Bio

• DNA Replication


  Occurs during interphase, identical copy of DNA is made

  
• Chromatin


  Not visible under light microscope as it is less condensed
• Chromosome


  Visible under light microscope as they are more condensed

  
• Histones have a positive charge, DNA have a negative charge (due to its phosphate groups)
• DNA replication occurs during interphase

  
• Chromatin condenses to form chromosomes

  
• Homologous Chromosomes


  • Same size
  • Same position of centromere
  • Same gene at same position
  • One from father, one from mother

  
• Cell Cycle


  Sequence of events occurring between formation of cell and its division into daughter cells
• Stages of the cell cycle

  • Interphase (cell growth, organelles replicate, DNA replicate)
  • Mitosis
  • Cytokinesis

  
• Mitosis


  • A nuclear division that produces two daughter nuclei
  • Daughter nuclei are genetically identical to parent nucleus, and contain the same number of chromosomes as parent cell

  
• Somatic cells


  Non reproductive cells = body cells except gametes
• Importance of Mitosis


  • Growth
  • Repair
  • Asexual reproduction

  
• Stages of Mitosis


  1. Prophase (early prophase & late prophase)

  2. Metaphase

  3. Anaphase

  4. Telophase

  
• Each chromosome consists of a pair of sister chromatids

  
• DNA Replication


  New DNA and histones are synthesised

  
• Early Prophase


  1. Nuclear membrane breaks down

  2. Chromatin condenses and shorten into chromosomes

  
• Late Prophase (Prometaphase)


  1. Chromosomes continue to condense

  2. Spindle fibres (made of microtubules) form and attach to kinetochores at centromeres of chromosomes

  
• Metaphase


  Chromosomes align at the metaphase plate / equator
• Anaphase


  1. Centromere divide

  2. Sister chromatids are pulled apart (separate) and move to opposite poles of the cell

  
• Telophase


  1. Chromosomes arrive at the poles

  2. Chromosomes decondense and uncoil into chromatin

  3. Nuclear membrane reforms

  4. Spindle fibres disappear

  
• Cytokinesis


  1. Separates cytoplasm to form two daughter cells

  2. Cleavage furrow in animal cells

  3. Cell plate formation in plant cells

  
• Cytokinesis is not part of mitosis
• Infectious diseases can be spread from person to person whereas non-infectious diseases cannot
• Infectious diseases


  Diseases caused by pathogens that can be spread from person to person
• Non-infectious diseases


  Diseases not caused by pathogens and cannot be spread from person to person
• Infectious diseases


  • Influenza
  • Pneumonia
  • Covid-19
  • HIV/AIDS
  • Malaria

  
• Non-infectious diseases


  • Asthma
  • Diabetes
  • Osteoporosis
  • Dust allergy
• Pathogen


  Disease causing microorganisms
• Examples of pathogens


  • Bacteria
  • Viruses
• Non-infectious diseases are not caused by pathogens. They can be inherited, caused by environmental factors, or caused by lifestyle factors
• How infectious diseases spread

  1. Droplets in the air

  2. Direct contact

  3. Contaminated food and water
• Bacterial cell


  • Does not have a membrane-bound nucleus
  • Has a single circular DNA as its genetic material
  • Has a cell wall, ribosomes, small circular DNA molecules called plasmids and one or more flagella

  
• Virus


  • Has a protein coat enclosing its genetic material, which is either DNA or RNA
  • Does not have cellular structures, such as a cell membrane, cytoplasm or organelles
  • Does not grow, move, feed, respire or excrete
  • Can reproduce, but only when it enters a living cell
  • Requires a living host cell to obtain necessary materials for reproduction
• Pneumococcus is a Gram-positive, spherical shaped bacteria that thrive in the throat and nasal passage of humans
• Pneumococcal disease caused by pneumococcus can be treated with antibiotics
• Not all bacteria are disease causing (pathogenic); some bacteria species are non-pathogenic
• Examples of pathogenic bacteria

  • Pneumococcal bacteria
  • Mycobacerium bovis
  • Bacillus anthracis
  • Clostridium tetani
  • Vibro cholerae

  
• Examples of non-pathogenic bacteria

  • Escherichia coli
  • Lactobacillis acidophilus
• Gram-positive cells


  Have a simple cell wall that consists of a thick layer of peptidoglycan
• Gram-negative cells


  Have less peptidoglycan in their cell wall but are structurally more complex with the presence of an outer membrane