DNA- THE MOLECULE OF LIFE Link STRUCTURE OF DNA DNA (Deoxyribonucleic Acid): DNA is a long, stringy, twisted molecule made up of nucleotides that carries genetic information. DISCOVERIES Rosalind Franklin, 1952, was studying the structure of DNA using X-ray diffraction ; helix 1953, JAMES WATSON & FRANCIS CRICK Saw Franklin’s image and finalized the structure of DNA Called it a “double-helix” STRUCTURE OF DNA Composition: DNA is composed of nucleotides. The nucleotide is the monomer. Three parts of a nucleotide: 1. 5-Carbon Sugar: Deoxyribose 2. Phosphate Group 3. Nitrogen Base DOUBLE HELIX: WHY? double helix because it consists of two long strands of nucleotides which are twisted together and when untwisted resemble a ladder. The sides of the ladder are made of alternating deoxyribose sugars and phosphate groups held together by covalent bonds. The “rungs” of the ladder are made up of pairs of nitrogen bases. They follow the “base-pairing rule”. BASE PAIRING NITROGEN BASES There are four different types of nitrogen bases: Purines: Composed of two rings 1. Adenine (A) 2. Guanine (G) Pyrimidines: Composed of one ring 3. Cytosine (C) 4. Thymine (T) NOTE: 5. Uracil (U) is found only in RNA, NOT in DNA BASE PAIRING RULE: A purine always pairs with a pyrimidine. A = T: Held together with two hydrogen bonds forming a double bond. C = G: Held together with three hydrogen bonds forming a triple bond. BONDS The “rungs” of the ladder are attached to the sugar part of the side (NOT the phosphate group). The nitrogen bases are held together by weak hydrogen bonds. These weak bonds break apart easily. FUNCTIONS OF DNA: DNA codes for proteins and hormones to be made. Proteins result in genetic traits. Hormones result in your body functioning The order or sequence of the 4 different nucleotide base pairs and the number of them determines what proteins are made and therefore, what genetic traits are present. DNA REPLICATION (11/15) Definition: The process of copying DNA Purpose: Gives new cells produced in mitosis and meiosis a complete set of chromosomes. Where Does DNA Replication Occur? Nucleus When Does DNA Replication Occur? The S phase of interphase in the cell cycle STEPS OF REPLICATION: 1. DNA untwists and enzymes break the hydrogen bonds between the nitrogen bases. The DNA “unzips”. 2. Free-floating nucleotides pair with each unzipped strand following the base pairing rule (A with T and C with G). · Each strand of DNA acts a template. · Hydrogen bonds hold the base pairs together. 3. the two new identical molecules of DNA are twisted back up by enzymes. Link to animation of process DNA replication song: “Backstreet Boys” Result: Two identical copies of DNA each composed of one original and one new strand. Why is replication so important? It occurs during interphase so that each new daughter cell will have a complete set of chromosomes at the end of mitosis. RNA AND TRANSCRIPTION RNA: Ribonucleic Acid A nucleic acid molecule that is similar to DNA but has different functions. Structure: Composed of RNA nucleotides and is a helix link WHAT IS THE DIFFERENCE? RNA differs from DNA in four ways: 1. RNA is single stranded not doubled. 2. Has uracil instead of thymine (still a pyrimidine). 3. ribose instead of deoxyribose 4. There are 3 types of RNA and only one type of DNA TYPES OF RNA: 11/17 1. mRNA (messenger): copies instructions in DNA and carries these to the ribosome. The message. TRANSFER RNA tRNA (transfer): carries amino acids to the ribosome. Contains the anticodon (group of three complementary nitrogen bases to the codon on mRNA). RIBOSOMAL RNA rRNA (ribosomal): makes up the ribosome. It “reads” the mRNA by grouping mRNA together into codons (groups of 3 nitrogen bases.) PROTEIN SYNTHESIS: the process where information in DNA is used to build proteins. Consists of two processes transcription and translation. Transcription: A strand of DNA is copied into a complementary strand of mRNA WHY DOES THIS HAPPEN? Why? DNA cannot leave the nucleus because it is too big needs a “messenger” to carry the information for making proteins to the ribosomes. mRNA smaller ,single stranded and only a portion of the DNA is copied so it can leave the nucleus. PROCESS: 1. DNA is untwisted in only the parts that contain the information needing to be copied. 2. DNA is unzipped by enzymes 3. Free floating mRNA nucleotides pair with one of the unzipped strands of the DNA following the base pairing rule. 4. Note: Uracil replaces thymine. 5. Only one strand of DNA acts as a template. The other just “hangs out” until the process is over. 6. mRNA breaks from the DNA template and the mRNA and goes to a ribosome. 7. The two strands of DNA zip back up, reforming the H- bonds RESULT: A single strand of mRNA is made with information copied from DNA for the building a specific protein. link Link to animation TRANSLATION 11/21 The process of converting or translating information in a sequence of nitrogen bases in mRNA into a sequence of amino acids that make a protein. Before translation can begin, transcription of the DNA into mRNA must occur. TRANSLATION : mRNA, 3 CONTINUED rRNA and tRNA are all involved steps: mRNA attaches to the ribosome (rRNA). (The rRNA slides along the mRNA like a bead on a string.) rRNA “reads” the mRNA in groups of three nucleotides called a codon. (AUG) called the initiator or start codon. There are three special “stop” codons: UAA, UAG and UGA. * this is where the protein ends. Link Animation link AMINO ACIDS 20 different amino acids and 64 different codons. Each amino acid may have more than one codon but each codon specifies for only one amino acid. MRNA CODON CHART MRNA CODON CHART – LET’S TRY IT! MUTATIONS 11/23 Def. Changes in the genetic material (DNA) Mutations can occur in two different types of cells: 1. Somatic (body) cells 2. Gamete (sex) cells Mutations that occur in somatic (body) cells usually result in killing that body cell only. Mutations that occur in gamete (sex) cells means that every cell of the developing fetus/baby will have that mutation. TYPES OF MUTATIONS IN GAMETE CELLS 2 Types: 1. Gene Mutations 2. Chromosomal Mutations 2 types of Single Gene Mutations: a. Point Mutation: a single point in the DNA sequence is affected. POINT MUTATIONS (CONTINUED) Can be a substitution in which one base is changed into another base. DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA Amino Acid:Met - Arg - Thr - Leu DNA: TAC GTA TGG AAT mRNA: AUG CAU ACC UUA Amino Acid:Met - His - Thr - Leu 2. FRAMESHIFT MUTATION: a single gene or nitrogen base is deleted or added. from the mRNA sequence causing a shift in the “reading frame” of the genetic message. Can be an insertion Can be a deletion FRAMESHIFT MUTATIONS More dramatic affect. may change every amino acid that follows the point of the mutation •can alter a protein so much that it is unable to perform its normal functions 2ND TYPE OF MUTATION IN GAMETES 5 types of Chromosomal 1. Deletion 2. Duplication 3. Inversion 4. Translocation 5. Non-disjunction Mutations: DO NOT WRITE: JUST LISTEN! Deletion: Involves the loss of all or part of a chromosome. Duplication: Involves the production of extra copies of parts of the chromosome. Inversion: Reverses the direction of parts of a chromosome. Translocation: When one part of a chromosome breaks off and attaches to another chromosome. Non-disjunction: Means “not coming apart”. When homologous chromosomes fail to separate properly during meiosis. QUEST ON CH. 12 & 13 IS ON : November 29th = Blue Classes! November 30th= Gold Classes!