Chapter 13 Notes - Exam 3 PDF

Chapter 13 Altering the Genetic Material: Mutation and DNA Repair  histone tails ! nucleosomes Modifying & chromatin-remodeling · acetylation of histone tail ! V O...

Chapter 13 Altering the Genetic Material: Mutation and DNA Repair  histone tails ! nucleosomes Modifying & chromatin-remodeling · acetylation of histone tail ! V O 13.2 Causes of Mutations Section 13.2 Learning Outcomes 1. Analyze the results of the Lederbergs’ experiment, and explain how they were consistent with the random theory of mutation 2. Discuss the difference between spontaneous and induced mutations, and provide examples 13.2 Causes of Mutations The Lederbergs Showed That Mutations Are Random Events The experiments of Joshua and Esther Lederberg addressed questions about the cause of mutations They documented the presence of E. coli cells that were resistant to T1 bacteriophage (a virus that infects bacteria) Loading… 13.2 Causes of Mutations The Lederbergs Used Replica Plating to Show That Mutations Are Random Events Data indicated that the mutations happened before exposure to the virus, consistent with these mutations occurring randomly How do mutations occur? Usually, DNA Damage comes first, then Mutations Follows This direct nucleotide insertion error can be reversed if detected by Mismatch Repair proteins. Damaged DNA can be repaired by Loading… multiple damage repair systems. No nucleotide changes. Mutations can be locked into the genome after damage occurs if: a. The DNA polymerases tasked with repair can insert wrong nucleotide(s). b. Damage is not repaired, but DNA replication continues anyway. Daughter cells then inherit mutated DNA. How do mutations occur? Spontaneous Mutations: 1. DNA polymerase matches the wrong base to the template Original error rate: 1 error/100,000 basepairs After proofreading: 1 error/1 billion basepairs 1. 2. 3. 4. How do mutations occur? Spontaneous Mutations: 2 and 3. Types of DNA damage. Can be repaired or… The repair DNA polymerase can insert wrong nucleotide(s) 1. 2. 3. 4. How do mutations occur? Spontaneous Mutations: 4. Transposons, aka “jumping genes” can disrupt genes 1. 2. 3. 4. How do mutations occur? 1. 2. chromosome break How do mutations occur? 1. 2. chromosome Can be break “repaired” correctly or incorrectly 13.1 Consequences of Mutations Section 13.1 Learning Outcomes 1. List the different ways that mutations affect the sequence of a gene 2. Outline how mutations in Loading… a protein-encoding gene may affect the amino acid sequence of a polypeptide 3. Explain how mutations can occur outside the coding sequence and affect gene expression 4. Distinguish between mutations in somatic cells and germ-line cells 13.1 Consequences of Mutations Gene Mutations Alter the DNA Sequence of a Gene A point mutation affects only a single base pair within the DNA A base substitution involves a change where one base is replaced by another Ex: T (in top strand) was replaced by G, and corresponding A (in bottom strand) was replaced with C A single base pair can be added or deleted and cause a point mutation Ex: A single base pair (A-T) has been added to the sequence 13.1 Consequences of Mutations Gene Mutations May affect the Amino Acid Sequence of a Polypeptide A point mutation within the coding region may be classified as a silent mutation, missense mutation, nonsense mutation, or frameshift mutation based on the impact on the polypeptide 13.1 Consequences of Mutations Gene Mutations That Occur Outside of Coding Sequences Can Influence Gene Expression Mutations within noncoding sequences can affect gene expression too Noncoding sequence is anything that is not transcribed by RNAP (examples below)  13.1 When do mutations occur? During meiosis (gamete formation) Will not affect you, but can be transmitted to your offspring. During mitosis of somatic cells May affect you, but will not be transmitted to your offspring 13.3 DNA Repair Section 13.3 Learning Outcomes 1. List the general features of DNA repair systems 2. Describe the steps of nucleotide excision repair (NER) 13.3 DNA Repair All living organisms require the ability to repair damage to DNA to minimize mutation Cells contain several systems that detect and repair damage 13.3 DNA Repair Nucleotide excision repair (NER) is the most common DNA repair system; it is found in all eukaryotes and prokaryotes The region encompassing several nucleotides in the damaged strand is removed The intact strand is used as a template for “resynthesis” of a normal complementary strand