exam 1 final Flashcards
what are the size ranges of prokaryotes
Size: 0.20 to 2.0 um in diameter 2-8 um in length
1735 – Carolus (Carl) Linnaeus
established the system of nomenclature (naming) for organisms which assigns each organism 2 names…
A. Genus is the 1st name and is always Capitalized and underlined or italicized.
B. Specific epithet or species is the 2nd name and is not capitalized, but is underlined or italicized.
Example:
1. Staphylococcus aureus or
- Staphylococcus aureus*
2. Escherichia coli or Escherichia coli
1867 - Joseph Lister
English surgeon
initiates aseptic surgical techniques.
He began soaking surgical dressings in a mild solution of carbolic acid (phenol) which kills bacteria.
This reduced the incidence of infections and deaths in surgical patients.
Founder of aseptic surgery
1876 -83 Robert Koch
proved the germ theory of disease
discovered a rod-shaped bacteria now known as Bacillus anthracis in the blood of cattle that had died of anthrax.
He cultured the bacteria and injected samples of the culture into healthy animals which became sick and died.
Koch isolated the bacteria in the blood and found it to be the same as the original bacteria isolated.
Experimental procedure used to relate specific microbe to a specific disease is known as Koch’s postulate
1881 - developed pure culture and staining techniques.
• 1882 - discovered Mycobacterium tuberculosis, the causative agent of
tuberculosis.
• 1883 - discovered Vibrio cholerae, the
causative agent of cholera.
1880 - Louis Pastuer
developed immunization techniques based on Edward
Jenner’s work with smallpox (vaccination)
• Avirulent form of bacterium causing fowl cholera can induce immunity against subsequent infections by virulent counterpart.
Vaccine: cultures of avirulent microorganism used for preventative inoculations
also discovered Streptococcus pneumoniae (1881), the causative agent of pneumococcal pneumonia.
1885 - Theodor Escherich
of Germany discovered Escherichia coli, the
causative agent of urinary tract infections and traveler’s diarrhea.
1887 - Richard Julius Petri
of Germany introduced a covered dish for growing microorganisms on a solid medium. (petri dish)
1890 - Paul Ehrlich
of Germany proposed a theory of immunity in which antibodies are responsible for immunity.
- Discovery of chemotherapy—treatment of disease by use of chemical substances (i.e. synthetic drugs & antibodies)
- Magic bullet — substance that could target and destroy the pathogen without harming the host
- Salvarsan (arsenic derivative; 1910)— chemotherapeutic agent against syphillis
1892 - Dmitri Iwanowski
of Russia discovered a filterable organism (virus) caused tobacco mosaic disease.
- What determines whether a person will contract a disease?
a. the disease producing properties of the microorganism
b. the resistance of the body.
1928 - Alexander Fleming
Scottish physician and bacteriologist
discovered the antibiotic, penicillin, by accident
Thus he discovered a mold (fungus), Penicillium chrysogenum which could inhibit the growth
of bacteria.
Adenosine Triphosphate = ATP
is the principal energy-carrying molecule (potential form of energy).
- is composed of adenine, ribose, and 3 phosphate groups
- energy is released when a phosphate is removed ATP———–>ADP + Pi + Energy
Algae:
DIVERSITY OF MICROORGANISMS - are photosynthetic eukaryotes. - wide varieties of shapes. - are members of the kingdom Protista. - reproduction is sexual or asexual.
Beneficial Activities of Microorganisms
1. Microorganisms degrade dead plants and animals and recycle chemical elements such as nitrogen, carbon, oxygen, sulfur, and phosphorus.
Example - bacteria and fungi return carbon dioxide to the atmosphere when decomposing organic matter…carbon cycle
Example - Nitrogen fixation - converting nitrogen gas into ammonia (i.e. Rhizobium species)
2. Microorganisms are used to decompose
organic matter in sewage…recycle water and prevent pollution (bioremediation) of rivers and oceans
Bioremediation: use of microorganisms to remove environmental pollutant
(Zoogloea ramigera).
3. Microorganisms (i.e. Bacillus thuringiensis) cause disease in insects and thus can be used as a biological control in insect pests (instead of pesticides which harm the environment).
-
Microorganisms can be used to produce food such as:
a. soy sauce (Aspergillus oryzae (fungi) b. yogurt (Streptococcus thermophilus)
for acid production,
Lactobacillus bulgaricus for flavor and aroma).
