Podcast
Questions and Answers
What major concept did Phoebus Levene's tetranucleotide theory propose about the structure of DNA?
What major concept did Phoebus Levene's tetranucleotide theory propose about the structure of DNA?
- DNA consists of only four nitrogenous bases.
- DNA has a complex, varied structure.
- DNA can be formed from multiple flavors of nucleotides.
- DNA is made up of nucleotides in equal proportions. (correct)
What distinguishes deoxyribose from ribose in its chemical structure?
What distinguishes deoxyribose from ribose in its chemical structure?
- Deoxyribose has a hydroxyl group at 2'.
- Deoxyribose contains one less oxygen atom than ribose. (correct)
- Ribose is used in DNA while deoxyribose is found in RNA.
- Ribose has one less carbon atom than deoxyribose.
Which nitrogenous base is NOT found in DNA?
Which nitrogenous base is NOT found in DNA?
- Thymine
- Adenine
- Uracil (correct)
- Cytosine
What type of bond links the 3' carbon of one nucleotide to the 5' carbon of another in DNA?
What type of bond links the 3' carbon of one nucleotide to the 5' carbon of another in DNA?
How did Chargaff's findings challenge Levene's tetranucleotide theory?
How did Chargaff's findings challenge Levene's tetranucleotide theory?
What type of chemical bonds are formed between the sugar and phosphate groups in nucleotides?
What type of chemical bonds are formed between the sugar and phosphate groups in nucleotides?
What was one of the implications of Levene's tetranucleotide theory on the perception of DNA as genetic material?
What was one of the implications of Levene's tetranucleotide theory on the perception of DNA as genetic material?
What important aspect of DNA's structure is defined by the existence of polarity?
What important aspect of DNA's structure is defined by the existence of polarity?
What did Chargaff determine about the base composition in organisms?
What did Chargaff determine about the base composition in organisms?
Which structural motif did Linus Pauling describe?
Which structural motif did Linus Pauling describe?
What was a key technique used by Pauling to study molecular structures?
What was a key technique used by Pauling to study molecular structures?
What occurs when light passes through an opening comparable to its wavelength?
What occurs when light passes through an opening comparable to its wavelength?
What was the result of using two slits in a diffraction experiment?
What was the result of using two slits in a diffraction experiment?
Who demonstrated that diffraction could occur around a solid object?
Who demonstrated that diffraction could occur around a solid object?
What does a closer diffraction spot indicate in an X-ray diffraction pattern?
What does a closer diffraction spot indicate in an X-ray diffraction pattern?
What happens to the interference fringes when features are spatially separated?
What happens to the interference fringes when features are spatially separated?
What type of bond holds complementary base pairs together in DNA?
What type of bond holds complementary base pairs together in DNA?
What structural feature does the Watson-Crick model of DNA include?
What structural feature does the Watson-Crick model of DNA include?
What is the main reason Levene's tetranucleotide theory was ultimately dismissed?
What is the main reason Levene's tetranucleotide theory was ultimately dismissed?
Which of the following nitrogenous bases is a purine?
Which of the following nitrogenous bases is a purine?
Flashcards
What are the 4 nitrogenous bases in DNA?
What are the 4 nitrogenous bases in DNA?
Adenine, Guanine, Cytosine, and Thymine are the four nitrogenous bases found in DNA. They are the building blocks of DNA.
What type of sugar is found
in DNA?
What type of sugar is found in DNA?
Deoxyribose is a 5-carbon sugar that is part of the DNA backbone.
What is a nucleoside?
What is a nucleoside?
A nucleoside is formed when a nitrogenous base is attached to a sugar molecule. The bond between the base and the sugar is called a glycosidic bond.
What is a nucleotide?
What is a nucleotide?
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What is DNA?
What is DNA?
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What is the 5' to 3' directionality of DNA?
What is the 5' to 3' directionality of DNA?
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What is the tetranucleotide theory?
What is the tetranucleotide theory?
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What is Chargaff's rule?
What is Chargaff's rule?
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What are Chargaff's rules?
What are Chargaff's rules?
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Who is Linus Pauling and what major contribution did he make to science?
Who is Linus Pauling and what major contribution did he make to science?
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What is X-ray crystallography and how does it work?
What is X-ray crystallography and how does it work?
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What is the significance of the 'cross' in X-ray diffraction patterns?
What is the significance of the 'cross' in X-ray diffraction patterns?
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How do distances in the molecule relate to the diffraction pattern?
How do distances in the molecule relate to the diffraction pattern?
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What was significant about 'Photo 51'?
What was significant about 'Photo 51'?
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Study Notes
DNA Structure
- In 1930, Phoebus Levene demonstrated that DNA's building blocks are nucleotides.
- Nucleotides consist of phosphate, deoxyribose sugar, and a nitrogenous base.
- Nitrogenous bases include Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
- Levene's tetranucleotide theory (1909): DNA was simple and repetitive. It was incorrect to assume that DNA is not a genetic material.
Sugar in DNA
- DNA uses deoxyribose sugar.
- Ribose sugar, instead of deoxyribose, contains a hydroxyl group at the 2' carbon.
Nitrogenous Bases
- Purines:
- Adenine (A)
- Guanine (G)
- Pyrimidines:
- Cytosine (C)
- Thymine (T)
- Uracil (U - only in RNA)
Nucleosides and Nucleotides
- A nucleoside forms from a base and the sugar.
- A nucleotide is a phosphorylated nucleoside.
- Sugar connects to the base via glycosidic bonds
- Phosphate groups attach to the sugar.
Nucleotide Nomenclature
- Nucleotides are named based on the base (A, G, C, or T) and the number of phosphate groups (mono-, di-, or tri-phosphate).
- Examples include dAMP, dADP, and dATP.
DNA Structure Summary
- The DNA backbone is a chain of alternating sugar and phosphate groups.
- Bases are linked to the sugar and face inwards.
- DNA is a double helix with the strands running antiparallel (5' to 3' and 3' to 5').
- Complementary base pairing (A with T, G with C) holds the two strands together via hydrogen bonds.
- DNA has a defined polarity (5' and 3' ends).
Chargaff's Rules (1950)
- The amount of adenine equals thymine, and the amount of guanine equals cytosine in DNA.
- The base ratio differs between different organisms.
X-Ray Crystallography
- X-ray diffraction patterns of DNA could reveal the structure.
- X-ray images revealed DNA's helical structure.
Importance of Photo 51
- Rosalind Franklin and Raymond Gosling produced Photo 51 (X-ray image of DNA) with hydrated DNA.
- The X-ray was crucial for deciphering DNA's double helix structure.
The Watson-Crick Model (1953)
- James Watson and Francis Crick deduced the double helix structure of DNA using X-ray diffraction data and Chargaff's rules.
- The model had a double helix with antiparallel strands and specific base pairing.
- The sugar-phosphate backbones are on the outside, and the bases face inward.
- The base-pairs are stacked in a way to produce a minor and major groove in the structure of DNA.
DNA Structural Variants
- DNA exists in several forms (A-, B-, and Z-DNA).
- Variations are dependent on environmental conditions such as hydration.
- B-DNA is most prevalent under physiological conditions (water).
- A-DNA occurs under low-hydration conditions and some other conditions (e.g presence of other molecules or solvents)
- Z-DNA is a left-handed double helix.
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Description
Test your knowledge on the structure of DNA, including its building blocks, nucleotides, and sugar components. This quiz covers key concepts such as nitrogenous bases and the differences between nucleosides and nucleotides. Prepare to explore the intricate details that make up genetic material.
