Ib biology HL: A2.1- The origins of cells

A2.1.1-6

RNA first hypothesis ( write it down as a list )

1. RNA was formed from inorganic sources.

2. RNA was able to replicate using ribozymes.

3. RNA was able to catalyse protein synthesis.

4. Membrane compartmentalisation occurred.

5. Inside the cell, RNA was able to produce both protein and DNA.

6. DNA took over as the main genetic material because it is more stable.

7. Proteins took over as the catalytic form (enzymes) because they are more capable of variability.

metabolism

that chemical reactions have place in the organism: catalytic molecules are present to help chemical reactions

response to stimuli

detecting changes in their outer environment and reacting accordingly ( moving towards or away from a chemical

Homeostasis

ability to maintain internal environment regardless of external environment eg active transport through lipid layer ( cell membrane ) of ions

movement

ability to change position, usually in response to stimuli. Specialised organelles such as flagella, cillia or pseudopodia

growth

increase in volume over time, or in multicellular organisms, increase in number of cells

reproduction

the production of offspring, without external factors,

Nutrition

The intake or production of nutrients.

excretion

The removal of metabolic waste

acronim for characteristics of a living thing

MR HM GREN

why is there uncertainty over how first living things have been created ? list

• cells spontaneously originated a very long time ago, so much of the evidence is destroyed or distorted, so it is very difficult to study

• The very first protocells did not fossilise.

• It is thought that cells originated deep in the ocean, making it challenging to reach and collect samples for analysis.

• There is uncertainty surrounding the exact conditions on pre-biotic Earth, which means scientists cannot replicate the exact conditions that would have existed

conditions for first cells being created

Catalysis, self-replication of molecules, self-assembly and the emergence of compartmentalisation were necessary requirements in the evolution of the first cells.

lipid bilayer

fatty acids spontaneously coalesced into a bilayer; a double layer of lipid molecules which encloses a space in which the chemical makeup can be different than the environment’s

Evidence for LUCA

All organisms use the same nucleotide triplets (codons) to code for animo acids

the theory in which an ancestral cell takes in two prokariotic cells and they become a mitochondrion and chloroplast

endosymbiosis

Miller Urey experiment faults

• used less CO2 and NO3 than thought to have been in the atmosphere

• used more CH4 and NH3 than thought to have been in atmosphere

• uv rays were not taken into account

• failed to create nucleotides

conditions which allowed life to evolve

• higher temps

• higher carbon dioxide and methane concentration

• little/no oxygen and nitrogen presence

• lighting - provides energy

• uv light

spontaneous formation of vesicles

• spontaneous coalescence of fatty acids

• formation of bilayers, which eventually become spherical