Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Medical Microbiology > Chapter 8 - Microbial Genetics and Antibiotic Resistance > Flashcards

Chapter 8 - Microbial Genetics and Antibiotic Resistance Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What is a genotype?

A

An organisms genetic makeup (DNA)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a phenotype?

A

The expressed properties that are encoded in the genotype

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is vertical gene transfer?

A

The flow of genetic information from one generation to the next (parent to offspring)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is semiconservative replication?

A

Each new double-stranded DNA molecule contains one original strand and one new strand

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the process of transcription in prokaryotes?

A

Initiation: RNA polymerase binds to the promoter, and DNA unwinds at the beginning of a gene

Elongation: RNA is synthesized by complementary base pairing of free nucleotides with the nucleotide bases on the template strand of DNA

Termination: Transcription reaches the terminator, RNA and RNA polymerase are released, and the DNA helix re-forms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is mRNA?

A

Messenger RNA

Synthesized during transcription

Carries coded information for making proteins to the ribosomes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is rRNA?

A

Ribosomal RNA

Forms part of the ribosomes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is tRNA?

A

Transfer RNA

Binds to and carries correct amino acids and adds them to the polypeptide chain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the process of translation?

A

tRNA carrying first amino acid is paired with the start codon on the mRNA
- First tRNA moves to the P site and a tRNA carrying the second amino acid enters the A site

First amino acid joins the second by a peptide bond

Ribosome moves along the mRNA unitl the second tRNA is in the P site
- Next codon to be translated is brought into the A site
- First tRNA now occupies the E site

Second amino acid joins to the third by another peptide bond, and the first tRNA is released from the E site

Ribsoome continues moving along the mRNA. and new amino acids are added to the polypeptide

When ribosome reaches a stop codon, the polypeptide is released

The last tRNA is released, and the ribosome comes apart
- Released polypeptide folds into a protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is a promoter?

A

The starting site on a DNA strand for transcription of RNA by RNA polymerase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a sense (coding) strand?

A

Strand of DNA that encodes a protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is an anti-sense (complementary) strand?

A

DNA strand that does not encode a protein but is complementary to the coding strand

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the differences between prokaryotic and eukaryotic DNA?

A

Prokaryote:
- Single circular chromosome in nucleoid
- Small
- Typically single copy
- Asexual reproduction - binary fission
- No introns in DNA
- Sometimes overlap control/operons

Eukaryote:
- More than 1 chromosome in nucleus
- Diploid (2 copies)
- Linear
- Histone packing
- Sexual reproduction - mitosis/meiosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are plasmids?

A

Piece of extra-chromosomal DNA found in prokaryotes

Circular and supercoiled

Easily transferred

No standard size - can be large or small

Non-essential genes

Collect genes that are deeemed valuable - antibiotic resistance, selective advantages, genetic flexibility, toxins, etc.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is an inducible operon, an example of one, and how does it work?

A

Starts off, transcription must be turned on

Ex: lac operon

Repressor active, operon off - normal state of inducible operon is off
- lacI gene is transcribed and translated into a repressor protein
- Repressor binds to the operator, which physically blocks RNA polymerase from transcribing

Repressor inactive, operon on - lactose enters the cell and is converted into allolactose
- Inducer molecule, allolactose, binds to the repressor protein, which inactivates the repressor - can no longer block transcription
- Structural genes are transcribed, leading to the production of enzymes needed for lactose catabolism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a repressible operon, an example of one, and how does it work?

A

Start in on position, gets turned off

Ex: trp operon

Repressor inactive, operon on
- Repressor is inactive, so transcription and translation proceed, leading to the synthesis of tryptophan

Repressor active, operon off
- When the corepressor tryptophan binds to repressor protein, the activated repressor binds with the operator, preventing transcription from the operon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is recombination?

A

New chromosome with a genotype different from that of the parent results from the combination of genetic material from two organisms

This new arrangement of genes is usually accompanied by new chemical or physical properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the 3 types of recombination?

