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Erwin Shrdinger, What is Life, 1944

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Title: Erwin Shrdinger, What is Life, 1944


1
Erwin Shrödinger, What is Life, 1944
What is Life?
  • What is the characteristic feature of life? When
    is a piece of matter said to be alive? When it
    goes on 'doing something', moving, exchanging
    material with its environment, and so forth, and
    that for a much longer period than we would
    expect an inanimate piece of matter to 'keep
    going' under similar circumstances.

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Biology is Beautiful!
  • Biology is full of amazing diversity
  • At a conceptual level, biology uses amazingly
    complex systems of biochemistry, structure, and
    behavior
  • The way these complex systems function together
    will keep us involved in fascinating discovery
    for generations.

4
Patterns of Life
Life builds from the bottom up Life assembles
itself into chains Life needs an inside and an
outside Life uses a few themes to generate many
variations Life organizes with information Life
encourages variety by reshuffling
information Life creates variety with
mistakes Life occurs in water Life runs on
sugar Life works in cycles Life recycles
everything it uses Life maintains itself by
turnover Life tends to optimize rather than
maximize Life is opportunistic Life competes
within a cooperative framework Life is
interconnected and interdependent
5
  • So how would you define Life?
  • Can it be defined, or only described
  • (inductive vs. deductive thinking)

6
Definition of Life (Themes of Biology)
  • Metabolism (energy utilization)
  • Self-reproducing
  • Responds to its environment
  • Growth Development
  • Homeostasis regulation
  • Evolution
  • Made up of cells with membrane and DNA

7
A Thermodynamic Definition of Life
  • The Second Law of Thermodynamics states that
    Left to themselves, all systems will eventually
    decay into uniform disorder, and all energy will
    be dissipated as heat (maximum entropy).
  • Living things have found a loophole in this law
    by creating order in one place by using energy
    and increasing entropy elsewhere in the universe.
  • The processes we associate with life occur far
    from equilibrium -- life demands the active
    maintenance of structures in defiance of entropy,
    structures which if left to themselves, would
    decay and disappear.

8
Life is Metabolism
  • Living things need to maintain their highly
    organized structure against a hostile world
    (entropy).
  • In order to do this, they consume high energy
    molecules, derive useful energy from carefully
    controlled chemical reactions, and release the
    resulting waste products.
  • Therefore, we can very simply define life as
    that which eats.

9
Homeostasis
  • Biological systems (cells, organisms, ecosystems)
    maintain stable internal conditions despite
    changes in the environment.
  • Homeostasis requires constant work
  • obtain food, remove waste products
  • counter changes from the environment
  • a multiplicity of dynamic equilibria rigorously
    controlled by interdependent regulation mechanisms

10
Regulation
  • Every cellular system must be regulated
  • respond to environmental changes
  • respond to changes in internal chemical
    concentrations
  • developmental changes as the cell grows,
    reproduces and/or specializes
  • Feedback regulation
  • a metabolic product blocks the reactions that
    produce that product
  • Communication between cells
  • cell surface sensors trigger internal processes
  • signaling pathways - pass the message from one
    molecule to another

11
Growth Development
  • Living things grow
  • Each organism has a distinct life cycle
  • It changes in some fundamental ways from the
    time it is born until the time it is ready to
    reproduce
  • May respond to environmental changes by a complex
    program of physical, metabolic and/or behavior
    changes
  • Multicellular organisms have cellular
    specialization.
  • May have different physical forms at different
    stages of the life cycle
  • At some point, mammals are just a sperm an egg

12
Evolution
  • Evolution explains both the diversity and the
    unity of life.
  • Evolution is the central organizing principle of
    all biology.
  • Variation in many traits among the members of a
    species (DNA mutations)
  • Competition between members of a species for
    limited resources
  • Survival (and reproduction) of the fittest

13
Life is Cells
  • Everything alive is made up of cells.
  • Every living thing is either a single-celled
    creature, or a creature composed of many living
    cells.

14
Are Viruses Alive?
Adenovirus Coronavirus HIV
-Cells? -Metabolism? -Self-replicating?
15
The Cell Theory of Life
  • Omnis cellula e cellula or literally All
    cells from cells
  • In more precise language
  • All living things are made up of cells. 
  • All cells come from pre-existing cells. 
  • There is no spontaneous generation (under current
    conditions) 

16
Properties of Cells
  • Every cell is bounded by a membrane and contains
    a full set of instructions necessary for its
    operation and reproduction.
  • Every cell uses the same operating system
  • instructions are stored in the DNA molecule
  • DNA is transcribed into RNA
  • RNA is translated into protein
  • There are hundreds of thousands of different
    proteins used by living things, but all of them
    are made from the same twenty amino acids

17
So What is a Cell?
  • In its simplest description, a cell has 3
    essential parts
  • a membrane that defines the boundary of the cell
  • inner material called cytoplasm
  • DNA that contains the information that the cell
    requires to live and reproduce.

18
Cell Membranes
  • All cells have membranes which are made up of
    phospholipid molecules - similar to fat
    molecules.
  • Phospholipids are composed of two parts, a
    phosphate ion, which forms a negatively charged,
    water soluble head, and long fatty acid tails
    which are non-polar and insoluable in water.

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Phospholipids form membranes
  • A small group of phospholipids in water will
    self-assemble into a micelle
  • non-polar hydrocarbon tails on the inside and the
    phosphate heads pointing out into the water.

21
Liposomes
  • A larger amount of phospholipids will form a
    bi-layer membrane phosphates pointing out and
    the fatty acids in the middle.
  • This bilayer membrane tends to form a liposome
    with some water trapped inside.

