1. Properties of Life on Earth

2. What is life?
As a group, discuss and then list the basic defining characteristics of life. (Consider living things and what they have in common.)
Compare your list to another group’s list. Which items were similar/different?
Do you agree with their list? If not, why not?
Are there any changes you would make to your list? If yes, what and why? If no, why not?

3. What is Life? Characteristics:
Order - provides a basic frame from which to build.
Reproduction - creates more of its own kind.
Growth & Development - Increases in complexity.
Energy Utilization - nourishment.
Response to Environment - interacting with stimuli.
Evolutionary Adaptations - changes as needed and required for survival.

4. Simplest Definition
Life is something that can reproduce and evolve through natural selection.

5. The Basic Building Blocks of Life – Cells
Cells - microscopic units in which living matter is separated from the outside world by a membrane.

6. Similarities! All living cells share a great many similarities!
All pass hereditary information through DNA
They have similar chemical processes
Why the similarities?
Likely answer: All life ON EARTH shares a common ancestor.

7. Chemistry of Life
All life on Earth is made up of more than 20 different chemical elements; however just 4 make up 96% of living matter: Oxygen, Carbon, Hydrogen & Nitrogen. Remaining elements include calcium, phosphorus, potassium and sulfur.

8. Importance of Carbon Why do we say life is carbon-based?
All cells are carbon-based; thus all life is carbon-based.
Carbon permeates the world of life—from the energy-requiring activities and structural organization of cells, to physical and chemical conditions that span the globe and influence ecosystems everywhere.

9. Carbon’s Bonding Behavior
Outer shell of carbon has 4 electrons; can hold 8
Each carbon atom can form covalent bonds with up to 4 atoms

10. Why is carbon so important?
It combines with other elements to make complex molecules. Atoms are linked together by chemical bonds.
Carbon can bond with 1 to 4 atoms at a time- eventually building organic molecules.
Hydrocarbons - prevalent molecules with hydrogen and carbon.
The simplest Carbon molecules are generally referred to as organic molecules.

11. (ball-and-stick model)
Bonding Arrangements
Carbon atoms can form chains or rings
Other atoms project from the carbon backbone
Glucose
(ball-and-stick model)

12. Methane: Simplest Organic Compound
Structural formula
Ball-and-stick model
Space-filling model H C

13. Functional Groups
Here are some functional groups that bond to carbon chains.

14. What about Silicon?
Is other element based life possible? Maybe silicon based life since it too can be 4-bonded.
Why is silicon unlikely?
2 strikes:
The bonds formed by silicon are weaker than those formed by Carbon. Fragile! Can’t exist long in water!
Silicon does not normally form double bonds, only single bonds. Limits chemical reactions and variety of structure.

15. Cell Components
All the major components of cells are made from complex organic molecules.
The large molecular components of cells fall into four main classes:
Carbohydrates
Lipids
Nucleic acids
Proteins

16. Carbohydrates Provides energy to cells
Make important cellular structures (cellulose)

17. Lipids Store energy for cells (fats) Major ingredient of cell membrane
Can spontaneously form membranes in water

18. Proteins Are large molecules built from long chains of amino acids
Serve as structural elements in cells
Are catalysts for biochemical reactions in cells (enzymes)

19. Amino Acids
amino = a nitrogen atom bonded to two hydrogen atoms and a carbon atom
Amino acids also have a carboxyl group (COOH)
Amino acids differ by the sets of atoms bonded to the central carbon
More than 70 different amino acids found in nature
Found in meteorites, comets, floating in clouds in space
Most life on Earth builds proteins from only 20 of them

20. What do the amino acids tell us?
Only 20 used in most life
Few or one common ancestor
Living cells use left-handed amino acids, while non-living cells use both.
ONE common ancestor

21. Nucleic Acids DNA and RNA!
(Deoxyribonucleic Acid and Ribonucleic Acid)
DNA and RNA are responsible for allowing cells to function according to precise, heritable instructions.
Changing the DNA results in mutation, evolution, and new species.

22. Basic Cell Types
Prokaryotes - smaller, simpler, more numerous cells (single-celled) with no cell nuclei.
E. Coli and Samonella are examples.
Major branches are Bacteria and Archaea.
Eukaryotes - larger, more complex cells (single- or multi-celled) with cell nuclei.
Amoebas

23. The 3 Domains of Life on Earth
Modern biologists classify life into three broad domains:
Bacteria, Archaea and Eukarya.
Detailed studies of DNA in different organisms suggest that archaea are more closely related to Eukarya than are Bacteria. So Archaea and Eukarya split from Bacteria and then split from each other.
This may mean that the division of cell types (prokaryotes and eukaryotes) may not be as fundamental as it looks.

24. Metabolism: The Chemistry of Life
refers to all chemical reactions that occur in living organisms.
Basic metabolic needs:
A source of raw material with which to build new things.
A source of energy to fuel metabolism.

25. Raw Source Material
How do you support a wide variety of molecules and metabolic processes with limited varieties of source material?
A wide variety of ENZYMES to catalyze particular chemical reactions
They all use ATP (Adenosine Triphosphate) to store and release energy. So, living cells use outside energy to produce ATP, which is then used to provide energy for other cellular reactions. And ATP is recyclable.

