Bacteria Flashcards
(44 cards)
1
Q
Similarities between prokaryotic and eukaryotic cells
4
A
- Both have cell membrane
- Both have cytoplasm
- Both have ribosomes
- Both have DNA
2
Q
Features of prokaryotic cells e.g. bacteria
A
- cell wall made of peptidoglycan
- slime capsule
- plasmid
- flagellum
- pili
- 70S ribosomes
- mesosomes
- circular DNA
- unicellular
- no membrane bound organelles
- can reproduce asexually via binary fission
3
Q
Features of eukaryotic cells e.g. plant and animal cells
A
- nuclear membrane
- rough endoplasmic reticulum
- smooth endoplasmic reticulum
- golgi apparatus
- mitochondria
- centrioles
- 80S ribosomes
- lysosomes
- nucleolus
- linear DNA
- reproduce sexually via mitosis and meiosis
- has membrane bound organelles
- cell-surface membrane (made of cellulose in plants
4
Q
Differences between prokaryotes and eukaryotes
6
A
- Prokaryotes have no organelles but eukaryotes do
- Prokaryotes are smaller in size
- Prokaryotes have circular DNA in cytoplasm but eukaryotes have linear DNA in chromosomes in nucleus
- Prokaryotes have complex cell wall with peptidoglycan, eukarytoes have simple structure
- Prokaryotes can have capsules, frimbriae but eukaryotes don’t
- Prokaryotes have smaller ribosomes
5
Q
Characteristics of extremophiles
A
- Live in the most extreme conditions in the world
- High temperatures
- High salt
- Alkali
- Acid
- Digestive tracts
- Even in petrol!!!
- Abundant in the plankton of the open sea
6
Q
Characteristics of bacterial cell wall
A
- Bacterial cell walls are very rigid to protect the cell from rupturing
- This strength is provided by the mucopeptide peptidoglycan which is unique to bacteria
- The cell wall is antigenic, often contains toxic molecules and is a common site for antibiotic action (e.g. penicillin’s)
- Although all bacteria contain peptidoglycan there are 2 basic types of cell walls which differ in structure and composition
- Differentiated by a GRAM STAIN
7
Q
What are lipopolysaccharides
A
- Used by gram negative bacteria
- Otherwise known as endotoxin
- Important virulence factor, for evading phagocytosis and a barrier to certain antibiotics (e.g. penicillin)
8
Q
Chacteristics of gram negative bacterium cell wall
4
A
- have lipopolysacharides (endotoxin) on the outer membrane
- has an outer membrane that protects against the environment and some antibiotics
- the peptidoglycan is thinner so not so highly crosslinked
- 1nm thick
9
Q
Chacteristics of gram possitive bacterium cell wall
4
A
- have teichoic acid on the outside of the cell wall
- has no outer membrane that protects the peptidoglycan
- the peptidoglycan is thicker so highly crosslinked
- 10nm thick
10
Q
Why do bacteria produce capsules and slime layers
A
- Sticky substance made of polysaccharides/peptides or both
- Functions in survival (immune evasion of pathogens) and forming biofilms (attachment & communication),
- Protects against dehydration and may stop nutrients leaving the cell
CAPSULE = firmly attached and highly organised (all pathogens which cause meningitis have capsules) E.g. Streptococcus pneumoniae
S(LIME)- LAYER - unorganised and loosely attached e.g Pseudomonas aeruginosa
11
Q
Why do bacterial cells have flagella
A
- Long whip like structure required for motility
3 components: - long spiral filament made of many including flagellin and acts as a propeller
- attached to a hook which can transmit torque
- attached to motors that drive their rotation
12
Q
Why do bacterial cells have frimbriae/pilli
A
- Hair-like appendages, shorter, stronger and thinner than flagella
- Fimbriae/pili involved in forming biofilms and attachment of cells.
