I. Chemical Evolution of Life
A. Modern Proof
1. Stanley Miller, 1950, duplicated conditions of early
earth’s atmosphere and oceans in a lab: formed
complex organic molecules, nucleotides
2. Sidney Fox (USA) created MACROMOLECULES in the lab
a. They can carry on a few simple chemical reactions
b. they can "bud off" smaller macromolecules
4. Discoveries in Western Australia of the first living
cells, 3.6 BILLION years old (Earth = 4.7 Billion)
III. WHY EARTH?
A. Proper distance from the sun (not too hot or cold)
B. Proper size (to trap an atmosphere, block radiation
that could break covalent bonds, denature proteins
C. Has the proper elements (CHNOPS)
IV. Why not Spontaneous Generation? (other than the birth of the
first cell)
A. Early people believed in frogs coming from mud, hair
from horses tails, maggots from meat
1. By 19th century, REDI had disproved large organisms
undergo spontaneous generation (with classic maggot
from rotting meat experiment)
2. Scientists still believed germs could "pop up" from
nowhere
a. Louis Pasteur proved microbes are found in air,
using specially-designed swan-necked flasks
V. CHEMOTROPHS - probably the first cells
A. Eat chemicals abundant in early earth (H2S): produces
sugar through chemosynthesis IN THE DARK
B. Include the most ancient prokaryotes
C. Are found in geyser pools at high temperatures-in deep
ocean trenchs at high temperatures
D. A simple mutation could have created the ability to
make sugar using LIGHT and giving off oxygen (not found in
early atmosphere) - a PHOTOTROPH
E. A simple mutation could have disabled chemosynthesis,
making it necessary for the bacteria to become HETEROTROPHS,
eat outside food
VI. Prokaryotes
A. Most simple cell, belong to the Kingdom Monera
1. cell membrane + CELL WALL
2. No membrane-bound organelles
3. NO NUCLEAR MEMBRANE (DNA in strands in mid cell)
4. If phototrophic, chlorophyll in long strands
B. Include bacteria, blue-green "algae" (or “cynobacteria”)
VII.Eukaryotes
A. Much more complex
1. contain MANY membrane-bound organelles, nuclear
membrane
B. Includes ALL animals, plants, protists, and fungi
VIII. Multicellular Evolution
A. First fossil = 750 MILLION years ago (one-celled organisms
ruled the planet for at least 2,750,000,000 years)
B. Each cell basically still has the same game plan - similar
to a one-celled organism
1. Humans = over 100+ different types of cells, each specialized
IX. Microscopes and Body Scans
A. A human eye's resolving power (ability to distinguish
between lines) = 1/10 mm (If closer, the lines merge into
a single line)
B. SIZES
1. One MICROMETER = 1/ 1,000,000 of a meter
2. One NANOMETER = 1/1,000,000,000 of a meter
C. Light microscopes (compound & binocular) will improve
the human eye approx. 500 times
D. Transmission Electron Microscope (T.E.M.)
1. Aims a beam of electrons instead of light waves THROUGH
a specimen
2. 200,000 times better than the eye.
3. Preparation of specimen for Transmission Microscope
a. Since cells are up to 70% water, need to be dyed
to show
up, block light rays
b. Some stains are hydrophobic, some hydrophillic
(different organelles stain different colors, density)
E. Scanning Electron Microscope (S.E.M.)
1. Works like sonar, using electrons to bounce off specimen's
surface
2. Limited resolution but GREAT 3-D effect!
3. Preparation of specimans for E.S.M.
a. THICK tissues need to be made THINNER
1) First embedded in wax, then sliced with
a MICROTOME
2) Some specimans are "shadowed" with metal,
for reflection, contrast
b. ALL THESE PROCESSES KILL CELLS (you may be looking
at an artifact, not a true cell part)
F. Dark-Field Microscopes
1. Appropriate for LIVING CELLS
2. Light comes from the side,
makes huge shadows and contrasts
G. Phase-contrast Microscopes
1. Waves of light are set up, bounced off the specimen
2. The interference caused by the shape of the cell Is
plotted on a computer, projected
H. Computerized Tomography Scan (CT or “CAT” Scans)
1. Uses an ultra-thin x-ray beam, goes through soft tissues
and bone absorbing different
amounts of beam intensity. An x-ray detector
on the opposite side of body part being
scanned measures the intensity of the beam and your
tissues appear as different
shades of gray. Bone appears as white, softest
tissues black.
