Lecture 5 Protozoa-Trypanosomatids

Question 1

Protozoa

Answer 1

-eukaryotic, single cell organisms that can be free living or parasitic in nature

Question 2

Protozoa move by three basic types of organelles

Answer 2

-pseudopodia
-flagella
-cilia

Question 3

Flagella are composed of

Answer 3

-a central axoneme formed by nine peripheral and one central pair of microtubules
-an outer sheath that is the continuation of the outer membrane
¤ a kinetosome (basal body), that gives origin to
the axoneme, lies at the bottom of flagellar
pocket
¤ the flagellum may bend back along and loosely
attached to the lateral cell surface, forming a
finlike undulating membrane

Question 4

Protozoa Reproduction

Answer 4

-either asexual or sexual

Question 5

What are the different patterns that asexua reproduction follows?

Answer 5

-Binary fission: in which one divides into two.
-The plane of fission is random in amebas
-longitudinal in flagellates
-transverse in ciliates

Question 6

Multiple fission

Answer 6

-occurs in some amebas and in apicomplexa.
-in this type of division the nucleus and other essential organelles divide repeatedly before cytokinesis. Thus a large of daughter cells are produced simultaneously

Question 7

Amphimictic

Answer 7

Involving the union of gametes from two parents

Question 8

Automictic

Answer 8

One parent give rise to both gametes

Question 9

Encystation

Answer 9

¤ Many protozoa can secrete a resistant covering and enter a resting
stage, or cyst.
¤ Cyst formation is particularly common among parasitic protozoa as
well as among free-living protozoa found in temporary bodies of
water that are subject to drying or other harsh conditions.
¤ Cysts provide protection against unfavorable conditions and serve as
sites for reorganization and nuclear division, followed by
multiplication after excystation.
¤ Conditions favoring encystation are not fully understood, but in most
cases they involve adverse environmental events such as food
deficiency, desiccation, increased tonicity, decreased oxygen
concentration, pH or temperature change.
¤ In species in which the cyst is a resistant stage, a return of favorable
conditions stimulates excystation.

Question 10

Protozoans metabolism are divided between

Answer 10

-photosynthetic: they synthesize carbohydrates in chloroplasts
-Nonphotosynthetic or heterotrophic: require their energy in the form of complex carbon molecules and their nitrogen int the form of a mixture or preformed amino acids.

Question 11

In what conditions do protozoans live in?

Answer 11

-live in tissues with low oxygen and glucose availability and have adapted their metabolism to such conditions

Question 12

Protozoan Flagellates

Answer 12

-flagellates are protozoans
over 50,000 and a small number are pathogenic to humans
-are very small
-have one or more flagellates that propel them their the host

Question 13

Trypanosomatids

Answer 13

-trypanosomes are unicellular hero flagellates which belong to the class kinetoplastea
-kinetoplastea are parasitic that have a single nucleus, mitochondria, and flagella
-have a prominent accumulation of mitochondrial DNA
-They show a variety of forms varying from long, thin, motile spindle shapes
to spherical organisms in which the flagellum is reduced to a tiny stub.

Question 14

Trypanosomes are classified in 2 groups

Answer 14

-¤ Salivarian: salivarian trypanosomes replicate extracellularly in the blood and
tissue fluids of mammals and in the digestive system of tsetse flies. Their
distribution is restricted to Sub-Saharan Africa.
¤ There are several species that are host-specific.
¤ Trypanosoma congolense and Trypanosoma vivax are the major
pathogens of cattle and goats.
¤ Trypanosoma brucei brucei is a parasite of cattle
¤ Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense
these are the causative agents of sleeping sickness in humans
¤ Stercorarian: multiply extracellularly in the digestive system of various
Rhodnius, Triatoma and Panstrongylus species – reduviid bugs. Infection of
mammalian hosts occurs when infected bug faeces are rubbed into the bite
site, and in this host, the parasites multiply intracellularly

Question 15

Trypanosomatids Morphology

Answer 15

-show a variety of forms varying from long thin ,motile spindle shapes to spherical organisms to which the flagellum is reduced to a tiny stub.

Question 16

Amastigotes

Answer 16

-contains a nucleus, basal body structure called a blepharoplast and a damsel paranasal body.
-the large single nucleus id usually located off center
- blepharoplast gives rise to and is attached to an axoneme

Question 17

Promastigote morphology

Answer 17

¤ The large single nucleus is located in or near the center of the long slender body.
¤ The kinetoplast is located in the anterior end of the organism.
¤ A single free flagellum extends anteriorly from the axoneme.

Question 18

Epimastigote Morphology

Answer 18

-the body is wider than the promastigote
-the large single nucleus is located in the posterior end of the organism
-the kinetoplast is located anterior to the nucleus.
-an undulating membrane, measuring half the body length, forms into a free flagellum at the anterior end of the epimastigote.

Question 19

Tryposmastigote Morphology

Answer 19

¤ The typical trypomastigote measures 12 to 35 μm long by 2 to 4 μm wide, and may often
assume the shape of the letters C, S or U in stained blood films
¤ The long slender trypomastigote is characterized by a posteriorly located kinetoplast from
which emerges a full body length undulating membrane.
¤ The single large nucleus is located anterior to the kinetoplast.
¤ An anterior free flagellum may or may not be present.

Question 20

How is the shape of parasites maintained

Answer 20

maintained by a corset of microtubles which spiral around the parasite

Question 21

Three organelles are important in cellular metabolism

Answer 21

• The mitochondrion: they possess only
  one that changes depending on the
  metabolic state of the parasites.
• The glycosomes: contain most enzymes
  of glycolysis and parts of several additional
  pathways.
• Acidocalcisomes: acidic compartment
  that stores polyphosphates and calcium.

Question 22

Cell surface protein variation

Answer 22

-* African trypanosome parasites are
densely coated in a single Variant
Surface Glycoprotein (VSG).
* While growing in the bloodstream of
humans and other mammals
Trypanosoma brucei species evade
the host immune response by
switching from the expression of one
VSG coat to another.
* This requires selection and activation
of a single new VSG gene from a
huge number of possible VSG
variants encoded throughout the
genome.
* Switching VSG expression is based in
DNA recombination events that result
in chromosome translocations drawn
from more than 2,000 VSGs.