EUKARYOTE CELL ULTRASTRUCTURE

Primary Cell Structure That which can be seen using the light microscope © P Billiet © 2010 Paul Billiet ODWS

Ultrastructure That which can be observed under the electron microscope

EUKARYOTE CELL ULTRASTRUCTURE DIMENSIONS MAIN FUNCTIONS ORGANELLE 10 µm diameter Cell division, protein synthesis Nucleus 1.0 to 12.5 µm Respiration pathways Mitochondrion 5 to 10 µm diameter Photosynthetic pathways Chloroplast 0.5 to 3.0 µm diameter Digestion, recycling & isolation Lysosome Cisternae: 0.5µm thick, l-3µm diameter Secretion, reprocessing, lysosome synthesis Golgi apparatus 26 to 56 nm thick Support, Golgi apparatus synthesis Endoplasmic Reticulum (ER) 20 nm diameter Protein synthesis Ribosome © 2010 Paul Billiet ODWS

NUCLEUS (latin kernel) TEM Nucleus of a rat hepatocyte Image Credit: www.sinauer.com

NUCLEUS (pl nuclei) 10 µm Usually spherical occupying up to 75% of the cell volume © 2010 Paul Billiet ODWS

NUCLEUS Chemical composition Protein: Up to 90%, HISTONES rich in basic amino acids. Deoxyribonucleic Acid (DNA) about 20% (acidic) Ribonucleic Acid (RNA) 5 to 20% Nuclei usually contain about 10% CHROMATIN = Histone + DNA = NUCLEOPROTEIN. © 2010 Paul Billiet ODWS

NUCLEUS Functions Main site of DNA in eukaryotic cells Preservation, replication and expression of genetic information It makes RNA for protein synthesis It copies DNA for cell division © 2010 Paul Billiet ODWS

MITOCHONDRION (gk mitos = thread khondrion = granule) TEM of mitochondrion from mouse kidney cell Image Credit: University of Georgia

MITOCHONDRION (pl. mitochondria) outer membrane inner membrane Mitochondrial envelope Inter membrane space Cristae Inner matrix 1.0 to 12.5 µm © 2010 Paul Billiet ODWS

MITOCHONDRION Pigments Cytochromes Functions The inner membrane contains the enzyme necessary for the synthesis of Adenosine Triphosphate (ATP) The mitochondria are closely associated with the pathways of respiration These metabolic pathways are divided up and supported by the membranes © 2010 Paul Billiet ODWS

CHLOROPLAST (Gk chloros = green plast = form or shape) TEM chloroplast Image Credit: University of Wisconsin

CHLOROPLAST Grana Thylakoid membrane Frets outer membrane inner membrane Chloroplast envelope Starch grains Grana Frets Thylakoid membrane Stroma 5 to 10 µm © 2010 Paul Billiet ODWS

CHLOROPLAST Pigments Mainly chlorophylls with carotenoids and others Function: Photosynthesis The metabolic pathways are closely associated with the membranes as in the case of the mitochondrion © 2010 Paul Billiet ODWS

Organelles and evolution Both chloroplasts and mitochondria are double membrane bound They involved in energy reactions They contain extranuclear DNA and characteristic small ribosomes of their own This has led biologists to believe that there may be some similarity in their origins in the cells of eukaryotes. The endosymbiotic theory © 2010 Paul Billiet ODWS

LYSOSOME Image Credit: http://www.biokurs.de/

LYSOSOME Not discovered by electron microscopy but by centrifugation and enzyme analysis Some scientists suggest that they are not present in plant cells Structure: Simple, spherical, single membrane bound Lysosomes contain a large number of CATABOLIC enzymes. Catabolic enzymes digest materials by hydrolysis © 2010 Paul Billiet ODWS

Enzymes found in lysosomes SUBSTRATE Acid phosphatase Phosphate esters Acid ribonuclease RNA Acid deoxyribonuclease DNA Glycosidases Polysaccharides Protease Proteins and peptides Lipase Lipids Phospholipase Phospholipids More than 40 types of enzymes are known to occur in lysosomes. © 2010 Paul Billiet ODWS

LYSOSOME Function Digestion of compounds taken in by the cell by endocytosis Recycling of material within the cell © 2010 Paul Billiet ODWS

GOLGI APPARATUS Image Credit: International Journal of Morphology

GOLGI APPARATUS Golgi vesicles transport the materials from one cisterna to the next Cisternae are flattened sacs Transport vesicles bring material from the endoplasmic reticulum to the entry face Golgi vesicles take transformed materials from the exit face to their destination © 2010 Paul Billiet ODWS

GOLGI APPARATUS Functions Processing and packaging Synthesising lysosomes to contain the potentially dangerous catabolic enzymes Producing secretory vesicles e.g. mucus Making more plasma membrane © 2010 Paul Billiet ODWS

ENDOPLASMIC RETICULUM (ER) Image Credit: www.lifesci.sussex.ac.uk/

ENDOPLASMIC RETICULUM (ER) Rough ER Smooth ER Transport vesicles Lumen which can occupy up to 10% of the cell volume Membranes © 2010 Paul Billiet ODWS

ER Functions Not easy to study the ER is that it is difficult to extract intact ER starts the biosynthetic pathways form many protein and lipid molecules in the cell These continue in the Golgi apparatus Rough ER has ribosomes attached to it as opposed to Smooth ER The proteins are made on rough ER will eventually be secreted outside the cell © 2010 Paul Billiet ODWS

RIBOSOME Image Credit: www.palaeos.com/ Image Credit: British Society for Cell Biology

RIBOSOME NOT membrane bound Found both in pro- and eukarotes The subunits are synthesised separately in the nucleolus of the nucleus of eukaryotes Large ribosome subunit Small ribosome subunit © 2010 Paul Billiet ODWS

RIBOSOME single free-floating attached to rough ER Distribution in the cytoplasm single free-floating attached to rough ER linked together as a POLYRIBOSOME or POLYSOME Function: Protein synthesis Chemical composition Protein + RNA in other words it is a nucleoprotein © 2010 Paul Billiet ODWS

The relationship between organelles Nucleus ER Golgi apparatus Lysosome Ribosomes Endocytosis Exocytosis © 2010 Paul Billiet ODWS