2. Shows internal soft tissues better than conventional
x-rays, without surgery.
I. Magnetic Resonance Imaging Scans (MRI Scans)
1. Hydrogen atoms in the water of your tissues respond
to a magnetic field through the
polarity of water. The Magnetic Field Resonator
measures the response of your ato ms
(greater response in higher water content tissues)
and the data is processed by a
computer to create a 3-D representation of your body.
2. “Slices” can be selected electronically from the computer
model and displayed on
a TV monitor or printed.
3. Particularly useful for imaging areas where soft &
hard tissues meet
(spine, nerves, etc) Uses no x-rays.
J. Ultrasound Scans
1. A wand-like device produces high-frequency sound waves
and reflected waves are detected and transformed into
an image that can be displayed on a TV monitor or photographic print.
Uses no harmful rays, sharpness of the image depends
on sophistication of the equipment & operator skill.
2. Is often used to view unborn fetuses in the worm, without
risk to mother or child.
HOW CELLS ARE ORGANIZED
I. General characteristics
A. Although varied, basically all similar in structure'
B. Cell membrane allows the interior of the cell to differ
form its surroundings (maintain homeostasis)
C. Size = 10 - 30 micrometers (need to be SMALL)
1. need large surface to volume ratio
2. need lots of membrane for LOTS of materials to pass
through
3. diffusion only works well across very short distances
4. nucleus can only handle so much info at once - would
short out if cells were much larger
5. cells tend to be spherical because of cohesion, surface
tension. A strong structural shape, stable
a) to obtain other than a spherical shape, a cell
needs internal and/or external support (cell walls,
microtubules, support from adjacent cells)
6. EXCEPTION: a newly fertilized egg (ostrich the
largest)
a) zygote divides rapidly to get surface ratio up
as high as possible
II. History
A. Von Leevenhook - invented the first truly workable,
finely- tuned microscope (made the best lenses, the finest
instruments)
1. The first to describe Protists
2. Equated a Protist's organelles to organs (hence, the
name)
a) organelles work together like organs to provide
a variety of cell functions
b) the cell is BUSY, many things going on at once.
III. Cell components
A. Cell membrane (7-9 nm thick)
1. composed of Phospholipids, embedded with globular proteins
2. short carbohydrate chains on the outer portion of globular
proteins act as receptors for hormones, antibodies
3. Same basic structure for all organelle membranes
a) DOUBLE-LAYERED ORGANELLES= lysosomes, chloroplasts
(and all other plastids), mitochondria
B. Cell wall (found in plants, protists, prokaryotes, fungi)
1. made of cellulose (in Fungi, chitin)
2. cemented to other cell walls w/pectin laid down by
the middle lamella
3. Growth is accomplished vis CELL ELONGATION (from middle)
4. Mature cells may have a secondary cell wall laid down BETWEEN the cell membrane + primary cell wall (wood)
C. Cytoplasm (fluid between cell membrane + nuclear membrane)
1. ALL fluid in cell = PROTOPLASM
2. Cytoplasm contains organelles, supporting members
a. Microtubules (scaffolding)
1) holds cell shape
2) allows for attachment of organelles
3) directs flow of material through cell
b. Microfibers (smaller: 6-8 micrometers)
1) used in motile cells to support movement
c. Intermediary fibers (function unknown)
D. Vacuoles (vesicles)
1. membrane-bound space filled with water + dissolved
solutes in plant cells
a) provides support in plant cells, gives TURGOR,
prevents PLASMOLYSIS
2. In animal cells, usually called "vesicles" (usually
smaller, rounder)
