4.2 - Metabolism Vs Replication And The RNA World Flashcards
Why do we needs further constraints from biology and chemistry?
There is a problem that there are so many prebiotic environments in which the geochemistry may have allowed the origins of life to occur
What are cells like?
Even the most simplified, fundamental components of a cell are incredibly complex. Integrated informational, metabolic, catalytic and compartment-forming subsystems.
What is the combined perspective?
A solution will be found when all approaches converge on some commonality
It uses a combined perspective to understand the jump from chemistry to biology
(Replication vs metabolism and the RNA world)
What is the metabolism?
It is the sum of anabolic and catabolic reactions in the cell
What is catabolism vs Anabolism?
Catabolism = using matter to make energy
Anabolism = using energy to make matter
What is replication?
When a molecule makes a copy of itself
What is transcription and translation?
Making the proteins that power living cells
Central dogma = DNA -> RNA -> Protein
Did replication or metabolism come first?
The reactions of metabolism only work when catalysed by enzymes.
Such biomolecules require RNA to produce them, but the enzymes themselves require energy from metabolism.
If enzymes came first then how would the information have been encoded?
Replication first
It was discovered in the 1980’s that the RNA can perform some of the enzymatic functions needed for replication.
- We already know RNA can store genetic information. Replication results in complementary chains that rarely contain genetic mutations (Darwinian evolution)
- RNA molecules with catalytic properties similar to enzymes are called ribozymes
- Folded up chains of RNA results in different shapes and different chemical reactions
- Some can create more nucleotide bases
What is the RNA world hypothesis?
RNA as information storage and metabolism control represented the Great Leap Forward in prebiotic chemistry.
- RNA is everything - common to all life
- RNA can self replicate and replicate other RNA
(Did RNA act as a ‘jack of all trades’ molecule in the first steps to complex life? This is where biology meets chemistry to tackle the origin of life)
How do you get self sustaining, replicating RNA in the first place?
- There is now a broad acceptance that prebiotic chemistry comprises a ‘dirty RNA world’ with a multitude of chemical reactions taking place, some of which led to the molecules that evolved towards modern day cells.
- The first biological cells didnt necessarily have the same bio molecular machinery ‘modern’ biology has, even microorganisms that sit near the bottom of the evolutionary tree
- ‘Metabolism first’ researchers can just focus on chemical reactions, many of which can be spontaneous reactions catalysed by inorganic materials (this is where chemistry meets geology)
What is RNA made of?
RNA is made up of 4 different chemical building blocks
- Adenine
- Guanine
- Cytosine
- Uracil
Were these 4 RNA bases able to form at the same time?
- Research discovered that C and U could form in early earth conditions but not G and A
- Different reaction conditions could produce G and A but not C and U
What are Guanine and Adenine known as?
The corresponding bases are known as purines
What conditions were all 4 nucleosides able to exist at?
All 4 nucleosides could be produced in unified chemical conditions.
Using starting reactants, plausible prebiotic atmosphere/ volcanic molecules for early earth.
What do all geological inputs require?
- Wet-drying cycles
- Metals like Zn, Fe, Cu
- Swings in pH from strongly acidic to mildly acidic
What is really important in metabolism?
Transition metals are very important in metabolism.
They are required for enzymes to act as catalysts in many biochemical reactions (also called metalloenzymes)
- They are required for making metalloproteins (Fe in hemoglobin)
- They are required for other organic molecules eg. Mg in chlorophyll
What happened regardless of how LUCA arose and if RNA or metabolism arose first?
It rapidly evolved into an astounding array of metabolism that utilise the geochemical ingredients available on Earth.
What are photoautotrophs?
They are organisms that use light energy and inorganic carbon to produce organic materials.
What are photoheterotrophs?
They are organisms that use light energy and get their carbon from organic compounds
What are chemoautotrophs?
They are organisms that get their energy from chemical reactions and their carbon from C02 (inorganic)
What are chemoheterotrophs?
They are organisms that get their energy from chemical reactions but get their carbon from organic compounds
What are metabolic reactions?
They are redox reactions, which are chemical reactions in which electrons are transferred between 2 reactants participating within the reaction.
What is oxidation vs reduction?
Oxidation = It is the loss of electrons / an increase in the oxidation state of a chemical or atoms
Reduction = It is the gain of electrons / a decrease in the oxidation state of a chemical or atoms
In photosyntheses the C02 is reduced (gains electrons) and the H20 is oxidised (loses electrons)
What is the electron accepter in respiration?
Oxygen gains electrons and becomes reduced
What is the electron acceptor in anaerobic respiration?
An electron acceptor other than oxygen is used such as:
- N03- ‘Nitrate reduction’
- S04- ‘Sulfate reduction’
- C02- ‘Methanogenesis’
Does anaerobic or aerobic respiration produce more energy?
Aerobic respiration produces more energy
What is the electron diner in chemelithotrophy?
The electron donor is inorganic
Sulfur -> Sulfate
Hydrogen -> Water
Ammonia -> Nitrite
Ferrous Iron -> Ferric iron
Hydrogen sulphide -> Sulfur
What are microbial mats made up of?
They are made up of manny different types of microorganism, using different metabolisms
- They form layered structures which can be mm-cm thick
- They can be aerobic or anaerobic
What is evidence of past microbial mats?
They can be fossilised in the geological record
- Some of the oldest evidence for life on earth is in the form of fossilised microbial mats such as stromatolites
What does the origin of life research require?
It requires input from many disciplines such as chemistry (prebiotic building blocks), geoscience (early environmental conditions) and biology (earliest life forms)
What is currently the most likely theory for the origin of life?
The ‘Dirty RNA World’ theory which thinks that in earliest life, RNA self-replicated, stored information and catalysed chemical reactions
- It evolved into the myriad of metabolic reactions and the microbial diversity observed on both early and modern earth
