Module 4: Flashcards
Main differences between bacterial and eukaryotic cells (3)
No nucleus
Peptidoglycan cell wall
Circular chromosome
What do bacterial cells have instead of a nucleus?
Nucleoid
Functions of peptidoglycan cell wall
Provides strength to cell with its rigidity
Protect cells from osmotic pressure/ lysis
Maintains cell shape
What kind of structure does peptidoglycan form in the cell wall?
Mesh-like
Two alternating units of carbohydrate backbone
NAG (N-acetylglucosamine)
NAM (N-acetylmuramic acid)
What cross-links peptidoglycan chains to form rigid cell wall in bacteria?
Transpeptidass (enzyme)
What is the cross-bridge and side chain in peptidoglycan called?
Peptide cross bridge
Tetrapeptide side chain
Gram-positive bacteria
Have a thick peptidoglycan layer (20-80nm) outside plasma membrane
Gram-negative bacteria
Thin layer of peptidoglycan between two membranes (plasma and outer)
Long flexible appendage that motile bacteria possess
Flagella
How does a flagella move a cell?
By acting as a propeller
Three major sections of the flagellum
Long filament
Hook
Basal body
Long filament (flagellum)
End part which extends into surrounding medium
Composed of flagellin(protein) subunits
Hook (flagellum)
Curved section connecting the filament to the cell surface
Basal body (flagellum)
Anchors flagellum into cell membrane by plates or rings
Chemotaxis
Bacteria move along a concentration gradient toward a chemical attractant/ away from a chemical repellent
They do this as they are already moving (tumbles and runs)
Fimbriae
Structure with adhesive properties- causes bacteria to stick to surfaces
An inherited trait
How do fimbriae differ from flagella? (3)
They are shorter, more numerous and aren’t involved in motility
Glycocalyx
Gelatinous polysaccharide and/ or polypeptide outer covering
Forms a sticky mesh work of fibres
Glycocalyx capsule
Organises and defined structures attached firmly to cell wall
Glycocalyx slime layer
Disorganised (without cell shape) and attached loosely to cell wall
Three functions of capsules (glycocalyx)
Virulence factors- protect bacteria from phagocytosis and being engulfed by immune cells
Adherence to cell surfaces and structures such as catheters
Prevent desiccation- drying out
When are bacterial endospores formed and germinated?
During unfavourable growth conditions (formed)
Under favourable conditions (germinated)
In which kind of bacteria are endospores present?
Gram-positive
What are two factors that trigger endospore formation?
Nutrient starvation
High cell density
Two properties of endospores
Resistant to heat, harsh chemicals, antibiotics, disinfectants etc.
Dormant stage of bacterial life cycle (long time)
Which domain are microorganisms in?
All three, but primarily prokaryotes (bacteria and archaea)
Why are prokaryotes so dominant?
They have a fast growth rate- the smaller the organism the faster it grows
It can evolve quickly
Binary fission
The process by which microorganisms can replicate themselves (one cell to two cells)
Asexual reproduction
Are the daughter cells of binary fission genetically identical?
Yes
How were prokaryotes able to become dominant in history?
They were the sole inhabitants for about 1.7 billion years, so they could colonise most habitats
Have them extreme ecological and biological diversity
Closed batch culture system
A form a cell culturing
A limited supply of nutrients is provided
Cells have to change once nutrient supply is used up
We can manipulate this system
Four phases of microbial growth (feast and famine)
Lag
Exponential
Stationary
Death
Describe ‘feast and famine’ (microbial growth)
Lag phase: period between when the organism is put in, and when it starts growing
(At this point it is getting ready for growth, bio synthetic reactions are starting to run)
Exponential phase: cells are actively dividing and population is doubling at a constant time interval
Stationary phase: cryptic growth (organisms consume other cells)
Death phase: equilibrium between growing and dead cells is skewed towards death
What kind of chemical is penicillin?
Antibiotic
How does penicillin work?
Kills bacteria by blocking cell wall synthesis
Only affects dividing cells (growing bacteria)
Persister
A cell that isn’t replicating
Three things prokaryotes need to multiply
Carbon source (building blocks)
Energy source (electrons to drive metabolic reactions in the cell) can be chemical or light
Reducing power (molecules inside cell that can transfer energy between different parts of the cell)
Why can we call molecules ‘natures batteries’?
Chemical energy is stored in their bonds
Which is the most common energy currency in cells?
