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DNA STRUCTURE & REPLICATION WHAT IS DNA? Organic molecule Nucleic acid WHERE IS IT LOCATED? In the Nucleus Organized as chromosomes DNA STRUCTURE OF DNA Made of nucleotides Shaped like a twisted ladder “Double helix” = two twisted strands DNA STRUCTURE Nucleotides have 3 parts: Deoxyribose sugar Phosphate group Nitrogen base Two types of bases Purines Adenine Guanine Pyrimidines Thymine Cytosine BASE PAIRING RULES: cytosine-guanine (C-G) adenine- thymine (A-T) LADDER SHAPE (SIDES & RUNGS) Sides: Phosphoric Acid Deoxyribose Sugar Phosphoric Acid Rungs: A-T T-A G-C C-G WATSON & CRICK’S DOUBLE HELIX: In 1953, James Watson and Francis Crick suggested the model for the structure of DNA. This shape is called a double helix. WHAT IS DNA’S FUNCTION ? Provide Hereditary Instructions Provides the chemical code for every trait Is a “blueprint” for making Proteins DNA REPLICATION Copying DNA The number of chromosomes doubles It occurs during Interphase (S) 2n to 4n 2N 2N STEPS FOR DNA REPLICATION: DNA unzips 1. Corresponding bases pair with the existing DNA strand 2. DNA reforms 3. 4. Enzyme = helicase enzyme = polymerase 2 new strands twist into helix Identical Strands Where do these new nucleotides come from? The cell makes them (from DNA instructions). PROTEIN SYNTHESIS DNA to Protein Ch 11.2 14 REVIEW OF DNA REPLICATION DNA unwinds & unzips (helicase) Free nucleotides match with DNA nucleotides & bond together (polymerase) Replicated DNA contains 1 original strand + 1 new strand. 15 GENES & PROTEINS Regulate cell functions Form cell structures like muscle filaments, walls of blood vessels, and transport proteins Enzymes control chemical reactions 16 DNA provides the instructions to make proteins Different proteins have different functions: Proteins are made of amino acids Sequences of DNA nucleotides contain information for assembling a chain of amino acids that make up a protein. RNA 1. 2. 3. Single stranded Ribose sugar Bases: Adenine (A) – Uracil (U) Guanine (G) – Cytosine (C) Analogy: In a factory, DNA = instructions for building a car (proteins) and RNA = the workers who build it. 17 A nucleic acid like DNA Different from DNA: 18 TYPES OF RNA Messenger RNA (mRNA) Brings information from the DNA in the nucleus to the cytoplasm Found in the nucleus & cytoplasm Robosomal RNA (rRNA) Makes up ribosomes, which clamp onto the mRNA and build protein Found only in cytoplasm Transfer RNA (tRNA) Transports amino acids to the ribosome to build a protein Found only in cytoplasm 19 TRANSCRIPTION 20 The process of making RNA from DNA: 1. Enzymes untwist & unzip the DNA (just like replication) 2. RNA nucleotides pair with complementary DNA nucleotides on one of the DNA strands (Making mRNA) 3. Once base pairing is complete, mRNA breaks away and leaves the nucleus TRANSCRIPTION A C G U A G C DNA Code 21 T mRNA 22 PROCESS OF TRANSCRIPTION 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 THE GENETIC CODE (like letters in the English alphabet) Proteins are written in the language of amino acids (like characters in the Chinese language) 43 Think of the genetic code as a language: DNA and RNA are written in the language of nucleotides THE GENETIC CODE AUG = start UAA, UAG, & UGA = stop The genetic code is universal – all organisms use the same code. 44 Codon = each set of 3 nucleotides of mRNA that code for a specific amino acid 64 combinations of nucleotide codons are possible The order of nucleotides determines the order of amino acids in a protein Some codons give instructions USING A CODON CHART Examples: What amino acids are coded for by each of these: AUG 1. Methionine (START) CCG 2. Proline (pro) UAA 3. STOP GAC 4. Aspartic acid (asp) 45 TRANSLATION 46 The process of converting the information of mRNA into a sequence of amino acids Takes place in the ribosomes in the cytoplasm When mRNA leaves the nucleus and enters the cytoplasm, ribosomes attach to it like clothespins on a clothesline. More than one ribosome at a time THE IMPORTANCE OF TRNA In order for proteins to be built, amino acids need to be carried to the ribosomes. Each tRNA molecule attaches to only ONE type of amino acid. tRNA molecules contain anticodons that are complementary to mRNA codons 47 tRNA has the same nucleotides but is has a different shape for its function THE PROCESS OF TRANSLATION 1. 