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Questions and Answers
What are the three domains of life as per the three-domain system introduced by Carl Woese?
Archaea, Bacteria, Eukaryote
James Watson and Francis Crick were the first to publish a paper on the structure of DNA.
True
Which scientist is known for performing X-ray diffraction studies of DNA?
What is the primary repeat distance of DNA fibers observed in X-ray diffraction studies?
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What type of molecule is DNA?
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Which of the following are types of nitrogen-containing bases found in DNA?
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What sugar molecule is found in nucleotides of DNA?
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The backbone of DNA consists of alternating sugar-______ sequences.
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What type of bond exists between adenine and thymine in DNA?
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What is the most common DNA structure in solution?
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RNA molecules are typically double-stranded.
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Which base is found in RNA but not in DNA?
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Study Notes
The Three Domain System
- Carl Woese proposed the three-domain system in 1990, which classifies cellular life into: Archaea, Bacteria, and Eukaryotes.
- The key difference from earlier classifications is the separation of Archaea from Bacteria.
Structure of DNA
- DNA is a two-stranded molecule with a unique double helix shape.
- The structure of DNA was determined by James Watson and Francis Crick, following research from other scientists like Linus Pauling, Maurice Wilkins, and Rosalind Franklin.
- X-ray diffraction studies by Rosalind Franklin and Maurice Wilkins revealed that DNA molecules are helical with two periodicities:
- a primary repeat of 3.4 Ã…
- a secondary repeat of 34 Ã…
DNA Nucleotides
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Each strand of DNA is made up of nucleotides.
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Each Nucleotide consists of:
- a phosphate molecule
- a sugar molecule called deoxyribose, containing five carbons
- a nitrogen-containing region, called a base.
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There are four types of nitrogen-containing bases:
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T) in DNA only
Nucleosides vs. Nucleotides
- A nucleoside consists of one of the four DNA bases attached to the C1' position of a sugar.
- The sugar in deoxynucleosides is 2'-deoxyribose.
- Nucleosides differ from nucleotides as they lack phosphate groups.
DNA Backbone & Hydrogen Bonds
- The DNA backbone is a polymer with an alternating sugar-phosphate sequence.
- The phosphate molecules connect to the sugar molecules at both the 3'- and 5'-hydroxyl groups in ester links, also known as "phosphodiester" bonds.
- Hydrogen bonds hold the two strands together, linking specific bases:
- Adenine (A) forms two hydrogen bonds with Thymine (T).
- Guanidine (G) forms three hydrogen bonds with Cytosine (C).
Complementarity & Directionality
- The two strands of DNA are antiparallel, meaning they run in opposite directions.
- The strands are complementary, meaning A always pairs with T and G always pairs with C.
- Base pairing creates a stronger G-C bond compared to an A-T bond due to the three hydrogen bonds present.
DNA Structure in Solution
- The most common DNA structure in solution is the B-DNA.
- The B-DNA conformation can change under different conditions, leading to A-DNA or Z-DNA.
- A-DNA, B-DNA, and Z-DNA differ in their handedness, width, and length.
- Z-DNA is a left-handed helix, while A-DNA and B-DNA are right-handed.
RNA vs. DNA
- RNA molecules are single-stranded, while DNA is double-stranded.
- RNA contains ribose sugar (with an –OH at the 2' C position) compared to the deoxyribose sugar in DNA which has an –H at that position.
- Uracil (U) replaces Thymine (T) in RNA.
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Description
Explore the fundamental concepts of cellular classification and the structure of DNA in this quiz. Learn about the three-domain system proposed by Carl Woese and the double helix shape of DNA discovered by Watson and Crick. Test your knowledge on nucleotides and the significant contributions of various scientists to our understanding of DNA.
