Microbiology: Prokaryotes vs Eukaryotes
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Questions and Answers

What is a key difference between prokaryotic and eukaryotic cells?

  • Number of cell membranes
  • Size of the cell
  • Presence of DNA
  • Presence of a nucleus (correct)

    • Which of the following statements correctly describes bacterial cells?

  • They have multiple linear chromosomes.
  • They contain mitochondria.
  • They are usually larger than eukaryotic cells.
  • They typically have a cell wall. (correct)

    • What does the Gram stain primarily differentiate between?

  • Live and dead bacteria
  • Cell shape and size
  • Gram-positive and Gram-negative bacteria (correct)
  • Bacteria and viruses

    • What cellular structures are absent in prokaryotes?

    <p>Organelles</p> Signup and view all the answers

    Which type of bacteria is classified as Gram-positive?

    <p>Streptococcus pneumoniae</p> Signup and view all the answers

    What is the process by which bacteria divide?

    <p>Binary Fission</p> Signup and view all the answers

    Which of the following is NOT a requirement for bacterial growth?

    <p>Hormones</p> Signup and view all the answers

    In bacterial growth, what process breaks down organic substrates to derive energy?

    <p>Catabolism</p> Signup and view all the answers

    What is the shape of bacterial DNA?

    <p>Circular</p> Signup and view all the answers

    What components are nucleotides of DNA made of?

    <p>Base, Deoxyribose, Phosphate</p> Signup and view all the answers

    How many genes are estimated to be found in a typical bacterial genome?

    <p>4000</p> Signup and view all the answers

    What can influence bacterial growth in terms of environmental conditions?

    <p>Oxygen levels</p> Signup and view all the answers

    What drives the emergence of antibiotic-resistant bacteria?

    <p>Genetic variation processes</p> Signup and view all the answers

    What is the principal component of the bacterial cell wall that prevents osmotic lysis?

    <p>Peptidoglycan</p> Signup and view all the answers

    Which statement best describes the Gram-positive cell envelope?

    <p>It has multiple layers of peptidoglycan.</p> Signup and view all the answers

    What is one function that the capsule or slime layer provides to bacterial cells?

    <p>Offers protection from phagocytosis</p> Signup and view all the answers

    Which type of bacteria can form spores to withstand adverse conditions?

    <p>Gram-positive bacteria</p> Signup and view all the answers

    Which of the following describes biofilms?

    <p>Aggregates of bacteria forming a structured layer.</p> Signup and view all the answers

    What role do flagella play in bacteria?

    <p>Facilitation of motility</p> Signup and view all the answers

    Why are biofilm infections particularly difficult to treat?

    <p>Biofilms prevent antibiotic penetration.</p> Signup and view all the answers

    What is a characteristic of Gram-negative bacteria compared to Gram-positive bacteria?

    <p>Presence of an outer membrane</p> Signup and view all the answers

    What is the most common source of genetic variation?

    <p>Gene mutations</p> Signup and view all the answers

    What are the three types of gene mutations?

    <p>Substitution, Deletion, Insertion</p> Signup and view all the answers

    What is the possible consequence of a substitution mutation?

    <p>No effect on protein function</p> Signup and view all the answers

    What occurs as a result of a deletion mutation?

    <p>Misreading of triplet codons</p> Signup and view all the answers

    What is a frameshift mutation?

    <p>A deletion or insertion that alters the reading frame</p> Signup and view all the answers

    What can potentially result from frameshift mutations?

    <p>Production of non-functional proteins</p> Signup and view all the answers

    Which of the following types of mutations usually affect only one amino acid?

    <p>Substitution</p> Signup and view all the answers

    Which genetic elements can carry antibiotic resistance genes?

    <p>Plasmids</p> Signup and view all the answers

    Which enzyme is responsible for unwinding double-stranded DNA during transcription?

    <p>Helicase</p> Signup and view all the answers

    What is the role of RNA polymerase in the process of transcription?

    <p>It adds nucleotides to the growing RNA strand</p> Signup and view all the answers

    How does the ribosome contribute to protein synthesis?

    <p>It threads the mRNA to decode it</p> Signup and view all the answers

    What defines an open-reading frame (ORF) in gene structure?

