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UNIT 1:  CELLULAR FUNCTIONS

  E.  Nucleic Acids

  ·         these are the building blocks of the hereditary molecules DNA and RNA

·         DNA holds the information (in a specific code) that determines the formation of substances found in living things, that ultimately determines the physical characteristics of the individual organism itself

·         RNA is involved in the synthesis of protein molecules that are determined by the DNA

·         nucleic acids are made of monomers called nucleotides

·         the subunits of nucleotides are:

• a nitrogenous-containing base
• a five carbon pentose sugar molecule
• a phosphate group

·         the nitrogenous-containing base may be a pyrimadine (one ring), or a purine (two rings)

·         there are three types of pyrimidines; cytosine (C), thymine (T), and uracil (U)

·         there are two types of purines; adenine (A) and guanine (G)

·         uracil (U) is only present in RNA, not DNA

·         thymine (T) is only present in DNA, not RNA

·         the pentose-ribose sugar of DNA lacks an oxygen, thus giving DNA the name deoxyribonucleic acid

·         the pentose-ribose sugar of RNA contains oxygen , thus giving RNA the name ribonucleic acid

·         Figures 1.30, p. 26, and 1.31, p. 27, show that the sugar-phosphate chain of DNA form the backbone of the molecule, while the bases that are attached to each backbone face each other in the interior portion

·         the bases, from each backbone, pair up with each other in a special arrangement – A with T (always), and G with C (always)

·         due to the specific nature of the functional groups of each base pair, 2 H-bonds form between A and T, while 3 H-bonds form between G and C

·         these base pairings – called complimentary base pairs form the “step” part of the ladder structure of DNA

·         the special arrangement of the base pairs causes the DNA molecule to become a twisted structure – called a double helix

·         RNA has the same basic sugar-phosphate backbone

·         however, it’s different than DNA in the following ways:

• it exists as a single strand, whereas DNA is a double strand
• its pentose-ribose sugar contains a hydroxyl group, which is replaced with a hydrogen in DNA
• its function is to help in the construction of protein molecules, whereas DNA codes for the sequencing of the polypeptide

·         one very important nucleotide in living systems is ATP – adenosine triphosphate

·         ATP is a monomer containing a pentose sugar attached to both an adenine base, forming the adenosine part, plus a tail of three phosphate groups

·         each phosphate group in the “tail” of ATP possesses an over all negative charge, which results in very strong forces of repulsion within the tail itself

·         because of this high instability within the tail region, when the third phosphate breaks off (due to the action of an enzyme and hydrolysis) a net release of energy results, which is known as an exergonic reaction

·         this particular amount of energy is the generic amount of energy used by all living cells to perform any reaction necessary that requires work

·         the ATP molecule can be considered the “energy currency” of all living things

·         Figure 1.32, p. 28, illustrates how ATP is hydrolyzed

·         after ATP is hydrolyzed and energy is released, ADP (adenosine diphosphate) and a phosphate result

·         the energy from the burning of glucose (cellular respiration), together with the action of a special enzyme, ATPase, help re-attach the phosphate group back onto the ADP – a process that requires energy to proceed – known as an endergonic reaction

Homework:              1.  1-8, p. 28

                                2.  be able to explain the meaning of each key term found on p. 33

                                3.  read over and understand “Essential Understandings” found on p. 33

                                4.  1-27, pp. 34-35 of “Understanding Concepts” and “Applying Inquiry/Communication Skills”