A.2

• Cell Theory:-

  All organisms must be made up of one or more cells

  Cells are the smallest unit of life

  All cells come from pre-existing cells
• 1 micrometer is 1 x 10 ^ -6 meter (0.000001m)
• 1 nanometer (nm) is 10^-9 m (0.000000001m)
• Magnification size = measured size of image/ actual size of image (same units)
• Prokaryote cells are smaller than 1 micrometer and are simple, consisting of organisms like bacteria and archae - usually small and unicellular
• Prokaryote cells consist of cell walls, plasma membrane, flagella, pilli, ribosomes, and the nucleoid.
• The cell wall protects and maintains the shape of the cell, composed of carbohydrate complex peptidoglycan. Bacteria might have an additional polysaccharide layer, making it adhere to teeth, skin and food easily.
• Plasma membrane is found inside the cell wall and has a similar composition to eukaryotes.
• Some bacterias contain hair like growths called pilli used for attachement. Main function is to join bacterial cells in preparation for DNA transfer from one cell to another for sexual reproduction.
• Some bacteria have flagella which is longer than pilli, and is used for movement and is attached to the cell wall and plasma membrane.
• Cytoplasm occupies the interior space of the cell, where all cellular processes take place within the prokaryote cells in the cytoplasm.
• Ribosomes are present in all prokaryote cells. Their function is sites of protein synthesis, and occur in large number and are composed of two sub unites, a protein and ribosomal RNA.
• The nucleoid region is non-compartmentalized containing long, single, continuous circular thread of DNA. Nucleoid region is not surrounded by a membrane.
• Eukaryote cells range in diameter ( 5 to 100 micrometers).
• All eukaryotes have cytoplasmic regions containing cytosol.
• Cytoskeletons are fibres composed of proteins and maintains:

  • cell structure
  • anchoring of organelles (some)
  • aiding cellular movements
  • providing means for some organelles to move within cell.
• Endoplasmic reticulum are extensive tubes ranging from the nucleus to the plasma membrane.
• Smooth endoplasmic reticulum does not have any ribosomes. Is responsible for production of membrane phospholipids and cellular lipids, sex hormones, detoxification of drugs in liver (Ca 2+ ions), transportation of lipids-based compounds and helps the liver to release glucose into the blood stream when needed.
• The Rough endoplasmic reticulum have ribosomes attached to it on the exterior of its channels, and is responsible for both protein synthesis and protein transport.
• Ribosomes do not have an exterior membrane, and conduct protein synthesis within the cell. Maybe attached to the cytoplasm or be free from attachment to the surface of the ER. Made from RNA and a protein. Eukaryotes have size 80s and prokaryotes have 70S subunits.
• Lysosomes are intracellular digestive centers that come from the golgi apparatus. Are vesicles and are extremely acidic necessary for the enzymes to hydrolyze macromolecules.
• Golgi Apparatus consist of flattened sacs called cristernae stacked on top of eachother, functions in packaging collection and modification of products.
• Mitochondria are rod shaped organelles that appear through out the cytoplasm, and have circular DNA, and a double membrane. Filled with matrix, the cristae provides a large SA within for chemical reactions to occur and produces ATP, and usually have 70s type ribosomes.
• Nucleus are usually isolated for DNA, and have double membrane and nuclear envelope. Nuclear envelope is present for communication between cell's cytoplasm.
• Chloroplasts is usually in algae or plants and have its own DNA and 70S ribosomes. Interior of chloroplasts include grana which are made up of stacks of thylakoids and stroma, necessary for photosynthesis.
• Centrosome is in all eukaryote cells and have a pair of centrioles, in an assembly of microtubes, providing structure/movement.
• Vacuoles are storage bound organelles usually founded in golgi apparatus, membrane bound and occupy a lot of space.
• Unicellular organisms still manage to carry out life functions by

  • cell membrane controlling movement in and out of cells
  • isolation and storage of harmful waste by vacuoles
  • vacuoles carry out digestion, providing nutrients for cells
  • cilia/flagella allows movement
  • Mitochondria allow energy production
  • Ribosomes provide building blocks for growth repair.
• Some eukaryotic cells are unique/atypical

  • This can be shown by having multiple nuclei in a joint single cell, like the difference in septate hyphae and coenocytic hyphae.
  • Phloem Sieve Tube allows transportation within a multicellular plant, by being connected end to end.
  • Human blood cells specialize in carrying oxygen through out the body, hence does not have a nucleus.
• Endosymbiotic theory presents a mechanism by which this progression to eukaryotic cells may have occurred:

  • About 2 billion years ago a larger cell that had a nucleus and was capable of reproduction engulfed a smaller prokaryotic cell that could produce energy (mitochondria)
  • These two cells developed a mutually beneficial(symbiotic) relationship forming a single organism.
  • The smaller cell went through a series of changes to become a mitochondrion.
• Larger cell benefits the bacteria prokaryote by providing protection and carbon compounds as energy source, and the bacteria benefits the larger cell by proving ATP.
• Most evidence supports the endosymbiotic theory including mitochondrion charasteristics:

  • similar size to bacterial cells
  • divide by binary fission
  • divide indpendentley
  • 70S ribosomes
  • Produce their own proteins
  • Two membranes
  • Circular DNA
  • Have inner membrane
• Structural features of Viruses:

  • Small & fixed size
  • Nucleic acid, RNA or DNA as genetic material
  • Enclosed by boundary protein called capsid
  • Does not contain cytoplasm inside capsid
  • Posses a few enzymes (if any)
• Capsid is a viral protein boundary and is based on the presence of specific amino acids during bonding. Capsid contains specialized proteins that allows the virus to penetrate the host cell membrane.
• Shapes of Viral organisms:

  Helical, polyhedral, spherical and complex

  
• Bacteriophage Lambda

  • Capsid head holding DNA core
  • Tail fibers attaching to host cell
  • A tail sheath consisting of proteins to drive tail tube through outer membrane
  • DNA is injected through tail to host cell

  
• Covid 19

  • Spherical shape
  • single stranded RNA
  • Envelope outside capsid
  • Spike proteins on envelope (numerous)

  
• Human Immuno Deficiency Virus

  • envelope outside capsid
  • two identical strands of RNA
  • Reverse transcriptase allows production of DNA using viral RNA
  • Retrovirus: Makes a DNA copy of RNA code
  • Envelope spikes are made up of glycoproteins
• Each Virus needs a specific host of living cell to replicate.
• The Lytic Cycle:-

  1. Attachment: The phage attached to the host cell
  2. Penetration: Penetration of host cell
  3. Biosynthesis: Phage DNA directs synthesis of viral components inside the host cell
  4. Maturation: components are assembled into virions
  5. Release: host cells lyse and new virions are released. Lytic cycles involves the lysosome enzyme.