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Flashcards in Microbiology Deck (89)
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1
Q

What are the general characteristics of fungi?

A

Fungi are eukaryotic chemoheterotrophic organisms that absorb food and nutrients through chitinous cell walls. They can be either unicellular (yeast) or multicellular (mold, mushrooms) and may reproduce either sexually or asexually.

2
Q

What are the functions of the mycelium of a fungi?

A

A mycelium absorbs nutrients, aids in decomposition of organic matter, and is involved in fungal growth and reproduction.

3
Q

Describe what occurs during:

the asexual reproductive cycle of fungi

A

In many fungi, asexual reproduction occurs in the sporangium (n) found on the cellular walls of reproductive hyphae cells of the mycelium (n). Haploid spores (n) are formed in the sporangium by mitotic divisions and then released to germinate on a suitible substrate. Fungi may also undergo budding and fragmentation.

4
Q

Describe what occurs during

the sexual life cycle of fungi

A
5
Q

Viruses are considered non-living because they…

A
  1. Lack both organelles and a cytoplasm
  2. Do not respond to external stimuli
  3. Do not grow by increasing in size
  4. Are unable to independently undergo metabolic functions and instead replicate using the host’s metabolic machinery
6
Q

Define

virion

A

a complete extracellular viral particle composed of a capsid-enclosed viral genome and in some cases a tail region and/or an envelope

7
Q

The capsid region of a virus may contain either ____ or ____ but not both.

A

DNA; RNA

8
Q
A

The image depicts a typical bacteriophage, with a capsid head region containing either single stranded or double stranded DNA or RNA and a protein tail region.

9
Q

Compared to bacteria and animal cells, viruses are ____ in size and additionally lack both a ____ and ____.

A

smaller; cytoplasm; organelles

10
Q

Define:

bacteriophage

A

a virus that infects bacteria, recognizable by its capsid head region (which encloses the viral genome) and its distinct protein “tail” region (which gets the genome through the bacterial cell wall)

11
Q

Define:

capsid

A

protein coat surrounding viral genome that has a polyhedral or helical structure

12
Q

Define:

<font><span>viral envelope</span></font>

A

a bilayer lipid membrane, made up of both viral and host proteins, which encloses the capsid and plays a major role in infection and pathogenisis

13
Q

Viruses can be classified in 4 general categories, based on whether they have…

A

DNA:

  • ssDNA (single stranded)
  • dsDNA (double stranded)

RNA:

  • ssRNA (single stranded)
  • dsRNA (double stranded)
14
Q

A virus cannot perform its own metabolic functions, therefore it must [insert phrase] in order to reproduce.

A

utilize the metabolic machinery of the host cell in order to reproduce.

15
Q

The six basic stages in the lytic viral life cycle are:

A
  1. Adsorption
  2. Penetration
  3. Uncoating
  4. Protein Synthesis/Replication
  5. Maturation
  6. Release
16
Q

Describe what occurs during:

the adsorption stage of the lytic viral life cycle.

A

During the adsorption stage the virus attaches itself to the membrane of a host cell. Viral attachment proteins recognize specific receptors on the outside of the cell, therefore only cells that have the appropriate receptors are susceptible to viral attack. For enveloped viruses adsorption may also occur through fusion or endocytosis.

17
Q

Define:

endocytosis

A

a form of active transport in which substances enter the cell enclosed in vacuoles/vesicles formed from the cellular cytoplasmic membrane

18
Q

Identify the process in the image below:

A

The image depicts the adsorption stage of the life cycle of an HIV virion. HIV is in the process of attaching to the CD4 receptor on the plasma membrane of a T-cell.

19
Q

Describe what occurs during:

the penetration stage of the lytic viral life cycle.

A

During the penetration stage the virus infiltrates the host cell. Enveloped viruses may either fuse with the plasma membrane or enter using an endosome. Non-enveloped viruses may either cross the plasma membrane directly or be taken in by an endosome.

