CELLS

• Kingdoms in Biology


  • Animal
  • Plant
  • Bacteria
  • Fungi
  • Protoctista
• Animal and Plant


  • Multicellular organisms made up of billions of cells working together
• Bacteria, Fungi, Protoctista


  • Microorganisms made up of one or a few cells
• Viruses are not defined as living organisms because they do not have the standard components of a cell – acellular, and cannot perform MRS GREN without a host
• All living organisms are made from cells (multicellular = millions, microorganism = one/few), all cells have 4 properties = DNA, ribosomes, cytoplasm, cell membrane
• Eukaryotic cells


  Animal/plant cell, has membrane bound organelles (nucleus, endoplasmic reticulum, golgi body, lysosome, mitochondra)
• Prokaryotic cells


  Bacteria, has no membrane bound organelles
• Forms of Reproduction


  • Sexual
  • Asexual
• Sexual Reproduction


  Uses 2 parents (each provides a gamete which fuse to form a zygote, zygote develops into organism)
• Asexual Reproduction


  Uses 1 parent to produce genetically identical offspring
• Zygote development into an organism


  1. Zygote is a stem cell

  2. Stem cell divides by mitosis to make many stem cells

  3. Each stem cell differentiates into specialised cell

  4. Each specialised cell divides by mitosis to make many copies and form a tissue

  5. Different tissues join to form an organ

  6. Different organs join to form an organ system

  7. This is surrounded by the Body
• Tissue


  A group of specialised cells
• Organ


  Made of different tissues
• Organ system


  Different organs working together
• Components of an Animal Cell


  • Organelles (nucleus, endoplasmic reticulum, golgi body, lysosomes, mitochondria, ribosomes)
  • Cytoplasm
  • Cell Membrane
• Nucleus


  • Contains DNA (made of genes, genes code for making proteins)
  • DNA wrapped around histones to form Chromatin
  • Has a double membrane, called Nuclear Envelope, which contains pores
  • At centre is Nucleolus – produces mRNA (copy of a gene)
  • Rest of nucleus made of Nucleoplasm (contains the DNA/chromatin)
• Endoplasmic Reticulum


  • Rough ER has ribosomes on it, makes proteins
  • Smooth ER has no ribosomes on it, makes lipids/carbohydrates
• Golgi body


  • Modifies and packages proteins
  • Packages them into vesicles for transport
  • Digestive enzymes are placed into lysosomes (vesicles with membranes around them)
• Mitochondria


  • Site of respiration, releases energy, produces ATP (energy carrier molecule)
  • Has a double membrane, inner membrane folded into Cristae (increases surface area for enzymes of respiration)
  • Middle portion called Matrix
• Ribosomes


  • Attached to RER
  • Site of protein synthesis
• Components of a Plant Cell


  • Organelles (nucleus, endoplasmic reticulum, golgi body, lysosomes, mitochondria, chloroplast, vacuole, ribosomes)
  • Cytoplasm
  • Cell Membrane
  • Cell Wall
• Chloroplast


  • Organelle for photosynthesis
  • Has double membrane
  • Contains discs called thylakoids
  • Thylakoids contain chlorophyll
  • Stack of thylakoids called granum
  • Thylakoids surrounded by a fluid called stroma
• Vacuole


  Surrounded by a membrane called a tonoplast, contains Cell Sap (water, sugar, minerals)
• Bacteria


  • No nucleus – loose DNA in the form of a single loop and plasmid
  • No membrane bound organelles: smaller ribosomes, mesosomes – infolding of cell membrane for respiration
  • Cytoplasm
  • Cell Membrane & Cell Wall (made of peptidoglycan/murein)
  • Some have a Capsule (reduce water loss, protect from phagocytosis) and Flagella (movement)
• Virus


