The Cell: Basic Unit of Life Prokaryotes and the Evolution of Eukaryotes.
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Transcript of The Cell: Basic Unit of Life Prokaryotes and the Evolution of Eukaryotes.
The Cell: Basic Unit
of Life
Prokaryotes and the Evolution of
Eukaryotes
• Universe is 10-20 billion years old
• Atmosphere H first then other gases
• Earth solidifies 4.1 bya
• 1st photosynthetic prokaryotes 3.5 bya
Figure 16.1C
= 500 million years ago
Earliest animals; diverse algae
Earliest multicellular eukaryotes?
Earliest eukaryotes
Accumulation of atmosphericO2 from photosyntheticcyanobacteria
Oldest known prokaryotic fossils
Origin of life?
Formation of Earth
Bil
lio
ns
of
ye
ars
ag
o
Early earth and the origin of life
Universal Cell Components
• cell membrane• cytoplasm• genetic material (DNA)• ribosomes
– for protein synthesis
Campbell Fig. 7.4
Figure 16.2a-0
Cocci Bacilli Spirochete
BacteriaThe Smallest, Simplest Cells
ALL BACTERIA ARE PROKARYOTES.0.5-3m
Prokaryotic Features
• DNA is in a single-stranded loop – No chromosomes, mitosis, or meiosis– Lack a membrane-bound nucleus
• No mitochondria, chloroplasts, or other organelles
• Cell walls are chemically unlike any eukaryote cell walls
Bacterial Cell FeaturesCampbell Fig.
7.4
Advanced Prokaryote Features
Campbell Fig. 27.5
Campbell Fig. 27.6
compare Campbell Fig. 27.9
• interior membranes• bacterial flagellum• some are photo-autotrophic
Bacteria are Important
• Pathogens (“disease-causing”) are parasites on living cells and organisms
• Decomposers rot dead material, recycling essential nutrients
• Mutualists with -– plants: root-knot rhizobia fix nitrogen– fungi: cyanobacteria are part of lichens– animals: intestinal bacteria digest
cellulose
Commercial Bacteria
• Lactose-users make yogurt and cheese• Soil bacteria make many antibiotics• Intestinal bacteria used as “lab rats” in
cell biology• Cyanobacteria are important for marine
and freshwater food chains
3 Domains of Life
• Archaea are also prokaryotes• Recently separated from Bacteria
– Cell wall chemistries are different – Archaea genes more like eukaryotes’
• Only Eukarya have a proper nucleus
Phylogeny of Domains
Bacteria Archaea Eukarya
prokaryotes
Archaea
• unusual environmental tolerances: – extreme halophiles– extreme thermophiles– methanogens
Campbell Fig. 27.10
• true cell nucleus:– nuclear membrane– linear DNA, organized into
chromosomes– replicate by mitosis and meiosis
• Plants, animals, and fungi are eukaryotes.
• Many unicellular algae and protozoans are also eukaryotes.
Eukaryotes
Evolution of Eukaryotic CellsCampbell Fig. 28.2
Step 1: Nuclear and endo-plasmic membranes (kingdom Archezoa)
Step 2: Organelles acquired by symbiosis (remaining 7 kingdoms)
Organelles
• Bacteria that were parasites, became mutualists– mitochondria burn sugars, etc., for energy– chloroplasts photosynthesize more energy– chloroplasts were lost during evolution of
many living eukaryotes, such as animals and fungi
MitochondrionCampbell Fig. 7.17
ChloroplastCampbell Fig. 7.18
External and internal membranes
(compare to early stages of eukaryote cell evolution)
Cytoplasmic Movements
microfilaments in cell
Campbell Fig. 7.27
Eukaryote Locomotion
All is based on contractile fibers
• mitotic spindle and centrioles
• eukaryote flagellum and cilia
• ameboid movement and cytoplasmic streaming
9 + 2 double fibrils
Campbell Fig. 4.18
Flagellum Cilia
Early earth and the origin of life
• Universe is 10-20 billion years old
• Atmosphere H first then other gases
• Earth solidifies 4.1 bya
• 1st photosynthetic prokaryotes 3.5 bya