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Transcript
“…sparked by just the right combination
of physical events & chemical processes…”
Origin of Life
Millions of years ago
1000
1500
2000
2500
3000
3500
Paleozoic
PROTEROZOIC
PRECAMBRIAN
500
Cenozoic
Mesozoic
ARCHEAN
0
Colonization of land
by animals
Appearance of animals
and land plants
First multicellular
organisms
Bacteria Archae- Protista Plantae Fungi
bacteria
Animalia
Oldest definite fossils
of eukaryotes
Appearance of oxygen
in atmosphere
Oldest definite fossils
of prokaryotes
4000
Molten-hot surface of
earth becomes cooler
4500
Formation of earth
The evolutionary tree of
life can be documented
with evidence.
The Origin of Life on Earth
is another story…
The Origin of Life is a Hypothesis
• Special Creation
– Was life created by a supernatural
or divine force?
– not testable
• Extra-terrestrial Origin
– Was the original source of organic
(carbon) materials comets &
meteorites striking early Earth?
– testable
• Spontaneous Abiotic Origin
– Did life evolve spontaneously from
inorganic molecules?
– testable
Conditions on early Earth
• Reducing atmosphere
– water vapor (H2O), CO2, N2, NOx, H2, NH3, CH4, H2S
– lots of available H & its electron
– no free oxygen
low O =
• Energy source
– lightning, UV radiation,
volcanic
What’s missing
from that
atmosphere?
2
organic molecules
do not breakdown
as quickly
Origin of Organic Molecules
Electrodes discharge
sparks
(lightning simulation)
• Abiotic synthesis
– 1920
Oparin & Haldane propose
reducing atmosphere
hypothesis
– 1953
Miller & Urey
test hypothesis
Water vapor
CH4
NH3
Mixture of gases
("primitive
atmosphere")
H2
Condenser
Water
• formed organic compounds
– amino acids
– Adenine
• Show Miller Urey
Animation
Heated water
("ocean")
Condensed
liquid with
complex,
organic
molecules
Stanley Miller
University of Chicago
produced
-amino acids
-hydrocarbons
-nitrogen bases
-other organics
Why was
this experiment
important??!
Organic monomers/polymer
synthesis
• These molecules served as
monomers of building blocks for
the formation of more complex
molecules, including proteins &
nucleotides.
• Joining of the monomers
produced polymers with the
ability to replicate, store &
transfer information.
• The RNA World hypothesis
proposes that RNA could have
been the earliest genetic
material.
RNA~ DNA template?
Evidences of Life
Deep Sea Vents
Stromatolites
Key Events in Origin of Life
• Origin of Cells (Protobionts)
– lipid bubbles
 separate inside from outside
 metabolism & reproduction
• Origin of Genetics (1st Genetic Material!)
– RNA is likely first genetic material
– multiple functions: encodes information (self-replicating),
enzyme, regulatory molecule, transport molecule (tRNA,
mRNA)
• makes inheritance possible
• makes natural selection & evolution possible
• Origin of Eukaryotes
– endosymbiosis
How might the first cells have
originated?
• Hypothesis: chemical evolution or the
chemosynthetic theory: life developed from
non-living materials eventually, by the process
of natural selection, over hundreds of millions
of years, became able to self-replicate and
metabolize.
This hypothesis presumes that at least 4 steps
happened to bring about this chemical evolution
• The abiotic (nonliving) synthesis and
accumulation of small organic monomers like
amino acids or nucleotides
• The Joining of monomers into polymers.
• The self-assembly of molecules into droplets
that had chemical characteristics inside
different from the environment outside.
