lecture 13

Question 1

where did the first living things come from?

Answer 1

1) simple inorganic compounds -> information containing biomolecules?
2) source of energy for constructing larger molecules?
3) how did polymers (RNA or polypeptides) form?
4) protect biomolecules form harsh environment?

Question 2

chemistry of Titan (Saturn’s largest moon)

Answer 2

nitrogen, methane, ethane, acetylene, propane, benezene, and hydrogen cyanide.
- in labs on Earth, this mix yields amino acids and nucleotide bases.

Question 3

natural conditions can give rise to

Answer 3

building blocks of life. if life is found on Titan (or elsewhere), then we would double our sample size from N=1 to N=2 for understanding the conditions required for new life to form.

Question 4

definition of life:

Answer 4

• populations capable of evolving by natural selection.
• possession of a genotype and a phenotype.
• growth and reproduction.
• ability to evolve.

Question 5

which came first: proteins or DNA?

Answer 5

proteins:

• amino acid chains
• perform functions
• propagation?

DNA:

• nucleic acid chains
• store information
• perform functions?

Question 6

1980s

Answer 6

discovery of ribozymes, RNA enzymes.

Question 7

catalytic RNA

Answer 7

• information storage.
• > information transmission.
• > > perform biological functions.
• > > phosphorylation, amino-acyl transfer, peptide-bond formation, carbon-carbon bond formation.

Question 8

ribozymes

Answer 8

discovered in a protozoan (Tetrahymena thermopila). self-splicing introns.

Question 9

RNA world hypothesis

Answer 9

catalytic RNA molecules were a transitional form between nonliving matter and the earliest cellular life. predicts that RNA is ancient.

Question 10

Ribozymes posses both:

Answer 10

1) genotype - nucleotide sequence

2) phenotype - catalyze chemical reaction on a subtrate.

Question 11

evidence that RNA is ancient:

Answer 11

1) translation of genetic information into protein is highly conserved and universal.
2) ribosomes are built from rRNA, and amino acids are assembled into proteins with tRNA, which is translated using mRNA.
3) ribonucleotide triphophates (ATP and GTP) are the basic biological energy source of life.

Question 12

can ribozymes evolve?

Answer 12

• challenge ribozyme to catalyze reaction involving DNA substrate.
• add primer that is complementary to the substrate tail picked up…
• … and reverse transcriptase to make cDNA copy of ribozymes that succeeded in catalyzing reaction within DNA substrate.

Question 13

ribozyme adaptation

Answer 13

some mutations increased catalytic efficiency 100%.

Question 14

self-replicating RNA?

Answer 14

• lab experiments can evolve ribozymes capable of ligation.

- lab experiments can evolve ribozymes that can synthesize another smaller ribozyme.

Question 15

panspermia hypothesis

Answer 15

life arose elsewhere and traveled to earth through space.

• evidence: murchison meteorite - 9/28/1969 @ 11 am. 5 sq. miles of debris.
• organic compounds: amino acids: gly, ala, gln, val, pro. L (and D) stereoisomers.

Question 16

earth environment 4 billion years ago options…

Answer 16

1) oxidizing: high abundances of oxygen and carbon dioxide.
2) reducing: hydrogen, methane, ammonia.
3) intermediate.

Question 17

earth history is full of bombardments by

Answer 17

meteors and comets. they contain organic molecules.
- kinetic energy of impact vaporizes meteorite and ejects excess heat into the atmosphere. 200+ km diameter impact would heat atmosphere to 1500 C for 1000 years.

Question 18

Oparin-Haldane

Answer 18

Earth contained the right mix of inorganic molecules for the formation of biological components (nucleotides and amino acids).

1) simple to organics.
2) polymers.
3) protection.

Question 19

evidence for first life on earth:

Answer 19

• evidence from rocks of 3.7 billion year old life on earth.
• 3.26 billion year old fossils.
• 590 million: complex, eukaryotic; 950 million: complex, eukaryotic; 1.5 billion: maybe complex?
• 2 billion eukaryotic algae.

Question 20

infer characteristics of LUCA using a

Answer 20

phylogeny.

Question 21

diversity of archaea:

Answer 21

• single celled, prokaryotes
• genes for transcription/translation closer to eucarya.
• many in extreme environments.
• environmental sequencing.
• methane from hydrogen and CO2.

Question 22

LUCA divides into a clade of bacteria and into a clade of archaea and eucarya.

Answer 22

• ~60 genes shared among all cellular organisms in all domains (45 are ribosomal).
• information storage: all extant organisms have DNA.

Question 23

horizontal gene transfer

Answer 23

organisms swap genes.

Question 24

new concepts:

Answer 24

• instead of bifurcating tree there is the reticulating network.
• instead of tree of life there is the genealogy of life.
• instead of LUCA there is community.

Question 25

diversification hypotheses (pics in slides)

Answer 25

universal gene exchange, ring of life, chronocyte, and three viruses.