Bacterial Cell Structure (External) Flashcards
List the three domains into which living organisms are classified. Are organisms in different domains related? Explain.
eukaryote, archaea, bacteria. the base of each domain diverged from a common ancestor roughly 3 billion years ago.
Describe and compare the basic cellular organization of prokaryotic and eukaryotic cells. Is one group organized while the other is not? Explain.
prokaryotes do not have membrane-bound organelles, while eukaryotes do (specifically a nucleus, hence the name). both are organised, grocery bag vs. backpack analogy.
In a single sentence, describe the basic structure of the cell membrane. Of what types of molecules is it composed, and how are they arranged?
a polar-permeable phospholipid bilayer interwoven with cholesterol, which acts as a kind of antifreeze, and integral (internal or transmembrane) and peripheral (surface) proteins, used for enzymatic functions, transport, and signalling.
In a single sentence, describe the basic function of the cell membrane.
form the bound between interior and exterior environment by regulating movement into and out of the cell.
Describe the fluid mosaic model of membranes.
a two-dimensional fluid structure of lipids with a mosaic of proteins embedded within.
Describe the semipermeable nature of the cell membrane.
membranes are selectively permeable, they allow certain substances to pass through unrestricted (such as water) and restrict others (such as polysaccharides).
Describe the key ways in which the bacterial cell membrane differs from its eukaryotic counterpart.
cell membranes in eukaryotes and bacteria are fundamentally similar, but differ in phospholipid composition. additionally bacterial membranes generally lack sterols, are more heavily in-folded, and are involved in energy transformations.
lysozyme
one of the proteolytic (breakdown of protein or peptides into amino acids) enzymes found in lysosomes and other body fluids (such as tears, saliva, etc.) that catalyze (breakdown) the protein wall of bacteria, especially gram positive bacteria, making lysozymes a vital part of our first-line defense against bacterial infection.
lysosome
organelles that contain powerful enzymes to assist in destroying cellular debris and the breakdown of proteins, the last compartment of the endocytic pathway.
Why do you think the cell wall structures of archaea are more diverse than those of bacteria?
archaea inhabit a wide range of extreme environments
What are archaea cell walls made of?
they are very diverse. while none possess peptidoglycan, some possess pseudopeptidoglycan which acts in a similar manner.
glycocalyx
gell like layer external to cell wall, found in many bacteria, generally formed of polysaccharides, some are made of polypeptides or a combination of both.
what are the two main forms of glycocalyx?
capsule (which is distinct and gelatinous), and slime layer (which is diffuse and irregular)
key functions of glycocalyx
attachment (enabling bacteria to adhere to surfaces and grow as a biofilm), protection from desiccation, avoid detection by host immune system (camouflages the bacteria cell surface to mimic those of host cells so that bacteria are not immediately detected).
biofilm
any group of microorganisms in which cells stick to each other on a surface. these adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (hmmm, like a glycocalyx maybe?).
S strain bacteria
S. pneumoniae colonies that possess a glycocaylax, pathogenic. named for its smooth appearance under a microscope.
R strain bacteria
S. pneumoniae colonies that do not possess a glycocaylax, not pathogenic. named for its rough appearance under a microscope.
sheath
in some aquatic bacteria, a tube surrounding a linear chain of cells (like tennis ball tube packaging), serves to attach bacteria to solid objects to favourable substrates while protecting bacteria from predators.
name the types of filamentous appendages
flagella (plural flagellum), fimbriae (plural fimbria), pili (plural pilus)
where would one find a filamentous appendage?
anchored in the plasma membranes of bacterial cells, protruding form the surface, not enclosed by a membrane.
what are filamentous appendages made of?
hollow tubes of repeating proteins
flagella
long, hollow tubes of repeating proteins that extend beyond the cell surface, responsible for motility, can be used to identify and characterise some types of bacteria. (singular flagellum).
are bacterial flagella the same or different from eukaryotic flagella?
different in both structure and function, eukaryotic flagellum (or cilia, a similar structure) are covered by membrane whilst bacterial flagellum are not.
what are the basic components of flagella?
