Campbell: Biology - Chapter 16 PDF

Campbell: Biology Twelfth Edition Chapter 16 The Molecular Basis of Inheritance Copyright © 2021, 2017, 2014 Pearson Education,...

Campbell: Biology Twelfth Edition Chapter 16 The Molecular Basis of Inheritance Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Chapter 16 Learning Objectives ▪ Understand how we know that DNA is the genetic material of cells/organisms (concept 16.1) ▪ Know the structural details of DNA (Concept 16.2) ▪ Understand the process of DNA replication, including the enzymes and proteins that carry out the work (concept 16.2) ▪ Know the levels of chromosome structure (concept 16.3) Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved CONCEPT 16.1: DNA is the genetic material—HOW DO WE KNOW? Early in the 20th century, the identification of the molecules of inheritance posed a major challenge to biologists The role of DNA in heredity was first discovered by studying bacteria and the viruses that infect them Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Evidence That DNA Can Transform Bacteria The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928 Griffith worked with two strains of a bacterium, one pathogenic and one harmless Evidence That DNA Can Transform Bacteria When he mixed heat-killed remains of the pathogenic strain with living cells of the harmless strain, some living cells became pathogenic He called this phenomenon transformation, now defined as a change in genotype and phenotype due to assimilation of foreign DNA Later work by Oswald Avery, Maclyn McCarty, and Colin MacLeod identified the transforming substance as DNA Many biologists remained skeptical, mainly because little was known about DNA Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Evidence That Viral DNA Can Program Cells More evidence for DNA as the genetic material came from studies of viruses that infect bacteria Such viruses are called bacteriophages (or phages) A virus is DNA (sometimes RNA) enclosed by a protective coat, often simply protein Phages have been widely used as tools by researchers in molecular genetics Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Evidence That Viral DNA Can Program Cells In 1952, Alfred Hershey and Martha Chase showed that DNA is the genetic material of a phage known as T2 They designed an experiment showing that only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection They concluded that the injected DNA of the phage provides the genetic information Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.4 Inquiry: Is protein or DNA the genetic material of phage T2? Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Animation: The Hershey-Chase Experiment Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Concept 16.2: The structure of DNA DNA is composed of 4 DNA nucleotide pairs, (A+T, C+G) Phosphodiester bonds covalently link each nucleotide within a single DNA strand Each DNA strand exhibits polarity with 5’ and 3’ ends Antiparallel DNA strands held together by H-bonds Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Animation: DNA and RNA Structure Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved DNA vs RNA: Key Differences DNA RNA Double stranded Mostly single stranded Deoxyribose sugar Ribose sugar Thymine (T) Uracil (U) Stays in nucleus Transported to cytosol replicated transcribed Stores hereditary info Uses hereditary info to build proteins Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.9 Base pairing in DNA Purines (A & G) have double C-N rings Pyrimidines (C, T & U) have single C-N rings Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Building a Structural Model of DNA After DNA was accepted as the genetic material, the challenge was to determine how its structure accounts for its role in inheritance Maurice Wilkins and Rosalind Franklin used a technique called X-ray crystallography to study molecular structure Franklin produced a picture of the DNA molecule using this technique Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Building a Structural Model of DNA Franklin’s X-ray crystallographic images of DNA allowed James Watson to deduce that DNA was helical The X-ray images also enabled Watson & Crick to deduce the width of the helix and the spacing of the nitrogenous bases The pattern in the photo suggested that the DNA molecule was made up of two strands, forming a double helix Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Where are they now? Rosalind Franklin died of ovarian cancer in 1958 (likely resulting from her constant exposure to x-rays) Wilkins, Watson, & Crick awarded Nobel prize in 1962 Wilkins died 2004 at 88 Frances Crick died 2004 at 88 James Watson still alive, 95 yrs old – Racist, sexist, all-around not nice guy Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Reviewing DNA Strx-Group activity Group A: Basic components: What are the three main components of a nucleotide, the building block of DNA? What are the four nitrogenous bases found in DNA, and which ones are purines and pyrimidines? What is the difference between deoxyribose sugar and ribose sugar, and which one is found in DNA? How does DNA differ from RNA? Group B: Structure: What molecules make up the "backbone" of a DNA strand? Explain the phosphodiester linkage that connects nucleotides in a DNA strand. Explain the concept of "antiparallel" strands in a DNA molecule. What type of bonds hold the base pairs together in a DNA molecule? Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved CONCEPT 16.2: DNA replication and repair Resemblance of offspring to parents relies on accurate replication of DNA prior to meiosis and its transmission to the next generation Replication prior to mitosis ensures the faithful transmission of genetic information from a parent cell to the two daughter cells Watson and Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material The copying of DNA is called DNA replication Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.1b How does DNA replication transmit genetic information? Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The Basic Principle: Base Pairing to a Template Strand Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication This is referred to as semiconservative replication Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved DNA Replication: The mechanism The copying of DNA is remarkable in its speed and accuracy More than a dozen enzymes and other proteins participate in DNA replication Replication in bacteria is best understood, but evidence suggests that the replication process in eukaryotes and prokaryotes is fundamentally similar Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Getting Started Replication begins at particular sites called origins of replication, where the two DNA strands are separated, opening up a replication “bubble” A eukaryotic chromosome may have hundreds or even thousands of origins of replication Replication proceeds in both directions from each origin, until the entire molecule is copied Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Date Lecture Topic Lab Today Ch 16 Labs as normal F 11/17 Ch 16 M 11/20 Ch 16, DNA lab quiz due Mon Labs-meet with your research group W 11/29 Ch 17 Tues-Thurs labs-meet F 12/1 Ch 17 with your research group M 12/4 Ch 17 Research Proposal DUE No labs W 12/6 Ch 20 F 12/8 Ch 20 M 12/11 Review No labs W 12/13 Final Exam 8:00-10:00am Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 16.13 Origins of replication in E. coli and eukaryotes Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Animation: Origins of Replication Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Getting Started At the end of each replication bubble is a replication fork, a Y-shaped region where parental DNA strands are being unwound Helicases are enzymes that untwist the double helix at the replication forks Single-strand binding proteins bind to and stabilize single-stranded DNA Topoisomerase relieves the strain of twisting of the double helix by breaking, swiveling, and rejoining DNA strands Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.14 Some of the proteins involved in the initiation of DNA replication Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Synthesizing a New DNA Strand DNA polymerases require a primer to which they can add nucleotides The initial nucleotide chain is a short RNA primer This is synthesized by the enzyme primase The completed primer is five to ten nucleotides long The new DNA strand will start from the 3′ end of the RNA primer Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Synthesizing a New DNA Strand Enzymes called DNA polymerases catalyze the synthesis of new DNA at a replication fork Most DNA polymerases require a primer and a DNA template strand The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.15 Addition of a nucleotide to a DNA strand Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Modified office hours next week Monday (11/18) 1:00-1:50pm Tuesday (11/19) 3:00-3:50pm Wednesday (11/20) 1:00-1:50pm Thursday (11/21) anytime between 8:00-11:00am Friday (11/22) 1:00-1:50pm Monday (11/25) 1:00-1:50pm Tuesday (11/26) nope After Thanksgiving break-back to normal Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Antiparallel Elongation The antiparallel structure of the double helix affects replication DNA polymerases add nucleotides only to the free 3′ end of a growing strand; therefore, a new DNA strand can elongate only in the 5′ → 3′ direction The DNA polymerase synthesizes a leading strand continuously, moving toward the replication fork Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved BioFlix® Animation: Synthesis of the Leading Strand Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Antiparallel Elongation To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.17 Synthesis of the lagging strand Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved BioFlix® Animation: Synthesis of the Lagging Strand Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Animation: DNA Replication: An Overview Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.UN03 Summary of DNA replication Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Table 16.1 Bacterial DNA replication proteins and their functions Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Proofreading and Repairing DNA Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Proofreading and Repairing DNA DNA can be damaged by exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes In nucleotide excision repair, a nuclease cuts out and replaces damaged stretches of DNA Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Evolutionary Significance of Altered DNA Nucleotides The error rate after proofreading and repair is low but not zero Sequence changes may become permanent and can be passed on to the next generation (only via gametes) These changes (mutations) are the source of the genetic variation upon which natural selection operates and are ultimately responsible for the appearance of new species “Dethroning the dogma of ‘mutations occur at random’” by Randy Guliuzza, Institute for Creation Research – Article is posted on Canvas in Module IV Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Replicating the Ends of DNA Molecules For linear DNA, the usual replication machinery cannot complete the 5′ ends of daughter DNA strands There is no 3′ end of a preexisting polynucleotide for DNA polymerase to add on to Thus, repeated rounds of replication produce shorter DNA molecules with uneven ends This is not a problem for prokaryotes, most of which have circular chromosomes Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.21 Shortening of the ends of linear DNA molecules Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Replicating the Ends of DNA Molecules Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called telomeres Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules It has been proposed that the shortening of telomeres is connected to aging Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Replicating the Ends of DNA Molecules Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved CONCEPT 16.3: Chromosome Structure In the eukaryotic cell, DNA is precisely combined with proteins in a complex called chromatin Chromosomes fit into the nucleus through an elaborate, multilevel system of packing Proteins called histones are responsible for the main level of DNA packing in interphase chromatin Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved CONCEPT 16.3: Chromosome Structure Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 16.24 “Painting” chromosomes Every chromosome occupies a specific area within the nucleus Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Animation: DNA Packing Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved CONCEPT 16.3: Chromosome Structure Histones can undergo chemical modifications that result in changes in chromatin condensation These changes (called epigenetics) can also have multiple effects on gene expression Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Environmental factors: Exposure to environmental stressors like famine, toxins, or extreme stress during critical developmental windows can induce epigenetic changes that may be passed on to future generations. Intergenerational trauma: Studies suggest that individuals exposed to severe trauma may exhibit epigenetic changes that could potentially be inherited by their children, impacting their susceptibility to mental health issues. Maternal nutrition: A mother's diet during pregnancy can influence the epigenetic profile of her developing fetus, potentially impacting the child's health later in life. https://pmc.ncbi.nlm.nih.gov/articles/PMC3521963/#:~:text=However%2C%20a%20few%20examples%20of,generations%2C%20and%20multigenerational%20effects%20of https://pmc.ncbi.nlm.nih.gov/articles/PMC3521963/#:~:text=However%2C%20a%20few %20examples%20of,generations%2C%20and%20multigenerational%20effects%20of Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved