biology 2 exam 1 material

unit 25 and 26

Hypothesis for how the first living cells were produced (steps)

1. The abiotic synthesis of small organic molecules (monomers);

2. The joining of monomers into macromolecules;

3. The packaging of these macromolecules into protocells, droplets with membranes that maintained a distinct internal chemistry;

4. The origin of self-replicating molecules that eventually made inheritance possible

how did earth form

Earth formed about 4.6 billion years ago, condensing from a vast cloud of dust and rock surrounding the sun

Why was it unlikely for life to have originated or survived in the first few hundred million years?

The planet was bombarded by huge bodies of rock and ice left over from the formation of the solar system.

These collisions generated enough heat to vaporize all available water and prevent the formation of the seas.

The First Atmosphere (1)

May have been reducing (electron adding), thick with water vapor along with nitrogen with its oxides (carbon dioxide, methane, ammonia, hydrogen, and hydrogen sulfide)

The First Atmosphere Experiment

Conducted by Stanley Miller 1953, he created a simulation that mimics the conditions of early earth, he discharged sparks in the atmosphere of gases and water vapor, the experiment produced various amino acids as suggested by Oparin-Haldane hypothesis

Oparin-Haldne Hypothesis

conditions on early Earth favored the synthesis of organic compounds from inorganic precursors. They reasoned that this could not happen today because high levels of oxygen in the atmosphere attack chemical bonds. A reducing environment in the early atmosphere would have promoted the joining of simple molecules to form more complex ones. Energy to produce organic molecules likely from lightning and uv rays from the sun

Growing Atmospheric composition hypothesis

primarily of nitrogen and carbon dioxide, which is neither reducing nor oxidizing. Recent Miller- Urey experiments using neutral atmosphere produces organic molecules as well. Only areas near volcanoes had reductive atmospheres.

Other hypothesis for location of origin of life

The first organic compounds formed near volcanoes or deep-sea vents, where hot water and minerals gush into the ocean from Earth’s interior. Deep-sea vents, called alkaline vents, release water that has a high pH (9-11) and is warm(40-90°C) rather than hot, an environment that may have been more suitable for the origin of life

Abiotic Synthesis

The formation of organic molecules from non-living matter, a key process in theories of the origin of life.

Significance of Murchinson Meteorite

Some of the organic compounds from which the first life on Earth arose may have come from space. The 4.5-billion-year-old carbonaceous chondrite Murchison meteorite collected in southern Australia was found to contain more than 80 amino acids, in similar proportions to those produced in the Miller-Urey experiment. These amino acids contained an equal mix of D and L isomers and could not have been contaminants from living organisms on Earth. Living things make and use only L isomers. Recent studies have shown that the Murchison meteorite also contained other key organic molecules, including lipids, simple sugars, and nitrogenous bases such as uracil (RNA base).

2009 and 2016 Study

2009: Determined that abiotic synthesis of RNA monomers (cytosine and uracil) can occur spontaneously from simple precursor molecules.

2016: amino acid polymers (adenine and guanine) spontaneously produced from dripping amino acids on hot sand, clay, or rocks. polymers could have acted as weak catalyst for reactions on early earth.

abiotic orgin hypothesis

Predicts that monomers should link to form polymers without

enzymes and other cellular equipment

Unlike Protiens

polymers are a complex mix of linked and cross-linked amino acids

Two Properties Life is Defined By

reproduction and energy processing (metabolism)

DNA Molecules

carry genetic information, including the information needed for accurate

replication.

• The replication of DNA requires elaborate enzymatic machinery, along with a copious supply of nucleotide building blocks provided by cell metabolism

All about Vesicles

• fluid filled compartment bound by membrane-like structure

• may have provided the necessary self-replicating molecules and metabolism like source that must have appeared in protocells

• exhibit some properties of life such as reproduction, metabolism, and an internal chemistry different from its surroundings

• can form spontaneously when lipids and other organic molecules are added to water (the hydrophobic molecules in the mixture form a bilayer at the droplet surface, much like the

  lipid bilayer of a membrane)

• can “reproduce” and expand in size without diluting their contents

• may absorb montmorillonite particles, including those on which RNA and other organic

  molecules have become attached

• can increase the rate of self-assembly by adding montmorillonite, a soft mineral clay produced by the weathering of volcanic ash

• Have a selectively permeable bilayer and can

  perform metabolic reactions using an external source of reagents—another important prerequisite

  for life.

First genetic material

Likely RNA, not DNA.

Thomas Cech and Sydney Altman

Found that RNA molecules not only play a central role in

protein synthesis but also are important catalysts in modern cells

Ribosomes

An RNA catalyst that can make complementary copies of short pieces of RNA when supplied with nucleotide building blocks

Why Can RNA sequences form through abiotic conditions

• Unlike double-stranded DNA, single-stranded RNA molecules can assume a variety of three-dimensional shapes specified by their nucleotide sequences.

• RNA molecules have both a genotype (nucleotide sequence) and a phenotype (three-dimensional shape) that interact with surrounding molecules.

• Under particular conditions, some RNA sequences are more stable and replicate faster and with fewer errors than other sequences.

Fossil Records

An incomplete chronicle of evolutionary change. Few organisms are preserved as fossils. Many fossils that do form are later destroyed by

geologic processes, and only a fraction of them are discovered. The fossil record is biased in favor of species that persisted for a long time, that were abundant and widespread, that lived in certain environments, and that had hard parts that fossilized readily. Despite its limitations, the fossil record provides a detailed account of biological change over geologic time.

When did the first unicellular eukaryotes appear? What is the Significance?

They appeared 1.8 billion years ago. This was significant because this was the result of serial endosymbiosis and created a platform for the production of multicellular organisms

When did the first multicellular eukaryotes appear? What is the significance?

They appeared about 1.3 billion years ago but larger more diverse eukaryotes did not appear in fossil records until about 600 million years ago. These fossils, referred to as the Ediacaran biota, were of mostly soft-bodied organisms. The diversification of the Ediacaran Biota set the stage for another evolutionary change: the Cambrian Explosion

Cambrian Explosion

The phenomenon of the sudden appearance of present-day animal phyla in fossils (about 535-525 million years ago). This is significant because The Cambrian explosion resulted in the appearance of predators over 1 m in length emerged that had claws and other features for capturing prey; simultaneously, new defensive adaptations, such as sharp spines and heavy body armor, appeared in their prey.

When did the colonization of land happen and what was the significance?

Some prokaryotes have been found to live on earth since 3.2 billion years ago, however larger eukaryotes did not colonize land until about 500 million years ago. The gradual evolutionary shift out of aquatic environments allowed reproduction on land to be possible. Vascular plants began to form and internally transport materials. Vascular plants’ production of oxygen and absorption of CO2 would eventually help create the atmospheric composition that allowed modern life to form.

Significance of outgroups in creating phylogenetic trees

Outgroups share a common ancestor with the study group but lack its derived traits, serving as a reference point to differentiate ancestral traits from derived traits and establish evolutionary lineages.

How can a suitable out group be determined

Morphology- the study of the shape or form of something

Paleontology- the study of life in the geologic pass (through fossils primarily)

Embryonic Development

Gene Sequences