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Algae and the origin of Eukaryotic Cell (Euglenoids euglena…
Algae and the origin of Eukaryotic Cell
Origin of Eukaryotic Cells
Organelles
Prokaryotes lack membrane- bound organelles
Ribosomes of prokaryotes are 70S
Eukaryotes have nuclei and mitochondria
80S ribosomes in eukaryotes
Origin of Mitochondria and Plastids
Origin of Plastids
Types of Cytokinesis
involves a phragmoplast, consisting of short microtubules
in some green algae, cytokinesis occurs by a phycoplast
occur in algae
Origin of Mitochondria
Nuclear Structure and Division
AS Prokaryotic Cell Grows
plasma membrane expands
DNA circles are separated from each other
DNA of eukaryotes are separated from the cytoplasm
Eukaryotic nuclei are haploid or diploid
meiotic nuclear division occurs as part of sexual reproduction
unusual nuclear characteristics may represent lines of evolution
Nuclei of dinoflagellates have no histones
DNA Structure
In Prokaryotes
contains few introns
mRNA processing is simple
DNA is naked
In Eukaryotes
long, capable of carrying thousands of genes
large segments of DNA do not code for any type of RNA
DNA is more elaborately packed
Green Algae
Life Cycles
Dibiontic species
there is an alternation of generation between haploid and diploid
Monobiontic species
haploid phase represents the individual
diploid cell
zygote
capable only of meiosis
In unicellular algae
no sexual reproduction
alternation of isomorphic generations
alternation of heteromorphic generations
gametes are produced in gametangia
spores are formed in sporangia
Representative Genera
Filamentous Species
Laminar Species
Motile Colonial Species
Coenocytic Species
Parenchymatous Species
Unicellular Species
Body Construction
Filamentous body: if cells are held tightly
Membranous body: results if the orientation is controlled precisely
Nonmotile colonies: occur if the cells lose their flagella
Parenchymatous body: if cell division occurs regularly in all three planes
motile colonies: cells adhere loosely resulting in a colony
Coenocytic or Siphonous body: results if karyokinesis occurs without cytokinesis
Green Algae and Embryophytes
Streptophytes
monophyletic clade
Archaeplastids
based on the original plastid endosymbiosis
Brown Algae and Their Relatives
The Heterokonts
Diatoms
wall composed of frustules
Diatomaceous earth
hundreds of meters thick
Yellow- Green Algae
mostly in fresh water
Vaucheria consists of a long tubular coenocyte
Brown Algae
exclusively marine
grow in the littoral zone
storage product is laminarin
Golden- Brown Algae
consists of around 70 genera and 325 species
coccolithophorids
remains of both diatoms and golden-brown algae
Dinoflagellates
spindle does not form
mostly motile and unicellular
nuclear envelope and nucleolus persist throughout mitosis
Oomycetes
diverse in structure and nutrition
lack chloroplasts
parasitic or saprophytic
sexual reproduction occurs
Euglenoids
photosynthetic euglenoids have chlorophylls a and b
Euglenoid chloroplasts are extremely sensitive to antibiotics
mostly unicellular
Swim with two flagella
during mitosis, spindle microtubules form within the nucleus
Euglena is a representative example
