Astrobiology Block I

What are isotopes?

Atoms with different numbers of neutrons and the same number of protons

What is ionic bonding?

The force of attraction between positively and negatively charged ions; ionic bonds are strong

What is covalent bonding?

Sharing of outer shell electrons between atoms, taking place between atoms with small differences in charge

What is Van der Waals bonding?

Attraction between molecules due to the electric dipole forces between atoms or molecules; exists between all atoms or molecules

What is hydrogen bonding?

Found in molecules containing -OH groups; hydrogen atom can bond with 2 atoms, allowing a hydrogen bond between 2 atoms/structures

How are ionic bonds used by life?

Protein chains are connected together by an ionic bond; ionic bonds are difficult to break apart at room temperature

How are covalent bonds used by life?

Thermal motion cannot break covalent bonds, so molecules can form

How is hydrogen bonding used by life?

In DNA, hydrogen bonding holds the 2 sides of DNA together, but the weak hydrogen bond can be easily split apart to allow the DNA to divide and multiply

What does a phase diagram show?

Temperature on the x axis, Pressure on the y axis, showing the state of matter at a given pressure and temperature

What is the significance of the negative melting curve in the water phase diagram?

There is a range of temperatures at which increasing the pressure will cause water to turn from solid into liquid

How has the history of water on Mars changed?

Modern Mars’ pressure is too low for water to exist in liquid form, but Ancient Mars’ pressure was high enough for water to exist in liquid form

What is the triple point on a phase diagram?

Below the triple point, matter can exist in only ice or gas form

What is the critical point?

Above the critical point, matter cannot exist in gas form

What is plasma + where is it found?

Plasma is gas which consists of ions (some/all of the outer shell electrons stripped away), found in stars & lightning

What is degenerate matter + where is it found?

Collection of free, non-interacting particles, occurring at very high density or low temperature/pressure, found in white dwarf stars & neutron stars

What are the astrobiological consequences of plasma?

Plasma is has not been found in life, but 99% of the known visible universe is made up of plasma

What are the astrobiological consequences of degenerate matter?

Degenerate matter has not been found in life, makes up neutron stars and black holes, impact which planets could host life, can cause mass extinction events

What are the CHNOPS elements?

Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur

What is the significance of the CHNOPS elements?

They are the elements that are required for life on Earth; their bond energies are very similar so it takes little energy for them to link together

Why is carbon the backbone for life on Earth?

Easy for Carbon to link with CHNOPS elements due to similar bond energies, links are stable once made, wide range of double and triple bond configurations, millions of possible organic compounds

Why is silicon not the basis for life?

Silicon + oxygen = sand, forms unstable compounds with other elements, silicon is in mineral rocks

What are the 4 classes of biological molecules?

Proteins, sugars, lipids, nucleic acids

What are proteins used for in life?

Constructed from amino acids, proteins form chains which form molecules

What are sugars used for in life?

Storage and transport of energy, providing structural support

What are lipids used for in life?

Used in cell membranes and storing energy

What are nucleic acids used for in life?

DNA is assembled from chains of nucelic acids

What does it mean for amino acids to be chiral?

L-amino acids and D-sugars - this is arbitrary, but molecules need to be able to recognise each other

What is the structure of DNA?

DNA is made up of a repeating chain of a ribose sugar, phosphate group and a base

What are the 4 bases of DNA?

ATGC

What is RNA?

Molecule which acts as a messenger for DNA, providing genetic information to ribosomes for protein synthesis

Why is water a suitable solvent for life?

Readily dissolves many ions, large heat capacity, high heat of vapourisation, cosmically abundant

Why might ammonia be a suitable solvent for life?

Readily dissolves many chemicals, could allow for chemical chains similar to amino acids, less viscous than water, high heat of vapourisation, high heat capacity

Why is ammonia not a suitable solvent for life?

Narrow temperature range (-78C to 34C)

What are the major features of a cell?

Energy system, membrane & information system

What are the 2 types of cell?

Prokaryotes (no nucleus), eukaryotes (nucleus)

How are membranes formed?

Phospholipids are made up of a phosphate group (hydrophilic) and fatty acid tails (hydrophobic). The hydrophilic end is attracted to the water and the hydrophobic end is repelled by the water. The two ends line up to form a membrane

What is DNA?

Deoxyribose nucleic acid; double-stranded, holds genetic information about the organism

What is RNA?

A single-stranded messenger molecule which transfers genetic information from the nucleus to the ribosome so that protein synthesis can take place

How does DNA duplicate?

Parental strands separate, each base generates a new pair, the entire structure is duplicated, new DNA strands are created

What is the process of DNA -> Proteins?

Transcription from DNA to RNA, then translation from RNA to proteins

What is the process of DNA transcription?

DNA enters the RNA Polymerase, the DNA unwinds such that mRNA is formed from pairing with one strand, the DNA rewinds and separates from the mRNA upon exiting the RNA Polymerase

What is the “primary transcript” in DNA?

Length of RNA that results from transcription

What is the process of mRNA translation?

