Endosymbiotic Theory

Cell

The smallest unit of life that displays all the properties of life

1. All organisms are composed of cells 2. Cells are the basic units of structure and function in organisms 3. Cells come only from preecisting cells because they are self-reproducing

Cell theory

Surface-area-to-volume ratio

Ratio of a cell’s outside area to its internal volume, this limits the maximum size of a cell

Plasma Membrane

The enclosing part of the cell which separates the cell’s interior from the environment

Cytoplasm

Made of cytosol in which other components of the cell are found

DNA

The genetic material of the cell

Ribosomes

Synthesize proteins

Characteristics of Prokaryotes

Lack membrane-enclosed internal compartments like the nucleus, usually have a cell wall containing peptidoglycan, believed to be much like the first cells, organisms in archea and bacteria

Generalized structure of a prokaryotic cell

Chromosomal DNA is localized in a nucleoid, ribosomes are in the cytoplasm, the cell membrane is surrounded by a cell wall (the other structures may be present in some, but not all becteria)

Families of Eukaryotic Cells

Fungi, plantae, animalia, protista

lower surface area to volume ratio

Since Eukaryotic cell are larger than prokaryotic cells, they have a…

Result of prokaryotic.cells being smaller than eukaryotic cells

Surface area to volume ratio is more favorable for moving material in and out of the cell, they lack modifications found in eukaryotes that aid internal transport

Explains how eukaryotic cells evolved from prokaryotic cells

What does endosymbiotic theory explain?

Endosymbiotic Theory

Large prokaryotic cells engulfed (consumed) smaller bacteria capable of specific functions. Instead of being digested, these bacteria lived symbiotically inside the host. Over time, they became organelles

Evidence Supporting Endosymbiotic Theory

• Mitochondria and chloroplasts show prokaryotic traits

  • Have their own circular DNA (like bacteria)

  • Contain 70S ribosomes (same size as bacterial ribosomes)

  • Reproduce by binary fission within the cell (multiply and divide)

  • Have double membranes (inner one bacterial in origin)

  • Similar size to modern bacteria