Cells

• Prokaryotic cells are single celled organisms with a simple structure.
• Eukaryotic cells are in multicellular organisms (animals and plants) have a complicated internal structure.


  The internal structure: membrane bound nucleus, cytoplasm.
• Chemical reactions fundemental prcoess of life and require enzymes and specific conditions.
• Metabolism involves synthesis (building up) and breaking down of molecules.
• Nucleus has coded genetic infomantion in the form of DNA molecules

  • DNA directs the synthesis of all protiens required by the cell.
  • DNA controlse metabolic activities in the cell of the cell.
• DNA is contained within the nuclear envelope to protect it from damage in the cytoplasm.

  • Nuclear envelope contains nuclear pores to allow molecules to enter and exit the nucleus.
  • DNA itself is too large to leave the nucleus so is transcribed into smaller RNA which are exported via nuclear pore.
• DNA associates with histones which are protiens, formed in Chromatin. 


  Chromatin coils and contenses to form chromasomes.
• Nucleolus is the area within the nucleus and is responsible for producing ribosomes.

  • Made of protiens and RNA to produced rRNA which is then combined with protiens to form ribosomes.
• Mitrocondria are the site of cellular respiration where enegery is stored.

  • Makes organic molecules avalible for the production of ATP.
  • Very active cells have lots of mitrocondria.
• Mitrocondria have a double membrane.

  • Inner membrane is highly folded and formes a cristae and a matrix which contains a fluid interior.
  • Membrane with the cristae has high amounts of enzymes for aerobic respriation.
  • Mitrocondria contains Mitrocondrial DNA.
  • Mitrocondria produce thier own enzymes.
• Vesicles membranous sacs that store and transport materials inside the cell.

  • Single membrane with a fluid inside.
• Lysosomes are specialised vesicles that contain hydraulic enzymes.

  • Break down waste material in cells
  • Have an important role in the immune system, break down pathogens.
  • Play an important role in apoptosis.
• Cytoskeleton is in cytoplasm and eurkaryotic cells, providing structure and stability of a cell, the movement within the cell.

  • Microfillimants are contractile fibers formed with actin. Responsible for cell movement and cytokinesis.
  • Microtubuals are globular tubulin protiens polymerise to form tubes that form a scaffold like structure. Act as trackers for organsisms (vesicles). Form spindle fibers for mitosis.
  • Intermediate fibers are fibers whcih give mechanical strength to cells.
• Centrioles are component of the cytoskeleton in eukaryotic cells.

  • Composed of microtubuals.
  • Two centrioles form the centrosome, which forms spindle fibres.
  • Position flagella and cilia.
• Flagella and Cilia are extensions of cells.
• Flagella are on cells to enable mobility and can be used as sensory receptors to detect chemical changes.
• Cilia are mobile or stationary.

  • Stationary Cilia, present on surface of cells and have sensory functions (nose).
  • Mobile Cilia, beat in a rhythmic manner to create a current to cause fluids etc to move (trachea to move mucus or fallopian tube to move egg).
  • Each cilium have 2 microtubuals surrounded by 9 pairs of microtubuals (9+2 arrangement). The parallel microtubuals slide to cause cilia to move.
• Organelles for protein synthesis, cells need to synthesise proteins for internal use and secretion.
• Endoplasmic reticulum is a network of membranes with cisternae (flattened sacs) and is connected to outer membrane of nucleus.

  • Smooth endoplasmic reticulum responsible for lipid and carbohydrate synthesis and storage.
  • Rough endoplasmic reticulum has ribosomes bound to the surface and is responsible for storage and synthesis of proteins.
  • Secretory cells that release hormones or enzymes have a rough endoplasmic reticulum.
• Ribosomes can be free floating in cytoplasm or attached to rough endoplasmic reticulum.

  • Ribosomes are constructed of RNA molecules made in nucleolus of the cell and the site of protein synthesis.
  • Mitochondria, prokaryotic cells and chloroplasts contain ribosomes.
• Golgi Apparatus is compact structure formed of Cisternae and doesn't contain ribosomes.

  Golgi Apparatus modifies and packages proteins into vesicles.
• Protein Production: proteins are synthesised on the ribosomes bound to the endoplasmic reticulum.
• Protein Production pt2

  1. Pass into cisternae

  2. Packaged into transport vesicles

  3. Vesicles move towards Golgi Apparatus

  4. Vesicles fuse with cis face of Golgi Apparatus

  5. Proteins structurally modified before leaving Golgi Apparatus

  6. Secretory vesicles carry proteins to be released from cell

  7. Vesicles fuse with cell surface membrane releasing contents by exocytosis

  8. Some vesicles form lysosomes containing enzymes for use in cell
• Plant cells have a cellulose cell wall.

  Cellulose is a complex carbohydrate.
• Cellulose cell wall is freely permeable so substances can pass in and out of the cell.
• Cell wall in plant give the cell shape.
• The contents of the cell press against the cell wall making it rigid. This supports the cell and plant as a whole. Also acts as a defence mechanism protecting the contents of the cell against invading pathogens.
• Plant cells have vacuoles which are membrane lines sacs in the cytoplasm containing cell sap.
• Plant cells contain large permanent vacuoles which are important for turgor pressure and maintaining the cell shape.
• Membrane of vacuoles is called a tonoplast and is made of a single layer of plasma membrane which is selectively permeable which means only small molecules can pass through.
• Chloroplasts are responsible for photosynthesis in plant cells.
• Chloroplasts are found in the green parts of plants (leaves).
• Chloroplasts are a double membrane structure. Fluid that is contained within the chloroplast is called stroma.
• Chloroplasts have an internal network of membranes which formed fattened sacs called thylakoids.
• Several thylakoids stacks is called granum.
• The grana are joined together by membranes called lamellae.
• Grana contains chlorophyll pigments where light dependant reactions occur during photosynthesis.
• Starch produced in photosynthesis is stored as starch grains.
• Chloroplasts contain DNA and ribosomes so can make their own proteins.
• Internal membranes provide a large surface area needed for enzymes, proteins and pigments needed for photosynthesis.