Cell Ultrastructure
- Magnification → increases the size of an object
- Resolution/resolving power → ability to distinguish between adjacent points
Table 1-10-2: Microscopes (1)
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Cell wall (plant cells only)
- Made up of cellulose fibres which provide strength
- Cell does not burst if surrounding solutions become dilute
Nucleus (5µm)
- Contains chromosomes (genes made of DNA which control cell activities)
- Separated from the cytoplasm by a nuclear envelope
- The envelope is made of a double membrane containing small holes
- These small holes are called nuclear pores (100nm)
- Nuclear pores allow the transport of proteins into the nucleus
Rough Endoplasmic Reticulum (rough ER)
- Have ribosomes attached to the cytosolic side of their membrane
- Found in cells that are making proteins for export (enzymes, hormones, structural proteins, antibodies)
- Thus, involved in protein synthesis
- Modifies proteins by the addition of carbohydrates, removal of signal sequences
- Phospholipid synthesis and assembly of polypeptides
Smooth Endoplasmic Reticulum (smooth ER)
- Have no ribosomes attached and often appear more tubular than the rough ER
- Necessary for steroid synthesis, metabolism and detoxification, lipid synthesis
- Numerous in the liver
Ribosomes (20-30nm)
- Small organelles often attached to the ER but also found in the cytoplasm
- Large (protein) and small (rRNA) subunits form the functional ribosome
- Subunits bind with mRNA in the cytoplasm
- This starts translation of mRNA for protein synthesis (assembly of amino acids into proteins)
- Free ribosomes make proteins used in the cytoplasm. Responsible for proteins that
- go into solution in cytoplasm or
- form important cytoplasmic, structural elements
- Ribosomal ribonucleic acid (rRNA) are made in nucleus of cell
Golgi apparatus
- Stack of flattened sacs surrounded by membrane
- Receives protein-filled vesicles from the rough ER (fuse with Golgi membrane)
- Uses enzymes to modify these proteins (e.g. add a sugar chain, making glycoprotein)
- Adds directions for destination of protein package - vesicles that leave Golgi apparatus move to different locations in cell or proceed to plasma membrane for secretion
- Involved in processing, packaging, and secretion
- Other vesicles that leave Golgi apparatus are lysosomes
Vacuole and vesicles
- Membranous sacs of liquid which store substances - vacuoles are storage areas
Lysosomes (0.05 to 0.5 micron)
- Performs intracellular digestion - more numerous in cells performing phagocytosis
- Limiting membrane keeps digestive enzymes separate from the cytoplasm
- Lysosomal enzymes digest particles
- They function optimally at pH 5 and are mostly inactive at cytosolic pH
- Lysosomal enzymes are synthesized on rough ER
- Transferred to the Golgi apparatus for modification and packaging
- Primary lysosomes are small concentrated sacs of enzymes (no digestion process)
- Primary lysosomes fuse with a phagocytic vacuole
- Become secondary lysosomes
- Digestion begins
- Nutrients diffuse through lysosomal membrane into the cytosol
Mitochondria (1µm in diameter and 7µm in length)
- Mostly protein, but also contains some lipid, DNA and RNA
- Power house of the cell
- Energy is stored in high energy phosphate bonds of ATP
- Mitochondria convert energy from the breakdown of glucose into adenosine triphosphate (ATP)
- Responsible for aerobic respiration
- Metabolic activity of a cell is related to the number of cristae (larger surface area) and mitochondria
- Cells with a high metabolic activity (e.g. heart muscle) have many well developed mitochondria
Chloroplast (4-6µm in diameter and 1-5µm in length)
- Only in photosynthesising cells (plants)
- Light energy, CO2, and H2O are converted to produce carbohydrates and O2
- Inner membrane has folds, called lamellae (where chlorophyll is found), which surround a fluid, calledstroma
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