Question

lesson objectives
identify the chemical components of dna.
discuss the experiments leading to the identification of dna as the molecule that carries the genetic code.
describe the steps leading to the development of the double - helix model of dna.
lesson summary
the components of dna dna is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds. nucleotides may be joined in any order.
a dna nucleotide is a unit made of a nitrogenous base, a 5 - carbon sugar called deoxyribose, and a phosphate group.
dna has four kinds of nitrogenous bases: adenine, guanine, cytosine, and thymine.
solving the structure of dna
erwin chargaff showed that the percentages of adenine and thymine are almost always equal in dna. the percentages of guanine and cytosine are also almost equal.
rosalind franklins x - ray diffraction studies revealed the double - helix structure of dna.
james watson and francis crick built a model that explained the structure of dna.
the double - helix model the double - helix model explains chargaffs rule of base pairing and how the two strands of dna are held together. the model showed the following:
the two strands in the double helix run in opposite directions, with the nitrogenous bases in the center.
each strand carries a sequence of nucleotides, arranged almost like the letters in a four - letter alphabet for recording genetic information.
hydrogen bonds hold the strands together. the bonds are easily broken allowing dna strands to separate.
hydrogen bonds form only between certain base pairs - adenine with thymine, and cytosine with guanine. this is called base pairing.
the components of dna
for questions 1 - 5, complete each statement by writing in the correct word or words.

1. the building blocks of dna are
2. nucleotides in dna are made of three basic components: a sugar called, and a nitrogenous
3. dna contains four kinds of nitrogenous bases: and
4. in dna, can be joined in any order.
5. the nucleotides in dna are joined by bonds.

Explanation:

Step1: Recall DNA building blocks

DNA is made of nucleotides.

Step2: Identify nucleotide components

Nucleotides have deoxyribose sugar and a nitrogenous base.

Step3: List nitrogenous bases

Adenine, guanine, cytosine, and thymine are in DNA.

Step4: Note nucleotide - order flexibility

Nucleotides can be joined in any order.

Step5: Determine bond between nucleotides

Covalent bonds join nucleotides in DNA.

Answer:

1. nucleotides
2. deoxyribose; base
3. adenine, guanine, cytosine, thymine
4. nucleotides
5. covalent