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bacterial growth Flashcards

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1
Q

what are cocci bacteria?

A

the simplest shape of bacteria
they are spherical e.g. staphylococcus aureus
the planes of division affect the shape of cells
the shape can vary

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2
Q

what are the different forms of cocci bacteria?

A

formed from different planes of division
diplococci is 2 spheres
streptococci is a chain of spheres
tetrad is 4 spheres
sarcinae is 8 spheres (4 on top of 4)
staphylococci is a big ball of spheres

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3
Q

what are rod bacteria and what are the different forms of rod bacteria?

A

elongated cells e.g. E. coli
they can be single (single bacillus)
2 rods (diplobacilli)
a chain of rods (streptobacilli)
or clumps of rods (coccobacillus)

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4
Q

how do curved bacteria form and how is their shape maintained?

A

filaments in the cytoskeleton are all arranged on one side of the cell e.g. vibrio cholerae
the shape is maintained through generations as the cell divides the distribution of filaments is conserved

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5
Q

how do spiral bacteria form?

A

they have a filament in the cell membrane that allows them to move in a corkscrew motion
e.g. titanospirillum velox

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6
Q

what are exotic-shaped bacteria and how do they form?

A

randomly shaped bacteria
have many appendages that give them strange shapes

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7
Q

what is the morphology of bacteria through their cell cycle?

A

they can exist as swarmer cells that are curved and can move through their environment
they form a stalk that extends and allows the cell to adhere to surfaces
when the cell is anchored to a surface it undergoes asymmetrical division
the stalk remains the same and the rest of the cell generates a daughter cell called a swarmer progeny cell

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8
Q

how does the size of bacteria give them an advantage?

A

the size of bacteria varies depending on the strain but they are usually small
this gives them a larger surface area to volume ratio
this maximises nutrient exchange for growth
the intracellular nutrient content is more concentrated which speeds up enzymic reactions
evolution is faster as they take less energy to divide and there is a higher selection rate of mutations

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9
Q

how does the colour of bacteria give them an advantage?

A

a lot of bacteria produce pigments e.g. staphylococcus aureus produces the pigment staphyloxathin giving it a yellow colour
these pigments often have a role in the immune response of bacteria or act as an antioxidant

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10
Q

what causes bacteria to have a smell?

A

the smell is usually from secondary metabolites produced from the bacteria and is specific to the strain

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11
Q

how are chromosomes arranged in bacteria?

A

always double stranded DNA
mostly single chromosome
vary in size
the bacterial genome is smaller than eukaryotes
the chromosomes are described as nucleoid because they are highly compacted in the cell by supercoiling and complexing with proteins

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12
Q

how are plasmids arranged in bacteria?

A

always double stranded DNA
variable copy number, large plasmids make less copies as it takes more energy
important for horizontal gene transfer for evolution
they carry genes for antibiotic resistance which can be spread between cells during transfer

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13
Q

what is the structure of bacterial genes?

A

no introns
continuous open reading frames so fewer isoforms
they have operons so one transcript codes for a series of proteins
their genes are smaller than eukaryotes

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14
Q

what are operons?

A

a functional unit of DNA containing multiple genes that are controlled by a single gene promotor

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15
Q

how does transcription occur in bacteria?

A

there is only one polymerase that has different adaptors for the transcription of certain sets of genes
the transcription site is in the cytoplasm and there is no modification of the mRNA

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16
Q

how is transcription initiated in bacteria?

A

the polymerase scans the DNA and forms a lose complex
the sigma factor (an adaptor) assembles from different subunits and recognises the start codon
it binds to DNA upstream of the start codon and unwinds it forming an open complex where the polymerase starts transcription

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17
Q

what are the 2 methods that bacteria use to terminate transcription?

A

rho-independent and rho-dependent
they both depend on specific sequences in RNA

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18
Q

what is the rho-independent method of transcription termination?