• The ability to replicate
~2 bya
First Eukaryotes
• Development of internal membranes
– create internal micro-environments
– advantage: specialization = increase efficiency
• natural selection!
infolding of the
plasma membrane
plasma
membrane
endoplasmic
reticulum (ER)
nuclear envelope
nucleus
DNA
cell wall
Prokaryotic
cell
Prokaryotic
ancestor of
eukaryotic
cells
plasma
membrane
Eukaryotic
cell
1st Endosymbiosis
• Evolution of eukaryotes
– origin of mitochondria
– engulfed aerobic bacteria, but
did not digest them
– mutually beneficial relationship
• natural selection!
internal membrane
system
aerobic bacterium
mitochondrion
Endosymbiosis
Ancestral
eukaryotic cell
Eukaryotic cell
with mitochondrion
2nd
Endosymbiosis
• Evolution of eukaryotes
Eukaryotic
cell with
mitochondrion
– origin of chloroplasts
– engulfed photosynthetic bacteria,
but did not digest them
– mutually beneficial relationship
• natural selection!
photosynthetic
bacterium
chloroplast
Endosymbiosis
Eukaryotic cell with
chloroplast & mitochondrion
mitochondrion
Theory of Endosymbiosis
• Evidence
– structural
• mitochondria & chloroplasts
resemble bacterial structure
– genetic
Lynn Margulis
• mitochondria & chloroplasts
have their own circular DNA, like bacteria
– functional
• mitochondria & chloroplasts
move freely within the cell
• mitochondria & chloroplasts
reproduce independently
from the cell
Molecular & genetic evidence from existing and extinct
organisms indicates all organisms on Earth share a
common ancestral origin of life
Molecular building blocks are
common to all life forms
Common genetic code are
shared by all modern
organisms.
Metabolic pathways are conserved across all currently
recognized domains (bacteria, archea, & eukarya)
The Universal
Tree of Life
1. Last common ancestor of
all living things.
2. Possible fusion of
bacterium with archea
making eukaryotes
3. Symbiosis of
mitochondrial ancestor with
ancestor of eukaryotes
4. Symbiosis of chloroplast
ancestor with ancestor of green
plants
Cambrian explosion
• Diversification of Animals
– within 10–20 million years most of the major phyla of
animals appear in fossil record
543 mya
FUNCTIONS OF
LIFE
In order to perform these
functions…what do we need?
CELLS!!!!
Parts of the Cell Theory
• All organisms are composed of one or
more cells.
• Cells are the smallest units of life
• Cells can only come from pre-existing
cells.
Evidence to support cell theory
• Through the use of microscopes scientists
have amassed even more credibility on the
part of cells being the smallest unit of life.
• As of this date we have not been able to
find an organism that is not made of at
least one cell.
• Louis Pasteur performed experiments to
support the principle that all cells come
from other cells.
Various Microscopes Used Today
Light Microscope
Scanning Electron Microscope (SEM)
Electron Microscope (EM)
What’s the Difference between the
TEM and SEM?
Transmits a beam of
electrons through a thin
section of a specimen.
How do EM’s get
Such high magnification
& resolution?
Perceives the excited
electrons coming off of the
surface or the gilded surface
of a specimen.
How has biology been limited by
available technology in the past?
What kinds of things were
correctly postulated before the
technology we have today?
How are scientists still limited by
available technology?
Fig. 4.3 A scale of visibility
http://learn.genetics.utah.edu/content/cells/scale/
PROKARYOTIC VS EUKARYOTIC
CELLS UNDER THE MICROSCOPE
BESIDES SIZE..WHAT
ELSE IS DIFFERENT
BETWEEN
PROKARYOTE CELLS
AND EUKARYOTE
CELLS?
GET TOGETHER
WITH A PARTNER
AND COME UP
WITH AS MANY
DIFFERENCES AS
POSSIBLE. THE
WINNERS GET
CANDY!!!
PROKARYOTIC
• Smaller & simpler
• Less than 10µm in diameter
• DNA in ring form without
protein
• DNA is free floating
• No mitochondria
• 70S (svedberg unit) ribosomes
• No internal
compartmentalization to form
organelles
• Thought to be the 1st cells on
Earth.
• Reproduce by Binary Fission
• EX: BACTERIA
EUKARYOTIC
• Bigger & more complex
• More than 10µm
• DNA with proteins as
chromosomes/chromatin
• DNA enclosed in nucleus
• Mitochondria is present
• 80S ribosomes
• Internal compartmentalization
present to form many types of
organelles.
