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biosci 101 > Microbiology > Flashcards

Microbiology Flashcards

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1
Q

What is the difference between gram + and gram - bacteria?

A

Gram + bacteria has a thick peptidoglycan layer (which is its cell wall) which traps crystal violet and masks the safranin dye
Gram - bacteria has a thin peptidoglycan layer followed by an upper layer of a second membrane with the phosphate heads covered in carbohydrates, the crystal violet easily washes away and the safranin shows through

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2
Q

What are the three ways of categorising bacteria based on energy source, carbohydrate source and oxygen requirements?

A

phototroph, chemotroph
autotroph, heterotroph
aerobic, anaerobic

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3
Q

Define symbiosis

A

ecological relationship between two species in close contact

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4
Q

What are the three symbiosis relationships?

A

Mutualism - both prokaryote and host benefit off of each other
Commensalism - one species benefits, the other is neither harmed or helped
Parasitism - one species benefits and host is harmed (usually not killed tho)

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5
Q

What environment did Prokaryotes originate from?

A

hot and anaerobic

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6
Q

What are the two lineages of prokaryotes?

A

Bacteria and archaea

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7
Q

What features of the archaea are similar to eukaryotes?

A

no peptidoglycan
several RNA molecules
has introns
sometimes has histones

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8
Q

What is an odd feature of archaea?

A

They can grow at very high temperatures

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9
Q

What issues does the biofilm that bacteria produce cause?

A

medical issues - antibiotic resistance

industrial issues - fonterra

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10
Q

How does the bacteria living on humans benefit us?

A 
digests food 
synthesis of vitamins 
metabolizes drugs 
defence against pathogens 
activates and supports the immune system
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11
Q

Did the flagellum of the eukaryote and prokaryote evolve from each other?

A

No - eukaryotes do not have a motor

proteins and mechanism of both flagellum are different

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12
Q

What are the two methods of regulating transcription?

A

1) the degree of condensation of chromosomal DNA - eukaryotes only - chromatin is ‘puffed’ out
2) regulation by specific DNA binding proteins - both prokaryote and eukaryotes, this switches transcription on or off

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13
Q

What is the most common way of controlling gene expressions?

A

Transcriptional control

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14
Q

What are the two ways that bacteria respond to their environmental changes?

A

1) Modify the activity of enzymes already made

2) Alter the enzymes being produced (transcriptional control)

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15
Q

What is the enzyme that breaks down lactose into galactose and glucose?

A

Beta-galactosidase

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16
Q

What is an operon?

A

Genes that are grouped close together and code for proteins with related functions

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17
Q

What is laci?

A

lac repressor (regulatory gene), which codes for an active repressor protein that binds to the operator to prevent RNA polymerase from binding to it.

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18
Q

What is the lac promoter?

A

Area on DNA where RNA polymerase binds

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19
Q

What is the lac operator?

A

control region

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20
Q

What is the lac Z?

A

Region of DNA which codes for Beta galactosidase

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21
Q

What is the lac Y?

A

lac permease

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22
Q

What is the lac A?

A

acetylase

23
Q

What is a POLYCISTRONIC mRNA?

A

When an mRNA molecule codes for more than one protein

24
Q

How does the negative control of the lac operon work, when lactose is absent?

A

When the lactose is absent, repressor is active as the lac i gene codes for a repressor protein (which is an allosteric protein) which binds to the operator region of the DNA.
RNA polymerase can’t create RNA of lacZ, lacY or lacA as it is blocked by the repressor protein.

25
Q

How does the negative control of the lac operon work, when lactose is present?

A

Lactose changes the conformational shape of the lac repressor
repressor becomes inactive
RNA polymerase transcribes lac Z, Y and Aas a single POLYSCISTRONIC mRNA molecule.

26
Q

How does positive control the lac operon work?

A

via cAMP-CAP complex (which is an allosteric protein) which switches on promoter for RNA polymerase,
meaning RNA polymerase bind better to DNA

27
Q

If glucose is absent cAMP is

A

high

28
Q

If glucose is present cAMP is

A

low

29
Q

How do bacteria divide?

A

Binary fission

30
Q

Explain how genetic diversity arises in bacterial populations

A

Spontaneous mutations are rare but in bacteria, short generation times mean that they are a significant source of genetic diversity.
Low mutation rate coupled with short generation times (20 mins)
called vertical gene transmission

31
Q

Explain homologous recombination

A

Recombination involves breakage and rejoining of DNA strands

• In homologous recombination, breaks in closely related DNA molecules are rejoined to form crossovers

32
Q

Explain transformation of DNA

A

Transformation is the uptake of free DNA from the environment
• Bacteria that can take up DNA from the environment are said to be competent- this can occur naturally or be induced by chemical treatments