filament, hook, basal body
flagella filament
long, hollow shaft of identical globular modules of repeating protein (flagellin), secreted through the hollow core and built up in helical fashion
flagella hook
a bend in the flagella beyond the cell envelope
flagella basal body
the motor of the flagella, embedded in the cell
cell envelope
cell envelope refers to both the cell wall and cell membrane
flagellin
the main protein that makes up flagella in bacteria
flagellum
long, hollow tubes of repeating proteins that extend beyond the cell surface, responsible for motility, can be used to identify and characterise some types of bacteria. (plural flagella.
flagella basal body
anchors the filament, composed of multiple proteins, structure differs between bacteria.
can flagellum be used to identify species? why or why not?
yes, because the number and arrangement are variable between species.
what directions can flagellum propel an organism?
forward only (runs), allows for directional changes by rotating in space at random (tumble), but never allows for movement in reverse.
what are polar flagellum?
x
how fast do bacterial flagellum rotate?
up to 100,00 rpm.
what fuels flagella movement?
electrochemical gradient, either H or Na ions, which flow through the plasma membrane near the basal body.
L-ring, MS-ring, P-ring (flagella basal body rings)
Gram-positive organisms have two of these basal body rings, one in the peptidoglycan layer and one in the plasma membrane. Gram-negative organisms have four such rings: the L ring associates with the lipopolysaccharides, the P ring associates with peptidoglycan layer, the M ring is embedded in the plasma membrane, and the S ring is directly attached to the plasma membrane. The flagellum filament ends with a capping protein.
how fast can flagella propel bacteria?
up to 60 cell lengths per second.
how do bacteria alternate between forward propulsion (runs) and rotation (tumbles)?
alternating the rotation of their flagella.
how do bacteria “choose” where to travel?
through suppression of the rotation of the cell (favouring forward movement) when travelling in the direction of an attractant.
what do you call movement in response to a chemical stimulus?
chemotaxis
chemotaxis
bacterial movement in response to a chemical stimulus.
how is chemotaxis accomplished?
through receptors on the surface of the cell that can detect chemicals and their concentrations.
what do cells do to bacterial flagella when cell surface receptors detect an attractant increasing in concentration?
suppress the direction of spin that would result in the rotation of the cell.
what do cells do to bacterial flagella when cell surface receptors detect an attractant decreasing in concentration?
allow the direction of spin that would result in the rotation of the cell.
phototaxis
bacterial movement in response to light stimulus.
aerotaxis
bacterial movement in response to oxygen concentration.
magnetotaxis
bacterial movement in response to a Earth’s magnetic field.
what do you call movement in response to a light stimulus?
phototaxis
what do you call movement in response to oxygen concentration?
aerotaxis
what do you call movement in response to a magnetic field?
magnetotaxis
do flagellum have any use other than movement?
aside from movement, flagellum also allow for burrowing, attachment, protein injection
how does yersina pestis inject proteins into host cells?
using a modified flagellum that is non-motile and acts as a hypodermic needle. pestis pumps YOPS though the modified flagellum instead of flagellin.
YOPS
Yersinia Outer ProteinS, proteins injected though modified flagellum used to infect immune cells of hosts.
fimbriae
numerous sticky, rod-like hollow protein extensions.
how are fimbriae different from flagella?
shorter, not made of flagellin, often hundreds per cell.
purposes of fimbriae
adhere to bacteria (as in a biofilm) or other surfaces (host infection); communication in biofilms.
pili
specialised type of fimbriae (ex. a sex pilus), generally few per cell at most.
sex pilus
a hollow protein tube that tranferrs DNA from one bacterium to another (conjugation).
conjugation
a temporary cytoplasmic bridge between bacteria that transfers single-stranded DNA one way from one bacteria to another, which serves to increase genetic variation in a population.
difference between pili and flagella
pili are shorter and thinner
peritrichous bacteria
flagella projecting in all directions (like E. coli)
amphitrichous bacteria
amphitrichous bacteria have a single flagellum on each of two opposite ends (only one flagellum operates at a time, allowing the bacteria to reverse course rapidly by switching which flagellum is active)
lophotrichous bacteria
lophotrichous bacteria have multiple flagella located at the same spot on the bacteria’s surfaces which act in concert to drive the bacteria in a single direction. In many cases, the bases of multiple flagella are surrounded by a specialized region of the cell membrane, the so-called polar organelle
monotrichous becteria
monotrichous bacteria have a single flagellum
integral proteins (cell envelope)
in a cell membrane, refers to proteins inserted in the membrane (including trans-membrane proteins)
peripheral proteins (cell envelope)
in a cell membrane, refers to proteins associated with the membrane surface
functions of proteins in a membrane
used for transport, as enzymes, for signalling
what genus of bacteria generally possess sterols in their phospholipid membrane?
