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Extra planetary origin of water on Earth and its retention

Water is likely to have originated from meteorites because they have a similar D/H ratio to the water in oceans. Water was retained on earth due to gravity and temperature being able to make the water liquid and the atmosphere keeps the water from evaporating.

Goldilocks zone

A zone in space where the distance to the sun is ideal and allows for liquid water. Necessary for life (habitable zone)

Conditions on early earth and the prebiotic formation of carbon compounds

Lack of free oxygen resulted in less ozone, high methane and co2 concentrations thus more ultra violent light radiation. Electrical storms and high temperatures. Conditions may have caused carbon compounds to form such as amino acids spontaneously as these conditions do not exist now. 

Cells are smallest unit of self sustaining life

Viruses do not follow the processes of life and they require a host cell to reproduce. For example, cannot perform self replication and metabolism. 

Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers

Formation of a membrane bound compartment is needed to allow internal chemistry to become that different from the outside compartment.

Challenging of explaining spontaneous origin of cells

First protocells did not fossilize. Cells require previous cells to divide and reproduce. Requirements for the evolution of the first cells, self assembly, emergence of compartmentalisation, catalysis, self replication of molecules.

RNA as first presumed genetic material

Can be replicated and has similar catalytic function to enzymes. Can also be genetic material. So it may have acted initially as both the genetic material and the enzymes of the earliest cells. Ribozymes in the ribosomes are still used to catalyse peptide bond formation during protein synthesis.

Origin of eukaryotic cells by endosymbiosis

It is suggested that all eukaryotic cells evolved from a common ancestor that endocytosed a prokaryotic cell which performed aerobic respiration or photosynthesis. Instead of killing/consuming the cell, the eukaryotic cell let the prokaryotic cell live as it carried out aerobic respiration or photosynthesis, providing energy for the cell, evolving into mitochondria/chloroplast. It is also thought that the chloroplasts in some eukaryotes also had a endosymbiotic origin.

Evidence: Both mitochondria and chloroplasts have 70s ribosomes and they contain double strands of DNA and they have circular DNA. Some mitochondria and chloroplasts are susceptible to certain antibiotics, just like bacteria.

Cell differentiation as the process for developing specialized tissues in multicellular organisms

When an immature, unspecialized cell becomes a more specialized cell type with a distinct structure and function. Often triggered by changes in the environment.

Evolution of multicellularity

Has evolved repeatedly. Many fungi, eukaryotic algae and all plants and animals are multicellular. Allows for larger body size and cell specialization. 

Adaptations of the mitochondrion for production of ATP by aerobic cell respiration

A double membrane with a small volume of intermembrane space, large surface area of cristae and compartmentalization of enzymes and substrates of the Krebs cycle in the matrix.

Adaptations of the chloroplast for photosynthesis

The large surface area of thylakoid membranes with photosystems, small volumes of fluid inside thylakoids, and compartmentalization of enzymes and substrates of the Calvin cycle in the stroma.

Functional benefits of the double membrane of the nucleus

Pores are required in the nuclear membrane to act as gateways. It is also needed so the nucleus membrane can break into vesicles during mitosis and meiosis. Can control what comes in and out. 

Structure and function of free ribosomes and of the rough endoplasmic reticulum

Free ribosomes synthesize proteins for inside of cell while ribosomes on RER usually synthesize proteins for use outside of the cell (transport and secretion).

Diversity of structure in viruses

Viruses are highly diverse in their shape and structure. Genetic material may be RNA or DNA, which can be either single- or double-stranded. Viruses can have enzymes such as reverse transcriptase and integrase. Some viruses are enveloped in host cell membrane and others are not enveloped. Virus examples include bacteriophage lambda, coronaviruses and HIV.

Lytic cycle of a virus

Viruses rely on a host cell for energy supply, nutrition, protein synthesis and other life functions. Virus hijacks cellular machinery and uses it to replicate, cell then lyses and virus spreads to other host cells. Use bacteriophage lambda as an example of the phases in a lytic cycle. Bacteriophage lambda is an example of the phases in the lytic cycle.

Lysogenic cycle of a virus

Virus integrates its genetic material into host cell’s DNA. This genetic material is copied along daughter cells. Virus may remain dormant for certain period of time and then change to lytic cycle. Bacteriophage lambda is an example

Evidence for several origins of viruses from other organisms

The diversity of viruses suggests several possible origins. Viruses share an extreme form of obligate parasitism as a mode of existence, so the structural features that they have in common could be regarded as convergent evolution. The genetic code is shared between viruses and living organisms.

Rapid evolution in viruses

Reasons for high rates of evolution in viruses. RNA cannot proofread thus more frequent genetic changes and natural selection. Mutation rates are high. Large population sizes. This means that new vaccines need to be made frequently in order to be effective against the viruses. Examples of rapidly evolving viruses are HIV and Influenza

Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers

Phospholipids have a outer head that is hydrophilic (water loving) and a hydrophobic tail (water hating). When there are enough of them, they position themself so that the tails are inwards and the heads outwards.

Led to compartmentalised regions.

Role of clathrin in formation of vesicles

Protein

The clathrin coats the cytoplasmic surface of the membrane and helps to form the vesicles. 

It forms a lattice structure causing membrane to form inward, making a clathrin coated pit. 

Adaptins link clathrin to cargo receptors 
Vesicle buds of and then the clathrin coat is removed. 

Origin of viruses and evidence

Progressive hypothesis: Virus evolved by taking and and modifying cell components

Regressive hypothesis: Viruses arose by the loss of a cellular component.

Evidence: Viruses have variations in shape and structure. Genetic material can be different, either RNA or DNA. Some viruses are endocytosed by the cell. This suggests that they evolved multiple times and not only from one common ancestor. Yet they share similar structures and variations which is convergent evolution as these origins have developed similar characteristics because all viruses share obligate parasitism.  

Structural features common to viruses

Not many structural features are shared by viruses: small, fixed size, nucleic acid (DNA or RNA as genetic material), a protein capsid, no cytoplasm, few or no enzymes.

Retroviruses

Retroviruses like HIV use the enzyme reverse transcriptase to convert their RNA genome into DNA, which is than integrated into the host cell’s DNA. Enzyme integrase helps to do this.  

Evaluate the Miller Urey experiment

Positives: This experiment proved that the first organic molecules need for life formed spontaneously from inorganic components.

Negatives: The conditions for the atmosphere were not fully accurate, electrical sparks were used, however, UV radiation was also a energy source on early Earth. The experiment didn’t show that nucleotides were created, which are building blocks of DNA and RNA.