The Cell

Cell Theory The cell is the basic structural and functional unit of life The organism activity depends on individual and collective activity of cells Biochemical activities of cells are dictated by sub-cellular structure For the Continuity of life the cellular basis is required

Cell Structure

Plasma Membrane Separates intracellular fluids from extracellular fluids Plays a dynamic role in cellular activity Double Layered (bi-layer) of lipids with imbedded, dispersed proteins Bi-layer consists of phospholipids, cholesterol, and glyco-lipids Glycolipids are lipids with bound carbohydrate Phospholipids have hydrophobic and hydrophilic bipoles

The phospholipid bi-layer is a selectively permeable lipid bilayer found in all cells. It contains a wide variety of biological molecules, primarily proteins and lipids Theses structures are involved in a vast array of cellular processes such as cell adhesion ion channel conductance cell signaling. The plasma membrane also serves as the attachment point for both the intracellular cytoskeleton and, if present, the cell wall.

Stephen Taylor http://sciencevideos.wordpress.com

Stephen Taylor http://sciencevideos.wordpress.com

Fluid Mosaic Model

Functions of Membrane Proteins

Functions of Membrane Proteins

Membrane Junctions Adherance junctions: Tight junction – impermeable junction that encircles the cell Desmosome – anchoring junction scattered along the sides of cells Hemi-desmosomes: anchoring the basal cell aspect to the basement membrane Gap junction – a nexus that allows chemical substances to pass between cells

Adhering junctions

Membrane Junctions

Tight junctions

Membrane Junctions

Intercellular Junctions Hemi-desmosome Intercellular Junctions

Gap Junctions

Gap Junctions

Nucleus: The Cell's Brain The nucleus is the most prominent organelle and can occupy up to 10% of the space inside a cell. It contains the equivalent of the cell's gray matter—its genetic material, or DNA. In the form of genes, each with a host of helper molecules, DNA determines the cell's identity, masterminds its activities, and is the official cookbook for the body's proteins. The nucleus is surrounded by two pliable membranes, together known as the nuclear envelope. Normally, the nuclear envelope is pockmarked with octagonal pits about an inch across (at this scale) and hemmed in by raised sides. These nuclear pores allow chemical messages to exit and enter the nucleus.

Cell Nucleus The nucleus is surrounded by two pliable membranes, together known as the nuclear envelope. Normally, the nuclear envelope is pockmarked with octagonal pits about an inch across (at this scale) and hemmed in by raised sides. These nuclear pores allow chemical messages to exit and enter the nucleus. If you exclude the nucleus, the rest of the cell's innards are known as the cytoplasm.

Golgi Apparatus Stacked and flattened membranous sacs Functions in modification, concentration, and packaging of proteins Transport vessels from the ER fuse with the cis face of the Golgi apparatus Proteins then pass through the Golgi apparatus to the trans face Secretory vesicles leave the trans face of the Golgi stack and move to designated parts of the cell

Role of the Golgi Apparatus

Endomembrane System System of organelles that function to: Produce, store, and export biological molecules Degrade potentially harmful substances

System includes: Nuclear envelope, smooth and rough ER, lysosomes, vacuoles, transport vesicles, Golgi apparatus, and the plasma membrane

Lysosomes Spherical membranous bags containing digestive enzymes Digest ingested bacteria, viruses, and toxins Degrade nonfunctional organelles Breakdown glycogen and release thyroid hormone Breakdown un-useful tissue Breakdown bone to release Ca2+

Endoplasmic Reticulum (ER) Interconnected tubes and parallel membranes enclosing cisternae Continuous with the nuclear membrane Two varieties – rough ER and smooth ER

Endoplasmic Reticulum (ER) Gough ER External surface studded with ribosomes Manufactures all secreted proteins Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes

Smooth ER Tubules arranged in a looping network Catalyzes the following reactions in various organs of the body In the liver – lipid and cholesterol metabolism, breakdown of glycogen and, along with the kidneys, detoxification of drugs In the testes – synthesis of steroid- based hormones In the intestinal cells – absorption, synthesis, and transport of fats In skeletal and cardiac muscle – storage and release of calcium

Stephen Taylor http://sciencevideos.wordpress.com