A

General recombination
- Reciprocal exchange of DNA between a pair of DNA sequences
- Anywhere on chromosome
- Typified by the exchanges occurring in bacterial transformation, bacterial recombination, and bacterial transduction

Site-specific recombination
- The integration of a viral genome into the bacterial chromosome

Replicative recombination
- The movement of genetic elements as they switch position from one place on the chromosome to another

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is natural selection?

A

The surivial and reproduction of bacteria with a new genotype that is favored by natural environments

Results in huge diversity of microbes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is a mutation?

A

Permanent change in the base sequence of DNA

Genotypic change can result in phenotypic change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the 3 main categories of mutations?

A

Base substitution - single base in the DNA sequence is replaced with a different base

Insertion - an extra base is added in the DNA sequence

Deletion - a base is removed from the original DNA sequence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the 4 types of mutations that result from base substitutions, insertions, or deletions?

A

Nonsense - generates a stop codon that wasn’t there before

Missense - causes a change in amino acid

Silent - nucleotide changes but the amino acid doesn’t change

Frameshift - changes the codon reading frame

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is a spontaneous mutation?

A

A mutation that occurs randomly because of mistakes made during DNA replication

Occur in the absence of mutation-causing agents

24
Q

What are mutagens?

A

Agents in the environments, like chemicals and radiation, that directly or indirectly bring about mutations

25
Q

What are the 3 types of chemical mutagens?

A

Cause base substitutions

Nucleoside analogs
- Mimic a nucleoside and is put in instead of a normal one
- As next strand replicates, it puts in a new base

Nucleotide-altering chemicals
- Change the actual structure of the nucleotide - cleave off important pieces to change base

Frameshift mutagens
- Puts itself into double stranded DNA so it becomes incorporated into the DNA

26
Q

What are the 2 types of radiation mutagens?

A

Cause large-scale mutations

Ionizing radiation
- Form free radicals that cause single or double strand breaks in DNA

Nonionizing radiation
- Cause cross-links between adjacent pyrimidies (dimers)
- Exposure to UV light causes adjacent thymines to form a dimer, which disrupts their normal base pairing

27
Q

What is mutation rate?

A

The probability that a gene will mutate when a cell divides

28
Q

How do mutagens affect mutation rates?

A

Increase the rate of mutation from the spontaneous rate (1 in 10^6) to 1 in 10^5 - 10^3

29
Q

How does positive (direct) selection of mutants work?

A

Detection of mutant cells by rejection of the unmutated parent cells

Expose bacterial cells to an environmental change, and those who are mutated to survive in environment will live and those who are unmutated will die, indicating which are mutants

30
Q

How does negative (indirect) selection work?

A

Selects a cell that cannot perform a certain function

Uses replica plating

31
Q

What is the process for replica plating?

A

Bacteria culture spread on nutrient agar plate (both mutant and non-mutant will grow) this is MASTER PLATE

Master plate pressed onto sterile velvet - picks up some cells of every colony

Velvet pressed on two agar plates, one nutrient agar and one with the environmental conditions you are testing for mutation

Replica plates are then incubated, allowing cells to grow and form colonies

Results: Prototrophs grow on both types of media, auxotrophs only grow on nutrient agar

32
Q

What is an auxotroph?

A

A mutant microbe that has a nutritional requirement that is absent in the parent

33
Q

How would you select for antibiotic resistant bacteria?

A

Positive (direct) selection

Plate bacteria on a medium containing antibiotic

The few cells that have an antibiotic-resistant mutation will grow and form colonies, whereas the normal susceptible bacteria will not grow

34
Q

What is a carcinogen?

A

Substances that cause cancer in animals/humans

35
Q

What is the process for an Ames test, and what is it used for?

