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The structure of DNA Essay

-DNA is a polymer of nucleotides

-Each nucleotide consists of a nitrogenous base, a sugar, and a phosphate group

-The sugar in DNA is a pentose sugar called deoxyribose

-The different kinds of bases are adenine, thymine, guanine, and cytosine

-In DNA, there is a 1:1 ratio of nucleotide bases: number of adenine = number of thymine and number of guanine = number of cytosine

-DNA consists of 2 strands in a shape called a double helix

-Double helix is 2-nm in diameter

-The strands have a sugar-phosphate backbone

-The two strands are held together by hydrogen bonds

-The rungs of the helix consist of purine/pyrimidine rings

-Adenine and guanine are purines

-Purines have two organic rings

-Cytosine and thymine are pyrimidines

-Pyrimidines have a single organic ring

-Pyrimidines pair with purines to form rungs of helix (adenine with thymine and guanine with cytosine)

-Adenine and Thymine form 2 hydrogen bonds

-Guanine and Cytosine form 3 hydrogen bonds

-The helix makes one full turn ever 3.4 nm along its length

-Bases are stacked .34 nm apart

-Ten layers of base pairs in each turn of the helix

-Replication is explained by the Semiconservative model

-When a double helix replicates, each of the two daughter molecules will have one old strand derived from the parent molecule and one newly made strand

-DNA replication involves unzipping the DNA molecule into 2 strands

-Each strand acts as a template to assemble a new, complementary strand

-Results in two identical double-stranded molecules of DNA

-How DNA replication occurs

-Helicase unwinds the DNA forming a replication fork (Y-shaped region where the new strands of DNA are elongating)

-Single-stranded DNA binding proteins prevent single strand of DNA from recombining

-RNA Primase initiates DNA replication at special nucleotide sequences called origins of replication. RNA Primase uses short segments of RNA nucleotides called RNA primers

-DNA polymerase attaches to the RNA primers and begins elongation by adding the DNA nucleotides to the complementary strand. DNA polymerase moves in a 5′ -> 3′ direction along each template strand

-Leading strand (3′ -> 5′ template) is assembled continuously as the DNA uncoils

-Lagging strand (5′ -> 3′ template) is assembled in short Okazaki fragments

-DNA ligase joins the short Okazaki fragments

-Mutations are changes in the genetic material of a cell

-Point mutations are chemical changes in just one or a few base pairs in a single gene

-Recombinant DNA is DNA in which genes from two different sources are linked

-Recombinant technique takes plasmid DNA from a bacteria and adds a gene of interest to it

-Plasmid is put back into bacteria and bacteria replicates itself; results in DNA of interest being replicated by the bacteria

-To obtain gene of interest, scientists use restriction enzymes

-Restriction enzymes are enzymes that cut DNA molecules at a limited number of specific locations

-Cut DNA in a reproducible way

-Each enzyme cuts only certain sequence of nucleotides

-Cut DNA into DNA fragments with a sticky end

-Sticky end will form hydrogen-bonded base pairs with complementary single-stranded stretches on other DNA molecules cut with same enzyme

-DNA ligase is used to join fragments of DNA together

-Using cloned DNA, scientists can add it to damaged DNA and correct point mutations

-Polymerase chain reaction (PCR) is a technique by which any piece of DNA can be quickly copied many times without using cells

-DNA to be replicated is incubated in a test tube with special kind of DNA polymerase, supply of nucleotides, and short pieces of synthetic single stranded DNA that serve as primers for DNA synthesis

-PCR can be used to create a large quantity of a certain type of DNA and help in making enough DNA for use in evidence of crimes

-Gel electrophoresis (DNA fingerprinting) separates DNA on the basis of the rate of movement through a gel under the influence of an electric field

-Restriction enzymes cut the DNA up into restriction fragments

-Each band consists of DNA molecules/fragments of the same length

-Used for paternity, crime scenes, or isolating certain genes

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