Unit 6 Origins of Life + Major Events

What are the common functions/structures of living things?

• made up of >1 cell

• uses energy

• grow + reproduce

• adapt + evolve

• maintain homeostasis

• common set of molecules

• sense + respond to stimuli

What is cell theory?

living things are made up of >1 cells

• a cell is the simplest collection of matter considered to be alive

When did the Earth form?

4.6 bya

What is the timeline/order of Earth’s major events?

1. Earth froms- 4.6 bya

2. Earliest evidence of life (1st prokaryotes)- 3.5 bya

3. Oxygen revolution - 2.5 to 1 bya

4. 1st eukaryotes- 2.1 bya

5. 1st multicellular eukaryotes- 2.1-1.5 bya

6. Cambrain explosion- 535-525 mya

7. Colonization of land by fungi, plants + animals- 500 mya

What is the composition of cells?

oxygen, hydrogen, nitrogen, + carbon

What are the 4 main macro molecules?

1. lipids= fats + plasma membrane

2. proteins= amino acids

3. nucleic acids= DNA/RNA (nucleotides)

4. carbohydrates= sugars

What is the 4 stage hypothesis?

the formation of life (cells) → chemical/physical processes a + natural selection acted to produce the 1st molecules + eventually 1st cells

Stages of the 4 stage hypothesis

1. small organic compounds

2. large organic molecules

3. Protocells

4. RNA replication

(steps 3+4 interchangeable)

Stage 1 - building blocks

• atmosphere contained thick vapors + compounds → large amounts of CO2, N, methane, H, HSO4, + ammonia

• Earth cooled + oceans formed- 3.9 bya

• supported by Miller and Urey’s experiment= production of AA’s in a lab by replicating early Earth conditions, (supports Haldane’s hypothesis)

What is Haldane’s hypothesis?

organic molecules formed from simple ones w/ the addition of energy from UV/lightning

Stage 2- Macromolecules

AA’s + hot rocks (catalyst)= macromolecules

• evidence: these can form spontaneously in lab

What is a protocell?

large, ordered structure enclosed by a membrane which encapsulates cell components

• energy generated via metabolism which enables characteristics of life such as growth + reproduction

Stage 3- Protocell evidence

• protocells have been found to occur in nature → however if lipids are put in a tube of water they will not form a protocell

• several other experiments show that given the right conditions protocells can + will form

Stage 4- Self Replicating RNA

• DNA → RNA → proteins

• for dna to replicate itself it needs enzymes

• rna can act as both an information molecule + an enzyme

• RNA world hypothesis

What is the RNA world hypothesis?

proposed self replicating RNA molecules were precursors to current life, which is based on DNA, RNA, + proteins

• perhaps natural selection acts upon RNA molecules that can self replicate the fastest + leave the most descendants

What is the 1st single celled organism? (3.5 bya)

fossilized stromatolites → prokaryote + sediment

Characteristics of prokaryotes

• abundant + diverse

• live anywhere + everywhere

• simpler + smaller than eukaryotes

• no organelles

What is the oxygen revolution?

• Earths early atmosphere didn’t have O2 → O2 has biological origin

• O2 dissolves in H2O + reacts w dissolving FE → precipitates + accumulates… once H2O sat w O2 → some will enter atmosphere

• 2.7 bya

• evidence of atmosphere O2= rust made by O2+Fe

Earliest photosynthesis

• cyanobacteria= 1st organisms to make organic compounds using CO2 + H2O → photosynthesis

• 2.7 bya

Where did eukaryotes come from?

evidence suggests some organelles used to be prokaryotic cells living on their own + were ‘eaten’ by another prokaryotic cell + the relationship was beneficial to both

• endosymbiosis

What is endosymbiosis?

symbiotic cell relationship in which one organism lives inside the body or or cell of another one

What is the endosymbiotic theory?

says that mitochondria + chloroplasts were formerly prokaryotes

What are the 4 steps of endosymbiosis?

1. a prokaryote ingested some aerobic bacteria, the aerobes were protected + produced energy for the prokaryote

2. over a long time, the aerobes become mitochondria, no longer able to live on their own

3. some primary prokaryotes also ingested cyanobacteria which contain photosynthetic pigments

4. the cyanobacteria become chloroplasts no longer able to live on their own

Evidence for the endosymbiotic theory

• size

• reproduction is similar

• similar molecules inside (DNA, proteins, + ribosomes)

• similar molecules in plasma membrane

Independent multicellularity

although fungi, plants+ animals arose from single celled ancestors they arose from different ones

• multicellularity evolved independently multiple times

Benefits of multicellularity?

• protection

• increased size

• division of labor → more complexity

• longer lives (can replace cells)

Drawbacks of Multicellularity?

• if 1 group of cells fail, organism could fail too (cancer)

• more energy required to function

• higher risk of infection