12.2 BIOLOGY

Which of the following statements correctly describes Chargaff's contribution to the study of DNA?

Chargaff showed that adenine and thymine were found in equal percentages in DNA, but he did not know this was because of base-pairing.

What is the chronological order of the important discoveries in the structure of DNA?

Chargaff's ratios of nucleotides ®Â Franklin makes an X-ray diffraction photo of DNA ® Watson and Crick identify the double helixÂ

DNA is a nucleic acid made up of nucleosomes joined into long strands or chains by covalent bonds.

False

Which scientist made x-ray diffraction photos of DNA?

Franklin

Which of the following best describes Rosalind Franklin's contribution to our understanding of the structure of DNA?

She purified large amounts of DNA, stretched the fibers so the strands were parallel, and used an X-ray beam to produce an image of the molecule

Which scientist(s) figured out that the shape of a DNA molecule is a double helix?

Watson and Crick

Which of the following forms a base pair with thymine?

adenine

Which of the following is a nucleotide found in DNA?

deoxyribose + phosphate group + cytosine

The Watson and Crick model of DNA is a(an) _, in which two strands are wound around each other.

double helix

Watson and Crick discovered that covalent bonds hold base pairs together at the center of a strand of DNA.

false

_ are weak bonds that hold the two strands of DNA together, but also allow the DNA to separate and replicate.

hydrogen bonds

DNA makes a good molecule for storing information because

its bases can be joined together in any order, like the letters of the alphabet can be strung to form different words.

Rosalind Franklin contributed to the understanding of DNA by

producing images of DNA molecules using X-rays.

If covalent bonds held the two strands of nucleotides together, the two strands could not easily separate and _.

replicate

Watson and Crick discovered the two strands in DNA

run in opposite directions.

What structural problem prevents adenine from pairing with guanine?

the bases are both long

Because of base pairing in DNA, the percentage of

thymine molecules in DNA is about equal to the percentage of adenine molecules

Chargaff contributed to the understanding of DNA by figuring out that the percentages of adenine and thymine were almost equal in any sample of DNA.

true

The nucleotides within a DNA strand may have different nitrogenous bases, but all have identical sugar molecules.

true

Watson and Crick used the image of DNA taken by Franklin in their work to figure out the structure of DNA.

true

What did Rosalind Franklin contribute to the effort to identify the structure of DNA?

x-ray diffraction photos of the DNA molecule