    <p>A coding sequence that can be translated into protein</p> Signup and view all the answers

    What is one clinical significance of plasmids?

    <p>They can confer antibiotic resistance</p> Signup and view all the answers

    Which process involves the decoding of mRNA by ribosomes and tRNA?

    <p>Translation</p> Signup and view all the answers

    What happens during the termination phase of transcription?

    <p>Terminator sequences signal the end of transcription</p> Signup and view all the answers

    Which enzyme is responsible for joining Okazaki fragments during DNA replication?

    <p>Ligase</p> Signup and view all the answers

    What is the main reason antibiotic misuse can lead to antibiotic resistance?

    <p>Antibiotics can increase mutation rates</p> Signup and view all the answers

    Which structural feature differentiates Gram-positive bacteria from Gram-negative bacteria?

    <p>Thicker cell wall</p> Signup and view all the answers

    Which of the following is not a mechanism by which plasmids can contribute to antibiotic resistance?

    <p>Facilitating biofilm formation</p> Signup and view all the answers

    What role do mutations play in the development of antibiotic resistance in bacteria?

    <p>They contribute to genetic diversity</p> Signup and view all the answers

    Which statement best describes the importance of biofilms in bacterial infections?

    <p>They can shield bacteria from immune responses.</p> Signup and view all the answers

    What is the characteristic feature of Gram-negative bacteria in terms of their cell envelope composition?

    <p>High lipid content in their cell envelope</p> Signup and view all the answers

    Which statement accurately describes the effect of alcohol treatment on Gram-positive bacteria?

    <p>It makes the cell envelope impermeable.</p> Signup and view all the answers

    What is the primary function of the cytoplasmic membrane in bacteria?

    <p>Regulating the transport of molecules</p> Signup and view all the answers

    Which of the following bacteria is known to not stain with the Gram method due to its unique cell structure?

    <p>Mycobacteria</p> Signup and view all the answers

    Which morphological shape is classified as cocci in bacteria?

    <p>Spherical</p> Signup and view all the answers

    What occurs to the crystal violet-iodine complex during the staining process of Gram-negative bacteria?

    <p>It diffuses out due to high lipid content.</p> Signup and view all the answers

    What role do plasmids play in bacterial cells?

    <p>They carry additional genetic information.</p> Signup and view all the answers

    Which component is specifically involved in the transport of molecules within the cytoplasmic membrane?

    <p>Permeases</p> Signup and view all the answers

    What process do bacteria primarily use for cell division?

    <p>Binary fission</p> Signup and view all the answers

    What is an essential requirement for bacteria to grow?

    <p>Organic substrates</p> Signup and view all the answers

    Which of the following best describes the structure of bacterial DNA?

    <p>Circular, double-stranded helix</p> Signup and view all the answers

    What factor is NOT typically required for bacterial growth?

    <p>Thick cell wall</p> Signup and view all the answers

    Which component is NOT part of a nucleotide in DNA?

    <p>Ribose</p> Signup and view all the answers

    How does genetic variation contribute to bacterial adaptability?

    <p>It creates selective pressures.</p> Signup and view all the answers

    Which factor can influence bacterial growth in an anaerobic environment?

    <p>Lack of oxygen</p> Signup and view all the answers

    What is the approximate number of genes in a typical bacterial genome?

    <p>4000 genes</p> Signup and view all the answers

    What initiates the transcription process in bacterial gene expression?

    <p>RNA polymerase binding to promoter region</p> Signup and view all the answers

    Which molecule serves as the template during protein translation?

    <p>Messenger RNA</p> Signup and view all the answers

    What is the role of RNA polymerase in bacterial transcription?

    <p>Adding nucleotides to the growing RNA strand</p> Signup and view all the answers

    Which of the following accurately describes plasmids in bacteria?

    <p>Extrachromosomal DNA that replicate independently</p> Signup and view all the answers

    During which phase of transcription does RNA polymerase begin producing an RNA transcript?

    <p>Elongation</p> Signup and view all the answers

    What function do tRNA molecules serve in the process of translation?

