Chapter 7 Notes DNA Structure and Replication
Chapter 7 Notes DNA Structure and Replication BIOL 04102-03
Northwest Missouri State University
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This 5 page Class Notes was uploaded by Sarah Morse on Friday October 7, 2016. The Class Notes belongs to BIOL 04102-03 at Northwest Missouri State University taught by Dr. Dieringer in Fall 2016. Since its upload, it has received 4 views. For similar materials see General Biology in Biology at Northwest Missouri State University.
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CHAPTER 7 DNA STRUCTURE AND REPLICATION DNA AS EVIDENCE 1. How can scientists use DNA to identify a person? a. Chemical makeup of this molecule. i. Blueprint of life. b. Deoxyribonucleic Acid, or DNA. i. Common to all life forms. ii. Hereditary molecule that is common to all life forms. iii. Passed from parents to offspring. iv. Instruction manual from which we are built. 2. Where can you find DNA? a. The molecule exists inside the nucleus of almost every cell in our body in the form of chromosomes. i. A single, large DNA molecule wrapped around proteins. 1. Chromosomes are located in the nuclei of most eukaryotic cells. ii. Strands of DNA would around proteins. b. 23 pairs of chromosomes. i. Inherit one chromosome from each parent. rdi. Total of 46. c. 23 pair of chromosomes is sex chromosomes. i. X and Y ii. Determine sex. iii. Fathers pass on X and Y. iv. Mothers pass on X and X. 3. Infographic 7.1 What is DNA and where is it found? a. DNA is the hereditary molecule common to all living organisms. i. It is the instruction manual from which an organism is built. b. Each human has 23 pairs of chromosomes. i. One chromosome each from the parents. rd ii. 23 determines sex. c. DNA exists in the nuclei of most cells. d. DNA molecules are organized into discrete structures called chromosomes. i. If a single DNA molecule were stretched out it would be 1 to 3 meters long. ii. Each chromosome consists of a single, long DNA molecule wrapped around proteins. UNRELIABLE EVIDENCE 1. Error rates a. The rate at which experts have falsely validated its claims. 2. To identify perpetrators, forensic scientists examine the specific sequence of nucleotide bases along one strand of a person’s DNA. a. DNA is unique. b. DNA is made up of two strands of subunits linked together in long chains. i. These subunits are called nucleotides. 1. The building blocks of DNA. 2. Sugar 3. Phosphate a. Binds to sugar. 4. Base ii. The two strands of linked nucleotides pair up and twist around each other to form a spinal-shaped double helix. 1. The spiral structure formed by two strands of DNA nucleotides bound together. 2. Sugar and phosphate form a backbone 3. The bases form the internal ‘rungs’ a. Held together by hydrogen bonds. c. 4 different types of nucleotide bases: i. Adenine ii. Thymine iii. Guanine iv. Cytosine d. The order of the nucleotide bases is a key form of genetic information in cells. i. Provides the instructions for making proteins. 3. Infographic 7.2 DNA is made of two strands of nucleotides. a. DNA is a double-stranded molecule. i. each of the two strands consists of a chain of subunits called nucleotides that are bonded together. 1. Adenine 2. Thymine 3. Guanine 4. Cytosine ii. Nucleotides are building blocks of DNA. b. Nucleotide structure i. Each nucleotide consists of three parts: 1. Sugar 2. Phosphate 3. One of four bases a. A, T, G, C. c. Hydrogen bonding, or base pairing, between the bases of each strand holds the strands together. i. Bases pair in a specific pattern: 1. A with T, two bonds 2. C with G, three bonds d. DNA sequences are unique i. The four nucleotides occur billions of times. ii. The particular sequence makes a person unique. BROWN GETS A BREAK 1. DNA Profile. a. A visual representation of a person’s unique DNA sequence. MAKING MORE DNA 2 1. Forensic scientists use a method to increase, or amplify, the amount of DNA in a sample. a. The method takes advantage of the way cells normally make more DNA in the process of DNA replication. i. The natural process by which cells make an identical copy of a DNA molecule. ii. Occurs throughout our lives whenever cells reproduce. iii. Two strands of nucleotides in a DNA helix do not pair up randomly. 1. Consistent pattern. 2. A and T 3. C and G b. The two strands of the double helix are complementary. i. Two strands of DNA are said to be complementary in that A always pairs T and G always pairs with C. ii. They fit together like pieces of a puzzle. 2. Steps of replication a. The helix is unwound and the two strands unzip from each other. b. An enzyme called DNA polymerase builds a new strand of DNA along the unzipped strands i. Free nucleotides floating inside the cell’s nucleus are added to each new strand in a sequence that is complementary to the nucleotide sequence on the original template strands. 