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1. What are the 3 components of this DNA nucleotide? 2. What is the function of DNA in the cell? Genetics DNA and Genes DNA: The Molecule of Heredity Contributors to DNA Discovery • 1943 Oswald Avery: DNA carries genetic information • 1952 Franklin took the first picture of DNA using X-RAY Contributors to DNA Discovery 1953 - Watson & Crick proposed the structure of DNA 1962 - Nobel Prize to Watson and Crick • “FATHERS OF DNA” Contributors to DNA Discovery • So? Was it that clear cut?? • What event occurred allowing Watson and Crick to discover the DNA structure? What is DNA? • Deoxyribonucleic Acid – determines an organism’s traits – ultimately determines the structure of proteins. • body is made up of proteins • body’s functions depend on proteins called enzymes. The Structure of DNA • DNA is a polymer made of nucleotides. • Nucleotides have three parts: – simple sugar – phosphate group – nitrogenous base. • composed of one atom of phosphorus surrounded by four oxygen atoms. carbon ring structure that contains one or more atoms of nitrogen. Nitrogenous base Phosphate group Sugar (deoxyribose) • Deoxyribose is the simple sugar in DNA The structure of nucleotides • In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). *always pair Adenine (A) Thymine (T) * always pair Cytosine (C) Guanine (G) The structure of nucleotides • Thus, in DNA there are four possible nucleotides, each containing one of these four bases. • Nucleotides join together to form long chains. – Formed by covalent bonds – These chains are known as the Double Helix The structure of nucleotides **** The importance of nucleotide sequences Chromosome The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein. Genes and Proteins • Proteins make up the structure of an organism AND control all of the organism’s chemical reactions to keep it alive DNA and Cell Division DNA to Protiens • Remember…DNA ultimately determines structure of proteins. • These proteins are what makes “us” and enables “us” to function….. • So how do we get these specific proteins??? Replication of DNA • Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes.( Interphase) • The DNA in the chromosomes is copied in a process called DNA replication. • Without DNA replication, new cells would have only half the DNA of their parents. Cells Start Here: Transcription • Transcription results in the formation of one single-stranded RNA molecule. – takes place in the nucleus • mRNA, which is seen in here, takes the instructions from the nucleus to the cytoplasm. What is RNA? • RNA is single stranded •The sugar is ribose •Rather than thymine, RNA contains a similar base called uracil (U). Uracil Hydrogen bonds Adenine Why RNA??? • DNA provides workers with the instructions for making the proteins, and workers build the proteins. • The workers for protein synthesis are RNA molecules. Back to Copying DNA…. • Once mRNA is in the cytoplasm… Ribosomal RNA (rRNA) binds to the mRNA and uses the instructions to assemble the amino acids in the correct order. • This starts Translation Translation: From mRNA to Protein • Translation is the process of converting the information in a sequence of nitrogenous bases in mRNA into a sequence of amino acids in protein. • Translation takes place at the ribosomes in the cytoplasm. The role of transfer RNA Amino acid • Each tRNA molecule attaches to only one type of amino acid. Chain of RNA nucleotides • An anticodon is a sequence of three bases found on tRNA. Transfer RNA molecule Anticondon The role of transfer RNA Ribosome mRNA codon The role of transfer RNA • The first codon on mRNA is AUG, which codes for the amino acid methionine. • AUG signals the start of protein synthesis. • Then the ribosome slides along the mRNA to the next codon. The role of transfer RNA Methionine tRNA anticodon The role of transfer RNA • A new tRNA molecule carrying an amino acid pairs with the second mRNA codon. Alanine The role of transfer RNA • The amino acids are joined when a peptide bond is formed between them. Methionine Alanine Peptide bond The role of transfer RNA • A chain of amino acids is formed until the stop codon is reached on the mRNA strand. Stop codon The Genetic Code The Messenger RNA Genetic Code First Letter U U Phenylalanine (UUU) A G Third Letter G