The Role of the Endomembrane System in the Evolution of Eukaryotic

Cell FunctionChapters 6 and 7

The Cell Theory

• All living organisms are composed of cells.• The cell is the basic unit of life.• Cells arise from pre-existing cells…except

the first cell???

Key Events in the Evolution of Cells

• Be able to describe the event and place it in sequence (approx. dates)

• Identify key terms• Discuss supporting evidence • Visuals?

* Considering organizing events in a table

Evolution of Eukaryotic Cells• Endosymbiosis –Describe the steps of the

theory

A theory needs evidence…

• mtDNA and cpDNA• Ribosomes and

protein synthesis• Size/Structure• Double membranes• Binary Fission

More evidence for Eukaryotic Cells

Archean Molecular Fossils and the Early Rise of Eukaryotes• Abstract: Molecular fossils of biological

lipids are preserved in 2700-million-year-old shales from the Pilbara Craton, Australia. The presence of abundant 2αmethylhopanes, which are characteristic of cyanobacteria, indicates that oxygenic photosynthesis evolved well before the atmosphere became oxidizing. The presence of steranes, particularly cholestane and its 28- to 30-carbon analogs, provides persuasive evidence for the existence of eukaryotes 500 million to 1 billion years before the extant fossil record indicates that the lineage arose.

Evolution of Eukaryotic Cells

• Definition of Eukaryotic –contains a nucleus and membrane bound organelles

• Membrane structures meets function!

Phospholipid Bilayer

Why???• Hydrophilic • Hydrophobic

Term: Amphipathic

Diversity of lipid composition leads to diversity of functions

• What keeps membranes flexible?

• Unsaturated vs. Saturated fats

• Role of cholesterolo Depends on

temperature• Warm Temperatures• Low Temperatures

How are proteins arranged in the membrane?

• Proteins are embedded in membranes rather than sandwiched.

• Evidence: freeze fracture technique

Freeze Fracture Technique and Scanning Electron Microscope (SEM)

Images

Structure of integral proteins allows them to embed in the membrane using

hydrophobic forces• Amphipathic

• Aquaporin is an example of an amphipathic protein that spans the cell membrane and has a hollow core to allow water to pass through

Aquaporin

• Where might the hydrophobic parts be?

• Hydrophilic?

• How might influx of water be controlled?

Fluid Mosaic Model

• Proteins (and lipids) can shift laterally throughout the cell membrane

• How is the above experiment evidence of this concept?

Endomembrane System• Be able to describe the role of each organelle in the

pathway of protein production

Exocytosis• Production and Secretion of an “exogeneous” protein

o Identify and sequence the organelles involved in protein synthesis and secretion

What about an “endogenous” protein?

Biovisions video

• Inner Life of a Cell – animation that portray the dynamic activity within a cell.