1. A with T 2. C with G c. Result is two complete double-stranded molecules of DNA. 3. Infographic 7.3 DNA structure provides a mechanism for DNA replication. a. When cells reproduce, they first must replicate their DNA so that each new cell contains a copy of the DNA molecule. b. Complementary base pairing between DNA strands guides replication of two new strands. 4. DNA replication is a remarkably accurate process. a. Polymerase enzyme adds about 1000 nucleotides per second. b. Rarely makes mistake. 5. Polymerase chain reaction (PCR) a. A laboratory technique used to replicate, and thus amplify, a specific DNA segment. b. Similar to DNA replication which occurs naturally. c. Takes place in a test tube. d. From a starting sample of just a few molecules of DNA, PCR can make billions of copies. e. How it works: i. Add nucleotides to a small sample of DNA, DNA polymerase enzyme, and primers. 1. Primers a. Short segments of DNA that act as guideposts and flag the section to which DNA polymerase should bind to begin replication. ii. DNA is heated to separate the strands. iii. Then cooled to allow nucleotides to be added. 3 6. Infographic 7.4 The polymerase chain reaction amplifies small amounts of DNA. a. The polymerase chain reaction (PCR) is similar to naturally occurring DNA replication. i. Except that it occurs in a test tube and only replicates specific regions of a DNA molecule. b. During each round of PCR: i. The two nucleotide strands separate. ii. Each strand serves as a template for the addition of nucleotides according to base-pairing rules. 1. A with T 2. C with G iii. Heating separate DNA strands. iv. Cooling allows DNA polymerase to pair new nucleotides with the original template strands. DNA PROFILING: HOW IT WORKS 1. Once DNA evidence is obtained, the next step is to analyze it. a. Genome i. One complete set of genetic instructions encoded in the DNA of an organism. b. Scientists employ PCR to amplify specific segments of DNA and analyze just these segments. i. Short Tandem Repeats 1. Blocks of repeated DNA sequences found at points along our chromosomes. 2. Noncoding a. Do not contain instructions for making proteins. 3. Nonsense words in our DNA. 4. Two copies of STR 2. Infographic 7.5 DNA profiling uses short tandem repeats. a. No two people have the same exact nucleotide sequence. b. The specific regions of DNA that forensic scientists analyze are those that contain short tandem repeats (STR). i. Short stretches of repeated DNA sequences. ii. People differ in the number of copies of an STR sequence found along their chromosomes. 3. Gel electrophoresis a. Separates the replicated STRs according to length. b. Shorter STRs i. Those with fewer numbers of repeats. ii. Are smaller and travel farther in the gel. c. Longer STRs i. Do not travel as far. d. Visualized with a detection technique known as fluorescence. i. Same kind of light released from glowing jellyfish. ii. Separated segments of DNA create a specific pattern of bands that is unique to each person. 1. DNA profile 4. Infographic 7.6 Creating a DNA Profile 4 a. Collect cells from crime scene evidence and extract DNA. b. Amplify multiple STR regions by PCR. c. Separates STRs by gel electrophoresis. i. PCR products are inserted into a gel. ii. An electric current applied to the gel causes polar DNA to migrate through it. iii. Shorter fragments travel farther. iv. Longer fragments remain near the top. d. Compare STR banding patterns. i. The gel shows the results of three different STR regions analyzed from the DNA in a crime scene sample and in three suspects. 1. Green, red, and blue bands. 2. Different STR lengths result in two bands. 3. Identical STR lengths result in single bands. CHAPTER 7 SUMMARY 1. DNA is the hereditary molecule of all living organisms. a. DNA contains instructions for building an organism. 2. DNA sequences determine the genetic uniqueness and relatedness of individuals. 3. The DNA in a eukaryotic cell is packaged into chromosomes located in the nucleus. 4. Humans have 23 pairs of chromosomes in their cells a. One chromosome of each pair inherited from the mother and father. 5. DNA is a double-stranded molecule that forms a spiral structure known as a double helix. 6. Each strand of DNA is made of nucleotides bonded together in a linear sequence. 7. There are four distinct nucleotides a. Adenine b. Thymine c. Guanine d. Cytosine 8. The two linear strands of a DNA molecule are bonded together by complementary pairing of A with T and C with G. 9. Complementary pairing of DNA strands guides DNA replication a. A fundamental part of cell reproduction. 10.PCR enables scientists to vastly increase the number of copies of specific DNA sequences. 11.Forensic scientists use noncoding DNA sequences known as STRs to create a DNA profile. 12.STRs are blocks of repeated sequences of DNA a. People differ in the number of times the sequences are repeated along their chromosomes. b. A DNA profile is more accurate and reliable than many other forms of evidence. 5