RVHS 15. Organisation of Genomes - Prokaryotes 9477

River Valley High School 2025 JC1 H2 Biology Lecture Topic 15: Organisation of Genomes – Prokaryotes 1 River Valley High School 2025 JC1 H2 Biology Lecture Topic 15: Organisation of Genomes – Prokaryotes Name: ( ) Class: 25J__ Date: References Title Author Biology (8th edition) Campbell and Reece Biology of Microorganisms (12th edition) Madigan, Martinko, Dunlap, Clark Biological Science 2 (3rd edition) Green, Stout and Taylor Molecular Biology of the Cell (5th edition) Alberts, Johnson, Lewis, Raff, Roberts and Walter Foundations in Microbiology (7th edition) Talaro Microbiology (4th edition) Baker, Griffiths, Nicklin Website URL Description http://highered.mcgraw- hill.com/sites/0072556781/student_view0/chapter13/ Narrated animations on transformation, transduction and conjugation (by selecting the animation quiz) H2 Biology Syllabus 9477 (2025) Candidates should be able to use the knowledge gained in the following section(s) in new situations or to solve related problems. Related Topics Content Organisation of Genomes – Viruses Role of bacteriophage in bacterial transduction Control of Gene Expression Regulation of gene expression Molecular techniques in the study of gene expression Learning Outcomes 1A. Organelles and Cellular Structures d. Describe the structure of a typical bacterial cell (small and unicellular, peptidoglycan cell wall, circular DNA, 70S ribosomes and lack of membrane-bound organelles) 2B. Organelles and Cellular Structures a. Describe the structure and organisation of prokaryotic genomes, (including DNA/RNA, single -/double- stranded, number of nucleotides, packing of DNA, linearity/circularity and presence/absence of introns). d. Outline the mechanism of asexual reproduction by binary fission in a typical prokaryote and describe how transformation, transduction and conjugation (including the role of F plasmids but not Hfr) give rise to variation in prokaryotic genomes. Lecture Outline I. Bacterial Cell A. Bacterial cell structure B. Bacterial genome II. Bacterial Reproduction III. Genetic Recombination in Bacteria A. Transformation B. Transduction C. Conjugation

River Valley High School 2025 JC1 H2 Biology Lecture Topic 15: Organisation of Genomes – Prokaryotes 2 I. Bacterial Cell Bacteria are the most diverse and widespread prokaryotes, colonising almost all habitats on Earth. They are unicellular and have diameters ranging from 0.5 -5 µm, much smaller than many eukaryotic cells. Despite its small size, a bacterium is able to achieve its life functions all within a single cell. Structure of a typical bacteria cell. Electron micrograph of a bacteria cell. Internal Structures Structure Function 1. Nucleoid ⬧ Non-membrane-bound ⬧ A region of cytoplasm where bacterial chromosome is found ⬧ Appears lighter than surrounding cytoplasm in electron micrographs ⬧ Contains one double stranded , circular DNA molecule ⬧ Presence of large amount of RNA and RNA polymerase involved in transcription and translation 2. Plasmids ⬧ Extra-chromosomal genome ⬧ Small circular DNA molecule, not part of bacterial chromosome. ⬧ Replicate independently from bacterial chromosome. ⬧ Carry a few genes which code for proteins that are not required for survival. ⬧ These proteins, when expressed, might result in characteristic s that confer advantages in stressful environments (e.g. antibiotic resistance). (KIV: Isolating, Cloning and Sequencing DNA) 3. Ribosomes ⬧ 70S (unlike 80S in eukaryotes) ⬧ Give cytoplasm a granular appearance ⬧ Required for polypeptide synthesis 4. Storage granules ⬧ Small particles found in cytoplasm ⬧ Stores nutrients and reserves (e.g. glycogen, lipids, ions) A. Bacterial cell structure

River Valley High School 2025 JC1 H2 Biology Lecture Topic 15: Organisation of Genomes – Prokaryotes 3 Surface Structures Structure Function 1. Membrane 1.1 Plasma membrane ⬧ Phospholipid bilayer containing proteins ⬧ Selectively permeable barrier that regulates the transport of material in and out of the bacterial cell ⬧ Proteins involved in the transport of ions, nutrients and waste across the membrane ⬧ Energy transduction as it contains enzymes involved in ATP synthesis (KIV: Energetics) 1.2 Mesosomes ⬧ Infoldings of the plasma membrane ⬧ Increases surface area for aerobic cellular respiration ⬧ Aids in separation of cells into daughter cells during binary fission ⬧ Participate in cell wall synthesis 1.3 Outer membrane ⬧ Gram-negative bacteria have an additional outer membrane surrounding cell wall ⬧ Similar to plasma membrane except that it contains specialized types of lipopolysaccharides1 and lipoproteins ⬧ Lipid portions of lipopolysaccharides are toxic. ⬧ Helps to protect bacterium from the body’s defence ⬧ Confers more resistance to antibiotics because it impedes entry of drugs that damage the cell wall Structure of cell walls and membranes of gram-positive (left) and gram-negative bacteria (right) 2. Cell wall ⬧ Consists of peptidoglycan (sugars cross- linked by short polypeptide chains) ⬧ Maintains cell shape ⬧ Protects bacteria from osmotic lysis 3. Capsule/ Slime layer ⬧ Thick jelly -like material surrounding surface of some bacterial cell wall ⬧ Sticky l ayer of polysaccharide (sometimes protein) ⬧ Helps in adherence to surfaces or other individuals in a colony ⬧ Protects bacteria from environmental factors (e.g. dehydration , antibiotics, phagocytosis by white blood cells) 1 Lipopolysaccharides are lipid molecules bound to polysaccharides Electron micrograph showing mesosomes in bacterial cell

River Valley High School 2025 JC1 H2 Biology Lecture Topic 15: Organisation of Genomes – Prokaryotes 4 Appendages Structure Function 1. Flagella (Singular: flagellum) ⬧ Hollow cylindrical thread made of proteins ⬧ Bacteria cells may possess none, one or multiple flagella ⬧ For motility 2. Pili (Singular: pilus) ⬧ Hollow hair-like structure made of protein pilin ⬧ There are two types of pili: o Fimbriae (singular: Fimbria): Short attachment pili. Facilitates attachment to cells or surfaces o Sex pili: Long conjugation pili Facilitate transfer of genetic materials between two bacteria. Structure of bacterial genome The genome of bacteria is considerably different from that of eukaryotes. 1. Bacteria cells are haploid, with only one set of chromosomes. 2. They lack membrane-bound nucleus. A bacterium’s chromosome is located in the nucleoid. 3. Bacterial genome consists of one double-stranded, circular chromosome, whose structure includes fewer proteins than that found in linear chromosomes of eukaryotes. 4. A bacterium may have none, one or multiple smaller rings of extra -chromosomal DNA, known as plasmids. Plasmids carry only a few genes and its replication is independent of that for bacterial chromosome. Plasmids confer selective advantage and can be integrated into the chromosome. 5. Bacterial chromosomes (~ 1100 µm in length) are compacted about 1000 fold to f it into the bacterial cell (1-2µm in diameter). This involves formation of loop domains , facilitated by DNA -binding proteins (unlike histone proteins in eukaryotes); and subsequent supercoiling by DNA gyrase. B. Bacterial genome Circular chromosome DNA folded into chromosomal domains by association with proteins. Supercoiled and looped DNA, Formation of loop domain Supercoiling

River Valley High School 2025 JC1 H2 Biology Lecture Topic 15: Organisation of Genomes – Prokaryotes 5 Organization of bacterial genome Bacterial genome has compact genetic organization. 1. Size of ba