Lecture 5 Protozoa-Trypanosomatids Flashcards
Protozoa
-eukaryotic, single cell organisms that can be free living or parasitic in nature
Protozoa move by three basic types of organelles
-pseudopodia
-flagella
-cilia
Flagella are composed of
-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
Protozoa Reproduction
-either asexual or sexual
What are the different patterns that asexua reproduction follows?
-Binary fission: in which one divides into two.
-The plane of fission is random in amebas
-longitudinal in flagellates
-transverse in ciliates
Multiple fission
-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
Amphimictic
Involving the union of gametes from two parents
Automictic
One parent give rise to both gametes
Encystation
¤ 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.
Protozoans metabolism are divided between
-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.
In what conditions do protozoans live in?
-live in tissues with low oxygen and glucose availability and have adapted their metabolism to such conditions
Protozoan Flagellates
-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
Trypanosomatids
-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.
Trypanosomes are classified in 2 groups
-¤ 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
Trypanosomatids Morphology
-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.
Amastigotes
-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
Promastigote morphology
¤ 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.
Epimastigote Morphology
-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.
Tryposmastigote Morphology
¤ 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.
How is the shape of parasites maintained
maintained by a corset of microtubles which spiral around the parasite
Three organelles are important in cellular metabolism
- 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.
Cell surface protein variation
-* 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.
