Origin of Cells

Compare and contrast the atmospheric conditions of the early Earth with the atmosphere of today

Temperatures were likely to have been higher in the early Earth than now because of the lack of free oxygen, resulting in a lack of stratospheric ozone layer.Without this layer more UV light would have penetrated to the Earth’s surface since ozone isn’t absorbing them, increasing radiation and activation energy for chemical reactions. Higher concentration of methane and carbon dioxide (greenhouse gases) also trapped these infrared radiation to increase surface temperature.

The atmosphere included ammonia (NH3), nitrogen, methane, water, and higher level of carbon dioxide compared to today’s atmosphere

Lightning could have also triggered these chemical processes that resulted in spontaneous formaiton of carbon compounds such as amino acids, simple sugars, nucleotides, and fatty acids that formed the building blocks of early cells.


In current Earth, these spontaneous reactions would not be possible as there are high levels of oxygen in order to sustain life and lower temperatures compared to early Earth.

Why is the origin of cells highly debated among scientists?

Hypothesis must be testable but since it is impossible to recreate conditions on early Earth 100% accurately it is difficult to know how cells were created

How was the Miller-Urey experiment made?

With an apparatus with boiling water to produce steam (high temperatures in early Earth)

Mixing steam with gases (methane, hydrogen ammonia) that recreated atmosphere (there wasn’t lot of methane in early Earth though)

Electrical discharge (lightning) not UV light

Condenstion of water (cooling atmospheric gases)

After a week they found that the condesned mixrture contained trace of simple organic molecules, especially amino acids (but they tend to remain as monomers rather than forming proteins in water). Unable to generate nucleotides

Define archea and eubacteria (prokayrotes)

Archea: Cell walls made of pseudopeptidoglycan

Eubacteria: Cell wals made of peptidoglycan

Explain how hydrothermal vents could have provided the necessary conditions for the synthesis of organic compounds.

Fissil evidents indicates that LUCA may have been an autrotrophic extremphile (orgnaims that lives in extreme climate) with lots of hydrogen, carbon dioxide, and iron

Hydrothermal vents provide high temperatures which provide activation energy for chemical reactions.

Hydrothermal vents release chemical compounds/elements such as hydrogen, methane, ammonia.

These compounds could have reacted to form simple organic compounds such as amino acids, simple sugars.

Mineral surfaces in hydrothermal vents could have acted as catalysts to increase rate of organic synthesis reactions.

What material are the cell wals of plant, fungai and prokaryotes?

Plant: Cellulose

Prokaryote: Petidoglycan

Fungi: Chitin

Describe how the formation of a cell membrane would have been a critical step in the evolution of living cells.

Formation of cell membrane created distinct internal environment

Allowed concentration of molecules needed for biochemical reactions

Provided protective barrier from external environment

Enabled regulation/selective passage of substances in/out of cell

Facilitated development of metabolic pathways and energy production

Essential for maintaining cellular homeostasis

Outline the ways unicellular organisms can carry out each of nutrition, movement and excretion.

Nutrition: Diffusion through cell membrane/engulfement/phagocytosis (white blood cells surrounds and destroys foreign substance + removes dead cells)/photosynthesis/digestion by enzymes in vacuoles/endocytosis

Movement: Flagella/cilia

Excretion: Simple diffusion/active transport/exocytosis/vacuoles storage

Define fossilization

Extremely rare and random event in which organic material is persevered over geological timescales, often occurring under specific conditions such as rapid burial and mineralization. Fossil record may also suggeset the sequence in which groups of species evolved and the timing of the appearance of other species.

What are the techniques and how they function in order to find the ages of fossils?

Carbon dating: a method that determines age based on the decay of carbon-14 isotopes in the fossil, useful for dating organic materials up to about 50,000 years old because organisms stops absrobing new carbon and the amount of carbon -14 decreases over the years.

Radiometric dating: Measures amount of naturally occcuring radioactive substances (caarbon 14/potassium 40/argon 40) to measure date of fossil

Genomic analysis: Changes occur in DNA over time. Estimate average time of mutation that take place and extrapolating it back through time in order to find date of common ancestor. Amino acid/protein composition can also be used in similar way since DNA codes for amino acid/protein.

Define common ancestor

The most recent species where 2 or more different speices have evolved. Same ancestor is where different species were formed like humans and chimpanzees.

Define chemosynthesis

Inorganic molecules oxidized to release energy to make glucose. For example hydrothermal vents use energy from hydrogen sulfide to create sugars to support other organisms and themselves in ecosystem.

Define extremophile

Organism that lives in extreme conditions (temperature, acidity, alkalinity, salinity, pressure, chemcial concentration)

List the properties and functions of LUCA proteins

anerobic

CO₂ fixing (converted CO₂ into glucose)

H₂ dependent (uses molecular hydrogen as energy sources instead of sunlight)

N₂ fixing (converted nitrogen into ammonia for synthesis of amino acids)

thermophilic (survived in areas of high temperatures, up to 122˚C)

Autotrophic extremphile organisms that lived in hydrothermal vents (seawater and magma meet on ocean floor) for rich environment of carbon dioxide, iron, and hydrogen.

Define the term RNA world hypothesis

The RNA world hypothesis suggests that self-replicating ribonucleic acid (RNA) molecules were the primary form of life on early Earth as it can serve both genetic and catalytic functions like ribozymes before the evolution of DNA and proteins.

