Acid nucleic

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ACID NUCLEIC VÀ NGUỒN GỐC
SỰ SỐNG
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NUCLEIC ACIDS
Two classes of nucleic acids are found in cells
Deoxyribonucleic acid
DNA
Ribonucleic acid
RNA
Many of the functions of these
nucleic acids are related or
overlapping
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NUCLEIC ACIDS
DNA
Polymer of deoxynucleotides
Genetic material of all cellular life and of some viruses
Organized into “genes”
Blueprints for proteins
RNA
Polymer of nucleotides
Genetic material of some viruses
Intermediates in gene expression
Ribosome components
Some possess enzyme-like activity
“Ribozymes”
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(DEOXY)RIBONUCLEOTIDES
Nucleic acids are polymers
DNA monomers are deoxyribonucleotides
RNA monomers are ribonucleotides
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(DEOXY)RIBONUCLEOTIDES
Nucleic acid monomers consist of three parts
Sugar
Nitrogenous base
Phosphate group(s)
These three parts
are assembled by
condensation
reactions
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(DEOXY)RIBONUCLEOTIDES
Both DNA and RNA possess a pentose sugar
Ribose in RNA
Deoxyribose in DNA
Lacks the 2’ OH group possessed by ribose

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(DEOXY)RIBONUCLEOTIDES
Both DNA and RNA possess four nitrogenous bases
Guanine
Adenine
Cytosine
Thymine (in DNA)
Uracil (in RNA)
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(DEOXY)RIBONUCLEOTIDES
One or more phosphate groups are attached to the 5’ carbon of
(deoxy)ribose
Triphosphates used
in polynucleotide
synthesis
Only one is
incorporated into
a DNA or RNA
chain
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(DEOXY)RIBONUCLEOTIDES
Some ribonucleotides have additional functions
e.g., ATP is
involved in
energy transfers
within cells
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POLYNUCLEOTIDES
Nucleotides are joined via condensation reactions
3’ OH and 5’ phosphate OH
New nucleotides are added to
the 3’ end of growing chain
Two strands of double-stranded
polynucleotides are NOT
covalently linked
Interact through H-bonds
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POLYNUCLEOTIDES
Structure of a single strand of DNA or RNA
Backbone of alternating sugar
and phosphate groups
Nitrogenous bases projecting
from this backbone
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POLYNUCLEOTIDES
Most DNA and some RNA is double-stranded
Bases project from the sugar-phosphate backbone
Bases of two strands interact through H-bonds
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POLYNUCLEOTIDES
DNA is organized into units called genes
A gene is a blueprint for a protein
RNA is an intermediate in gene expression
DNA  RNA  protein
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ORIGIN OF LIFE
Life on Earth initially arose amidst a sea of various biological molecules
e.g., Amino acids, sugars, purines, ATP, etc.
The production and accumulation of these biological molecules preceded the origin of life on Earth
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ORIGIN OF LIFE
Stanley Miller and Harold Urey recreated the assumed early atmosphere (1953)
Contained H2O, H2, CH4,
and NH3
Lacked free O2
Energy input in forms of
heat and electrical sparks
Mimic geothermal heat
and lightning
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ORIGIN OF LIFE
The initial Miller-Urey experiment and various similar experiments succeeded in producing:
All 20 amino acids
Several sugars
Lipids
Purines and pyrimidines
ATP (when phosphate
was added)
etc.
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ORIGIN OF LIFE
The atmosphere replicated in these experiments likely differed from the earth’s early atmosphere
Atmosphere likely possessed little or no O2
Atmosphere likely possessed more CO, CO2, and N2 than that in Miller’s experiment
Still, the Miller-Urey experiment did demonstrate that key organic molecules critical to life could be produced abiotically from inorganic precursors
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ORIGIN OF LIFE
Other researchers have used combinations of gases based on our current understanding of Earth’s early atmosphere
Similar results were achieved
Organic molecules can be abiotically produced in an atmosphere composed primarily of H2O, CO, CO2, and N2
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REFERENCES
Campbell, Neil A. and Reese, Jane B. Biology, 7th edition. Pearson Education, Inc. 2005.
Campbell, Neil A., Reese, Jane B., Taylor, Martha R., and Simon, Eric J. Biology, Concepts and Connections, 5th edition. Pearson Education, Inc. 2006.
Nester, Eugene W., Anderson, Denise G., Roberts, C. Evans Jr., and Nester, Martha T. Microbiology, A Human Perspective, 5th edition. McGraw-Hill Companies, Inc. 2007.
Limson, Janice. 2002. http://www.scienceinafrica.co.za/2002/june/lactose.htm