33
Q

Explain transduction

A

Transduction is the transfer of bacterial DNA from one cell to another via a bacteriophage
• During replication of a lytic phage, the host chromosome is degraded and used a a source of nucleotides for new phage genomes
• Occasionally a large host DNA fragment is still present in the cell as the phage genomes are being packaged into head particles and can be included instead of the phage genome
• After lysis of the infected cell, the defective phage particle can adsorb to another cell and inject its DNA
• The bacterial genes transferred by such a phage particle may replace the homologous region of the recipient bacterial chromosome

34
Q

Explain conjugation

A

Conjugation is plasmid-mediated transfer of DNA from one bacterial cell to another
• Plasmids are small, circular DNA molecules carried as single or multiple copies by some bacteria in addition to the bacterial chromosome
• Plasmids encode genes responsible for their own replication and maintenance

Cells carrying an F plasmid are described as F+ and those that do not are F-
• When F+ cells divide, the offspring usually are also F+
• During conjugation the F+ cell acts as a donor, transferring a parental strand of F factor DNA across the mating bridge to an F- (recipient) cell
• Each parental strand of F factor DNA then acts as a template for synthesis of the second strand in the donor and recipient cells
• The original donor is still F+ and the recipient is now also F+

all via a sex pilus

35
Q

What is an HFR cell?

A

Hfr indicates high frequency recombination

36
Q

What is transposition?

A

DNA sequences that move around the genome
in prokaryotes it is cut and paste
in eukaryotes in is copy and paste

37
Q

What does the virus structure consist of?

A

Genomes - dna or rna
protein coat - made of capsomeres
may have a membrane layer
may have complex shapes

38
Q

What is an example of a rod shaped virus?

A

tobacco mosaic virus

39
Q

What is an example of a round shaped virus? (polyhedral with triangle faces)

A

adenovirus

40
Q

What is an example of a virus with a membrane layer?

A

HIV

41
Q

Explain the process of virus replication:

A

adsorb surface of host cell (this depends on the protein-protein or protein-carbohydrate interactions)
enter cell
uncoat genome
replication of genome (DNA viruses can use host cell’s DNA polymerase, but RNA viruses must code for their own RNA dependant RNA/DNA polymerase)
transcribe and translocate viral genes
assemble progeny virions
exit infected cell

42
Q

Explain the process of T4 phages replication:

A

attachment via tail fibres
inject genome
contain enzymes that hydrolyse host genome (hydrolysis of host genome)
exit via lysis of infected cell

43
Q

Explain the process of λ phage replication:

A

Phage λ is an example of a phage that can undergo lytic replication or alternatively replicate in a bacterial cell without killing it
• Such phages are called temperate phages and their non-lytic replication is described as lysogenic
• Lysogeny is established when the λ DNA genome integrates into a specific site in the bacterial chromosome
• The integrated λ DNA is known as a prophage. One of the prophage genes codes for a repressor protein that prevents transcription of most of the other prophage genes
Each time the host E. coli cell divides, the prophage DNA is replicated along with the bacterial chromosome
• A single infected cell soon gives rise to a large population of cells carrying the integrated prophage DNA
• In response to environmental signals such as UV radiation, the λ genome exits the bacterial genome, re-circularises and initiates a lytic cycle of replication that kills the host cell

44
Q

What differs a retro virus from any other virus strain?

A

It contains reverse transcriptase

45
Q

Explain the process of HIV replication:

A

Attachment is between the VIRAL GLYCOPROTEIN and CD4 receptor on T cell.
Entry is via entry mediated endocytosis
Viral RNA genome is replicated by REVERSE TRANSCRIPTASE:
single stranded RNA –> RNA-DNA hybrid –> double stranded DNA –> integrates to form –>PROVIRUS
virus can remain latent for a long time
later viral replication increases
exit from cell is via BUDDING through the viral membrane layer

46
Q

What are the four ways a virus can be spread?

A

feacal-oral route e.g. polio
respiratory e.g. chicken pox/flu
contact e.g. HIV
arthropod vectors e.g. Zika virus through mosquitos

47
Q

What are two ways in which you can control viral diseases?

A 
Vaccines
Antiviral drugs (they usually interfere with virus replication) e.g. Relenza
48
Q

How do plant virus infections spread?

A

through PLASMODESMATA

49
Q

Role of reverse transcriptase?

A

It catalyzes the formation of DNA from an RNA template

50
Q

Difference between lytic and lysogenic cycle?

A

Lytic cylce involves the rupture of the host cell and escape of virions
Lysogenic cycle involves the incorporation of Viral genome into the host cells dna (called prophage)

51
Q

What is a provirus?

A

“Provirus” is the name given to double-stranded viral DNA that has been incorporated into a host cell’s genome.

52
Q

Why does mRNA only last a few minutes?

A

So that new mRNA can be produced to changes in environmental factors

53
Q

Mutations in the repressor gene or the operator or promoter regions may

A

abolish transcription of the operon– a mutation in the promoter may destroy the RNA polymerase binding site

permanently turn on transcription – mutations in the regulatory gene may inactivate the repressor

biosci 101 (6 decks)

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