DNA Structure (Chapter 16)
Tight helical fiber
(7)
What are chromosomes made of?
(DNA and Proteins) Long DNA molecules are associated with proteins that allow DNA to coil and pack.
Purines are
2 linked ring structures (nucleic acids)
A nucleotide consists of:
A nucleotide consists of three things: A nitrogenous base, which can be either adenine, guanine, cytosine, or thymine (in the case of RNA, thymine is replaced by uracil). A five-carbon sugar, called deoxyribose because it is lacking an oxygen group on one of its carbons. One or more phosphate groups.
A to ___ C to ___
A to T C to G
Erwin Chargaff observed that the proportions of adenine (A) and thymine (T) bases were always equal, as were the proportion of guanine (G) and cytosine (C). Chargaff's observation suggests which of the following statements?
Chargaff's observation was an important clue to the A-T and G-C pairings that Watson and Crick eventually proposed.
Chargaff's rules
Chargaff's rules states that DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine
What are the chemical components of a DNA molecule?
DNA is composed of a sequence of subunits, each containing a phosphate, a deoxyribose sugar, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G), or cytosine (C).
In a nucleosome, the DNA is wrapped around
Histones
Why do histones bind tightly to DNA?
Histones are positively charged, and DNA is negatively charged.
Which of the following is true of DNA during interphase?
It exists as chromatin and is less condensed than mitotic chromosomes. Chromatin is the term for the loosely coiled DNA observed in cells during interphase. Even during interphase, however, parts of the chromosome may still be rather tightly coiled and packed.
What did Rosalind Franklin's famous photo 51 show?
The "X" pattern of the X-ray crystallography image matched the shape that Crick predicted for a helix.
In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.
The nitrogenous base is attached to the sugar's 1' carbon and the phosphate group is attached to the sugar's 5' carbon.
What did the structure of DNA's double helix suggest about DNA's properties?
The structure of DNA suggested that the order of bases contains information. Because A is always paired with T and G with C, the order of bases on one strand determines the order on the other strand. Thus, if a DNA molecule were unwound, each strand could be copied into a complementary strand, producing an exact replica of the original molecule.
Which of the following statements describes a eukaryotic chromosome?
a single linear molecule of double-stranded DNA plus proteins
chromosome consists of ____ of ___ made up of ___ ____ ___ composed of ____ that consist of ___ wrapped around ____ molecules called ___
chromosome consists of LOOPS of SUPERCOILS made up of TIGHT HELICAL FIBERS composed of NUCLEOSOMES that consist of DNA wrapped around PROTEIN molecules called HISTONES
It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?
sequence of bases
Pyrimidines are
single-ring structures (nucleic acids)
In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.
thymine ... cytosine
Nucleic acids are assembled in the _____ direction.
→ 5' to 3' →New nucleotides are added to the 3' end of a growing polynucleotide.
In the 1950s, when Watson and Crick were working on their model of DNA, which concepts were well accepted by the scientific community?
→Chromosomes are found in the nucleus. →Chromosomes are made up of protein and nucleic acid. →Genes are located on chromosomes. →When Watson and Crick began working on their model, scientists knew that genes were found on chromosomes in the nucleus and that chromosomes were composed of proteins and nucleic acid. Watson and Crick were two of the few to focus on the nucleic acid, DNA, instead of proteins.
In the early 1950s, many researchers were racing to describe the structure of DNA using different approaches. Which of the following statements is true?
→Jim Watson and Francis Crick built theoretical models, incorporating current knowledge about chemical bonding and X-ray data. →Different scientists took different approaches to understanding the structure of DNA, based upon their training and the tools available. In the end, the problem was solved using all these different approaches.
Which of these is a difference between a DNA and an RNA molecule?
→With some exceptions, DNA is a double-stranded molecule and RNA is a single-stranded molecule. →RNA has an extra O in the sugar (ribose instead of deoxyribose) →DNA contains thymine, whereas RNA contains uracil.