Lecture 1 - Intro + Host Defense Flashcards
Bacteria are broadly classified by their _____.
The two most commonly encountered are ____ and ____.
Shapes
Cocci; Rods
Cocci have different arrangements based on what?
their planes of division
*cocci have distinct ARRANGEMENTS based on their planes of division
What are the four types of planes of divisions that cocci can undergo?
1) One plane
2) Two planes
3) Three planes
4) Random planes
Match the terms to their definitions regarding the structural organization of a prokaryotic cell.
1) Cell wall
2) Capsule
3) Ribosome
4) Fimbrae/pilli
A) used for attachment to surfaces and bacterial mating
B) translational machinery, protein synthesis
C) provides cell shape and protection from osmotic stress
D) polysaccharide layer outside of cell wall, provides protection from osmotic stress and host immune system
1) Cell wall: provides cell shape and protection from osmotic stress
2) Capsule: polysaccharide layer outside of cell wall, provides protection from osmotic stress and host immune system
3) Ribosome: translational machinery, protein synthesis
4) Fimbrae/pilli: used for attachment to surfaces and bacterial mating
Match the terms to their definitions regarding the structural organization of a prokaryotic cell.
1) Plasma membrane
2) Nucleoid
3) Flagellum
4) Inclusion body
A) localization of DNA
B) site of storage of carbon, phosphate and other substances
C) selectively permeable barrier, nutrient & waste transport, location of many metabolic processes (respiration), mechanical boundary of the cell, detection of environmental cues for chemotaxis
D) used for cellular movement
1) Plasma membrane: selectively permeable barrier, nutrient & waste transport, location of many metabolic processes (respiration), mechanical boundary of the cell, detection of environmental cues for chemotaxis
2) Nucleoid: localization of DNA
3) Flagellum: used for cellular movement
4) Inclusion body: site of storage of carbon, phosphate and other substances
What are the four critical functions of the cell wall?
1) Aids in determining cell shape, provides rigidity and integrity
2) Ensures that the cell is protected from OSMOTIC LYSIS
3) Protects cell from TOXIC SUBSTANCES
4) can contribute to pathogenesis for some pathogenic bacteria
Bacteria can be classified by their cell walls structure.
What are the two types? How are they different?
1) Gram-positive: bacteria have a SINGLE membrane and a THICK cell wall composed of peptidoglycan.
2) Gram-negative: bacteria have TWO MEMBRANES separated by a periplasm that contains a THIN peptidoglycan layer.
Briefly answer the questions regarding the general structure of the gram positive bacterial cell wall.
1) What is teichoic acid?
2) What does the periplasmic space contain?
1) Teichoic acids are linked to peptidoglycan. They are glycerol-phosphate or ribitol phosphate carbohydrate copolymers that assist in providing cell wall rigidity.
2) Contains hydrolytic enzymes and proteins for nutrient processing and uptake.
Which statement is true?
1) Gram positive bacterial cell wall contain a homogenous thick peptidoglycan layer.
2) Teichoic acid is found in both gram positive and gram negative bacteria.
1!
For 2) Teichoic acid is found ONLY IN gram-positive bacteria.
Fill in the blanks regarding the structure of the peptidoglycan subunit:
1) It contains two sugar derivatives: ________ and _______.
2) NAM is linked to a _________ consisting of _____, ____, _____, and _____.
3) To created a ______ polymer, peptidoglycan subunits can be __________.
1) N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
2) tetrapeptide; L-alanine; D-glutamic acid; meso-DAP (or L-lysine); D-alanine
3) Meshlike; cross-linked
There are two methods of how peptidoglycan subunits can form CROSS-LINKS.
Describe them and mention which one is common in gram-negative and gram-positive bacteria.
1) Direct cross-linking between subunits: carboxyl group of D-alanine is linked to amino group of DAP. Common in GRAM-NEGATIVE bacteria.
