Chapter 17 Notes - Final - Biology PDF

Chapter 17 The Simpler Genetic Systems of Viruses and Bacteria 17.1 General Properties of Viruses Section 17.1 Learning Outcomes 1. Compare and contrast...

Chapter 17 The Simpler Genetic Systems of Viruses and Bacteria 17.1 General Properties of Viruses Section 17.1 Learning Outcomes 1. Compare and contrast types of viruses with regard to their host range, structure, and genomes  17.1 Genetic Properties of Viruses Viruses are nonliving particles with nucleic acid genomes that must be taken up by living cells to replicate Viruses are considered nonliving because They are not composed of cells They do not use energy, carry out metabolism, maintain homeostasis, or reproduce on their own Loading… Viruses infect all types of organisms Tobacco mosaic virus was the first virus discovered Many biologists study viruses; there is public interest in their ability to cause disease  17.1 Genetic Properties of Viruses Viruses Are Remarkably Varied, Despite Their Simple Structure A virus is a small infectious particle that consists of nucleic acid enclosed in a protein coat Over 4,000 different types of viruses have been studied; they differ greatly in their characteristics 17.1 Genetic Properties of Viruses Viruses Are Remarkably Varied, Despite Their Simple Structure Viruses differ in their host range, structure, and genome composition The host range is the number of species and cells a virus can infect; It may be broad (ex: 150 species) or narrow (a specific cell type) Loading… All viruses have a protein coat called a capsid, which varies in shape and complexity Many viruses that infect animal cells have a viral envelope, lipid bilayer derived from the host cell The viral genome may be composed of DNA or RNA, may be single- or double-stranded, and may be linear or In class practice: Q1 circular Fig 18.2, Biology, Brooker 17.1 Genetic Properties of Viruses Viruses Are Remarkably Varied, Despite Their Simple Structure 17.1 Genetic Properties of Viruses Viruses Are Remarkably Varied, Despite Their Simple Structure Viruses that infect f bacteria Bacteriophages. may have complex protein coats 17.2 Viral Reproductive Cycles Section 17.2 Learning Outcomes 1. Describe the 6 steps in viral reproductive cycles and distinguish between the lysogenic and lytic cycles 2. Describe how emerging viruses such as HIV arise and spread through populations 3. Explain how an understanding of virus structure and reproduction can aid in the development of drugs to combat viruses  17.2 Viral Reproductive Cycles Viral Reproductive Cycles Consist of Common Steps The viral reproductive cycle results in the production of new viruses and generally follows 5 to 6 steps Details of the steps vary and there are alternative cycles Virus Attachment to surface of host cell - Entry of viral genome into host cell Integration into host’s chromosomal DNA; occurs for some viruses that carry a gene that encodes integrase enzyme that integrates DNA into host cell ! Synthesis of viral components – the host cell machinery synthesizes new copies of the viral genome and viral proteins Viral assembly – synthesized components are assembled into new viruses Release of new viruses into the environment; phages lyse their host cell and enveloped viruses bud from the host cell  In Class Practice Q2 Working with the people near you answer the following question Question 2: Order the following cut-outs according to the steps of the viral reproductive cycle. Now, draw the steps of the viral reproductive cycle in the space below. 17.2 Viral Reproductive Cycles Viral Reproductive Cycles Consist of Common Steps Virus DNA gets placed in our 1) NA to use our machinery Loading… 17.2 Viral Reproductive Cycles Viral Reproductive Cycles Consist of Common Steps 17.2 Viral Reproductive Cycles Viral Reproductive Cycles Consist of Common Steps SARS-CoV-2 binds to a receptor called the ACE2 receptor 17.2 Viral Reproductive Cycles Viral Reproductive Cycles Consist of Common Steps If not blocked by the immune system, virions (infective form of a virus outside a host cell) migrate to the lower respiratory tract where they infect the alveoli cells These gas exchange units are rich in ACE2 proteins  17.2 Viral Reproductive Cycles Viral Reproductive Cycles Consist of Common Steps Some bacteriophages may follow either a lytic cycle or a lysogenic cycle During the lytic cycle, new phages are made and the bacterial cell is lysed; during the lysogenic cycle, the integrated phage DNA, called prophage, is replicated along with the DNA of the host cell Integrating phage DNA? Constant replication (NOLYSIS) Phage integrates in DNA cell lyses (breaks) to release new phages. Fig 18.5, Biology, Brooker In class practice: Q3  17.2 Viral Reproductive Cycles Viral Reproductive Cycles Consist of Common Steps During the lysogenic cycle, viruses integrate their genomes into a host chromosome; the resulting prophage/provirus can be latent for a long time Virus that goes to "sleep" wakes up Environmental conditions influence whether or not viral DNA is integrated into a host chromosome and how long the virus remains in the lysogenic cycle The herpesvirus called varicella-zoster can switch from the latent form to the active form that produces new virus particles The initial infection causes chickenpox; the virus can be latent for many years If the virus becomes active again, it can cause shingles; the blisters follow the path of the neurons that carry the virus Fig 13.7, Fundamentals of Anatomy & Physiology, Martini et al.; Pearson  In-Class Activity 1 This will be an interactive activity where students will be instructed to move around the room and trade beads with the people around them. Each round will consist of students trading with 2-3 people and then sitting back down. Students will trade with different people each round. Following each round, as a class, we will graph the number of students with a red bead.  