20
Q

Describe what occurs during:

the uncoating stage of the lytic viral life cycle

A

During the uncoating stage, proteolytic enzymes remove the capsid from the nucleic acid of the virus. This stage always occurs in the cytoplasm of the host cell because this is where proteolytic enzymes are found.

21
Q

The uncoating stage of the lytic viral life cycle occurs in the…

A

cytoplasm of the host cell

22
Q

The eclipse period occurs between what two stages of the lytic viral life cycle?

A

uncoating and maturation stages

23
Q

Define:

eclipse period

A

the period between the end of the uncoating and the beginning of the maturation stages in the viral life cycle in which no intact infectious virions are seen within the host cell

24
Q

Describe what occurs during

the protein synthesis stage of the lytic viral life cycle

A

During the protein synthesis stage, viral nucleic acids and proteins are replicated and viral parts are synthesized using the metabolic machinery of host cell (ie. ribosomes, tRNA, mitochondria, golgi apparati, enzymes, etc). The virus is not infectious as this stage occurs during the eclipse period.

25
Q

Where does the protein synthesis stage occur in most DNA viruses? How about RNA viruses?

A

DNA viruses: occurs mostly in the nucleus of the host cell

RNA viruses: occurs solely in the cytoplasm of the host cell

26
Q

Describe what occurs during:

the maturation stage of the lytic viral life cycle

A

During the maturation stage, viral parts, such as the capsid, completed during the protein synthesis stage, are assembled around the replicated viral genome. The exact assembly process differs for enveloped and non-enveloped viruses.

27
Q

For enveloped viruses, what happens during the maturation stage?

A

During the maturation stage, a capsid is formed around the viral genome and viral envelope glycoproteins are transported to and embedded in the plasma membrane of the host cell.

28
Q

Compared to events occurring during the maturation stage of enveloped viruses, what DOES NOT happen during the maturation of non-enveloped viruses?

A

The maturation of non-enveloped viruses does not involve the transport of glycoproteins to the cytoplasmic membrane of the host cell, a process that occurs during the maturation of enveloped viruses.

29
Q

For non-enveloped viruses, what happens during the maturation stage?

A

During the maturation stage, a capsid is formed around the viral genome.

30
Q

Describe what occurs during:

the release stage of the lytic viral life cycle

A

During the release stage, the newly replicated assembled viruses exit the cell. Typically, non-enveloped viruses are released by lysis and enveloped viruses exit by budding from the cytoplasmic membrane of the host cell.

31
Q

Compare the lytic and lysogenic viral life cycles.

A

Lytic cycle:

results in the immediate production of virulent (infectious) viruses; occurs in both eukaryotes and prokaryotes

Lysogenic cycle:

viruses lie latent within host cells and are passed on in subsequent cell divisions until the lytic cycle is triggered at a later time; occurs mostly in bacteria/prokaryotes

32
Q

Define:

<font><span>lytic viral life cycle</span></font>

A

a six step replication pathway in which the virus rapidly multiplies within the cell and is released by cell lysis or budding

33
Q

Define:

lysogenic viral life cycle

A

The lysogenic viral life cycle is a replication pathway in which the viral genome is incorporated with host cell DNA. This provirus lies latent and replicates during subsequent host cell divisions until an event triggers the lytic cycle releasing virions from a multitude of infected cells.

34
Q

Define:

cell lysis

A

Cell lysis is degeneration of the cytoplasmic membrane of a cell often due to viral, enzemic or osmotic mechanisms. It can be thought of as “cell bursting”.

35
Q

Define:

retrovirus

A

an enveloped RNA virus that contains two identical (+) ssRNA molecules and uses the enzyme reverse transcriptase to transcribe viral RNA into DNA

36
Q

What is reverse transcriptase?

A

an enzyme used by retroviruses to convert their two RNA strands into DNA

37
Q

What are the five major steps in the retrovirus life cycle?

A
  1. Fusion
  2. Reverse Transcription
  3. Integration
  4. Transcription
  5. Budding

(these steps are interrelated with the stages of general viral life cycle)

38
Q

Describe what occurs during:

the fusion step in the retroviral life cycle.