26. ATP All living cells use the same molecule: ATP. This is a nucleotide.
Figure 6.6b Page 101

27. Diagram of Mitochondria
Diagram of a Cell
Diagram of Mitochondria

28. Step 1:
Proton gradient is built up as a result of NADH (produced from oxidation reactions) feeding electrons into electron transport system.
Step 2:
Protons (indicated by + charge) enter back into the mitochondrial matrix through channels in ATP synthase enzyme complex. This entry is coupled to ATP synthesis from ADP and phosphate (Pi)

29. Classifying Life by its Metabolic Needs: Carbon Usage of Cells
Heterotrophs - Any organism that gets carbon by eating. (Animals)
Autotrophs – Any organism that gets carbon from CO2. (Trees, etc.)

30. Classifying Life by its Metabolic Needs: Engergy Sources: Light or Chemicals
Photosynthesis – the sunlight energy conversion mechanism in plants.
Photoheterotrophs - get energy from sun.
Chemoheterotrophs - get energy from chemical processes (all animals).
Photoautotrophs - get energy from sun.
Chemoautotrophs – cells that get energy from inorganic chemicals.

31. 4 Metabolic Classifications
These are quite general and they ought to apply equally well to life elsewhere. Therefore, unless we are missing something, it seems likely that all life should function much like cells on Earth.

32. Life’s Metabolic Needs: The Importance of Water
1. Allows some organic materials to dissolve and making them available.
2. Gives organic chemical transport ability for food and wastes.
3. Is involved in reactions for storage and release of energy (especially from ATP).
One final necessity in metabolism: liquid water
On Earth water plays 3 key roles in metabolism.

33. DNA and Heredity: The Importance of DNA
DNA holds the operating instructions for living organisms. Has a double helix (3D spiral) structure connected by DNA bases. Only four bases are common to life on Earth:
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
T can only pair with A; C can only pair with G.

34. Click to view animation.
DNA Structure
Click to view animation.

35. Replication The DNA replication mechanism is complex but rapid.
The DNA “unzips” between the base pairs.
The unzipped strand serves as a template for making a new strand.
This results in 2 identical strands of the original DNA. When a cell divides, a copy goes to each daughter cell. (the basis for heredity)
This is a complex process using more than a dozen special enzymes, each with its own task (unwind the helix, make new pairs, check for errors, etc.)
Errors can occur and lead to mutations and evolultion

36. DNA and Heredity: How is heredity encoded in DNA?
Gene - an instruction for building a single protein or cell. (Basic functional unit for heredity.
Genome - the complete sequence of DNA bases in an organism.
Gene: Within a large DNA molecule, isolated sequences of DNA bases represent the instructions for a variety of cell functions. One sequence may provide the instructions for building a piece of RNA, a protein, or other things. This is a sset of instructions for an individual function – a GENE.
Genome: The complete sequence of DNA bases in an organism (including all genes). The human genome consists of about 3 billion DNA bases, between 20,000 and 25,000 genes. (per Human Genome Project Oct 2004)
According to the new findings, researchers have confirmed the existence of 19,599 protein-coding genes in the human genome and identified another 2,188 DNA segments that are predicted to be protein-coding genes.

37. The Genetic Code A set a rules for reading DNA
Genetic “words” consist of 3 bases
ACTCAGCTTCAACGG becomes
ACT CAG CTT CAA CGG
Each “word” represents either a particular amino acid or a stop/stop instruction.
There are only 64 three-letter “words” that can be built with the 4 letters. Most living organisms need about 20 proteins. REDUNDANT!
ACC and ACA both represent the same amino acid.
It appears that the codes for amino acids only depend on the first 2 bases in the “word”
ACC ACA ACT ACG all code for the same amino acid
Did the genetic code once depend only on two-base words? Did we evolve to three?

38. So, what does RNA do?
RNA participates in carrying out the genetic instructions through:
Transcription - copies DNA from one strand to another.
Translation - helps attach amino acids into chains to make proteins.

39. Transcription

40. Transcription Movie

42. Translation Movie

43. Mutations
changes in the DNA code or structure that are not pre-programmed
When a mutation occurs, it might not affect the functionality of the protein much (or at all if the 3rd base is substituted). However, sometimes you’ll get dramatic effects.
The most dramatic effects are seen from nucleotide deletion OR ADDITION. Then, everything after the change is affected.
If the mutation is NOT lethal, then it will be copied every time the DNA is replicated. It’s a permanent change. It will affect the offspring of all single-celled organisms or multi-celled organisms only if the mutation occurs is a reproductive cell.
If the mutation helps the organism in some way to thrive, it is more likely to reproduce and the trait is passed again. This is the basis for evolution and natural selection.

44. Sickle-Cell
Sickle-cell disease is simply a change of one base. It causes blood cells to form a sickle shape, which can clog up tiny blood vessels. This can be deadly! (more than 100,000 people die each year!)
Because humans have 2 copies of each gene, this isn’t usually a problem. You only get the disorder if both copies have the mutation. If only one copy has it, then you’ll have a hard time catching malaria! A good mutation!