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S250 CourseMAMMALIAN CELL
ULTRASTRUCTURELECTURE 1
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THE CELL• 1. All living things are composed of cells
and cell products.• 2. The cell is the basic unit of structure and
function of all living things.• 3. All cells come from the division of pre-
existing cells.• 4. An organism as a whole can be understood
through the collective activities and
interactions of its cells.Virchow 1855
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THE CELL
• Nucleus – control centre of cell
• Nucleoplasm – material within nucleus
• Cytoplasm – contains cytosol/organelles
• Plasma Memebrane - outer boundary of cell
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CELL ULTRASTRUCTUREORGANELLES
• 1 Nucleus/Nucleolus• 2 Endoplasmic Reticulum +/- Ribosomes• 3 Golgi Apparatus
• 4 Mitochondria• 5 Lysosomes – (Endo/exocytosis)
• 6 Peroxisomes• 7 Filaments
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NUCLEUS
• Structure: Largest organelle. Round or oval body locatednear cell centre. Surrounded by nuclear envelope composedof two membranes. Envelope contains nuclear poresthrough which messenger molecules pass to cytoplasm. No
membrane-bound organelles present in nucleus, whichcontains coiled strands of DNA known as chromatin .• Function: Stores and transmits genetic information in the
form of DNA . Genetic information passes from nucleus to
cytoplasm, where amino acids are assembled into proteins.
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NUCLEOLUS• Structure: Densely stained filamentous structure with
nucleus. Consists of proteins associated with DNA inregions where information concerning ribosomal proteins
is being expressed.• Function: Forms ribosomal particles that then pass into
cytoplasm, where they function as sites of proteinsynthesis.
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Endoplasmic Reticulum
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GRANULAR ENDOPLASMIC RETICULUM• Structure: Extensive work of flattened sheets. Encloses a
space that is continuous throughout the organelle andcontinuous with the space formed by the two nuclear envelopemembranes. Has ribosomal particles attached to its cytosolicsurface.
• Function: Proteins are synthesized on the attached ribosomesultimately distributed to other organelles or secreted from cell.
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CELL ULTRASTRUCTURERIBOSOMES
(A) Bound to ER and (B) Free in cytoplasm• Each ribosome composed of a large number of proteins
and several RNA molecules.• Ribosomes synthesize proteins from amino acids using
genetic information sent by messenger molecules fromDNA in the nucleus.
• Proteins synthesized on the free ribosomes are releasedinto cytosol.
• Proteins are synthesized by ribosomes attached to ER passinto the lumen to the Golgi apparatus.
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GOLGI APPARATUS
• Structure: Series of cup-shaped,closely opposed, flattened,membranous sacs; associatedwith numerous vesicles.Generally, a single Golgiapparatus is located in central
portion of cell near nucleus.
• Function: Concentrates,modifies and sorts newlysynthesized proteins prior totheir distribution, by way of the
Golgi vesicles, to other organelles or their secretionfrom cell.
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MITOCHONDRIA• Structure: Rod or oval-shaped body
surrounded by two membranes. Inner membrane folds into matrix of themitochondria, forming cristae.
• Function: Major site of ATP Production.O2 utilisation and CO2 formation.Contains enzymes of Krebs cycle andoxidative phosphorylation.
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CELL ULTRASTRUCTURELysosomes
• Highly specialised intercellular digestive system.• Spherical or oval organelle surrounded by a single
membrane.
• Break down bacteria and debris from dead cells that have been taken into the cell.
• May also break down cell organelles that have beendamaged and are no longer functioning normally.
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CELL ULTRASTRUCTUREPEROXISOMES
• Oval bodies covered by a single membrane (similar structure to LYSOSOMES by chemically different)
• Consume oxygen (in smaller mounts thatMITOCHONDRIA)
• Destroy certain products formed from oxygen e.g.
hydrogen peroxide – can be toxic to cells.
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CELL ULTRASTRUCTUREFILAMENTS
• MICROFILAMENTS –major part of cytoskeleton.• INTERMEDIATE FILAMENTS – in cells subject to
mechanical stress.
• MUSCLE THICK FILAMENTS – found only in musclecells.• MICROTUBULES - most rigid of cytoskeletal filaments.
- associated with movements of partcells – cell division (CENTRIOLES)
- extensions on surface of epithelialcells (CILIA)
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