Cell Structure And Taxonomy

Microbiology and Parasitolgy - Chapter II

CELL STRUCTURE AND TAXONOMY

What is a cell? The fundamental living unit of any organism.  Metabolism- refers to all of the chemical reactions that occur within a cell.  What are the importance of metabolism?  Growth, reproduction and irritability.  Mutation-accidental changes in the genetical material. 

Cells are classified as… 

Prokaryotes Do not have complex system of membranes and organelles.  Bacteria and Archaea 

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Eukaryotes More complex cells, containing true nucleus and many membrane bound organelles.  Algae, protozoa, fungi, plants, animals and humans. 

Acellular and Cellular Microbes

Relative Sizes of Microorganisms

Eukaryotic Cell

eu=true; karyo=nucleus  Have true nucleus, DNA is enclosed by a nuclear membrane.  10X larger than most prokaryotic cells. 

Eukaryotic Animal Cell

Eukaryotic Cell Structures      

Cell Membrane Nucleus Cytoplasm Endoplasmic Reticulum Ribosomes Golgi Complex

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Lysosomes and Peroxisomes Mitochondria Plastids Cytoskeleton Cell Wall Flagella and Cilia

Cell Membrane 

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Enclosed and keep the cell intact. Composed of large molecules of proteins and phospholipids. Like a “skin” Regulates passage of substances in and out. Selective permeability

Nucleus 

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Controls the functions of the entire cell. “command center” 4 components:    

Nucleoplasm Nuclear membrane Chromosomes Nucleolus

back

Cytoplasm 

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Semifluid, gelatinous nutrient matrix Contains the “organelles” Organelles has highly specific functions which maintains the cells and allow it to properly perform its actvities.

Endoplasmic Reticulum 

Highly convoluted system of membranes that are interconnected to form a transport network tubules and flattened sacs within the cytoplasm.  

Rough ER Smooth ER

Ribosomes 

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18 to 22 nm in diameter consists of rRNA play important part in protein synthesis free or attached in the RER

Golgi Complex 

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Stack of flattened, membranous sacs Packages newly synthesized proteins into small, membraneenclosed vesicles for storage within the cell or export outside the cell (exocytosis). “packaging plants”

Lysosomes and Peroxisomes 

Lysosomes 

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contain lysozyme and other digestive enzymes phagocytosis and autolysis

Peroxisomes 

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where hydrogen peroxide is both generated and broken down found in mammalian liver cells

Mitochondria 

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Where most of the ATP (energy carrying molecules) are formed by cellular respiration. Energy is released from glucose molecules and other nutrients to drive other cellular functions.

Plastids 

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Contains various photosynthetic pigments. Chloroplasts- one type of plastid, contain a green, photosynthetic pigment called chlorophyll. Found in plant cells and algae.

Cytoskeleton 

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System of fibers present throughout the cytoplasm. Strengthen, support and stiffen the cell, giving its shape. 

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Microtubules- slender, hallow tubules (tubulins). Microfilaments- Slender, thread-like contractile structures which facilitate cell contraction.

Cell Wall 

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External structures that provide rigidity, shape, and protection. May contain cellulose, pectin, lignin, chitin and some mineral salts. 

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Cellulosepolysaccharide, present in algae and plants Chitin- present in fungi and exoskeleton of arthropods.

Presence or absence of cell wall in various types of cells.

Flagella and Cilia Flagella- relatively long, thin structure, the organelle of locomotion.  Cilia- tend to be more shorter (hairlike), thinner and more numerous 

Prokaryotic Cells 10X smaller than eukaryotic cells  Very simple cells than eukaryotic cells  Do not contain membrane-bound organelles  Reproduce by binary fission  Includes bacteria and archaeans 

Typical Prokaryotic Cell

Prokaryotic Cell Structure

Cell Membrane  Chromosome  Plasmid  Cytoplasm  Cytoplasmic particles 

Bacterial Cell Wall  Glycocalyx  Flagella  Pili (Fimbriae)  Endospores 

Cell Membrane  

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Enclose the cytoplasm Similar in structure and function to the eukaryotic cell membrane. Consists of proteins and phospholipids. Selectively permeable

Chromosome 

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Consists of a single, long, supercoiled, circular DNA molecule. Serves as the control center of the bacterial cell. Capable of replicating itself, guiding cell division, and directing cellular activities.

A bacterial cell may contain between 850 and 6,500 genes

Plasmid 

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Small, circular molecules of doublestranded DNA that are not part of the chromosome. May contain 10 to hundred genes May or may not be present in bacterial cell.

Cytoplasm 

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Semi-fluid, consists of water, enzymes, dissolved oxygen, waste products, essential nutrients, proteins and carbohydrates, and lipids. No organelles.

