CHAPTER 3 CELL STRUCTURE AND TAXONOMY

Introduction to Microorganisms

A. Definitions1. Cell – fundamental living unit of any organism

- Cells are classified as..Procaryotes

Do not have complex system of membranes and organelles Bacteria and Archaea

Eucaryotes More complex cells, containing true nucleus and many membrane bound organelles. Algae, Protozoa, fungi, plants, animals, and humans

2. Metabolism – refers to all the chemical reactions that occur within a cellImportance of metabolism – growth, reproduction, and irritability

3. Mutation – accidental changes in genetical material

B. EUCARYOTES

- from a Greek word meaning “true nucleus”- DNA is enclosed by a nuclear membrane- Eucaryotic cells reproduce either by mitosis or meiosis

MITOSIS- Refers to nuclear division – the equal division of one nucleus into two genetically identical

nuclei- Chromosomes are copied and allocated equally two daughter cells- The genosomes of the off spring are identical to the parent’s genome- Either haploid or diploid cells can divide by mitosis

MEIOSIS

- Two parents give rise to offspring that have unique combinations of genes inherited from both parents- Only diploid cells can undergo meiosis.- Diploid cells are changed into haploid cells-Ex: Human diploid cells – 46 chromosomes

Human haploid cells – 23 chromosomes

Eucaryotic Cell Structure

A. Cell Membrane - is like a “skin” around the cell, separating the contents of the cell from the outside world- regulates the passage of nutrients, waste products, and secretions into and out of the cell – selective permeability. (only certain substances may enter and leave the cell)

B. Nucleus - “Command center” of the cell because it unifies, controls, and integrates the functions of the entire cell.- Three components: Nucleoplasms, Chromosomes, Nuclear membrane a. Nucleoplasm – a type of protoplasm that is the gelatinous matrix or base material of the nucleus b. Chromosomes – are embedded or suspended in the nucleoplasm c. Nuclear membrane – the “skin” around the nucleus; it contains holes (nuclear pores) through which large molecules can enter the nucleus.

C. Nucleolus - where rRNA molecules are manufactured. The rRNA molecules then become part of the structure of ribosomes.

D. Cytoplasm - It is where most of the cell’s metabolic reactions occur.- where we can find insoluble storage granules and cytoplasmic organelles (ER, ribosomes, golgi complex, mitochondria, centrioles, etc.)

E. Endoplasmic Reticulum

- is a highly convulated system of membranes that are interconnected and arranged to form a transport network of tubules and flattened sacs within the cytoplasm.

F. Ribosomes - consist mainly of ribosomal RNA (rRNA) and protein- plays an important role in the synthesis (manufacture) of essential proteins.- Two subunits: 60S subunit & 40S subunit. – produced in the nucleus-The subunits are then transported to the cytoplasm where they remain separate until such time as they join together with a messenger RNA (mRNA) molecule to initiate protein synthesis. When united, the 60S and 40S form an 80S ribosome.

G. Golgi Complex - connects or communicate with ER- it completes the transformation of newly synthesized CHONs into mature functional ones and packages them into vesicles for storage within the cell or export outside the cell.- referred to as “packaging plants”.

H. Lysosomes - small vesicle that originate at the GC. They contain lysozyme that breakdown foreign material taken into the cell by phagocytosis.- Lysozyme also aid in breaking down worn out parts of the cell and may

destroy the entire cell by autolysis.I. Peroxisomes - it is where hydrogen peroxide is both generated and broken down.

- it contains the enzyme catalase which catalyzes the breakdown of H2O2 into H2O and O2.

J. Mitochondria - “power plants” ; “power houses” or “energy factories”- it is where most of the ATP molecules are formed by cellular respiration.- ATP- Adenosine Triphosphate (energy necessary for cellular function)

K. Plastids - energy- producing organelle in plant cells.- sites of photosynthesis- conversion of light energy into chemical energy.

L. Cytoskeleton - Three types of cytoskeletal fibers: microtubules, microfilaments, intermediate filaments.- serve to strengthen, support, and stiffen the cell and give the cell its shape.- Microtubules and microfilaments are essential for cell division, contraction, motility, and the movement of chromosomes within the cell.- Microtubules are composed of spherical protein subunits called tubulins.

M. Cell Wall - external structure that provides rigidity, shape, and protection.- simpler in structure in eukaryotic cells and may contain cellulose, pectin, lignin, chitin, and some mineral salts.- cell walls of algae and plants – contain a polysaccharide, cellulose.- cell walls of fungi – contain a polysaccharide, chitin.

N. Flagella & Cilia a. Flagella – responsible for motilityb. Cilia – are also organelles of locomotionc. Eukaryotic flagella and cilia are structurally more complex than bacterial flagella.

C. PROCARYOTES

- from a Greek word meaning “prenucleus”- are about 10 times smaller than Eukaryotes- possess no membranes other than the cell membrane that encloses the cytoplasm.- reproduces via Binary Fission.

BINARY FISSION- the parent cell (one cell) in half to become two daughter cells. DNA replication (duplication of

chromosomes) must occur prior to the actual splitting of the parent cell so that each daughter cell will possess the same genetic information as the parent cell.

Procaryotic Cell Membrane

A. Cell Membrane - encloses the cytoplasm- consists of proteins and phospholipids.- it controls which substances may enter or leave the cell.

B. Chromosome - consists of a single, long, supercoiled, circular DNA molecule which serves as the control center of the bacterial cell.- capable of duplicating itself, guiding cell division, and directing cellular activities.

C. Plasmids - extrachromosomal DNA- small, circular molecules of double-stranded DNA that are not part of the chromosome.- it may contain from fewer than 10 to several hundreds of genes.