In-Class Activity 1 If you have a red bead, please come to the front of the room. If you have a white bead, please take a seat/ remained seated. Each of you will receive a card. Please read the card carefully and follow the action given on each card.  In-Class Activity 1 With the people around you please answer the following questions 1. How does the number of red beads increase over time? 2. Why did the number of red beads continue to grow after government intervention? 3. What is the importance of government intervention in helping manage viral disease spread?  17.2 Viral Reproductive Cycles Emerging Viruses Have Arisen Recently and May Rapidly Spread Through a Population Emerging viruses typically arise via mutations in pre-existing viruses Human immunodeficiency virus (HIV) has killed over 30 million from 1981 – 2021. HIV is the causative agent of acquired immune deficiency syndrome (AIDS) The virus destroys a type of white blood cell called a helper T cell, disabling many aspects of the immune system Emerging virus come from mutations ? viruses. NOT NEWLY SYNTHESIZED pre-existing -  17.2 Viral Reproductive Cycles Emerging Viruses Have Arisen Recently and May Rapidly Spread Through a Population Emerging viruses typically arise via mutations in pre-existing viruses Severe acute respiratory coronavirus 2 (SARS-CoV-2) causes the infection called coronavirus disease 2019 (COVID-19). 6 million people died globally from March 2020-March 2022.  Immune Defense Against Pathogens is mediated by Antibodies Antibodies help destroy pathogens in 3 major ways: Source: Lumenlearning. com Natural infection or Vaccination are the means that we make antibodies.  Have the host make Use only the viral Use the intact virus only a few viral DNA/RNA proteins The whole virus or viral component is recognized by the host immune cells. Activated B cells make antibodies that recognize these particles. The next time you are infected, you have an army of antibodies that will bind and neutralize the virus.  Case Study: Vaccines Nevada's diverse population creates challenges in maintaining consistent vaccination coverage. Consider the following two cities: 1. City A: Las Vegas o High vaccination rates (95% or higher) due to proactive public health campaigns, access to healthcare, and high compliance with school vaccination requirements. 2. City B: Boulder City o Lower vaccination rates (75%) due to vaccine hesitancy, misinformation in local communities, and limited public health outreach.  Case Study: Vaccines With the people around you answer the following questions 1) How would the measles outbreak likely differ between Las Vegas and Boulder City? 2) How would individuals who cannot get vaccinated (e.g., infants, immunocompromised individuals, cancer patients, etc.) fare in each city during the outbreak? 3) Which City do you predict would be better protected? What are some things that you could do to help increase protection in the less protected city? 17.3 Genetic Properties of Bacteria Section 17.3 Learning Outcomes 1. Outline the key features of a bacterial chromosome 2. Describe the 2 processes that compact the bacterial chromosome 3. Outline the structure and functions of plasmids 4. Diagram the process of cell division in bacteria  17.3 Genetic Properties of Bacteria Bacteria Typically Have Circular Chromosomes That Carry a Few Thousand Genes Genes of bacteria are found in bacterial chromosomes Usually a single type of chromosome; may have multiple copies Each chromosome is tightly packed within a nucleoid region Chromosomes are usually circular and are composed of DNA and proteins Usually only a few million base pairs long Typically contain a few thousand genes; most genes encode proteins Have a single origin of replication site that organizes the initiation of DNA replication  Activity 2: Bacterial Chromosome Compaction Can I have 5 volunteers who will come on the stage for this activity.  17.3 Genetic Properties of Bacteria The Formation of Chromosomal Loops and DNA Supercoiling Make the Bacterial Chromosome Compact Bacterial cells are small; a typical bacterial chromosome must be compacted about 1,000 fold to fit inside the cell Compaction involves the formation of loops and DNA supercoiling Loop domains are formed through interaction with DNA- binding proteins Loading… Enzymes called topoisomerases twist the DNA and control the degree of supercoiling  Knowledge Check: In-class practice Q5 Can the term "chromatin" be applied to bacterial chromosomes, and why or why not? A. Yes, because bacterial chromosomes are also composed of DNA and proteins that package the genetic material. B. No, because chromatin refers specifically to the DNA-protein complexes found in eukaryotes, not prokaryotes. C. Yes, because bacteria have histones similar to those in eukaryotes to help organize their DNA. D. No, because bacterial chromosomes are linear and lack any packaging structures. Bacteria DON'T have nucleosomes or histones !  