Module 1 - Origin + Energy-Generating Systems

Question 1

What are the three main types of evidence for the earliest life on Earth?

Answer 1

So-called microfossils in ancient rocks
Stable isotope analysis of carbon
Fossilised stromatolites

Question 2

Name the two scientists who first proposed the Primordial Soup hypothesis

Answer 2

Haldane and Oparin

Question 3

What three main factors made the early atmosphere inhospitable to life?

Answer 3

High temperatures (over 100C)
Lack of liquid water
High levels of UV radiation

Question 4

What is a key criticism of the Urey-Miller experiment?

Answer 4

The gases used did not accurately mimic the gases in the early atmosphere

Question 5

Why are hydrothermal vents now considered a plausible location for the first formation of life? (3 Reasons)

Answer 5

There is an abundance of consistent chemical energy sources
These environments were protected from the (likely) very hostile conditions on the surface
The potential for mineral compartmentalisation in these structures

Question 6

Three reasons why RNA is preferred over DNA as the hypothetical initial replicating polymer?

Answer 6

RNA is single-stranded and more able to fold
RNAs are known to self-replicate
RNAs can have inherent enzymatic activity

Question 7

Name the 5 main “Steps/Stages” of the development of the RNA World

Answer 7

1. Pre-biotic synthesis of RNA and proteins
2. RNAs able to self-replicate
3. Lipid-bound vesicles form, containing RNAs (cellular life)
4. Proteins take over some catalytic functions
5. (More stable) DNA evolves as the coding polymer from RNA

Question 8

Name the four gases mainly present in the early atmosphere, the one key missing gas and whether the conditions were reducing or oxidising

Answer 8

Methane, CO2, Ammonia, Nitrogen; NO OXYGEN; reducing conditions

Question 9

Describe the most likely metabolism mechanism of the first cells

Answer 9

A primitive membrane-bound hydrogenase enzyme spans the cell membrane;
Hydrogen acts as an electron donor, Elemental Sulphur as an electron acceptor;
A proton gradient is produced to drive ATP Synthesis via a primitive ATPase

Question 10

When did the first eukaryotic cells probably appear?

Answer 10

Approx 1.5-2 bya

Question 11

How are alignments used in modern phylogenetics?

Answer 11

Alignments are hypotheses as to how sequences have diverged over time (since a last common ancestor);
An algorithm can minimise mismatches by adding gaps - the more gaps required the more distantly related

Question 12

Are the actual evolutionary distances generally greater or smaller than those calculated from alignment

Answer 12

GREATER (i.e. more distant)

The corrected distance must take into account REVERSIONS and MULTIPLE MUTATIONS AT THE SAME SITE

Question 13

Name the four factors that make a gene/sequence useful for phylogenetics

Answer 13

1. Gene present in all organisms of interest
2. Not laterally transferred
3. An appropriate level of sequence conservation/divergence
4. Large enough to contain a record of the historical information

Question 14

Which gene is generally the most useful for phylogenetics and why?

Answer 14

16s rRNA:
1. it contains both VERY CONSERVED and VERY DIVERSE regions (conserved regions make alignment easier, diverse regions allow closely related species to be distinguished)
2. It is part of the core translation machinery - so it has been conserved in ALL BACTERIAL SPECIES with a preserved function

Question 15

What did Carl Woese propose based on RNA sequencing?

Answer 15

That there may be a third domain of life besides prokaryotes and eukaryotes (ARCHAEA)

Question 16

Name and define the two types of chemotrophs

Answer 16

Chemoorganotrophs - use organic chemicals e.g. glucose as an energy source

Chemolithotrophs - use inorganic chemicals e.g., hydrogen, Fe2+ etc

Question 17

Why (chemically speaking) is anaerobic respiration less efficient than aerobic respiration?

Answer 17

Oxygen is at the bottom of the “electron tower,” so it is most efficient to use oxygen as the final electron acceptor

Question 18

Name some other chemicals which can act as alternative electron acceptors instead of oxygen

Answer 18

Nitrogen and sulphur, carbon dioxide, iron compounds

Question 19

How do fermentation and respiration fundamentally differ in their mechanisms of ATP synthesis?

Answer 19

Fermentation: SUBSTRATE LEVEL PHOSPHORYLATION (ATP directly synthesised from energy-rich intermediate)

Respiration: OXIDATIVE PHOSPHORYLATION (ATP produced from proton motive force, via electron transport)

Question 20

Describe how redox balance is involved in fermentation

Answer 20

Electrons must be removed onto NAD+ to form NADH (reduced form)

Question 21

What happens in fermentation to allow NAD+ to be recycled (if no electron acceptor is present)

Answer 21

The electrons are used to reduce organic compounds to fermentation products (e.g., alcohols/acids) which are excreted from the cell

Question 22

Name the 5 bacterial phyla containing photosynthetic species

Answer 22

Chlorobi (Green sulfur), Chloroflexi, Cyanobacteria, Proteobacteria, Firmicutes

Question 23

What is the difference between oxygenic and anoxygenic phototrophs?

Answer 23

Oxygenic: reducing power comes from water (resulting in O2 production)
Anoxygenic: reducing power comes from a variety of chemicals (e.g., H2S)

Therefore not all photosynthesis produces oxygen!

Question 24

Name 3 specific “things(?)” that are thought to have been essential to the formation of the first living cells

Answer 24

Montmorillite clay; liposomes; Self-Replicating RNAs

Question 25

Name 2 conditions in the early atmosphere which may have been essential for the formation of life, and why?

Answer 25

UV radiation; Lightning Strikes
(they have been shown to catalyse condensation reactions when in reducing conditions -> may have led to formation of first organic compounds)