CHAPTER 4 Flashcards
nucleic acids
polymers specialized for storage, transmission, and use of genetic information
DNA
deoxyribonucleic acid; has deoxyribose; has thymine
RNA
ribonucleic acid; has ribose; has uracil
nucleotides
monomers for nucleic acid: pentose sugar + nitrogenous base + phosphate group
two forms of nitrogenous bases?
-pyrimidines: single ring
-purines: fused double-ring
types of pyrimidines
-Cytosine
-Thymine
-Uracil
types of purines
-Adenine
-Guanine
how are nucleotides linked?
-through phosphodiester bonds
-phosphate groups link the 3 carbon in one sugar to the 5 carbon in another sugar
-nucleic acids grow in the 5’-to-3’ direction
DNA base?
-purines: adenine (A) & Guanine (G)
-pyrimidines: cytosine (C) & thymine (T)
complementary base pairing
purines pair with pyrimidines by hydrogen bonding
-can also take place between RNA and DNA
RNA base
-single-stranded, but base pairing can occur between different regions of the molecule which results in 3D structures
-RNA has uracil (U) instead of thymine
DNA
-two strands form a double helix
-all DNA molecules have the same structure
-genetic information is carried in the sequence of base pairs
Transcription
DNA sequences are copied into RNA
Translation
RNA sequence specifies the sequence of amino acids in a polypeptide
gene expression
transcription + translation
replication
when DNA reproduce itself
what does DNA replication & transcription depend on?
it depends on the base-pairing properties of nucleic acids
genome
the complete set of DNA in an organism
genes
sequences of DNA that are transcribed into RNA
hereditary information
DNA carries hereditary information from one generation to the next; closely related living species have more similar base sequences than do species that are more distantly related
what DNA sequencing used for?
to trace evolutionary relationships
other roles for nucleotides?
-ATP: energy transfer in biochemical reactions
-GTP: energy source ini protein synthesis
-cAMP: essential in many processes, including hormone action
-carried in synthesis and breakdown of carbohydrates and lipids
spontaneous generation? who disproved it?
some forms of life arose from decaying matter; Francesco Redi disproved this in 1668
what experiment disproved spontaneous generation
an experiment by Louis Pasteur showed that microorganisms can arise only from other microorganisms
describe the experiment
jar 1: meat was exposed to air and flies. maggots formed in the meat
jar 2: fine cloth covering jar meat was exposed to air but not flies. no maggots formed
jar 3: lid coving jar, meat was no exposed to air or flies. no maggots formed
what are the two theories on how life first originated?
- chemical evolution
- life came from outside earth
chemical evolution
-conditions on primitive earth led to information of simple molecules such as amino acids, which led to formation of life forms
-Miller and Urey (1950s) experimented with reconstructing those primitive conditions using gases thought to be in the early atmosphere: H2, NH3, CH4, H2O
what did Miller and Urey experiments spark?
-volcanoes many also have added CO2, N2, H2C, and SO2 to the atmosphere
-adding these gases to the experimental atmosphere results in formation of many more small organic molecules
life came from outside earth
-some meteorites contain molecule such as purines, pyrimidines, and amino acids, suggesting that living organisms might have reached earth within a meteorite
-some question if organisms could survive in a meteorite
what are plausible explanations of how polymers formed?
-possible conditions including powdered clays, hydrothermal vents, and hot pools (similar to early earth conditions)
what is a key to the origin of life?
-the appearance of catalysts (today catalysts are proteins called enzymes)
-proteins are synthesized from information in nucleic acids
what came first, nucleic acids or protein catalysts?
-RNA may have been the first catalyst; which is a nucleic acid
-the 3D shape and other properties of some TNA molecules (ribozymes) are similar to enzymes
-RNA could have acted as a catalyst for its own replication and for synthesis of proteins.
-DNA could eventually have evolved from RNA
evidence supporting the “RNA world” hypothesis
-ribose can be formed in prebiotic chemical synthesis experiments
-peptide linkages are catalyzed by ribozymes today
-in retroviruses, reverse transcriptase catalyzes synthesis of DNA from NRA
-short, naturally occurring RNA molecules catalyze polymerization of nucleotides in experimental settings
-an artificial ribozyme has been developed that can catalyze assembly of short RNAs into a longer molecule that is an exact copy of itself
what must occur for life to occur
life must have been concentrated in a compartment
-living cells now are separated from their environment by a membrane
what does a membrane allow for cells
-allows cells to maintain a chemical composition that is different from the external environment
what do fatty acids form in water?
they form a lipid bilayer around a liquid compartment
what are protocells? what do they allow?
A self-organized sphere of lipids proposed as a stepping-stone to the origin of life; these allow small molecules such as sugar and nucleotides to pas through
what happens when nucleotides pass through the bilayer?
if short nucleic acid strands capable of self replication are placed inside protocells, nucleotides can pass through the bilayer and e incorporated into polynucleotide chains
protocells may be reasonable model for the evolution of cells?
-they are organized systems of parts with substances interacting, in some cases catalytically
-the interior is distinct from the exterior environment
-capable of limited replication
cyanobacteria
based on fossil evidence found in Australia cyanobacteria which are single celled algae that photsynthesize which means carbon was needed; since carbon has isotopes it a good way to date things
carbon isotopes
-carbon isotopes indicative of photosynthesis were found I the fossils and also showed that several other types of bacteria were present as well
-probably took 500million to 1billion years for the first cells to appear on earth