ATP
The sun of all energy reactions inside a cell is called ____
Metabolism
Catabolism
Breaking substrates into products (building blocks/ simpler compounds)
Releasing energy
Anabolism
Harvesting building blocks from the environment to synthesises macromolecules and other cellular constituents
Used energy
Organisms that get energy from light
Phototroph
Organism that gets energy from chemical compounds
Chemotroph
Organisms that use carbon dioxide
Autotroph
Organisms that get carbon from organic compounds
Heterotroph
Photoautotroph
Organism that gets energy from light and carbon from carbon dioxide
Chemoautotroph
Organism that gets its energy from chemical compounds and gets its carbon from carbon dioxide
Photoheterotroph
Organism that gets energy from light, and carbon from organic compounds
Chemoheterotroph
Organism that gets energy from chemical compounds and carbon from organic compounds
If there is no growth in a closed batch culture system, have all cells died?
No, the death rate and growth rate are in balance
Microbial ecology
The study of interrelationships among microorganisms and their environment
Microbiome
All microorganisms and their genes within a particular environment
Populations of microbial species interact/ communicate to form ________
Communities
Enrichment culture
Providing the temperature and chemical conditions in the lab that encourage the growth of specific groups of microbes
Mesocosm
Experimental system that simulates real-life conditions
Two potential goals of braking a bond (metabolism)
Harvesting of building blocks
Harvesting of energy
How do intermediates play a role in bacteria redox reactions?
Example of intermediates
They shuttle energy from an oxidation (energy carrier)
NADH/NADPH2
Primary producers
What do they do?
Autotrophs
Fix CO2 into sugars
Decomposers
What do they do?
Heterotrophs
Require fixed carbon (rather than CO2), and recycle it back into CO2
What is the process of
Carbon—> macromolecules —> cells
And what else is required for this process?
Anabolism
Energy
Chemotrophs can use energy from either _____ or ______ compounds
Organic
Inorganic
Which is the electron donor in redox reactions, chemical energy or light energy?
Chemical energy (e.g. H2S)
Two types of photosynthesis
Oxygenic (non-cyclic photophsophorylation)
Anoxygenic (cyclic photophosphorylation)
Which type of photosynthesis uses both photsystems I and II?
Non-cyclic/ oxygenic
How does non-cyclic/ oxygenic photosynthesis generate oxygen?
Strips H2O of its electrons
What are the energy products of non-cyclic/ oxygenic photosynthesis (2)?
How are they produced?
ATP (cytochrome complex)
and NADPH (electrons reduce NADP+)
Which photosystem does cyclic/ anoxygenic photosynthesis use?
Photosystem I
Product of anoxygenic/ cyclic photosynthesis
ATP (no O2)
What do both cyclic and non-cyclic photosynthesis do?
Use light for energy and fix carbon
How can many different microbes share the same metabolism (photosynthesis) in the same environment?
Light is a common resource
They absorb a specific wavelength of light to avoid competition
How can oxygen dependent organisms live in anoxic environments?
Create cables to shuttle electrons into oxic zone- allows them to breathe
Are viruses cellular or acellular?
Acellular
How do viruses survive? Why?
By infecting a host
They have no metabolic abilities of their own
How do viruses multiply?
By relying on biosynthesis machinery of host cell
Which cells do viruses infect?
All types
Two parts of a protein (sometimes third)?
DNA/ RNA
Capsid (protein coat)
Sometimes envelope
Subunits of the capsid
Capsomers arranged in a precise pattern around the nucleic acid
Three types of symmetry of capsomer arrangement
Helical
Icosahedral- 20 face polyhedron (looks like a ball)
Complex- head is icosahedral and tail is helical
What shape can viral nucleic acid be? (3)
Linear
Circular
Segmented
Four possible forms of nucleic acid in viruses
ssRNA
dsRNA
ssDNA
dsDNA
Bacteriophage
What benefit could they have?
A virus that infects and replicates in bacteria
Potential treatment for diseases caused by bacteria
Lyric infection (5 steps)
- Attachment- receptor recognises compatible virus
- Entry of phage DNA and degradation of host DNA
- Synthesis of viral genomes (using host nucleotides) and proteins (using host ribosomes)
- Self assembly
- Release- virus produces lysozyme which cleaves NAM-NAG bonds in peptidoglycan wall
Lysogenic cycle
- Phage DNA integrates into bacterial chromosome
- Prophage is copied with bacterial chromosome
- Cell divisions create many infected bacteria
Sometimes a prophage exits the bacterial chromosome (still within the cell) and initiates a lyric cycle
Prophage
Bacteriophage DNA within a host cell
Lysogen/ lysogenic bacterium
Infected/ host bacterium in a lysogenic cycle
How does HIV become fatal?