Mycoplasma
name two examples of sterols in a cell membrane
cholesterol, ergosterol
describe the difference between bacterial and eukaryotic phospholipid composition
bacterial phospholipids generally have different chemical groups (such as sugars) attached to the phosphate, which are immunologically important
microvilli
bacteria outfoldings common in eukaryotic membranes, contrasts with bacterial infolds.
what does infolding accomplish for bacterial cell membranes?
increases surface area and facilities transport and energy transformations
what defines the outer boundary of the cell?
plasma membrane
give an example of a structure external to the cell membrane
cell wall, glycocalyx, other answers acceptable
give an example of a structure internal to the cell membrane
organelles, DNA, other answers acceptable
spherical bacteria are termed what?
coccus (plural cocci)
plural of coccus
cocci
singular of cocci
coccus
coccus bacterium
a spherically shaped cell
cocci bacteria
spherically shaped cells
bacillus bacterium
a rod shaped cell
bacilli bacteria
rod shaped cells
plural of bacillus
bacilli
singular of bacilli
bacillus
rod shaped bacteria are termed what?
bacillus (plural bacilli)
coccobacilli bacteria
cells shaped like very short rods (think hybrids of cocci and bacilli bacterium)
vibrio bacteria
cells shaped like short, curved rods
short, curved bacteria are termed what?
vibrio
short, rod-like bacteria are termed what?
coccobacilli
spirillum
cells shaped like a long, curved rod forming spirals
cells shaped like a long, curved rod forming spirals are termed what?
spirillum
cells shaped like long helices are termed what?
spirochaete
spirochaete
cells shaped like long helices
what is unique about spirochaete cells?
Spirochaetes are distinguished from other bacterial phyla by the location of their flagella, sometimes called axial filaments, which run lengthwise between the bacterial inner membrane and outer membrane in periplasmic space. These cause a twisting motion which allows the spirochaete unique motility. When reproducing, a spirochaete will undergo asexual transverse binary fission.
what determines future arrangement of cell colonies?
the relative planes on which the cells divide
give an example of a species that forms in a diplococcus arrangement?
Neisseria gonorrheae
give an example of a species that form long chain arrangements?
Streptococcus pneumoniae
what is the difference between chain or diplococcus arrangements?
both start in a similar manner, with cells dividing along one plane, but diplococcus cells (as the name implies) only form groups of two cells, while chains may be of varying lengths
cubical packets
when cocci divide in two or three perpendicular planes, they form cubical packets
what results from cocci dividing along two or three perpendicular planes?
a cubical packet
give an example of a genus that forms cubical packets?
Sarcina
what results from cocci dividing along random planes?
clusters
clusters
when cocci divide along random planes
give an example of a genus that forms clusters
Staphylococcus
what kind of grouping do Staphylococcus cells generally form?
clusters
what kind of grouping do Sarcina cells generally form?
cubical packets
how are bacterial cell arrangements important to humans?
identification
give an example of a bacteria that lives in a swarm multicellular association?
Myxobacteria
give an example of a biofilm multicellular association?
dental plaque
give examples of bacterial appendages:
flagella, pili
list surface layers of a bacterial cell
sheath, glycocalyx, cell wall, (other answers acceptable)
describe the function(s) of the bacterial cell wall
determines the shape of the organism, restricts water uptake and prevents bursting due to osmotic pressure
how are the two main groups of bacteria distinguished?
by their cell wall structure, Gram-positive or Gram-negative
what are the two sugars that form the polymer portion of peptidoglycan?
n-acetylmuramic acid and n-acetylglucosamine (abbreviated NAM, NAG respectively)
what is the linear polymer of peptidoglycan termed?
a glycan chain
what kinds of cells have peptidoglycan?
bacterium only
what forms the cross-linkages between glycan chains?
tetra- or pentapeptides
what connects the linear polymers in peptidoglycan?
