Gilmour 1

Question 1

define stromatolites

Answer 1

bulbous mass of CaCO3 formed by microbial mass

Question 2

what is the isotope ratio?

Answer 2

ratio of amounts of 2 isotopes of an element - may serve as biosignature

Question 3

what is a microfossil?

Answer 3

microscopic fossil in which CaCO3 deposits have filled in the form of ancient microbial cells

Question 4

what is cyanobacteria?

Answer 4

a phylum of O2 producing photoautosomes that contain chlorophyll a and b

Question 5

what are the 4 main theories of the origin of life?

Answer 5

chemical (prebiotic soup)
pansperma (life from space)
rna
hydrothermal vents

Question 6

4 main requirements for life are..

Answer 6

C/H/N/O/Mg/Ca/Na/K/Fe
no free O2 in the atmosphere
temp that allows liquid water
energy from sun and reducing minerals in metabolic pathways

Question 7

5 main pieces of evidence of early life on earth are..

Answer 7

stromatolites - outer layer photosynthetic microbes/inner layer sulphate reducing
isotope ratios - life requires C12 isotope, build up of this in rocks and depletion of C13
microfossils
chemical biosignatures - hopanoids found in 2.5 Gyr rocks
oxidation state - alternating Fe3+ deposits in rocks shows different levels of O2

Question 8

define ribozyme

Answer 8

an RNA molecule that is capable of catalyzing reactions

Question 9

what is a peptidyl transferase

Answer 9

an rRNA molecule with the enzymatic ability to form peptide bonds between neighbouring a/a’s

Question 10

name 3 reasons why RNA is the 1st proposed macromolecule

Answer 10

1) simplicity: only 4 nucleotides compared to 20 a/a’s
2) efficiency: takes less energy to form compared to DNA and uracil is made before thymine in biochem pathway
3) viruses: used as genetic material in some viruses

Question 11

name 5 pieces of evidence that show how ribozymes could have been a key part in the origin of life

Answer 11

1) they have catalytic properties (can cleave themselves and other key RNA molecules)
2) can synthesise complementary RNA strands
3) most complex ribozyme found in ribosome
4) peptide bond formation catalysed by peptidyl transferase (a ribozyme)
5) ribozymes are a v old part of cell machinery - may reflect ancient processes

Question 12

name 2 reasons why RNA isn’t the main form of replication now

Answer 12

1) proteins replaced ribozymes because of greater variety of catalytic possibilities
2) DNA is more stable than RNA

Question 13

why is the hydrothermal vent theory favoured over the RNA world and prebiotic soup theory

Answer 13

hydrothermal vent theory includes energy source (UV/lightening have been suggested but are not stable enough)

Question 14

how do bacteria/archaea and eukarya generate energy according to the hydrothermal vent theory

Answer 14

bacteria/archaea - H+ movement across cell membranes

eukarya - across organelle membranes

Question 15

what are the differences in alkali and acid vents?

Answer 15

acid: 350 degrees/pH1-2/H+ grad into seawater from hydrothermal fluid (TOO UNSTABLE)
alkali: geochemical not volcanic/150-200 degrees/pH9-11/walls of vents porous (H+ travels into vent)

Question 16

what is the significance of micelle formation and how is it proposed to occur?

Answer 16

micelles are a proto-cell which are required for all life

proposed method of formation is that temp differences in alkali vents precipitated fatty acids (f/a’s) into micelles