Leads to AIDS which weakens the immune system
Infections can’t be fought against
Replication of RNA enveloped virus (5 steps)
- Glycoproteins binds to receptor on host cell
- Virus fuses with host cell membrane and capsid is digested
- Enzyme reverse transcriptase turns ssRNA into dsDNA in two cycles (RNA to RNA/DNA TO DNA/DNA)
- dsDNA incorporated into host genome (provirus)
- mRNA is transcribed
- viral proteins and envelope glycoproteins are produced and transported by vesicles to membrane
- new viruses are produced and bud from host cell with viral envelope glycoproteins
Describe an example of a pathogenic virus
H1N1 influenza virus
Single stranded RNA, enveloped
Fatal when spread to lungs
Describe an example of a pathogenic fungi
Trichophyton spp. (Ringworm)
Colonies spread and immune system responds with inflammation around the edges of the colonies
What is a prion?
A protein (smallest form of microbe we know of)
Example of pathogenic prion
Kuru
A misfolded prion which causes degenerative brain disease
Turns normal prions in the brain into pathogenic prions
Example of pathogenic Protozoa
Plasmodium app. (Malaria parasites)
Invade red blood cells and utilise the hemaglobin
Example of pathogenic helminth
Ancylostoma (hook worm)
Example of pathogenic bacteria
Bacillus anthracis
Gram-positive, forms endospores, rod-shaped
Fatal when gets into lungs
Kochs postulates (4)
- Pathogen must be present in every individual with the disease
- Sample can be grown in pure culture
- Pure culture causes same disease when injected
- Microorganism can be recovered from injected host
These demonstrate that a specific pathogen causes specific disease symptoms
Four key stages of microbial pathogenesis
- Adherence to host cells (skin or mucus)
- Invasion of host tissues
- Replication within host tissues
- Disease causing damage to host tissues
7 classes of bacterial virulence factors
Fimbriae- bind to host cells
Motility- flagella- burrow into tissue
Internalin-related proteins- enzymes to invade tissue
Siderophores- bind iron
Capsules- resist phagocytosis
Endotoxins- cause inflammation
Exotoxins- can be fatal
Endotoxins
LPS (lipopolysaccharides) components found in membrane of gram-negative bacteria
They are released after the bacterial cell is detected
Effects of endotoxins
Fever
Inflammation
Blood clotting
Shock
(Strong immune responses)
Exotoxins
And their three types
Produced within living bacteria, then released into surrounding medium
Cytotoxins
Neurotoxins
Enterotoxins
Cytotoxins
Type of exotoxin which causes lysis of red blood cells
Neurotoxins
Type of exotoxins which cause paralysis (prevents release of ACh at NMJ)
Enterotoxins
Type of exotoxin which effects the gut (like dysentery)
Idea of selective toxicity
Killing microbial cells but not the human host cells
Six bacterial cell components targeted by antibiotic classes
Inhibition of cell wall synthesis Inhibition of protein synthesis Disruption of cytoplasmic membrane Inhibition of general metabolic pathway Inhibition of DNA/RNA synthesis Inhibition of pathogens attachment or entry
Example of an antibiotic that targets call wall synthesis
How does it work?
Penicillin
Inhibits the formation of peptidoglycan cross-links in bacterial cell walls
(It does this by effecting the enzyme that facilitates the amino acid stitching of NAM-NAG)
Antibiotic resistance
Pathogens develop the ability to defeat the antibiotics designed to kill them
How do pathogens develop antibiotic resistance?
Natural selection- those with a specific mutation that allow them to survive the antibiotic multiply
Name of the enzyme produced by bacteria used to destroy penicillin
Beta lactamase
Two types of gene transfer
Vertical gene transfer- inherited genes from ‘parent’
Horizontal gene transfer- acquired genes from external sources
How do we reduce the development of antibiotic resistance? (3)
Avoiding antibiotics for viral infections (don’t use them every time you have a cold)
Improving antibiotics to be more specific to certain bacteria
Develop technology to tell if infection is viral or bacterial
What is the DNA form in a bacterium?
Single circular chromosome
Plasmids
Small, circular self-replicating molecules of DNA in the cytoskeleton
Separate to main chromosome
Three strategies of horizontal gene transfer
Transformation
Transduction
Conjugation
Describe transformative gene transfer
Uptake of short fragments of naked DNA by naturally transformable bacteria
Describe transduction gene transfer
Bacteriophages transfer DNA (plasmid) from one bacterium to another
Describe conjugative gene transfer
Transfer of DNA via a sexual pilus physically connecting two bacteria
(DNA has to be unwound before passing through)
