Ch.7-1 What Does DNA Look Like

Watson and Crick built a DNA model that resembled a long, twisted ladder. This is because the structure of DNA is a double helix, with two strands that are twisted around each other like a spiral staircase. The ladder-like shape accurately represents the arrangement of the nucleotide bases, which are the building blocks of DNA, along the strands. Each rung of the ladder is formed by a pair of bases, which are connected by hydrogen bonds. Therefore, the description of a long, twisted ladder is an appropriate analogy for the DNA model constructed by Watson and Crick.

The four bases in DNA are represented by the letters A, T, G, and C. These letters stand for adenine, thymine, guanine, and cytosine respectively. Adenine pairs with thymine, and guanine pairs with cytosine in the DNA double helix structure. These four bases are the building blocks of DNA and play a crucial role in genetic information storage and transfer.

A nucleotide is a subunit of DNA that consists of a sugar, a phosphate, and a nitrogenous base. In DNA, nucleotides are the building blocks that make up the DNA molecule. The sugar and phosphate molecules form the backbone of the DNA strand, while the nitrogenous base (which can be adenine, thymine, cytosine, or guanine) pairs with another nitrogenous base on the opposite strand to form the rungs of the DNA ladder. Therefore, nucleotide is the correct answer as it accurately describes the components and structure of a DNA subunit.

Rosalind Franklin used X-ray diffraction to show that the shape of DNA is a spiral. X-ray diffraction is a technique that involves shining X-rays onto a sample and analyzing the pattern of scattered X-rays. Franklin's work provided crucial evidence for the helical structure of DNA, which later led to the discovery of its double helix shape by James Watson and Francis Crick.

DNA, which stands for Deoxyribonucleic acid, is the material that contains the information that determines the traits a living thing inherits. It is a complex molecule made up of nucleotides, which are the building blocks of DNA. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. The four nitrogenous bases found in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). The sequence of these bases in DNA is what carries the genetic information that determines an organism's traits. Therefore, DNA is the correct answer as it is the material where this information is stored.

The sides of the DNA "ladder" are made of sugar and phosphate. DNA is composed of two strands that are twisted together to form a double helix structure. Each strand is made up of repeating units called nucleotides, which consist of a sugar molecule (deoxyribose) and a phosphate group. These sugar-phosphate backbones run along the outside of the DNA molecule, providing stability and support for the nitrogenous bases (guanine, thymine, adenine, and cytosine) that make up the rungs of the ladder. Therefore, the correct answer is sugar and phosphate.

When a DNA molecule is being copied, it undergoes a process called DNA replication. During this process, the DNA molecule unwinds and separates into two strands. The splitting occurs down the middle of the molecule, with each strand acting as a template for the synthesis of a new complementary strand. This splitting down the middle allows for the replication of the DNA molecule, with each resulting molecule containing one original strand and one newly synthesized strand.

Thymine is one of the four possible bases in a string of DNA and it pairs with adenine. In DNA, the four bases are adenine (A), thymine (T), cytosine (C), and guanine (G). Thymine always pairs with adenine through hydrogen bonding, forming a base pair. This base pairing is a crucial mechanism for DNA replication and the transmission of genetic information.

Cytosine is the complementary base to guanine in DNA. In DNA, the bases always pair up in a specific way: adenine with thymine and guanine with cytosine. This is due to their chemical structure and the hydrogen bonding patterns they can form. So, if guanine is present in a DNA strand, its complementary base will always be cytosine.

The "rungs" of the DNA ladder are a pair of bases. In the structure of DNA, the bases (adenine, thymine, cytosine, and guanine) pair up with each other, forming the steps of the DNA ladder. Adenine always pairs with thymine, and cytosine always pairs with guanine, held together by hydrogen bonds. This base pairing is crucial for DNA replication and the transmission of genetic information.