Cell Membranes And Organelles-2 PDF

CELL MEMBRANES AND ORGANELLES-2 Dr. Selma Yılmaz Department of Medical Biology  THE BASİC STRUCTURES AND FUNCTİONS OF THE MAJOR ORGANELLES İN ANİMAL AND PLANT CELLS  The cell is in a dynamic flux  In the light microscope, a live cell exhibits myriad movements r...

CELL MEMBRANES AND ORGANELLES-2 Dr. Selma Yılmaz Department of Medical Biology  THE BASİC STRUCTURES AND FUNCTİONS OF THE MAJOR ORGANELLES İN ANİMAL AND PLANT CELLS  The cell is in a dynamic flux  In the light microscope, a live cell exhibits myriad movements ranging from the translocation of chromosomes and vesicles to the changes in shape associated with cell crawling and swimming The basic structures and functions of the major organelles in animal and plant cells The basic structures and functions of the major organelles in animal and plant cells  All eukaryotic cells contain a nucleus and numerous other organelles in their cytosols  Different types of organelles and smaller vesicles enclosed within their own distinctive membranes  Unique proteins in the interior and membranes of each type of organelle largely determine its specific functional characteristics  The nucleus, mitochondrion, and chloroplast are bounded by two bilayer membranes separated by an intermembrane space.  All other organelles are surrounded by a single membrane.  Cells also differ considerably in shape and in the prominence of various organelles and substructures. The basic structures and functions of the major organelles in animal and plant cells  Plant and fungal cells contain most of the organelles found in an animal cell but lack lysosomes  Instead, they contain a large central vacuole that subserves many of the functions of a lysosome.  A plant cell also contains chloroplasts, and its membrane is strengthened by a rigid cell wall.  In plants, the cell wall, which is built mainly of cellulose, is the major determinant of cell shape and imparts rigidity to cells  Animal cells, which lack a wall, are surrounded by an extracellular matrix consisting of collagen, glycoproteins, and other components that give strength and rigidity to tissues and organs.  Cell Component Structure Function Concept 6.3 Nucleus Surrounded by nuclear Houses chromosomes, made of The eukaryotic cell’s genetic envelope (double membrane) chromatin (DNA, the genetic instructions are housed in perforated by nuclear pores. material, and proteins); contains the nucleus and carried out The nuclear envelope is nucleoli, where ribosomal by the ribosomes continuous with the subunits are made. Pores endoplasmic reticulum (ER). regulate entry and exit of materials. (ER) Ribosome Two subunits made of ribo- Protein synthesis somal RNA and proteins; can be free in cytosol or bound to ER Concept 6.4 Endoplasmic reticulum Extensive network of Smooth ER: synthesis of The endomembrane system membrane-bound tubules and lipids, metabolism of carbohy- regulates protein traffic and (Nuclear sacs; membrane separates drates, Ca2+ storage, detoxifica-tion performs metabolic functions envelope) lumen from cytosol; of drugs and poisons in the cell continuous with the nuclear envelope. Rough ER: Aids in synthesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Golgi apparatus Stacks of flattened Modification of proteins, carbo- membranous hydrates on proteins, and phos- sacs; has polarity pholipids; synthesis of many (cis and trans polysaccharides; sorting of Golgi faces) products, which are then released in vesicles. Lysosome Membranous sac of hydrolytic Breakdown of ingested substances, enzymes (in animal cells) cell macromolecules, and damaged organelles for recycling Vacuole Large membrane-bounded Digestion, storage, waste vesicle in plants disposal, water balance, cell growth, and protection Concept 6.5 Mitochondrion Bounded by double Cellular respiration Mitochondria and chloro- membrane; plasts change energy from inner membrane has one form to another infoldings (cristae) Chloroplast Typically two membranes Photosynthesis around fluid stroma, which contains membranous thylakoids stacked into grana (in plants) Peroxisome Specialized metabolic Contains enzymes that transfer compartment bounded by a hydrogen to water, producing single membrane hydrogen peroxide (H2O2) as a by-product, which is converted to water by other enzymes in the peroxisome  CELL MEMBRANE and CELL WALL Plasma membrane controls movement of molecules in and out of the cell and functions in cell-cell signaling and cell adhesion. Cell wall, which is built mainly of cellulose, is the major determinant of cell shape and imparts rigidity to cells  Cell walls and membranes have similar functions.  