    <p>They transport amino acids to the ribosome</p> Signup and view all the answers

    Which component is essential for the termination of transcription in bacteria?

    <p>RNA polymerase</p> Signup and view all the answers

    What is the potential consequence of having plasmids with multiple antibiotic resistance genes in bacteria?

    <p>Ability to confer resistance to various antibiotics</p> Signup and view all the answers

    What is the main function of peptidoglycan in bacterial cells?

    <p>To maintain cell shape and prevent osmotic lysis</p> Signup and view all the answers

    Which structure is primarily associated with the Gram-negative bacterial cell envelope?

    <p>Outer membrane with lipopolysaccharide</p> Signup and view all the answers

    What role do capsules and slime layers play in bacterial cells?

    <p>Provide protection from phagocytosis and antibiotics</p> Signup and view all the answers

    Which characteristic is unique to Gram-positive bacteria?

    <p>Has multiple layers of peptidoglycan</p> Signup and view all the answers

    What is a key reason biofilm infections are challenging to treat?

    <p>Biofilms form protective layers that antibiotics cannot penetrate</p> Signup and view all the answers

    What is the primary function of pili in bacterial cells?

    <p>Adherence to surfaces</p> Signup and view all the answers

    Which type of bacteria is unable to form spores?

    <p>Gram-negative</p> Signup and view all the answers

    Which feature of the Gram-positive cell wall contributes to its antigenic properties?

    <p>Teichoic and lipoteichoic acids</p> Signup and view all the answers

    Which statement accurately distinguishes the absence of cellular structures in prokaryotes compared to eukaryotes?

    <p>Prokaryotes lack mitochondria and chloroplasts.</p> Signup and view all the answers

    What characteristic is critical for the differentiation between Gram-positive and Gram-negative bacteria during staining?

    <p>The presence of a thick peptidoglycan layer in Gram-positive bacteria.</p> Signup and view all the answers

    In terms of gene expression, which process directly follows transcription in bacteria?

    <p>Translation of the mRNA into proteins.</p> Signup and view all the answers

    What is the primary role of plasmids in bacterial cells?

    <p>To carry genes that can confer antibiotic resistance.</p> Signup and view all the answers

    Which of the following relates best to the process of bacterial growth?

    <p>Bacterial growth is exponential during the logarithmic phase.</p> Signup and view all the answers

    What structural feature is primarily responsible for the osmotic integrity of bacterial cells?

    <p>Peptidoglycan layers</p> Signup and view all the answers

    Which statement accurately reflects the composition of the Gram-positive cell envelope?

    <p>Has multiple layers of peptidoglycan</p> Signup and view all the answers

    What role do pili play in bacterial cells?

    <p>Facilitate adherence to surfaces</p> Signup and view all the answers

    Which of the following correctly describes the Gram-negative cell envelope?

    <p>Contains an outer membrane with lipopolysaccharides</p> Signup and view all the answers

    What is a significant challenge in treating biofilm-related infections?

    <p>Biofilm cells are less accessible to antibiotics than planktonic cells.</p> Signup and view all the answers

    Which characteristic is true of bacterial spores?

    <p>They provide protection against environmental stress.</p> Signup and view all the answers

    What role does the capsule play in bacterial cells?

    <p>Acts as a barrier to antibiotic penetration</p> Signup and view all the answers

    What is a key function of flagella in bacteria?

    <p>Enabling motility and chemotaxis</p> Signup and view all the answers

    What is the primary method by which bacteria reproduce?

    <p>Binary fission</p> Signup and view all the answers

    What is the primary source of energy for bacterial growth?

    <p>Enzymatic breakdown of substrates</p> Signup and view all the answers

    Which component of bacterial DNA directly contributes to its structural integrity?

    <p>Base pairing</p> Signup and view all the answers

    Which factor does NOT typically influence bacterial growth conditions?

    <p>Presence of preservatives</p> Signup and view all the answers

    What characteristic of the bacterial genome allows for rapid adaptation to hostile environments?

    <p>Presence of plasmids</p> Signup and view all the answers

    What role does catabolism play in bacterial cells?

    <p>Production of energy</p> Signup and view all the answers

    How does bacterial variation contribute to clinical microbiology?