tetra- or pentapeptides
where would one find pentapeptides, what are they made of and what do they do?
between glycan chains in the peptidoglycan of a bacterial cell wall, made of chains of five amino acids, they link the glycan chains together and provide structural integrity to the peptidoglycan.
where would one find tetrapeptides, what are they made of and what do they do?
between glycan chains in the peptidoglycan of a bacterial cell wall, made of chains of four amino acids, they link the glycan chains together and provide structural integrity to the peptidoglycan.
in peptidoglycan, linear polymers are linked together by tetra- or pentapeptides, to which sugar are these peptides attached?
n-acetylmuramic acid (NAM)
NAM
n-acetylmuramic acid
NAG
n-acetylglucosamine
what is the arrangement of n-acetylglucosamine and n-acetylmuramic acid in peptidoglycan?
linear alternating chains, termed glycan chains
what is the difference in composition of peptidoglycan between Gram-negative and Gram-positive cells?
peptide cross-linkages are joined directly in Gram-negative cells, through peptide interbridges in Gram-positive cells
roughly what percent of the cell envelope does the wall comprise in a Gram-postive cell?
40-80%
roughly what percent of the cell envelope does the wall comprise in a Gram-negative cell?
10%
If a bacterial cell does not retain crystal violet during a Gram stain procedure, what can be said about the peptide interbridges that connect the peptide cross-linkages between the linear polymers in peptidoglycan?
they do not exist (the tetra- or pentapeptides are joined directly in Gram-negative cells)
which type of cell has short peptide interbridges connecting the cross-linkages in its peptidoglycan?
Gram-positive cells
what is referred to lazily as the “sugar backbone” when referencing the bacterial cell wall?
linear chains of sugar polymers, made up of NAM and NAG
what is a tetrapeptide chain made of?
amino acids
what kinds of substances would a Gram-positive cell wall be permeable by?
Sugars, amino acids, ions
teichoic acid
negatively charged homopolymers of phosphorylated subunits that confer rigidity to the cell wall and helps adherence to host cells (termed an adhesin). Teichoic acids are not found in Gram-negative bacteria. They can be covalently linked to N-acetylmuramic acid of the peptidoglycan layer, to the lipids of the cytoplasmic membrane, or to the tetrapeptide crosslinkage between N-acetylmuramic acid units. Teichoic acids that remain anchored to lipids are referred to as lipoteichoic acids, whereas teichoic acids that are covalently bound to peptidoglycan are referred to as wall teichoic acids.
adhesin
In the crudest sense, bacterial adhesins serve as anchors allowing bacteria to overcome environmental shear forces, thus remaining in their desired environment. However, bacterial adhesins do not serve as a sort of universal bacterial Velcro. Rather, they act as specific surface recognition molecules, allowing the targeting of a particular bacterium to a particular surface such as root tissue in plants, lacrimal duct tissues in mammals, or even tooth enamel.
are Gram-postive cell walls positively or negatively charged and by what mechanism?
negative, charge conferred by the phosphate groups found on teichoic acids protruding from their cell walls
give two examples of homopolymers that comprise teichoic acid in a Gram-positive cell wall
ribitol-phosphate, glycerol-phosphate
wall teichoic acids
teichoic acids that are covalently bound to peptidoglycan, either covalently linked to N-acetylmuramic acid of the peptidoglycan layer or to the tetrapeptide crosslinkage between N-acetylmuramic acid units.
lipoteichoic acids
teichoic acids that are covalently bound to lipids of the cytoplasmic membrane, a major constituent of the cell wall of Gram-positive bacteria. shares many pathogenic similarities with endotoxins (lipopolysaccharide), released from the bacterial cells mainly after bacteriolysis (e.g. by lysozyme).
which is more complex, Gram-negative or Gram-positive cell walls?
