DNA Structure and Nucleotides Quiz

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Questions and Answers

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?

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?

Thymine

Adenine

Uracil (correct)

Cytosine

What type of bond links the 3' carbon of one nucleotide to the 5' carbon of another in DNA?

Phosphodiester bond Signup and view all the answers

How did Chargaff's findings challenge Levene's tetranucleotide theory?

He found that nucleotides were not present in equal proportions. Signup and view all the answers

What type of chemical bonds are formed between the sugar and phosphate groups in nucleotides?

Ester bonds Signup and view all the answers

What was one of the implications of Levene's tetranucleotide theory on the perception of DNA as genetic material?

It implied DNA was repetitive and too simple for genetic encoding. Signup and view all the answers

What important aspect of DNA's structure is defined by the existence of polarity?

Each DNA strand has a 5’ end and a 3’ end. Signup and view all the answers

What did Chargaff determine about the base composition in organisms?

% T = % A and % G = % C Signup and view all the answers

Which structural motif did Linus Pauling describe?

Alpha helix Signup and view all the answers

What was a key technique used by Pauling to study molecular structures?

X-ray crystallography Signup and view all the answers

What occurs when light passes through an opening comparable to its wavelength?

Diffraction Signup and view all the answers

What was the result of using two slits in a diffraction experiment?

Complex double slit interference pattern Signup and view all the answers

Who demonstrated that diffraction could occur around a solid object?

Augustin Fresnel Signup and view all the answers

What does a closer diffraction spot indicate in an X-ray diffraction pattern?

Smaller actual distance in the target Signup and view all the answers

What happens to the interference fringes when features are spatially separated?

Distant features produce widely separated reflections Signup and view all the answers

What type of bond holds complementary base pairs together in DNA?

Hydrogen bonds Signup and view all the answers

What structural feature does the Watson-Crick model of DNA include?

Anti-parallel strands Signup and view all the answers

What is the main reason Levene's tetranucleotide theory was ultimately dismissed?

It did not account for genetic variability. Signup and view all the answers

Which of the following nitrogenous bases is a purine?

Guanine Signup and view all the answers

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.