Diploma in Microbiology MIC102 CHAPTER 1 The Cell Membrane & The Cell Wall Lecturer: Pn Aslizah Bt Mohd Aris /

Chapter outline ◦ The cell membrane  The cell membrane regulates the flow of materials into and out of a cell.  It is selectively permeable, meaning that only certain materials can pass through the membrane.  A cell membrane consists of a bilayer of phospholipids with protein molecules jutting through one or both layers.

The cell wall ◦ Prokaryotes, fungi and some protists also have cell walls ◦ Prokaryotic cell wall  The prokaryotic cell wall consists of long polymers called peptidoglycans.  Some prokaryotic cell walls have a second, outer layer composed of lipoproteins and lipopolysaccharides. ◦ Eukaryotic cell wall  The eukaryotic cell wall has three parts: the primary cell wall, the middle lamella, and the secondary cell wall.  The primary cell wall, composed mainly of cellulose, is the innermost layer of the wall.  The middle lamella contains polysaccharides called pectins.  The secondary cell wall is the outermost layer. It consists of cellulose and a strengthening material called lignin.

The cell membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell The general structure of a biological membrane is a double layer of phospholipids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cell Membrane

The fluid-mosaic model of the cell membrane

TEM of a plasma membrane (a) (b) Structure of the plasma membrane Outside of cell Inside of cell 0.1 µm Hydrophilic region Hydrophobic region Hydrophilic region PhospholipidProteins Carbohydrate side chain Fig. The plasma membrane

Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include: ◦ Cell walls of plants ◦ The extracellular matrix (ECM) of animal cells ◦ Intercellular junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Differences between animal cell and plant cell?

Cell Walls of Plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plant cell walls may have multiple layers: ◦ Primary cell wall: relatively thin and flexible ◦ Middle lamella: thin layer between primary walls of adjacent cells ◦ Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall Plasmodesmata are channels between adjacent plant cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plant cell walls Secondary cell wall Primary cell wall Middle lamella Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata 1 µm

The Extracellular Matrix (ECM) of Animal Cells Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin ECM proteins bind to receptor proteins in the plasma membrane called integrins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Extracellular matrix (ECM) of an animal cell EXTRACELLULAR FLUID Collagen Fibronectin Plasma membrane Micro- filaments CYTOPLASM Integrins Proteoglycan complex Polysaccharide molecule Carbo- hydrates Core protein Proteoglycan molecule Proteoglycan complex

 Support  Adhesion  Movement  Regulation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Functions of the ECM:

Intercellular Junctions Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact Intercellular junctions facilitate this contact There are several types of intercellular junctions ◦ Plasmodesmata ◦ Tight junctions ◦ Desmosomes ◦ Gap junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plasmodesmata in Plant Cells Plasmodesmata are channels that perforate plant cell walls Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plasmodesmata between plant cells Interior of cell 0.5 µm Plasmodesmata Plasma membranes Cell walls

Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Intercellular junctions in animal tissues Tight junction 0.5 µm 1 µm Desmosome Gap junction Extracellular matrix 0.1 µm Plasma membranes of adjacent cells Space between cells Gap junctions Desmosome Intermediate filaments Tight junction Tight junctions prevent fluid from moving across a layer of cells

Terms to know active transport - Transport in which a cell must expend energy. Active transport occurs against a concentration gradient. basal body - A structure found at the connection of cilia and flagella with the cell membrane. It is composed of microtubules in a circular configuration of nine triplets. cell membrane - The structure which surrounds the cell and regulates the movement of materials into and out of the cell. It is composed mostly of phospholipids. cell wall - A structure found in most prokaryotes and some eukaryotes which gives the cell greater structure. In prokaryotes, it is composed of peptidoglycans, and in eukaryotes, it consists or polysaccharides, pectins, and lignin. cilia - Tiny hairs along the outside of the cell membrane which are used to move the cell and capture food particles. chloroplast - The organelle in which photosynthesis takes place. It contains chlorophyll. chromoplast - An organelle in which photosynthesis take place. It contains pigments other than chlorophyll, resulting in a color other than green. contractile vacuole - An organelle which pumps excess water of a cell to prevent it from bursting. endoplasmic reticulum - A network of tunnels which extend away from the nucleus, used for the transport of proteins. facilitated diffusion - A method of transport across the cell membrane by which carrier proteins bond to a molecule on one side of the membrane, move through the membrane, and then release it on the other side. flagella - Large hairs which can whip back and forth to propel a cell. Golgi body - Stacks of membranous pouches which act as a transport station, packaging proteins from the endoplasmic reticulum and placing them into tiny vesicles.

Terms to know continued…. intermediate filament - A part of the cytoskeleton with a strong, ropelike structure which gives the cell strength and helps it to maintain its shape. leucoplast - Colorless plastids in autotrophs which store starch, proteins, and lipids. lysosome - A sac similar to a vacuole which contains powerful digestive enzymes used to break down large food particles. microfilament - A part of the cytoskeleton which consists of actin and aids in cell movement. microtrabeculae - Tiny fibers which interconnect all of the structures within the cell and help to give the cell shape. microtubule - Fibers which extend from the center of the cell to the cell membrane. They are involved in cell reproduction and are part of the composition of cilia and flagella. mitochondria - The organelle in which cellular respiration occurs. nucleolus - A structure within the nucleus at which ribosomes are created. nucleus - The organelle in eukaryotes which contains the cells DNA and thus indirectly controls protein production and the rest of the cell. passive transport - A form of transport which allows highly polar molecules to move through the cell membrane without the expenditure of energy. This may occur either through protein channels or facilitated diffusion. peroxisome - An organelle similar to a vacuole which contains oxidizing enzymes which can help neutralize toxic substances. pseudopod - Extensions of the cytoplasm toward which the rest of the cytoplasm tends to flow. Pseudopodia can be used for movement and the capture of prey. ribosome - Structures found mainly in the endoplasmic reticulum whose function is to synthesize protein based upon the code of a messenger RNA molecule. vacuole - Membrane-bound sacs within a cell used to hold food particles, water, etc. vesicle - A tiny vacuole, often used to carry protein molecules packaged at the Golgi bodies.

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