• EX: EVERYTHING EXCEPT
BACTERIA
Svedberg unit= amount of time it takes the ribosomes to be centrifuged to form a pellet
PROKARYOTIC CELL
What do you think
the functions are?
• Capsule - Found in some bacterial cells, this additional outer covering
protects the cell when it is engulfed by other organisms, assists in
retaining moisture, and helps the cell adhere to surfaces and nutrients.
• Cell Wall - Outer covering of most cells that protects the bacterial cell and
gives it shape.
• Cytosol - A gel-like substance composed mainly of water that also
contains enzymes, salts, cell components, and various organic
molecules; located in the cytoplasm. It is where organelles are found
• Cell Membrane or Plasma Membrane - Surrounds the cell's cytoplasm
and regulates the flow of substances in and out of the cell.
• Pili - Hair-like structures on the surface of the cell that attach to other
bacterial cells. Shorter pili called fimbriae help bacteria attach to
surfaces.
• Flagella - Long, whip-like protrusion that aids in cellular locomotion.
• Ribosomes - Cell structures responsible for protein production.
• Plasmids - Gene carrying, circular DNA structures that are not involved in
reproduction.
• Nucleiod Region - Area of the cytoplasm that contains the single bacterial
DNA molecule.
What do membrane-bound organelles
do for the cell?
• They give the cell compartments in which to perform
certain functions, under specific conditions, with all
the materials needed in one location.
How do you think prokaryotic cells
perform cellular functions without
compartmentalized cells?
• They have folds in their plasma membranes that act
as compartments.
CELL PARTS & FUNCTIONS
NUCLEUS
WHAT PARTS ARE IN THE NUCLEUS?
DNA, mRNA, histone proteins
surrounding DNA, free floating
nucleotides, ribosomal
subunits around the nucleolus
WHAT’S THE FUNCTION?
To protect the DNA
WHAT CAN YOU EXPECT FROM CELLS
THAT DON’T HAVE A NUCLEUS
AROUND THEIR DNA, SUCH AS
PROKARYOTES?
BECAUSE THE DNA IS EXPOSED,
PROKARYOTES HAVE A MUCH HIGHER RATE
OF DNA MUTATION.
RED BLOOD CELLS DO NOT HAVE A
NUCLEUS AT MATURITY. HOW DO
THEY FUNCTION WITHOUT IT?
AT MATURITY THEY HAVE ALL THE PROTEINS &
ENZYMES NEEDED FOR THE REMAINDER OF
THEIR SHORT LIFE SPAN
HOW DO RED BLOOD CELLS
REPRODUCE?
THEY DON’T. NEW RBC’S ARE MADE IN BONE
MARROW
If mature red blood cells have no
nucleus or DNA why do forensics need
blood for DNA analysis?
NUCLEOULUS
THE NUCLEOLUS IS ALSO
DNA BUT HAS A SEPARATE
NAME, EVEN THOUGH IT IS
NOT A SEPARATE
COMPARTMENT.
WHY DO YOU THINK THIS
REGION HAS ITS OWN
NAME?
IT APPEARS AS A DENSE REGION ON A LIGHT MICROSCOPE & WAS
ORIGINALLY THOUGHT TO BE A DIFFERENT COMPARTMENT, BUT WITH
IMPROVED TECHNOLOGY IT WAS RECOGNIZED AS A HIGHLY
STRUCTURED REGION OF DNA WITH CONSTANT ACTIVITY; THE DENSITY
IS DUE TO THE PRESENCE OF GRANULES & FIBERS HOLDING THE
RIBOSOMAL DNA IN PLACE.
RIBOSOMES
ENDOPLASMIC
RETICULUM
SMOOTH
Synthesizes lipids; detoxifies
drugs and poisons.
ROUGH
Helps synthesize proteins to
be exported from the cell.
