Structure of DNA

DNA Structure Lesson

by Jovita Cross

​What is a DNA

​DNA (Deoxyribonucleic acid) is a complex molecule that carries the genetic instructions in all living things.

​Where is DNA located in the cell?

​Prokaryotes (Bacteria) - the DNA is floating in the cytoplasm.

​Eukaryotes - the DNA and proteins are organized in chromosomes that are located in the nucleus

​Where is DNA located in the cell?

​What does DNA look like?

​It is a double helix, which means a twisted ladder. The sides or backbone are composed of alternating phosphate groups and sugar (deoxyribose).

​The rungs are composed of nitrogenous bases (A,T,C,G)

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​What are the monomers of DNA?

​Monomer means the smallest part.

​The smallest part of DNA is called a nucleotide.

​Three parts of a nucleotide:

​Side or Backbone:

​1. Phosphate

​2. Sugar (Deoxyribose)

​Steps or rungs

​3. Nitrogenous bases (A,T,C,G)

​ - carry the genetic instruction.

​Base Pairing Rules

​The nitrogenous bases have a certain way of pairing.

​Adenine always pairs with Thymine

​Cytosine always pairs with Guanine

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​This means the amount of A = T, the amount of C = G

​What determines the uniqueness of an organism?

​The sequence or order of the nitrogenous bases.