Exam 2 MicroBio Study Guide

FA25

what are the 3 ways to control microbial growth

1. physical and chemical (disinfectants, anitseptics)

2. chemotherapeutic drugs (antibiotics, synthetic drugs)

3. immune system and vaccines (non specific mechanisms, specific mechanisms, prevention)

what is sterilization

all forms of microbial life are destroyed includes bacterial endospores and viruses (there are no degrees to sterilization)

what is disinfection

destroys microbes on inanimate objects, getting rid of harmful microbes, NOT sterile

what is antiseptic

“against infection”, chemical disinfection of living tissues, antiseptics do not destroy the living tissues

what is sepsis

refers to the bacterial contamination

what is asepsis

the absence of significant contamination (not sterile)

what is bacteriostatic

stops growth, but does not kill

what is bactericidal

kills microorganisms

what is germicide

chemical agents that kill microbes but not necessarily the endospores

what is degerming

the process of reducing the number of microorganisms on a surface or object, typically by mechanical means

what is sanitization

sanitization is the process of reducing the microbial population on a surface or object to a level that is considered safe for its intended use

what is biocide

a substance or agent that destroys, deters, or controls, the growth of harmful microorganisms

what is germicide

any chemical agent, substance, or process that destroys microorganisms

describe filtration and how it suppresses microbial growth

passage of a substance through a screenlike material with vacuum behind filter, used for heat-sensitive materials, removes microbes that are bigger than the filtration holes

describe low temperature and how it suppresses microbial growth

it has a bacteriostatic effect, refrigeration, deep-freezing, lyophilization (freeze drying)

describe high pressure and how it suppresses microbial growth

denatures proteins (even without heat)

describe desiccation and how it suppresses microbial growth

absence of water prevents metabolism

describe osmotic pressure and how it suppresses microbial growth

uses high concentrations of salts and sugars to create hypertonic environment, causes plasmolysis

describe moist heat

• boiling/free flowing steam

  • disinfects not sterilizes

• free flowing steam

• pressurized steam (autoclaving)

  • sterilizes, 15 min will kill all organisms and their spores

one of the best methods for sterilization

• Pasteurization - reduces spoilage organisms and pathogens by heating materials for a short time

describe dry heat

• flaming (until its red hot)

• incineration (burning it)

• hot air sterilization (oven for a long time)

compare the effectiveness of moist heat and dry heat

wet steam is shorter time and less temperature because it’s easier to transfer heat with water molecules in the air rather than dry air

what are the 3 types of radiation that kill cells

there are 3 types:

• ionizing radiation

• nonionizing radiation

• microwaves

how does ionizing radiation kill cells

• (X-rays, gamma rays, electron beams)

  • ionizes water to create reactive hydroxyl radicals

  • damages DNA by causing lethal mutations

how does nonionizing radiation kill cells

• (ultraviolet)

  • damages DNA by creating thymine dimers, they try to bond with DNA and damages it

how do microwaves kill cells

kill by heat, not especially antimicrobial, radiation but transfer energy into water molecules → heats → denatures

define genetics

the study of genes

define genome

all the genetic information in a cell

define chromosome

structures containing DNA that physically carry hereditary information

define genes

segments of DNA that encode functional products, usually proteins

define genetic code

the universal set of rules that cells use to translate the information encoded in genes (DNA or RNA) into proteins, the essential molecules for life

define genotype

the genes of an organism

define phenotype

the expression of genes

define genomics

the study of the complete genetic material (genomes) of microorganisms

describe the process of DNA replication

1. topoisomerase and gyrase relax the genes

2. helicase separates the strands (breaking hydrogen bonds)