Cell membranes surround the cell and have the ability to regulate entrance and exit of substances, thereby maintaining internal balance and functions in cell-cell signaling and cell adhesion  These membranes also protect the inner cell from outside forces.  Cell walls are much stronger than cell membranes and protect cells from lysing (exploding) in extremely hypotonic (diluted) solutions.  Variation in biomembranes in different cell types the brain ventricles the discoid erythrocyte cell Intracellular Trafficking Between Membrane Bound Compartments endocytosis/exocytosis Endocytosis (green), Recycling (blue), Exocytosis (red)  Internal organisation of the cell Three pathways by which materials are moved to lysosomes: (1) The endocytic pathway: Soluble macromolecules are taken into the cell by invagination of coated pits in the plasma membrane and delivered to lysosomes through the endocytic pathway (2 ) The phagocytic pathway: Whole cells and other large, insoluble particles move from the cell surface to lysosomes through the phagocytic pathway ( 3 ) The autophagic pathway: Worn-out organelles and bulk cytoplasm are delivered to lysosomes through the autophagic pathway  Within the acidic lumen of lysosomes, hydrolytic enzymes degrade proteins, nucleic acids, and other large molecules Three pathways by which materials are moved to lysosomes  ENDOSOMES Endosomes internalize plasma-membrane proteins and soluble materials from the extracellular medium, and they sort them back to the membranes or to lysosomes for degradation. The endocytic pathway: In this process, a segment of the plasma membrane invaginates into a “coated pit,” whose cytosolic face is lined by a specific set of proteins including clathrin. Budding of Clathrin Coated Vesicle ENDOSOMES An EM of a section of a cultured mammalian cell Gold-labeled ovalbumin (black spots) is found in early endosomes (EE) and late endosomes (LE), but very little is present in autophagosomes (AV).  LYSOSOMES Lysosomes, which have an acidic lumen, degrade material internalized by the cell and worn-out cellular membranes and organelles.  Lysosomes vary in size and shape, and several hundred may be present in a typical animal cell; are digestive sacs that can break down macromolecules in the cell using the process of hydrolysis.  Lysosomes are acidic organelles that contain various hydrolases (lysosomal enzymes) that degrade worn-out cellular membranes and organelles or unneeded cellular components and material internalized by the cell. From this compartment, some membrane proteins are recycled back to the plasma membrane, some are transported to a late endosome where further sorting takes place.  Like waste disposal in a city, lysosomes help keep excessive or bulky macromolecules from building up in the cell.  Autophagy (“eating oneself”)  Autophagy (“eating oneself”): An aged organelle is degraded in a lysosome  Materials taken into a cell by endocytosis or phagocytosis also may be degraded in lysosomes  In phagocytosis, large, insoluble particles (e.g., bacteria) are enveloped by the plasma membrane and internalized White blood cells normally look like the cell on the left. Cells undergoing programmed cell death (apoptosis), like the cell on the right.  Deficiency in Lysosomal Enzymes Tay-Sachs disease is caused by a defect in one enzyme catalyzing a step in the lysosomal breakdown of certain glycolipids called gangliosides, abundant in nerve cells-with devastating consequences. Affected children die before their third birthday with enlarged nerve cells with swollen lipid-filled lysosomes (Sphingolipid catabolism) Cherry-red spot at macula in the retina (Tay-Sachs Disease)  VACUOLES and VESICLES Vacuole stores water, ions, and nutrients, degrades macromolecules, and functions in cell elongation during growth  They can hold many substances from organic molecules to simple excess water.  Plant cells contain one or more large vacuoles.  Vacuole stores water, ions, and nutrients, degrades macromolecules, and functions in cell elongation 1 during growth.  Osmotic flow of water into vacuoles generates turgor Plant Vacuoles. Electron micrograph of a pressure. thin section of a leaf cell Most plant cells contain at least one membrane limited internal vacuole.  