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Our Journey to Cosmos of the Cell - Properties
of Life |
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Cells are a
Unifying Concept
of Biology... the
Unity of LIFE...
&
CMB is the study of the
Molecular Chemistry
of cells |
the basic unit of LIFE is the
CELL… |
 |
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an inanimate mixture of
biomoleculesmwking which
have been selected |
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for their
fitness
to perform
certain biochemical
reactions... |
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reactions that characterize and
define
life. |
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[web-biomolecule
databases] |
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Every living thing
is cellular…
"The only life we know for
certain is cellular..."
H.J. Morowitz
-biologist & philosopher |
all class readings: are on the class
web pages |
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but, have you ever seen an
individual
living
cell
?
[ pics of
cells*
]
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 ATCC-CCL 2
- HeLa cells in
frozen ampuoles
@ -321
0F
frozen cultured cells show no signs of
life, not even simple chemical metabolism, if warmed to room temp...
"resurrection -
seem to come back to life"... they
move about, feed and metabolize, maybe reproduce.
American Type
Culture
Collection - Manassas, VA |
Human Life...
for centuries, life was defined in the unit of the
whole organism,
a cat, a bird, a human being...
but today life is
sum
of the lives of many
individual cells
making up a human body...
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Life
may be best defined in terms of the individual CELL,
and its
molecular
constituents. |
|
some ideas about life through the scientific age |
So what
exactly DEFINES Life ?
Most
biologists agree: life
exhibits certain "QUALITIES"
that equate to the living state and many
prefer to use an operational
description of what living
entities can do and perform
rather than to
use a strict
definition of
life...
thus we describe the
Attributes of the Living State:
1)
Autonomous Replication
-
Self-Replication of cells by cell division (Mitosis
&
Meiosis) pics*
two whole
copies of genome: maternal
& paternal hereditary info:
a
backup-redundancy
all cells store their hereditary
information in DNA, coded as genes.
(table
of sequenced genomes)
based in the
semi-conservative replication of DNA (complementary
templated polymerization)
► most defining
trait of the living state…
2)
Life had an Origin
-
Life begets Life...
"all cells are derived from preexisting cells"...
►
Prime Directive: Rudolph
Virchow
states (1858) this as a prime directive of life.
all individual organisms come from a single cell
& all individual cells in an
organism are descended from fertilized egg.
eliminates
Spontaneous Generation
[
Redi &
Pasteur
experiments
]
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All living things have evolved from a common
ancestral cell, through processes that include
natural selection and
genetic drift acting on heritable genetic
variation.
►
LUCA -
Last
Universal
Common
Ancestor*
-
LUCA
was likely a hyper-thermophilic organism living near
hydrothermal vents?,
but
new data suggests it may have lived at temps below 500.
SUPPORTING
EVIDENCE that all cells are derived from a single
PRIMORDIAL cell...
This hypothesis is based upon the
circumstantial evidence...
mostly
it's the
commonality
that occurs
in all current known living organisms, such as:
1. all living things are
composed of very similar
organic molecules:
the same
proteins, lipids, carbohydrates, similar
nucleic acids etc...
2. all
proteins, the biological catalysts responsible for life's chemical
reactions,
are made from one set
of 20 standard
amino acids...
a-amino
acids & L-stereoisomers...
3. all contemporary
organisms carry their genetic information in nucleic acids [DNA/RNA]
and use the
same genetic
CODE.
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3)
Life exhibits EMERGENT
PROPERTIES...
a large scale, group behavior in a system,
which doesn't
seem to have any clear explanation in terms of the system's
constituent parts.
ex: oxygen
- colorless, odorless, tasteless, reactive
GAS that supports
combustion
hydrogen -
colorless, odorless, tasteless,
reactive GAS that is flammable
water -
H2O - a non-flammable chemically
reactive polar LIQUID that exist in 3 phases
ex: metal Na is explosive &
gas chlorine is poisonous --> edible table salt
NaCl*
Emergent properties
are
unexpected, nontrivial results of
relatively simple interactions by
relatively simple components. Emergent properties seem to be a
consequence of complexity
from which unpredicted behaviors and patterns emerge.
from a mix of biomolecules
thus emerges a complexity that exhibits properties we call
life:
4)
Life requires a Critical
Level of
molecular
COMPLEXITY...
