Marks – Reading Quizzes and Assignments
●
Reading Quiz:
–
●
0 NCR, 4 NCR+, 7 CR, 8 CR+, 0 CR++
Assignments:
–
0 NCR, 0 NCR+, 2 CR, 15 CR+, 0 CR++
Missed Assignments, Quizzes
●
Put answers up on web page as soon as possible
●
Can't accept late assignments
●
Will accept short (~1 page) writeups for 2 points
on
–
Items in the news
–
Project topics
Summary of Last Class
●
●
Chemical building blocks of life: polymers, long
chains of similar elements (monomers)
–
Amino acids -> components of protein
–
Nucleotides -> components of DNA, RNA
–
DNA: storehouse of genetic information
–
RNA: translates DNA to protein
–
Protein: molecular machines
Amino acids seem to form quite easily in Hydrogenrich environment: Urey-Miller experiment
Feedback:
●
Most unclear item from last week's readings?
What we're going to cover today
●
From Biochemistry to Biology
–
Exponential Growth
–
Phylogenic Trees
–
Viruses
–
Prokaryotes
●
●
Archaebacteria
Bacteria
–
Photosynthesis
–
Eukaryotes
–
Sexual Reproduction
–
Biological Complexity
–
Web of Life
Exponential Growth
●
●
●
●
In processes involving selfreplication (like life), exponential
growth naturally arises
Effects all facets of growth
Imagine a `cell' that divides every
generation (or that has two
children, and then then parent
dies)
Generation 1 (1 cell)
Exponential Growth
●
Generation 2 (2 cells)
Exponential Growth
●
Generation 3 (4 cells)
Exponential Growth
●
Generation 4 (8 cells)
Exponential Growth
●
Generation 5 (16 cells)
Exponential Growth
●
Generation 6 (32 cells)
Exponential Growth
●
Generation 7 (64 cells)
Exponential Growth
●
Generation 8 (128 cells)
Exponential Growth
●
Generation 9 (256 cells)
Exponential Growth
●
Generation 10 (512 cells)
Exponential Growth
●
●
●
Such growth is said to be
exponential, or geometric.
Once the process is
exponential, everything is
exponential:
–
Number of children
–
Number of reproductions
–
Amount of area/resources
needed
–
Rate of growth
Anything with a fixed
`doubling time' is exponential
Exponential Growth
●
●
This exponential growth is the
source of the intense
competition for resources
underlying evolutionary
adaptation
Very soon, resources begin
getting scarce; any species or
mutation which has an
advantge has a much better
chance of thriving
Exponential Growth
●
●
●
Everything starts happening
faster as exponential growth
proceeds
Mutation rate; in mammals, ~1
per 100,000 reproductions per
gene
By generation 10, ~512
individuals. How long before
significant number of
mutations expected in a given
gene?
Exponential Growth
●
●
●
Everything is exponential
By generation 20, already
expect ~20 mutations
That too is exponentially
increasing
●
By generation 25, > 600
●
By generation 30, > 20000
●
Dividing by 100,000 just
means it takes a little longer
before it takes off
Tree of Life
●
Phylogenetic tree
●
`Family Tree' of species
●
●
Distance from neighbors, root
indicates how genetically different
Three distinct branches:
–
Archaea (includes
`extremophiles)
–
Bacteria
–
Eukaryotes (includes all life
visible to naked eye)
Building a Phylogenetic Tree
●
Inferred ancestor
Evolution Time
●
Inferred ancestor
●
●
Genetic Distance
●
Difficult: Only have genetic
information from the present.
Can take genetic informtion from
present day species and examine
differences
Number of differences in genome:
`genetic distance'
Simplest: if constant mutation rate,
can work backwards and see how
long ago two species must have
first differed
Can infer most recent common
ancestor
Virus
●
Not Included
●
Self-replicating DNA or RNA
●
Not self sufficient
●
●
Requires the mechanisms of a living cell
to propagate it
As a result, much smaller than bacteria
(largest virus ~ smallest bacteria)
Virus
●
●
Propagates by latching onto target cell
Virus usually has `spikes' on its outer
coating which allow it to target
particular sorts of cells
Virus
●
●
●
Propagates by latching onto target cell
Virus usually has `spikes' on its outer
coating which allow it to target
particular sorts of cells
Inserts its own genetic information
(DNA, or RNA) into cell
Virus
●
●
●
●
●
Propagates by latching onto target cell
Virus usually has `spikes' on its outer
coating which allow it to target
particular sorts of cells
Inserts its own genetic information
(DNA, or RNA) into cell
Cells machinery begins processing this
genetic information as if it was its own
Replicates copies of virus
Virus
●
●
●
●
●
●
Propagates by latching onto target cell
Virus usually has `spikes' on its outer
coating which allow it to target
particular sorts of cells
Inserts its own genetic information
(DNA, or RNA) into cell
Cells machinery begins processing this
genetic information as if it was its own
Replicates copies of virus
Eventually cell dies, new copies of virus
escape
Virus
●
Alive?
–
Inert RNA/DNA/protein until
collides with target cell
–
Incapable of independent action,
growth, reproduction
–
Not generally considered to be
living.