What are the evidences that prove RNA might’ve arosed before DNA

RNA is capable of storing genetic info

Presence of ribozymes also show that RNA have the abilty to catalyze reactions.

DNA requires RNA for its synthesis (RNA primers)

The basic chemical reaction of ribosome to join amino acids is catalyzed by RNA.

RNA is able to self-replicate

Define central dogma

Idea that the transfer of genetic information from DNA to mRNA is irreversible. If it happens it can’t be reveresed.

Define the primordial (prebiotic) soup hypothesis

Proposed by Alexander Oparin and Haildane, stating that the high levels of UV light in pre-biotic Earth caused to formation of biological molecules such as amino acids, peptides, ribose, nucleobases, fatty acids, nucleotides, and oligonucleotides.

Proof of this: The nucletoides are extremely efficient at reducing the harmful effects of UV radiation meaning that it protects biological moleucles like DNA/RNA

RNA is more likely to form chains in the presence of strong UV light, suggesting that RNA moelcules undergo more chemical reactions to form polymers (chains).

List the gases which cause the greenhouse effect

Carbon dioxide, methane, nitrous oxide.

List the three common features shared by all cells

Plasma membrane (boundary that sperates inside of cell from the environment)

Metabolic processes that allow energy generation, growth, self-maintenance, and reproduction

Genetic material (DNA or RNA that contains instructions for synthesis of RNA molecules and proteins)

Define cell theory

1. Cell is smallest unit of life

2. All living organisms is made up of one or more cells

3. Cells arise from pre-existing cells (can not happen spontaneously)

Why are viruses defined as non-living? What are some features that is shares with living organisms?

They are non-cellular (no organelles to carry out metabolism independently. Must infect cells in order to replicate and conduct metabolism)

Does not respond to enviornmental stimuli like living cells

Can’t maintian homeostasis (internal balance) like temperature or light

Contains genetic mateiral (DNA or RNA) for making parts of virus or enzyme

Virus genome mutates a lot (help them evolve through natural selection like living organisms)

Define evolution

The process that transformed life on Earth from its beginnings to the diversity of forms today.

Outline the steps that would be needed for the formation of living cells from nonliving materials

Synthesis of simple organic molecules (sugars/amino acids)
Assembly of moelcules to polymers

Development of self-replication molecules like nucleic acids

Internal chemistry within cell that is different from surrounding environment (homeostasis)

Define the competing theories for the origin of life (protocell, gene, metabolism)

Protocell-first: Simple cell-like strucutre with metabolism appeared before genetics

Gene-first: Genetic moelcules (RNA) aroused spontaneously that can replicate emerged first and led to cells

Metabolism first: Self-sustaining chemical reactions came first that eventually gave rise to cells and genetic systems.

Define protocells

Simple pre-cellular structures that can maintain an internal environment and carry out basic life functions. Has few molecules inside them. They are considered a precursor to true cells.

State how the spontaneous formation of vesicles was formed.

Early cells (protocells) formed simple membranes made of fatty acids because they naturally form strucutres in water (hydrophobic tail and hydrophilic head). They form small bubbles called vesicles that might’ve trapped chemicals inside which created a special internal environment. First step toward real cells.

List the steps of the evolution of cell membranes

1. Protocells formed from fatty acid because of its stability and large quantities in early Earth

2. Condenseation of fatty acids to glycerol to form triglycerides = make more stabliziing membranes

3. Phosphorylation (addition of phosphate to triglycerides) formed the simplest phospholipid

Describe two properties of RNA which may have contributed to the origin of life

Its ability to act as a catalyst and self-replicate.

Explain why LUCA (the Last Universal Common Ancestor) is thought to be the evolutionary link between the abiotic phase of Earth’s history and the biotic phase

The universal DNA genetic code is shared in every species and creature such as proteins and ATP. More than 350 widely occurring protein families have been identified in prokaryotes.

What are the evidences in ancient rocks that helped scientist to describe the prebiotic atmosphere

There were traces of oxygen, high concentration of methane (predicted from volcanoes), high carbon dioxide contraction (also from emission from volcanoes)

How can cells be cultured?

Cells that can be grown in labs such as HeLa cells

What are the features of a cell?

Must have a stable, partially permeable membrane that surrounds cell components, genetic material that can be passed on when new cells are formed

How was the evidence of the origin of carbon compounds found?

Through Urey-Miller’s experiment in which an apparatus was made to stimulate pre-biotic earth. After a week a pink solution was produced containing more than 20 different amino acids, fatty acids, and sugars like glucose. Some cases showed nucleotide bases and simple polymers of these molecules. This showed it was possible for carbon compounds to form spontaneously on Earth. (No life produced only organic compounds)

Define the RNA world hypothesis

The hypothesis that RNA is the first primary genetic material, not DNA because it was capable of storing genetic information. It is able to self-replicate and act as a catalyst. Some viruses (non-living) use RNA as their genetic material.

What is archaea/bacteria?

Prokaryotes that stem from the same universal common ancestor (LUCA). These branches of the prokaryotes combined to form the branches of eukaryotes of complex cells

What are the factors that determine the strength of a theory

• Observations the theory explains and the predictions it supports

• If new observations don’t support theory = theory adjusted or rejected

• More observations and data that are predicted/proven true by theory = stronger the theory