- Using biotechnology and recombinant DNA technology, bacteria, can be used to produce human proteins:
a. insulin
b. factor VIII
c. tissue plasminogen activator d. growth hormone
e. use in gene therapy
Carbohydrates
- Are sugars and starches (chain of glucose)
- Basic building block = Monosaccharide (simple sugars) - General composition: (CH2O)n
- 3 major groups:
- monosaccharides: contains 3-7 C atoms;
i. e. glucose, fructose, galatose, deoxyribose, ribose - disaccharides: formed by the bonding of 2 monosaccharides in a dehydration synthesis reaction
i. e. glucose + fructosesucrose glucose + galactoselactose
glucose + glucosemaltose
conjugated proteins
modified protines
ex
- glycoproteins contain sugars
- nucleoproteins contain nucleic acids 3. metalloproteins contain metal atoms 4. lipoproteins contain lipids
Edward Jenner
1798
developed the first vaccine for smallpox
milkmaid couldn’t get smallpox because she had already been sick with cowpox, a much milder disease
Jenner decided to test this story:
collected scrapings from cowpox blisters and made inoculations with this material by scratching the arm of a healthy volunteer with the cowpox contaminated needle.
The person became mildly sick but recovered and never
contracted either cowpox or smallpox
Francesco Redi
Opposition to spontaneous generation: 1668
expirament:
3 jars with decaying meat and sealed them tightly, no maggots
• 3 jars with decaying meat and left them open, maggots • There were doubter still…magical substance in fresh
air was needed for spontaneous generation to occur…
Functions of carbohydrates:
a. provide a source to produce energy, mainly ATP, for the cell.
b. function as food reserves
c. Deoxyribose sugar is backbone of DNA (deoxyribose nucleic acid).
d. are components of cell walls of bacterial cells
Functions of proteins
- Structural proteins
- microfilaments for movement of cells
- cell membranes or cell walls
- carrier proteinstransport molecules into and out of cells - Enzymes: catalyze chemical reactions 3. signaling molecules
- Toxins are produced by certain bacteria;
Bacteriocins: proteins produced by some bacteria that kill other bacteria.
- Hormones for regulatory function (i.e. insulin) 6. Antibodies for immune function
Fungi
- are eukaryotes. - are members of the kingdom Fungi. - are unicellular (yeasts) or multicellular (mushrooms). - True fungi have cell walls composed of chitin. - Yeasts are oval-shaped microorganisms larger than bacteria. - Molds are typical fungi. - reproduce sexually (meiosis) or asexually (mitosis).
give at least 3 examples of microorganisms and the food product they are make.
a. soy sauce (Aspergillus oryzae (fungi) b. yogurt (Streptococcus thermophilus)
for acid production,
Lactobacillus bulgaricus for flavor and aroma).
c. cheese (Propionibacterium species produce holes in Swiss cheese by producing carbon
dioxide. )
d. bread (San Francisco sourdough bread requires
Saccharomyces exiquus and Lactobacillus
sanfrancisco) .
e. alcoholic beverages (wine requires the yeast
Saccharomyces cervisiae ).
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hydrophilic amino acids
- basic
- lysine (lys)
- argininine (arg)
- Histidine (his)
- acidic
- asparate (asp)
- glutamate (glu)
- polar amino acids
- serine (ser)
- threonine (thr)
- asparagine (asn)
- Glutamine(gln)
- thyrosine (tyr)
hydrophobic amino acids
- Alanine (ala)
- valine (val)
- Isolucine (ile)
- Lucine (leu)
- Methinonine (met)
- Phenylalanine (phe)
- Tryptophan (Trp)
John Needham
Proponent of spontaneous generation 1745
He heated nutrient fluids (chicken broth and corn broth), cooled it, and then poured it into covered flasks, the solutions were teeming with microorganisms.
Needham claimed that the microbes developed spontaneously from the fluids.
Lazzaro Spallanzani
1765
disproved Needham conclusion
- suggested that microorganisms from the air probably entered the solutions from the air after they were boiled.
- showed that nutrient fluids heated after being sealed did not develop microbial growth.
