Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The principle that cells can only be formed by the division of pre-existing cells is a cornerstone of Biology. This disproves spontaneous generation, as evidenced by Louis Pasteur's experiments in the s.
Pasteur's swan-neck flask experiment demonstrated that swan-necked flasks containing sterile broth remained free of microbial growth unless the neck was broken, allowing to enter from the air.
The first cells must have arisen from non-living material. This process is hypothesized to have occurred in four stages: 1. Abiotic synthesis of simple organic molecules (monomers), 2. Assembly of these monomers into polymers, 3. Development of self-replicating molecules (the RNA world hypothesis), and 4. Packaging of these molecules into membranes with an internal chemistry different from their surroundings (protocells).
The Miller-Urey experiment simulated early Earth conditions using a mixture of , , , and vapor. By applying electrical sparks (simulating lightning), they successfully synthesized amino acids and other organic compounds.
The Endosymbiotic Theory explains the origin of eukaryotic cells. It suggests that mitochondria and chloroplasts were once free-living prokaryotic cells that were engulfed by a larger anaerobic prokaryote via endocytosis.
Evidence for Endosymbiosis can be remembered by the acronym MADDR: Membranes (double membrane bound), Antibiotics (susceptibility to certain antibiotics), DNA (contain naked, circular DNA), Division (reproduce via binary fission-like processes), and Ribosomes (contain ribosomes).
The genetic code is universal; with very few exceptions, the same codons specify the same amino acids in all organisms. This suggests that all life evolved from a single common ancestor.
📐Formulae
💡Examples
Problem 1:
Explain why the RNA world hypothesis is a preferred model for the origin of life over a DNA-centered model.
Solution:
RNA possesses two critical properties that DNA and proteins do not share in a single molecule: 1. It can store genetic information (like DNA) and 2. It can act as a catalyst (like enzymes) in the form of ribozymes. DNA requires proteins for replication, and proteins require DNA for coding, creating a 'chicken-and-egg' paradox. RNA solves this by being self-sufficient.
Explanation:
In the early stages of life, a single molecule type likely fulfilled both the role of information storage and metabolic catalysis.
Problem 2:
Identify the features of mitochondria that provide evidence for their origin as independent organisms.
Solution:
- They have their own circular, naked DNA, similar to bacterial DNA. 2. They possess ribosomes, typical of prokaryotes ( is typical for eukaryotes). 3. They have a double membrane, where the inner membrane is of the original cell and the outer is derived from the host's vesicle. 4. They divide independently by binary fission.
Explanation:
These features are characteristic of prokaryotic cells and are not found in other organelles like the Golgi apparatus or Endoplasmic Reticulum.