Ultrastructure of cells Subtopic 1.2

THE BIG PICTURE Eukaryotes are much more complex than Prokaryotes. Eukaryotes are 10 to 100 μm in diameter. Prokaryotes are 0.1 to 5.0 μm in diameter. Eukaryotes have a membrane enclosed nucleus and membrane bound organelles – compartmentalization.

Prokaryotes 1.2.1 Considered to be the earliest and most primitive type of cell. Originated ~ 3.5 billion years ago. Includes two kingdoms: bacteria and archaea. They are simple unicellular organisms, with no internal compartmentalization. Compartmentalization refers to the formation of compartments within the cell by membrane bound organelles.

Draw and label the parts of the prokaryotic cell Cell wall Plasma membrane Cytoplasm Pili Flagella 70 S ribosomes Nucleoid Naked DNA

Prokaryotic Cellular Structure functions Cell wall It protects the cell, maintains its shape and prevents it from bursting in hypotonic media. Plasma membrane It controls the movement of substances in and out of the cell. Cytoplasm It is the medium that fills up the cell and is the site of all metabolic reactions. Pili These are protein filaments on the cell wall that help in cell adhesion and in transferring of DNA between two cells. Flagella (these are much longer than pili) They are responsible for the locomotion of the organism. 70 S ribosomes It is the site of protein synthesis. Nucleoid (with naked DNA, that is DNA not associated with proteins) It controls all the activities of the cell as well as reproduction of the organism. Plasmids It is a small circle of DNA that carries a few genes that very often confers resistance to antibiotic/s to the cell.

Prokaryotic reproduction Splitting in half to produce two genetically identical cells. This is a type of asexual reproduction. The process: The semi-conservative replication of DNA. Segregation of the two copies of DNA to opposite ends of the cell. Attachment of the two DNA loops to the membrane. Elongation and pinching off of the membrane to form two separate cells.

Binary fission https://youtu.be/dZzFTHKfZSg https://youtu.be/j8_xoM8Wwgs

Eukaryotes 1.2.2 Nucleus is a membrane-bound structure that isolates the genetic material from the other parts of the cell. Includes four kingdoms: Animalia, plantae, fungi and Protista. As small as a unicellular organism just a few micrometers big (yeast) to multicellular such as the blue whale.

Armillaria ostoyae Largest living organisms on the planet. A fungus growing in forests in North America. Measured to span several hundred hectares (1 hectare = 10,000 m2) in size. https://youtu.be/gB_ysfuvz0w

Advantages of compartmentalization Greater efficiency of metabolism: Enzymes and substrates are confined and therefore much more concentrated in the particular organelles responsible for specific functions. It allows the establishment of localized conditions: such as optimum pH for specific enzymes to work. The isolation of toxic or damaging substances away from the cytoplasm such as the storage of hydrolytic enzymes in lysosomes. The flexibility of changing the numbers and position of organelles within the cell based on the cell’s requirements.

Draw and label the parts of the eukaryotic cell Plasma membrane 80S ribosomes Nucleus Mitochondrion Membrane bound organelles such as rough endoplasmic reticulum, Golgi apparatus, chloroplasts, vacuole (a large central is only present in the plant cell), pinocytotic vesicles and lysosomes (often absent from plant cells where the vacuoles fulfil the role of lysosomes). Cell wall (if you are drawing a plant cell).

Organelle functions Cellular structures Function Plasma membrane It controls the movement of substances in and out of the cell. Cytoplasm It fills up the cell and holds all organelles. It also contains several enzymes that catalyze several reactions (such as glycolysis) occurring within the cytoplasm. Mitochondria (singular: mitochondrion) They perform cellular respiration. 80S Ribosomes They are the site of protein synthesis. Nucleus It controls all the activities of the cell as well as the reproduction of unicellular organisms. Rough endoplasmic reticulum It transports the protein produced by the ribosomes on its surface to the Golgi apparatus. Golgi apparatus Its main function is to process and package proteins which are ultimately released in Golgi vesicles. Lysosomes  They contain hydrolytic enzymes and play important roles in the destruction of engulfed microbes in white blood cells as well as in the destruction of old cellular organelles. Centrioles (absent from plant cells) They play an important role in the process of nuclear division by helping in the establishment of the microtubules. Vacuole (absent from animal cells) It helps in the osmotic balance of the cell and in the storage of substances. It may also have hydrolytic functions similar to lysosomes. Cell wall (absent from animal cells) It protects the cell, maintains its shape and prevents it from bursting in hypotonic media. Chloroplast (absent from animal cells) These are ‘plastids’, that is organelles containing pigments (in this case mainly chlorophyll) and are responsible for photosynthesis. 

Exocrine gland CELL Exocrine gland secretes enzymes into a duct. Pancreatic exocrine cells secrete digestive enzymes via the pancreatic duct into the duodenum, where this aid the digestion of food. Since enzymes are proteins, it implies that the exocrine cells need to have an extensive protein synthesis machinery in place, as well as Golgi apparatus that produce vesicles containing these enzymes. The vesicles merge with the plasma membrane to release their content into the small intestine.

palisade mesophyll cells Palisade mesophyll cells, contain many chloroplasts. These organelles are the site of photosynthesis. In plants, the palisade mesophyll tissue contains the greatest number of chloroplasts per cell and is positioned right under the upper epidermis where is it can trap the highest amount of light. The main function of the palisade mesophyll cells is to photosynthesize.

Microscopy 1.2.3 Electron microscopes have a much higher resolution than light microscopes. Light microscope resolution: 200 nm Electron microscope resolution: 0.1 nm Microscope resolution is the shortest distance between two separate points in a microscope’s field of view that can still be distinguished as distinct entities.

https://youtu.be/znSQ9A7OPVc https://youtu.be/eSKTFXv5rdI https://youtu.be/fToTFjwUc5M

Interpreting Electron micrographs https://youtu.be/oSd7Dlx56Xg