a) used in exo and endocytosis, storage
E. Nucleus (main computer of the cell)
1. has a lipoprotein DOUBLE-LAYERED MEMBRANE
2. Dotted with nuclear pores to allow passage of larger
particle such as ribosomes
3. Contains CHROMATIN (DNA not condensed into chromosomes)
4. Contains NUCLEOLI (usually 2)
a) the assembly site of ribosomes
b) contains rRNA
5. DNA never leaves nucleus
F. Ribosomes
1. the assembly site for proteins
2. Made in 2 sizes (50s and 30s subunits)
3. the more protein a particular type of cell needs to
make, the more ribosomes it will have
G. Endoplasmic Reticulum ( Freeway system of the cell)
1. amount of E.R. varies with cell activity
2. ROUGH E.R.
a) found in cells that need to carry material OUT
of the cell
b) has ribosomes associated on it
3. SMOOTH E.R.
a) found in both one-celled and multicelled organisms
b) feeds newly made proteins from the ROUGH E.R.
to the GOLGI BODY
c) in a one-celled organism, transports newly-made
proteins to needed portions of the cell
d) believed to be the site of some lipid synthesis,
also
H. Golgi Body
1. Membrane-bound sacs that pinch off vesicles to send
products to the cell's surface
2. Contain and store
a) glycoproteins
b) polysaccharides
c) lipoproteins
I. Lysosomes ("killer" organelles)
1. really bags of destructive enzymes
2. Can inject + kill bacteria, viruses (in white blood
cells)
3. digest food in vacuoles of protists
J. Mitochondria (powerhouse of the cell)
1. Largest and most numerous of organelles
a) low energy cells may have 2,500
b) high energy cells may have 5,000 - 10,000 / cell
2. Produces ATP within the CRISTAE (folds)
a) the more active the mitochondria, the more cristae
K. Plastids (FOUND ONLY IN PLANTS)
1. Double-membraned
2. Leucoplasts
(store starch)
3. Chloroplasts
(contain chlorophyll, photosynthesize, produce AND CONSUME AGAIN
ATP
4. Chromoplasts
(contain color pigments: pigment in animals are contained in vesicles within
skin cells)
HOW CELLS MOVE
I. ALL cells move (whether by cytoplasmic streaming, chromosome
movement, mitosis, flagella, cilia, etc.)
A. In true muscle cells, contractile assemblies made of
fibrous proteins MYOSIN + ACTIN work to move muscle bundle
fibers.
1. Actin found in great variety of cells by itself
a) in plants, cause cytoplasmic streaming, internal
movement
b) in protists on up, WORKS MICROTUBULES, spindle
fibers to separate chromosomes during mitosis
B. Many cells (and one-celled organisms) move by flagella or
cilia movement (sperm, microvilli, collar cells in sponges,
etc)
1. Both are moved by ATP ----> ADP
2. Both have the same basic structure
3. Flagella (Longer than cilia, usually used for gross
movement, prey capture)
a) structure = nine pairs of fused microtubules,
with one long pair (unfused) in center
b) BASAL BODY constructs the flagella, directs its
movement (middle pair creeps up and down against
each other for whip-like action)
1) Structure = nine triplets of microtubules,
none in center.
2) transmits ATP to system
4. Cilia (shorter, may cover the exterior of a cell, move
materials along a tract)
a) same structure and action as flagella
5. CENTRIOLE = same structure as basal body, different
function
a) organized spindles during mitosis
b) gives energy (ATP) to full chromosomes apart
6. Bacterial Flagella
a) not enclosed in cell membrane, like normal flagella
b) structure= small globular protein in a triple
helix
c) covers exterior of bacterium, rotates itself
to move forward
HOW CELLS COMMUNICATE
I. Cell Walls (must have breaks between walls)
II. Cell membranes (animal cells)
III. Chemical communication
A. Cells release enzymes + hormones to affect other cells
1. can inhibit cell division (cytokinesis) by "contact
inhibition"
a) if their are too many cells in a crowded area,
they stop dividing (ex. bacteria on an agar plate)
2. can increase cell division in order to distribute
the species (ex. slime molds)
HOW THINGS GET IN AND OUT OF CELLS
I. Membrane Structure
A. Fluid mosaic model
1. The Phospholipids can move about, concentrate in different
areas at different time (lump or spread out)
2. Composition = 40% lipids, 60% proteins
a. Globular proteins act as facilitators of ion
and molecular movement in and out of cell
1) "Integral proteins" imbedded in the membrane
may have pores of hydrophillic regions down their
middle, allowing polar substances to pass through
2) Other integral proteins may have a carbohydrate
chain on the outside and a PERIPHERAL
PROTEIN on the interior end (substances
binding onto the carbo may cause a tertiary change in
shape, releasing the peripheral protein to
bind to another enzyme within the cell, causing a "chain
reaction" often found in hormone response.
