Chapter 02

Life Builds from the Bottom Up

• Every individual is a colony of smaller individuals

• Our ancestors were similar to bacteria that evolved from self-replicating molecules

• Bacteria invented all of life’s essential chemical systems

Cooperating Communities of Cells

• The taste buds on our tongues are small communities of cells

From Bottom Up to Top Down

• As multicellular creatures evolved, they created new environments for already existing simpler creatures

• Bacterial and viral parasites evolved after their hosts; it is likely many parasites have become simpler than their ancestors were

Viruses

• Viruses cannot exist without using another organism’s molecular machinery to travel and reproduce

Sponge• Cells function as a

cooperating group of individuals

• Different types of cells cooperate to maintain constant water flow,trap food, maintain shape, and transport nutrients and waste

Life Assembles Itself Into Chains

• Chains: simple units linked together in long flexible strands

• Sequence of links in a chain molecule conveys information

Chain Molecules

• Information chains: store and transmit information (example – genes)

• DNA and RNA are made of four different nucleotides

Chain Molecules

• Working chains: carry out business of living (example – proteins)

• Proteins are made of twenty different amino acids

Information Chain to Working Chain

• Genes carry information that becomes proteins

Protein Folding

• Shapes that proteins take depend on the interactions among the amino acids that make up the protein chain

Reading Information

• Living creatures have the ability to read environmental information

• Proteins imbedded in cells are activated and altered by tiny differences in their surroundings

Life Needs an Inside and an Outside

• Life’s molecules must be kept close together so that they can meet frequently and react readily

• Cell membrane maintains an inner environment that is different from the outside

Cell Membrane

• Consists of double layer of fat molecules• Water-liking heads of fat molecules face

outside, fat-liking tails face inward• Second row of fat molecules aligns tail to tail

with outer layer, heads facing inward• Several pumps imbedded in membrane move

materials in and waste out

Cell Membrane

Protein Pump

Membranes

• Outer cell membrane: plasma membrane

• Nucleus surrounded by membrane enclosing DNA

• Mitochondria are surrounded by membranes

• Mitochondria and chloroplasts use inner membranes for electron conduction

Membranes

Membrane Functions

• Keep things out of cells that aren’t wanted

• Bring things into cells that are needed and keep them there until used

• Conduct waste material out of cells

Plasma Membrane

• Some molecules can pass across the lipid bilayer; others cannot

Gaia HypothesisEarth as Organism

• Atmosphere, oceans, soils, living organisms comprise a biosphere

• Terrestrial vegetation acts as protective membrane for the land

• Atmosphere acts as membrane for the earth

Inward Similarity – Outward Diversity

• All living creatures are based on a small number of underlying patterns and rules

• Simple rules, used in different contexts, produce great variety

Homology

Different Proportions – Same Pattern

• Differences in shape are a matter of proportion

• The fundamental pattern is the same

Different Proportions – Same Pattern

Patterns of Multiplication

• Dividing and adhering cells can occupy space in four basic ways

Organization with Information

• Genes contain information on how and when to make proteins

• Proteins work collectively to perform life’s functions

Enzymes

• Proteins that act as chemical reaction facilitators (catalysts)

• Perform straightforward chemical tasks at incredible speeds without being changed in the process

Enzymes

• Teams of enzymes work in a coordinated fashion to maintain life

EnzymesExample: Glycolysis

• Ten enzymes convert six-carbon glucose into three-carbon pyruvate

• Two ATP (energy molecules) are produce from one glucose

Combining Information

• Nature creates new combinations by exchanging information

• Large number of combinations can result from a small number of variables

Genetic Information

• Each of us has two sets of genes – one from our mother and one from our father

• Many matched pairs of genes are not exactly alike

• Differences in our genes account for our uniqueness

Recombining Genetic Information

• In making sperm and eggs, our genetic information chains are brought together lined up, recombined and separated so that each sperm and egg gets half

• In mating, we combine the recombined chain with one from the mate

Recombining Information

Making Eggs and Sperm

Combining Genetic Information

• With each alteration in information, creatures become better or worse suited to their environment

• Better suited individuals survive to reproduce and pass on their genetic information

Selective Breeding

• Genes are purposefully recombined to control the characteristics of an organism

By selecting only chickens with elaborate head plumage to breed with one another, breeders can quickly vary the appearance of these chickens

Genetic Engineering

• Genes from one organism are inserted into another, turning that organism into a factory for making specific proteins

Cloning a Human Gene in a Bacterium

Cloning a Human Gene in a Bacterium

Accidents Ensure Novelty

• Cellular mechanisms make errors in copying genes

• Altered gene sequence changes the information being transmitted and can show up in the offspring as a defect

• Once in a while, the alteration is an improvement that makes the offspring better adapted for survival

Improving Mutation

• Wrinkled skin increases surface area and cools the elephant more efficiently, allowing the elephant to grow larger

• Albinism, a defect in pigmentation, allows polar bears to blend into their surroundings

Mutations – Good or Bad?

