Topic 3

• Nucleus


  • Surrounded by a double membrane called the envelope
  • Contains DNA wrapped around histone proteins in chromatin
  • Contains a nucleolus which is the site of ribosome production
• Rough Endoplasmic Reticulum (RER)


  • A series of flattened sacs enclosed by a membrane with ribosomes on the surface
  • Folds and processes proteins made on the ribosomes
• Smooth Endoplasmic Reticulum (SER)


  • A system of membrane-bound sacs
  • Produces and processes lipids
• Golgi Apparatus


  • A series of fluid-filled, flattened and curved sacs with vesicles surrounding the edges
  • Modifies and packages proteins and lipids
  • Produces lysosomes
• Mitochondria


  • Usually oval shaped and bound by a double membrane
  • The inner membrane is folded to form cristae
  • Contains the enzymes needed for cellular respiration
• Centrioles


  • Hollow cylinders containing a ring of microtubules arranged at right angles
  • Involved in cell division
• 80S Ribosomes


  • Composed of two subunits
  • The site of protein synthesis
• Lysosomes


  • Vesicles containing digestive enzymes
  • Bound by a single membrane
• Protein Trafficking


  1. Proteins are produced on ribosomes

  2. Proteins folded and processed in RER

  3. Proteins transported from RER to Golgi Apparatus in vesicles

  4. Proteins modified in Golgi Apparatus

  5. Golgi Apparatus packages proteins into vesicles to be transported around the cell

  6. Some proteins leave the cell by exocytosis
• Cell Wall


  • The cell's rigid outer covering made of peptidoglycan
  • Provides the cell with strength and support
• Slime Capsule


  • Protective slimy layer which helps the cell to retain moisture and adhere to surfaces
• Plasmid


  • Circular pieces of DNA
• Flagellum


  • A tail-like structure which rotates to move the cell
• Pili


  • Hair-like structures which attach to other bacterial cells (allowing the exchange of plasmids)
• 70S Ribosomes


  • Composed of two subunits
  • The site of protein synthesis
• Mesosomes


  • Infoldings of the inner membrane
  • Their function is debated with many scientists believing they are just artefacts from the preparation process for microscopy, while others believe they contain enzymes required for respiration
• Ovum


  • Contains the zona pellucida which is a protective coating the sperm have to penetrate
  • Contains a haploid nucleus
  • Contains cortical granules which release substances to harden the zona pellucida
  • Surrounded by follicle cells
• Spermatozoa


  • Contains many mitochondria to provide energy for rotation of the flagellum
  • Contains acrosomes which contain digestive enzymes to break down the zona pellucida
• Fertilisation


  1. Sperm head meets zona pellucida, acrosome reaction occurs

  2. Sperm head fuses with egg cell membrane, sperm nucleus enters egg cell

  3. Cortical reaction occurs, zona pellucida hardens

  4. Nuclei fuse, full set of chromosomes restored, forming a diploid zygote
• Locus


  The location of a gene on a chromosome
• Autosomally linked


  Alleles on the same chromosome are inherited, to a greater or lesser extent, as if they were the same gene
• Recombination


  The separation of linked genes during meiosis
• Sex-linked


  Genes that occur on the X chromosome
• Some genetic disorders are sex-linked and therefore are much more common in men because the Y chromosome is smaller than the X chromosome, so if men don't have another copy of the allele for a particular characteristic, they only need one copy for the allele to be expressed
• Mitosis


  A process of cell division that produces two genetically identical daughter cells
• Cytokinesis


  The division of the cytoplasm, producing two daughter cells
• Interphase


  The stage of the cell cycle where the cell grows and DNA replicates (G1), chromosomes are replicated and begin to condense (S), and the cell prepares to divide by replicating organelles (G2)
• Crossing over


  The exchange of sections of DNA between homologous chromosomes
• Independent assortment


  The various combinations of ways maternal and paternal chromosomes can be distributed between the two daughter cells
• Translocation


  • The swapping of genes, not between alleles in a homologous pair, involves genes breaking off one chromosome and joining to another
• Polysomy


  • More than two chromosomes in a pair, e.g. Down's Syndrome - trisomy-21
• Monosomy


  • Less than two chromosomes in a pair, e.g. Turner's Syndrome - monosomy of the sex chromosomes where the one chromosome present is an X
• Multipotent


  Cells that can give rise to many different types of cells
• Pluripotent


  Cells able to give rise to many types of specialised cells, but not placental cells
• Totipotent


  Cells that can give rise to all/any types of specialised cells, including placental cells
• Embryonic stem cells


  Stem cells collected from embryos
• Adult stem cells


  Stem cells collected from adult bone marrow
• Differential gene expression


  Allows cells to become specialised, involves a stimulus acting on unspecialised cells, activator and repressor molecules binding to promoter regions, active genes being transcribed to produce RNA, mRNA being translated on ribosomes to produce protein, and the protein having the ability to change the structure and function of cells
• Phenotype


  The characteristics of an organism, which result from the interaction of the genes of the organism with the environment in which it lives
• Continuous variation


  Variation in a characteristic that shows a range of values