Gram-negative, it possesses an additional membrane external to the peptidoglycan termed an “outer membrane” and contains only a thin layer of peptidoglycan (located in the paraplasm which is between the two membranes).
periplasm
the space between the membranes in a Gram-negative cell envelope.
how many membranes does a Gram-negative cell possess in its cell envelope? a Gram-postive?
two, one.
outer membrane
the outward most membrane in a Gram-negative cell envelope, located past the periplasm.
what is the difference between the innermost and outer membranes of a Gram-negative cell envelope?
the innermost membrane is a phospholipid bilayer, while the outer membrane is a phospholipid monolayer underneath an outer monolayer of lipopolysaccharides.
what basic similarity is there between lipoteichoic acids and lipopolysaccharides?
both function as endotoxins.
what basic difference is there between lipoteichoic acids and lipopolysaccharides?
lipoteichoic acids are found in Gram-positive cell envelopes, while lipopolysaccharides are found in Gram-negative cell envelopes.
LPS layer
the external leaflet of the outer membrane in Gram-negative cells, composed of lipopolysaccharides which function as an endotoxin.
where would one find lipid A?
the lipid portion of the LPS layer of a Gram-negative cell wall.
porin
porins are beta barrel proteins that cross a cellular membrane and act as a pore through which molecules can diffuse. unlike other membrane transport proteins, porins are large enough to allow passive diffusion, i.e., they act as channels that are specific to different types of molecules. present in the outer membrane of Gram-negative bacteria and some Gram-positive bacteria of the group Mycolata (mycolic acid-containing actinomycetes), the mitochondria, and the chloroplast.
what do porin proteins facilitate?
movement of small hydrophilic molecules into the periplasmic space while excluding many other molecules, including some antibiotics
periplasm
periplasm is a gel-like substance rich in water, nutrients, digestive enzymes, enzymes that build peptidoglycan, and other substances secreted by the cell
what occupies the periplasmic space?
peptidoglycan and periplasm
why do enzymes exist in the periplasmic space outside the innermost cell membrane?
to break down larger nutrient molecules into smaller molecules that can be absorbed.
give an example of a genus that defies identification with Gram stains?
Mycobacterium
give two examples of species that defy identification with Gram stains?
Mycobacterium tuberculosis, Mycobacterium leprae
what is unusual about the cell wall structure of Mycobacterium?
it contains up to 60% mycolic acid, a waxy lipid that provides protection against adverse environmental conditions.
why is it difficult to use a Gram stain to identify Mycobacterium?
the mycolic acid in their cell wall is waxy and difficult to stain with water-based dyes.
how does mycolic acid benefit tuberculosis?
The presence of mycolic acids gives M. tuberculosis many characteristics that defy medical treatment. They lend the organism increased resistance to chemical damage and dehydration, and prevent the effective activity of hydrophobic antibiotics. In addition, the mycolic acids allow the bacterium to grow readily inside macrophages, effectively hiding it from the host’s immune system. Mycolate biosynthesis is crucial for survival and pathogenesis of M. tuberculosis.
mycolic acid
a waxy lipid, comprising up to 60% of the cell envelope of species in the genus Mycobacterium, that protects against desiccation, antibiotics, acids, alkalis, detergents, oxidation. also renders Gram stains inconclusive, requires acid-fast staining.
what fundamental trait do members of the genus Mycoplasma lack?
a cell wall, made up for by the presence of mycolic acid.
from what genus arise the smallest free-living cells, and why are they so small?
Mycoplasma, because they lack a cell wall which generally accounts for a large portion of a cell’s dry weight.
what confers strength and rigidity to organisms from the genus Mycoplasma, and how does this differ from standard bacteria?
sterols in the membrane of Mycoplasma (produced from cholesterol obtained from the environment) make up for the lack of a cell wall, which is the standard means by which bacteria maintain structural integrity.
what considerations must be made for Mycoplasma in light of their lack of a cell wall?
although their membranes contain sterols (unlike most other bacteria), this does not provide the same protection against osmotic pressure, thus Mycoplasma must colonise osmotically protected environments such as animal bodies.
what are antimicrobials?
compounds that target and disrupt unique bacterial structures (such as peptidoglycan) without affecting human cells.
generally, how does penicillin work?
