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Cell structure and function.docx

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York University
Natural Science
NATS 1670
Motti Anafi

CELLS The Cell Theory o The cell theory was first developed during the mid-1600s with the discovery of the microscope o All living organisms are made of cells o New cells are created by old cells divided into two o Anthony Van Leeuwenhoek, considered the father of microbiology, was the first one to observe and describe single-celled organisms o The evolution of the microscope has allowed for the invention of electron microscopy which reveals the structures of smaller organisms (such as viruses) o New cells are the basic building units of life and are created by division o Prokaryotic vs Eukaryotic o P: no organelle structures, smaller, free swimming DNA o E: organnelle sturctures, organized, *they have a nucleus o The Eukaryotic Cell - o Organisms are classified as either unicellular or multicellular o unicellular organisms are made up of one cell, such as bacteria and yeast o multicellular organisms are made of several to billions of cells, such as plants and animals Structures of the Cell PLASMA MEMBRANE o It is a flexible, fluid mosaic structure/barrier o Bilayers of the naturally occurring phospholipids are flexible jelly- like fluids o Separates the inside of a cell from the outside environment and from other cells o Forms a stable barrier between two polar (watery) compartments o It creates a stable and solid barrier because the inside of the membrane is occupied by the hydrophobic fatty acid chains = the membrane is impermeable to water o Provides a surface for chemical reactions to occur o Chemicals bind to receptors in membrane, message is sent to the cytoplasm and the action is carried out o Cancer causes problems with the receptors by antibodies attaching to the receptors, impeding chemical messages to reach the cell o Herceptin (HER2) turns genes on and off. In cancer, it is over- expressed, and causes cancer cells to reproduce uncontrollably o It regulates the passage of materials (nutrients and waste) into and out of cells o Membrane structure: o Phospholipids are the basic function of membranes and are made of two parts: i) the "head" has positive and negative charges, and is hydrophilic (is attracted to water) and ii) fatty acid "legs" charge and are hydrophobic(repelled by water) o When trying to remember the difference between hydrophilic and hydrophobic, remember that "phobic" is to be scared of something (hydrophobic = has phobia of water = stays away from water) o Water has no charge (H atoms have negative charge, O atom has positive charge), which is why the neutrally charged "tails" repell it o One theory of the beginning of life suggests that phospholipids became attracted due to their polarity.As they grew, they started to divide into a larger unit o There are two layers of phospholipids, with tails in the centre and heads on the outside o Integral membrane proteins can be found in the membrane. They make channels to allow nutrients and waste in and out o Oligosaccharides are sugars found in the cell membrane Phospholipid Structure o Phospholipids have a hydrophilic and a hydrophobic part o most naturally occuring phospholipids form bilayers spontaneously when they are dispensed in water Plasma Membrane Structure - Structure of the Plasma Membrane – » The “head” group, the phosphate and glycerol, is polar and hydrophilic: o Associate with water o From both sides of the membrane » The long ‘tail” is nonpolar and hydrophobic: o Repelled by water o The hydrophobic portion of two molecules of more tend to associate with each other. o Like drops of oil in water. Phospholipid Chemical Structure - The Plasma Membrane a Stable Barrier o between 2 polar (watery) compartments o because the interior of the phospholipid bilayer is occupied by hydrophobic fatty acid chains, the membrane is impermeable to water- soluble molecules The Plasma Membrane a flexible Barrier o Bilayers of the naturally occurring phospholipids are flexible jelly like fluids, not solids. Cell Membrane/ Plasma Membrane Components Definitions The cell membrane/ Plasma membrane Aflexible barrier that separates the extracellular and intracellular fluid compartments Lipids (Fluid Mosaic Model, FMM) Athin structure composed of a double layer called a bilayer of organic compounds of carbon, hydrogen and oxygen Hydrophobic Water hating Hydrophilic Water loving Lipid Molecules (FMM) Has a hydrophobic side that avoids water and is settled on the interior of the lipid bi-layer. It is made of fatty acid and it is non-polar. Exterior and Interior Face (FMM) Is in contact with the polar side of the lipid structure called the head The head (FMM) Is hydrophilic and is polar – consists of positive and negative charges Types of protein Peripheral, integral and glycoprotein o Attached loosely to either the Peripheral proteins interior or exterior of the bi-layer o Gives support to plasma membrane Functions of Peripheral Protein o Joins cells together o Handles changing in cell shape during o cell division and muscle contraction o They project through the lipid Integral Proteins bilayer o Can be in contact with both extracellular and intracellular sides. o Has a hydrophilic side and a hydrophobic side that interacts with the non-polar and polar heads of the lipid bilayer o Intercellular joining Functions of Integral Protein o Recepto
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