Cell structure

Cell structure

1. Nucleus

   • Contains DNA
   • DNA arranged into long thin threads known as chromosomes
   • In most cells the chromosomes are arranged in homologous pairs
   • Surrounded by nuclear envelope
   • This has pores to allow communication between the nucleus and cytoplasm

2. Plasma membrane

   • Sea of phospholipids - arranged as a bilayer
   • Intrinsic and extrinsic proteins float within the phospholipids
   • Selectively permeable barrier - controls movement of substances between the internal and external environments

3. Lysomes

   • Formed by the golgi apparatus
   • Contain digestive enzymes - proteases and lipases
   • Important to protect the cell from the effect of these enzymes before they are released at the cell surface membrane or into a phagocytic vesicle

4. Mitochondria

   • 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

5. Ribosomes

   • 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 thatgo into solution in cytoplasm or form important cytoplasmic, structural elements
   • Ribosomal ribonucleic acid (rRNA) are made in nucleus of cell

6. 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 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

7. 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

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