Sickle Cell Disease: • Result of mutation in hemoglobin gene• Causes inflammation and tissue

destruction, but provides some protection against malaria

• Sickle cell disease is common in equatorial Africa where malaria is endemic

Mutations

Mutations are generally caused by:

• Mistakes made by DNA duplicating machinery when cells divide

• X-rays or UV and cosmic radiation impinging on DNA

• Certain toxic chemicals interacting with DNA

Life Occurs in Water

• Life began in water

• Our cells are 70% water

• Most of the essential molecules of life dissolve and transport easily in water

Water

• Polar molecule

• Forms weak bonds with itself and with many other types of molecules

Water

• Expands when it freezes, making ice less dense than liquid water

• Ice provides an insulating layer that prevents further freezing of lakes, rivers, and oceans

Water Organizes and Orients Molecules

• Water molecules attract and repel charged molecules and therefore orient them

Water Organizes and Orients MoleculesPhospholipids in Cell Membrane

• Hydrophilic (water-liking) charged ends orient towards water molecules

• Hydrophobic (water-shunning) fatty tails stay away from water

Life Runs on Sugar

Sugars:• Energy-packed

chains of three to seven carbon atoms with hydrogen and oxygen

• Glucose: six carbon atoms; life’s central sugar

=

Photosynthesis Preview

• Plants, marine algae, and certain bacteria convert CO2 and hydrogen from water into sugar using energy from sunlight

Respiration Preview

• Plants, algae, bacteria, and animals transform energy from sugar’s bonds into ATP, which powers all of life’s work

• Carbon and oxygen are discarded as CO2

• Hydrogen is linked to oxygen from the air and is discarded as H2O

Sugar

• Starting material for assembly of amino acids and nucleotides

Life Works in Cycles

• Each protein performs a simple task in assembly-line fashion

• Initial protein keeps track of overall output; as products pile up or become scarce, it adjusts speed of overall operation

Life Works in CyclesSelf-Correcting

Maneuvers:

• A feedback loop is maintained between the owl’s eyes, brain, wing and tail muscles and the mouse’s movements

Circular Flow of Materials

• Intake and output are balanced in the living world

• One organism’s waste is another’s food or building material

• End product of one process becomes the starting point of another

Fever Feedback

Breathing Feedback

Circular Flow of MaterialsPhotosynthesis and Respiration

• O2, byproduct of photosynthesis, is essential for respiration

• CO2 waste from respiration is taken up by plants for photosynthesis

Carbon Cycling

Life Maintains Itself by Turnover

• Organisms routinely take apart molecules and reassemble them

• Turnover provides flexibility

• Change in environment often calls for new proteins which can be made from disassembled old ones

Cell Turnover

• Cells that turn over in days or weeks – liver, intestine, skin

Cell Turnover

• Cells that rarely turn over – neurons

Life Maintains Itself by Turnover

• Turnover requires a constant supply of raw materials and energy

• The bottom layer of these skin cells is fed by tiny blood vessels, providing a constant supply of raw materials

Life Maintains Itself by Turnover

• In the digestive tract, starches and fats are broken down into smaller molecules, which diffuse through the finger-like cells of the intestinal mucosa into the bloodstream

Optimize Rather than Maximize

• Life operates elaborate signaling and management systems to maintain optimum levels

• Maximizing any single value tends to reduce flexibility in the overall system, so that it may not be able to adapt to adverse environmental change

Optimize Rather than Maximize

• In times of crisis, the most specialized (maximized) organisms tend to become extinct; the most adaptable (least specialized) survive

• Following a mass extinction, adaptive radiation (evolution of many different species from a few ancestors) occurs on a large scale

Optimal Surface-Volume Relationships

Life is Opportunistic

• Life makes do with whatever is available in its surroundings

• Life flourishes even in the world’s harshest places

• The genetic code and the protein structure of all living things permit great flexibility

Competition and Cooperation

Strategies for fitting in:

• Every creature acts in its own interest

• The living world works through cooperation

Competition and Cooperation

• Creatures are self-interested, but not self-destructive

• Self-defeating strategies get weeded out by evolution

Competition and Cooperation

Predator/Prey Relationship:

• Usually predators can take only the smallest, weakest, or most unhealthy of their prey species, leaving the better adapted members to survive and reproduce

From Predation to Cooperation

• Ancestors of chloroplasts and mitochondria originally acted as small predators, invading larger bacteria

• They exploited, but did not destroy their host

Interconnected and Interdependent

Co-evolution:

• Any successful change of strategy by one organism will create a ripple of adjustments in the community

Interconnected and Interdependent

• As moths develop better ways to hear (and avoid) predator bats, bats must develop better ways to hunt moths