  • DNA or RNA (if RNA, also has a enzyme called reverse transcriptase to turn RNA into DNA)
  • Protein Coat called Capsid and Lipid Coat
  • Attachment proteins on outside
  • (Infects host cells by attaching using their attachment protein, send in their DNA which uses the cell to make the viruses components and uses the cell membrane to make the viruses lipid coat, hence, producing copies of the virus and destroying the host cell)
• Chromosome


  • DNA in coiled form
  • Formed during interphase of cell division (mitosis/meiosis) in Animals/Plants
  • Made of 2 identical/sister chromatids joined by a centromere
  • Carries 2 copies of the same DNA molecule
• Homologous pair of chromosomes


  • A pair of chromosomes: 1 maternal (from mother)/1 paternal (from father)
  • Carries same genes but different alleles – there are 23 pairs in humans
• Cell Division


  • Formation of new cells in multicellular organisms (animals & plants)
  • 2 methods = mitosis & meiosis
  • Mitosis = produces genetically identical cells for growth & repair of tissues
  • Meiosis = produces genetically different haploid cells as gametes for sexual reproduction
• Mitosis (cell cycle)


  Produces 2 genetically identical cells, diploid (have full set of chromosomes/DNA)
• Benefit of Mitosis


  • Growth and repair of tissues
• Stages of Mitosis


  1. Interphase (G1: protein synthesis, S: DNA replication, G2: organelle synthesis)

  2. Prophase: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form

  3. Metaphase: Chromosomes line up in middle of cell and attach to spindle fibre via centromere

  4. Anaphase: Spindle fibres pull, centromere splits, sister chromatids move to opposite sides

  5. Telophase: Chromatids uncoil, nucleus reforms (left with 2 genetically identical nuclei)

  6. Cytokinesis: Separating cell into 2 (each receives a nucleus and organelles/cytoplasm)
• DNA mass in mitosis halves
• Chromosome number in mitosis stays the same (diploid)
• Cancer


  Formation of a tumour due to uncontrolled cell division (uncontrolled mitosis)
• How uncontrolled cell division occurs


  1. Due to mutation of DNA/cells forming cancer cells

  2. Mutation can occur randomly or due to mutagens (chemicals/radiation)

  3. Cancer cells are rapidly dividing cells (like hair cells, skin cells, red blood cells), they spend less time in interphase and more time in the other stages (mitosis)
• Treatments for Cancer


  • Surgery (aim is to remove tumour)
  • Chemotherapy (using drugs that inhibit mitosis in rapidly dividing cancer cells, problem also affect normal healthy cells causing side effects)
  • Radiotherapy (radiation used to destroy cancer cells)
• Meiosis


  Produces 4 genetically different cells, haploid (half the amount of chromosome/DNA)
• Benefits of Meiosis


  • Produces gametes which will be used in sexual reproduction in animals & plants (2 gametes fuse to form a zygote, zygote develops into organisms)
• Stages of Meiosis


  1. Interphase (G1: protein synthesis, S: DNA replication, G2: organelle synthesis)

  2. Meiosis I (Prophase I: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form, crossing over occurs

  3. Metaphase I: Homologous pair of chromosomes line up in middle of cell and attach to spindle fibre via centromere by random assortment

  4. Anaphase I: Spindle fibres pull, homologous pair of chromosomes separate to opposite sides by independent segregation

  5. Telophase I: Chromosomes uncoil, nucleus reforms (left with 2 nuclei))

  6. Meiosis II (Prophase II: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form

  7. Metaphase II: Chromosomes line up in middle of cell and attach to spindle fibre via centromere by random assortment

  8. Anaphase II: Spindle fibres pull, centromere splits, sister chromatids move to opposite sides by independent segregation

  9. Telophase II: Chromatids uncoil, nucleus reforms (left with 4 genetically different nuclei))

  10. Cytokinesis: Separating cell into 4 (each receives a nucleus and organelles/cytoplasm)
• Crossing Over


  • Occurs in Prophase I of Meiosis I
  • Homologous pairs of chromosomes wrap around each other and swap equivalent sections of chromatids – produces new combination of alleles