Bacteria constantly remodel their peptidoglycan cell walls, simultaneously building and breaking down portions of the cell wall as they grow and divide. β-Lactam antibiotics present in penicillin inhibit the formation of peptidoglycan cross-links in the bacterial cell wall; this is achieved through binding of the four-membered β-lactam ring of penicillin to the enzyme DD-transpeptidase. As a consequence, DD-transpeptidase cannot catalyze formation of these cross-links, and an imbalance between cell wall production and degradation develops, causing the cell to rapidly die. The enzymes that hydrolyze (break) the peptidoglycan cross-links continue to function, even while those that form such cross-links do not. This weakens the cell wall of the bacterium, and osmotic pressure becomes increasingly uncompensated—eventually causing cell death (cytolysis). In addition, the build-up of peptidoglycan precursors triggers the activation of bacterial cell wall hydrolases and autolysins, which further digest the cell wall’s peptidoglycans. The small size of the penicillins increases their potency, by allowing them to penetrate the entire depth of the cell wall.
what is the functional portion of penicillin?
β-Lactam ring.
β-lactam ring
A β-lactam (beta-lactam) ring is a four-membered lactam. (A lactam is a cyclic amide). It is named as such because the nitrogen atom is attached to the β-carbon relative to the carbonyl. The simplest β-lactam possible is 2-azetidinone.
what kind of antibiotic is penicillin?
a β-lactam antibiotic.
list three types of β-lactam antibiotics
penicillins, cephalosporins, carbapenems.
what type of chemical compound can be used to inhibit the synthesis of bacterial cell walls, and what method does this substance use?
β-lactams, they irreversibly competitively inhibit transpeptidase enzymes that form the amino acid cross-links between NAM (n-acetylmuramic acid) in peptidoglycan, causing lysis due to osmotic pressure.
are β-lactams more effective in Gram-positive or Gram-negative cells, and why?
more effective against Gram-positive bacteria, as transpeptidase enzymes are found in the periplasmic space of Gram-negative cells and β-lactams can be excluded from this space by porin channels.
some β-lactam derivatives are modified to pass through porin channels.
what is the difference between β-lactam and vancomycin antibacterials?
β-lactams irreversibly competitively inhibit transpeptidase, while vancomycin binds directly to pentapeptide and excludes transpeptidase from adding new amino acids to the cross-links between n-acetylmuramic acid sugars in the glycan chain of peptidoglycan. end result of cell lysis is the same.
what is the difference between β-lactam and bacitracin antibacterials?
β-lactams irreversibly competitively inhibit transpeptidase, which links glycan chains in peptidoglycan together; bacitracin blocks transport of n-acetylmuramic acid (NAM) and n-acetylglucosamine (NAG) sugars to the glycan chain, disrupting formation of peptidoglycan. end result of cell lysis is the same.
what is the difference between vancomycin and bacitracin antibacterials?
vancomycin binds directly to pentapeptide and excludes transpeptidase from adding new amino acids to the cross-links between n-acetylmuramic acid (NAM) sugars in the glycan chain of peptidoglycan; bacitracin blocks transport of n-acetylmuramic acid (NAM) and n-acetylglucosamine (NAG) sugars to the glycan chain, disrupting formation of peptidoglycan. end result of cell lysis is the same.
transpeptidase
a bacterial enzyme that cross-links peptidoglycan tetrapeptide cross-links to form rigid cell walls. In Gram-positive bacteria, the peptidoglycan tetrapeptide cross-links are connected by a tetra-/pentapeptide interbridge, whereas, in Gram-negative bacteria, the peptidoglycan tetra-/pentapeptide cross-links are covalently bound directly to each other.
proteolytic
the breakdown of protein or peptides into amino acids
how does lysozyme kill bacterial cells?
The enzyme functions by attacking peptidoglycans (found in the cell walls of bacteria, especially Gram-positive bacteria) and hydrolyzing the glycosidic bond that connects N-acetylmuramic acid with the fourth carbon atom of N-acetylglucosamine. It does this by binding to the peptidoglycan molecule in the binding site within the prominent cleft between its two domains. This causes the substrate molecule to adopt a strained conformation similar to that of the transition state, inhibiting normal bond formation.
what is the counterstain used in Gram staining?
safranin
what is the primary stain used in Gram staining?
crystal violet
what is alcohol used for in Gram staining?
a decoloriser that removes crystal violet from cell walls.
what is iodine used for in Gram staining?
a mordant (a substance, typically an inorganic oxide, that combines with a dye or stain and thereby fixes it in a material).
mordant
a substance, typically an inorganic oxide, that combines with a dye or stain and thereby fixes it in a material.
