Diploma in Microbiology Diploma in Microbiology

MIC102MIC102 CHAPTER 1 CHAPTER 1

The Cell MembraneThe Cell Membrane&&

The Cell WallThe Cell WallLecturer: Pn Aslizah Bt Mohd Aris06-4832168 / 016-7377621

Chapter outlineChapter 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 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 plasmamembrane

(a)

(b) Structure of the plasma membrane

Outside of cell

Inside of cell 0.1 µm

Hydrophilicregion

Hydrophobicregion

Hydrophilicregion Phospholipid Proteins

Carbohydrate side chain

Fig. The plasma membrane

Extracellular components and connections Extracellular components and connections between cells help coordinate cellular between cells help coordinate cellular

activitiesactivities

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 Differences between animal cell and plant cell?animal cell and plant cell?

Cell Walls of PlantsCell Walls of PlantsThe 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

Pla

nt ce

ll walls

Secondary cell wallPrimary cell wallMiddle lamell

a

Central vacuoleCytosol

Plasma membrane

Plant cell walls

Plasmodesmata

1 µm

The Extracellular Matrix (ECM) of Animal The Extracellular Matrix (ECM) of Animal CellsCells

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

Plasmamembrane

Micro-filaments

CYTOPLASM

Integrins

Proteoglycancomplex

Polysaccharidemolecule

Carbo-hydrates

Coreprotein

Proteoglycanmolecule

Proteoglycan complex

Support

Adhesion

Movement

Regulation

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Functions of the ECM:

Intercellular JunctionsIntercellular 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 CellsPlasmodesmata 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

Interior of cell

0.5 µm

Plasmodesmata Plasma membranes

Cell walls

Tight Junctions, Desmosomes, and Gap Tight Junctions, Desmosomes, and Gap Junctions in Animal CellsJunctions 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 tissuesTight junction

0.5 µm

1 µmDesmosome

Gap junction

Extracellularmatrix

0.1 µm

Plasma membranesof adjacent cells

Spacebetween

cells

Gapjunctions

Desmosome

Intermediatefilaments

Tight junction

Tight junctions preventfluid from moving

across a layer of cells

Terms to knowTerms 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….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.

STOP !!! Don’t STOP !!! Don’t overworkedoverworked