Cell Division, Diversity, and Organisation

• Cell Cycle

  A) G1

  B) organelle

  C) Protein

  D) storing energy

  E) s

  F) DNA replication

  G) G2

  H) mitochondria

  I) chloroplasts

  J) Protein synthesis

  K) G0

  L) job

  M) always

  N) divide

  O) damaged

  P) old

  Q) erythrocytes

  
• Chromosomes

  • Each species has unique chromosome number per cell:
  • Humans (46, 23 pairs)
  • Chimpanzees (48, 24 pairs)
  • Fruit flies (8, 4 pairs)
  • Dogs (78, 39 pairs)
  • Onions (12, 6 pairs)
  • In pairs in nucleus
  • Humans have 23 homologous pairs
  • One of each from mother and father)
  • Only one odd pair; sex chromosomes (XY male and XX female) Y is substantially smaller
  • Most animal species and half plant species are diploid (2n)
  • Few are haploid (n)
  • Some, including many plants, are polyploid
  • One DNA molecule
  • Average human DNA spread out would stretch to sun (from Earth) and back 400 times
• Cell Cycle

  • Before problems arise, cells divide into 2 daughter cells; if they can
  • E.g. stem (animals) and meristematic (plants) cells lose ability as they specialise
  • E.g. neurones, blood cells, etc
  • Cell cycle shows different stages of cell's life (G1 → S → G2 → M → C)
  • Controlled by checkpoints at intervals
  • Checkpoints:
  • G_1 Checkpoint: Checks if cell goes through cycle
  • DNA mutations
  • Any damage
  • Cell age
  • G_2 Checkpoint: Checks cell is ready for mitosis, all went as planned
  • Metaphase Checkpoint: Checks all chromosomes are attached to spindles and ready for anaphase
• Pre Cell Division

  • Each chromosome must be replicated
  • Two identical chromatids (replicates)
  • Held together at Centromere
  • Chromatids must be supercoiled (30nm thickness to 500nm)
  • Visible chromosomes
  • Supercoiled chromosomes cannot perform normal cell functions, so must be as quick as possible
  • DNA Replication mistake:
  • Mutation
  • Happen ~50,000 to 500,000 daily
  • Most are repaired immediately by DNA polymerase
  • Occasionally they survive
• Examples of Specialised Cells

  • Neutrophils:
  • Nucleus becomes multilobed
  • Granular cytoplasm (lots of lysosomes with hydrolytic enzymes and other chemicals)
  • May phagocytose (ingest and kill microbes)
  • Squamous Epithelial Cells:
  • Flat
  • Usually lining surfaces that require a smooth fluid flow or areas require very thin surface
  • Ciliated Epithelial Cells:
  • Columnar or cuboidal-shaped
  • Tiny projections on exposed surface (cilia; made of microtubules)
  • Beat synchronised to move mucus, made by Goblet Cells, along