DNA Structure and Replication AHSGE Review white Ch 11.1 DNA Structure A DNA molecule is made of 2 strands of repeating subunits called nucleotides. Each nucleotide is made of 3 parts: 1. Simple sugar called Sugar (deoxyribose) deoxyribose. Phosphate 2. Phosphate group group (These both form the Nitrogenous ‘backbone’ or sides of base the DNA molecule.) 3. Nitrogenous base (adenine, guanine, cytosine, or thymine) The bases form the ‘rungs of the ladder.’ Practice! Match this DNA strand with its complementary strand. TCGTTCATAATCGCTGCATA AGCAAGTATTAGCGACGTAT Question 1 Which of the following is NOT a component of DNA? A. simple sugars B. phosphate groups C. nitrogenous bases D. proteins The answer is D. Question 2 Which of the following correctly comprises a complimentary base pair? A. adenine – thymine B. thymine – guanine C. guanine – adenine D. cytosine – thymine The answer is A. Question 3 Which of the following makes up the backbone of a DNA molecule? A. ribose sugar, phosphate group B. nitrogen base, ribose sugar C. deoxyribose sugar, nitrogen base D. deoxyribose sugar, phosphate group The answer is D. Replication of DNA Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes. DNA is copied during interphase prior to mitosis and meiosis. It is important that the new copies are exactly like the original molecules. The DNA in the chromosomes is copied in a process called DNA replication. Without DNA replication, new cells would Video have only half the DNA of their parents. Copying DNA New DNA molecule Original DNA Strand Free New DNA Nucleotides New DNA Strand molecule Original DNA Strand Original DNA Steps for DNA Replication 1. Separation of strands: an enzyme breaks the hydrogen bonds holding the strands together. 2. Base pairing: Free nucleotides floating in the surrounding area attach to the exposed nucleotides on the DNA strands. 3. Bonding of bases: The sugar and phosphate of each nucleotide bond to form the backbone as the nitrogen bases bond down the center of the ‘ladder.’ Results of Replication •After DNA replication is DNA complete, two identical molecules of DNA are produced. Replication • Each newly made molecule of DNA has a strand of the original DNA molecule and a newly made strand.
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