3) Other integral proteins will act as CARRIER
PROTEINS and allow very specific ions to bind on
one surface and carry the ion through the membrane due to tertiary hydrophobic/hydrophillic
changes
II. Transport across membranes
A. Polar substances (HARD JOB!)
1. can go through "pores" in integral proteins
2. can go through momentary openings in the movement of
the lipid membrane
3. can attach to a "carrier" protein, be carried through
B. Non-polar substances (MUCH EASIER)
1. include O2, CO2
2. Just need to attach to a non-polar spot on an integral
protein, cause a slight shape change, slip through
C. Entry rate is limited (limited number of carrier proteins)
D. Sodium/Potassium pump (an active transport system)
1. Most cells need to maintain an unequal concentration
of Na+ and K+ on either side of a cell membrane (used
to generate nerve impulses)
2. Na+ low INSIDE cell, K+ low OUTSIDE cell
3. Need to actively transport these ions across to maintain
proper concentrations
4. Energy from ATP is used to attach Na+ to the carrier
protein, causing a tertiary change in shape, carrying
the ion through.
III. Movement of Water
A. Water potential
1. High water potential = Purer water, LESS SOLUTE
2. Low water potential = less water, MORE SOLUTE
3. water moves across a membrane from HIGH w.p. to LOW
w.p.
4. Things that can affect water flow
a. Gravity
b. Pressure
c. Solute concentration
B. Bulk flow (overall movement of water)
1. LARGE AREAS of a fluid moving from one part of multicellular
organism to another part (swallowing water, blood flow)
C. Diffusion
1. Random movement of molecules (gases, liquids, etc)
from one concentrated area to a less concentrated area.
2. Eventually reaches DYNAMIC EQUILIBRIUM (same number
of molecules in all areas
ex. dye in a liquid, perfume spreading through a
room
D. Movement DOWN A GRADIENT (from high concentration to
low concentration - ex. osmosis, diffusion)
E. Movement UP A GRADIENT (from low concentration to high concentration - going against the flow) ex. active transport
F. Osmosis (diffusion of WATER through a semipermeable membrane)
1. A special case - can carry dissolved nutrients through
cell membranes
IV. Types of concentrations
A. Isotonic - two solutions of equal solute concentration
(no net movement between them)
B. Hypotonic - a solution with LESS solute than a second solution (movement is from hypotonic solution to second solution)
C. Hypertonic - a solution with MORE solute than a second solution (movement is from second solution INTO hypertonic solution)
V. Problems in living organisms
A. Diffusion across a cell membrane
1. H2O, O2, CO2, a few others an easily diffuse across
a cell membrane
2. Limits cell size
B. Countercurrent Principle
C. How to gain or remove excess water
1. Protists
a. be isotonic with surroundings
b. if hypertonic, get rid of excess water via contractile
vacuoles
2. Higher organisms
a. Fluid areas remain isotonic with surroundings
(blood in vertebrates)
b. find a way to prevent diffusion in or out of
body (thick, waterproof skin, scales, etc.)
VI. Osmotic Potential
A. The pressure required to stop the osmotic movement of
water across a membrane
B. TURGOR (the water pressure within cells that maintains
rigid cell walls)
1. Plants = hypertonic, let water IN
2. water diffuses into cells, is stored in vacuoles
3. cell elongation occurs via water pressure (increased
turgor)
a. Once secondary cell walls are laid down, no more
expansion
D. Plasmolysis (loss of turgor in cells)
1. water diffuses OUT of cells
2. Plants wilt
VII. Movement of large particles
A. Endocytosis ( ingestion)
1. Pinocytosis
(ingestion of liquid substances)
2. Phagocytosis
(ingestion of solid substances)
B. Exocytosis (the excretion of solid or liquid substances)