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Transcript
Phys 214. Planets and Life
Dr. Cristina Buzea
Department of Physics
Room 259
E-mail: [email protected]
(Please use PHYS214 in e-mail subject)
Lecture 12. The nature of life on Earth. Evolution.
Defining life. Cells
February 1st
Contents
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Textbook pages 148-164
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What is life?
Evolutionary adaptation
The mechanism of evolution
Natural selection
Cells - basic units of life
Earth - Carbon based life
Silicon based life
Molecular components of cells
Movie (13 minutes) Award winning series - Cosmos. Carl Sagan.
(Not found online)
What is life?
1. Order
2. Reproduction
3. Grows and develops
4. Energy
5. Responds to the environment
6. Evolutionary adaptation
Molecules in living organisms exhibit order.
They are arranged in patterns that make cell
structures.
Exception: crystals.
The presence of order in living organisms is a necessary
condition, but not a sufficient condition for life
Spiral patterns in two single celled organism
Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley
What is life?
1. Order
2. Reproduction
3. Grows and develops
4. Energy
5. Responds to the environment
6. Evolutionary adaptation
Living organisms reproduce or are products of
reproduction. All organisms have finite lifetimes
and eventually die. Reproduction corrects for this.
The type of reproduction that occurs between human
beings is referred to as sexual. Bacteria reproduce by
the process of cell division (asexual).
Exceptions:
Mule - is sterile and cannot reproduce even though it is the
product of reproduction between a horse and a donkey
Viruses - incapable or reproducing on their own, need a living
organism.
Prions - infectious proteins, mad cow disease.
A single-celled organism (amoeba) dividing into two cells.
Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley
What is life?
1. Order
2. Reproduction
3. Grows and develops
4. Energy
5. Responds to the environment
6. Evolutionary adaptation
Living organisms grow and develop in patterns
in part by heredity, traits passed to an organism
from its parents.
Exception:
fire
Nile crocodile emerging from its shell.
Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley
What is life?
1. Order
2. Reproduction
3. Grows and develops
4. Energy
5. Responds to the environment
6. Evolutionary adaptation
Energy utilization in living organisms is
one of the most basic requirements of life,
without which organisms could not maintain
order, grow, and reproduce.
Exceptions: Some organisms can survive for very
long period of times in dormant state.
Tube worms living near deep-sea vents obtain energy from
chemical reactions made possible in part by heat released
from the volcanic vent.
Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley
What is life?
1. Order
2. Reproduction
3. Grows and develops
4. Energy
5. Responds to the environment
6. Evolutionary adaptation
Life interacts with the surroundings and
responds to environmental changes.
Exceptions: human-made devices
(thermostat)
A jackrabbit’s ears flush with blood, the blood flow adjusts
automatically to help the animal maintain a constant
temperature by adjusting the heat loss from the ears.
Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley
What is life?
1. Order
2. Reproduction
3. Grows and develops
4. Energy
5. Responds to the environment
6. Evolutionary adaptation
Life evolves as a result of the interactions
between organisms and the environment,
leading over time to evolutionary
adaptations that make species better suited
for the environment.
When the adaptations are significant, these organisms
may be very different from their ancestors – that they
constitute a new species.
A pygmy seahorse is camouflaged in its coral surroundings.
Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley
Evolutionary adaptation
Species = groups of organisms that are genetically distinct.
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the precise border between the two species is not always clear (especially
micro-organisms)
Once a species is identified is given a name consisting of two parts:
italics
Genus
(generic)
Homo
sapiens
Horses and donkeys
Equus caballus and Equus asinus
Species
(specific)
Evolutionary adaptation
Of the six basic properties of life, biologists consider the most fundamental to
be evolutionary adaptation.
Evolution - ancient idea
Anaximander (c. 610-547 B.C.) – life arose in water and evolved to more
complex forms
Empedocles (c. 429-432 B.C.) – creatures poorly adapted perish
Jean Baptiste Lamark – early 1800 – relationship between fossils and living
organisms = life forms evolved by gradually adapting to perform
successfully in their environments; not able to explain how evolution
worked
Charles Darwin – “The origin of species” 1859
The mechanism of evolution
Charles Darwin – “The origin of species” 1859
Fact 1: Overproduction and competition for survival
population has the potential to produce more offspring than the
environment can support (food, shelter) = > competition for
survival
Fact 2. Individual variations: individuals vary in many heritable
traits; some traits make them better to compete for survival
Conclusion: unequal reproductive success = natural selection
Individuals whose traits best enable them to survive and reproduce
will, on average, leave the largest number of offspring that in
turn survive to reproduce.