PEROXISOMES Peroxisomes detoxify various molecules and also break down fatty acids to produce acetyl groups for biosynthesis without the production of ATP. Peroxisomes Degrade Fatty Acids and Toxic Compounds: All animal cells (except erythrocytes) and many plant cells contain peroxisomes, a class of roughly spherical small organelles. Peroxisomes contain several oxidases—enzymes that use molecular oxygen to oxidize organic substances, in the process forming hydrogen peroxide (H2O2), a corrosive substance, which kills bacteria in neutrophiles: 2 H2O + O2 →2 H 2O2 Peroxisomes also contain copious amounts of the enzyme catalase, which degrades hydrogen peroxide to yield water and oxygen: 2 H 2O2 → 2 H2O + O2 (CATALASE)  In erytrocyte, glutathione peroxidase degrades hydrogen peroxide to yield water and oxygen: 2 H 2O2 → 2 H2O + O2  PEROXISOMES Oxidation of Very Long Fatty Acids (VLFAs) (over 21Carbons) in Peroxisomes. Mitochondria is the site of the beta- oksidation of short, medium, and long chain fatty acids, producing ATP. Beta- Very Long Fatty Acids (VLFAs) metabolized down to acetyl groups in the peroxisomes and then transported to the mitochondria for the rest of the fatty acid oxidation. No ATP production in peroxisome.  Peroxisomes (P) Mitochondria (M) and the Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (ER). EM showing various organelles in a rat liver cell. Two Peroxisomes (P) lie in close proximity to Mitochondria (M) and the Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (ER). The Endoplasmic Reticulum Is a Network of Interconnected Internal Membranes.  Function of Hexose Monophosphate (HMP) Shunt Cell requires NADPH for a variety of function including: Produces sugars for biosynthesis (ribose 5-P for nucleotides) Maintenance of a supply of reduced glutathione to protect against reactive oxygen species (ROS) Bactericidal activity in polymorphonuclear leukocytes (PMN) These important roles are cell specific. (HMP) Shunt  Glucose 6-Phosphate Dehydrogenase Deficiency Because red blood cell contain a large amount of oxygen, they are prone to spontaneously generate ROS that damage protein and lipid in the cell. Oxidant Stress [in the presence of reactive oxygen species (ROS)]: Hemoglobin Denaturation (Heinz bodies) : Hemoglobin may precipitate. Membrane Damage (Hemolytic Anemia): Membrane lipids may undergo peroxidation, weakening the membrane and causing hemolysis. Peroxides are rapidly destroyed by the glutathione peroxidase/ glutathione reductase system in the red blood cell (to avoid these complications). NADPH required by glutathione reductase is supplied by the HMP shunt in the erythrocyte. Hemolysis crisis response to: Certain drugs Ingestion of fava beans (in a subset of patients) Overwhelming infections ( often pneumonia -viral and bacterial-) or infectious hepatitis. Diabetic ketoacidosis Beta-Oxidation of Fatty Acids  The Endoplasmic Reticulum (ER) There are two types of endoplasmic reticulum (ER): 1. Smooth endoplasmic reticulum (ER) synthesizes lipids and detoxifies certain hydrophobic compounds. 2. Rough endoplasmic reticulum (ER) functions in the synthesis,processing, and sorting of secreted proteins, lysosomal proteins, and certain membranes.  Generally, the largest membrane in a eukaryotic cell encloses the endoplasmic reticulum (ER)—an extensive network of closed, flattened membrane-bounded sacs called cisternae  This extensive network makes up approximately one half of all membranous tissue of the cell and is the site of membrane and protein synthesis.  The Endoplasmic reticulum is a network of interconnected internal membranes.  The ER system is much like a road system along which industry can be found. Goods are manufactured and shipped to needed areas via the road system.  RIBOSOMES Ribosomes are the site of protein synthesis (may be free in the cytoplasm or attached to rough endoplasmic reticulum & the nucleus) 1.Structure - not membrane-bound; made up of RNA & protein. 2. Function - sites of protein synthesis (where amino acids are assembled into polypeptides).  The ribosomes carry out manual labor in the form of protein synthesis for the nucleus.  They bring together all the raw ingredients such as RNA (copies of the original DNA blueprints) and amino acids to assemble proteins.  The proteins created are essential to cell and organismal function.  Think of proteins as machinery for cell functions much like electricity and plumbing are essential in a real city.  For example, enzymes are a type of protein without which life  PROTEIN TARGETING: Signal Sequences of Proteins Although all translation of eukaryotic nuclear genes begins on ribosomes free in the cytoplasm, the proteins being translated may belong in other locations. Proteins are synthesized either on free ribosomes or on ribosomes bound to Endoplasmic reticulum (ER). Especially important among these signals are: 1. N-terminal hydrophobic signal sequence for secreted or plasma membrane or lysosomal proteins: Used to ensure translation on the rough ER (RER). Ribosomes bind to endoplasmic reticulum when proteins they are synthesizing contain an N-terminal hydrophobic signal sequence or leader sequence. Secreted or plasma membrane or lysosomal proteins are synthesized on bound ribosomes. Lysosomal proteins are tagged by mannose-6-phosphate in Golgi complex. Ribosomes remain free when proteins they are synthesizing lack a leader sequence. Proteins synthesized on free ribosomes will remain in the cytosol unless they contain a tag to direct them to the nucleus, mitochondria, or peroxisomes. 