A

During fusion, glycoproteins on the retroviral envelope interact with specific proteins on the plasma membrane of the host cell, enabling the envelope to fuse (combine) with the plasma membrane.

39
Q

In the retroviral life cycle, which step follows fusion?

Describe what occurs during this step.

A

Reverse transcription

During reverse transcription, the retrovirus enters the cytoplasm where its two ss-RNA strands are transcribed and synthesized into one ds-DNA by the enzyme reverse transcriptase.

40
Q

Describe what occurs during:

the integration step of the retroviral life cycle

A

During the integration step, the newly formed viral ds-DNA is transported into the nucleus where it is integrated with host DNA forming a viral-host DNA hybrid called a provirus

41
Q

In the integration stage of the retroviral life cycle, a viral-host DNA hybrid called a ____ is formed

A

provirus

42
Q

Describe what occurs during:

the transcription stage of the retroviral life cycle

A

During the transcription stage, the provirus is transcribed by host RNA polymerase forming mRNA and retroviral RNA molecules. The mRNA is then translated by the host’s metabolic machinery into glycoprotein and capsid components. The RNA and components are then assembled into capsids.

43
Q

Describe what occurs during:

the budding stage of the retroviral life cycle

A

During the budding stage, the assembled retroviral capsids interact with viral glycoproteins on the plasma membrane of the host cell causing it to bud and pinch off, releasing enveloped retroviral virions.

44
Q

Define:

transduction

A

a form of genetic recombination in which bacterial DNA is transferred from one bacterium to another by a bacteriophage which accidentally obtained chromosomal host DNA within its capsid

45
Q
A

transduction

46
Q

Define:

prokaryote

A

A prokaryote is an organism that lacks a membrane-bound nucleus and is further characterized by a nucleoid, cell wall and membrane, cytoplasm, flagella,and ribosomes. Two domains of prokaryotes exist: Bacteria and Archaea

47
Q

Lacking a nuclear membrane, bacteria are ____ organisms that have their single circular chromosome and RNA centered in the ____ region instead.

A

prokaryotic; nucleoid

48
Q

As bacteria do not undergo mitosis, they must lack a ____.

A

mitotic apparatus

49
Q

Bacteria have a ____ in the nucleoid region. As a result, their genes are expressed only once and they are therefore considered to be ____.

A

singular circular chromosome; haploid

50
Q

Compared to organelles found in a(n) ____ animal cell, what organelles does a(n) ____ bacteria cell lack?

A

eukaryotic; prokaryotic

A prokaryotic bacteria cell lacks a nucleus, mitochondria, golgi apparatus, lysosomes and an endoplasmic reticulum.

51
Q

If bacteria lack mitochondria and other organelles responsible for metabolism in eukaryotic animal cells then how do they generate energy?

A

Bacteria gain energy from either photosynthesis, chemotropy or by ingesting organic matter. As they lack metabolic organelles, many biochemical reactions are carried out through the use of proton pumps, or other concentration gradients, across membranes.

52
Q
A

A) bacilli, rod shaped
B) spirilli, spiral shaped
C) cocci, spheric or elliptical

53
Q

What do the terms gram-positive bacteria and gram-negative bacteria mean?

A

Gram-positive and gram-negative are classifications of bacteria made on the basis of whether or not their cell walls react to a dye called Gram Stain. Gram-positive bacteria retain the stain and gram-negative do not.

54
Q

Bacteria and other prokaryotic cells have a ____ that surrounds the plasma membrane.

A

cell wall

55
Q

What are the differences in the cell wall structure of gram positive and gram negative bacteria?

A

Gram-positive bacteria have a thick layer of peptidoglycans, which are composed of sugars and amino acids.

Gram negative bacteria have a more complex, dual layer cell wall. A thin layer of peptidoglycans lies adjacent to the plasma membrame and is separated by a fluid-filled periplasmic space from an outer membrane composed of phospholipids and negatively charged lipopolysaccarides.

56
Q
A

The image depicts a prokaryotic cell propelling itself with flagella.

57
Q

Flagella are necessary for cellular _______.

What would probably happen to a bacterial cell if it lacked flagella?

A

motion

Without flagella, the bacterium would be immobilized as it would be unable to propel itself.

58
Q

Define:

flagella

A

Flagella (s. flagellum) are extracellular whip-like structures that are responsible for motility in many eukaryotic and prokaryotic cells. In bacteria they are protein rods that are attached to the cell wall by a hook and a swivel. In eukaryotic cells they have a microtubular core and are covered by a membrane.

59
Q

What structure is responsible for bacterial motility? How does it work?

A

Flagella are responsible for bacterial motility. Movement is caused by the rotation of the whip-like external structure that is activated by a protein complex that spans the cell wall/membrane and fueled by a proton pump.

60
Q

Define:

binary fission

A

Binary fission is the process by which bacteria reproduce. The single bacterial chromosome attaches to opposite ends of the cell wall as it replicates. The cell is gradually lengthened until it divides by cytokineses into two equivalent halves. Although cell growth by this method is exponential, no genetic recombination occurs.

61
Q

What are the three main steps by which DNA replication occurs in prokaryotic cells?

A
  1. Initiation
  2. Elongation
  3. Termination
62
Q

Describe what occurs during:

the initiation step of DNA replication in prokaryotes

A

Although the initiation step is not yet fully understood, it appears to occur at replication initiation sites on DNA. It is at these sites that proteins begin separating the two strands and the replication complex, made up of a multitude of enzymes, is assembled.

63
Q

Describe what occurs during:

the elongation step of DNA replication in prokaryotes

A
  1. DNA Helicase separates the two template strands of DNA.
  2. DNA Polymerase III moves along the template, synthesizing a complementary strand.
  3. DNA Ligase joins the free strands of adjacent segments together.
64
Q

The leading strand of DNA has a [3’/5’] free end, while the lagging strand has a [3’/5’] end

A

The leading strand of DNA has a 3’ free end, while the lagging strand has a 5’ free end.

65
Q

During DNA elongation, why does the lagging strand lag behind the leading strand?

A

The lagging strand runs in the 5’-3’ direction while the leading strand runs in the 3’-5’ direction . DNA Polymerase III can only “read” the 3’-5’ end and it must move in the opposite direction of the helicase on the lagging strand in order to create the complemenary strand. As a result, it copies DNA in a series of approximately 200 nucleotide long sequences.

66
Q

Describe what occurs during:

the termination step of DNA replication in prokaryotes

A

Although the termination step is not yet fully understood, it appears that in some prokaryotes it occurs when the two replication complexes collide. In others it occurs at specific points on the DNA molecule itself.

67
Q

Bacteria reproduce by ____ ____, a process in which no genetic recombination occurs. However, bacteria have a high degree of genetic adaptability. What accounts for this high degree?

A

binary fission

The processes of mutation, transformation, transduction, and binary fission can introduce new genetic material into bacterial DNA and therefore account for the high degree of bacterial genetic adaptability.

68
Q

What accounts for antibiotic resistance in bacterial cells?

A

Bacteria can acquire a resistance to antibiotics through spontaneous mutations or through the acquisition of genes from already resistant bacteria by transduction, transformation or conjugation.

69
Q

Can a bacterium that is resistant to penicillin lose its antibiotic resistance?

A

Yes. A bacterium can acquire and lose genes that code for antibiotic resistance through genetic exchange and mutation. The reverse process, however, is more likely to occur at a slower rate.

70
Q

How are bacterial genes that code for antibiotic resistance spread on a population level?

A

In bacterial populations, antibiotic resistance generally spreads both vertically, from parent to daughter cell, and horizontally, from one bacteria to another.

71
Q
A

Lag phase: No significant growth occurs as bacteria are not acclimated to the new environment.

Exponential Growth Phase: Bacteria replicate exponentially by binary fission.

Stationary phase: There is no net growth as the growth rate = death rate due to a lack of nutrients and a build-up of waste.

Death phase: With the unfavorable conditions described above becoming worse bacteria begin to die and population declines.

