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DNA Structure 1 DNA I DNA is often called the blueprint of life. I In simple terms, DNA contains the instructions for making proteins within the cell. I DNA is universal. 2 DNA… codes for proteins Proteins are important: • Your skin, muscles & bones are made of protein • All chemical reactions needed for life (such as eating, running, thinking, etc) depends on enzymes which are proteins. 3 Watson & Crick’s Model Watson and Crick first discovered the double helix structure of DNA in 1953. They walked into the office of a scientific publication and announced, “We have found the secret of life”. 4 Why do we study DNA? DNA Its central importance to all life on Earth I Medical benefits such as cures for diseases and understanding cancer and birth defects I Better food crops- genetic engineering I CSI – criminal investigations I Chromosomes and DNA Where is DNA found? I DNA is the material the makes up our genes which code for certain traits and proteins. I Our genes are on our chromosomes. I Simply…Chromosomes are made up of a chemical called DNA. DNA – The Double Helix Molecule I DNA is a very long polymer. I The basic shape is like a twisted ladder or zipper. I The DNA double helix has two strands twisted together. One Strand of DNA phosphate I The backbone of the molecule is alternating Phosphate deoxyribose I and Deoxyribose sugar I The teeth are Nitrogenous bases bases One Strand of DNA IOne strand of DNA is a polymer of nucleotides. IOne strand of DNA has many millions of nucleotides. nucleotide Nucleotides One deoxyribose together with its phosphate and base make a nucleotide. O O -P O O C C C Phosphate O C C O Deoxyribose Nitrogenous base 10 Four Nitrogenous Bases DNA has four different bases: I Cytosine C T I Adenine A I Guanine G I Thymine Two Kinds of Bases in DNA IPyrimidines are single ring bases. IPurines are double ring bases. N N C O C C N C N N C C C N N C N C Purines: Adenine & Guanine I Adenine and guanine each have two rings of carbon and nitrogen atoms. I All Grandmas are Pure (purines) N C Adenine N C C N O N C N N C N C C C N Guanine C N N C Pyrminidines: Thymine & Cytosine I Thymine and cytosine each have one ring of carbon and nitrogen atoms. I King Tut and Cleopatra lived in Pyramids (pyrimidines) N O C C O C C N C Thymine N O C C N C N C Cytosine Two Stranded DNA I Remember, DNA has two strands that fit together something like a zipper. I The teeth are the nitrogenous bases but why do they stick together? 15 I N N C C guanine C C N cytosine C C N N N C I The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. The bonds between cytosine and guanine are shown here with dotted lines O I C N Hydrogen Bonds N C O Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine I Adenine always pairs up with thymine I Adenine is bonded to thymine here I N N N C adenine C N O C thymine N C C N N C O C C C C Chargraff’s Rule: I Adenine and Thymine always join together A T I Cytosine and Guanine always join together C G DNA by the Numbers Each cell has about 2m of DNA. I The average human has 75 trillion cells. I The average human has enough DNA to go from the earth to the sun more than 400 times. I DNA has a diameter of only 0.000000002 m. I The earth is 150 billion m or 93 million miles from the sun. DNA Replication DNA Replication I DNA replication produces two molecules from one I Each strand serves as a pattern to make a new DNA molecule. I Begins as an enzyme that breaks the hydrogen bonds between the nitrogen bases and unzips the strand. Replication Continued I Nucleotides that are floating free in the nucleus bond to the single stands by base pairing. I Another enzyme bonds these new nucleotides into a chain. I Each new strand formed is a complement of one of the original I DNA Replication Animation DNA Replication Let’s Practice: Write the complimentary strand for DNA… TGACCGAT ACTGGCTA TGGCCAATATA ACCGGTTATAT Protein Synthesis I Proteins form key cell structures and regulate cell functions (enzymes) I The protein’s “code” is supplied by the DNA in the nucleus. I But proteins are “manufactured” in the ribosomes in the cytoplasm. I So how does protein synthesis occur? Protein Synthesis I Step 1: Transcription (to re-write) • DNA is too large to go from the nucleus to the cytoplasm, so only pieces of DNA are copied into RNA. This RNA then travels from the nucleus to the cytoplasm. I Step 2: Translation (to make useful) • The RNA is then made into something useful, like assembling amino acids into proteins in the ribosome RNA I RNA is a single strand I The simple sugar in RNA is ribose I Nitrogen bases in RNA: • Adenine • Guanine • Cytosine • Uracil (replaces thymine bonds with adenine) Types of RNA I Messenger RNA (mRNA) = brings information from the DNA in the nucleus to the cell’s cytoplasm I Ribosomal RNA (rRNA) = part of the ribosome that clamps onto the mRNA and helps to assemble