Podcast
Questions and Answers
What is the diameter of the DNA helix mentioned in the text?
What is the diameter of the DNA helix mentioned in the text?
How are the planes of the bases oriented with respect to the helix axis?
How are the planes of the bases oriented with respect to the helix axis?
Which statement about the positioning of purine and pyrimidine bases is correct?
Which statement about the positioning of purine and pyrimidine bases is correct?
How are the planes of sugars oriented in relation to the bases in the DNA helix?
How are the planes of sugars oriented in relation to the bases in the DNA helix?
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How are adjacent bases separated along the helix according to the text?
How are adjacent bases separated along the helix according to the text?
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What type of bonds hold the two chains of DNA together?
What type of bonds hold the two chains of DNA together?
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Which scientist conducted chemical analysis that provided important clues about DNA's structure?
Which scientist conducted chemical analysis that provided important clues about DNA's structure?
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What type of pairing of bases is considered most important in the DNA double helix structure?
What type of pairing of bases is considered most important in the DNA double helix structure?
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Why did Watson and Crick deduce that adenine must pair with thymine and guanine with cytosine?
Why did Watson and Crick deduce that adenine must pair with thymine and guanine with cytosine?
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What important discovery did Erwin Chargaff's chemical analysis reveal about DNA?
What important discovery did Erwin Chargaff's chemical analysis reveal about DNA?
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Study Notes
Nucleic Acids
- Nucleic acids are composed of pentose sugar, nitrogenous base, and phosphate molecules.
- There are two types of nucleic acids: DNA (deoxynucleoside phosphate) and RNA (nucleoside phosphate).
Nucleoside
- A nucleoside is a combination of a nitrogenous base and a sugar molecule.
- The sugar molecule is usually ribose or deoxyribose.
- The base is linked to the sugar molecule at carbon 1, and the phosphate group is linked to the sugar molecule at carbon 5.
Pentose Sugars
- Pentose sugars are 5-carbon monosaccharide molecules.
- There are two types of pentose sugars: ribose and deoxyribose.
- Ribose is the pentose sugar found in RNA.
- Deoxyribose is the pentose sugar found in DNA, and it lacks one oxygen atom at carbon 2.
Nitrogenous Bases
- Nitrogenous bases are heterocyclic amines that can accept a proton.
- There are two types of nitrogenous bases: purine and pyrimidine.
- Purine bases have a double-ringed structure and include adenine and guanine.
- Pyrimidine bases have a 6-membered ring structure and include cytosine, thymine, and uracil.
- Adenine and guanine are found in both DNA and RNA, while thymine is only found in DNA and uracil is only found in RNA.
Phosphodiester Bond
- A phosphodiester bond is a chemical bond formed between the hydroxyl group of one nucleotide and another nucleotide.
- It is the bond between two nucleotides, with the 5' end of one nucleotide and the 3' end of another.
Nomenclature
- Nucleotides are named based on the nitrogenous base and the sugar molecule.
- Examples of nucleotide names include deoxyadenosine monophosphate (dAMP), deoxyguanosine monophosphate (dGMP), and deoxythymidine monophosphate (dTMP).
DNA Structure
- The DNA double helix structure was discovered by James Watson and Francis Crick in 1953.
- The structure consists of two helical polynucleotide chains coiled around a common axis.
- The chains run in anti-parallel directions, and the phosphate and deoxyribose units are outside the helix.
- The purine and pyrimidine bases are inside the helix, and the planes of the bases are perpendicular to the helix axis.
- The diameter of the helix is 20A, and the adjacent bases are separated by 34A along the helix.
- The helical structure repeats after 10 residues on each chain at intervals of 34A.
- The two chains are held together by hydrogen bonds between pairs of bases.
- Adenine pairs with thymine, and guanine pairs with cytosine.
- Any sequence of bases may occur along a polynucleotide chain, and the precise sequence of bases carries genetic information.
Chargaff's Rule
- Chargaff's Rule, also known as the Fidelity Rule, states that the concentration of adenine is equal to that of thymine, and the concentration of guanine is equal to that of cytosine.
- This rule was discovered by Erwin Chargaff in 1950 and provided important clues about the structure of DNA.
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Description
Test your knowledge on the basic monomer building blocks of nucleic acids, composed of a pentose sugar, nitrogenous base, and phosphate molecules. Learn about nucleosides, which are formed when a purine or pyrimidine base is linked to a sugar molecule, usually Ribose or Deoxyribose.