22
Cells are Liposomes
  • A cell is a liposome
  • The membrane creates and inside and an outside.
  • Cellular processes such as osmosis and active
    transport cause the accumulation of very
    different concentrations of molecules inside
    vs. outside

23
Membrane Proteins
  • A cell membrane also contains many proteins
  • some on the outer surface
  • some on the inner surface
  • some buried inside
  • some passing all the way through
  • Some of these proteins are assembled into complex
    structures such as pores that selectively allow
    specific materials to move through the membrane
  • Others are receptors that function as sensory
    devices for molecules outside the cell and
    transmit signals to other molecules on the
    inside.

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Prokaryote vs. Eukaryote
  • There are two basic types of cells
  • Prokaryotes (bacteria)
  • Eukaryotes (everything else)
  • Prokaryotes are smaller and simpler than
    eukaryotic cells
  • no cell nucleus
  • DNA is organized in a single circular chromosome
  • plus some smaller circles called plasmids
  • Prokaryotes have existed on earth for about 4
    billion years, but eukaryotes first appeared
    about 1.7 billion years ago.

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Prokaryote Grow Faster
  • Prokaryotes can multiply faster than eukaryotic
    cells
  • They have shorter genetic instructions to be
    replicated (less DNA)
  • The replication process goes about ten times as
    fast
  • Prokaryotes don't combine and specialize to form
    multicelled creatures.

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Prokaryote Diversity
  • Bacteria come in a wide variety of types
  • blue-green algae,
  • free living vs. pathogens,
  • anaerobic vs. oxygen requiring,
  • thermophilic, halophiles, etc.
  • Prokaryote diversity is much greater than that of
    eukaryotes, but it is difficult to define a
    species of bacteria

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Archaebacteria
  • There are two vastly different types of
    prokaryotes.
  • Archaebacteria live in extreme environments (deep
    ocean volcanic vents, hot springs, etc).
  • At a molecular level, archaebacteria are actually
    more different from eubacteria than bacteria are
    different from eukaryotes
  • There is evidence that archaebacteria are the
    oldest kind of life on earth.
  • Concept of 5 or 6 kingdoms of life
  • Concept of 2 domains archaea and everything else

32
Three Domains of Life
  • Note that plants, animals and fungi radiate from
    a common origin, but protists do not.
  • Archaea may be closer to eukaryotes than to
    bacteria.

33
Eukaryotes
  • Eukaryotic cells are much more complicated than
    prokaryotic cells, primarily due to the existence
    of internal membrane compartments (organelles).
  • Eukaryotic cells keep their DNA on multiple
    chromosomes in a nucleus enclosed by a nuclear
    membrane.
  • usually have two whole copies of their genome
    (diploid) that is two copies of each
    chromosome.

34
Organelles
  • Mitochondria and chloroplasts are membrane bound
    cellular sub-structures that have their own DNA.
  • These two organelles enable eukaryotic cells to
    conduct respiration and photosynthesis,
    respectively.
  • Mitochondria and chloroplasts have internal
    memberanes
  • There is considerable evidence to suggest that
    mitochondria and chloroplasts originated as
    prokaryotic cells that were incorporated into
    early eukaryotic cells.

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Sub-cellular Structures
  • Other membrane structures exist in some
    eukaryotic cells
  • endoplasmic reticulum (site of protein
    processing)
  • lysosome (protein degradation)
  • vacuole (storage in plant cells)
  • There are also single celled eukaryotes -
    protists

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Protists
  • Protists are an extremely diverse group of
    eukaryotes
  • single celled organisms such as algae, amoeba,
    paramecium, plasmodium, euglena
  • some colonial organisms Volvox, brown
    algae-kelp, slime mold (no cellular
    specialization)
  • Genetic evidence suggests that various groups of
    protists may have evolved separately
  • they are more evolutionarily distant from plants
    and animals and from each other, than animals are
    from plants.
  • some have chloroplasts, some have a contractile
    vacuole, some have cilia or flagella that are
    used for movement or to create currents of moving
    water

42
paramecium
amoeba
diatoms
euglena
43
volvox
stentor
44
Plant vs. Animal cells
  • Although they are both eukaryotes, there are some
    fundamental differences between plant and animal
    cells.
  • Plant cells have a cell wall, chloroplasts, and
    vacuoles.
  • Photosynthesis!
  • Animal cells are specialized into many more
    different cell types, some of which are mobile
    within the organism.

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Multi-cellular
  • Eukaryotic cells are able to combine and
    specialize to create multicelled organisms such
    as animals, plants and fungi
  • Cells specialize and cooperate
  • Differentiation into specialized cell types
  • create tissues and organs
  • control of gene expression
  • as a developmental process

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Plants
  • Plants conduct photosynthesis
  • transform light energy into sugars, starches,
    proteins and fats
  • absorb carbon dioxide and produce oxygen
  • Simple body structure
  • Leaf, stem, root
  • More complex reproductive structure flower
  • Cells have chloroplasts and central vacuole
  • Woody tissue has cellulose and lignin in cell
    walls

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Fungi
  • At a cellular level, fungi resemble plants
  • They have a cell wall, and only form a few
    specialized cell types
  • Genetically, they are quite distinct, with a
    number of unique life cycle adaptations
    (multicellular haploid organisms with a diploid
    reproductive stage).
  • Parasitic or saporophitic life style
  • mushrooms
  • yeast
  • plant diseases
  • fungal infections

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Kingdoms of Life
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Tree of Life
  • Since all life has a common organization, it is
    possible to group living things according to
    their similar properties.
  • The most informative groupings reflect the
    relationships among both currently living and
    extinct organisms
  • shows the course of evolution that led from a
    single common ancestor to the present diversity
    of living things
  • This organization is known as a phylogenetic tree
  • The best trees are based on comparisons of DNA
    and protein sequences.
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