Lipids
Are “fat”
- Lipids
- Are composed of C, H, O
- Are nonpolar molecules; can’t dissolve in water
- F(x)s: energy source
- constituent of plasma membranes and cell walls
Types of lipids:
Triglycerides = simple lipids or fats
Complex lipids
- Steroids
Louis Pasteur
1861 demonstrated that microorganisms are present in the air and that they can contaminate sterile solutions, but air itself does not create microbial life.
During a job on understanding why wine and beer sour, discovered that microorganisms called yeasts convert sugars to alcohol in the absence of air.
This is called FERMENTATION (1857).
Discovered pasteurization (1864)…process of
heating to kill bacteria to reduce/prevent spoilage
This was the first link that microorganisms can cause changes in organic materials.
that microorganisms might cause disease
introduced germ theory of disease
nucleic acids
Nucleotides are the basic building blocks of nucleic acids (DNA and RNA molecules—genetic material)
• Are composed of
– Phosphate group
– Pentose: 5-carbon sugar molecule
-deoxyribose vs ribose – Nitrogenous Base
Deoxyriboucleic Ribonucleic Acid Acid
Peptide bond
joins the amino end of one aa to the carboxyl end of another aa
phospholipids
(glycerol, 2 fatty acid, phosphate group)
- has polar and non-polar ends
- is major constituent of cell membranes—phospholipid bilayer
Prions
(Proteinaceous infectious particles) infectious proteins. Unlike bacteria or viruses, prions do not require any DNA or RNA infectious. A prion is a misfolded protein has lost its normal conformation and function while acquiring the ability to convert other molecules of the same protein from the conformation into the abnormal prion form. This form of self propagation explains the infectious nature of prions. In all of the prion proteins
studied, the transformation between the normal and prion forms occurs through a dramatic change in the protein’s three-dimensional structure. Prions cause diseases such as Creutzfeldt-Jakob disease (CJD; Kuru) in humans, in sheep (scrapie), and bovine spongiform encephalopathy (BSE or mad-cow disease).
prokaryotes
(“prenucleus”)Its genetic material is not enclosed in a nuclear membrane
Protein chain (polypeptide)
is formed by amino acid monomers joined together by covalent peptide bonds
Protein: Structure
Primary (1o) structure:
– The linear sequence of amino acid
– Also known as the protein sequence
- Secondary (2o)structure:
– It is the regularly repeating conformation of the
peptide backbone
– Helix; Strands sheets; turns
– A polypeptide usually has different secondary structures at different regions
– Is dependent on the amino acid sequence of the different regions.
– Structure is stabilized by H-bonds
- Tertiary (3o) structure:
– Is the 3D arrangement of all the polypeptide’s amino acid residues
– Is formed by packing various combinations of 2o structures
– Structure is stabilized by a variety of non- covalent bonds between aa side chains (i.e. hydrophobic)
- Quaternary structure:
– The overall structure and organization of more than one polypeptide chain
– Each polypeptide chain in this protein is referred to as a subunit.
Amino acids (aa)
are the monomeric building blocks of proteins
There are 20 different aa.
All organisms on earth have the same 20 aa.
Each protein being synthesized are made from the different arrangements of the aa.
Each aa monomer has 4 different groups attached to the central carbon atom (C)
The nature of an aa is based on the composition of its side chain.
- 20 different aa20 different side chains
- Each side chain differ in: – Size
Hydrogen
– Shape
– Charge
– Hydrophobicity
Protozoans:
- unicellular eukaryotes - are members of the kingdom Protista - are classified according to their means of locomotion 1. cytoplasmic streaming (amoebas) 2. flagella 3. cilia - shapes vary - can live free or as parasites. - reproduction is sexual or asexual. (Fig. 1.1c)
1884 - Hans Christian Gram
developed a differential staining technique
called the Gram stain which differentiates bacteria into 2 groups, gram (-) and gram (+).
Rudolf Virchow
1858 Theory of biogenesis: living cells can arise only from preexisting living cells
special amino acids
cysteine (cys)
glycine (gly)
proline (pro)
Theory of biogenesis:
living cells can arise only from preexisting living cells
There are five different nitrogenous bases:
Triglycerides
are formed by the dehydration reaction of one glycerol with 3 fatty acids.
- glycerol have 3 hydroxyl (-OH) groups attached to 3 C atoms
- fatty acids are composed of long hydrocarbon (H-C) chains ending with carboxyl (-COOH) group.
