lecture 1-Cell organelles 3.pdf

CELLS AND CELL ORGANELLES Dr. Sarray Sameh, pH.D  What is cell?  A cell (Latin cella meaning “small room”) is the structural and functional unit of life  Cells are of different size and shape which is related to its specific function Cells are able to make mor...

CELLS AND CELL ORGANELLES Dr. Sarray Sameh, pH.D  What is cell?  A cell (Latin cella meaning “small room”) is the structural and functional unit of life  Cells are of different size and shape which is related to its specific function Cells are able to make more cells like themselves: New cells can only come from existing cells  Types of cells Prokaryotic cell: lack a nucleus or membrane- bound structures (e.g.-bacteria) Eukaryotic cell: have nucleus and membrane-bound organelles (animal, plant, fungi…)  Organelles A membrane bound structure that carries out specific functions (Cellular machinery), Organelles do not float freely within the cytosol (liquid portion of cell) but are interconnected and joined by a framework called as cytoskeleton.  Organelles in Eukaryotic cells – Nucleus – Ribosomes – Endoplasmic reticulum (smooth and rough) – Golgi apparatus – Lysosomes – peroxisomes – Mitochondria – Cytoskeleton……  The Nucleus Large organelle Spherical or oval shaped structure  Most cells have a single nucleus, although Red Blood Cells (RBCs) have none and skeletal muscle cells have multiple nuclei. Main functions: The control center of the cell : -Control gene expression and - Involved in DNA replication during the cell cycle. 1- Structure: Nuclear envelope Nucleoplasm Chromatin Nucleolus - Nuclear envelope A double-layered membrane (outer and inner membrane) perforated with nuclear pores Nuclear pores control the flow of material going in and out of the nucleus. The outer layer is connected to the endoplasmic reticulum, communicating with the cytoplasm of the cell.  - Nucleoplasm Viscous liquid (jelly-like) within the nucleus All the materials “float” inside Contains one or more nucleoli (the site of ribosomal subunits production) Function: – Helps the nucleus keep its shape and – serves as the median for the transportation of important molecules within the nucleus - Chromatin Comprised of DNA and proteins. There are two types based on function:  Euchromatin (less compact DNA and contain genes that are frequently expressed)  Heterochromatin (more compact form and contain non transcribed genes  Ribosomes - Are the sites of protein synthesis - Are either attached to the reticulum endoplasmic or free in the cytoplasm. - No membrane present 1- Structure Consists of two subunits: – Large subunit – Small subunit 2- Functions: Ribosomes bind to an mRNA chain and use it as a template for protein synthesis. Proteins are synthesized, either on free ribosomes (nuclear, mitochondrial and peroxisomal proteins) or on ribosomes bound to endoplasmic reticulum (proteins secreted from the cell or destined to lysosomes).  Endoplasmic Reticulum (ER) Two types: Smooth and rough – Smooth (No ribosomes attached): Rough (ribosomes attached): Structure: A network of tubular (smooth) or flattened (rough), sacs interconnected. The membranes of the ER are connected with the outer membrane of the nuclear envelope. Functions: - Smooth: site of synthesis of lipids and steroid hormones; - Rough: site of protein synthesis Endoplasmic reticulum occurs in all types of eukaryotic cells, Except in RBCs and sperm cells.  Golgi Complex/Golgi Apparatus/ Golgi bodies/ Golgi. 1- Structure Consists of stacks, flattened membranous sacs. Two major regions are described within the Golgi complex: Cis Golgi: closest to ER, and Trans Golgi: near to the cell membrane 2- Functions of Golgi Apparatus: Modifies, sorts, packages and transports protein received from RER: – Cis Golgi receives vesicles containing proteins from the ER. – Vesicles fuse with the cis-Golgi membrane and the content of the vesicle enter Golgi. – as they pass through layers of the Golgi, the proteins undergo modifications to become functional; Molecular tags are added to the fully modified proteins: indicate where the substance is to be shipped!  Mitochondria Powerhouses of the cell (ATP is produced). Number may vary depending on the activity of the cell: active cells such as muscles cells, liver and kidney cells are very active cells and require ATP at high rate; have many mitochondria. 1- Structure Elongated or rod shaped Composed by: Outer mitochondrial membrane Contains large number of enzymes involved in biological oxidation and transmembrane proteins that allows molecules to pass. Inner mitochondrial membrane -Highly folded; Folds are called cristae; it contains proteins. Matrix space within the inner membrane contains circular DNA, ribosomes, fat and enzymes for different metabolic processes. Intermembrane space the space between the outer and inner membranes  Kearns-Sayre syndrome: caused by a defect in mitochondrial DNA leading to a paralysis of eye muscles and degeneration of the retina.  Lysosomes 1- Structure Is a single membrane-bound organelle Spherical shape, Acidic luminal pH (4.5 to 5), enabling the optimal activity of many enzymes, including hydrolases, proteases, lipases, glycosidases.. The lysosomal membrane has a proton pump that pump H+ into the lumen, thereby creating the acidic pH characteristic of lysosomes 2- functions of lysosomes: The lysosome is the main degradative organelle in eukaryotic cells, digesting many different types of macromolecules: - Phagocytosis: is the digestion of extracellular materials such as microorganisms taken up by endocytosis; - Autophagy (Self-eating system): is a normal physiological process; digests unwanted or damaged cell parts to maintain homeostasis.  Disorders caused by faulty or absent lysosomal enzymes lysosomal storage disorders (LSDs): are inherited disorders resulting from a lack of specific enzymes that break down certain lipids (fats) in the body cells buildup of certain fatty substances in certain organs causing an enlargement of these organs and this can affect their function. E.g – Tay-Sachs disease (TSD) : missing lysosomal enzyme required for the digestion of digest a lipid found in nerve cells. As a result, the lipid accumulates, the lysosomes swells with undigested lipid and nerve cells are damaged  Peroxisomes Similar in structure to lysosomes but has smaller size and different composition. Contain more than 50 enzymes E.g., catalase which decompose hydrogen peroxide (H2O2) to yield water and oxygen Functions: Oxidation of very long chain fatty acids (VLCFA). Hydrogen peroxide metabolism and detoxification Peroxisomes are abundant in the liver where they produce bile salts and cholesterol….  Zellweger syndrome: occurs due to lack of peroxisomes or defect in the enzymes in peroxisomes in liver, kidney and brain, resulting in improper fatty acid metabolism and defective detoxification. Individuals do not survive beyond 6 months of age.  Cytoskeleton A network of protein filaments that extend throughout the cytoplasm -supports the shape of the cell -keeps organelles in fixed locations -helps move materials within the cell Cytoskeleton fibers include: Microtubules: largest filaments; long and hollow cylinder ; composed by protein tubulin ( and  tubulin); provide organization to the cell and move materials within the cell Intermediate filaments: provide structural stability Microfilaments: thinnest elements responsible for cellular contractions, crawling…