AP Biology - Unit 3: Origins & Cellular Life

Atmosphere with a lot of CO₂ (Necessary Conditions)

(to form C- containing organic molecules) AND reducing compounds (with a lot of H’s) to donate e-, to form bonds and build larger, more complex molecules 

High surface temps (Necessary Conditions)

due to radioactive decay in the interior provides lots of kinetic energy to drive convection to carry molecules into the atmosphere where they are exposed to

Other sources of energy (Necessary Conditions)

(lightning, UV radiation) provides energy necessary to build complex molecules (endergonic reactions)

Endergonic reaction

An endergonic reaction requires energy input and results in products with higher energy than the reactants. This energy is usually provided by an external source like heat or light. Examples include photosynthesis and ATP synthesis.

Miller – Urey Experiment 

simulated early Earth's atmosphere to test if organic molecules could form from inorganic compounds, used a closed system with water, methane, ammonia, and hydrogen, and applied electrical sparks like lightning. After a week, they discovered the formation of amino acids and other organic compounds. This experiment supported the idea that life's building blocks could have originated on Earth naturally.

Miller – Urey Experiment raw materials

• CO, CO₂ for the carbon backbone

• H₂S, NH₃, CH_4, H₂ “Reducing atmosphere” (H ions to bond) 

Miller-Urey Experiment Products

• Amino acids

• DNA/RNA bases

• Carbon rings

• Lipids

Oparin’s Bubble Theory 

• explains how these chemicals could have come to be contained in membranes to become cells

• life arose from non-living chemicals inside primitive envelopes of lipids or proteins that would have formed spontaneously in a watery environment (water organizes nonpolar molecules) and contain molecules that can replicate

First cells

• Prokaryotic (no nucleus)

• No internal membranes (organelles)

• Naked DNA (no histones)

• All bacterial

Common ancestors of first cells

• Prokaryotic

• Heterotrophic

• Naked DNA (no histones)

• No introns

Eubacteria or “true bacteria”

disease causing

• no internal membranes or organelles (except ribosomes)

• Naked DNA - lacks histones for packaging so uncoiled

• No introns (non-coding regions)

• Peptidoglycan cells wall

• Susceptible to antibiotics

Blue Green Algae - cyanobacteria

 are autotrophs 

true bacteria (strep, staph)

are heterotrophs

Archaebacteria or “ancient bacteria”

• extremophiles (heat, pH, salt tolerant)

• mainly anaerobic (chemosynthesis)

• No internal membranes or organelles except ribosomes

• Naked DNA -no  histones for packaging 

• Some introns

• No peptidoglycan cell walls 

• So no susceptibility to antibiotics

Endosymbiosis

How one prokaryotic cell was engulfed by another and they lived happily ever after TOGETHER!

Mitochondria & Chloroplasts appear to have been bacteria that were engulfed because…

• they have a second membrane (b/c they were engulfed) 

• they are the same size and shape as bacteria

• the have their own (bacterial – no histones) DNA

• they reproduce by binary fission like bacteria do!

Domain Eukaryote

(true nucleus), developed by endosymbiosis

• Membrane bound organelles (including nucleus)

• cellulose/chitin cell wall

• Not affected by antibiotics

• Packaged DNA - coiled on histone proteins

• Introns - non coding regions

Sexual Reproduction 

introduces variability by recombination between individuals 

Multicellularity

when cells specialize and divide up life functions 

Protists

unicellular, eukaryotic, autotrophic or heterotrophic 

Fungi

multicellular, eukaryotic, heterotroph 

Plantae

as above but w/ photosynthesis – autotrophs (self feeders), nonmotile

Animalia

multicellular – heterotrophs (other feeder) 

Cell Membrane 

Regulates movement

Cytoplasm

Semi liquid filling H₂O & protein

Organelles

Membrane bound has specific chem. rx

Nucleus

contains DNA

Cell Theory

• All organisms composed of cells

• Cells are smallest intact living things

• Cells come only from other cells

Limits on cell size depends on the ratio of

surface area outside and volume inside

Surface area outside

Amount of cell membrane through which the cell can absorb materials

Volume inside

The amount of cyctoplasm including organelles which must be kept supplied w/ nutrients

Because volume increases much faster than surface,

area large cells starve or build up toxins faster than they can be removed

Small cells have less volume

per unit of surface area

Large cells have less surface

through which to feed their large volume

The solution is cells must…

divide as they grown before they get too large 

Practice diagrams

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