Viruses :
- are so small that they can only be seen with an
electron microscope.
- are not cellular.
- are parasites which require a host cell to replicate itself.
- simple structure:
- Core contains the nucleic acid (DNA or RNA)
- Protein coat surrounds core
- Lipid envelope may surround coat
What are the effects of the normal flora of microorganisms in the human body?
protect us against dis- ease by preventing the overgrowth of harmful microbes, and others produce useful substances such as vitamin K and some B vitamin
What proportion of the microorganims are pathogenic?
Only a minority of microorganisms are pathogenic (disease producing). about 1%
Which type of fatty acid (saturated or unsaturated) is more easily packed together?
saturated
Complex lipids:
- contains elements (i.e. phosphorus, nitrogen, sulfur) in addition to C, H, O
- Examples are waxes and glycolipids.
- cell walls of bacteria belonging to the genus
Mycobacterium contain waxes & glycolipids; provides distinguishing staining characteristic
(acid-fast stain)
- example: phospholipids (glycerol, 2 fatty acid, phosphate group)
has polar and non-polar ends
- is major constituent of cell membranes—phospholipid bilayer
Which nucleotide is present in DNA?
Simple stain
is an aqueous or alcohol solution of a single basic dye
- is used to highlight the entire microorganism so that cellular shapes and structures are visible.
- A mordant may be added to the simple stain to:
increase the affinity of a stain for the specimen
coat a structure (such as a flagellum) to make it thicker.
- Examples of simple stains: 1. methylene blue (blue) 2. carbolfuchsin (red)
3. crystal violet (purple) 4. safranin (pink)
mordant
may be added to the simple stain to:
increase the affinity of a stain for the specimen
coat a structure (such as a flagellum) to make it thicker.
Differential Stains
react differently with different bacteriacan be used to distinguish them
- 2 types of differential stains 1. Gram Stain
2. Acid-Fast Stain
Gram Stain
was developed in 1884 by the Danish microbiologist
Hans Christian Gram
- differentiates/classify bacteria into 2 large groups
a. gram positive (+) purple
b. gram negative (-) pink
gram stain procedure
- Apply crystal violet which colors all bacteria purple (primary stain)
• Wash off w/ddH O. 2
- Apply iodine, a mordant, all bacteria still purple.
- Wash with ethanol or ethanol- acetone solution, a decolorizing agent
- Gram + bacteria will be purple; Gram - bacteria will be colorless
- wash off w/ddH2O
- stain with safranin, a counterstain.
- Gram (-) will be pink; Gram (+) will be purple - wash off w/ddH2O
- blot dry 19
- examine microscopically
Gram-positive
no membrane covering peptidoglycan wall
Gram (+) bacteria have a thicker cell wall composed of peptidoglycan than gram (-) bacteria
Gram-negative
outer membrane covers peptidoglycan wall
Gram (-) bacteria have a thin layer of peptidoglycan and outside of that, a layer of lipopolysaccharide
Negative Staining for Capsules
- capsule: a gelatinous covering of some microbes;
confers virulence(polysacharide or polysacharide protine)
- is more difficult than other types of staining procedures because capsules are soluble in water and may be removed during washing.
Negative staining for capsuls: Procedure
a. Mix bacteria with Nigrosine, an acidic dye which provides a
dark purple background.
b. Spread dye as in negative staining.
c. Stain slide with crystal violet, basic dye to stain bacteria (purple)
d. Capsules will appear as colorless halos surrounding purple bacterial cells against a dark purple background.
- Gram stain: Procedure why it works
rystal violet and iodine can go through the thick cell wall, but once inside form a complex (CV-I) which can not go out of the cell.
- gram (+) bacteria stain purple because of the trapped CV-I complex
- gram (-) bacteria will be colorless because the alcohol wash disrupts the lipopolysaccharide and allow the CV-I complex to be washed out of the cell
- gram (-) bacteria are pink because of the counterstain with safranin
- Gram stain is most consistent when used on young, growing bacteria.
result of gram staining provide information for proper treatment of disease
- Generally, gram (+) bacteria are easily killed by penicillin and sulfonamide drugs.
- Gram (-) bacteria are resistant to these drugs, but are more susceptible to streptomycin, chloramphenicol, and tetracycline.