A

it requires a palindromic GC-rich sequence located upstream from a AT-rich sequence
the GC-rich sequence is transcribed and forms a hairpin loop structure
the hairpin loop and AT-rich sequence cause the polymerase to fall apart

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19
Q

what is the rho-dependent method of transcription termination?

A

rho proteins form hexamers (made up of 6 subunits) that recognise and bind to a GC-rich sequence
they wrap around the RNA and unwind the RNA-DNA duplex and release the RNA polymerase

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20
Q

how is translation controlled in bacteria?

A

it is performed by ribosomes and tRNA but it happens at the same time as transcription
as mRNA is being transcribed ribosomes are attached and perform translation
bacterial ribosomes are 70S (eukaryotic are 80S)

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21
Q

how is the metabolism of bacteria controlled?

A

needs an energy source, electrons and carbon
bacteria can combine sources of energy
electrons and carbon can be extracted from organic or inorganic molecules

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22
Q

what are the different metabolic types of bacteria?

A

phototrophs use sunlight for energy
chemotrophs use preformed molecules for energy
organotrophs use organic sources for electrons (methane)
lithotrophs use inorganic sources for electrons (sulfur, nitrates)
heterotrophs use organic sources for carbon (amino acids, carbohydrates)
autotrophs use inorganic sources for carbon (CO2)

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23
Q

what is the gram stain used for?

A

to check if a sample contains more than one strain of bacteria and used to tell what type of bacteria is present
used in hospitals

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24
Q

what is the method for gram staining?