    <p>Facilitating the emergence of resistant pathogens</p> Signup and view all the answers

    What is the approximate number of genes found in a typical bacterial genome?

    <p>4,000 genes</p> Signup and view all the answers

    What is the main purpose of DNA gyrase in the process of DNA replication?

    <p>To catalyze the negative supercoiling of DNA</p> Signup and view all the answers

    How does DNA polymerase ensure the accuracy of DNA replication?

    <p>By proofreading and correcting incorrect bases</p> Signup and view all the answers

    What is the significance of the 5’ to 3’ directionality of DNA polymerase during replication?

    <p>It dictates the direction in which new nucleotides are added</p> Signup and view all the answers

    What are the short DNA fragments formed on the lagging strand called?

    <p>Okazaki fragments</p> Signup and view all the answers

    In which phase of DNA replication does proofreading occur?

    <p>Elongation</p> Signup and view all the answers

    What is the role of RNA primase in the process of DNA replication?

    <p>To lay down RNA primers for DNA polymerase</p> Signup and view all the answers

    What event marks the termination of DNA replication?

    <p>The formation of two identical daughter helices</p> Signup and view all the answers

    What would happen if DNA gyrase function were disrupted?

    <p>Tension in the DNA structure would increase</p> Signup and view all the answers

    What is the primary function of RNA polymerase during transcription?

    <p>It adds nucleotides to the growing RNA strand.</p> Signup and view all the answers

    Which component plays a crucial role in the decoding of mRNA into a protein?

    <p>Ribosomes and tRNA</p> Signup and view all the answers

    During which stage of transcription does RNA polymerase bind to the DNA?

    <p>Initiation</p> Signup and view all the answers

    What is one characteristic of plasmids that distinguishes them from chromosomal DNA?

    <p>Plasmids can replicate independently of chromosomal DNA.</p> Signup and view all the answers

    Which phase of protein synthesis involves the formation of peptide chains?

    <p>Translation</p> Signup and view all the answers

    How do transfer RNA (tRNA) molecules contribute to protein synthesis?

    <p>They transport amino acids to the ribosome.</p> Signup and view all the answers

    What is the purpose of proofreading by DNA polymerase during replication?

    <p>To correct errors in the newly synthesized DNA strand.</p> Signup and view all the answers

    Which enzyme is crucial for joining Okazaki fragments during DNA replication?

    <p>Ligase</p> Signup and view all the answers

    Study Notes

    Prokaryotes vs Eukaryotes

    • Prokaryotes do not possess a nucleus, cell wall or organelles, whereas Eukaryotes have all three.

    Microscopy of Bacteria

    • Used to determine bacterial cell shape, color, and size.
    • The Gram stain is the most crucial differential staining method in Microbiology.

    Cell Wall Structure

    • Peptidoglycan is a unique polysaccharide that gives bacteria their shape and prevents osmotic lysis.
    • Gram-positive bacteria have many layers of peptidoglycan and a thick cell wall.
    • Gram-negative bacteria have one layer of peptidoglycan and a thin cell wall.

    Gram-positive Cell Envelope

    • Contains multiple layers of peptidoglycan along with techoic and lipotechoic acids which extend into the environment.
    • These acids aid in adherence and act as antigenic determinants.

    Gram-negative Cell Envelope

    • Contains an outer membrane with a phospholipid-lipopolysaccharide (LPS) bilayer which acts as a molecular sieve controlling the entry of molecules into the cell.
    • LPS also helps with bacterial attachment and resistance to phagocytosis.

    Clinically Important Bacterial Structures

    • Flagella provide bacteria with motility and chemotaxis.
    • Pili aid in bacterial adherence.
    • Capsules and slime layers protect bacteria from phagocytosis and antibiotics, and facilitate adhesion.
    • Spores (formed by some Gram-positive bacteria) provide protection from adverse conditions.

    Bacterial Biofilms

    • Biofilms are communities of bacteria that form on surfaces and excrete substances that bind them together.
    • Biofilms are difficult to treat due to their structure, as antibiotics have a hard time penetrating them.