- Used for DNA transfer, called conjugation (bacterial sex) (how antibiotic resistance spreads)
13
Q
Why do bacterial cells have endospores
A
- Only in Gram positive Firmicutes e.g. bacillus and clostridia
- Endospore is a dormant (metabolically inactive) form of the bacterium which is highly resistant to adverse environmental conditions (high temperature, high UV irradiation, chemical or enzymatic destruction and antibiotics)
- When conditions are good again they can become active again
14
Q
How much smaller are viruses to bacteria
A
- 10-fold
- Bacteria 1- 2 micrometers vs Viruses 100 - 60 nanometers
15
Q
When were microorganisms first cultured
A
1880’s
16
Q
How did the tree of life start
A
- By Aristotle
- Started as plants and animals only
17
Q
Who made archaea a domain
A
Karl Woese
18
Q
Which type of bacteria is less vulnerable to antibiotics and why
A
- Gram negative bacteria
- Because the outer membrane with lipopolysacharides provides protection to the cell wall
19
Q
What are persisters
A
- They are a subpopulation of bacteria that are able to survive in stressful conditions, such as antibiotics, reactive oxygen, acid pH, or starvation
20
Q
What are the common shapes of bacterial cells
A
- Bacilli (rods)
- Cocci
21
Q
What is happening when bacteria enter the stationary phase of growth
A
Some bacteria are not growing
22
Q
How do bacteria divide
A
Binary fission
Logarithmic
23
Q
What are the 4 phases of bacterial growth
A
- Lag phase
- Exponential phase
- Stationary phase
- Death phase
24
Q
What happens during the lag phase of bacterial growth
A
- Slow growth
- Time required to start up cell functions
- Period which the chemical composition of the cells necessary for exponential growth is established
25
What happens during the exponential phase of bacterial growth
* Exponential growth
* Time when cells are growing at their maximum doubling time (µmax) in the conditions provided. Characterised by N = N(0)2^n
* Nutrients are in excess
* By consuming nutrients and releasing toxic chemicals the cells constantly modify the growth environment until it no longer supports rapid growth
26
What happens during the stationary phase of bacterial growth
- Numbers remain stable
- Stationary phase is characterised by a stable population consisting of some growing bacteria, some dying and some bacteria in stasis.
- There is a limiting factor
27
What happens during the death phase of bacterial growth
* Population decreases in size
* Cell death > cell growth
* Cells self destruct so other cells can feed off of it
28
What are the 5 ways to measure microbial growth
1. Directly
- Microscopically
- Flow cytometer (counts cells passing through a light detector)
- Plate counts (cultivation)
2. Indirectly
- Optical density (turbidity)
- Measuring respiration
29
What is dark field microscopy
A microscope in which an object is illuminated only from the sides so that it appears bright against a dark background
30
What is fluorescence microscopy
Any microscope that uses fluorescence to generate an image
31
What is flow cytometry
- Counts the number of particles
- Can be combined with dyes to determine numbers of viable bacteria
32
What is optical density
* Using a spectrophotometer
* The amount of light which can be transmitted through a bacterial culture can be measured.
* As the bacteria culture grows the turbidity increases and so does the optical density
33
How can bacteria be counted by measuring metabolic activity
* Measuring respiration (e.g. production of CO2, reduction of dyes)
34
Adv and disadv of counting bacteria using microscopy
Adv:
1. Cheap
Disadv:
1. human error
2. time consuming
3. not stable/moving making it difficult
35
Adv and disadv of counting bacteria using plate cultivation
Adv:
1. on a plate so can do further testing
Disadv:
1. not all bacteria can be cultured
2. error prone
36
Adv and disadv of counting bacteria using optical density
Adv:
1. efficient
Disadv:
1. can not identify what bacterial cells are alive or dead
2. cells can clump making it harder to count
37
Adv and disadv of counting bacteria by measuring respiration
Adv:
1. can identify if the cells are alive
2. good for antibiotic testing
Disadv:
1. can not identify how many cells are dead
38
Adv and disadv of counting bacteria using flow cytometry
Adv:
1. reproducible
2. fast
3. automated
Disadv:
1. expensive
2. special containment is needed if pathogens need to stay contained
39
What are the 3 ways to grow bacteria
1. Broth (liquid) - enrichment of bacteria and for performing growth curves
2. Agar (solid) - observe the colonial morphology which aids identification, assess purity of a culture
3. Sloppy agar (semi-solid) - demonstrates motility, preserving bacteria
40
What are the 5 ways of identifying bacteria
1. Colour
2. Shape
3. Size
4. Smell
5. Effect on media (e.g. haemolysis, colour change)
41
What are the 3 non-culturable bacteria
1. Syphilis
2. Leprosy
3. Chlamydia
42
Why are biochemical tests helpful
* Analysis of sugar fermentation products (acids, alcohol, gas, etc)
* Ability to utilise specific sugars
* Analysis of enzymes
* Growth under aerobic and anaerobic conditions
43
What are 3 modern molecular technologies for identifying bacteria
1. RTPCR - to find RNA instead of DNA then gel electrophoresis
2. Whole genome sequencing
3. Mass spectrometry
44