A
  1. a culture cell suspension is taken and spread onto a glass slide
  2. when the cells have dried a crystal violet stain is added which penetrates the surface of the bacterium
  3. iodine is added to complex with the crystal violet dye
  4. the sample is washed with alcohol or acetone to dissolve the cell envelope
  5. a counter stain such as safranin is added
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25
what are the 2 results you can get from a gram stain?
cells are either stained violet if they are gram positive or pink if they are gram negative
26
what is the main difference between gram positive and gram negative bacteria?
gram positive bacteria have a thick peptidoglycan layer and no outer membrane gram negative bacteria have a thin peptidoglycan layer and an outer membrane
27
how does crystal violet dye stain gram positive and negative bacteria differently?
in gram positive bacteria the crystal violet dye goes into the cell wall and complexes with iodine forming a purple colour in gram negative bacteria crystal violet dye binds to the outer membrane and is dissolved by alcohol so when safranin is added it will form a pink colour
28
what is the structure of S-layers?
made up of proteins that self-assemble into a crystalline network that surrounds the cell non-covalently bound to the cell surface
29
what are the differences between the S-layer in gram positive and gram negative bacteria?
in gram positive bacteria the S-layer can interact directly with peptidoglycan or with cell wall polymers that are attached to peptidoglycan in gram negative bacteria the S-layer is bound to lipopolysaccharides in the outer cell membrane via binding domains
30
what is the structure and role of capsules?
made up of polysaccharides (carbohydrates) sometimes made up of amino acids they are covalently bound to peptidoglycan in gram positive covalently bound to outer membrane in gram negative they keep the cell surface hydrated and provide resistance against host phagocytes and bacteriophages (virulence)
31
what is the structure and role of the exopolysaccharide layer in bacteria?
made up of polysaccharides not covalently bound to the cell surface they initiate the production of biofilm for cells to prevent the access of pathogens (virulence)
32
what is xanthan gum?
the exopolysaccharide layer of the bacteria xanthomonas compestris
33
what is the structure of outer membranes in gram-negative bacteria?
asymmetrical phospholipid bilayer proteins such as porins (form channels) lipoproteins such as braun lipoprotein (covalently linked to peptidoglycan) LPS (activates immune system)
34
what is the structure and role of peptidoglycan?
dynamic 3D structure, elastic many layers in gram-positive single layer in gram-negative maintains the shape of the cell and forms the exoskeleton it is resistant to osmotic stress only present in bacteria
35
36
how is peptidoglycan targeted by things outside the cell?
used by polymers as an anchoring point targeted by antibiotics
37
what is the structure of the cytoplasmic membrane in bacteria?
symmetrical phospholipid bilayer composition of polar head varies contains transport proteins and hopanoids
38
what are hopanoids in the cytoplasmic membrane of bacteria?
cyclic molecules that maintain fluidity and permeability of the membrane
39
what happens to bacterial growth at the minimum temperature?
metabolic reactions start happening the membrane becomes less fluid and more rigid
40
what happens to bacterial growth as the temperature increases and at the optimum?
as temperature increases so does the rate of metabolic reactions metabolic and growth rate is highest at the optimum temperature
41
what happens to bacterial growth at the maximum temperature?
proteins are denatured and the cytoplasmic membrane is damaged due to thermal lysis (breaking the cell wall)
42
what are psychrophiles and thermophiles?
psychrophiles are bacteria that have a low optimum temperature thermophiles are bacteria that have a high optimum temperature
43
how are psychrophiles adapted to growing at low temperatures?
increased membrane fluidity more unsaturated fatty acids antifreeze proteins and cryoprotectants enzymes have more alpha helices so more flexible
44
how are thermophiles adapted to growing at high temperatures?
supercoiled DNA and G-C rich stabilises DNA ether-linked phospholipids and single lipid bilayer makes membrane more stable thermostable proteins with more ionic bonds protein repair systems
45
what are acidophiles, alkaliphiles and neutrophiles?
acidophiles are bacteria that grow best in acidic conditions alkaliphiles are bacteria that grow best in alkaline conditions neutrophiles are bacteria that grow best in neutral pH
46
how are acidophiles adapted to growing in areas with a high concentration of protons?
membrane more stable and less permeable DNA/protein repair systems use protons as exchangers (antiporters) they have a flagella that is powered by protons reverse membrane potential (more potassium ions)
47
how are alkaliphiles adapted to growing in areas with a low concentration of protons?
they grow in area rich in sodium ions which they use in metabolic reactions such as powering the flagella and generating ATP high affinity transporters for cations
48
how do bacterial cells react to being in an area with a low concentration of ions (hypotonic)?
the cell maintains a similar condition and the cell wall prevents the cell bursting when water moves in
49
how do bacterial cells react to being in an area with a high concentration of ions (hypertonic)?
the ions are concentrated within the cell and water moves out
50
what are halophiles, halotolerants and non-halophiles?
halophiles are bacteria require a high salt concentration/high osmolarity for growth halotolerants are bacteria that can grow in high salt concentrations but their optimum is a low salt concentration non-halophiles are bacteria that require a low salt concentration/low osmolarity for growth
51
how are halophiles adapted to growing in areas with a high salt concentration?
