PHYSIOLOGICAL ROLE OF CELL ORGANELLE

Transcription

1 PHYSIOLOGICAL ROLE OF CELL ORGANELLE LEARNING OBJECTIVE At the end of lecture students should be able to know, Membranous structures of cell Explain the chemical and physical characteristics pf the cell membrane and describe the role of proteins and carbohydrates in it, Describe the structure of endoplasmic reticulum and its symthesis function. Differenciate the role of golgi apparatus from that of endoplasmic reticulum, Describe lysosomes fromation and its principal constituents, Describe the structure of mitochondria,and signififance of enzymes located in the mitochondria; shelves, Explain briefly the role of mitochondria in the formation of ATP. Discuss role of ATP in the cell, Explain the special characteristics of the chemical substance adenosine triphosphate that allow it to function as energy currency in the cell. Explain the mechanism of pinocytosis and phagocytosis, Descibe the digestive vesicle and the event that take place in it, Cell Basic unit of structure and function in living things. Smallest independently functioning unit.

2 Organization Of The Cell. Cell membrane. Cytoplasm. Nucleus. SUBSTANCES THAT MAKE UP CELL. LIPIDS (Normally up to 2%, in fat cells up to 85%): o Form cellular and intra cellular membranes. o Energy CARBOHYDRATES (1 to 6%): o Source of nutrition o Structural function MINERALS / IONS: o Provide inorganic chemicals for cellular reactions CELL MEMBRANE Cell membrane envelopes the cell, it is a thin, pliable elastic structure 7.5 to 10 nanometers thick.

3 COMPOSITION: Proteins 55% Phospholipids 25%, Cholesterol 13% Carbohydrates 3% Composition of Cytoplasm Cytosol: Clear fluid portion of cytoplasm in which inclusions, particles and organelles are dispersed. Organelles:

4 Endoplasmic reticulum, Golgi apparatus, Lysosomes, Mitochondria, Peroxisomes, Ribosomes, Microtubules, Microfilaments. ENDOPLASMIC RETICULUM Endoplasmic reticulum (ER) forms an interconnected network of tubules, vesicles, and cisternae within cells. o Rough Endoplasmic Reticulum: Synthesize Proteins. o Smooth Endoplasmic Reticulum: Synthesize lipids and steroids. The Golgi apparatus functions in association with the endoplasmic reticulum. small transport vesicles (also called endoplasmic reticulum vesicles, or ER vesicles) continually pinch off from the endoplasmic reticulum and shortly thereafter fuse with the Golgi apparatus. In this way, substances entrapped in the ER vesicles are transported from the endoplasmic reticulum to the Golgi apparatus. The transported substances are then processed in the Golgi

5 apparatus to form lysosomes, secretory vesicles, and other cytoplasmic components. SMOOTH ENDOPLASMIC RETICULUM synthesis of steroid hormones (endocrine cells of gonad and adrenal cortex) detoxification of organic molecules (ethanol, barbiturates) glucose release from liver Ca2+ sequestration GOLGI APPARATUS The Golgi apparatus (also Golgi body or the Golgi Complex) is an organelle found in most eukaryotic cells The Golgi is composed of stacks of membrane-bound structures known as cisternae (singular: cisterna). An individual stack is sometimes called a dictyosome FUNCTION OF THE GOLGI APPARATUS

6 To process and package macromolecules, such as proteins and lipids,. After their synthesis and before they make their way to their destination; it is particularly important in the processing of proteins for secretion. forms a part of the cellular endomembrane system. Has a putative role in apoptosis Plays an important role in the synthesis of proteoglycans. Cells synthesize a large number of different macromolecules. Integral in modifying, sorting, and packaging these macromolecules for cell secretion (exocytosis) or use within the cell. GOLGI APPARATUS DURING MITOSIS The Golgi apparatus will break up and disappear following the onset of mitosis, or cellular division. During the telophase of mitosis, the Golgi apparatus reappears.

7 VESICULAR TRANSPORT The vesicles that leave the rough endoplasmic reticulum are transported to the cis face of the Golgi apparatus. Where they fuse with the Golgi membrane and empty their contents into the lumen. EXOCYTIC VESICLES Vesicle contains proteins destined for extracellular release. After packaging the vesicles bud off and immediately move towards the plasma membrane. Where they fuse and release the contents into the extracellular space in a process known as constitutive secretion. Antibodies release by activated plasma B cells. Secretory vesicles Vesicle contains proteins destined for extracellular release. After packaging the vesicles bud off and are stored in the cell until a signal is given for their release. When the appropriate signal is received they move towards the membrane and fuse to release their contents. This process is known as regulated secretion. Nurotransmitter release from neurons.