D. Cytoplasm - consist of water, enzymes, dissolved oxygen, waste products, essential nutrients, CHONs, CHO, and lipids.- complex mixture of materials required by the cell for its metabolic functions.

E. Cytoplasmic Particles a. Ribosomes – sites of CHON synthesis; 7OSb. Cytoplasmic Granules – consist of starch, lipids, sulfur, iron, & other stored substances.

F. Bacterial Cell Wall - it defines the shape of bacterial cells- it provides rigidity, strength, and protection.- main constituent: Peptidoglycan- Cell walls of bacteria:“Gram-Positive bacteria” – have thick layer of peptidoglycan combined with teichoic acid and lipoteichoic acid molecules“Gram-Negative bacteria” have thinner layer of peptidoglycan, but this layer is covered with a complex layer of lipid macromolecules

- Genus Mycoplasma – do not have cell wallsG. Glycocalyx (slime layer & capsules)

- a slimy, gelatinous material produced by the cell membrane and secreted outside of the cell walla. Slime Layer- is not highly organized and is not firmly attached to the cell wall - enable certain bacteria to glide or slide along solid surfaces. - ex: Pseudomonas sp. – produce a slime layer that plays a role in the disease that it cause.B. Capsule – is highly organized and firmly attached to the cell wall. - consist of polysaccharides, which may be combined with lipids and proteins, depending on the bacterial species. - ex: H. influenza, K. pneumonia, N. meningitides, S. pneumonia - capsules serve an antiphagocytic function. - can be detected using a negative stain whereby the bacterial cell and background become stained. - immunologic test: Capsular swelling ( Quellung Reaction)

H. Flagella - are thread-like protein (flagellin) appendages that enable bacteria to move (motile)- the number and arrangement of flagella can be used for classification and identification purposes.- ex: Salmonella sp.

Flagellar Arrangement1. Monotrichous – one flagellum2. Amphitrichous – one or more flagella at each end3. Lophotrichous – a tuft of flagella at one end4. Peritrichous – flagella all over the surface

Test for motility:a. Wet mount and Hanging drop method – differentiates true motility from Brownian movementb. growth in a semi-solid medium Motile- growth of bacteria is away from the inoculation line Non- Motile – growth of bacteria is confined along the inoculation line.

I. Pili (Fimbriae)

E. coli fimbriae

- are hair-like structures, most often observed on Gram (-) bacteria.- composed of protein called pilin- much thinner than flagella, have a rigid structure and are not associated with motility.- two types of Pili:a. Ordinary Pili – enables bacteria to adhere or attach to host cells (tissues within the human body) – can cause urethritis and cystitisb. Sex pili – enables transfer of genetic material from one bacterial cell to another – (a process known Conjugation).

J. Spores (Endospores)

Bacillus thuringiensis with terminal endospore.

- Sporulation- process of spore formation- resistant to heat, cold, drying and most chemicals- when dried spore lands on a moist, nutrient-rich surface, it germinates, and a new vegetative bacterial cell emerges.- ex: Bacillus sp., Clostridium sp.- location of spores within the cell:a. Central – spore is produced at the center of cellb. Terminal – spore is produced at the very end of cellc. Subterminal spore is produced elsewhere in the cell

D. Comparison Between Eucaryotic and Procaryotic Cells

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

Flagella or cilia 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

Cell Wall When present, of simple chemical constitution; usually contains cellulose

Absent Of complex chemical constitution, containing peptidoglycan

Photosynthesis Present Absent Present in cyanobacteria and some other bacteria

E. Prokaryotic Cell Reproduction

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.)

F. 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.

G. Taxonomy

o Taxonomy is the science of classification of living organism.

o Consists of 3 but interrelated areas:

o Classification- arrangement of organisms into taxonomic groups (taxa).

o Nomenclature- assignment of names

o Identification- process of determining whether an isolate belongs to a taxa.

H. Microbial Classification

o Carolus Linnaeus- established the binomial nomenclature

o genus + specific epithet

o Genus- capitalize the first letter

o Specific epithet- not capitalized

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

I. 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

J. Examples of Bacteria Named after the Diseases That They Cause

BACTERIA DISEASE

Bacillus anthracis Anthrax

Chlamydophila pneumonia Pneumonia

Chlamydophila psittaci Psittacosis (“parrot fever”)

Chlamydia trachomatis Trachoma

Clostridium tetani Tetanus

Clostridium botulinum Botulism

Corynebacterium diphtheriae Diphtheria

Francisella tularensis Tularemia (“rabbit fever”)

Klebsiella pneumoniae Pneumonia

Mycobacterium leprae Leprosy

Mycobacterium tuberculosis Tuberculosis

Mycoplasma pneumoniae Pneumonia

Neisseria gonorrheae Gonorrhea

Neisseria meningitides Meningitis

Streptococcus pneumoniae Pneumonia

Vibrio cholera Cholera

K. The 5 Kingdom Classifications

Founded in 1969 by Robert H. Whittaker.

Bacteria and archaeans are in the Kingdom Prokaryotes (or Monera)

Algae and Protozoa are in the Kingdom Protista (organisms in this kingdom are reffered to as protists)

Fungi are in the Kingdom Fungi

Plants are in the Kingdom Plantae

Animals are in the Kingdom Animalia

Viruses are not included in the Five-Kingdom System of Classification because they are acellular

The Five-Kingdom Classification Scheme

Modern Classification

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

Reference: Burton, G. (2007). Burton's Microbiology for the Health Sciences (8th ed.). Baltimore: Lippincot Williams & Wilkins.