1.5 The origin of cells September 4th Pick up your science journal Announcement: Learning portfolio

EQ: How do we know how life began?

1.5.1 Cells can only be formed by the division of pre existing cells Louis Pasteur made a nutrient broth by boiling water containing yeast and sugar Swan-necked flask Omne vivum ex vivo (All life from life)

1.5.2 The first cells must have arisen from non-living material

1.5.2 Recipe for the origin of life The synthesis of simple organic molecules (amino acids) from inorganic molecules (water, carbon dioxide, ammonia) The assembly of these molecules into polymers (e.g. polypeptides from amino acids) Formation of polymers that can self-replicate to allow for inheritance of characteristics Development of membranes with internal chemistry different from their surroundings

1.1.2 Cells carry out all functions necessary for life growth: an irreversible increase in size homeostasis: keeping conditions inside the organisms within tolerable limits metabolism: chemical reactions inside the cell, including cell respiration to release energy nutrition: obtaining food, to provide energy and the materials needed for growth reproduction: producing offspring either sexually or asexually sensitivity: perceiving and responding to changes in the environment Image source: www.fcps.edu

The cell theory All living things are made of one or more cells The cell is the smallest unit of life All cells come from pre-existing cells

Limitations to the cell theory Striated muscle fibers: multi-nucleated, long (30 mm) Fungal hyphae: multi-nucleated Giant algae (Acetublaria): large (100 mm) Viruses: living or not?

2. What is the evidence for the cell theory? All living things are made of one or more cells microscopes allow us to observe that all living things are either unicellular or multicellular Robert Hooke: pioneering microscopist, cork cell Antonio Van Leeuwenhook: master lens maker, animacules

2. What is the evidence for the cell theory? The cell is the smallest unit of life nothing smaller than a cell can survive independently subcellular structures cannot survive independently (nuclei, ER, golgi, chloroplasts, mitochondria) the lower limit on cell size is about 200nm, large enough for DNA, ribosomes, and membranes

Why do cells look so different? Stem cells = Cells that retain capacity to divide and differentiate along different pathways

Why do cells look so different? multicellular organisms can differentiate into a variety of interdependent cell types each specialized to carry out a subset of functions  greater efficiency cellular differentiation achieved through differential gene expression all cells in an organism have identical DNA

4. Relative sizes of cells molecules: ~ 1 nm cell membrane thickness: ~ 10 nm viruses: ~ 100 nm bacteria: ~ 1 µm organelles: up to 10 µm eukaryotic cells: up to 100 µm http://www.cellsalive.com/howbig.htm http://learn.genetics.utah.edu/content/cells/scale/

Cell size molecules: ~ 1 nm cell membrane thickness: ~ 10 nm viruses: ~ 100 nm bacteria: ~ 1 µm organelles: up to 10 µm eukaryotic cells: up to 100 µm http://www.cellsalive.com/howbig.htm

Why is the cell small?

Why is the cell small? Surface area determines rate of exchange Volume determines metabolism As cell size increases, volume increases proportionally faster than SA => SA: V ratio decreases Low SA reduces rate of exchange while high V increases metabolic demands Cell cannot meet needs of metabolic demands

Cell size Stephen Taylor (i-biology)

Stephen Taylor (i-biology)

Stephen Taylor (i-biology)

Stephen Taylor (i-biology)

Stephen Taylor (i-biology)

Stephen Taylor (i-biology)

Stephen Taylor (i-biology)

Science of perception: Law of closure

ATM, floppy disk, hard drive

1.7 Systems biologists “Whole is greater than the sum of its parts” Put together the parts that make up a system and then observe the properties of that 'emerge' from the system “Emergent properties”: occurrence of unexpected characteristics or properties in a complex system Reductionism = reduce phenomenon to its constituent parts. Smallest parts are predictable then the system as a whole is predictable. No new properties will arise from the sum of the parts

What do the components of the watch do individually? What do they do when they are put together in the right way? William Paley: Complexity of X necessitates a designer (as a watch)