Unit 4 VCE Biology: Cell membranes &_organelles

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