produce counteractive solutes to balance osmotic pressure aquaporins regulate water movement ions stabilise S-layer have osmolites
52
what are reactive oxygen species (ROS)?
derivatives of oxygen that are toxic to cells e.g. superoxide, hydrogen peroxide and hydroxyl radical
53
how are aerobic bacteria adapted to protect themselves against ROS?
they contain enzymes that detoxify ROS by converting them into water
54
what are obligate and facultative aerobes?
obligate aerobes are bacteria that need oxygen to survive facultative aerobes are bacteria that can survive with or without oxygen both contain ROS enzymes
55
what are microaerophiles?
bacteria that need a very specific concentration of oxygen to survive they dont use ROS enzymes
56
what are aerotolerant anaerobes and obligate anaerobes?
aerotolerant anaerobes are bacteria that dont need oxygen to survive but still contain some ROS enzymes obligate anaerobes can't survive in oxygen and dont contain ROS enzymes
57
why is bacterial growth always logged on a graph?
bacterial growth is exponential
58
what happens in lag phase (stage 1) of a bacterial growth curve and what does it look like on the graph?
metabolism starts but there is no cell division it is the flat part at the start of the graph
59
what happens in log phase (stage 2) of a bacterial growth curve and what does it look like on the graph?
there is an exponential increase in the bacterial population this is where the graph increases
60
what happens in stationary phase (stage 3) of a bacterial growth curve and what does it look like on the graph?
microbial deaths and the number of new cells produced are equal this is the flat part of the graph in the middle
61
what happens in death phase (stage 4) of a bacterial growth curve and what does it look like on the graph?
the population decreases this is where the graph decreases at the end
62
what is the thermal death point and thermal death time of bacteria?
thermal death point: the minimal temperature at which all organisms are killed in 10 minutes in a liquid thermal death time: the minimal time to kill all bacteria in a liquid at a given temperature
63
how does heat kill bacteria?
by dissolving the cytoplasmic membrane
64
what are 4 methods of killing bacteria?
moist heat dry heat pasteurisation ionizing radiation
65
how is ionizing radiation used to kill bacteria and when is it used?
DNA is destroyed by double strand breaks and reactive oxygen species produced by removing electrons it uses gamma and X-rays used in the food industry and to sterilise medical equipment
66
how is non-ionizing radiation used to kill bacteria and when is it used?
DNA damaged by double strand breaks and illegitimate base pairing it uses UV rays used to decontaminate surfaces
67
when is filtration used to kill bacteria and what are the most common filters?
used to sterilise air or liquids that would be damaged by heat nucleopore and membrane filters are used to remove bacteria from a solution depth filters are used for gases
68
what are bacteriostatic, bactericidal and bacteriolytic antimicrobial agents?
bacteriostatic agents: stop the growth of bacteria and stop them multiplying bactericidal agents: stop the growth of bacteria and kill them bacteriolytic agents: stop growth of bacteria, kill them and destroy them using lytic enzymes
69
what are sterilants, disinfectants and antiseptic and germicide antimicrobial agents?
sterilants: completely destroy all forms of bacteria including spores disinfectants: kill bacteria but not spores antiseptics and germicides: inhibit the growth of or kill bacteria but not spores (only ones used on living tissue)
70
what are phenolic compounds, when are they used and how do they kill bacteria?
aromatic derivatives used for odour control in sewers and as a local anaesthetic it disrupts the cytoplasmic membrane and denatures proteins
71
how do alcohols kill bacteria and what is the active concentration?
denature proteins and dissolve lipids disrupting the cytoplasmic membrane active concentration is between 60-85%
72
what are aldehydes, how do they kill bacteria and what else are they used for?
alkylating agents modify proteins and DNA causing cell death can be used to preserve biological samples
73
what are quaternary ammonium compounds and how do they kill bacteria?
derivatives of ammonium interact with phospholipids in the cytoplasmic membrane used as detergents
74
what are the 2 types of halogen releasing agents and how do they kill bacteria?
chlorine-releasing agents: form chlorinated bases in DNA and oxidise proteins e.g. bleach iodine-releasing agents: target DNA and proteins
75
how can bacteria resist antibiotics?
using enzymes to hydrolyse or modify the antibiotics to inactivate them prevent antibiotics from entering the cell prevent the antibiotics from reaching their target targeting the antibiotic to affect a different pathway
76
how does antibiotic resistance happen?
they are overused and misused
77
what does an antibiotic need to be successful?
it must be selectively toxic so it only kills bacteria it must inhibit the pathogenesis or virulence of bacteria it must be stable and effective it mist be cost-effective
78
what are beta-lactams and how do they work?
they bind covalently to D, D-transpeptidases to stop peptidoglycan being assembled and synthesised
79
how are bacteria resistant to beta-lactams?
they contain enzymes called beta-lactamases that hydrolyse beta-lactams they develop low affinity penicillin binding proteins that bind to beta-lactams and prevent them binding to their target
80
how are gram-negative bacteria resistant to antibiotics?
they have transporters remove beta-lactams and target them to a different pathway they can overproduce different systems to secrete beta-lactams from the bacteria
81
what did Pasteur, Koch and Fleming theorise and discover?
Pasteur suggested the theory of germs Koch suggested the relationship between microbes and diseases Fleming discovered penicillin

Microbiology (9 decks)

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