origin of cells

conditions on early earth

lack of free oxygen and therefore ozone, higher concentrations of carbon dioxide and methane, resulting in higher temps and ultraviolet light penetration. conditions may have caused a variety of carbon compounds to form spontaneously. High UV cus no ozone

characteristics of living organisms

1. homeostasis – maintain a constant internal environment

2. metabolism - all catabolic and anabolic reactions in a cell

3. nutirition - assimilation of food materials

4. contains genetic information

5. excretion – removal of waste from metabolism

6. growth - increase in number of cells

7. sensitivity - increase in number of cells

8. reproduction

why are viruses non-living

cannot reproduce without a host, cannot respond to stimuli, do not grow, no cells for metabolism or homeostasis, dont have cells

catalysis (a necessary requirement for the evolution of the first cell)

enzymatic control over which chemical reactions occur

example: enzymes

gives rise to: cellular metabolism

Self assembly (a necessary requirement for the evolution of the first cell)

reversible intermolecular bonds between monomers (mobile polymers)

example: amino to proteins

gives rise to: enzymes, units of heredity, compartmentalisation (division into areas surrounded by membranes

compartmentalisation

seperation of structures and processes into separate areas of the cell

example: nucleus

give rise to: unique chemical environments provides protection from reactive metabolites, enables the regulations of metabolic pathways

self replication

a molecule is able to replicate itself

example self replicating RNA which can also function as an enzyme

give rise to: Evolutions

Miller Urey experiment

1. heat

2. water (primordial ocean)

3. gases (methane, ammonia, hydrogen, water vapor)

4. electrical spark (lightning)

5. condenser

Miller Urey experiment evaluation

strengths:

1. amino acids can be spontaneously generated

2. can be replicated

3. modelled after prebiotic earth conditions

Limitations:

1. remains debate on actual atmosphere

2. experiment did not produce all organic materials required for life

3. simulations could not account for all conditions

last universal common ancestor (LUCA)

all cells on earth share characteristics, including a genetic code that was inherited from a common ancestral population of cells

Cladograms (most probable sequence of divergence between groups of organisms. extinct organisms are dotted)

LUCA is not the first form of life. first forms were probably membrane surrounding a self-replicating molecule like RNA

Small single-celled prokayotic cell 3.8 billion years of age

what type of organism was luca

oligated anaerobe (no oxygen

chemoautotroph → energy from hydrogen. turned carbon to nitrogen and organic molecules

lived in extreme heat

approaches used to estimate dates

earth is over 4.5 billion years old, life existed by at least 3.8 billion years ago

1. chemical evidence

2. biomarkers

3. fossil evidence

4. genetic evidence

chemical evidence

well-preserved rocks isostopes ratios suggests living organisms

biomarkers

molecular fossils of lipids and other organic compounds (lipids preserve better than DNA)

Fossil evidence

hydrothermal vents on the sea floor are thought to be earliest habitabe environments on the planet, proposed location for LUCA.

fossiled evidence in ancient sea floors and tubes in rocks formed by bacteria

genetic mutations

how much time has passed since they shared a common ancestor, mutation rate of biomolecules (no. of dif. in genome is proportional to the time since they divided)

however mutation rate may not be consistent

vesicles

every cell has a membrane that separates its interior from the environment, some interal structures are membrane-bound

1. vesicles

2. micelles

3. bilayers

early cell membranes may be made of fatty acids (easier to form and are amphipathic)

glycerol + phosphate + fatty acid + spontaneous formation of phosolipids

used to transport molecules

compartmentalize metablic processes within cells

grow plasma membrane

RNA as first genetic material

1. can self-replicate

2. form complementary template sequence that can be used to produce new identical molecules

3. act as catalyst (involved in peptide bond formation and intron splicing in modern cells)

evidence: ribose is readily produced in lab experiments

deoxy is harder to make

DNA is chemcially more stable (uracil is more susceptible to mutation than thymine

DNA replaced RNA as repository of genetic information.