Module 7
1. Module 7
1.5. Page 3
Module 7—Molecular Genetics: DNA, RNA, and Protein Synthesis
Lesson Summary
This lesson addressed the following focusing questions:
- What is the history of the discovery of DNA?
- What is the structure of DNA?
- What is the significance of finding the DNA code?
The discovery that DNA is the molecule responsible for heredity and the discovery of DNA’s structural characteristics go hand-in-hand. Once scientists could see, and were able to closely examine, the structure of DNA, it became obvious that this molecule had to be responsible for passing genetic information on to the next generation. Throughout this lesson you have learned about some of the many scientists who contributed to solving these scientific questions. Every experiment and discovery built on the last, pushing forward toward the eventual result—the structure and function of DNA.
The double helix that Watson and Crick modelled would not have been possible without the x-ray image from Rosalind Franklin. The complementary base pairing in Watson and Crick’s model may not even have been thought of without the information from Phoebus Levene and his identification of the four nucleotides and their respective percent compositions. In this lesson, you have learned about the history of the identification of DNA and the structure of DNA. In the next lesson you will see how DNA’s structure directly determines its function.
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
adenine (A): a nitrogenous base of the purine group; complementary base pairs with thymine
antiparallel: describes the property by which the 5’ to 3’ phosphate bridges run in opposite directions on each strand of nucleotides in a double-stranded DNA molecule
Chargaff’s rule: in any sample of DNA, there is a constant relationship in which the amount of adenine is always approximately equal to the amount of thymine, and the amount of cytosine is always approximately equal to the amount of guanine
complementary base pairs: refers to the hydrogen-bonded, nitrogenous base pairs of adenosine and thymine, and of cytosine and guanine in the DNA double helix
cytosine (C): a nitrogenous base of the pyrimidine group; complementary base pairs with guanine
deoxyribose sugar: a ring-shaped sugar; has one less oxygen than ribose sugar
DNA (deoxyribonucleic acid): a double-stranded nucleic acid molecule that governs the processes of heredity in the cells of all organisms
It is composed of nucleotides containing a phosphate group, a nitrogenous base, and deoxyribose.
double helix: spiral ladder shape of the DNA molecule, made up of two long strands of nucleotides bound together and twisted
guanine (G): a nitrogenous base of the purine group; complementary base pairs with cytosine
mutation: a change in the sequence of bases on the DNA molecule
nitrogen base: an organic molecule containing nitrogen; two types present in DNA: double-ringed purines (adenine and guanine) and single-ringed pyrimidines (cytosine and thymine)
nucleotide: the repeating unit (monomer) of DNA; two strings of nucleotides joined in the middle by hydrogen bonds form a DNA molecule; each nucleotide is made up of a deoxyribose sugar, a nitrogenous base, and a phosphate group
phosphate: an inorganic phosphate group (POPO43–)
RNA: ribonucleic acid; a short, single strand composed of nucleotides with a nitrogen base, ribose sugar, and phosphate group; nitrogen bases include adenine, guanine, cytosine, and uracil; has a role in protein synthesis
thymine (T): nitrogenous base of the pyrimidine group; complementary base pairs with adenine
uracil (U): a nitrogenous base found only in RNA, not DNA; replaces thymine when paired to adenine
Watson and Crick: credited with co-discovery of the structure of DNA; received the Nobel Prize for their work