2. Phosphorylation of mannose residues for lysosomal enzymes: Important for directing an enzyme to a lysosome. 27 The targeting process for proteins that carry signal sequences: Synthesis of Secretory, Membrane, and Lysosomal Proteins TRAFFICKING OF PROTEINS SYNTHESIZED ON BOUND OR ON FREE RIBOSOMES Proteins are synthesized either on free ribosomes or on ribosomes bound to endoplasmic reticulum. 1.TRAFFICKING OF PROTEINS SYNTHESIZED ON BOUND RIBOSOMES Ribosomes bind to endoplasmic reticulum when proteins they are synthesizing contain an N-terminal signal sequence or leader sequence. Proteins synthesized on bound ribosomes enter the lumen of the endoplasmic reticulum, then move to the Golgi complex, and then be secreted from the cell. Proteins destined to function in lysosomes receive a mannose-6- phosphate tag in the Golgi. Proteins secreted from the cell are released either in a constitutive or in a regulated manner. 2. TRAFFICKING OF PROTEINS SYNTHESIZED ON FREE RIBOSOMES Ribosomes remain free when proteins they are synthesizing lack a leader sequence. Proteins synthesized on free ribosomes will remain in the cytosol unless they contain a tag to direct them to the nucleus, mitochondria, or peroxisomes.  TRAFFICKING OF PROTEINS SYNTHESIZED ON BOUND OR ON FREE RIBOSOMES Trafficking of proteins synthesized on bound ribosomes. Trafficking of proteins synthesized on free ribosomes. (Adapted from lippincott’s cellmolbiol)  1. The signal mechanism for targeting proteins to the ER 1 Ribosome 5 mRNA 4 Signal ER peptide Signal membrane 3 peptide SRP Protein removed 6 SRP 2 receptor CYTOSOL protein ER LUMEN Translocation complex 1. TRAFFICKING OF PROTEINS SYNTHESIZED ON BOUND RIBOSOMES Attachment of ribosomes to ER. (Adapted from lippincott’s cellmolbiol)  1. TRAFFICKING OF PROTEINS SYNTHESIZED ON BOUND RIBOSOMES Traffi cking from ER to Golgi complex in transport vesicles. Glycosylation in the lumen of the ER. Modifications of proteins within the Golgi complex. 1. TRAFFICKING OF PROTEINS SYNTHESIZED ON BOUND RIBOSOMES Trans Golgi network and onward 1. Lysosomes 2. Secretion from the cell Constitutive and regulated secretions. Proteins secreted from the cell are released either in a constitutive or in a regulated manner. 2. TRAFFICKING OF PROTEINS SYNTHESIZED ON FREE RIBOSOMES Transport into peroxisomes Proteins synthesized on free ribosomes will remain in the cytosol unless they contain a tag to direct them to the nucleus, mitochondria, or peroxisomes Transport into mitochondria  2. Phosphorylation of Mannose and Lysosomal Enzymes  Lysosomal enzymes are glycosylated and modified in a characteristic way.  Most importantly, when they arrive in the Golgi komplex, specific mannose residues in their oligosaccharide chains are phosphorylated.  This phosphorylation is the critical event that removes lysosomal enzymes from the secretion pathway and directs them to lysosomes.  Genetic defects affecting this phosphorylation produce I-cell disease in which lysosomal enzymes are released into the extracellular space and inclusion bodies accumulate in the cell, compromising its function. Tay-Sachs Disease I-Cell Disease, Major Symptoms  Rough facial expression, hyperplasia of the gum , large tongue  kranofacial abnormalilies, join immobility, eklem immobilitesi, clubfoot, claw-hand, scoliosis  Physokomotor retardation, slow growth  Cardiorespiratory failure with death iusually in first 10 years 36 2. Phosphorylation of mannose residues for lysosomal enzymes: Important for directing an enzyme to a lysosome. Genetic defects affecting this phosphorylation produce I-cell disease, an autosomal recessive disorder that results as a consequence of defective targeting of lysosomal hydrolases to the lysosomes; lysosomal enzymes are released into the extracellular space and inclusion bodies accumulate in the cell, compromising its function. I-cell disease is characterised by coarse facial features, skeletal abnormalities and severe psychomotor retardation that rapidly progresses leading to death between 5 and 8 years of age.  GOLGI APPARATUS and Vesicules Golgi complex processes and sorts secreted proteins, lysosomal proteins, and membrane proteins synthesized on the rough ER. Secretory vesicles store secreted proteins and fuse with the plasma membrane to release their contents.  