CELL STRUCTURE & FUNCTIONS

 Introduction  Eucaryotic cell structure  Procaryotic cell structure  Differences between Procaryotic & Eukaryotic cells. Eukaryotic cells.  Reproduction of organisms & their cells. cells.  Gram stain Outline

Introduction - Cell is defined as the fundamental living unit of any organism. - Cell is important to produce energy for metabolism (all chemical reactions within a cell) - Cell can mutate (change genetically) as a result of accidental changes in its genetic material (DNA). - Some microrganisms are procaryotic, some are eucaryotic, & some are not cells at all (Viruses) - Viruses are composed of only a few genes protected by a protien coat, & may contain few enzymes. - Cytology: the study of the structure and functions of cells.

Eucaryotic cell structure  Eucaryotic cells: have a true nucleus, & the DNA is enclosed by a nuclear membrane.  They are 10 times larger than Procaryotic cells.

Cell membrane  It’s composed of large molecules of protiens & phospholipids (certain types of fats).  The cell membrane is seperating the contents of the cell from the outside world.  It has the property of selective permiability: only certain substances may enter & leave the cell

Cell Membrane  Phospholipid bi-layer that separates the cell from its environment.  Selectively permeable to allow substances to pass into and out of the cell.

Nucleus  Double membrane-control, & integrates the functions of the entire cell.  Consider the command center of the cell.  Separates the genetic material from the rest of the cell.

Parts of the nucleus:  Chromatin - genetic material of cell in its non-dividing state.  Nucleoplasm is the gelatenous matrix of the nucleus, like cytoplasm.  Nucleolus - dark-staining structure in the nucleus that plays a role in making ribosomes.  Nuclear envelope - double membrane structure that separates nucleus from cytoplasm.

Cytoplasm  Is a gel-like matrix of water, enzymes, nutrients, wastes, and gases and contains cell structures (organelles).  Fluid around the organelles called cytosol.  Most of the cells metabolic reactions occur in the cytoplasm.

The Endoplasmic Reticulum  The endoplasmic reticulum (ER)  Accounts for more than half the total membranes in many eukaryotic cells  The ER membrane: is continuous with the nuclear envelope  There are two distinct regions of ER  Smooth ER, which lacks ribosomes  Rough ER, which contains ribosomes

Rough Endoplasmic Reticulum  Network of continuous sacs, studded with ribosomes.  Manufactures, pro-cesses, and transports proteins for export from cell (vesicles)  Continuous with nuclear envelope.

Smooth Endoplasmic Reticulum  Similar in appearance to rough ER, but without the ribosomes.  Involved in the production of lipids, carbohydrate metabolism, and detoxification of drugs and poisons.  Stores calcium.

Ribosomes  Are the sites of protein synthesis.  Found attached to the Rough endoplasmic reticulum or free in the cytoplasm.  60% RNA and 40% protein.  Protein released from the ER are not mature, need further processing in Golgi complex before they are able to perform their function within or outside the cell.

Golgi Apparatus  Modifies proteins and lipids made by the ER and prepares them for export from the cell (exocytosis).  Encloses digestive enyzymes into membranes to form lysosomes.  Consists of flattened membranous sacs called cisternae

Lysosome  Single membrane bound structure.  Contains digestive enzymes that break down cellular waste and debris and nutrients for use by the cell.  Originate at the Golgi complex.  Are the

Lysosome  They contain lysozymes & other digestive enzymes that breakdown foreign material taken into the cell by phagocytosis (e.g Amebas, and certain types of WBCs “phagocyte”).  Also these enzymes may breakdown parts of the cell or destroy the entire cell by process called autolysis if the cell damaged or deteriorated.  They contain up to 40 enzymes for digestion

Peroxisomes  They are similar to lysosome but smaller.  Peroxisomes contain the enzyme catalase, which breakdown of hydrogen peroxide into water and oxygen.  Found mainly in liver and kidney cells  Main function is detoxification of toxic materials.

Mitochondrion  Membrane bound organelles that are the site of cellular respiration (ATP production)  Mitochondria are enclosed by two membranes  A smooth outer membrane  An inner membrane folded into cristae

Chloroplast  Site of photosynthesis  Membrane bound structure.  Contains chlorophyll  Found only in plants

Cytoskeleton  The cytoskeleton  Is a network of fibers extending throughout the cytoplasm Microtubule 0.25 µm Microfilaments

Roles of the Cytoskeleton: Support, Motility, and Regulation  The cytoskeleton  Gives mechanical support to the cell  Is involved in cell motility, which utilizes motor proteins

Components of cytoskeleton: 1) Microfilaments  Solid rods of globular proteins.  Important component of cytoskeleton which offers support to cell structure.

Components of cytoskeleton: 2) Microtubules  Microtubules  Shape the cell  Guide movement of organelles  Help separate the chromosome copies in dividing cells

Components of cytoskeleton: 2) Microtubules Centrosomes and Centrioles  The centrosome  Is considered to be a “microtubule-organizing center”  Contains a pair of centrioles

Components of cytoskeleton: 2) Microtubules Centrioles  Found only in animal cells.  Self-replicating  Made of bundles of microtubules.  Help in organizing cell division.

Cell Wall  Protects and gives rigidity to plant cells  Formed from fibrils of cellulose molecules in a “matrix” of polysaccharides and glycoproteins.

Cilia and Flagella  External appendages from the cell membrane that aid in locomotion of the cell.  Cilia also help to move substance past the membrane.

Animal Cell vs. Plant Cell

Prokaryotic vs. Eukaryotic

Procaryotic cell strucure  Are about 10 times smaller than eucaryotic cells.  Reproduction of these cells by binary fission.  Binary fission: the simple division of one cell into two cells, following DNA replication, & the formation of a separating membrane & cell wall.

Procaryotic cell strucure  Cytoplasm is surrounded by a cell membrane, a cell wall (usually), & sometimes a capsule or slime layer.