Questions and Answers
What do the letters DNA stand for?
deoxyribonucleic acid
DNA is composed of smaller subunits known as ___?
nucleotides
What are the three parts of a nucleotide?
phosphate group, 5-carbon sugar, nitrogen base
What are the four nitrogen bases found in DNA?
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Two of the nitrogen bases are single ring structures known as ___ and they are ____ and ____.
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The other two nitrogen bases are double ring structures known as ___ and they are ____ and ____.
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Who is the scientist who discovered that A=T and C=G?
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Who took a photograph using a process called X-ray diffraction which provided clues about the structure of DNA?
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Who were the two scientists that discovered the structure of the DNA molecule?
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According to chemical analysis, a chromosome is composed of half ___ and half ___.
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DNA looks like a ladder twisted into a shape known as a ___?
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The two molecules that make up the sides of the ladder or the side portions of a DNA molecule are ___ and __.
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What are the molecules that meet across the middle, forming the steps of the 'ladder' called?
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Which nitrogen bases always pair together?
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Purines will only bind with pyrimidines.
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According to Chargaff's rules, the percentages of ___ are equal to those of thymine and the percentages of ___ are equal to those of guanine in the DNA molecule.
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The nitrogen bases are held together in the center of the molecule by ___ bonds.
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The nitrogen bases are bound to the sugar phosphate by ___ bonds.
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According to the principle of base pairing, hydrogen bonds could form only between adenine and cytosine.
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The type of sugar found in DNA is ___?
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Thin strands of DNA wrapped around proteins called ___ look like beads on a string.
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The process in which DNA builds an exact duplicate of itself is known as ___?
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During replication, the two nucleotide chains separate and each chain serves as a ___ for a new nucleotide chain.
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What are short stretches of DNA that have a specific sequence of nucleotides where replication begins called?
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During replication, enzymes called helicase untwist the double helix, separating the two parental strands and opening a ___.
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A ___ is a 'Y' shaped region at the end of each replication bubble where the new strands of DNA are elongating.
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What are the enzymes called that move along the separated strands assembling the new chains of DNA?
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The replication of DNA begins at one end of the molecule and proceeds to the other end.
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DNA replication occurs simultaneously at many sites along the molecule speeding up the process of replication.
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When replication is complete, how many identical copies of the DNA molecule have been produced?
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Each DNA molecule resulting from replication has one original strand and one new strand.
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What enzyme also proofreads each new DNA strand to ensure that an exact copy has been made?
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DNA may become damaged from exposure to which items?
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The damaged segment of DNA is cut out by enzymes called ___?
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The resulting gap is filled in with new nucleotides by ___.
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Other enzymes, called ___ seal the free ends of the new DNA to the old DNA, making the strand complete.
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Study Notes
DNA Structure and Composition
- DNA stands for deoxyribonucleic acid, a molecule essential for genetic information storage.
- Composed of smaller subunits known as nucleotides, each nucleotide consists of three parts: a phosphate group, a 5-carbon sugar (deoxyribose), and a nitrogen base.
- The four nitrogen bases in DNA are adenine, guanine, cytosine, and thymine.
- Nitrogen bases are categorized as purines (adenine, guanine) and pyrimidines (thymine, cytosine): purines are double-ring structures, while pyrimidines are single-ring structures.
Key Figures in DNA Discovery
- Erwin Chargaff discovered the complementary base pairing rules: A pairs with T and C pairs with G.
- Rosalin Franklin used X-ray diffraction to create images that provided insights into the DNA structure.
- James Watson and Francis Crick are credited with proposing the double helix structure of DNA.
DNA Structure
- The DNA molecule resembles a twisted ladder, known as a double helix.
- The sides of the ladder consist of alternating phosphate and sugar molecules.
- The "steps" of the ladder are formed by pairs of nitrogen bases, held together by hydrogen bonds.
- Base pairing: A (adenine) always pairs with T (thymine), while C (cytosine) pairs with G (guanine).
DNA Replication
- DNA replication is the process in which DNA makes an exact copy of itself.
- It begins at specific sequences called origins of replication.
- Helicase enzymes unwind the double helix, separating parental strands and creating a replication bubble.
- The replication fork is the "Y" shaped region where new DNA strands elongate.
Enzymatic Roles in Replication
- DNA polymerase enzymes synthesize new DNA strands by assembling nucleotides along the separated strands, serving as templates.
- Replication is not linear; it occurs simultaneously at multiple sites along the DNA, increasing speed.
- DNA polymerase also proofreads newly synthesized strands to ensure accurate replication.
- Nucleases remove damaged segments of DNA, while DNA polymerase fills gaps with new nucleotides.
- Ligases seal the ends of new DNA strands to the original DNA, completing the replication process.
DNA Integrity and Repair
- DNA can be damaged by chemicals, radiation, X-rays, ultraviolet light, and cigarette smoke.
- Methods for repairing DNA include cutting out damaged segments with nucleases and filling gaps with nucleotides using DNA polymerase, followed by sealing with ligases.
Important Facts
- Each completed replication yields two identical copies of the DNA molecule.
- Each new DNA molecule consists of one original strand and one newly synthesized strand, reinforcing the semiconservative model of replication.
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Description
This quiz explores the essential components of DNA, including its structure, composition, and key figures involved in its discovery. Test your knowledge on nucleotides, nitrogen bases, and the double helix model proposed by Watson and Crick. Discover how Chargaff and Franklin contributed to our understanding of DNA.