Schaeffer-Fulton Endospore Stain
a. Apply malachite green to heat-fix smear on slide and steam heat for 5 minutes. Spores will stain green and cells will be colorless.
b. Wash
c. Counterstain with safranin, which will stain the cells
pink. Spores will be green. d. Wash
Acid-Fast Stain
stain binds to bacteria that have a waxy materia(mycolic acid and evades immune system and phagocytosis happens) l in their cell walls
- used to identify all bacteria in the genus Mycobacterium Ex. Mycobacterium tuberculosis causes tuberculosis. Ex. Mycobacterium leprae causes leprosy.
- used to identify the disease-producing strains of the genus Nocardia
- Flagella Staining
Flagella are structures of locomotion.
- Staining flagella involves using a mordant and carbolfuchsin to build up the diameters of the flagella until they become visible under the light microscope.
- It is a tedious and delicate staining procedure.
TransmissionElectronMicroscopy (tem)
- can resolve objects as close as 2.5 nm
- Magnification is from 10,000X to 100,000X.
- Only a very thin section (about 100 nm) of a specimen can be studied effectively
- can’t obtain 3D image
- Specimens must be fixed, dehydrated, and viewed under vacuum; therefore, shrinkage and distortion may occur; may get artifacts
Acid-fast stain: Procedure
a. Apply carbolfuchsin to heat-fixed smear and gently heat to enhance penetration and retention of the dye. (All organisms will be red.)
b. Wash
c. Decolorize with acid-alcohol.
- Acid-fast organisms will be red since carbolfuchsin is soluble in the waxy material of the cell wall
- Non-acid-fast organisms will be colorless since these organisms do not have the waxy material in their cell walls to retain the carbolfuchsin
d. Counterstain with methylene blue.
- Acid-fast organisms will be red.
- Non-acid-fast organisms will be blue.
Fluorescence microscopy:
- uses an ultraviolet source of illumination that causes fluorescent compounds to emit light.
- Some organisms fluoresce naturally.
- Other organisms can be stained with fluorescent dyes called fluorochromes.
- Specimens appear as luminescent objects against a dark background
Combine a fluorochrome to a
specific antibody for a specific antigen.
Allow the antibody to combine with the specific antigen
Wash to remove non-specific binding
Thefluorochrome-antibody- antigen fluoresces under UV light
- is useful in diagnosing syphilis and rabies or detecting specific cell types, tissues, or structures
(Fig. 3.6a)
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Scanning Electron Microscope: (sem)
- Image is 3-dimensional
- It can study surface structures of intact cells & viruses
- resolves objects as close as
20 nm
- Magnification is 1000X to 10,000X
Power of resolution of human eye, light microscope, and electron microscope:
Endospore (Spore) Staining
Endospores are resistant, dormant structures within a cell which protects the microbe from adverse environmental conditions.
- are formed by 7 genera of bacteria (including Bacillus and Clostridium)
- do not stain with ordinary stains because the dyes do not penetrate the wall of the endospore.
- 2 methods used:
- A. Schaeffer-Fulton endospore stain - B. Dorner endospore stain
Dorner Endospore Stain
a. Put carbolfuchsin, red, in a test tube
b. Add several loopfuls of organism
c. Boil in a beaker of water for 10 minutes
- *Spores will be red, cells colorless.**
d. Add several loopfuls of the carbolfuchsin- bacteria
mixture to a drop of nigrosine on a slide e. Smear mixture
- Bacterial cells will be colorless against dark purple background (Negative Staining).
- Endospores inside the cells will be red.
Compound Light Microscope:
- Resolution
- cannot resolve structures smaller than 0.2 um, therefore,
cannot be used to observe viruses.
- commonly used to observe various stained (killed) specimens and to count microbes.
- Specimen appears colored against a bright background.
- Maximum magnification is about 2000X (200x oil immersion)
Darkfield microscopy:
used for examining live microorganisms that do not stain easily, or are distorted by staining, or are invisible in brightfield microscopy
- uses a special condenser with an opaque disc that blocks light from entering the objective directly.
- Specimen appears light against a black background.
- can be used to detect Treponema pallidum, causative agent for syphilis
Electron microscopy:
- uses beam of electrons (shorter wave length) instead of light
- Structures smaller than 0.2 um can be resolved (viruses, cellular structures)
- There are 2 types:
1. Transmission electron microscope (TEM) 2. Scanning electron microscope (SEM)
What is resolution?
