Collin College BIOL. 2401 Chapter 3 Cellular Organelles. Cellular Organelles : a quick review 1
Cellular Organelles : a quick review Some Definitions : Cytoplasm material between plasma membrane and the nucleus Cytosol largely water with dissolved protein, salts, sugars, and other solutes Cytoplasmic organelles internal metabolic structures surrounded by membranes Other structures occur that are not surrounded by membranes (cytoskeleton, centrioles, and ribosomes) Inclusions chemical substances such as glycosomes, glycogen granules, and pigment Cell Nucleus Nucleus is surrounded by selectively permeable double membrane barrier containing pores. Outer membrane is continuous with the rough ER and is studded with ribosomes Pore complex regulates transport of large molecules into and out of the nucleus 2
Cell Nucleus Within the nucleus is the chromatin, nucleoli, and distinct compartments rich in specific sets of proteins Chromatin = 30% DNA ( our chromosomes) and 60 % globular proteins called histones. The rest (10%) is newly forming RNA chains ( e.g. mrna) The genetic library with blueprints for nearly all cellular proteins is contained in the DNA; it dictates the kinds and amounts of proteins to be synthesized Nucleolus is the area where active RNA synthesis occurs as well as ribosomal assembly. Chromatin Threadlike strands of DNA and globular proteins called histones DNA wraps in a regular fashion around histones, creating structures called nucleosomes (allows for packing lots of DNA into a small space) Histones also play a role in gene regulation Chromatin forms condensed, barlike bodies called chromosomes when the nucleus starts to divide 3
Endoplasmic Reticulum Tubular Membrane-bound organelle: The Rough ER (RER) : External surface studded with ribosomes Manufactures all secreted proteins Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes Endoplasmic Reticulum The Smooth ER has no Ribosomes and 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 4
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 such as new membrane components Enzymes for lysozymes Products to be exported out of the cell. Golgi Apparatus 5
Golgi Apparatus Cisterna Rough ER Proteins in cisterna Membrane Vesicle Products exported out of the cell Golgi apparatus Secretory vesicles Pathway 1 Proteins Secretion by exocytosis Extracellular fluid Golgi Apparatus Cisterna Rough ER Proteins in cisterna Membrane Vesicle Vesicle incorporated into plasma membrane Coatomer coat Golgi apparatus Pathway 2 Products incorporated into membrane Plasma membrane Secretion by exocytosis Extracellular fluid 6
Golgi Apparatus Cisterna Rough ER Proteins in cisterna Phagosome Membrane Vesicle Lysosomes containing acid hydrolase enzymes Pathway 3 Products distributed within the cell Golgi apparatus Secretory vesicles Plasma membrane Extracellular fluid Lysosomes Spherical membranous bags containing digestive enzymes with a variety of break-down functions. They originate from the RER. Digest ingested bacteria, viruses, and toxins Degrade nonfunctional organelles Breakdown glycogen and release thyroid hormone Breakdown non-useful tissue Breakdown bone to release Ca2+ Secretory lysosomes are found in white blood cells, immune cells, and melanocytes 7
Lysosomes Peroxisomes Similar Membranous sacs as Lysosomes, but containing oxidases and catalases Detoxify harmful or toxic substances Neutralize dangerous free radicals Free radicals are highly reactive chemicals with unpaired electrons (i.e., O 2 ) that can cause molecular and tissue damage Most often associated with ageing mitochondria and toxins 8
EndoMembrane System Flow Refers to the 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 EndoMembrane System Flow 9
Mitochondria Double membrane structure with shelf-like cristae Provide most of the cell s ATP via aerobic cellular respiration Contain their own DNA and RNA The higher the ATP demand of a cell, the more mitochondria they contain. Cytoskeleton Cytoskeleton is made from protein structures that provide internal strength and flexibility. These structures are not surrounded by membranes. There are three main types of cytoskeleton protein building structures. 10
Cytoskeleton Microfilaments : the thinnest structures and made from actin protein subunits. Often involved in cell motility and cell strenghtens the cell surface. Intermediate filaments are made from a variety of proteins and constructed in a woven rope fashion. They provide tensile strength. Cytoskeleton Microtubules are tubular structures made from protein subunits called tubulin. They determine the overall shape of a cell and provide areas for organelles to attach to. They are very dynamic and can rapidly disassemble and reassemble, thus grow shorter or longer depending on the needs of the cell. They are for example found in structures such as the centrioles, spindle apparatus, cilia and flagella. 11
Cytoskeleton With the help of motor proteins (such as kinesins and dyneins proteins), structures can be pulled along these microtubule railroad tracks 12