DNA strand. Step 2: Add New Base Pairs Step 2: Add New Base Pairs Semiconservative Replication Step 3: Joining Base Pairs – DNA polymerase removes primer and fills in the place with nucleotides. – DNA ligase joins the sections to make each strand continuous. – At the end of replication 2 new strands of daughter DNA are produced. • Each is made of ½ old DNA and ½ new DNA DNA Replication Prokaryotes/Eukaryotes Prokaryotes • Circular DNA strand replicated in one section • 2 directions • DNA is shorter. Eukaryotes • Replicated in several sections • 2 directions. • DNA is longer. 12.3 Vocabulary • • • • • • • • RNA Messenger RNA Ribosomal RNA Transfer RNA Transcription RNA Polymerase Codon Translation Section 3 DNA, RNA, and Protein Standards: 2.2, 4.1, 4.3-4.4 Objectives: • Explain how messenger RNA, ribosomal RNA, and transfer RNA are involved in the transcription and translation of genes. • Summarize the role of RNA polymerase in the synthesis of messenger RNA. • Describe how the code of DNA is translated into messenger RNA and is utilized to synthesize a particular protein. Why Proteins are Important • DNA “code of life” or “genetic code” because it contains the code for each protein that organisms need. • Proteins (or protein messages) determine how an organism looks & functions. Why Proteins are Important • Gene – segment of DNA that contains instructions for making a protein. – Specific location on a chromosome – Controls inherited trait expression that is passed on for generations. • Ribosomes make proteins DNA RNA • Problem: DNA contains instructions for making proteins but DNA can’t leave the nucleus. • Solution: RNA will take DNA’s instructions to the ribosomes for protein synthesis. RNA just speaks a different language than DNA. RNA • RNA is a nucleic acid called Ribonucleic Acid • Single stranded • Composed of nucleotides: – Sugar Ribose – Phosphate Group – Nitrogen Bases: • G bonds with C • A bonds with (U) uracil • NO (T) RNA 3 Types of RNA: 1. mRNA (messenger RNA) – long strands of RNA formed complementary to one strand of DNA 2. rRNA (ribosomal RNA) – associated with proteins to form ribosomes in the cytoplasm 3. tRNA (transfer RNA) – small segments of RNA that transport amino acids to the ribosome RNA How Proteins are Made Part 1: Transcription (DNA mRNA) – occurs in nucleus – gene for a specific protein is turned ON and that gene is copied into mRNA Example: (DNA) T A C G G T A (mRNA) A U G C C A U • RNA Polymerase (an enzyme) – regulates RNA synthesis as DNA strand unwinds and unzips. – mRNA detaches and leaves nucleus and enters cytoplasm. TWO DNA strands rejoin. Transcription Transcription Practice 1. DNA mRNA CGTTAGCAACTG 2. DNA mRNA ACGTCAACGTTA Genetic Code • DNA codes for protein synthesis. • DNA varies among organisms N base sequence is different. • Amino acids make up proteins • 20 amino acids total • Codon – 3 base code (N base) 1 codon = 1 amino acid DNA CODON T A C This section of DNA represents a gene. C C G T A T • How many codons do you see in this gene? C A T C G A A T T • How many amino acids total make this protein? Genetic Code Genetic Code Practice Converting mRNA Amino Acids P. 338 1. 2. 3. 4. 5. 6. 7. 8. AUG = CUC = AAG = GGU = UAC = CAC = CAA = UGA = How Proteins are Made Part 2: Translation (mRNA Protein) – Occurs in cytoplasm at the ribosome – Interprets genetic message and builds proteins – mRNA attaches to a ribosome (rRNA) and is read 3 bases at a time (codon) How Proteins are Made Part 2: Translation (continued) • tRNA is activated by an enzyme and carries amino acids to the ribosome & drops them off. – 20 different types of tRNA molecules – tRNA structure: • Anticodon site – 3 nucleotide base complementary to the codon of mRNA; end of tRNA molecule • Amino acid attached on other end How Proteins are Made Part 2: Translation (continued) – Amino acids joins together in a chain by peptide bonds forming a protein. – Continues until STOP codon is read on the mRNA last amino acid is added protein breaks away from ribosome protein synthesis ends. Translation DNA mRNA Amino acid T A A U C G C G C G G C T A A U T A C G A U T A C G G C A U A U T A T A Methionine (start) • The section of DNA you see here is a gene; glycine isoleucine valine – Use the mRNA you see here and the chart in your book to figure out which amino acid will go into this protein. • Pg 338 alanine stop 12.4 Vocabulary • • • Gene Regulation Mutation Mutagen Section 4 Gene Regulation and Mutation Standards: 4.8 Objectives: • Summarize the various types of mutations. Gene Regulation • Gene Regulation – ability of an organism to control which genes are transcribed. – Transcription factors controls what and when genes are expressed to make proteins. – 2 Transcription Factors: 1. Guide & stabilize the binding of RNA polymerase 2. Controls rate of transcription Mutation • Mutation – permanent change (or alteration) in DNA. – Changes vary from… • One base pair (gene mutations) large segments of DNA (chromosomal mutations) • Beneficial harmful (maybe lethal) • Unnoticeable disorders or death Mutation • If mutant cell is a body cell (somatic cell) then daughter cells can be affected but mutation will not be passed to offspring aging and/or cancer. • If mutant cell is a gamete (sex cell) then mutation will be passed to offspring. Point Mutation • Point Mutation – change in one base pair (one nucleotide). – Missense Mutations (substitution) – codes for the wrong amino acid. Normal: AUG CAU UAC (histidine) Mutated: AUG GAU UAC (aspartate) – Nonsense Mutations (substitution) – change amino acid codon to a stop codon; terminates translation early proteins can’t function normally Normal: AUG CAU UAC Mutated: AUG UGA Frameshift Mutation • Frameshift Mutations – change the “frame” of the amino acid sequence by adding or deleting nucleotides changes the multiples of 3 codons. – Deletion Mutation – loss of a nucleotide Normal: AUG CAU UAC GUA Mutated: AUG AUU ACG UAU – Insertion Mutation – additions of a nucleotide Normal: AUG CAU UAC GUA Mutated: AUG CCA UUA CGU A Duplication Mutation • Duplication Mutation – entire codon(s) repeat; changes the number of amino acids used. Normal: AUG CAU UAC GUA Mutated: AUG CAU CAU CAU CAU UAC GUA How Mutations Occur • Can occur spontaneously during (meiosis) replication DNA polymerase may add the wrong nucleotide • Mutagens – substances which cause mutations; certain chemicals and radiation. • Most mutations repaired no effect Effects of Mutation • The shape of a protein controls how it works. – Shape is determined by amino acids. • Incorrect amino acids change protein’s shape protein may not work properly.