Like a post office, the golgi apparatus is used for shipping those goods created by the ER and ribosomes to the rest of cell.  Immediately after proteins are synthesized on ribosomes of the RER, most of them leave the organelle within small membrane bounded transport vesicles.  These vesicles, which bud from RER, not coated with ribosomes, carry the proteins to another membrane-limited organelle, the Golgi Complex.  GOLGI APPARATUS and Vesicules  Golgi complex processes and sorts secreted proteins, lysosomal proteins, and membrane proteins synthesized on the rough ER.  The stack of Golgi cisternae has three defined regions—the cis, the medial, and the trans.  The Golgi cisternae are organized as series of processing compartments. Processing: Trimming (removal of mannose residues, phosphorylation, addition of complex sugar units found in mature glycoproteins, sulfation Sorting: Secreted and Membrane Proteins are sorted for their final destination.  Secretory vesicles store secreted proteins and fuse with the plasma membrane to release their contents.  GOLGI APPARATUS and Vesicules Modifications of proteins within the The Golgi cisternae are Golgi complex. organized as series of Processes within the Golgi Glycosylation - Addition of carbohydrate processing compartments. Sulfation – Addition of sulfur Model of the Golgi complex based on Phosphorylation – Addition of phosphate three-dimensional reconstruction of Proteolysis – Cleavage of peptide bonds electron microscopy images The Golgi cisternae are organized as series of processing compartments.  GOLGI APPARATUS and Vesicules Diagram of a typical secretory cell tracing the pathway a) Electron micrograph of a thin section of a hormone-secreting cell from the rat pituitary. b) A protein ((a hormone, small red dots) to be secreted, on ribosomes (blue dots) of RER (1). Transport vesicles bud off and carry these proteins to the Golgi complex and from there to the plasma membrane (2-4).  The NUCLEUS Nucleus 1. Structure: a. nuclear envelope - Double membrane with nuclear pores that surrounds the nucleus. The outer nuclear membrane is continuous with the rough ER. b. chromosomes - Genetic material composed of DNA & associated; chromosomes are linear. Nucleus is filled with chromatin composed of DNA and proteins. 2. Function: a. carrier of the hereditary information, which exerts a continuing influence over the ongoing activities of the cell through protein synthesis; "control center of the cell." b. isolates the DNA in eukaryotic cells. c. In dividing cells is site of mRNA and tRNA synthesis.  The NUCLEUS  The nucleus houses the genome of a cell  The nucleus is the “brain” of the cell and controls all activity within the cell.  The nucleus, the largest organelle in animal cells  Nuclear envelope, a double membrane, encloses the contents of the nucleus, each one a phospholipid bilayer containing many different types of proteins  The inner and outer nuclear membranes are fused at numerous nuclear pores, through which materials pass between the nucleus and the cytosol.  The inner nuclear membrane defines the nucleus itself  The outer nuclear membrane is continuous with that of the rough ER  NUCLEOLUS Nucleolus is a nuclear subcompartment where most of the cell's rRNA is synthesized. Nucleolus is a nuclear subcompartment of the nucleus and is not surrounded by a membrane. The NUCLEUS/ NUCLEOLUS  Most ribosomal RNA is produced in the nucleolus.  In the nucleus outside the nucleolus are regions of heterochromatin.  Nucleus is filled with chromatin composed of DNA and proteins; in dividing cells is site of mRNA and tRNA synthesis. Nucleolus is a nuclear subcompartment. not surrounded by a membrane, where most of the cell's rRNA is synthesized.  Nucleus directs the production of proteins by using DNA as a blueprint. The NUCLEUS Chromosomes Karyotype EM of a thin section of a bone marrow stem cell The nucleolus (n) is a subcompartment of the nucleus (N) and is not surrounded by a membrane. Most ribosomal RNA is produced in the nucleolus. Darkly staining areas in the nucleus outside the nucleolus are regions of heterochromatin.  MITOCHONDRIA Mitochondria, which are surrounded by a double membrane, generate ATP by oxidation of glucose and fatty acids.  Mitochondria are found in both plant and animal cells and is the site of cellular respiration.  Most eukaryotic cells contain many mitochondria (up to 25 percent of the volume of the cytoplasm)  Mitochondria are among the largest organelles, exceeded in size only by the nucleus, vacuoles, and choloroplasts  Mitochondria contain their own DNA.  