3. replication fork is created

4. DNA polymerase adds nucleotides to the growing DNA strand in the 5’ → 3’ direction

5. DNA polymerase removes RNA primers, Okazaki fragments are joined by DNA ligase

describe protein synthesis

the essential process where DNA's genetic code is first transcribed into messenger RNA (mRNA) and then translated into amino acids at the ribosome, creating functional proteins

describe transcription

mRNA strand is made from DNA template

• RNA polymerase binds to the promoter sequence on the DNA

• new nucleotides added in 5’→3’

• transcription ends at the terminator sequence

describe translation

when mRNA is translated into protein

• translation starts at AUG

• ends at nonsense codons UAA, UAG, UGA

• tRNA molecules transport the required amino acids to the ribosome, they also have an anitcodon that base-pairs with the codon

describe RNA processing

primarily involves cleavage events and modifications of ribosomal RNA (rRNA), transfer RNA (tRNA), and messenger RNA (mRNA) to produce functional molecules or for degradation

gene expression

when the molecule the genes codes for has been produced

constitutive genes

they are expressed at a fixed rate (always expressed)

repressible genes

normally turned on and can be turned off

inducible genes

normally turned off and can be turned on

what does repression mean

inhibits gene expression and decreases enzyme synthesis

what does induction mean

turns on gene expression

what is an operon

set of operator and promoter sites and the genes they control

what is a promoter

start site - segment of DNA where RNA polymerase inititates transcriptoin of structural gene

what is an operator

traffic signal - segment of DNA that controls transcription of genes

what is the difference betwen antiseptic and disinfectant

antiseptics are applied to living tissues like skin to kill or inhibit microorganisms, while disinfectants are used on non-living surfaces such as countertops and medical equipment to kill pathogens

how to explain the results of the disk diffusion method

look for zone of inhibition around disks - how close the bacteria grows determines how resistant it is

compare protein synthesis between prokaryotes and eukaryotes

Protein synthesis is faster and coupled in prokaryotes, occurring simultaneously in the cytoplasm where transcription and translation are linked. In eukaryotes, transcription takes place in the nucleus, requiring mRNA processing, before being transported to the cytoplasm for translation

what is the regulation of the lac operon

structure: promoter, operator sites, structural genes, regulatory gene

inducible operon

what is the regulation of the trp operon

structure: promoter, operator sites, structural genes, regulatory gene

repressible operon

Explain pre-transcriptional regulation of gene expression in bacteria.

controls gene expression by influencing whether or not RNA polymerase can bind to the promoter and initiate transcription, using mechanisms like operator binding by repressors, activator proteins, and sigma factors

describe catabolite repression

• the level of glucose also affects the lac operon

• when glucose is depleted in a medium, ATP is low, so cAMP is high

• cAMP binds to the receptor protein which then binds to the lac promoter making it easier for the polymerase to bind and initiate transcription

• level of glucose controls catabolism of another sugar

• if glucose concentration is high, ATP is high. no cAMP so no expression of the lac operon (catabolite repression)

what is a mutation

a change in the genetic material (permanant), changes the genotype, may alter the phenoype

what can mutations be

neutral, beneficial, or harmful

what is a mutagen

agent that causes mutations

what is a spontaneous mutation

occur in the absence of a mutagen

what are the different types of mutations

• base substitution (point mutation)

  • missense mutation - base substitution results in change in an amino acid

  • silent mutation - base substitution results in NO change in amino acid sequence

  • nonsense mutation - base substitution results in a premature STOP codon

• base deletions and insertions

  • frame shift mutation - bases inserted and deleted results in a shift in the reading fram

what is gene transfer

movement of genetic information between organisms

what is recombination

combining genes (DNA) from two different cells, the resulting cells are called a recombinat

describe vertical gene transfer

occurs during reproduction or between generations of cells

describe horizontal gene transfer

the transfer of genes between cells of the same generation

describe ionizing radiation 

x rays and gamma rays causes the formation of ions that can oxidize nucleotides and break the deoxyribose-phosphate backbone

describe UV radiation (non ionizing)

causes thymine dimers

describe photolysases

separates thymine dimers (light repair)