17.3 Genetic Properties of Bacteria Plasmids Are Small, Circular Pieces of Extrachromosomal DNA In addition to chromosomal DNA, bacterial cells commonly contain plasmids that exist separately from the bacterial chromosome Occur naturally in many strains of bacteria and a few types of eukaryotic cells (ex: yeast) Vary in size; may contain a few genes to several dozen genes Have own origin of replication and replicate independently Plasmids are not usually necessary for survival, but they can provide growth advantages  17.3 Genetic Properties of Bacteria Plasmids Are Small, Circular Pieces of Extrachromosomal DNA Most plasmids fall into 5 categories:. Resistance plasmids (R factors) contain genes that confer resistance against antibiotics and other toxins. Degradative plasmids enable digestion and utilization of an unusual substance. Col-plasmids encode colicins, proteins that kill other bacteria. Virulence plasmids turn a bacterium into a pathogenic strain. Fertility plasmids (F factors) allow bacteria to transfer genes to each other  17.3 Genetic Properties of Bacteria Most Bacteria Reproduce by Binary Fission Most bacteria rapidly produce new cells through a process called binary fission Some species, such as E. coli, can divide every 20-30 minutes When placed on a solid growth medium, an E. coli cell and its daughter cells undergo repeated cell divisions and form a group of genetically identical cells called a bacterial colony A single cell can produce a visible colony of 10 to 100 million cells in less than a day!  17.3 Genetic Properties of Bacteria Most Bacteria Reproduce by Binary Fission Cell division of most bacterial species occurs by a process called binary fission DNA replication produces 2 identical copies of the chromosome The plasma membrane is drawn inward and new cell wall is formed, separating the 2 daughter cells Unless a mutation occurs, daughter cells are genetically identical to the mother cell; binary fission is a process of asexual reproduction Plasmids are replicated independently and are distributed into daughter cells during binary fission In class practice: Q6 17.4 Gene Transfer Between Bacteria Section 17.4 Learning Outcomes 1. Compare and contrast the three forms of gene transfer between bacteria: conjugation, transformation, and transduction 2. Define the process of horizontal gene transfer  9.1 Properties and Identification of the Genetic Material T Griffith’s Bacterial Transformation Experiments hi Indicated the Existence of a Genetic Material n k A surprising result occurred when a mix of live type R and heat- b killed type S bacteria was injected a The mouse died and living type S bacteria were isolated from c the blood k to Griffith postulated that a substance (genetic material) from the dead C type S cells had transformed the type R cells into type S h a Griffith could not pt determine the er biochemical 9 composition of the transforming substance  T ra Live avirulent R strain bacteria are transformed n into live virulent S strain bacteria sf or NON-INFECTING m DNA from Avirulent R killed S at strain strain io n o c c T ur hi s n in k m b o a u c se Virulent transformed k R strain that can to make own capsule C h a 37 pt er 17.4 Gene Transfer Between Bacteria Although bacteria reproduce asexually, they exhibit genetic Pe Contact , bu donor i recipient ! diversity; mutations and gene transfer are sources of diversity Gene transfer occurs in three different ways: conjugation, transformation, and fragment then spreads to goes to environment, recipient transduction. Strains are lineages of the same Phage infect donor species that have genetic differences bacterial chrom. fragments then to Spreads recipient cell. Eukaryotes = Linear chroms Prokaryotes = Circular chroms  Knowledge Check: Match the following images to the correct gene transfer method Transformation Conjugation Transduction  17.4 Gene Transfer Between Bacteria During Conjugation, DNA Is Transferred from a Donor Cell to a Recipient Cell In the early 1950s it was discovered that certain bacterial strains can donate genetic material during conjugation Ex: about 5% of E. coli strains found in nature can act as donors Donor strains contain a fertility plasmid that can be transferred to a recipient strain F+ cells have the fertility plasmid and F- cells do not The plasmid contains genes required for conjugation and may also carry genes that confer a growth advantage Sex pili are made by F+ cells and specifically bind to F- cells 17.4 Gene Transfer Between Bacteria During Conjugation, DNA Is Transferred from a Donor Cell to a Recipient Cell  17.4 Gene Transfer Between Bacteria In Transformation, Bacteria Take up DNA from the Environment In contrast to conjugation, bacterial transformation does not require direct contact between cells Living bacterial cells import a strand of DNA (typically derived from a dead bacterium) Frederick Griffith first discovered this process in 1928 while working with strains of S. pneumoniae Only competent cells with competence factors are capable of transformation Competence factors facilitate binding, uptake, and incorporation of DNA  17.4 Gene Transfer Between Bacteria In Transduction, Bacteriophages Transfer Genetic Material from One Bacterium to Another On rare occasion, a phage may pick up a piece of DNA from the bacterial chromosome When the phage infects another bacterium, it transfers this segment into the chromosome of its new host Transduction usually occurs because of an error in the lytic cycle; host DNA is accidentally enclosed as phage coat proteins are assembled 17.4 Gene Transfer Between Bacteria In Transduction, Bacteriophages Transfer Genetic Material from One Bacterium to Another  17.4 Gene Transfer Between Bacteria Horizontal Gene Transfer Is the Transfer of Genes Between the Same or Different Species Horizontal gene transfer refers to any process in which an organism incorporates genetic material from another organism without being the offspring of that organism Conjugation, transformation, and transduction are examples of horizontal gene transfer Roughly 17% of genes in E. coli and Salmonella typhimurium have been acquired by horizontal transfer during the past 100 million years Medical relevance of horizontal gene transfer is profound many antibiotic resistant strains of bacteria acquire resistance through horizontal gene transfer Fig 1.8, Biology, Brooker