Serine (UCU) Tyrosine (UAU) Cysteine (UGU) Serine (UCC) Tyrosine (UAC) Cysteine (UGC) Leucine (UUA) Leucine (UUG) Serine (UCA) Stop (UAA) Stop (UGA) Serine (UCG) Stop (UAG) Tryptophan (UGG) Leucine (CUU) Proline (CCU) Histadine (CAU) Arginine (CGU) Leucine (CUC) Proline (CCC) Histadine (CAC) Arginine (CGC) Leucine (CUA) Proline (CCA) Glutamine (CAA) Arginine (CGA) Leucine (CUG) Isoleucine (AUU) Proline (CCG) Glutamine (CAG) Arginine (CGG) Threonine (ACU) Asparagine (AAU) Serine (AGU) Isoleucine (AUC) Threonine (ACC) Asparagine (AAC) Serine (AGC) Isoleucine (AUA) Methionine; Start (AUG) Threonine (ACA) Lysine (AAA) Threonine (ACG) Lysine (AAG) Arginine (AGA) Arginine (AGG) Valine (GUU) Alanine (GCU) Aspartate (GAU) Glycine (GGU) Valine (GUC) Alanine (GCC) Aspartate (GAC) Glycine (GGC) Valine (GUA) Valine (GUG) Alanine (GCA) Alanine (GCG) Glutamate (GAA) Glutamate (GAG) Glycine (GGA) Glycine (GGG) Phenylalanine (UUC) C C Second Letter A U C A G U C A G U C A G U C A G DNAi •Triplet code •Translation http://www.pbs.org/wgbh/nova/body/rnai.html 1. Why is this exact base sequence important? 2. What may be the result of “wrong” base sequencing? Mutations • Organisms have evolved many ways to protect their DNA from changes. • In spite of these mechanisms, however, changes in the DNA occasionally do occur. • A mutation is any change in a DNA sequence. • Mutations can be caused by errors in replication, transcription, cell division, or by external agents. Mutations in reproductive cells • Mutations can occur in the reproductive cells. – This then becomes part of the genetic makeup of the offspring. – If the change makes a protein nonfunctional, the embryo may not survive. Mutations in body cells • What happens if powerful radiation, such as gamma radiation, hits the DNA of a nonreproductive cell, a cell of the body such as in skin, muscle, or bone? • If the body cell’s DNA is changed, this mutation would not be passed on to offspring. • The mutation may cause problems for the individual. The effects of point mutations • A point mutation is a change in a single base pair in DNA. • A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein. The effects of point mutations mRNA Normal Protein Stop Replace G with A mRNA Point mutation Protein Stop Frameshift mutations • A frameshift mutation is a mutation in which a single base is added or deleted from DNA. • A frameshift mutation shifts the reading of codons by one base. • This mutation would cause nearly every amino acid in the protein after the deletion to be changed. Frameshift mutations Deletion of U Frameshift mutation mRNA Protein Chromosomal Alterations • Chromosomal mutations are structural changes in chromosomes. • When a part of a chromosome is left out, a deletion occurs • A B C D E F G H A B C E Deletion F G H Chromosomal Alterations • When part of a chromatid breaks off and attaches to its sister chromatid, an insertion occurs. • The result is a duplication of genes on the same chromosome. A B C D E F G H A B C B C D E Insertion F G H Chromosomal Alterations • When part of a chromosome breaks off and reattaches backwards, an inversion occurs. A B C D E F G H A D C B E FGH Inversion Chromosomal Alterations • When part of one chromosome breaks off and is added to a different chromosome, a translocation occurs. AB C D E F GH WX Y Z W X AB C DE F GH Translocation Y Z Causes of Mutations • A mutagen is any agent that can cause a change in DNA. • Mutagens include radiation, chemicals, and even high temperatures. • Forms of radiation, such as X rays, cosmic rays, ultraviolet light, and nuclear radiation, are dangerous mutagens because the energy they contain can damage or break apart DNA. Causes of Mutations • The breaking and reforming of a doublestranded DNA molecule can result in deletions. • Chemical mutagens include dioxins, asbestos, benzene, and formaldehyde, substances that are commonly found in buildings and in the environment. • Chemical mutagens usually cause substitution mutations. Repairing DNA • Repair mechanisms that fix mutations in cells have evolved. • Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides. • These repair mechanisms work extremely well, but they are not perfect. • The greater the exposure to a mutagen such as UV light, the more likely is the chance that a mistake will not be corrected.