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