    Bacterial Growth

    • Bacteria divide by binary fission, where the chromosome duplicates and divides into two identical copies.
    • This results in exponential growth (1, 2, 4, 8, 16 etc.) and contributes to bacterial adaptability.
    • Growth requires energy, building blocks for cellular machinery, and appropriate environmental conditions like temperature, pH, and oxygen levels.

    Bacterial Genetics and Clinical Significance

    • Bacterial genome is the collection of genes on both the chromosome and plasmids.
    • It contains genetic information necessary for all cellular processes.
    • Understanding bacterial genetics is crucial for understanding:
      • Emergence of antibiotic resistance
      • Development of highly virulent pathogens
      • Development of therapies to combat bacterial infections

    Bacterial DNA

    • Bacterial DNA is a circular molecule of double-stranded DNA.
    • It contains about 4,000 genes and 5 million base pairs.
    • DNA replication has four main steps: initiation, elongation, proofreading and termination.
    • The main enzymes involved in replication are: helicase, DNA polymerase, ligase and gyrase.

    Gene Expression

    • Gene expression translates genetic information from DNA to proteins.
    • Genes can occur individually or in groups called operons.
    • Transcription occurs when RNA polymerase binds to a promoter region and copies the DNA to generate a messenger RNA (mRNA) transcript.
    • Translation is the process through which ribosomes and tRNA molecules decode the mRNA to create a polypeptide chain.

    Plasmids

    • Small circular extrachromosomal DNA molecules that can replicate independently.
    • Often carry genes that confer beneficial traits to the bacteria, such as antibiotic resistance.
    • Play a vital role in the spread of antibiotic resistance.

    DNA Mutations

    • Common source of genetic variation in bacteria.
    • They can be spontaneous or caused by mutagens.
    • Three types: substitution, deletion, and insertion.

    Mutation Effects

    • Substitution mutations can cause minor changes in the protein or even no change at all if they are silent.
    • Deletion mutations can cause frameshift mutations, where the reading frame is shifted, leading to a change in the subsequent amino acid sequence.
    • Insertion mutations can also lead to frameshift mutations and premature termination of translation.
    • Mutations are important to understand because they can lead to changes in the bacteria's functionality, like antibiotic resistance or a more virulent form of the pathogen.

    Gram Staining

    • Gram-positive bacteria stain purple, while Gram-negative bacteria stain pink
    • This differentiation occurs because of the unique composition of the cell envelope
    • Gram-positive bacteria have a thick peptidoglycan layer and a low lipid content, while Gram-negative bacteria have a thin peptidoglycan layer and a high lipid content
    • The alcohol treatment step in the Gram stain dehydrates the peptidoglycan layer of Gram-positive bacteria, making it impermeable to the crystal violet-iodine complex
    • Alcohol extracts the lipid content of the Gram-negative cell envelope, permeabilizing the cell membrane and allowing the crystal violet-iodine complex to diffuse out
    • The counterstain, neutral red, is then taken up by the Gram-negative bacteria, resulting in their pink color

    Non-Gram Stains

    • Some bacteria, like Mycobacteria, have a high wax content in their cell envelope and cannot be stained using the Gram method. These bacteria are stained using the Ziehl-Neelsen stain.
    • Mycoplasmas, the smallest known bacteria, lack a cell wall and cannot be stained using Gram stain.

    Bacterial Morphology

    • Cocci are spherical-shaped bacteria
    • Bacilli are rod-shaped bacteria
    • Some bacteria are curved or spiral-shaped

    Bacterial Cell Structure

    • The bacterial genome, or chromosome, carries the bacterial genetic information.
    • Plasmids, small circular DNA molecules, can also be present.
    • The cytoplasmic membrane surrounds the cytoplasm.
    • The cell wall is a rigid layer that surrounds the cytoplasmic membrane and gives the cell its shape.
    • Gram-negative bacteria have an outer membrane covering the cell wall. This outer membrane acts as a molecular sieve, controlling the entry of molecules into the cell.

