A2.1 Flashcards
Origins of Cells
Evolution of Cells
What is Homeostasis?
- Maintaining of a consistent internal environment even whene xternal change
- can be essential requirement of living organisms to maintain constant
- organisms differ in terms of how many things they keep constant: endotherms maintain internal temp while ectotherms (reptiles) don’t
Evolution of Cells
What is Primordial soup
- origin of living compounds began as a water-based sea of simple monomers (amino acids, carbon and hdyrogen chain)
- solution was supported by MILLER UREY experiment
Evolution of Cells
What are Vesicles?
- Term for any small ‘bubble’ of fluid surrounded by a phospholipid bilayer
- Forms automatically when phospholipids are in water and this is thought to be a model of how cells originate
- They also form by established membrances (like cell membrane/ golgi apparatus) breaking off.
Evolution of Cells
What is compartmentalisation?
- The separation of functions into specific regions of the cell (specific organelles), which allows multiple distinct metabolic functions to occur at the same time.
- Occurs to a small degree in prokaryotes/ bacteria and to a much larger extent in eukaryotic cells.
Evolution of Cells
What is Coalescence?
- Regarding vesicle or membrane formation.
- NATURAL coming together of things – (in this context) refers to fatty acids/ phospolipids naturally arranging themselves away from water, thus them coming together and automatically forming a ring like structure with water both inside and outside the ring.
Evolution of Cells
Abiotic Conditions of Early Earth vs Present
- Abiotic conditions found on early earth were different —-> may have allowed for SPONTANEOUS formation of compounds
Differences include:
- GASES: methane, ammonia, and hydrogen sulfide and little O2 and ozone.
- PENETRATION OF UV LIGHT: due to no ozone, leading to high temperatures.
- Regular Lightning
Evolution of Cells
Requirements for Life
For any organisms to be considered ALIVE must be able to perform:
- Metabolism
- Growth
- Reproduction
- Respond in some way to their environment (stimulis)
- Maintain homeostasis
- Use food for energy/ nutrition
Evolution of Cells
Three Principles of Cell Theory
- All organisms are composed of one (unicellular) or more cells. (multicellular)
- Cells are the smallest unit of life.
- All cells come from pre-existing cells.
Evolution of Cells
Requirements for cells to evolve
1) Catalysis - some sort of enzyme that can speed up slow chemical reactions.
2) Self replication of molecules needed.
3) Self assembly of those molecules into larger polymers and structures/ organelles.
4) Compartmentalisation – functions being assigned to organelles.
Evolution of Cells
Organic vs Inorganic compounds.
ORGANIC:
- Generally complex carbon (and hydrogen) based compound that is made in living organisms
- play a crucial role in living processes.
- Include carbs, lipids, proteins, and nucleic acid.
INORGANIC:
- Do not have to contain carbon (most do not)
- Often found outside of living organisms as well as inside them.
- Simpler.
Evolution of Cells
The Miller-Urey Experiment
Wanted to test the hypothesis that inorganic gases could react (with conditions similar to early Earth including heat and electrical activity) to create organic compounds.
- Found evidence of long C and H chain and amino acids –> this fluid containing simple monomers –> first step in evolution of life —> PRIMORDIAL SOUP.
Evolution of Cells
Fatty Acids and Vesicle Formation
Requirement to make a cell –> a boundary (CELL MEMBRANE).
- Phospholipids in an aqueous solution naturally form a barrier to create a vesicle (fluid surrounded by membrane.)
- Fatty acids were present in the ‘primordial soup’ then this same process could have created the cell membranes of early cells.
RNA World Hypothesis and LUCA
What are ribozymes?
A special type of RNA that can act as a catalyst.
- Play a role in protein synthesis.
- Also evidence that RNA could have actually been the first catalyst (needed for cells to develop) and evolved prior to protein based enzymes.
RNA World Hypothesis and LUCA
What are protocells?
A general term for any unit contained by a membrane that is completing cellular reactions.
- Likely the ancestors of modern cells that contained polymers inside a membrane.
- More compartmentalisation and self replication would develop for a true cell to exist.
RNA World Hypothesis and LUCA
What are radioactive isotopes?
An isotope is an unstable form of an element and a radioactive isotope emits radiation which means they are able to be measuremed effectively.
- Radioisotopes are used to date fossils —> fossils contain them as do living organisms.
- Isotopes are taken up at a consistent rate.
- When comparing how much of an isotope remains compared to how much initially would have been, fossils can be dated.
RNA World Hypothesis and LUCA
What is a half-life?
- The length of time it takes for half of a radioactive isotope to change into another stable element.
- This is known for the isotope and used to determine the age of fossils.
- Most commonly used radioactive isotope: Carbon 14.
RNA World Hypothesis and LUCA
What are index fossils?
Often a simple method can be used to approximate the age of fossils.
- Further down a fossil is, the older it is.
- Age can also be determined location in the same layer of Earth as fossils whose exact age has been determined.
- Index fossils –> widespread, abundant but clearly limited to a certain geological time – useful tool to compare other fossils to.
RNA World Hypothesis and LUCA
What are hydrothermal vents?
Hydrothermal vents are places where hot water emanates from beneath the ocean floot.
- Form when cracks of the crust of the seabed expose seawater to rocks below are heated by magma.
- Heated water rises and picks up minerals along the way.
- Despite extreme temp – and lack of O2 – life does exist there (tube worms that benefit from symbiotic bacteria)
RNA World Hypothesis and LUCA
Properties of RNA as the first genetic material
RNA Hypothesis argues that it may have been the furst nucleic acid to form rather than DNA.
Properties of RNA that led to this:
- Can spontaneously form from monomers as it is a simpler structures than DNA.
- Can copy itself so had self-replicating properties
- RNA can catalyse chemical reactions (evidenced by ribozymes)
RNA World Hypothesis and LUCA
Sequence of stages in the evolution of life
1) Sequence of events between early Earth and cell is proposed to be abiotic chemical compounds existed (methane) —>
2) that led to the creation of small organic compounds (primordial soup) —->
3) those assembled into polymers (aided by RNA catalysis) —>
4) membrances spontaneously formed around them due to amphipathic nature —>
5) a protocell exists —>
6) compartmentalisation leads to a true cell with organelles.
RNA World Hypothesis and LUCA
Evidences for a LUCA
One evidence for there being a common ancestor is the universal genetic code. (CCC always codes for protein.)
- 300 genes shared by all cells.
- Many of the same biomolecules exist in all cells and metabolic processes (cellular respiration and translation are very similar in all types of organisms).
RNA World Hypothesis and LUCA
Relative Dating vs Absolute Dating of Fossils
RELATIVE DATING:
- considers whether the fossil is comparatively older or younger than nearby, fossils, based on their placement in the rock. (lower is older).
ABSOLUTE DATING:
- attempts to determine determine an age in years and relies on carbon dating using the half life of radioisotope of carbon.
RNA World Hypothesis and LUCA
Evidence for LUCA in hydrothermal vents.
Scientists looked for genes that are common between both bacteria and archae –> found 355 genes + many associated with anaerobic processes and suggest the ancestor may have been from an environment low in oxygen and high in carbon dioxide, nitrogen and hydrogen.
- characteristics of hydrothermal vents.
- Evidence of very old fossils in the vents.
