BISC160 Chapter 4.docx

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University of Mississippi
Biological Science
BISC 160
Dr.Beckie Symula

Chapter 4 8/23/2013 3:53:00 PM 4.1 What are the chemical structures and functions of nucleic acids?  Nucleic acids are polymers specialized for the storage, transmission between generations, and use of genetic information.  DNA is a macromolecules that encodes hereditary information  RNA is an intermediate that is used to specify the amino acid sequences of proteins  Nucleotides are the building blocks of nucleic acids o Nucleotides consist of a pentose sugar, a phosphate group, and a nitrogen-base  Nitrogen base can be a six-membered single-ring pyrimidine, or a fused double-ring structure called a purine  Ribose differs from deoxyribose in that it has one less oxygen atom o The backbone of RNA and DNA consists of altering pentose sugars and phosphate groups o Nucleotides are joined by phosphodiester linkages  Between the sugar of one nucleotide and the phosphate of the next  Base pairing occurs in both DNA and RNA o Adenine and guanine are purines o Thymine and cytosine are pyrimidines o RNA contains uracil instead of thymine o Three factors make base pairing complementary:  The sites for hydrogen bonding on each base  The geometry of the sugar-phosphate backbone, which brings complementary bases near each other  The molecular sizes of the pair bases—stability o Diversity of DNA is found in its base sequence rather in the physical shape of the molecule(unlike proteins)  DNA carries information and is expressed through RNA o The information is encoded in the sequence of bases carried in its strands o Central dogma of molecular biology:  DNA can reproduce itself exactly (replication)  DNA can copy its information into RNA (transcription) o DNA replication usually involves the entire DNA molecule, but only relatively small sections of DNA are transcribed into RNA molecules o The complete set of DNA in a living organism is called its genome o The sequences of DNA that encode specific proteins are transcribed into RNA and are called genes  The DNA base sequence reveals evolutionary relationships Nucleotides have other important roles o ATP acts as an energy transducer in many chemical reactions o GTP serves as an energy source, especially in protein synthesis. Also plays a role in the transfer of information from the environment to cells o cAMP is a special nucleotide in which an additional bond forms between the sugar and phosphate group. It is essential in many processes, including the actions of hormones and the transmission of information by the nervous system 4.1 Summary: The nucleic acids DNA and RNA are polymers made up of nucleotide monomers. The sequence of nucleotides in DNA carries the information that is used by RNA to specify primary protein structure. The genetic information in DNA is passed from generation to generation and can be used to understand evolutionary relationships. 4.2 How and where did the small molecules of life originate?  Experiments disproved spontaneous generation of life o Spontaneous generation: some forms of life arose from inanimate or decaying matter o Francesco Redi tested spontaneous generation hypothesis o Pasteur showed microorganisms can arise only from other microorganisms, and that an environment without life remains lifeless.  Life began in water o Astronomers believe our solar system began forming 4.6 billion years ago  Star exploded to form the sun and bodies called planetesimals  Took 600 million years, called the Hadean, for chemical conditions on Earth to become just right for life  Life may have come from outside Earth o 1969 a meteorite fell to Australia, molecules of purines, pyrimidines, sugars, and ten amino acids were found  Scientists took care to avoid contamination  Amino acids on Earth are left-handed. In the meteorite they were right and left-handed forms  The isotope ratios for carbon and ydrogen in the sugars from the meteorite were different from the ratios of those elements found on Earth o 1984 meteorite found in Antarctica from Mars  water was found under its surface  4.5 billion years old; 13000 years on Earth  polycyclic aromatic hydrocarbons were present  magnetite was also found  Heat didn’t affect the rock because its magnetic field was reorganized when it went through the atmosphere  Prebiotic synthesis experiments model the early Earth o Chemical evolution: holds that conditions on primitive Earth led to the formation of
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