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Which type of mutation is considered adaptive?
DNA replication proceeds in one direction only.
False
What are the three phases of DNA/chromosome replication?
Initiation, Elongation, Termination
The process where a donor bacteria transfers genetic information to a recipient is called __________.
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Match the type of gene transfer with its description:
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What is the role of primase in DNA replication?
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Okazaki fragments are created during the leading strand synthesis.
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What term describes the science of using living systems to benefit humankind?
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Which nitrogenous bases are found in DNA?
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Chromosomes are circular in eukaryotic organisms.
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What is a point mutation?
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The process of converting mRNA into a protein is called ______.
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Match the types of mutations with their effects:
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What does the genotype of an organism represent?
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Mutations can only have harmful effects on an organism.
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What is the role of messenger RNA (mRNA) in protein synthesis?
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What component do all viruses share?
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Viruses can self-replicate without needing a host cell.
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Name one virus that is categorized as an enveloped virus.
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In the viral replication cycle, the stage where the viral genome enters the nucleus is called __________.
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Match the viral shedding mechanism with its description:
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Which mechanism is NOT a method of viral penetration?
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RNA viruses have lower mutation rates than DNA viruses.
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What are the two proteins found on the envelope of the influenza virus responsible for infection?
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What is the function of neuraminidase in the influenza virus?
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Antigenic drift results from the reassortment of viral genes.
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What is the primary result of antigenic shift in influenza viruses?
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The _____ is a glycoprotein on the surface of influenza virus that binds to sialic acid on host cell membranes.
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Match the following influenza-related terms with their definitions:
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What leads to the requirement for a new flu vaccine each year?
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Bacteriophages can be grown on agar plates without the need for host cells.
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In what year was Bacteriophage Lambda isolated?
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Study Notes
Microbial Genetics
- DNA is a biological molecule made up of nucleotides.
- Each nucleotide consists of a sugar (deoxyribose), phosphate, and a nitrogenous base.
- The four nitrogenous bases are adenine, thymine, guanine, and cytosine.
- Chromosomes are made up of DNA; they're circular in prokaryotes and linear in eukaryotes.
- A gene is a sequence of nucleotides located on a chromosome, known as a locus.
- Different versions of a gene are called alleles.
- The genotype is the complete collection of genes an organism can possess.
- The phenotype is the physical manifestation of an organism's genotype, influenced by both genes and the environment.
Protein Synthesis
- Transcription involves reading a specific DNA section to produce messenger RNA (mRNA).
- Translation involves interpreting mRNA to produce a specific protein.
- The genetic code, represented by codons (three mRNA bases), determines which amino acid is incorporated into a protein.
Mutations
- A mutation is a heritable change in an organism's DNA sequence.
- Mutations can lead to phenotypic variations compared to the "wild type," the most common form in nature.
Types of Mutations
- Point mutation: a single base is substituted or replaced.
- Insertion: addition of one or more bases.
- Deletion: removal of one or more bases.
Effects of Mutations on Proteins
- Silent mutation: no effect on protein function.
- Missense mutation: a different amino acid is incorporated, potentially altering protein function.
- Nonsense mutation: converts a codon into a stop codon, often resulting in a non-functional protein.
Adaptation and Mutation
- Mutations can be successful, neutral, or deleterious.
- Successful mutations can be considered adaptive, meaning they provide an advantage over non-mutants.
- Adaptation occurs when a successful mutation in a population spreads, becoming the dominant form.
DNA / Chromosome Replication
- DNA replication occurs in three phases: initiation, elongation, and termination.
- Initiation starts at the origin of replication (oriC), a specific DNA sequence.
- DNA strands are unwound at the oriC, creating two replication forks.
- Helicase unwinds the DNA strands.
Elongation
- Polymerase replicates the two DNA strands, but it can only extend an existing strand.
- Primase creates primers that initiate DNA replication.
- Replication occurs in both directions: leading and lagging strands.
- Okazaki fragments are created on the lagging strand, which are later joined by ligase.
- Topoisomerases (gyrase) manage DNA winding issues.
Termination
- Replication stops at the termination (Tus-Ter) sequence.
- Two new loops of replicated DNA are formed and migrate to opposite ends of the bacterium.
- A septum forms between the two daughter cells, resulting in cell division.
Gene Transfer
- Binary Fission: simple asexual cell division with no genetic diversity.
- Bacterial Conjugation: transfer of genetic information from a donor cell to a recipient cell, leading to genetic diversity.
- Bacterial Transformation: cells take up genetic information from the environment, resulting in new characteristics and genetic diversity.
- Bacterial Transduction: bacteriophages (viruses) infect bacteria, insert their DNA into the bacterial DNA, and replicate. They can then pick up both bacterial and viral DNA and transfer it to other bacteria.
Biotechnology
- The science of using living systems to benefit humankind.
- Genetic engineering involves altering the genetics of organisms to achieve desired traits.
What is a Virus?