Structural complexity and
information content are built up according to current paradigm
by combining simpler subunits into multiple complex combinations.
elements --> stable monomers --> polymers -->
metabolism --> supramolecular complexes --> organelles --> cells*
A
single cell
has no concept of the whole.
A cell runs by the
chemical rules built into its molecules.
A single cell can't do much without interaction with other cells,
but in combination
cells can
produce complex results such as
consciousness.
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5) Life exhibits
biochemical
autonomy, i.e., it carries on & regulates
METABOLISM:
biochemical activities in cells transform
energy (ATP) & molecules to sustain cells;
cellular energetics
occur via a few basic molecular reaction mechanisms
in all cells...
1.
cellular
redox reactions,
2.
capture of light energy in
photosynthesis,
3.
electron flow through carrier proteins,
4.
H+
ion
pumps.
5.
concentration gradients
across interfaces.
Life is
a chemical
system
far
from equilibrium...
µ
it consumes free energy, largely derived from photosynthesis, which is stored in
high-energy bonds
or
ionic
concentration gradients. The release of this
energy
is
coupled to thermodynamically unfavorable reactions to
drive biological processes:
µ ability of cells
to couple reactions (non-favored to favored) is a
unique property of life.
there are
no unique Laws
of chemistry or physics
just for the Living State...
ΔG
=
ΔH
-
T
ΔS
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7)
Life is manifest by the
absence of the living condition...
a lack of
the properties of the living state is itself definitional of living state.
death is
a deterministic event,
because
all
living beings
will eventually
die.
[death
&
taxes] |
Cells DIE
-
When metabolism ceases with
no prospect of starting again:
"Cell death is the collapse of the quantum state which has allowed living
matter to take energy from the
environment, while preventing an increase local entropy and
delaying the
the tendency of energy to be
dispersed or diffused".
Thus,
death is an irreversible final state.
Dead
organisms will never return to life
because they would be violating the Law of Entropy.
THE
LAW OF ENTROPY CAN BE TEMPORARILY
BLOCKED
(Life),
BUT THEY CAN NEVER BE
VIOLATED.
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Senescence
is process of aging.
Cellular senescence
is a phenomena where isolated cells show
a limited ability to divide in culture. The successive shortening of the
chromosomal
telomeres
with each
cell cycle
is also believed to influence the vitality of the cell, thus contributing to
aging. |
Cell
death plays a considerable role during physiological processes of multicellular
organisms,
particularly during embryogenesis and metamorphosis...
programmed cell death
is known as...
apoptosis*
&
description |
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Summary of
Some Basic Properties of
Life
& thus
Cells...
or
How Cells Work
- cells have an evolutionary origin
-
all cells are
derived from other cells...
originally from a single primordial
cell
[LUCA
some 3 bya]
via
Chemical Evolution???
cells:
highly complex mix of biomolecules (C,
O,
H,
N) ---> cellular structural complexity
cells show
organizational complexity - [
figure
9.5a pg
376 (mcb)]
[
animal*
& plant*
cells (fig
9.1 pg 373 - mcb)]
cells come in 2 fundamental
types - prokaryote &
eukaryote
(read pgs 1-4: mcb6e)*
cells obey laws of chemistry & physics
(the laws of Universe)
cells build and degrade numerous molecules,
generally via use of ATP
fig 1.14*
cells
extract energy
from environment and maintain a homeostasis
far from equilibrium
cells acquire and utilize energy
-via
metabolic pathways:
Glycolysis, Krebs,
ETC
cells metabolize - capable
of 1,000's of reactions (via
ENZYMES)
in protein pathways
cells are capable of self regulation -
series of ordered reactions that are self-adjusted
cells divide, grow, &
differentiate leading to cell
Form
& Function
cells osmoregulate - control
what gets in/out of
membranes
(organelle or plasma)
 *
read this
Summary of Basic Properties of
Cells & thus Life... continued
cells respond
to stimuli
- via external surface or
internal cell receptors
fig 1.16*
cells grow and
divide...
cells use nucleic acids for
genetic information
cells are capable of self-replication
-
Mitosis & Meiosis -
fig
1.17*
cells regulate their gene
expression (RNA and protein synthesis)
cells die
- absence of life may be a most defining characteristic of living?
apoptosis
- programmed cell death due to absence of certain growth signals -
fig 1.19*
via
cysteine-aspartic acid proteases (caspases)
-
next lecture.
Definition of a Cell* 
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