2) Cross-linking via peptide interbridges: tetrapeptide chain can link to adjacent chain via a peptide interbridge composed of GLYCINE residues. Common in GRAM-POSITIVE bacteria.
What does the cross linking between tetrapeptide chains result in?
It results in a highly dense INTERCONNECTED PEPTIDOGLYCAN NETWORK.
*gram-positive
(T/F) The composition and extent of crosslinking is shared between different bacterial species.
False!
The composition and extent of crosslinking CAN VARY between different bacterial species - contributes to DIVERSITY!
Which statement is false regarding the gram-negative bacterial cell wall?
1) There is a thin peptidoglycan layer.
2) There are proteins in the outer membrane that permit passage of small molecules.
3) LPS is bound to inner membrane.
4) In between the outer membrane and the plasma membrane, there is a periplasmic space and peptidoglycan layer.
3!
LPS is bound to the OUTER MEMBRANE.
Lipopolysaccharide (LPS) plays a role in?
1) Adhesion
2) Formation of permeability barrier
3) Pathogenesis
Describe the structure of an LPS.
It contains
1) O side chain (antigen) - series of sugar residues that DIFFER among and within species. may be recognized by host antibodies, but bacteria can alter the O antigen structure to evade host immune response.
2) Core polysaccharide - joins O side chain with lipid A
3) Lipid A - SIMILAR in all gram-negative bacteria. highly hydrophobic (fatty acid) and is inserted into the OUTER leaflet of the OUTER membrane.
Pili are ___, ____, _______ fibers that extend from the surface of many species of bacterial cells.
Pili are ___-like, _____-cored appendages.
short, thin, proteinaceous
hair; hollow
What is the function of pili?
1) Adherence to surfaces such as host epithelial cells, other bacteria or inner surfaces.
2) Some pili (Type IV pili) generate jerky motile forces referred to as TWITCHING MOTILITY.
3) TRANSFER OF DNA FROM CELL-TO-CELL (conjugation; horizontal gene transfer).
The capsule is a _________ layer that coats cell _____ exterior.
It is found in _______ and ______ bacteria.
Polysaccharide; wall
gram-negative; gram-positive
What are the functions of a capsule?
1) Protects PATHOGENIC bacteria from PHAGOCYTOSIS by host phagocytes (evasion of host immune system)
2) Protects against dehydration
3) Exclude viruses and other hydrophobic toxins
4) Can facilitate ADHESION
What are the 4 Koch’s Postulates?
1) The microorganism must be present in every case of the disease but absent from healthy organisms.
2) The suspected microorganisms must be isolated and grown in a pure culture.
3) The same disease must result when the isolated microorganism is inoculated into a healthy host.
4) The same microorganism must be isolated again from the diseased host.
*causal relationship between microorganism and disease
What are the limitations to Koch’s Postulates?
for 1) not all people infected by a bacteria may develop a disease - subclinical infection can sometimes be more common than clinically obvious infection (ASYMPTOMATIC CARRIERS)
for 2) some microorganisms are DIFFICULT TO CULTURE in the lab, cannot be grown in “PURE CULTURE”
for 3) ETHICS of human and animal models. lack of appropriate animal models - some human pathogens do not readily cause disease in animals.
List the seven basic steps of infection by PATHOGENIC bacteria.
1) Maintain a reservoir
2) Entry into host
3) Adhesion, invasion and persistence
4) Evasion of host defenses (to cause disease, pathogen must avoid local + systemic defenses)
5) Replication
6) Damage to host
7) Dissemination
What is a reservoir?
It is a SITE or NATURAL environment in which the pathogen normally resides and is primarily dependent for survival.
They can be ANIMATE (humans, arthropod, plant, animals) or INANIMATE (water, soil, food).
______ into the environment ensures bacterial dissemination.
When can passive escape of the bacteria occur?
Shedding
Passive escape of the bacteria may occur when the pathogen or its progeny leave the host in: WASTE PRODUCTS (urine/feces), SALIVA DROPLETS, and DESQUAMATED CELLS.