Ribosome locks around the mRNA, scans across the mRNA, when the correct tRNA binds with the RNA the corresponding amino acid is formed and creates a chain with the previously formed amino acid, the ribosome moves along the mRNA to the next triple

How do we detect organic material in space?

Atoms & molecules absorb specific wavelengths of radiation & produce certain frequencies of photons, so absorption and emission spectra can be used to identify them in space

Give & describe one location in space where organic compounds can be found

Diffuse Interstellar Clouds; they are old, very dilute, mostly atomics, permeated by UV radiation and contain very simple diatomic molecules such as CO

Why are interstellar grains important for astrochemistry?

They provide a surface on which chemical reactions can take place in very low pressure & low temperatures

What are PAHs?

Polycyclic aromatic hydrocarbons are stable, mostly made of carbon rings, abundant in meteorites, can act as a scaffold to form organic compounds

Why is radiation important for driving chemical reactions in space?

Provides energy in very low pressure and low temperature environments

Why is the discovery of interstellar organic chemistry important to our understanding of the possible origins of life?

Organic material (e.g. carbon compounds) is abundant in the universe

What are the principles behind the hierarchical classification of life?

There are prokaryotes (archaea & bacteria) and eukaryotes, each species has a binomial name consisting of the genus and the epithet

What is homology?

Similarity between species due to shared ancestry

What is analogy?

Similarity between species due to convergent evolution / similar environmental conditions

What is a monophyletic group?

A group on a phylogenetic tree includes a common ancestor and all of its descendants

How is DNA used to build a phylogenetic tree?

Organisms with similar morphologies or DNA are more likely to be closely related than organisms with different structures - ribosome DNA is highly preserved so is commonly used - greater number of different genes = higher evolutionary distance

What is Horizontal Gene Transfer?

HGT is the movement of genetic information between organisms which allows microbes to evolve (e.g. antibiotic resistance)

What are 2 examples of HGT?

Transduction - virus enters host cell, virus genome combines genetic information with host genome; Conjugation - genetic material from one cell has two strands, one strand transfers from donor cell to recipient cell, each cell’s genetic information duplicates so that it is double-stranded

Why does HGT make building genetic trees difficult?

The tree assumes parent-child evolution - in microbes, unrelated organisms can exchange genetic information, so a tree may not be accurate

How can phylogenetic trees be used to test hypotheses?

Phylogenetic trees can indicate the evolutionary history of species (e.g. in humans, African mtDNA types are basal, and non-African are derived, so human life began in Africa)

What are the astrobiological implications of phylogenetic trees & evolution?

It is possible multiple trees of life began and died, we can hypothesise that life on other planets came from different origins than life on Earth

What is catabolism?

The process by which a living organism obtains its energy

What is anabolism?

The process by which a living organism uses its energy

How does the electron transfer chain work?

An electron donor (e.g. carbon) supplies electrons. These electrons are passed along proteins in the cell membrane; the proteins are ordered in order of increasing electronegativity, so the electrons move to a lower energy level & energy is released. When the electron reaches the end of the protein chain, it is removed by an electron acceptor (e.g. oxygen).

What is ATP?

ATP is the universal energy currency for life, like a small battery containing energy needed for biological functions

How does the electron transfer chain generate a proton motive force?

The energy released as the electrons move along the ETC is used to pump protons from outside the membrane into the membrane, generating the proton motive force

What is chemiosmosis?

The process by which the protons moved into the cell membrane by the ETC are used to make ATP. Protons leave the cell membrane via an ATP synthase, generating ATP.

What is anaerobic respiration?

The terminal electron acceptor is not oxygen

What is a chemolithotroph & why are they interesting?

A type of microbe that obtains its energy by oxidising inorganic compounds, which may exist on planets like Mars that contain an abundance of rock

What is a redox reaction?

A reaction where one substance is oxidised and the other is reduced

What is Gibbs Free energy?

G = nFE, n=number of electrons, F=Faraday’s constant, E=redox potential difference - equal to the energy available from a redox reaction

What are the astrobiological consequences of Gibb’s Free Energy?

Gibb’s Free Energy can be used to predict availability in extreme environments

What are extremophiles?

Organisms which are adapted to thrive in extreme environments

Give 2 examples of an adaptation to an extreme environment

Psychrophilic microbes in cold environments - have altered cell membrane structure to prevent close packing - mixed saturated and unsaturated lipids in cell membrane; some microbes can withstand very high radiation doses by containing multiple copies of their genome and pigments to quench reactive oxygen states

What are the astrobiological consequences of extremophiles?

Extremophiles show that life can exist in extreme environments that are not habitable to humans

What are chemolithotrophs?

Organisms which use inorganic compounds as energy sources

Why are chemolithotrophs extremophiles?

They thrive in environments where energy is scarce

Why are extremophiles useful in industry?

Their adaptations can be useful in certain products, e.g. enzymes produced by thermophiles are useful for creating biological washing liquid

Why might microbes/extremophiles be useful in human space exploration?

Microbes’ biological adaptations could be used as an energy source/for terraforming as they can survive on extreme planets or in space