Cytoplasmic Particles 

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Many tiny particle in the bacterial cytoplasm. Most of these are clusters of ribosomespolyribosomes or polysomes. Site of protein synthesis.

Bacterial Cell Wall 

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Rigid exterior cell wall that defines the shape of bacteria. Consist of a complex macromolecule known as peptidoglycan. 

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Gram positive bacteria- thick layer Gram negative bacteria- thinner layer

Gram Stain 

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The most widely used procedure for staining bacteria. Developed over a century ago by Dr. Hans Christian Gram. Bacteria are grouped as Gram-negative and Gram-positive

Glycocalyx 

Slimy, gelatinous material produced by the cell membrane and secreted outside the cell wall. 

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Slime layer- not highly organized and is not firmly attached to the cell wall. Capsule- highly organized and firmly attached to the cell wall.

Flagella 

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Thread-like, protein appendages that enable the bacteria to move. Flagellated bacteria are said to be motile.    

monotrichous (A) lophotrichous (B) amphitrichous (C) peritrichous (D)

Pseudomonas aeruginosa

Spirillum

amphitrichous lophotrichous

Pili (Fimbriae) 

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Hair-like structures, most often observed on Gram-negative bacteria. Kinds: 

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Pili that enables transfer of genetic material from one bacterial cell to another (conjugation). Pili that enable bacteria to anchor themselves to surfaces.

E. coli fimbriae

Endospores 

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Formed by a few bacteria when the environment is unfavorable for their survival. Sporulation- process of forming endospore. Resistant to heat, cold, drying and most chemicals.

Bacillus thuringiensis with terminal endospore.

Sporulation

The Discovery of Endospores 

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John Tyndall concluded that certain bacteria can be killed by simple boiling, while others cannot be killed. Tyndallization Ferdinand Cohn called the small bodies inside the bacteria “spores”. He concluded that spores are heat resistant. John Tyndall

EUKARYOTIC CELLS PLANT TYPE

ANIMAL TYPE

PROKARYOTIC CELLS

Biologic distribution

All plants, fungi, and algae

All animals and protozoa

All bacteria

Nuclear membrane

Present

Present

Absent

Membranous structures other than cell membrane

Present

Present

Generally absent except for mesosomes and photosynthetic membranes

Microtubules

Present

Present

Absent

Cytoplasmic ribosomes (density)

80S

80S

70S

Chromosomes

Composed of DNA and proteins

Composed of DNA and proteins

Composed of DNA alone

When present, have a complex structure

When present, have a complex structure

When present, flagella have a simple twisted protein structure; prokaryotic cells do not have cilia

Absent

Cell Wall

When present, of simple chemical constitution; usually contains cellulose

Of complex chemical constitution, containing peptidoglycan

Photosynthesis

Present

Absent

Present in cyanobacteria and some other bacteria

Flagella or cilia

Prokaryotic Cell Reproduction 

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Prokaryotic cells reproduce by binary fission. One cell (parent cell) splits into half to become two daughter cells. Before a prokaryotic cell can divide into half, its chromosomes must be duplicated. Generation time- varies from one bacterial species to another (ex. E. coli, 20 mins.)

Eukaryotic Cell Reproduction Eukaryotic cell reproduce in a process called mitosis.  Mitosis the type of division that gives rise to daughter cells for the purpose of tissue growth, regeneration or asexual (vegetative) reproduction. 

Let’s Review….

INTERPHASE MITOSIS

PROPHASE

METAPHASE

TELOPHASE

ANAPHASE

Taxonomy 

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Taxonomy is the science of classification of living organism. Consists of 3 but interrelated areas:  Classification- arrangement of organisms into taxonomic groups (taxa).  Nomenclature- assignment of names  Identification- process of determining whether an isolate belongs to a taxa.

Microbial Classification 

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Carolus Linnaeusestablished the binomial nomenclature genus + specific epithet 

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Genus- capitalize the first letter Specific epithet- not capitalized

“sp.”- single specie, “spp.”- more than one specie

Taxonomic Hierarchies Species- group of related organism/strains  Genus- collection of related species  Family- collection of similar genera  Order- collection of similar families  Class- collection of similar orders  Phylum/Division- collection of similar classes  Kingdom- collection of similar phyla/divisions  Domain- collection of similar kingdoms 

The 5-Kingdom Classification  Founded

in 1969 by Robert H. Whittaker.  Prokaryotes were placed in Kingdom Monera.  Eukaryotes were placed in the other 4 kingdoms (Animalia, Plantae, Protista, & Fungi).

The Five-Kingdom Classification Scheme

Modern Classification 

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In 1978, Carl R. Woese proposed elevating the three cell types to a level above kingdom, called DOMAIN Cells are classified into three types:  ARCHAEBACTERIA  EUBACTERIA  EUKARYA

The Three-Domain Classification Scheme

That’s All Folks! Prepare for a long QUIZ next meeting!!