Resolution is the ability of lenses to distinguish between
two points at a specific distance apart.
What are the resolution power of the brightfield microscope vs. TEM and SEM?
BF
cannot resolve structures smaller than 0.2 um, therefore,
cannot be used to observe viruses.
TEM - can resolve objects as close as 2.5 nm
SEM- - resolves objects as close as
20 nm
What is the name of the organism that causes syphilis?
Treponema pallidum
What is the CV-I complex?
Crystal violet and iodine can go through the thick cell wall, but once inside form a complex (CV-I) which can not go out of the cell.
Which group of Gram bacteria is sensitive to penicillin and sulfonamide drugs? Which group of Gram bacteria is more sensitive to streptomycin, chloramphenicol, and tetracycline?
- Generally, gram (+) bacteria are easily killed by penicillin and sulfonamide drugs.
- Gram (-) bacteria are resistant to these drugs, but are more susceptible to streptomycin, chloramphenicol, and tetracycline.
What are the 4 functions of water?
- is one of the most important molecules
for living organisms
2. is the medium for most chemical reactions 3. is the most abundant molecule of most
living cells (~65-75%) 4. is a polar molecule, can form H-bonds
What are the 4 major macromolecules?
Proteins.
Carbohydrates.
Lipids.
Nucleic Acids
DNA can dentature in what conditions
Double stranded (ds) DNA can denature (melt) to single stranded (ss) DNA at high temperature, lower salt, or extreme pH conditions
conjugated proteins
modified protien
- glycoproteins contain sugars
- nucleoproteins contain nucleic acids
- metalloproteins contain metal atoms
- lipoproteins contain lipids
What are the functions of proteins
- Structural proteins
- microfilaments for movement of cells
- cell membranes or cell walls
- carrier proteinstransport molecules into and out of cells - Enzymes: catalyze chemical reactions 3. signaling molecules
- Toxins are produced by certain bacteria;
Bacteriocins: proteins produced by some bacteria that kill other bacteria.
- Hormones for regulatory function (i.e. insulin) 6. Antibodies for immune function
Purines and pyrimidines
Purines and Pyrimidines are nitrogenous bases that make up the two different kinds of nucleotide bases in DNA and RNA. The two-carbon nitrogen ring bases (adenine and guanine) are purines, while the one-carbon nitrogen ring bases (thymine and cytosine) are pyrimidines.
Adenosine Triphosphate = ATP
- is the principal energy-carrying molecule (potential form of energy).
- is composed of adenine, ribose, and 3 phosphate groups
- energy is released when a phosphate is removed ATP———–>ADP + Pi + Energy
Sarcinae
are cocci that divide in 3 regular planes and produce a cube- like group of 8
Archaea:
“exteme-ophile” - are prokaryotes - cell walls lack peptidoglycan - are found in extreme environments - There are 3 main groups of Archaea 1. Methanogens: produce methane gas as waste product 2. Extreme halophiles: salt-loving 3. Extreme thermophiles: heat-loving; live in hot sulfurous water such as hot springs in Yellowstone National Park.
Prokaryotes: Shape
-1. Spherical or coccus (pl. cocci)
- Diplococci = two cocci
- Streptococci = cocci in chains
- Tetrads = cocci that divide in two planes and remain in groups of four
- Sarcinae are cocci that divide in 3 regular planes and produce a cube- like group of 8
- Staphylococci are those that divide at random planes and form grape like clusters or broad sheets
Prokaryotes: Shape
- Rod-shaped, bacillus (bacilli, pl.)
- divide only across their short axis.
- Diplobacilli appear in pairs after division.
- Streptobacilli occur in chains. - Some have tapered ends like
cigars.
- Coccobacilli are oval and may look like cocci.
- Most appear as single rods.
- bacillus means:
a. bacterial shape
b. genus (i.e. Bacillus anthracis)
Prokaryotes: Shape
- Spiral
- have one or more twists; are never straight
- Vibrios are curved rods that look like commas.
- Spirilla have a distinctive helical shape like a corkscrew, fairly rigid bodies, and move by means of a flagella.
- Spirochetes are helical, flexible, and move by means of an axial filament
- Other spiral bacteria have more complex shapes and arrangements.