GOLGI APPARATUS
(AKA GOLGI COMPLEX)
Center of manufacturing,
warehousing, sorting, and shipping
LYSOSOMES
VACUOLES
MITOCHONDRIA
CHLOROPLASTS
HOW ARE THE MITOCHONDRIA AND
CHLOROPLASTS SIMILAR TO
PROKARYOTIC CELLS?
SIZE
BOTH HAVE THEIR OWN DNA
THEY ARE NOT PART OF
THE ENDOMEMBRANE
SYSTEM
THEY REPRODUCE IN
A SEMIAUTONOMOUS
MANNER
SOME PROTEINS NEEDED ARE MADE BY THEIR
RIBOSOMES LOCATED IN THEIR MEMBRANE & OTHER
PROTEINS ARE BROUGHT IN FROM THE CYTOSOL
Why might we do a mitochondrial
DNA test?
• It is most effective in determining siblings
– Mitochondrial DNA is past on by mom only so all
siblings will have the same mitochondrial DNA.
• US military uses it for identification of
skeletons from old war zones.
– Highly preserved compared to nucleus DNA
Why do mitochondria & chloroplasts have
so many membranes in them?
For increased surface area used for the
energy conversion processes that occur in
these organelles.
PLASTIDS- in plant cells not animal cells
• Leucoplasts- energy storage
Are colorless and store starch (amylose)
-mostly in roots & tubers
• Chromoplasts- color centers
Have pigments that give flowers and fruits
their color
• Chloroplasts- essential for photosynthesis
Contain green pigment (chloropyll) along with
enzymes & various molecules that aid them in
photosynthesis
PEROXISOMES
Seedlings have peroxisomes
in order to convert fatty acids
to sugar until it is able to
photosynthesize.
Produces hydrogen peroxide by transferring hydrogen to
oxygen.
-use oxygen to breakdown fatty acids
(send to mitochondria for cellular respiration fuel)
-in liver cells they detoxify alcohol & other harmful
compounds by transferring hydrogen from the
poisons to oxygen.
Once hydrogen peroxide is made, other enzymes within the
peroxisome changes it to water.
CENTRIOLES
CYTOSKELETON
SUPPORT, MOTILITY, AND
REGULATION
Fig. 4.19
Microtubules
(originate from centrosomes)
• Help determine/maintain cell shape
(by resisting compression)
• Involved in cell movement (flagella, cilia)
• Involved in the position of organelles within the cell
– function like tracks within the cell, on which cargoes of
materials like vesicles or organelles can be transported
• Involved in the movement of chromosomes during
cell division.
Antimitotics
• Cancer fighting drugs that inhibit microtubes
from breaking down and reassembly.
Microfilaments
• Maintain cell shape (bearing tension)
• Responsible for gross changes of cell shape
– Pseudopodia
– Muscle contractions
– Cleavage during cell division
– Phagocytosis.
MICROFILAMENTS
Intermediate Filaments
(keratin filaments)
• Permanent structures in the cell
• Helps maintain rigid cell shape
• Anchor organelles in fixed positions when
necessary (EX: nucleus)
Epidermolysis bullosa
simplex or EBS
People with a rare mutation
in their keratin genes that
prevents proper assembly
of keratin filaments have
skin cells that rupture from
even slight pressure
How are microtubules different from
intermediate filaments?
• Unlike intermediate filaments all microtubules are
made up of a single kind of protein called tubulin.
• Microtubules are assembled in such a way that they
have a polarity (that is, one end is different from the
other).
•
Microtubules are rapidly
assembled and broken down
many times within a short span of
time, while intermediate filaments
are more stable.
MICROTUBULES
INTERMEDIATE
FILAMENTS
MOTOR
PROTEINS
CELL WALL
EXTRACELLULAR STRUCTURE
MUCH THICKER THAN
PLASMA MEMBRANES
(ranging from 0.1micrometers
to several micrometers)
Outermost regions of various cell types
Cell
Outermost part
Bacteria
Cell wall of peptidoglycan
Fungi
Cell wall of chitin
Yeasts
Cell wall of glucan and mannan
Algae
Cell wall of cellulose
Plants
Cell wall of cellulose
Animals
No cell wall, plasma membrane secretes a mixture of sugar
& proteins called glycoproteins that forms the extracellular
matrix
Extracellular Matrix (ECM) of Animal
Cells
Intercellular Junctions
• How cells adhere to each other, interact with
each other, and communicate with each other.
