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NATS 1675 - Lecture 2

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York University
Natural Science
NATS 1675
Robert Crippen

January 9, 2013 NATS Lecture 2  Cell is stained with colour, otherwise there are no distinct features visible – cells are translucent  The cytoplasm contains networks of membranes and many other organelles suspended in a clear liquid (cytosol)  Organelle = tiny “organ” within a cell (An organ = a structure composed of several kinds of tissue capable of carrying out a particular function, a component of an organ system)  Cells -> tissues -> organs -> organ systems -> multicellular organism o Cells are the building blocks of all organs  Most organelles are bound by membrane, some do not have membrane – non-membranous – centrioles do not have a membrane  Animal kingdom, cells come in different sizes and shapes, each kind with a different function  Most cells in the human body range from 0.5 – 40 micrometers(um) in diameter  1 um = 1/1000 mm  Human egg referred to largest cell in human body – 100 um  Nerve cell in human body can be as long as a meter – but very thin in diameter  Plasma membrane is like a “skin” o Holds cell together o Its integrity and function are necessary to the life of a cell o The plasma membrane is composed of a phospholipid bilayer and is attached in embedded proteins that can change positions o Allows certain substance to pass through, keeps substances in and out o Phospholipid bilayer – sandwich of phosphates, fat (lipid) in between, and phosphates again, and proteins that can change positions  At room temperature this phospholipid bilayer is a liquid with the consistency of olive oil. The proteins consist of fibrous proteins (some of which act as receptors) and globular proteins. These include peripheral and integral proteins. Some integral proteins act as pores.  Proteins only on surface are peripheral – proteins that go through the membrane are integral – various substances go through pore  Some proteins move and act like revolving doors – bring molecules from outside to inside  Blood type based on protein markers – people with O type do not have any at all  Proteins also help identify the cell – some proteins help recognize viruses (foreign cells within body)  The plasma membrane provides three basic functions  1) It defines the boundary between the inside and the outside of the cell  2) It plays an important role in what passes in and out of the cell, i.e. it is a selectively permeable membrane, and  3) Regulates the internal cell environment, i.e. it maintains homeostasis  Homeostasis means a state of dynamic equilibrium in the bodies internal environment (Homeo = alike; stas = posture; sis = act of) o Can apply to cells, organ systems, etc. – maintenance of pH or acidity in blood is regulated by homeostasis  The nucleus is the largest structure within the cell. It is the control center of the cell, and each nucleus contains a complete set of blue prints for a given organism or individual. More specifically by the nucleus:  1) Plays the central role in cell division, and  2) Directs the metabolic activities of the cell  Metabolism = all the chemical changes that occur within cells  Nuclear envelope – contains nuclear pores  The contents of the nucleus are referre
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