A2.1 Origin of Cells Flash Cards

What are the two main propositions of the cell theory?

1) The fundamental unit of life is the cell. 2) All cells come from pre-existing cells.

Why is DNA considered a universal genetic code?

All cells store hereditary information using the same linear chemical code: DNA, and the genetic code is nearly universal across all life forms.

How do all cells perform biochemical functions?

All cells function as biochemical 'factories,' utilizing basic molecular building blocks and use proteins called enzymes to catalyze reactions.

What conditions characterized the pre-biotic Earth atmosphere?

Traces of oxygen, higher methane and carbon dioxide due to volcanic activity and meteorite bombardment, no ozone layer, and likely higher temperatures.

How did the lack of an ozone layer affect pre-biotic Earth?

More ultraviolet (UV) radiation reached Earth's surface, providing activation energy for chemical reactions necessary for forming organic compounds.

What is the significance of hydrothermal vents (white smokers) in the origin of life?

They provided early habitable environments with chemicals and conditions suitable for catalysis and formation of the first living cells.

What are the four key developments needed for the origin of the first cells?

Catalysis, self-assembly of polymers, compartmentalization by membranes, and self-replication of molecules.

What did the Miller-Urey experiment demonstrate?

It showed that under simulated pre-biotic conditions, a variety of organic compounds, including amino acids, could form spontaneously.

How do phospholipids form vesicles?

Phospholipids spontaneously assemble into bilayers in water, creating stable spherical vesicles with hydrophilic heads outwards and hydrophobic tails inwards.

What is the RNA world hypothesis in relation to early genetic material?

RNA likely acted as the first genetic material because it can store information, self-replicate, and catalyze reactions before DNA and proteins evolved.

Why might DNA have replaced RNA as the main genetic material?

DNA provides greater genetic stability than RNA, which has a higher mutation rate due to less accurate copying enzymes.

How can evidence from living organisms' genomes help understand the origin of cells?

Shared genes and protein families among bacteria and archaea trace back to a last universal common ancestor, informing about early life.

What defines the smallest units of self-sustaining life?

Cells are the smallest units capable of maintaining a highly ordered state, using energy, growing, dividing, and passing on hereditary information.

Why was spontaneous generation falsified?

Experiments by Pasteur and observations showed cells arise only from pre-existing cells, not spontaneously from non-living matter.

What is LUCA?

LUCA stands for the Last Universal Common Ancestor, the most recent common ancestor of all current life forms.

What evidence supports that LUCA lived near hydrothermal vents?

Genes identified in bacteria and archaea linked to anaerobic metabolism and carbon fixation imply LUCA thrived in environments rich in hydrogen, CO2, and iron like hydrothermal vents.

What are stromatolites and their significance?

Fossilized stromatolites are layered structures formed by cyanobacteria mats trapping sediments, providing evidence of early life dating back over 3.4 billion years.

What role do protocells play in hypotheses about the origin of life?

Protocells are membrane-enclosed compartments with self-replicating molecules that model possible intermediate steps between non-living compounds and living cells.

How do environmental conditions affect protocell membrane growth, based on experiments?

Protocells containing RNA are more likely to capture additional membrane material and grow than those lacking RNA, especially when swollen.

How do universal genetic code and similar cell structures support a common ancestor?

All life uses almost the same genetic code and cellular components like ribosomes, making it unlikely by chance and indicating inheritance from LUCA.

Cell

The fundamental unit of life; smallest unit of self-sustaining life.

Cell theory

All cells come from pre-existing cells; cells are the basic unit of life.

DNA

Linear chemical code storing hereditary information in all cells.

RNA

Intermediary molecule transcribed from DNA; can act as genetic material and catalyst.

Enzyme

Protein catalysts used in biochemical reactions in cells.

Pre-biotic Earth

Early Earth conditions before life evolved, with different atmospheric gases and conditions.

Hydrothermal vents

Submarine vents that may have provided conditions for the origin of life.

Stromatolite

Fossilized layered structures formed by cyanobacteria, evidence of early life.

LUCA (Last Universal Common Ancestor)

Most recent common ancestor of all current life forms.

Miller-Urey experiment

Experiment simulating pre-biotic conditions, producing amino acids and organic compounds.

Vesicles

Small fluid droplets enclosed by a phospholipid bilayer, possibly early cell models.

Phospholipid

Amphipathic molecule forming bilayers in water, basis of cell membranes.

Genetic code

Universal code of 64 codons used by almost all organisms to translate DNA/RNA into proteins.

RNA world hypothesis

Theory that RNA was the first genetic material before DNA evolved.

Natural selection

Process by which organisms better adapted to their environment tend to survive and reproduce.

Protocell

Simple vesicle-like structures with self-replicating molecules, models for early cells.

Catalysis

Acceleration of chemical reactions, necessary for early life processes.

Compartmentalization

Enclosure of cell contents by a membrane, essential for cell function.

Self-replication

Ability of molecules (like RNA) to replicate themselves, basis for inheritance.

Oxygenation of atmosphere

Increase in atmospheric oxygen due to photosynthesis, leading to ozone layer formation.

Convergent evolution

Independent evolution of similar features in species without common ancestry.

Banded iron rock

Rock with isotope ratios suggesting ancient biological activity.

Zircon particles

Oldest Earth crust fragments, with isotope ratios possibly indicating early life.