Biological Molecules

• Lipids are a diverse group of molecules that include fats, oils, waxes, and steroids.
• Fats are esters formed between glycerol and fatty acids.
• Transcription occurs in the nucleus, while translation takes place on ribosomes in the cytoplasm.
• Protein synthesis involves two main stages: transcription (DNA to mRNA) and translation (mRNA to protein).
• Polysaccharides are complex carbohydrates made up of long chains of monosaccharides.
• All living organisms are made of cells, there are several different types of cells, some of them sharing some common features
• Humans are made up of eukaryotic cells
• All eukaryotic cells contain a nucleus and membrane bound organelles
• Ultrastructure


  The more detailed structure of cells that can be obtained by using a microscope
• Nucleus


  • Surrounded by a double membrane called the envelope containing pores which enable molecules to enter and leave the nucleus
  • Contains chromatin and 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 & curved sacs with vesicles surrounding the edges
  • Processes and packages proteins and lipids
  • Produces lysosomes
• Mitochondria


  • Usually oval shaped, bound by a double membrane called the envelope
  • The inner membrane is folded to form projections called cristae with matrix on the inside containing all the enzymes needed for respiration
• Centrioles


  • Hollow cylinders containing a ring of microtubules arranged at right angles to each other
  • Involved in cell division
• Ribosomes


  • Composed of two sub units and are the site of protein production
• Lysosome


  • A vesicle containing digestive enzymes bound by a single membrane
• Cytoskeleton


  • Plays an important role in providing mechanical strength as well as aiding transport within cells and enabling cell movement
• Protein transport


  1. Proteins are produced on the ribosomes

  2. Proteins produced on the surface on RER are folded and processed in the RER

  3. The proteins are then transported from the RER to the Golgi apparatus in vesicles

  4. They are then modified in the Golgi apparatus

  5. Golgi apparatus packages proteins into vesicles to be transported around the cells where they're required

  6. Some proteins such as extracellular enzymes leave the cell by exocytosis
• Prokaryotic cells


  • Cell wall - Rigid outer covering made of peptidoglycan
  • Capsule - Protective slimy layer which helps the cell to retain moisture and adhere to surfaces
  • Plasmid - Circular piece of DNA
  • Flagellum - a tail like structure which rotates to move the cell
  • Pili - Hair-like structures which attach to other bacterial cells
  • Ribosomes - Site of protein production