Animal Cell Structure PDF

Animal Cell Structure All Cells are enclosed by the plasma membrane which forms a selective barrier allowing: 1. Nutrients to enter the cells. 2. Waste products to leave. The interior of cell is organized into many organelles ” specialized compartments surrounded by a separate membrane”...

Animal Cell Structure All Cells are enclosed by the plasma membrane which forms a selective barrier allowing: 1. Nutrients to enter the cells. 2. Waste products to leave. The interior of cell is organized into many organelles ” specialized compartments surrounded by a separate membrane” e.g. Nucleus, mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus All these organelles swim in the cytoplasm “ Cytosol”  Plasma Membrane: A thin membrane of a bout 0.005 µm (5nm) thickness. Usually surrounds every living cells and delimiting the cell from the environment around it. Function of Plasma Membrane: 1. Act as a barrier by keeping the constituents of the cell in and unwanted substances out. 2. Gate which allow the transport of nutrients and waste products in and out of the cells  Chemical Composition of Plasma Membrane: Plasma membrane Lipids Proteins Sterols Peripheral Integral Phospholipid “ “Extrinsic” “Intrinsic” s Cholesterol” proteins proteins  Phospholipids bilayer (Amphiphilic character): Have a glycerol head and two hydrocarbones tails. The head is attached to a phosphoryl group with a negative charge. The tails are hydrophobic “ repelled by water and dissolve in organic solvents”.  Sterols: Have a complex hydrocarbon ring structure that represents the lipid soluble part. And hydroxyl group part which represent the water soluble part.  Membrane proteins are of two types: 1. Peripheral “ Extrinsic” Proteins: Loosely attached by ionic bonds or calcium bridges to the electrically charged phosphoryl surface of the lipid bilayer. They are also attached to the intrinsic proteins. 2. Integral “ Intrinsic” Proteins : Firmly attached within the lipid bilayer. Many of them contain from 20-24 membrane-long amino acid sequences that may extend through and bind to the fatty acid internal region of the membrane. Many intrinsic proteins bear an outer surface of side chains of complex sugars which is involved in cell-to-cell recognitions.  Transport Across The Plasma membrane: Transport cross the plasma membrane Permeation Transport of Facilitated Diffusion Active Transport “ simple Diffusion” Particles Channel Carrier mediated mediated Diffusion Diffusion 1- Permeation “ Simple Diffusion”: Is the diffusion of substances in solution through a barrier. Lipid soluble and small molecules can permeate through the membrane. Large, water soluble molecules and electrically charged ions are repelled by the lipid bilayer. Proteins and sugar polymers do not permeate at all. e.g. Oxygen and alcohols diffuse through most membranes.  2- Facilitated Diffusion A- Membranes Channels: Also known as channel mediated diffusion. Electrically charged ions have a special holes “ channels” in the plasma membrane which allow specific ions and small molecules to diffuse through the lipid bilayer. These channels are integral proteins that cross the plasma membrane forming a hole or pore. Some channels open and close spontaneously while other are gated and operate by chemical action of signaling substance such as Ca2+, acetylcholine, glycine, or change in the electrical action potential. e.g. Na +, K +, Ca2+ channels.  Facilitated Diffusion by Transporter Proteins: Also termed carrier mediated diffusion. Some molecules like sugars and amino acids are too large to fit through the open channels. These vital substances move a cross the membrane by the action of membrane transporters. Transporters proteins are intrinsic proteins that have a highly specific binding site to which the moving substance bind. Substance traveling down their concentration gradient through the membrane and does not require energy “ Passive transport” e.g. Glucose and bicarbonate transporter  Active Transport: Molecules moving against their concentration gradient by using specific pumps. It requires the cell to spend energy from the hydrolysis of Adenosine triphosphate (ATP)