Prokaryotes: External Structures
- Glycocalyx
- Glycocalyx: general term used to describe substances that
surround bacterial cells
- are also called extracellular polymeric substances (EPS)
- It is a gelatinous polymer composed of polysaccharide, polypeptide, or both
- is viscous (sticky).
- is referred as a slime layer if glycocalyx is unorganized & loosely attached to cell wall
- is referred as a capsule if glycocalyx is organized and firmly attached to cell wall
- Capsules confer bacterial virulence (the degree to which a pathogen causes disease)
- capsules prevent from phagocytosis & dehydration & allow for substrate attachment
Prokaryotes: External Structures
- Flagellum (flagella, pl.): whip
- are long filamentous appendages
that move bacteria
- There are 4 arrangements of flagella:
a. monotrichous - single polar flagellum
b. amphitrichous - single flagellum at both ends of cell
c. lophotrichous - 2 or more flagella at one or both poles of the cell
d. peritrichous - flagella distributed over the entire cell
monotrichous
single polar flagellum
amphitrichous
single flagellum at both ends of cell
Flagellum: structure
- Three basic parts:
a. Filament is the long outermost region which is constant in diameter and contains the globular protein flagellin - not covered by membrane or sheath
b. Hook is the structure to which the filament is attached
c. Basal body anchors the flagellum to the cell wall and the plasma membrane.
(Fig. 4.8)
- It is composed of a central rod inserted into a series of rings.
lophotrichous
2 or more flagella at one or both poles of the cell
peritrichous
flagella distributed over the entire cell
Axial Filaments:aka endoflagellum
- are bundles of fibrils that arise at the ends of the cell
beneath the outer sheath and spiral around the cell.
- used as a form of locomotion by spirochetes such as Treponema pallidum, the causative agent of syphilis.
3. Rotation of filament causes spiral motion that resembles the movement of a corkscrew
Flagellum:
- Movement
aused by rotation of basal body.
- rotation is either clockwise or counter-clockwise around its long axis
- Eucaryotic flagella undulate in a wave-like motion
- Patterns of motility:
a. “Run” or “Swim” - when a bacterium moves in one direction for a period of time.
b. “Tumble” - abrupt, random changes in direction caused by a reversal of flagellar rotation - Taxis: the movement of a bacterium towards or away from a particular stimulus.
a. If the stimulus is lightphototaxis
b. If the stimulus is chemicalChemotaxis - positive chemotactic stimulus = attractant
- negative chemotactic stimulus = repellent
- ex. Light: a. if attractant → + phototaxis b. if repellent → - phototaxis
- Flagellum: Taxis
the movement of a bacterium towards or away from a particular stimulus.
a. If the stimulus is lightphototaxis
b. If the stimulus is chemicalChemotaxis - positive chemotactic stimulus = attractant
- negative chemotactic stimulus = repellent
- ex. Light: a. if attractant → + phototaxis b. if repellent → - phototaxis
Structure of peptidoglycan:
Prokaryotes: External Structures
- Pili:
- are hair like appendages attached to bacterial cells
- are shorter and thinner than flagella
- consist of a protein called pilin
- can occur at the poles of the bacterial cell or evenly distributed over the entire surface of the cell
- many gram (-) bacteria have pili - 2 types of pili
a. common pili (aka fimbriae) allows a cell to adhere to surfaces
b. sex pili join bacterial cells to allow transfer of DNA from one cell to anotherconjugation (“bacterial sex”)
Prokaryotes: Cell Wall
- The cell wall is a complex, semi rigid structure that surrounds the plasma membrane.
- Almost all prokaryotes have cell walls - is the site of action of some antibiotics - Functions:
- to prevent rupture of bacterial cells
- to maintain the shape of the bacterium 3. to serve as a point of
anchorage for flagella 4. to produce symptoms of
disease in some species
Prokaryotes: Cell Wall
Composition and Characteristics:
- is composed of called peptidoglycan (disaccharide + polypeptide)
- The disaccharide is composed of:
1. N-acetylglucosamine (NAG) 2. N-acetylmuramic acid (NAM) - alternating NAG and NAM form the carbohydrate backbone
- tetrapeptide side chain (4 amino acids) attach to each NAM
- Parallel tetrapeptide side chains may be linked by a
peptide cross-bridge
