Cellular Life

• Two cell types: prokaryotes & eukaryotes

• Cell structure

• Cell organelles & their functions

Origin of living cells: Prokaryotes

fossilized bacteria living bacteria

• prokaryotic cells (bacteria & archaea)• found as fossils: 3.5 billion years old• heterotrophic (not photosynthetic)

Living bacteria cells

Origin of eukaryotic cells

Endomembrane system• includes nuclear membrane, endoplasmic reticulum, etc.• derived from plasma membrane

Mitochondria & chloroplasts• endosymbiosis hypothesis• remnants of once free-living prokaryotes took up residence inside transitional prokaryotic-eukaryotic cell

Evidence for the endosymbiotic hypothesis

Mitochondria & chloroplasts:

• have own DNA

• protein synthesis similar to bacteria

• divide / replicate independently

Earliest eukaryotes similar to present-day unicellular

members of Kingdom Protista

Various Protists

flagellate algae

amoeba

paramecium

diatoms

cyanophytes

Multicellular forms of life probably arose from colony-forming protists

2 general categories of cellular life

Prokaryotic cells: bacteria, blue-green algae

• simple design - lack internal organelles

• primitive - first forms of life, mostly unicellular

• small - 1/10th size of eukaryotic cells

Eukaryotic cells: plants, fungi, animals, protistans• complex internal design - intracellular organelles• more derived than prokaryotic cells• larger than prokaryotic cells (10 – 100x their size)

Prokaryotic cell

Internal organelles & nucleusPresent in eukaryotic cell, lacking in prokaryotic

Red blood cells Bacteria on pin tip

The plasma membrane

• A semi-permeable barrier: some substances move easily across, others do not

• Membrane is permeable to water, not larger or ionized molecules

The plasma membrane:

composed of phospholipid molecules and protein

Important ideas:

• The concentration of water on either side of a cell membrane is related to solute concentration

• If membrane is not permeable to solute, water will move (osmosis) from region of low solute concentration to higher solute concentration

•region of higher solute concentration termed: hypertonic

•region of lower solute concentration termed: hypotonic

•if both regions the same: isotonic

Water will move (diffuse=osmosis) from hypotonic region to hypertonic region, until water concentration is the same

Normal blood plasma

Distilled water Very salty water

Cell is in: isotonic solution

hypotonic solution

hypertonic solution

Plant vs. animal eukaryotic cellsPlant cells have, in addition to preceding features:

1. Cell wall• exterior to plasma membrane, cellulose

2. Central vacuole• fluid-filled organelle• occupies most of cell interior• organic nutrient storage

3. Chloroplasts• organelles of photosynthesis

Eukaryotic cell - Plant

Eukaryotic cell - Animal

Endomembrane system

Endoplasmic reticulum (ER)

Rough - new membrane proteins & secretory proteins

Smooth - many functions including• Synthesizes lipids,• Detoxes poisons in bloodstream

Golgi apparatus• products from ER transported here• enzymes modify the products• distributes final molecules to appropriate organelles

C6H12O6 + 6O2 6CO2 + 6H2O + ATP

Glucose & oxygen react to yield carbon dioxide, water & ATP

Mitochondria: site of cellular respiration

Chloroplasts: site of photosynthesis

•Plants and algae only

•Convert solar energy to chemical energy (carbohydrates)

Cytoskeleton:• maintenance of cell shape &

organelle position• cell motility• movement of substances within cell

Cilia & flagella:

• cell motility

• movement of substances external to cell

ciliaflagellum

The nucleus• membrane bound region containing DNA

• segments of DNA (genes) have information for construction of other molecules

Nitrogenous Bases

of DNA

The building blocks (monomers) of nucleic acids

a nucleotide polymer

portion of a DNA double-helix