A

Uses bacteria to assess the mutagenic potential of chemical compounds

Based on observation that exposure of mutant bacteria to mutagenic substances may cause new mutations that reverse the effect of original mutation (reversions)
- Specifically measures reversion of histidine auxotrophs of Salmonella to histidine-synthesizing cells

Steps:
- 2 cultures are prepared of Salmonela that have lost ability to syntehsize histidine
- Suspected mutagen is added to experimental sample only
- Rat liver extract (activator) is added to both samples
- Each sample is poured onto a plate of medium lacking histidine and are incubated for 2 days
- Only bacteria whose histidine-dependent phenotype has mutated back to histidine-synthesizing will grow into colonies
- Test plates will show an increase in the number of histidine-synthesizing revertants if the test chemical is indeed a mutagen and potential carcinogen

36
Q

What is horizontal gene transfer?

A

Passage of genes to other microbes of the same generation

37
Q

What is crossing over?

A

Cell picks up foreign DNA and some of it inserts into the cell’s chromosome

Some of the genes carried by the chromosome will be shuffled

38
Q

What are the 3 mechanisms for horizontal gene transfer?

A

Transformation

Transduction

Conjugation

39
Q

What is transformation?

A

“Naked” DNA enters into another cell and can provide new genes to the cell

Recipient cell takes up donor DNA that is in the environment after another cell dies
- Donor DNA aligns with complementary bases
- Recombination occurs between donor DNA and recipient DNA

40
Q

What was Griffith’s experiment and what did it prove?

A

Demonstrated genetic transformation

Experiment:
- Living encapsulated bacteria injected into mouse – mouse died – colonies of all encapsulated bacteria were isolated from dead mouse
- Living nonencapsulated bacteria injected into mouse – mouse lived – a few colonies of nonencapsulated bacteria were isolated from mouse; phagocytes destroyed nonencapsulated bacteria
- Heat-killed encapsulated bacteria injected into mouse – mouse remained healthy – no colonies were isolated from mouse
- Living nonencapsulated and heat-killed encapsulated bacteria injected into mouse – mouse died – colonies of encapsulated bacteria were isolated from dead mouse

41
Q

What is transduction?

A

By a bacterial virus, DNA passed from one bacteria to another in a bacteriophage and then incorporated into the host DNA

Phage injects its DNA
- Phage enzymes degrade host DNA
- Cell synthesizes new phages that incorporate phage DNA and, mistakenly, some host DNA
- Transducing phage injects donor DNA
- Donor DNA is incorporated into recipient’s chromosome by recombination

42
Q

What is conjugation?

A

Plasmids transferred via a pilus

Donor cell attaches to a recipient cell with its pilus
- Pilus may draw cells together
- One strand of F plasmid DNA transfers to the recipient
- The recipient synthesizes a complementary strand to become an F+ cell with a pilus; the donor synthesizes a complementary strand, restoring its complete plasmid

43
Q

How do plasmids contribute to gene transfer?

A

Conjugation - donor bacterium transfer a plasmid to recipient through pilus
- Plasmids contain genes that have been collected because they are beneficial, these genes are then incorporated into the recipient

Transformation - plasmids can be released into the environment when bacteria die and lyse, allowing other bacteria to take up the plasmids and incorporate its genetic material

44
Q

How do plasmids contribute to resistance?

A

Plasmids often contain genes that provide resistance to antibiotics

Plasmids can move between bacteria through horizontal gene transfer, which allows different bacteria to take up these genes - spreads resistance rapidly

45
Q

What are 5 types of genes that plasmids carry?

A

Antibiotic resistance: resistance factors are plasmids that contain genes for antibiotic resistance

Virulence genes: some plasmids encode proteins that enhance pathogenicity of a bacterium

Metabolic genes: dissimilation plasmids code for enzymes that trigger catabolism of certain unusual sugars and hydrocarbons

Fertility genes: F factor is a conjugative plasmid that carries genes for sex pili and for the transfer of the plasmid to another cell

Bacteriocin genes: Some plasmids contain genes for synthesis of bacteriocins, which are toxic proteins that kill other bacteria

46
Q

Are plasmids essential for survival?

A

Not necessarily essential for the normal survival of bacteria, but they provide significant advantages under certain conditions, such as antibiotic presence or some environmental stresses

Can enhance bacterial adaptability and survival in different environments, but bacteria can survive without them in normal living conditions

47
Q

What are transposons and how do they contribute to the movement of genes within and between organisms?