    Cytoplasmic Membrane

    • Composed primarily of lipids and phospholipids.
    • Acts as an osmotic barrier, only allowing molecules smaller than glycerol to diffuse into the cytoplasm.
    • Site of energy production through oxidative phosphorylation.
    • Transports essential molecules via permeases using facilitated diffusion (passive) and active transport.
    • Involved in the synthesis of new cell wall material.
    • Anchors the chromosome.

    Bacterial Cell Wall

    • The main component of the cell wall is peptidoglycan, a unique polysaccharide that provides the cell with its shape and prevents osmotic lysis.
    • Gram-positive bacteria have multiple layers of peptidoglycan, accounting for 90% of their cell envelope material. In contrast, Gram-negative bacteria have a single layer of peptidoglycan, accounting for only 2-20% of their cell envelope material.
    • Penicillin disrupts peptidoglycan synthesis, targeting bacterial cell wall formation.
    • Many antigens are presented on the cell wall surface.

    Gram-Positive Cell Envelope

    • Contains multiple layers of peptidoglycan.
    • Contains teichoic acids and lipoteichoic acids, which extend into the environment around the cell.
    • These structures contribute to bacterial adherence and act as antigenic determinants.

    Gram-Negative Cell Envelope

    • Has an outer membrane composed of a phospholipid-lipopolysaccharide (LPS) bilayer.
    • This outer membrane provides an additional layer of protection for Gram-negative bacteria and is why alcohol does not dehydrate their cell walls during Gram staining.
    • LPS is responsible for bacterial cell adhesion, resistance to phagocytosis, and acts as a molecular sieve.

    Cell Appendages and Structures

    • Flagella are long, whip-like appendages that rotate and allow bacteria to move (chemotaxis).
    • Pili are shorter, hair-like appendages that aid in bacterial adherence.
    • Capsules and slime layers are polysaccharide or protein coatings that surround some bacteria. These layers provide protection from phagocytosis and antibiotics and facilitate bacterial adherence.
    • Spores are dormant structures formed by some Gram-positive bacteria to survive adverse conditions. Gram-negative bacteria cannot form spores.

    Bacterial Biofilms

    • Biofilms are communities of bacteria that adhere to surfaces and produce a slimy matrix that protects the cells.
    • Biofilm formation is a major factor in the persistence of many infections, making them more resistant to treatment.
    • Examples of biofilm infections include Pseudomonas aeruginosa in cystic fibrosis patients and Staphylococcus epidermidis infections associated with intravascular catheters.
    • Biofilm infections are difficult to treat because antibiotics have reduced access to the embedded bacteria and are poorly effective at dissolving the biofilm matrix.

    Bacterial Growth

    • Bacteria typically divide by binary fission, where a single cell divides into two identical daughter cells.
    • This process allows bacteria to rapidly multiply under favorable conditions.
    • For growth, bacteria require energy, building blocks for cellular machinery, and appropriate environmental conditions.

    Energy and Growth Requirements

    • Bacteria derive energy from the enzymatic breakdown of organic substrates (carbohydrates, lipids, proteins) in a process called catabolism.
    • Growth requirements for bacteria include water, carbon, nitrogen, inorganic salts, iron, temperature, pH, and oxygen.
    • Some bacteria are aerobic, meaning they require oxygen for growth, while others are anaerobic, meaning they do not require oxygen and may even be killed by its presence.

    Bacterial Genetics

    • Bacterial genetics is clinically relevant because it plays a crucial role in the emergence of antibiotic-resistant pathogens and pathogens with enhanced virulence.
    • Some antibiotics specifically target bacterial genetic processes.
    • Advancements in genetic methods facilitate the early detection of pathogens, enabling more timely treatment of patients.

    Bacterial Genome

    • The bacterial genome includes all the genetic information carried by a bacterium, both on its chromosome and on plasmids.
    • The bacterial chromosome is a circular molecule of double-stranded DNA.
    • The bacterial chromosome contains approximately 4,000 genes and 5 million DNA base pairs.

    DNA Replication

    • DNA replication is the process by which a bacterium replicates its chromosome.
    • Replication involves multiple steps, including:
      • Initiation
      • Elongation
      • Proofreading
      • Termination
    • Key enzymes involved in DNA replication include helicase, DNA polymerase, ligase, and gyrase.

    Gene Expression

    • Gene expression is the process by which bacteria decode the genetic information contained in DNA to produce proteins.
    • Gene expression involves two key steps:
      • Transcription
      • Translation

    Transcription

    • In transcription, RNA polymerase binds to a promoter region upstream of a gene and unwinds the DNA double helix.
    • RNA polymerase then transcribes the DNA sequence into an RNA transcript, also known as messenger RNA (mRNA).

    Translation

    • In translation, mRNA is threaded through a ribosome. The sequence of codons in the mRNA is then decoded by transfer RNA (tRNA) molecules, which carry specific amino acids.
    • Ribosomes link the amino acids together in the order specified by the mRNA sequence, ultimately forming a protein.

    Plasmids

    • Plasmids are small, circular, extrachromosomal DNA molecules that can replicate independently of the bacterial chromosome.
    • Plasmids can be transferred between bacterial cells, spreading genetic information and potentially conferring phenotypic advantages to the host cell.
    • Plasmids with multiple antibiotic resistance genes are prevalent in hospital bacteria, increasing the difficulty of treating infections.

    DNA Mutation

    • Mutations are changes in the DNA sequence that can occur spontaneously or be induced by environmental factors, including exposure to mutagens.
    • Mutations are a driver of genetic diversity and can lead to changes in bacterial phenotypes, such as antibiotic resistance or altered virulence.
    • Mutations can be beneficial, harmful, or neutral, depending on the specific change in the DNA sequence and the environmental context.

    Antibiotic Resistance

    • Antibiotic overuse and misuse contribute to the emergence of antibiotic resistance.
    • Continued exposure to antibiotics selects for bacteria that have developed resistance genes, allowing them to survive and proliferate.
    • This selective pressure leads to the increasing prevalence of antibiotic-resistant strains, posing a significant challenge to public health.

    Prokaryotes vs Eukaryotes

    • Prokaryotes lack a nucleus, cell wall, and cell organelles
    • Eukaryotes have a nucleus, no cell wall, and have cell organelles including mitochondria, chloroplasts, and endoplasmic reticulum

    Microscopy

    • Bacterial shape is determined by microscopy
    • Microbial appearance assessed by colour (stain) and size

    Gram Stain

    • Most important differential staining method in microbiology
    • Gram-positive bacteria (staphylococci) have many peptidoglycan layers and appear purple after staining
    • Gram-negative bacteria (Escherichia coli) have one peptidoglycan layer and appear pink after staining

    Bacterial Cell Wall

    • Peptidoglycan, a unique polysaccharide, is the main component, providing shape and preventing lysis
    • Penicillin disrupts peptidoglycan synthesis
    • Many cell wall antigens are presented

    Gram-Positive Cell Envelope

    • Multi-layered peptidoglycan
    • Contains teichoic and lipotechoic acids that extend outwards
    • Involved in adherence and antigenicity

    Gram-Negative Cell Envelope

    • Contains an outer membrane made of phospholipid and lipopolysaccharide (LPS) bilayer
    • Offers a lipid layer, which contributes to the difference in Gram staining
    • Involved in bacterial cell adhesion and resistance to phagocytosis
    • Acts as a molecular sieve, controlling molecule access to the cell wall and cytoplasmic membrane

    Cell Appendages and Other Structures

    • Flagella extend from the surface, and are involved in bacterial motility and chemotaxis
    • Pili extend from the surface involved in bacterial adhesion
    • Capsules and Slime layers (polysaccharide or protein) surround some bacteria
    • Capsules and Slime layers offer protection from phagocytosis and antibiotics, and are involved in bacterial adherence
    • Spores are formed by some Gram-positive bacteria for protection against adverse conditions
    • Gram-negative bacteria cannot form spores

    Bacterial Biofilms

    • Many infections involve biofilms, such as Pseudomonas aeruginosa in cystic fibrosis patients and Staphylococcus epidermidis in intravascular catheter related infections
    • Form when bacteria adhere to surfaces and secrete a slime-like substance for anchoring
    • Biofilm infections are difficult to treat due to resistance to antimicrobial agents

