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Origin of Life
“…sparked by just the right combination of physical events & chemical processes…”
“…sparked by just the right combination of physical events & chemical processes…”
Bacteria Archae-bacteria
AnimaliaFungiProtista Plantae
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Formation of earth
Molten-hot surface ofearth becomes cooler
Oldest definite fossilsof prokaryotes
Appearance of oxygenin atmosphere
Oldest definite fossilsof eukaryotes
First multicellularorganisms
Appearance of animalsand land plants
Colonization of landby animalsPaleozoic
Mesozoic
Cenozoic
Mill
ion
s o
f y
ears
ag
o
AR
CH
EA
N PR
EC
AM
BR
IAN
PR
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OZ
OIC
The evolutionary tree of life can be documented with evidence.The Origin of Life on Earth is another story…
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
• Energy source– lightning, UV radiation,
volcanic
low O2 = organic molecules do not breakdown as quickly
low O2 = organic molecules do not breakdown as quickly
What’s missingfrom thatatmosphere?
Water vapor
Condensed liquid with complex, organicmolecules
CondenserMixture of gases("primitiveatmosphere")
Heated water("ocean")
Electrodes discharge sparks(lightning simulation)
Water
Origin of Organic Molecules
• Abiotic synthesis– 1920
Oparin & Haldane propose reducing atmosphere hypothesis
– 1953Miller & Urey test hypothesis
• formed organic compounds– amino acids– Adenine
• Show Miller Urey Animation
CH4
NH3
H2
Stanley MillerUniversity of Chicago
produced-amino acids
-hydrocarbons-nitrogen bases-other organics
Why was this experimentimportant??!
Organic monomers/polymer synthesis
• These molecules served as monomers of building blocks for the formation of more complex molecules, including amino acids & 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?
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
First Eukaryotes• Development of internal membranes
– create internal micro-environments– advantage: specialization = increase efficiency
• natural selection!
infolding of theplasma membrane
DNA
cell wall
plasmamembrane
Prokaryoticcell
Prokaryotic ancestor of eukaryotic cells
Eukaryoticcell
endoplasmicreticulum (ER)
nuclear envelope
nucleus
plasma membrane
~2 bya
1st Endosymbiosis
Ancestral eukaryotic cell
Eukaryotic cellwith mitochondrion
internal membrane system
aerobic bacterium mitochondrion
Endosymbiosis
• Evolution of eukaryotes– origin of mitochondria– engulfed aerobic bacteria, but
did not digest them– mutually beneficial relationship
• natural selection!
mitochondrion
chloroplast
Eukaryotic cell withchloroplast & mitochondrion
Endosymbiosis
photosyntheticbacterium
2nd Endosymbiosis• Evolution of eukaryotes
– origin of chloroplasts – engulfed photosynthetic bacteria,
but did not digest them– mutually beneficial relationship
• natural selection!
Eukaryoticcell with mitochondrion
• Evidence– structural
• mitochondria & chloroplasts resemble bacterial structure
– genetic• mitochondria & chloroplasts
have their own circular DNA, like bacteria– functional
• mitochondria & chloroplasts move freely within the cell
• mitochondria & chloroplasts reproduce independently from the cell
Theory of Endosymbiosis
Lynn Margulis
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
Electron Microscope (EM)Scanning Electron Microscope (SEM)
Light Microscope
What’s the Difference between the TEM and SEM?
Transmits a beam of electrons through a thin section of a specimen.
Perceives the excited electrons coming off of the surface or the gilded surface of a specimen.How do EM’s get
Such high magnification& resolution?
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
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 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
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
NUCLEUSWHAT 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
SOME PROTEINS NEEDED ARE MADE BY THEIR RIBOSOMES LOCATED IN THEIR MEMBRANE & OTHER PROTEINS ARE BROUGHT IN FROM THE CYTOSOL
THEY REPRODUCE IN A SEMIAUTONOMOUS
MANNER
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
• Chromoplasts- color centers
• Chloroplasts- essential for photosynthesis
Are colorless and store starch (amylose)
-mostly in roots & tubers
Have pigments that give flowers and fruits their color
Contain green pigment (chloropyll) along with enzymes & various molecules that aid them in photosynthesis
PEROXISOMES
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.
Seedlings have peroxisomes in order to convert fatty acids
to sugar until it is able to photosynthesize.
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)
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
Epidermolysis bullosa simplex or EBS
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 WALLEXTRACELLULAR 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 FRACTIONIZATION
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
NUCLEUS
ROUGH ER
MITOCHONDRIA
LYSOSOME
SMOOTH ER
NUCLEAR ENVELOPE
GOLGI APPARATUS
PLASMA MEMBRANE
CELL WALLPILI NUCLEOID
PLASMA MEMBRANE
RIBOSOMES
Cell membrane
DESCRIBLE THE CELL PARTS THAT WOULD BE FOUND IN GREATER NUMBERS IN:
STOMACH CELLS:
POTATO CELLS:
WHITE BLOOD CELLS:
LIVER STORAGE CELLS:
MESOPHYLL (PLANT LEAF) CELLS:
MUSCLE CELLS:
ADIPOSE CELLS:
LIVER DETOX CELLS:
rough ER for secretion
vacuoles for storage
vacuole for starch storage
lysosomes to breakdown engulfed pathogens
chloroplasts for photosyntheis
mitochondria for ATP peroxisomes & smooth ER to break down toxins
vacuoles for storage
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