8 Lysosomal vesicles Vesicle contains proteins destined for the lysosome, an organelle of degradation containing many acid hydrolases, or to lysosome-like storage organelles. These proteins include both digestive enzymes and membrane proteins. The vesicle first fuses with the late endosome, and the contents are then transferred to the lysosome via unknown mechanisms. Digestive proteases destined for the lysosome. The vesicle first fuses with the late endosome, and the contents are then transferred to the lysosome via unknown mechanisms. Digestive proteases destined for the lysosome. GOLGI APPARATUS Lysosomes. Lysosomes membrane-walled sacs containing digestive enzymes Lysosomes are vesicles produced by the Golgi apparatus. Membranous bags of digesting enzymes. Lysosomes contain hydrolytic enzymes and are involved in intracellular digestion. Function of Lysosomes

9 Destroy particles taken in by endocytosis and phagocytosis. Remove and destroy worn out organelles. Removal of excess cells & tissues o "cell suicide Removal of bone matrix to release Ca +2 Steps in lysosomal formation: (1) The ER and Golgi apparatus make a lysosome (2) The lysosome fuses with a digestive vacuole (3) hydrolases digest the contents

10 Mitochondria Mitochondria are found in plant and animal cells. Mitochondria are bounded by a double membrane surrounding fluid-filled matrix. Mitochondrion structure Mitochondrion Generates most ATP o "power plant of the cell" Double membrane o outer smooth, sausage-shaped o inner folded with enzymes Contains own DNA, probably evolved from symbiotic bacteria Functions of Mitochondrium. The most prominent roles of mitochondrium is:

11 to produce ATP (i.e., phosphorylation of ADP) through respiration. Regulation of the membrane potential Apoptosis-programmed cell death Calcium signaling (including calcium-evoked apoptosis) Cellular proliferation regulation Steroid synthesis. Certain heme synthesis reactions Pinocytosis. Pinocytosis means ingestion of minuteparticles that form vesicles of extracellular fluid and particulate constituents inside the cell cytoplasm. Pinocytosis is the only means by which most large macromolecules, such as most protein molecules, can enter cells. In fact, the rate at which pinocytotic vesicles form is usually enhanced when such macromolecules attach to the cell membrane PINOCYTOSIS Figure demonstrates the successive steps of pinocytosis, showing three molecules of protein attaching to the membrane. These molecules usually attach to specialized protein receptors on the surface of the membrane that are specific for the type of protein that is to be absorbed. The receptors generally are concentrated in small pits on the outer surface of the cell membrane, called coated pits. On the inside of the cell membrane beneath these pits is a latticework of fibrillar protein called clathrin, as well as other proteins, perhaps including contractile filaments of actin and myosin. Once the protein molecules have bound with the receptors, the surface properties of the local membrane change in such a way that the entire pit invaginates inward, and the fibrillar proteins surrounding the invaginating pit

12 cause its borders to close over the attached proteins as well as over a small amount of extracellular fluid. Immediately thereafter, the invaginated portion of the membrane breaks away from the surface of the cell, forming a pinocytotic vesicle inside the cytoplasm of the cell. What causes the cell membrane to go through the necessary contortions to form pinocytotic vesicles remains mainly a mystery. This process requires energy from within the cell; this is supplied by ATP, a highenergy substance discussed later in the chapter. Also, it requires the presence of calcium ions in the extracellular fluid, which probably react with contractile protein filaments beneath the coated pits to provide the force for pinching the vesicles away from the cell membrane. PHAGOCYTOSIS Phagocytosis means ingestion of large particles, such as bacteria, whole cells, or portions of degenerating tissue. PHAGOCYTOSIS Phagocytosis occurs in the following steps: The cell membrane receptors attach to the surface ligands of the particle. The edges of the membrane around the points of attachment evaginate outward within a fraction of a second to surround the entire particle; then, progressively more and more membrane receptors attach to the particle ligands. All this occurs suddenly in a zipper-like manner to form a closed phagocytic vesicle. Actin and other contractile fibrils in the cytoplasm surround the phagocytic vesicle and contract around its outer edge, pushing the vesicle to the interior. The contractile proteins then pinch the stem of the vesicle so completely that the vesicle separates from the cell membrane, leaving the vesicle in the cell interior in the same way that pinocytotic vesicles are formed. THANK YOU.