PLANTS:
• PLASMODESMATA
•CYTOSOL PASSES THROUGH BETWEEN CELLS ALLOWING WATER
AND SMALL SOLUTES TO PASS FROM CELL TO CELL.
Animals:
Cells pressed together bound
together by specific proteins.
Prevent leakage of extracellular fluid
Like rivets, they fasten cells
together. Intermediate filaments
anchor desmosomes in the
cytoplasm.
Cytoplasmic channels from
one cell to the next.
Like plasmodesmatas in plants
CELL
FRACTIONATION
Producing pure components of a
mixture of cell parts.
The process involves two basic
steps:
-disruption of the tissue
-lysis of the cells, followed by
centrifugation
Variations among Eukaryotic Cells
Plant cells
• Exterior of cell includes cell
wall
• Have chloroplasts
• Possess large vacuole that’s
centrally located
• Store carbohydrates as
starch
• Do not contain centrioles
• Has a fixed often angular
shape
Animal cells
• Exterior of cell includes
plasma membrane
• No chloroplasts
• Vacuoles are usually not
present or are very small
• Store carbohydrates as
glycogen
• Have centrioles
• Is flexible and more likely to
be rounded in shape.
Cell Reproduction & Differentiation
• Multi-cellular organisms usually start as 1 cell.
• Cells reproduce at a rapid rate and go through
differentiation.
– This occurs to produce all the required cell types that
are necessary for the organisms well-being.
• Genes on a chromosome allow for this process to
occur.
– All cells contain all of the genetic information to make
the entire organism.
– Each cell becomes a specific type of cell depending on
which DNA segment becomes active.
Stem Cells
• Retain the ability to divide and differentiate.
• Plants have these cells in their meristematic
tissue (near root & stem tips).
– Gardeners take cuttings from stems or roots to grow a
new plant.
• In the 1980’s, pluripotent (embryonic stem cells)
were found in mice.
– Problem: stem cells can’t be distinguished on
appearance. They can only be isolated based on
behavior.
Research on using stem cells
• To replace differentiated cells lost due to
injury and disease.
– EX: Parkinson’s Disease & Alzheimer’s disease are
caused by loss of brain cells.
– EX: Certain types of diabetes deplete the pancreas
of essential cells.
• Using tissue specific stem cells
– Blood stem cells replace damaged bone marrow
GOLGI
APPARATUS
PLASMA MEMBRANE
NUCLEAR
ENVELOPE
NUCLEUS
ROUGH
ER
SMOOTH
ER
LYSOSOME
MITOCHONDRIA
PILI
RIBOSOMES
CELL WALL
PLASMA
MEMBRANE
NUCLEOID
Cell membrane
DESCRIBLE THE CELL PARTS THAT WOULD
BE FOUND IN GREATER NUMBERS IN:
STOMACH CELLS:
rough ER for secretion
LIVER STORAGE CELLS: vacuoles for storage
POTATO CELLS: vacuole for starch storage
WHITE BLOOD CELLS: lysosomes to breakdown engulfed pathogens
MESOPHYLL (PLANT LEAF) CELLS: chloroplasts for photosyntheis
MUSCLE CELLS:
LIVER DETOX CELLS:
mitochondria for ATP
ADIPOSE CELLS:
vacuoles for storage
peroxisomes & smooth ER to
break down toxins
How do cells recycle?
• Endomembrane system:
– Cycle phospholipids
• Lysosomes, peroxisomes, & rough ER:
– Breakdown macromolecule parts & reassemble
them
• Cytoskeleton:
– Constant flow of assembling & de-assembling
subunits.
Why are cells so efficient at recycling?
For the same reasons developing countries are good at
recycling; limited resources and limited energy