    Bacterial Growth and Metabolism

    • Bacteria grow in liquid broths and on nutrient agar plates
    • Divide by binary fission, resulting in exponential multiplication
    • Growth requires energy, nutrients (water, carbon, nitrogen, inorganic salts, iron), appropriate temperature, pH, and oxygen

    Bacterial Genetics in Clinical Microbiology

    • Genetic variation processes drive the emergence of antibiotic resistant pathogens and increased virulence
    • Some antibiotics target genetic processes
    • Genetic methods facilitate early pathogen detection for faster treatment

    Bacterial Genome

    • Consists of all genetic information carried by the bacterium on both the chromosome and plasmids
    • Circular molecule of double-stranded DNA
    • Contains around 4,000 genes and 5 million DNA base pairs

    DNA Structure

    • Composed of nucleotides consisting of a base (guanine (G), adenine (A), cytosine (C), thymine (T)), sugar (deoxyribose), and one or more phosphate groups
    • Bases extend from the sugar-phosphate backbone forming a helix or ladder-like structure
    • Double-stranded DNA is wound around its axis to form the double helix

    Supercoiling

    • Topoisomerase enzyme (DNA gyrase) catalyses negative supercoiling of DNA
    • Relieves tension in the structure
    • Accommodates replication and transcription

    DNA Replication

    • Process of generating an identical set of genes during cell division
    • Semi-conservative process: one strand acts as a template for the second strand
    • Replication occurs in four steps: initiation, elongation, proofreading, and termination

    Initiation

    • Happens at the origin of replication (oriC) on the chromosome
    • Helicase enzyme unwinds dsDNA to expose ssDNA for replication
    • Replication occurs in both directions from the growing forks

    Elongation

    • DNA polymerase attaches to DNA, catalysing the formation of the new strand
    • Adds complementary bases to the parent strand
    • Works in one direction (5' to 3')
    • Leading strand: continuously copied in the 5' to 3' direction
    • Lagging strand: copied discontinuously in the 5' to 3' direction, forming Okazaki fragments
    • RNA primase lays down RNA primers on the lagging strand
    • DNA ligase links the Okazaki fragments

    Proofreading

    • DNA polymerase has proofreading activity, correcting errors during replication
    • Mistakes lead to mutations

    Termination

    • Results in two identical daughter helices

    DNA Replication Summary

    • Enzymes involved: helicase, DNA polymerase, ligase, and gyrase

    Gene Expression

    • Bacterial decoding of genetic information in DNA to produce proteins
    • Occurs in two steps: transcription and translation

    Gene Structure

    • Genes can occur individually or in groups (operons)

    Transcription

    • Initiated at the promoter region
    • RNA polymerase copies DNA to produce an RNA transcript (mRNA)

    Translation

    • mRNA is decoded by ribosomes and tRNA molecules
    • Specifying the exact sequence of amino acids in a protein

    Transcription Process

    • RNA polymerase binds to promoter regions and unwinds dsDNA in short segments
    • Transcribes DNA into RNA

    Translation Process

    • mRNA is threaded through the ribosome
    • tRNA molecules transport amino acids to the ribosome for peptide chain formation

    Plasmids

    • Small, circular, extrachromosomal DNA molecules
    • Replicate independently and can be transferred between cells
    • Confer phenotypic advantages to the host cells
    • Multiple antibiotic resistance genes on plasmids make bacteria resistant to a variety of antibiotics

    DNA Mutation

    • Changes in the nucleotide sequence of DNA
    • Can occur spontaneously or due to external factors like radiation
    • Can lead to antibiotic resistance, altered virulence, or changes in metabolic pathways

    Summary of Bacterial Gene Expression

    • DNA is transcribed into mRNA by RNA polymerase
    • mRNA is translated into proteins by ribosomes
    • tRNA molecules carry amino acids to the ribosome for protein synthesis

    Importance of Bacterial Genetics in Clinical Microbiology

    • Understanding bacterial genetics is vital for:
    • Targeting specific bacterial processes with antibiotics
    • Developing new therapeutic strategies and diagnostic techniques
    • Monitoring and controlling the emergence of antibiotic resistance
    • Understanding bacterial evolution and adaptation
    • Preventing the spread of infectious diseases

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