[BSC 116] - Midterm Exam Guide - Everything you need to know! (56 pages long)

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BSC 116
MIDTERM EXAM
STUDY GUIDE
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History of Life on Earth:
Life on Earth is at least 3.5 billion years old
o Chemical/physical processes on early Earth may have produced simple cells in sequential
stages
Abiotic synthesis of small organic molecules
C, N, and small amounts of O in the atmosphere
Early atmosphere likely contained water vapor and chemicals released by
volcanic eruptions
Nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen,
hydrogen sulfide
No large amounts of oxygen
Atmosphere of early Earth was probably a reducing environment
Joining of these small molecules into macromolecules
Continuous growth until eventually forming a protein, carbohydrate, or fatty
acid
Packaging of molecules into "protobionts"
Origin of self-replicating molecules
o Atmosphere was much different than that of which we have today
Miller-Urey experiment- hypothesied that the atmosphere of early Earth was probably a reducing
environment
o Amino acids, nitrogenous bases, and other simple organic molecules
o Evidence for this hpothetical atmosphere is not entirely convincing
Another possibility- first organic compounds were synthesized near submerged
volcanoes and deep-sea vents
o One possible scenario:
Reducing environment gave rise to organic molecules (amino acids, nucleic acids,
lipids, etc
Catalytic RNA molecules (ribozymes) capable of self-replication former
Self-assembly of lipids into spheres (liposomes) gave these molecules a protective
environment
Protobionts- aggregates of abiotically produced molecules surrounded by a lipid membrane
o Key properties of life:
Replication and metabolism
Lipid bilayer could have provided compartmentalization for these tasks
o Could have formed with simple metabolic activities
Ribozymes can catalyze many different reactions
o Given enough time, early protobionts and their simple machinery may have replicated,
mutated and eventually developed enough metabolic machinery to be considered life
RNA world most likely gave rise to DNA-based life (more stable) using RNA as an intermediate to
protein synthesis
Studying the History of Life:
Fossils- preserved remains of living organisms
o Almost always in sedimentary rocks (accumulation of layers of sand, mud, silt, etc)
o Sediments and sedimentary rocks preserve the history of life- youngest near the surface,
oldest deeper
Movement of earth can change the trend
o New technology allows us to study fossils more in depth than before
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Discovering feather color, mapping capillary networks, CAT scans on dinosaur skulls,
etc.
The fossil record is biased in favor of species that:
o Existed for a long time
Had to die in the right place at the right time in the right environment for a fossil to
form
o Were abundant and widespread
o Had hard parts (fossilized easily)
Shells, bones, skulls, etc.
However, researchers are finding impressions in fossils of soft-bodied animals
Radiometric dating- inferring age of rocks and fossils based on amounts of radioactive elements
o Primary method of determining the age of a fossil
o Uses a mass spectrometer (separates and quantifies each isotope by mass)
o Half-life- the time it takes for half of the parent element to decay to the daughter element
Analysis- the sampled rock contains equal amount of U-235 and Pb-207
4.6 billion years ago (bya)- solar system forms
o On a 24-hour clock: 12:01 am
3.9 bya (roughly 3:00 am)- Earth cools, stabilizes, fewer volcanic eruptions
o No free oxygen
o Reducing atmosphere
o Abiotic (non-life) synthesis of small organic molecules (amino acids, bases, etc.) and
polymers
Replicated in lab
Recovered from meteorites
Earth Prior to Life:
3.9-3.5 bya:
o The RNA world- early pre- and proto-life probably depended on RNA, which carries
information and is catalytic
RNA enzymes = ribozymes
o RNA-based life > DNA-based
DNA is more stable
3.5 bya (roughly 4:00 am)- traces of first life
o The earliest living organisms- prokaryotes
Stromatolite- fossilized bacterial mats; identical in structure to extant bacterial mats
Oxygen- photosynthetic bacteria produce oxygen, which increases in concentration starting about
2.7 bya
o Red bands of iron oxide in rock mark concentrations of oxygen
o Roughly 3.5-2.1 bya (4:00 am-1:00 pm)- only life forms are bacteria
Oxygen Reductions- posed a challenge for most life forms
o Adaptations
Greater ability to harvet energy from sunlight
Cellular respiration
Drove evolution of multicellularity
Eukaryotes:
o Origin of eukaryotes (roughly 1:00 pm)
o "Hybrid" cells
Mitochondria and plastids (chloroplasts) are of bacterial origin
Engulfed by protoeukaryotes and establish symbiotic relationship
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