The Cell: Basic Unit

of Life

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

BacteriaThe Smallest, Simplest Cells

ALL BACTERIA ARE PROKARYOTES.

rod-shaped

spherical

Campbell Fig. 27.2

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 FeaturesCampbell Fig. 7.4

Advanced Prokaryote Features

Campbell Fig. 27.5

• interior membranes• bacterial flagellum• some are photo-autotrophic

Campbell Fig. 27.6

compare Campbell Fig. 27.9

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 LifeCampbell 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 Domainsprokaryotes

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 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

ChloroplastCampbell Fig. 7.18

MitochondrionCampbell Fig. 7.17

External and internal membranes

(compare to early stages of eukaryote cell evolution)