Evidence for evolution by natural selection
Darwin backed up his claim by
documenting cases of related
organisms adapted to different
environments or lifestyle.
The different species of finches found on the Galapagos islands are evidence of
Darwin’s theory of natural selection because they have all evolved adaptations
from a common ancestor to suit the environmental conditions found on
different islands.
Evidence for evolution by natural selection
Darwin discovered fossils of
extinct organisms clearly
related to modern organisms
(giant armadillos).
Darwin realized that natural
selection explains differences
not only between closely
related modern species
(finches), but larger changes
can occur over a long time ->
extinction of some species
and appearance of others.
Artificial selection – selective breeding of
domesticated plants and animals by humans
over the few thousands of years.
Dogs breeds with common ancestors –
Rottweilers and Chihuahuas
Evolution by natural selection
Evolutionary adaptations are related to changes that occur through time in
DNA
The most basic definition of life which takes account of the relative
importance of the six fundamental properties of living things is that life is
something that can reproduce and evolve through natural selection.
Evolution by natural selection
Movie (13 minutes)
Award winning series - Cosmos.
Carl Sagan.
Disk 2. Ch. 1-4. [0:00 – 13:00]
Natural selection, artificial selection.
Cells - the basic units of life
The basic biological structures of life on Earth are called cells.
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Some organisms consist of single cells, others are complex structures with trillions of
cells working cooperatively, having specialized tasks.
Life elsewhere might be composed of cells, might not have the same biochemistry as
Earth cells.
The fact that all cells used in life on Earth are based on the same biochemistry suggests that
all life on Earth shares a common ancestor.
only left-handed amino acids; the same molecule - ATP - to store and release energy; passes
hereditary information in the same way with DNA.
Earth life is carbon based
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Life on Earth made of more than 20
elements
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More than 96% of the mass of living
cells are made of carbon, hydrogen,
oxygen, and nitrogen
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The molecule that accounts for cell
structure and function - Carbon
Earth life is carbon based
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Carbon - ideal as a fundamental
building block of biological
molecules
It readily forms chemical bonds with
itself and other elements, allowing a
wide variety of complex molecules to
form!
4 = Maximum number of atoms that
carbon can bond
Single and double bonds
Chemists refer to molecules containing
carbon atoms as organic.
Complex organic molecule. One bond links C
to an amino group (green)
Silicon based life?
Is silicon an obvious alternative to carbon as a building block for
biological molecules?
It has a similar electronic structure to carbon, forming a maximum
of four bonds and, hence, but does it have a similar chemistry?
Silicon forms its strongest chemical bonds with oxygen.
Silicon based life - unlikely!
Reason why silicon is unsuitable as a building block for life compared to carbon
1. Silicon–silicon bonds are much weaker than carbon–carbon bonds
2. Silicon does not form multiple bonds with itself, limiting the complexity of
molecules it can form
3. SiO2 is a high melting point solid and, hence, cannot be used to transfer silicon
atoms like gaseous CO2 can be used to transport carbon atoms!!
Silicon ~ 1000 times more abundant in Earth crust than carbon
Life on Earth is based on carbon
Why?
Carbon (organic) molecules found in space - meteorites, interstellar dust, Jovian
satellites
Molecular components of cells
Carbohydrates
• MOST important role - shortterm energy storage
• Provide energy to cells (sugars
and starches)
• Make important cellular
structures (celulose - fibers of
cotton and linen, main
constituent of wood)
Lipids
• MOST IMPORTANT - Major
ingredient of cell membrane
(Membrane forming role critical in the origin of life spontaneously form membranes
in water)
• Long term energy storage
(known as fats)
Nucleic acids
Most important - the storage and transfer of
information
DNA - The basic hereditary material on Earth
RNA (ribonucleuc acid) - helps carry out instructions
contained in DNA
More on DNA later
Proteins
• basic functioning of living organisms
• Vast array of functions
• Structural elements
• Enzymes - important to almost all biochemical
reactions, including copying genetic material,
serving as catalysts
• Most important - enzymes - facilitate replication
of DNA and the reading of the genetic code
Amino acids
The basic molecular building blocks of proteins are amino acids.
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Amino refers to the amino group (one nitrogen and 2 hydrogen); also contain a carboxyl group
(CCOH).
Different amino acids - distinguished by different sets of atoms bonded to the central carbon
More than 70 amino acids identified, but life on Earth uses only 20! => all life on Earth
has a common ancestor.
Amino acids found in protein in life on Earth are all left-handed molecules.
Next lecture
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February 4th. Midterm exam review
Common mistakes
Calculations
Marking of calculations
I encourage you to solve the quantitative problems from the textbook!
February 6th - Midterm exam!
1 hour, multiple choice questions + images description + calculations