Download The Cell: Basic Unit of Life

The Cell:
Basic Unit
of Life
Stephen J. Salek
Prokaryotes and the
Evolution of
Eukaryotes
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
Universal Cell Components
•
•
•
•
cell membrane
cytoplasm
genetic material (DNA)
ribosomes
– for protein synthesis
Campbell Fig. 7.4
Bacteria
The Smallest, Simplest Cells
Campbell Fig. 27.2
rod-shaped
spherical
ALL BACTERIA ARE PROKARYOTES.
spirilliform
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 Features
Campbell
Fig. 7.4
Advanced Prokaryote Features
• interior membranes
• bacterial flagellum
• some are photo-autotrophic
compare Campbell Fig. 27.9
Campbell Fig. 27.6
Campbell Fig. 27.5
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
Campbell Fig. 27.1, 27.11, Table 27.2
• 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
prokaryotes
Bacteria
Archaea
Eukarya
Archaea
• unusual environmental tolerances:
– extreme halophiles
– extreme thermophiles
– methanogens
Campbell Fig. 27.10
Eukaryotes
• 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.
Evolution of Eukaryotic Cells
Campbell Fig. 28.2
Step 1: Nuclear and endoplasmic 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
Mitochondrion
Campbell Fig. 7.17
External and
internal membranes
(compare to early stages of
eukaryote cell evolution)
Chloroplast
Campbell Fig. 7.18