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MBB261 > Protozoa > Flashcards

Protozoa Flashcards

1
Q

What are the two main stages in the lifecycle of trypanosma brucei

A

mammalian blood (extracellular) and insect vector (tsetse fly)

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2
Q

Which organism (studied) have multiple nuclei?

A

Giardia lamblia, Tetrahymena thermophila

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3
Q

What molecule do T.brucei express as an antigenic variant?

A

Variant surface glycoproteins (VSGS)

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4
Q

How is monoallelic expression achieved of VSG’s?

A

Monoallelic expression occurs in expression site body, choice of body is by RNApol1 - associated with active bloodstream expression site.
Silencing of other expression sites by histone modifications and specific telomere binding proteins found at nuclear periphery

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5
Q

What is the purpose of VEX1 protein?

A

VEX1 is found at all VSG expression sites - can positively or negatively regulate expression of VSGs

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6
Q

What is important about the repeat structures found in bloodstream expression sites?

A

VSGs can be moved from the silent repertoire into active expression sites via homologous recombination using 70bp homology regions - RECOMBINATION SWITCHING

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7
Q

What are expression site associated genes useful for?

A

They are expressed from the promoter at bloodstream expression sites and are useful for survival in the host.

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8
Q

How does antigenic variation assist survival of some protozoa?

A

Antigenic variation allows for a switch in coat proteins every so often - which limits immune response in a host cell.
Can protect the other surface proteins from detection

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9
Q

What is transcriptional switching in t.brucei?

A

transcriptional switching occurs via DNA markers and regulatory factors - switches expression from one bloodstream expression site to another. (new VSG on coat)

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10
Q

Where is PfEMP1 expressed?

A

PfEMP1 is expressed on the surface of a red blood cell infected with Plasmodium falciparum.

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11
Q

What three methods of erthryocte interactions are mediated by PfEMP?

A
  1. cytoadhesion - helps stick erythrocytes to epithelial walls
  2. Rosetting - infected erythrocytes form clusters with uninfected blood cells
  3. Platelet mediated clamping
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12
Q

What is the purpose of PfEMP1 mediated interactions with erythrocytes?

A

The interactions with uninfected red blood cells prevents the infected cells being recycled in the spleen which will end up in destruction of Plasmodia

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13
Q

Which type of VAR gene would you find associated with H3K9Ac?

A

The (ONE) actively transcribed VAR gene.

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14
Q

What mechanism is involved in the switching of VAR genes?

A

Transcriptional control - Long non coding RNAs antisense to VAR genes are involved in the initiation of switching

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15
Q

What is the purpose of VAR Gene bouquet formation?

A

Var genes are found clustered at the nuclear periphery
This region is usually associated with heterochromatin (ie not expressed)
Allows increased rates of recombination between genes which increases variation

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16
Q

What key organelle exists in plasmodia which does not exist in free living organisms?

A

Apicoplast

17
Q

What is the key function of the apicoplast?

A

Biosynthesis of essential molecules eg IPP, fatty acids and Haem

18
Q

What is the mode of action of antimalarial drug Fosmidomycin?

A

blocks DOXP pathway for IPP biosynthesis - kills plasmodium cells

19
Q

In what stage of the Giardia lamblia life cycle are antigenic variants expressed? How many nuclei does it have at this stage?

A

Trophozoite stage - in the human intestine.

2 nuclei

20
Q

What are the two components of a VSP

A
  1. extracellular domain = CxxC motif

2. CRGKA cytoplasmic tail (hydrophobic)

21
Q

How is silencing of VSP genes achieved?

A

Transcript degradation - post transcriptional mechanism.

22
Q

What benefit does the cyst stage have to the trophozoite stage in G.lamblia?

A

The cyst stage can survive in hypotonic conditions - is protected by the cell wall.

23
Q

In what stage of G.lamblia will division of cells result in a daughter with a pair of non identical nuclei?

A

In the cyst stage (daughters are binuclear)

24
Q

What is diplomixis?

A

the transfer of genetic information between nuclei in the cell - gene conversion or whole chromosome transfer

25
Q

What are the key steps in the excision of an internal eliminated sequence?

A
  1. histone modification
  2. aggregation of chromatin
  3. excision of IES by domesticated transposase
26
Q

Why are there sequence differences in the micro and macronuclei of T.thermophila?

A

Micronucleus contains ‘germline’ equivalent genetic information. A lot of it is removed and can be broken into smaller chromosomes when forming the macro nucleus.

27
Q

In vegetative conditions how would you expect the macronucleus to divide?

A

a-mitotically. Each daughter cell gets a random distribution of the genome

28
Q

in poor conditions, how do micronuclei exchange meiotic products?

A

Via conjugation

29
Q

Why are Tetrahymena thermophila good model organisms for telomeres?

A

Part of the DNA editing from micro-macronucleus involves the removal of Breakage Eliminated sequences. This results in two new chromosomes being formed and de novo telomerisation at the ends.

30
Q

How are scnRNAs used in T.thermophila?

A

scnRNAs are generated in the meiotic DNA and bind to complementary sequences in the macronucleus, recruiting chromatin remodeling factors - resulting in their deletion from sequence (eventually)

31
Q

What are the two main components of KDNA?

A

Minicircles and maxicircles.

32
Q

Where would you find KDNA?

A

In the kinetoplast (eg in T.brucei)

33
Q

What is the function of a kinetoplast?

A

Houses the electron transport chain for oxidative phosphorylation

34
Q

How does the function of the kinetoplast change in the different life stages of T.brucei?

A

In the mammalian host - there is lots of glucose available so the organism does not undergo oxidative phosphorylation - only glycolysis. No TCA and Ox Phos proteins expressed
In insect vector - limited glucose. Kinetoplast more active, TCA and Ox Phos proteins expressed.

35
Q

What type of RNA editing occurs in the kinetoplast?

A

‘Pan-editing’ (ie very extensive) Lots of insertions and deletions of U residues in mRNAs lead by gRNAs.

36
Q

What is one of the key enzymes involved in the RNA editing process in the kinetoplast?

A

Terminal Uridyl Transferase (TUTase)

37
Q

What are Chromera velia and how are they a useful organism?

A

A free living photosynthetic relative to ampicocomplexans. Helped discover the evolutionary origin of the apicoplast

38
Q

Why in an evolutionary ancestor might the apicoplast have been used to synthesise IPP?

A

Because IPP is very energetically expensive to make so it made sense to have the site of production very close to the site of photosynthesis.

MBB261 (3 decks)

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