Prokaryotes
●
●
Simplest form of life
Includes bacteria (like E. Coli)
and archaebacteria
●
No complex internal structure
●
DNA lies together in a blob
●
●
●
Prokaryotic DNA consists of one
ring
Processes occur throughout cell
Many reproduce by cell division
(asexual)
Prokaryotes
●
Among the earliest forms of life
●
Earliest fossils: ~2.5 BYA
●
●
●
Evidence for life before that:
biomarkers
–
Differences in isotopic
abundances in Oxygen, sulfur
–
Increase in Oxygen
Microbes can leave `compression'
fossils, or leave more detailed fossils
in very fine silt
Here see fossils of algae, and modern
algae (round things)
Stromatalites
●
●
●
`Mat' of cyanobacteria (bluegreen algae)
Photosynthesis
Produce oxygen, lime, gel-like
secretion
●
Gel protects them from UV
●
Gel traps sand
●
●
●
Layers form as new generations
`born'
Rare now, but still found in parts
of Australia
Species remains nearly
unchanged for ~ 3 BY!
Prokaryotes
●
●
●
●
Consist of Bacteria, and the more
ancient Archaebacteria
Archaea: Carle Woese, U. of Illinois
Differences between the two: wall,
membrane structures; metabolism
Many of the `extremophiles' are in
domain Archaea.
Extremophiles
●
●
●
M. Jannaschii thrives near
underwater volcanic vents in
temperatures, pressures, darkness,
and lack of oxygen that would kill
other life
●
Unlike more
`advanced'
forms of life, prokaryotes thrive
in startling variety of
environments
Can live with, without, or only
without oxygen
Can live in very acidic, alkaline,
hot, cold, dark, or salty
enviroments
Early earth would have been
rich with these enviroments
Need For Oxygen
●
Existance of life with varying tolerances for
oxygen is consistant with our picture of early
Earth:
–
No free oxygen at start (tied up in CO2,
water)
–
Oxygen-intolerant life
–
Photosynthesis generated more and more
oxygen
–
Oxygen-ambivalent life
–
Finally enough oxygen that some species
could reliably depend on it
Photosynthesis
6 H2O + 6 CO2 -> C6H12O6 + 6 O2
●
●
●
A process that uses light
energy to convert water,
carbon dioxide to sugar (a
useful fuel) plus oxygen
Clorophyll is the key
molecule in this process
Absorbs some light, triggers
a chemical reaction
Photosynthesis
●
●
●
Suggestively, Clorophyll
absorbs mainly in blue/green
region of spectrum
Shorter wavelength -> more
energy, but is easily
absorbed by water
Photosynthesis powered by
green light can happen much
deeper underwater
Photosynthesis
●
●
●
Plants have specialized cell
units (chloroplasts) which
are dedicated to the process
of photosynthesis
In prokaryotes, process
happens throughout cell
Cholorophyll lives in the
thylkoid
Photosynthesis
Xtreme Photosynthesis
●
●
●
●
●
Green sulfur bacteria can photosynthesize with
very little oxygen or light around
Photosynthesize Sulfur using Hydrogen
Sulfide instead of water
Spit out Sulfur instead of Oxygen
Can even occur using infrared, instead of
green light
These conditions make it ideal for living near
volcanic vents
–
Lots of sulfur
–
Not so much light
Eukaryotes
●
●
●
●
●
Has a nucleus, and other
`organelles’
DIVISION OF LABOUR
Mitocondrion: energy
factory
Chloroplast (plants):
photosynthesis
Nucleus: protects DNA;
interface between DNA and
rest of cell
Eukaryotes
●
●
●
●
Because of increased
complexity, greatly
increased genetic
information
~100-1000x DNA of
prokaryote
Has to describe all of the
increased structure in cell
May reproduce sexually or
asexually
Sexual Reproduction
●
●
●
Allows greater mixing of
genes
Rather than waiting for
single mutation, can have
combination of genes
randomly generated
Greatly speeds up
evolutionary process for
complex organisms where
genes interact.
Cambrian Explosion
●
●
●
Soon after the arrival of
eukaryotes on the scene,
there was a huge explosion
of species
Cambrian Explosion
Exponential growth -> one
expects this, but before
sexual reproduction,
evolution occurred much
more slowly
Multicellular life
●
●
●
●
●
Development of cells that already divided labour
allowed for the next step
Multi-cellular life
Most mammals -- trillions or tens of trillions of
cells, all interdependant
Once cell was used to relying on one organelle
for some job, can `learn’ to rely on another cell
entirely to do job
Once this occurred, the possible combinations of
life forms skyrocketed (Cambrian Explosion)
Multicellular life
●
●
●
●
So many possibilities that
they never appear to repeat
Trilobite, an enormously
successful multicellular
animal, thrived for tens of
millions of years; extinct
with dinasaurs
Never to reappear
On the other hand, a
successful species can
survive indefinately (?)
–
Blue-Green Algae
Summary
●
●
Prokaryotes: Very simple, no nucleus/organelles,
wide variety of enviroments
Eukaryotes: `Division of labour' in cell.
Possibly originated with early symbiosis. Much
more DNA because of increased complexity
●
Eukaryotic life allowed multi-cellular life
●
Cambrian Explosion
●
Mutations
●
Sexual Reproduction speeds evolution
●
Species don't repeat
●
Intelligence...?
●
`Web of life'
Next Week
●
Half way mark
●
No reading quiz
●
●
Review of first half of class: Parts 1, 2, 3 of
textbook
Large assignment on first half of class