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Unit 4: Area of study 1: Biological macromolecules, cell membranes and organelles.
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Unit 3 VCE Biology
Cell membranes and organelles
Prokaryotic cell
Eukaryotic (animal) cell
Cell membrane – phospholipid bilayer
Cell membrane with embedded proteins
Two types of proteins in membranes:
• Integral proteins that are embedded or inserted into the cell membrane.
• Peripheral proteins that are attached to the surface of the cell membrane.
• The functions of these proteins include transportation, enzymes, receptor sites, cell adhesion and attachment to the cytoskeleton.
Through the cell membrane
• Diffusion (passive)• Osmosis (passive)• Facilitated diffusion (passive)• Active transport (requires energy)• Bulk transport (requires energy)
Diffusion
• Passive movement of molecules from an area of high concentration to low concentration.
• Concentration gradient is the difference in concentration between the two regions.
• Small, uncharged molecules (CO2, H20 and O2) move easily through the membrane.
• Works well over short distances, but slows once molecules enter the cell.
• Limits cell size.
Diffusion (passive)
Osmosis
• Osmosis is the process by which water moves through a semi-permeable membrane from an area of high concentration (of water) to lower concentrations.
• It is a passive process and therefor does not require energy.
Osmosis – diffusion of water
Facilitated diffusion
• Channel mediated - Some substances diffuse with the assistance of protein channels
• Carrier mediated - Substances move down the concentration gradient via specific carrier molecules. Slower than channel-mediated as the protein carrier has to change shape for each molecule it transports.
Facilitated diffusion - passive
Active Transport
• Movement of dissolved substances into or out of cells against a concentration gradient.
• Active transport requires energy and involves a carrier protein for each substance that is actively transported.
• Includes endocytosis (into cell) and exocytosis (out of cell).
• Transport vesicles fuse with the membrane to consume or excrete substances.
Active Transport
• Pinocytosis is when a liquid is consumed or excreted.
• Phagocytosis is when a solid substance is consumed or excreted.
• Cell walls lie outside the plasma membrane in plant, fungal and prokaryotic cells.
• Endocytosis and exocytosis can occur into and out of the cell vacuole.
Active Transport – requires energy
Bulk Transport – requires energy
The Nucleus
Mitochondrion
Ribosomes• Ribosomes are cell
organelles consisting of RNA and proteins, found in the cytoplasm and sometimes along the endoplasmic reticulum (RER).
• Ribosomes are responsible for assembling the proteins in a cell.
Nucleus with Rough Endoplasmic Reticulum (RER)
Lysosomes
Lysosomes
• Lysosomes serve as the cells digestive system.• They are membrane-bound organelles
containing enzymes that can break down individual proteins or complete micro-organisms.
• They are released from the golgi apparatus.
Chloroplasts in plant cells
Cytoskeleton
• The centrosome (in animal cells) creates microtubules that provide a spindle for mitosis and meiosis.
Image Sources
• http://commons.wikimedia.org/wiki/File:Prokaryote_cell_diagram.svg
• http://commons.wikimedia.org/wiki/File:Animal_cell_structure_en.svg
• http://commons.wikimedia.org/wiki/File:Plant_cell_structure.png
• http://commons.wikimedia.org/wiki/File:Osmotic_pressure_on_blood_cells_diagram.svg
• http://commons.wikimedia.org/wiki/File:1215_Cell_Membrane_Channels.jpg
Image Sources
• http://commons.wikimedia.org/wiki/File:Cell_membrane_detailed_diagram_en.svg
• http://commons.wikimedia.org/wiki/File:Diffusion.en.svg
• http://commons.wikimedia.org/wiki/File:Centrosome_(standalone_version)-en.svg
• http://commons.wikimedia.org/wiki/File:Endocytosis_types.svg