This phosphodiester bond creates the sugar phosphate backbone of DNA Structure

This phosphodiester bond creates the sugar phosphate

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This phosphodiester bond creates the sugar-phosphate “backbone” of DNA. Structure: Each has a nitrogenous base, a pentose sugar, and a phosphate. When attached together, the polymer also has a 5’ (“five prime”) and a 3’ (“three prime”) end. Nucleic acids are always made in the 5’ -> 3’ direction, which means the 5’ end represents the beginning of a nucleic acid strand and nucleotides are added to the 3’ end . Directionality is like a LEGO brick, which has a bumpy side and a side with holes when it is a single brick ( monomer ) or when several bricks are in a stack ( polymer ). The same DNA strand can be shown in different directions. DNA strands are often written in the 5’ to 3’ direction (as shown above left ), but the same exact DNA molecule can also be written with its 3’ end on the left (as shown above right ). Turning it doesn’t change the identity of the molecule. DNA is a Double Helix: How Bases Pair Together in DNA:
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The sugar-phosphate backbones of the two strands of DNA are separated by a constant distance, regardless of whether the base pair is A:T, G:C, T:A, or C:G. This constant distance for correct base pairs is often illustrated by showing the DNA in a ladder-like structure (below, left ) with the two sugar-phosphate backbones as the vertical supports and the base pairs as the rungs. However, in reality, the two strands of DNA twist around each other to generate the familiar double helix (below, right ).
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DNA Replication The Structure of DNA Allows it to be Copied: DNA replication allows each cell (and each person) to pass on a complete set of DNA to the next generation. Each strand of parental ("old") DNA (shown in blue) acts as a template for the synthesis of a complementary daughter ("new") strand (shown in red). Thus, the resulting double-stranded molecules are identical. DNA Replication: First, the DNA must be separated . This creates a replication “fork” where the two original strands separate. Next, the new DNA is synthesized by a protein known as DNA polymerase . DNA polymerase makes a polymer of DNA nucleotides. DNA polymerase takes individual nucleotides and matches them up to the parental sequence to ensure they are a correct pair. If the pairing is correct, DNA polymerase binds the nucleotide to the growing strand of DNA. However, DNA polymerase cannot start a new strand of DNA because it only binds to double-stranded nucleic acids. To get around this, it uses RNA primers . The addition of a primer to the single-stranded DNA creates a double-stranded nucleic acid “handle” to which DNA polymerase can attach and start making DNA. RNA primers are used at several places along the two strands of DNA - new DNA is created in fragments ( Okazaki fragments ).
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  • Winter '19
  • DNA, DNA Damage

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