Dna and virus, Essays (high school) of Biology

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Eukaryotic cell

• (^) In humans, as in other higher organisms, a DNA molecule consists of two strands that wrap around each other to resemble a twisted ladder whose sides, made of sugar and phosphate molecules, are connected by rungs of nitrogen- containing chemicals called bases. Each strand is a linear arrangement of repeating similar units called nucleotides, which are each composed of one sugar, one phosphate, and a nitrogenous base

Components of DNA

• (^) DNA is a polymer. The monomer units of DNA are nucleotides, and the polymer is known as a "polynucleotide." Each nucleotide consists of a 5-carbon sugar (deoxyribose), a nitrogen containing base attached to the sugar, and a phosphate group. There are four different types of nucleotides found in DNA, differing only in the nitrogenous base. The four nucleotides are given one letter abbreviations as shorthand for the four bases.

DNA crystel

Franklins work

Pyrimidine Bases

• (^) Cytosine and thymine are pyrimidines. The 6 stoms (4 carbon, 2 nitrogen) are numbered 1-6. Like purines, all pyrimidine ring atoms lie in the same plane

Deoxyribose Sugar

• (^) The deoxyribose sugar of the DNA backbone has 5 carbons and 3 oxygens. The carbon atoms are numbered 1', 2', 3', 4', and 5' to distinguish from the numbering of the atoms of the purine and pyrmidine rings. The hydroxyl groups on the 5'- and 3'- carbons link to the phosphate groups to form the DNA backbone. Deoxyribose lacks an hydroxyl group at the 2'- position when compared to ribose, the sugar component of RNA.

Nucleosides

• (^) A nucleoside is one of the four DNA bases covalently attached to the C1' position of a sugar. The sugar in deoxynucleosides is 2'-deoxyribose. The sugar in ribonucleosides is ribose. Nucleosides differ from nucleotides in that they lack phosphate groups. The four different nucleosides of DNA are deoxyadenosine (dA), deoxyguanosine (dG), deoxycytosine (dC), and (deoxy)thymidine (dT, or T).

Nucleotides

• (^) A nucleotide is a nucleoside with one or more phosphate groups covalently attached to the 3'- and/or 5'-hydroxyl group(s). The DNA backbone is a polymer with an alternating sugar-phosphate sequence. The deoxyribose sugars are joined at both the 3'-hydroxyl and 5'- hydroxyl groups to phosphate groups in ester links, also known as "phosphodiester" bonds

Features of the DNA Double Helix

• (^) Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral
• (^) The two polynucleotide chains run in opposite directions
• (^) The sugar-phosphate backbones of the two DNA strands wind around the helix axis like the railing of a sprial staircase
• (^) The bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase

• (^) DNA is a long polymer made from repeating units called nucleotides.[1][2] The DNA chain is 22 to 26 Ångströms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 Å (0.33 nm) long.[3] Although each individual repeating unit is very small, DNA polymers can be enormous molecules containing millions of nucleotides.

Watson and Crick Model

• (^) DNA is a long polymer made from repeating units called nucleotides.[1][2] The DNA chain is 22 to 26 Ångströms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 Å (0.33 nm) long.[3] Although each individual repeating unit is very small, DNA polymers can be enormous molecules containing millions of nucleotides.

• (^) Examine the view labeled "2 separate DNA strands". DNA normally occurs as two separate long polymers ("strands") that wrap around each other in a helical spiral around an imaginary helix axis. If you view the DNA from end on, you will see only a tight circle of atoms. The helix axis would be in the center of this circle

• (^) Normal B-DNA, as first described by Watson and Crick, is a right-handed helix. GC-rich DNA can also exist in a form known as Z-DNA, which forms a left-handed helix. Examine the view labeled "phosphate group location". DNA does not have smooth sides like a regular cylinder. Notice the grooves in the surface of the DNA molecule between the phosphate groups. Proteins that interact with DNA often make contact in these grooves