Genetic Material: Origin and Structure Flashcards
Describe the basic structure of nucleotides and DnA or RNA.
Nucleotides have a 5-carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and nitrogenous bases (A, C, and G in both; T in DNA, U in RNA).
What observations suggested that particular bases pair in DNA?
Chargaff examined the genomes of various organisms and noticed a 1:1 ratio for both A:T and G:C.
What are examples of chemicals that interact with specific features of the DNA helix?
Dapi is a minor groove intercalator that can inject fluorescence into the DNA helix.
Furanocoumarins is a major (and possibly minor) groove intercalator found in plants that can bypass the epidermis and cross link DNA strands covalently (not via hydrogen bonds as usual) when skin is exposed to the sun, preventing epidermal cells from replicating because DNA strands can no longer separate, leading to apoptosis.
Define “life,” at least according to NASA.
Life is a “self-sustaining chemical system capable of Darwinian selection.”
What are the essential features of a genetic material?
A genetic material must…
1. be able to store information
2. be able to express information
3. be able to replicate
4. be able to accommodate the introduction of variation (for evolution)
What makes RNA a particularly good candidate for being an original genetic material?
RNA encodes information for making proteins, has complex folding (raising potential for new functions DNA’s double helix is incapable of), is highly conserved across all life, is necessary for making protein, and could have potentially self-replicated.
Why is RNA necessary for making protein?
rRNA forms the large ribosomal subunit.
tRNAs are needed to pick up amino acids and incorporate them into peptide chains.
What are ribozymes?
RNA that can act as an enzyme
What are two examples of ribozymes?
ribonuclease-P
self-splicing introns
What observations and experimental evidence suggest that self-replicating ribozymes might have existed in nature?
Experimentally, self-replicating RNA polymerase ribozymes were selected over several generations. The original versions slowly added nucleotides to a template and could not handle hairpin templates, but then scientists selected ribozymes that could add single or triple nucleotides, which solved the problem without stopping. It’s plausible they could have also been selected naturally.
Are there any obstacles to the RNA World hypothesis?
- very complex chemistry contemporarily
- contemporary nucleotides don’t couple without chemical activation
- very limited phosphates (held in minerals, not free)
- adenine was possible abundant, but other nitrogenous bases weren’t
- non-biotic synthesis of ribose is unlikely; ribose is unstable enough as is
- solvent problems - polymeric RNA is unstable in water due to hydrogen bonds
- different cation availability
- no natural RNA polymerase ribozymes known
The complex chemistry of RNA contemporarily is a obstacle to the RNA World hypothesis. What can accommodate this?
Although RNA is difficult to construct contemporarily, the RNA world could have used hypoxanthine and various sugars.
What recent data suggest that an RNA-Peptide World might have occurred sooner than originally imagined?
Contemporary tRNAs have modified nucleoside bases that could have been relics of the RNA world.
Under plausible conditions, if RNAs are complementary, modified bases could allow for the coupling and transfer of amino acids into a peptide chain.
What is a nucleotide?
contains a sugar, a phosphate group on the 5’ carbon, and a nitrogenous base on the 1’ carbon; either DNA or RNA
What is a nucleoside?
a sugar and a nitrogenous base on the 1’ carbon, without a phosphate group