Mitochondria, which are surrounded by a double membrane, generate ATP by oxidation of glucose and fatty acids.  In animal and plant cells, most ATP is produced by large molecular machines located in two organelles, mitochondria and chloroplasts. An example: Acetyl coenzyme A or acetyl-CoA, its main function is to deliver the acetyl group to the citric acid cycle. Mitochondria The two membranes that bound a mitochondrion differ in composition and function a mitochondrion  Mitochondria Membranes  Mitochondria contain two membranes, differ in composition and function, an outer one and an inner one, separated by the İntermembrane space.  The outer membrane, composed of half lipid and half protein, is Highly permeable (up to 10000 dalton),  A protein-enriched inner membrane, which is much less permeable, composed of 20 percent lipid and 80 percent protein, is Extensively folded.  Mitochondria are the principal sites of ATP production in aerobic Cells:  The surface area of the inner membrane is greatly increased by a large number of infoldings, or cristae, that protrude into the matrix, or central Space.  Enzymes in the inner mitochondrial membrane and central matrix carry out the terminal stages of sugar and lipid oxidation coupled to ATP Synthesis. ATP is created which is used for energy by the cell.  ATP, the universal “currency” of chemical energy  In animal and plant cells, most ATP is produced by large molecular machines located in two organelles, mitochondria and chloroplasts. An example: Acetyl coenzyme A or acetyl-CoA main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production. Mitochondria in apoptosis When the process of programmed cell death or apoptosis is stimulated in a cell, proapoptotic proteins insert into the mitochondrial membrane, forming pores. A protein known as cytochrome c can then leave the intermembrane space of the mitochondria through the pores, entering the cytosol. Cytochrome c in the cytosol stimulates a cascade of biochemical events resulting in apoptotic death of the cell.  MITOCHONDRIA  Mutations or errors in some Asexual reproduction of mitochondrial genes (37 genes) can bacteria: binary fission result in disease. is very effective for  Most mitochondrial proteins, bacteria. however, are encoded by the genomic DNA of the cell’s nucleus.  Mitochondria self replicate or divide by fission, as do bacteria.  Mitochondria are actually believed to have arisen from bacteria that were engulfed by ancestral eukaryotic cells.  In most multicellular organisms, mitochondrial DNA (mtDNA) is maternally inherited.  CHLOROPLASTS Chloroplasts, which carry out photosynthesis, are surrounded by a double membrane and contain a network of internal membrane- bounded sacs  Chloroplasts are organelles found only in plant cells.  Photosynthesis a process in which the plant uses carbon dioxide, water and sunlight to create energy in the form of glucose for the plant cell as well as heterotrophs that consume the plant.  Except for vacuoles, chloroplasts EM of a plant chloroplast are the largest and the most The internal membrane vesicles characteristic organelles in the (thylakoids) are fused into stacks (grana), which reside in a matrix cells of plants and green algae. (the stroma).  Mitochondria and Cholorplast Both mitochondria and chloroplasts:  Have similar molecular mechanisms by which ATP is formed  Often migrate from place to place within cells  Also contain their own DNA, which encodes some of the key organellar proteins, encoded proteins are synthesized on ribosomes within the organelles. However, most of the proteins encoded in nuclear DNA are synthesized in the cytosol  CYTOSKELETON Cytoskeletal fibers form networks and bundles that support cellular membranes, that gives each cell its distinctive shape and high level of organization and participate in cell movement. It is important for cell movement and cell division (mitosis). Three views of the same cell. A cultured fibroblast cell.intermediate filaments are stained green; microtubules, blue; and microfilaments, red. All three fiber systems contribute to the shape and movements of cells.  2. Cell membranes and organelles-Review Questions What are the major organelles and their functions? Organelles with a double bilayer membranes, organelles without a cell membranes? What type of proteins synthesized on the bound or free ribosomes (where to go-protein trafficking ) When Ribosomes bind to endoplasmic reticulum and when they remain free? What are the two types of secretions of proteins from the cells? Why the targeting and phosphorylation of lysosomal proteins are important? Examples of diseases?