Functions of Cell Organelles and Cell Membrane 2020-2021 PDF

Prof. Nashwa Aly Abd El-Mottaleb Functions of cell organelles and cell membrane Code: CBF-103 By Nashwa Aly Abd El-Mottaleb Professor of Medical Physiology Faculty of Medicine...

Prof. Nashwa Aly Abd El-Mottaleb Functions of cell organelles and cell membrane Code: CBF-103 By Nashwa Aly Abd El-Mottaleb Professor of Medical Physiology Faculty of Medicine Assiut University 2020-2021 Prof. Nashwa Aly Abd El-Mottaleb 1 Functions of cell organelles and cell membrane Learning Objectives: At the end of the lecture the students should be able to: - Describe characteristics and functions of cell membrane. - Describe functions of various cell organelles Prof. Nashwa Aly Abd El-Mottaleb 2 - 1  Prof. Nashwa Aly Abd El-Mottaleb Most cells have three major subdivisions: - the plasma membrane, the nucleus and the cytoplasm. The plasma membrane It surrounds the cytoplasm. Its main function is the transport of substances The Nucleus Function: - Storage of the genetic material (DNA) - Synthesis of proteins - Cell division to form new cells The Cytoplasm The cytoplasm contains: - Organelles - Cytoskeleton - Cytosol. 3 Prof. Nashwa Aly Abd El-Mottaleb Plasma Membrane The plasma membrane is about 75-100 Angstrom and composed: 1. Lipids (fats): phospholipids and cholesterol. 2. Proteins. 3. Carbohydrate. I- Functions of the lipids a. Lipid bilayer. Phospholipids molecules have a hydrophilic water- soluble head and a hydrophobic water-insoluble tail. It acts as a semipermeable membrane. b. Cholesterol found near the fatty acid chains to prevent them from packing together, which would decrease membrane permeability. It controls much of the fluidity of the membrane Prof. Nashwa Aly Abd El-Mottaleb 4 2  Prof. Nashwa Aly Abd El-Mottaleb II- Functions of the membrane proteins 1-Integral or Trans-membrane proteins. - Channels transports small water- soluble substances - Carrier, selectively transport larger water-soluble molecules 2- Peripheral proteins. - Receptors that are bind to hormones, neurotransmitters on the outer surface of the membrane. - Enzymes They are located in the inner surface of the membrane. Prof. Nashwa Aly Abd El-Mottaleb 5 III- Functions of membrane carbohydrate (Glycocalyx) - The glycoprotein and glycolipid, on the outer-membrane surface serve as self-identity markers that enable cells to identify with each other and join to form tissues during embryonic development. - Immune reactions: Carbohydrates play a role in the ability of cells to distinguish between "self cells and foreign cells. - Involved in cell- to-cell attachment or interactions Prof. Nashwa Aly Abd El-Mottaleb 6 3  Prof. Nashwa Aly Abd El-Mottaleb Functions of plasma membrane: 1. Protective barrier. 2. Regulate transport in and out of the cell (selective permeability). 3. Allow cell recognition with specific molecules in the environment of the cell. 4. Provide a binding site to enzymes Prof. Nashwa Aly Abd El-Mottaleb 7 The Cytoplasm I- The Cell Organelles There are two categories organelles: Membranous and Non membranous organelles A-Membranous organelles enclosed by a membrane similar to the plasma membrane include: Endoplasmic reticulum, golgi apparatus, lysosomes, peroxisomes and mitochondria 1-Endoplasmic reticulum a-Rough Endoplasmic reticulum (RER) Ribosomes are attached to the ER Function: Synthesis of proteins Prof. Nashwa Aly Abd El-Mottaleb 8 4  Prof. Nashwa Aly Abd El-Mottaleb b- Smooth endoplasmic reticulum (SER) It does not contain ribosomes. Functions: 1-Abundant in cells specialized in lipid metabolism (steroids secreting cells) 2-Contain enzymes for detoxifying harmful substances in the liver 3-In muscle cells, called sarcoplasmic reticulum which stores calcium used in muscular contraction. 4-Serves as a central packaging and discharge site of molecules from the ER by forming transport vesicles that enclose the new molecules Prof. Nashwa Aly Abd El-Mottaleb 9 2-Golgi apparatus It consists of flattened, slightly curved, membrane-enclosed sacs closely associated with ER Functions Package and condense the protein and the steroid particles from ER then expelled it into the cytoplasm as secretory granules and lipid. When required, they discharge their contents outside the cell by exocytosis. Prof. Nashwa Aly Abd El-Mottaleb 10 5  Prof. Nashwa Aly Abd El-Mottaleb 3-Lysosomes Lysosomes are formed by budding from the Golgi complex. Functions 1. Contain many hydrolytic enzymes. 2. Remove worn-out organelles 4-Peroxisomes They arise from the ER and Golgi complex. Function - peroxisomes had powerful oxidative enzymes (detoxify various wastes products or foreign toxic compounds) and The major product generated in the peroxisome, H2O2, - contain most of the cell’s catalase Prof. Nashwa Aly Abd El-Mottaleb 11 5- Mitochondria They are the power generating units of the cell. It is used for synthesis of adenosine triphosphate (ATP) by process known as oxidative phosphorylation. Prof. Nashwa Aly Abd El-Mottaleb 12 6  Prof. Nashwa Aly Abd El-Mottaleb B-Non membranous organelles are not surrounded by membrane and in direct contact with the cytosol include: ribosomes, proteasomes, centrosomes & centrioles - Ribosomes They are the site of protein synthesis. - Some are attached to rough ER to synthesize the protein that are secreted by the cells (e.g. hormones). -The free ribosomes present in the cytoplasm to synthesize the protein that are not secreted by the cells (e.g. haemoglobin and protein in mitochondria and peroxisomes Prof. Nashwa Aly Abd El-Mottaleb 13 - Proteasomes They are cylinder shaped complex contain multiple protein digesting enzymes that degrade the unwanted intracellular protein. - Centrosomes & Centrioles The centrosome, or cell center, located near the nucleus, consists of the centrioles. The centrioles are a pair of short cylindrical structures that lie at right angles to each other at the centrosome’s center. The centrioles play an important role during cell division Prof. Nashwa Aly Abd El-Mottaleb 14 7  Prof. Nashwa Aly Abd El-Mottaleb II- Cytoskeleton is network of protein filaments that maintain the cell shape, and produce cell movement, thus serving as the cell’s “bone and muscle.” It has three elements: microtubules, microfilaments and intermediate filaments. 1. Microtubules They are long hollow structure made up of proteins called alpha and beta tubulin 1- It maintains the cell shape. 2- Involved in the movement of intracellular transport of membranous vesicles, macromolecular complexes, and organelles. 3- They are dynamic structures important for mitotic spindle of cell division and the function of cilia. 2. Microfilaments They are called the muscle of the cell. It made up of contractile proteins in the muscle (actin and myosin). It is responsible for cell movement (e.g. movement of microvilli of intestinal mucosa. 15 Prof. Nashwa Aly Abd El-Mottaleb 3. Intermediate filaments They are developed in region of cells subjected to mechanical stress, so provide strength for the cell. III- Cytosol Occupying about 55% of the total cell volume, the cytosol is the semiliquid portion, gel-like mass of the cytoplasm that surrounds the organelles. Three activities are associated with the cytosol: (1) enzymatic regulation of intermediary metabolism. (2) ribosomal protein synthesis. (3) storage of inclusions (fat, glycogen, and secretory vesicles). Prof. Nashwa Aly Abd El-Mottaleb 16 8