the amino acids in the correct order. I Transfer RNA (tRNA) = transports amino acids to the ribosome to be assembled into a protein. Protein Synthesis - Transcription I Similar to DNA replication, but the result is the formation of one single-stranded RNA molecule (mRNA) I Process: • Enzyme unzips the DNA molecule • Free RNA nucleotides pair with complementary DNA nucleotides • When pairing is complete, mRNA molecule breaks away. The DNA rejoins the original strand. The mRNA leaves the nucleus and enters the cytoplasm to join with the ribosome. Protein Synthesis - Transcription Let’s Practice: Write the complimentary strand for mRNA… TGACCGAT ACUGGCUA TGGCCAATATA ACCGGUUAUAU Protein Synthesis Protein Synthesis - Translation 1. Once the newly made mRNA leaves the nucleus, it attaches to the ribosome. 2. Ribosomes will “read” 3 nucleotides called codons in the mRNA code at a time. • Each codon codes for: – an amino acid – a START signal ( AUG ) – a STOP signal ( UAA, UAG, and UGA ) Codon Protein Synthesis - Translation 3. When the ribosome reads the start sequence ( AUG ), a tRNA molecule comes along with the anticodon ( UAC ) and the amino acid ( MET ). • The anticodon is the complementary sequence. anticodon Protein Synthesis - Translation 4. The ribosome then reads the next codons on the mRNA and tRNA transfers the amino acids to build the protein until a “stop” codon is read. Codon Chart for mRNA Let’s Break the Genetic Code 1. Start with DNA: TACTAGCTAACC 2. Write the complimentary strand for mRNA AUGAUCGAUUGG 3. Identify the codons on the mRNA AUG-AUC-GAU-UGG 4. Identify the anticodons on the tRNA UAC-UAG-CUA-ACC 5. Identify the amino acid sequence from the mRNA Met - Iso - Asp - stop Genetic Mutations I Any change in the DNA sequence is called a mutation. • Mutations can effect reproductive cells – Will be passed on to offspring • Mutations can effect body cells – Example = CANCER Genetic Mutations Everyone acquires some changes to their DNA during the course of their lives. I These changes occur in a number of ways. Sometimes there are simple copying errors that are introduced when DNA replicates itself. (Every time a cell divides, all of its DNA is duplicated so that the each of the two resulting cells have a full set of DNA.) I Other changes are introduced as a result of DNA damage through environmental agents including sunlight, cigarette smoke, and radiation. I Genetic Mutations I I I Our cells have built in mechanisms that catch and repair most of the changes that occur during DNA replication or from environmental damage. Some of these changes occur in cells of the body — such as in skin cells as a result of sun exposure — but are not passed on to children. But other errors can occur in the DNA of cells that produce the eggs and sperm. • These are called germline mutations and can be passed from parent to child. • If a child inherits a germline mutation from their parents, every cell in their body will have this error in their DNA. • Germline mutations are what cause diseases to run in families Genetic Mutations I Types of DNA Mutations: • Point mutation • Frameshift mutation • Inversion Not All Mutations are BAD! I Some result in characteristics that give the organism a greater chance of survival. I Example: Sickle cell anemia (deflated look of red blood cells) is caused by a mutation, however it is beneficial to people in Africa who often contract malaria – the parasite can no longer attach to their red blood cells, therefore they aren't affected Point Mutation I A change in a single base pair in DNA I Example: • THE DOG BIT THE CAT. • THE DOG BIT THE CAR. I Can change the entire structure of a protein, and effect the shape of the protein. Frameshift Mutation A single base pair in DNA is deleted or added. I Every codon after the deleted base would be different. I This type of mutation can make the DNA meaningless and often results in a shortened protein. I Example: I • THE DOG BIT THE CAT. • THE DOB ITT HEC AT. Inversion In an inversion mutation, an entire section of DNA is reversed. I A small inversion may involve only a few bases within a gene, while longer inversions involve large regions of a chromosome containing several genes. I Original: The fat cat ate the wee rat. I Inversion: The fat tar eew eht eta tac. I Causes of Mutations I Spontaneous: • Mistake in base pairing during DNA replication I Mutagen – agent that causes DNA change • High energy radiation – X rays • Chemicals – Dioxins, asbestos, benzene, cyanide, formaldehyde • High temperatures Mutation Video 4 Types of Chromosomal Mutations • Deletions occur when part of a chromosome is left out. video • Insertions occur when a part of a chromatid breaks off and attaches to its sister chromatid. • Inversion occur when part of a chromosome breaks off and is reinserted backwards. • Translocation occur when part of one chromosome breaks off and is added to a different chromosome video