Structure Of Eukaryotic Cells

• Structure of Nucleus.

  1. Nuclear envelope: double membrane surrounding nucleus, outer membrane continuous with the (R)ER of the cell.

  
  

  2. Nuclear pores: allow the passage of larger molecules, such as mRNA, out of the nucleus.

  
  

  3. Nucleoplasm: granular, jelly-like material making up the bulk of the nucleus.

  
  

  4. Chromosomes: protein-bound, linear DNA.

  
  

  5. Nucleolus: small spherical region(s) in nucleoplasm. Manufactures ribosomal RNA and assembles ribosomes.
• Function of Nucleus.

  1. Controls cell's activities - produces mRNA and tRNA - protein synthesis. Controls entry and exit of materials, and contains nuclear reactions.

  
  

  2. Retains genetic material in the form of DNA and chromosomes.

  
  

  3. Manufactures ribosomal RNA and ribosomes.
• Structure of Mitochondria.

  1. Double membrane surrounding organelle - controls entry and exit of material.

  
  

  2. Cristae - extensions of the inner membrane, providing a large surface area for the attachment of enzymes and other proteins during respiration.

  
  

  3. Matrix - makes up the remainder - contains proteins, lipids, ribosomes and DNA (allows mitochondria to produce own proteins) and some respiratory enzymes.
• Functions of Mitochondria.

  1. Sites of Krebs Cycle and oxidative phosphorylation pathway in aerobic respiration - responsible for ATP production.

  
  

  NB = found in high numbers in metabolically active cells which require much ATP.
• Structure of Chloroplasts.

  Found in plants and algae.

  
  

  1. Chloroplast envelope - double plasma membrane, highly selective, surrounds the organelle.

  
  

  2. Grana - stacks of disc-shaped thylakoid membrane.

  
  

  3. Thylakoids - contain chlorophyll used in photosynthesis, can be linked by lamellae to other grana.

  
  

  4. Stroma - fluid-filled matrix where Calvin Cycle takes place. Also contains starch grains.
• Functions of Chloroplasts.

  Site of Photosynthesis:

  
  

  LDR in thylakoid membranes.

  LIR in stroma.

  
  

  1. Granal membranes provide a large SA for LDR - photosystems, e- carriers and enzymes etc.

  
  

  2. Chloroplasts contain DNA and ribosomes - can quickly and easily manufacture some of the proteins needed for photosynthesis.
• Structure of Endoplasmic Reticulum.

  1. 3D system of sheet-like membranes - continuous with the outer membrane of the nuclear double membrane.

  
  

  2. Membrane contains a network of tubules and flattened sacs called cisternae.

  
  

  3. RER - ribosomes on the outer surface of the membranes.

  
  

  4. SER - lacks ribosomes on its surface and is often more tubular in its appearance.
• Function of Endoplasmic Reticulum.

  RER

  
  

  1. Large SA for protein/glycoprotein synthesis.

  
  

  2. Provides a pathway for material transport throughout the cell, especially for proteins.

  
  

  SER

  
  

  1. Synthesises, stores and transports lipids and carbohydrates.
• Structure of Golgi Apparatus.

  1. Compact system of flattened sacs and stacked membranes (cisternae).

  
  

  2. Vesicles - modified proteins and lipids transported to cell membrane where they fuse with it, and then egest contents to the outside.
• Functions of Golgi Apparatus.

  1. Form glycoproteins by adding carbs to proteins.

  
  

  2. Produce secretory enzymes, such as those secreted by the pancreas

  
  

  3. Secrete carbs, such as cellulose for plant cell walls.

  
  

  4. Transports, modifies and stores lipids.

  
  

  5. Forms lysosomes.
• Structure of Lysosomes.

  Golgi vesicles with proteases, lipase and lysozymes.
• Functions of Lysosomes.

  1. Hydrolyse foreign material ingested by phagocytes.

  
  

  2. Exocytosis of enzymes to destroy extra-cellular material.

  
  

  3. Autolysis - breaking down cells after death.

  
  

  4. Digest worn out organelles - can recycle chemicals.
• Structure of Ribosomes.

  1. Small cytoplasmic granules found in all cells, free-floating or associated with RER.

  
  

  2. 80S - found in eukaryotic cells, slightly larger.

  
  

  3. 70S - in prokaryotic cells, slightly smaller.

  
  

  4. 2 Subunits - large and small - contain ribosomal RNA and proteins.
• Functions of Ribosomes.

  Carry out translation stage of protein synthesis to produce polypeptides.
• Structure of Cell Wall.

  Found in plants, algae and fungi.

  
  

  1. Cellulose microfibrils embedded in a matrix - contribute to overall cell wall strength

  
  

  2. Middle lamella - marks the boundary between adjacent cell walls and cements adjacent cells together.
• Functions of Cell Wall.

  1. (Cellulose) - to provide strength to prevent cell wall bursting under pressure created by osmotic entry of water.

  
  

  2. To provide mechanical strength to the cell as a whole.

  
  

  3. Allows water to pass along it - contributes to the movement of water through the plant.
• Structure of Vacuoles.

  1. Fluid-filled sac bounded by a single membrane.

  
  

  2. Single membrane around it called tonoplast.

  
  

  3. Solution of mineral salts, sugars, amino acids, wastes and sometimes pigments
• Functions of Vacuoles.

  1. Support plants by making cells turgid.

  
  

  2. The sugars and amino acids can act as a temporary food source.