A

What:
- Segments of DNA that can move from one region of DNA to another
- Contain a gene for an enzyme (transposase) for cutting and resealing DNA (cut piece of DNA out of one place in chromosome and insert in another)
- Simple transposons only carry essential elements
- Complex transposons carry other genes (i.e. selective advantage such as antibiotic-resistant gene)

How:
- Transposon is excised from original location and inserted into a new site in the genome - can disrupt genes at new site and deactivate them
- May be carried between cells on plasmid or viruses, so they can spread from one organism to another through horizontal gene transfer

48
Q

How do genetic mutation and recombination contribute to natural selection?

A

Genetic mutation and recombination create diversity in future cell generations

Diversity provides the raw material for evolution, and natural selection is its driving force

Natural selection will act on diverse populations to ensure the survivale of those fit for that particular environment

49
Q

What are the 6 ways in which DNA is manipulated through recombinant DNA technology?

A

Restriction enzymes
- Cut DNA at specific sites in a specific way
- DNA from another place can be incorporated into cut DNA and sealed with ligase to create new DNA sequence

Vector
- Usually plasmids or phages that we use to transfer DNA

PCR
- Amplify and synthesize genes

Inserting foreign DNA into cells
- Transformation, electroporation, protoplast fusion
- Gene gun and microinjection

Libraries (cDNA and genomic)
- Genomic - take one organisms genome and chop it up with restriction enzymes and seal it into vectors, which you can then try and pull genes out
- cDNA – express genes and get mRNA and create a library in the same way as genomic

Selection of a clone

50
Q

How does natural selection for antibiotic resistance work?

A

Starting point is a large bacterial population mainly consisting of bacteria that are susceptible to antibiotics and a couple of bacteria that are antibiotic-resistant by chance
- A bactericidal antibiotic is added, which kills most of the susceptible bacteria in the population, which the resistant bacteria survives
- Only the resistant will continue to proliferate in the presence of the antibiotic and increases in number over time
- End result is a population of mainly resistant bacteria

Selection can occur at any site in the body to which the antibiotic reaches
- Antibiotic can select for resistance genes and mechanisms in both pathogenic bacteria and in commensal bacteria living in the body that have nothing to do with the infection in question

51
Q

What is the selective pressure for antibiotic resistance?

A

In presence of antimicrobial, microbes are either killed or, if they carry resistance genes, survive

Survivors will replicate, and their progeny will quickly become the dominant type throughout the microbial population

52
Q

How does mutation impact antibiotic resistance?

A

Most microbes reproduce by dividing every few hours, allowing them to evolve rapidly and adapt quickly to the new environmental conditions

During replication, mutations arise and some of these mutations may help and individual microbe survive exposure to an antimicrobial

53
Q

What are the 4 mechanisms of antibiotic resistance?

A

Blocking entry – slow or prevent entry of drug into the cell

Inactivation of antibiotic by enzymes – production of enzyme that destroys or deactivates drug

Alteration of target molecule – alter target of drug so it binds less effectively
- If antibiotic is supposed to bind to a specific target, but the target’s conformation is changed, it prevents binding

Efflux of antibiotic – pump antimicrobial drug out of cell before it can act

54
Q

What are the 7 contributing factors to development of antibiotic resistance?

A

Overuse

Inappropriate prescribing

Societal pressures

Inadequate diagnostics – “just-in case” or too broad

Hospital use – fertile environment

Agricultural use

Limited availability of new antibiotics

55
Q

What are the 4 ways to combat the development of antibiotic resistant bacteria?

A

Preventing infections, preventing the spread of resistance
- Proper individual hygiene to prevent infection so antibiotics are not needed

Tracking by CDC

Improving antibiotic prescribing/stewardship
- Only prescribing when absolutely necessary
- Not asking doctor for antibiotics when they’re not needed
- Not taking antibiotics from previous illness “just in case”

Developing new drugs and diagnostic tests

Medical Microbiology (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions