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Giardia AV Flashcards

(59 cards)

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1
Q

What phylum does Giardia belong to?

A

Metamonida

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2
Q

Is giardia intracellular or extracellular?

A

Extracellular

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3
Q

Giardia colonises?

A

The small intestine

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4
Q

Giardia was first observed by?

A

Antoni Van Leeuwenhoek who identified the trophozoites in his faeces

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5
Q

Giardia causes?

A

Giardiasis

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6
Q

Giardiasis can be caused by?

A

Contaminated drinking water, consuming cysts

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7
Q

Giardia is spread via which route?

A

The fecal oral route

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8
Q

What are the two forms of Giardia?

A

Trophozoites and cysts

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9
Q

Excystation occurs?

A

Due to the low pH of the stomach

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10
Q

Encystation occurs?

A

In the colon

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11
Q

Which form of Giardia can survive for months in cold water?

A

The cyst form

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12
Q

What is released during excystation?

A

Two trophozoites

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13
Q

Describe the lifecycle?

A

1) Cysts are consumed
2) Excystation occurs in response to the low pH of the stomach
3) Trophozoites attach to the small intestine via an adhesive disc and replicate via binary fission
4) Encystation occurs in the colon
5) Cysts are released in the faeces

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14
Q

Can trophozoites survive in the environment?

A

No

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15
Q

How do trophozoites replicate?

A

Via binary fission

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16
Q

What are the features of trophozoites?

A
  • Not environmentally hardy
  • Contain two transcriptionally active nuclei
  • Have 8 flagella in 4 pairs
  • Replicate via binary fission
  • Look like smiley faces
  • Extracellular parasites
  • Pear shaped
  • No obvious mitochondria or golgi bodies
  • Metabolically active
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17
Q

How do trophozoites attach to the small intestine?

A

Via an adhesive disk

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18
Q

How do trophozoites replicate?

A

Binary fission

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19
Q

How many nuclei are present in trophozoites?

A

2 transcriptionally active nuclei

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20
Q

What are the features of cysts?

A
  • Cysts are present in the faeces
  • Cysts are environmentally hardy
  • Cysts are able to survive in cold water in the environment for months
  • Cysts each give rise to two trophozoites
  • Cysts contain 4 nuclei and 4 axonemes due to duplication of organelles without cell division
  • Not metabolically active
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21
Q

What shape are trophozoites?

A

Pear shaped

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22
Q

Why was it thought that giardia was a primitive eukaryote?

A

Appear to be amitochondrion- appear to lack a mitochondria. Thought that giardia was a primitive eukaryote which branched off before the acquisition of the mitochondrion
Thought to be a molecular fossil

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23
Q

However, now we know that giardia lacks the mitochondrial structures due to?

A

Reductive evolution

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24
Q

What has reductive evolution resulted in?

Study These Flashcards
A

Has resulted in the mitosomes

The mitosomes are mitochondrion derived

25
What occurs in the mitosomes?
Iron sulfur cluster synthesis
26
What occurs in mitochondria?
There is ATP synthesis
27
Where is ATP made in giardia?
Cytosol
28
What are mitosomes?
Double membrane bound mitochondrial relics Formed via reductive evolution Site of iron-sulfur cluster synthesis
29
How are the mitosomes different to mitochondria?
Do not contain genes within them Mitosomes do not contain DNA Any mitosomal proteins are trafficked there
30
How are mitosomes similar to mitochondria?
Double membrane bound | Associated with ATP synthesis
31
The mitochondria degenerated into the mitosome through a process known as?
Reductive evolution
32
Antigen variation of what occurs in Giardia?
VSP
33
What is VSP?
Variant Specific Surface Protein
34
VSP is known as?
Variant Specific Surface Protein
35
Expression of VSP is?
Monoallelic
36
How many VSP variants are there?
~200
37
Are VSP genes telomeric?
Not necessarily
38
How is monoallelic expression of VSPs achieved?
RNAi
39
RNAi general process?
All VSP genes are transcriptionally active Transcripts of all the VSP genes are continually being produced There is silencing of all VSP transcript variants aside from one The transcript that is not silenced is the variant of VSP that will be expressed
40
How is it decided which transcript will not be silenced?
Unknown Thought it is due to the abundance of the transcripts There will be certain transcripts of a VSP variant which are more abundant and may be able to escape RdRP and silencing= this is the transcript that is expressed
41
What is the specific process of RNAi silencing?
mRNA of the VSP Antisense RNA is produced by RdRP The dsRNA/ RNA duplex is recognised by Dicer Cleavage into siRNA duplex by dicer siRNA is recognised by RISC and Argonaute complex Directed to mRNA that is complementary, silencing via the RISC complex and mRNA degradation
42
How many VSP genes are there?
~200
43
What is the VSP structure?
Variable N terminus Semi conserved C terminus Transmembrane domain Invariant cytoplasmic tail
44
VSP is expressed in which fashion?
VSP is expressed in a monoallelic fashion
45
Evidence for RNAi being the regulator of monoallelic expression?
If you disrupt the RNAi pathway you notice that more VSPs are expressed, expression is no longer monoallelic
46
How does switching occur?
Change in the levels of VSP transcript abundance
47
Why might switching occur in daughter cells?
May be possible that upon cell division the daughter cels receive varying abundances of VSP transcripts or siRNAs which may cause a switch to a different VSP variation.
48
How does Giardia mediate attachment?
Trophozoites attach to the small intestine via the adhesive disc
49
Giardiasis does not usually need to be treated as it is?
Self-limiting
50
How is the mitosome similar to mitochondria?
Double membrane bound Involved in ATP synthesis Contains mitochondrial proteins
51
How does the mitosome differ to mitochondria?
Site of iron sulfur cluster synthesis but ATP synthesis occurs in the cytosol Does not contain any DNA All the proteins must be trafficked to the mitosome
52
Giardia was thought to be?
A primitive eukaryote A molecular fossil Thought it was an amitochondriate which diverged before the acquisition of the mitochondrion
53
How many VSP genes are there?
~200
54
Are VSPs telomeric?
Not necessarily
55
Does VSP switching require DNA rearrangements?
No
56
Control of VSP is?
Post-transcriptional
57
VSP structure?
Variable N terminus Semi-conserved C terminus Transmembrane domain Invariant cytoplasmic tail
58
How can you alter the monoallelic expression and get multiple VSPs to be expressed?
Disrupt RNAi e.g. knockout gene encoding dicer
59
How might division into daughter cells mediate vsp switch?
During daughter cell production there may be variable amounts of vsp transcripts or vsp siRNAs delivered to the daughter cells. This may result in a switch to the expression of a different vsp variant e.g. in the daughter cells a different vsp transcript may be more abundant and escape silencing

Parasitology (17 decks)

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