- A virus is an acellular infectious agent that cannot self-replicate
- Viruses must infect a cell in order to make copies of itself
- Examples of viruses include Influenza, HIV, and Ebola
Viral Structure
- There is variation in viral structure but some common features exist
- Viral structures have an RNA or DNA genome
- They have a capsid of proteins
- They have an envelope lipid bilayer
- They have surface receptors - spikes of protein or glycoprotein
Viral Replication Cycle
- The replicative cycle of a virus depends upon its genome
- Replicative cycles for ssRNA viruses differ from dsDNA viruses
- The replicative cycle includes seven stages: Attachment, Penetration, Uncoating, Transport to the Nucleus, Synthesis (Transcription & Translation), Assembly and Release
Viral Replication Cycle: Attachment
- Proteins on the viral envelope or capsid recognize and bind with target host cells receptors
Viral Replication Cycle: Penetration
- The virus penetrates the host cell through one of three mechanisms:
- Direct penetration (naked viruses) - Only viral genome enters the host (typical of bacteriophages)
- Fusion - Viral envelope fuses with host membrane and the capsid containing the genome enters the cell (e.g. HIV)
- Receptor-mediated endocytosis - Attachment stimulates endocytosis of the entire virus (e.g. influenza)
Viral Replication Cycle: Uncoating
- The virus removes the capsid and the nucleic acid of the genome is exposed to the cytoplasm
Viral Replication Cycle: Transport to the Nucleus
- The viral genome enters the nucleus
Viral Replication Cycle: Synthesis (Transcription & Translation)
- Replication of the viral genome occurs (transcription in the nucleus)
- Viral proteins are produced (translation in the cytoplasm)
Viral Replication Cycle: Assembly
- New virions (complete virus) are assembled
- The genome and capsid are put together to form a new virus
Viral Replication Cycle: Release
- The viruses are released from the host cell (viral shedding) by one of the following three mechanisms: Apoptosis, Budding or Exocytosis
Viral Shedding: Apoptosis
- The host cell lyses and releases mature viral particles (naked viruses)
- The host cell dies
Viral Shedding: Budding
- The virus buds through the nuclear or plasma membrane, creating an envelope
- This does not kill the host
Viral Shedding: Exocytosis
- Viruses leave the host cell using vesicles but this process does not kill the host
Influenza Virus
- Influenza is an enveloped RNA virus
- RNA viruses make more “mistakes” than DNA viruses because they do not have self-regulation and cannot correct mistakes
- RNA viruses adapt readily to environmental changes because of high mutation rates
- The envelope is covered with two proteins (antigens) required for the infection process: Hemagglutinin (H) spike and Neuraminidase (N) spike
Influenza Virus: Hemagglutinin (H) Spike
- Hemagglutinin is a glycoprotein on the surface of the influenza virus
- It binds the virus to cells with sialic acid on the host cell membranes, such as cells in the upper respiratory tract or erythrocytes, helping the virus enter the cell
- Sialic Acid is a receptor found on most vertebrate cells
Influenza Virus: Neuraminidase (N) Spike
- Neuraminidase is an enzyme
- It helps the virus penetrate the mucus of the respiratory tract
- It also aids in viral shedding of influenza (budding), by cutting Sialic Acid from host glycoproteins as the virus is being released
Antigenic Variation
- Antigenic variation occurs in two ways with the Flu Virus: Antigenic Drift and Antigenic Shift
Antigenic Drift
- Antigenic drift results from point mutations of genes coding for Hemagglutinin & Neuraminidase
- These two proteins are the antigens that cause the formation of host antibodies
- Antigenic drift produces new strains of flu virus that host antibodies will not recognize
- Sufficient antigenic drift can cause a new flu epidemic (localized flu)
- Antigenic drift causes new formulations of flu vaccine every year
Antigenic Shift
- Antigenic shift results from gene re-assortment from two different viruses that infect the same cell
- Viruses exchange a large part of their genome
- The virus that emerges is antigenically different from either of the two viruses
- Antibodies formed from the two viruses are ineffective against the new combined virus genome
- H5N1 = bird flu
- H1N1 = swine flu
- This can lead to pandemics
Swine Flu Viroid
- This viroid was a result of a gene re-assortment
Bacteriophages
- Bacteriophages (or just phages) are viruses that only infect bacterial cells
- Phages (viruses) cannot be grown on agar plates like bacteria
- They must be grown using host cells, in this case bacteria
- For animal viruses, hens eggs or live animals can be used
Bacteriophage Lambda
- One of the earliest model systems for studying the physical nature of DNA and genes
- Isolated from an E. coli cell in 1951
- Lambda has contributed enormously to our understanding of molecular biology and protein synthesis mechanisms
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Description
This quiz covers essential topics in microbial genetics, including the structure of DNA, gene expression through transcription and translation, and the roles of mutations. Test your understanding of how genetic information is stored, expressed, and mutated in microorganisms.
