Introduction to Protista
First eukaryotes: large, organelles, nucleus
Evolved from prokaryotes
Grab bag of unrelated organisms
Split into several kingdoms in future classification systems
Introduction to Protista
Single-celled eukaryotes
Multicellular algae
Heterotrophs and autotrophs
Heterotrophic protists (to be studied in 1102)
Protozoa
Motile, feed on bacteria and small protists
Slime moulds
Motile feeding stage and fruiting stage which produces spores
Autotrophic protists
Single-celled, filamentous or multicellular
Only autotrophs in Biology 1001
Examples: Euglena, a motile single-celled protozoan
Ulva, a multicellular green alga
Eukaryotes have Internal Compartments
Eukaryotes have membranous organelles
Chief distinction from prokaryotes
Internal membranes compartmentalize
Boundary, separate unit
Organelles are like isolated test
tubes
Separate from surrounding cytoplasm (cytosol)
Membranes regulate the flow of molecular traffic
Interior chemical environment differs from cytoplasm [cytosol]
Organelles are like isolated test
tubes
Unique mix of chemicals (raw materials)
Unique set of enzymes
Specialized series of chemical reactions
Not all organelles are membranous
Ribosomes
Assemble proteins
Prokaryotes have ribosomes
Definition of an Organelle
unit of specialized function found
in the cytoplasm of the cell
The Nucleus is a Specialized Membranous
Organelle
Found in all eukaryotic cells
Some are multinucleated
Structure of Nucleus
Double membrane (called the nuclear envelope)
DNA+ proteins =chromatin
Chromatin: stringy, contain genes
Chromatin coils up into linear (rod-shaped) chromosomes
Structure of Nucleus
Double membrane has large pores
Nucleolus assemble ribosomes
Nucleoplasm contains dissolved nucleotides
Ribosomes and mRNA pass through the nuclear pores
DNA never leaves nucleus
Mitochondria are organelles found
in most Eukaryotes
Hundreds per cell
Two membranes: a smooth outer membrane and a greatly folded inner membrane
Finger-like folds called cristae
Two inner chambers: intermembrane space and matrix
Mitochondria produce ATP by cellular
respiration
Glucose + oxygenCcarbon dioxide and water
Energy stored in bonds of glucoseC ATP
Series of reactions (not a one step reaction)
Requires many enzymes
The major catabolic pathway
Where reactions of cellular respiration
occur
Some in the matrix (enzymes are concentrated)
Some on the inner membrane (where enzymes are attached)
Folding (cristae) increases the surface area for reactions
Chloroplasts are organelles
Found in all autotrophic eukaryotes
Photosynthesis
Structure of chloroplasts
Inner and an outer membrane creating two chambers
Thylakoids (folded membranes)
Thylakoid space (inside thylakoid)
Stroma surrounds thylakoids
Where reactions occur
Stroma
Surface of the thylakoids
Increase surface area
Thylakoid space
Links Membranous Organelles
Consists of ER, the nuclear envelope, Golgi, vacuoles, vesicles and the plasma membrane
Interchangeable membranes (not same composition)
The greatest part of the endomembrane system is the ER
Network of membranes
50% of the total membrane surface
series of channels (tubules) and sacs (cisternae)
Ribosomes are attached to rough ER
Smooth ER has no ribosomes
Functions of ER
Reactive surface (enzymes, large SA)
Attached to the nuclear membrane
Packaging service
Packaged in vesicles
Golgi are part of the endomembrane
system
series of flattened membranous sacs
receive vesicles from the ER (vesicles fuse)
repackage materials for export (secretion at the surface of the cell)
Golgi buds off vesicles
fuse with plasma membrane releasing their contents
The Origin of Membranous Organelles
Same as origin of eukaryotes
How did eukaryotes arise from prokaryotes?
Two theories: autogenous hypothesis, serial endosymbiosis hypothesis
The Autogenous Hypothesis
Organelles in the endomembrane system
Autogenous =or self producing
Endomembrane system evolved from infoldings of the prokaryotic plasma membrane
Became fragmented from the plasma membrane to form enclosed chambers (organelles)
Evidence for the autogenous hypothesis
Some prokaryotes have infoldings of their membrane
Endomembrane system has interchangeable membranes
The Serial Endosymbiosis Hypothesis
Chloroplasts and mitochondria may have been prokaryotes
Gained entrance to other prokaryotes
Established a mutualistic symbiotic relationship
Serial endosymbiosis has a series
of steps
Endomembrane system first (larger)
Mitochondria next
Then chloroplasts
Mitochondria were prokaryotes that
produce ATP
Oxidation of glucose
Like aerobic cellular respiration
Advantage to host cell: source of ATP
More efficient
Invader: a reliable source of glucose and a protected environment
Chloroplasts were autotrophic prokaryotes
Photosynthesis
Advantage to host: source of glucose
No longer heterotrophic
Feed its other hungry guests (the mitochondria)
Evidence for mitochondria and chloroplasts
being prokaryotes
Same size as prokaryotes
Endosymbiosis common e.g. corals
enzymes similar to enzymes of modern prokaryotes
own circular chromosomes (with no attached proteins) like prokaryotic chromosomes
Evidence for mitochondria and chloroplasts being prokaryotes
own tRNA, ribosomes
react to antibiotics
ribosomes similar to prokaryotes
divide independent of the host cell (by binary fission)
Other Differences Between Prokaryotes
and Eukaryotes
Membranous organelles, larger
Linear chromosomes with proteins (called histones)
Meiosis and mitosis evolved in the protists
Cytoskeleton
Cytoskeleton has many functions
Supports the cell
Maintains the shape of cells
Transport of cellular structures like vesicles and chromosomes
Cell motility
Cytoskeleton is a dynamic structure
Assembled or disassembled quickly
3 types of subunits each with different functions:
Microtubules
Microfilaments
Intermediate filaments
Microtubules
Hollow non-compressible
Girders or tracks for internal transport
Form spindle during mitosis and meiosis (separate chromosomes)
Cilia and flagella (9+2 arrangement) [pro are solid]
Microfilaments
Solid
Bear pulling forces and cause contractions (e.g. muscle contraction)
Intermediate
filaments
Solid
More permanent skeletal units
Maintain the shape of cells
Significance of the Cytoskeleton
serial endosymbiosishypothesis cannot explain it
eukaryotes are larger than prokaryotes because of ability to move materials faster internally
evolution of mitosis and meiosis due to the cytoskeleton
key to our understanding of eukaryotic evolution