what are the two different repairs for mutagens

photolyases - repairsultraviolet (UV)-induced DNA damage by splitting pyrimidine dimers (like thymine dimers), returning the DNA to its original form using blue light as an energy source

nucleotide excision repair - removes bulky, helix-distorting DNA lesions, such as those caused by UV radiation or chemical mutagens

what are the 3 ways for bacteria to transfer DNA

transformation, transduction, and conjugation (all horizontal gene transfer)

describe transformation

the uptake of DNA by a cell that is maintained in a heritable form

• competent cells - cells that can take up naked DNA

describe conjugation

• transfer of DNA via cell to cell contact

• requires conjugative plasmid

• F (fertility) factor - contains genes  for cell attachment and plasmid tranfer

• requires cell to cell contact and sex pilus

describe transduction

• DNA is transferred from a donor cell to a recipient via a bacteriophage (virus that infects bacteria)

what is generalized transduction

occurs with lytic viruses

accidental packing of bacteria into virus and sent into other bacteria

what is specialized transduction

occurs with prophages

when it separates from bacterial DNA, sometimes the virus has some bacterial DNA and is integrated into the new hosts DNA

what is the function of plasmids

self-replicating DNA molecules that carry genes providing beneficial traits, such as antibiotic resistance, and can be transferred between bacteria

what is the function of transposons

"jumping genes" — segments of DNA that can move from one location in the genome to another within the same cell or even to a different DNA molecule like a plasmid

describe the patterns of microbial death

if the death curve is plotted logarithmically, the death rate is constant

what are some factors that influence the effectiveness of microbial death

• the number of microbes - the more microbes, the longer it will take

• environmental influences - the presence of organic matter often inhibits the action of chemical antimicrobials

• time of exposure - often require extended exposure to affect more resistant microbes or endospores

• microbial characteristics - affect the choice of chemical and physical control methods

compare the effectiveness of moist heat and dry heat

mosit heat - kills microorganisms by coagulating proteins (denaturation) which is caused by breakage of hydrogen bonds that hold the proteins in their 3d structure, steam must contact items surface

dry heat - kills by oxidation effects, flaming, incineration, hot air sterilization

why is the lytic cycle used

viruses do not replicate on their own, they infect host cells to force cell to make copies.

what are the steps to the lytic cycle

1. attachment of phage to bacteria and it injects phage chromosome

2. breakdown of bacterial chromosome by phage specific enzyme

3. replication of phage chromosome

4. expression of phage genes to produce phage structural components

5. assembly of progeny phage particles

6. release of progeny phages by lysis of bacterial wall

what is a virulent phage

any phage that undergoes the lytic cycle

what is the lysogenic cycle

some viruses have a second cycle, lysogenic has lytic then lysogenic

1. phage DNA integrates into the bacterial chromosome, becoming a prophage

2. the bacterium produces normally, copying the prophage and transmitting it into daughter cells

3. a. many cell divisions produce a large population of bacteria infected. b. occasionaly a prophage exits the bacterial chromosome, initiating a lytic cycle

what factors determine if lytic cycle or lyspgenic cycle are activated

the concentration of viral particles (high concentration favors lysogeny), the state of the host cell (stress, DNA damage favors lytic), and environmental conditions like nutrient availability, temperature, and pH

why is time a factor when reducing bacteria

they do not all die at once they die logarithmically

do alcohols sterilze

NO they are disinfectants

what are the different types of sterilization

wet heat (autoclaving), dry heat, filtration, and radiation, and chemical methods, such as ethylene oxide (EtO) gas, hydrogen peroxide, and liquid chemical sterilants

why are autoclaves a good choice for sterlization

they use high-pressure steam to achieve high temperatures that effectively kill microorganisms, including bacteria, viruses, fungi, and spores. The steam penetrates materials better than dry heat, and the pressure raises the steam's temperature, allowing for faster and more efficient sterilization than methods like boiling