September 8 2015 BSC 215 READING 87 99 Cytoplasmic Organelles tiny cellular machines organelles allow the cell to by compartmentalized membrane bound organelles mitochondria peroxisome endoplasmic reticulum Golgi apparatus lysosome organelles not enclosed by a membrane ribosomes centrosomes organelle membrane is similar to plasma membrane so that substances can be transported b w the two Mitochondria energy production power plants of the cell some ATP is produces via glycolysis but most ATP is produced in the mitochondria human cell mitochondria each have their own DNA and enzymes required for protein synthesis Also they each have their own ribosomes ribosomes small granular organelles that participate in protein synthesis Membrane bound o Outer mitochondrial membrane smooth Large channels that permit molecules in cytosol to enter intermembrane space o Inner mitochondrial membrane numerous folds called cristae Pretty much impermeable to most solutes except those that have specific transport proteins Double membrane create 2 spaces w in mitochondria o Intermembrane space space b w the two membranes o Matrix innermost space Mostly only DNA mitochondrial proteins and enzymes Oxidative catabolism a series of rxns important to break down organic found here fuels found in the matrix o Only can be completed in the presence of oxygen Aerobic respiration 1 products of glycolytic catabolism other fuels are oxidized 2 energy released by these oxidation rxns is 3 used to drive ATP synthesis Peroxisome uses oxygen to carry out rxns their main rxn is to use molecular oxygen to oxidize and strip hydrogen atoms of certain organic molecules to produce hydrogen peroxide hydrogen peroxide oxidative enzymes are responsible for o oxidizing toxic substances ex ethanol these toxins are eliminated very important in kidney and liver cells o breaking down fatty acids products of this rxn are sent to cytosol to participate in anabolic respiration or go to mitochondria to be oxidized to ATP o synthesizing certain phospholipids these phospholipids are critical components of the plasma membrane of some nervous system cells often diseases in the peroxisomes affects the nervous system this hydrogen peroxide isn t harmful to the cell because when it accumulates an enzyme in the peroxisome turns the excess into water and oxygen o example benefit of compartmentalizing Ribosomes non membrane bound organelles that are the site of protein synthesis made up of 2 subunits each is made up of ribosomal RNA and proteins two types of ribosomes they are structurally the same just different places in the cell o free o bound suspended in the cytosol they make proteins that are used by to cytosol all ribosomes start out free but some will attach themselves to the ER or the nuclear envelope associated w membranes of other structures make proteins that will be exported from the cell transported to other organelles or inserted into the membrane The Endomembrane System Organelles that transfer molecules from vesicles that exchange proteins and other molecules are part of this system They synthesize modify and package molecules produced by the cell includes the ER Golgi and lysosomes Endoplasmic Reticulum Rough ER the large folded membrane surrounding the nucleus it is a highly folded phospholipid bilayer single continuous membrane enclosing a fluid filled space called the ER lumen Lumen contains enzymes that catalyze rxns membrane is covered in bound ribosomes polypeptides synthesized on bound ribosomes pass through RER membrane into the lumen where enzymes catalyze rxns that fold them into 3D shapes RER recognizes proteins that are shaped wrong and send them to the cytosol Many proteins that enter the RER are secretory proteins those destined to be exported from the cell o When the secretory protein is assembled it leaves the RER through a transport vesicle RER acts as a membrane factory membrane components for the entire cell are made there RER ribosomes also synthesize some cholesterol and phospholipids and inserts them into the membrane Smooth ER lacks bound ribosomes plays no roll in protein synthesis Functions o Calcium ion storage Important for muscle cells o Detoxification reactions o Lipid Synthesis Golgi Apparatus located b w RER and plasma membrane is a group of flattened membranous sacs filled with enzymes and other molecules proteins and lipids from ER are modified sorted and packed for export Sacs are not continuous like in the ER but separated from one another by thin spaces filled with cytosol Part that is closest to the ER receives transport vesicles from the ER and the farthest send the formed vesicles off Lysosomes digestive functions of cells membrane bound sacs that contain water and enzymes called acid hydrolases o these hydrolases are synthesized on bound ribosomes modified in the ER further modified in the golgi and then delivered to the lysosome in a transport vesicle Macromolecules are taken in by endocytosis and degraded These subunits are then released into the cytosol Lysosomes also degrade old organelles in a process called autophagy The Cytoskeleton cell s highways except that it can rapidly change to fit the changing needs of the cell internal framework for a cell Functions o Giving a cell its characteristic shape and size o Supporting the plasma and nuclear membrane as well as the organelles Cytoskeleton positions organizes and anchors organelles o Functioning in movement o Performing specialized functions in different cell types Types of filament Actin filaments or microfilaments o Thinnest filament o Composed of two intertwined strands of proteins subunits called actin o They provide structural support bear tension maintain shape o Myosin the motor protein associated w actin Myosin is capable of moving the whole cell Myosin actin filament interactions are responsible for contraction of muscle cells pinching of the cell in 2 in cell division membrane changes in endo exocytosis allow phagocytes to crawl w in our bodies in search of invaders Intermediate filaments o Intermediate in size o Long strands are twisted together to form ropes o Bends and twists but it is difficult to break o Functions They form most of the framework of the cell Anchor organelles Help organelles and nucleus maintain shape size Help tissues cells form to withstand stress Microtubules o Largest protein filament o Composed of subunits called tubulins Tubulins can be added removed from a microtubule allowing it to change