2. ○ 4. 5. 6. 48 3. A ribosome attaches to mRNA tRNA molecules carry amino acids to the ribosome and attach to the mRNA The ribosome slides down the mRNA to the next codon The first tRNA leaves the ribosome A new tRNA molecule carries another amino acid to the ribosome & enzymes join the two amino acids The process continues and a chain of amino acids forms When the ribosome reaches the stop codon, it detaches from the mRNA and the amino acid chain is released. 49 50 We have a Protein !!! MUTATIONS WHAT ARE MUTATIONS? Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring) May occur in gametes (eggs & sperm) and be passed to offspring ARE MUTATIONS HELPFUL OR HARMFUL? Mutations happen regularly Almost all mutations are neutral Chemicals & UV radiation cause mutations Many mutations are repaired by enzymes ARE MUTATIONS HELPFUL OR HARMFUL? Some types of skin cancers result from somatic mutations Some mutations may improve an organism’s survival (beneficial) TYPES OF MUTATIONS CHROMOSOME MUTATIONS Five types exist: Deletion Inversion Translocation Nondisjunction Duplication CHROMOSOME MUTATIONS May Involve: Changing the structure of a chromosome The loss or gain of part of a chromosome DELETION Due to breakage A piece of a chromosome is lost INVERSION Chromosome segment breaks off Segment flips around backwards Segment reattaches DUPLICATION Occurs when a gene sequence is repeated TRANSLOCATION Involves two chromosomes that aren’t homologous Part of one chromosome is transferred to another chromosomes TRANSLOCATION NONDISJUNCTION Failure of chromosomes to separate during meiosis Causes gamete to have too many or too few chromosomes Disorders: CHROMOSOME MUTATIONS Down Syndrome Chromosome 21 does not separate correctly. They have 47 chromosomes in stead of 46. Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence. CHROMOSOME MUTATIONS Cri-du-chat Deletion of material on 5th chromosome Characterized by the cat-like cry made by cri-du-chat babies Varied levels of mental handicaps SEX CHROMOSOME ABNORMALITIES Klinefelter’s Syndrome XXY, XXYY, XXXY Male Sterility Small testicles Breast enlargement SEX CHROMOSOME ABNORMALITIES XYY Syndrome Normal male traits Often tall and thin Associated with antisocial and behavioral problems SEX CHROMOSOME MUTATIONS Turner’s Syndrome X Female sex organs don't mature at adolescence sterility short stature SEX CHROMOSOME MUTATIONS XXX Trisomy X Female Little or no visible differences tall stature learning disabilities limited fertility CHROMOSOME MUTATION ANIMATION GENE MUTATIONS Change in the nucleotide sequence of a gene May only involve a single nucleotide May be due to copying errors, chemicals, viruses, etc. TYPES OF GENE MUTATIONS Include: Point Mutations Substitutions Insertions Deletions Frameshift POINT MUTATION Change of a single nucleotide Includes the deletion, insertion, or substitution of ONE nucleotide in a gene POINT MUTATION Sickle Cell disease is the result of one nucleotide substitution Occurs in the hemoglobin gene FRAMESHIFT MUTATION Inserting or deleting one or more nucleotides Changes the “reading frame” like changing a sentence Proteins built incorrectly FRAMESHIFT MUTATION Original: The fat cat ate the wee rat. Frame Shift (“a” added): The fat caa tet hew eer at. AMINO ACID SEQUENCE CHANGED GENE MUTATION ANIMATION REVIEW QUESTIONS 1. 2. 3. 4. 5. Where can mutations take place? What are the five types of mutations? What is nondisjunction? Name and summarize a genetic disorder. Explain how mutations are harmful and beneficial to humans.