72
Q

What is the difference between an obligate anaerobe and a facultative anaerobe?

A

An obligate anaerobe dies in the presence of oxygen. A facultative anaerobe does not need oxygen for growth but grows faster in the presence of oxygen.

73
Q

Oxygen is fatal to a(n) ____ ____ . Conversely, a(n)____ ____ needs oxygen for growth.

A

obligate anaerobe; obligate aerobe

74
Q

Define:

plasmid

A

A plasmid is an inherited unit of circular double-stranded DNA, found in the cytoplasm of prokaryotes. It replicates independently of the chromosomal DNA but can be integrated into the chromosome. Additionally, it is not essential for cell growth or reproduction.

75
Q

A bacterium can have many double-stranded ____ in the cytoplasm, but has only one ____, found in the nucleoid region.

A

plasmids; chromosome

76
Q

Define:

conjugation

A

a process that involves the exchange genetic material between two bacteria, an F+ (male) and an F- (female), through a bridge-like structure called a pilus

77
Q

Define:

pilus

A

A pilus is a “mating bridge” that links two bacteria together during conjugation. In order to form a pilus, a bacterium must posses the Fertility factor, or F-factor, plasmid.

78
Q

During conjugation, in order for a bacterium to be considered F+ what must it possess?

A

An F+ (male/donor) bacterium must possess the F-factor plasmid.

79
Q

During conjugation a “female” bacterium is [F+/F-] and is a [recipient/donor] and a “male” bacterium is [F+/F-] and is a [recipient/donor]

A

During conjugation a “female” bacterium is F- and is a recipient and a “male” bacterium is F+ and is a donor.

80
Q

Describe what occurs during:

conjugation

A

During conjugation a F+ (male) produces a bridge-like pilus in order to attach to a F- (female) bacterium. The cells are then linked just long enough to transfer a single strand of DNA, the F-factor, from the donor F+ to the F- cell. If this transfer is completed then both cells produce the complementary strand and become F+. If the F-factor was integrated with chromosomal DNA a portion of the bacterial genome may transfer as well, allowing for genetic recombination.

81
Q

Define:

F-factor

A

An F-factor, or fertility factor, is an episome (plasmid that can integrate into chromosomal DNA) that contains pillin genes. These genes code for pillus formation and regulation and allow conjugation to occur.

82
Q

Describe what occurs during:

transformation

A

During transformation, a competent bacterium incorporates naked DNA fragments from an external medium into its own genome. This process may occur either naturally or artificially.

83
Q

In order for natural transformation to occur what two requirements must be met?

A

In order for natural transformation to occur:

  1. a bacterium must lyse, releasing naked DNA fragments into the extracellular enviroment and
  2. the fragments must be taken in by a competent bacteria to be incorporated into the bacterial genome.
84
Q

Define:

**competent bacteria **

A

bacteria that are capable of taking in extracellular naked DNA particles and undergoing transformation

85
Q

What are the three steps of RNA transcription that occur in prokaryotic cells?

A
  1. Initiation
  2. Elongation
  3. Termination
86
Q

During the initiation step of RNA transcription, a core enzyme called ____ works with multiple ____ to initiate RNA synthesis.

A

RNA polymerase; sigma factors

87
Q

Describe what occurs during:

the initiation step of RNA transcription in prokaryotes

A

During the initiation step of RNA synthesis a complex of RNA polymerase and sigma factors binds to a promotor sequence on the DNA. The polymerase forces a DNA segment apart and the synthesis of a new RNA strand commences only on the3’-5’ DNA template strand.

88
Q

What is the function of activator and repressor proteins in RNA transcription? In the prokaryotic cell as a whole?

A

Activator and repressor proteins control initiation by triggering or halting RNA synthesis respectively. On a larger scale, because they control RNA synthesis, they control gene expression in prokaryotes.

89
Q

In prokaryotes RNA transcription and translation are ____ and often occur [at different times/simultaneously].

A

In prokaryotes RNA transcription and translation are coupled and often occur simultaneously.