Ch 8 DNA: The Chemical Nature of the Gene

Question 1

nucleotides

Answer 1

a large, number of linked, repeating units

each contains a sugar, a phosphate, and a base

Question 2

ribose

Answer 2

RNA’s sugar, has a hydroxyl group (–OH) attached to the 2’-carbon atom

Question 3

deoxyribose

Answer 3

DNA’s sugar, has a hydrogen atom (–H) at this position and therefore contains one oxygen atom fewer over all

Question 4

two purines found in DNA and RNA

Answer 4

adenine and guanine (A and G), which differ in the positions of their double bonds and in the groups attached to the six-member ring

Question 5

three pyrimidines common in nucleic acids

Answer 5

cytosine (C), thymine (T), and uracil (U)

cytosine is present in both DNA and RNA; however, thymine is restricted to DNA, and uracil is found only in RNA

Question 6

nucleoside

Answer 6

a deoxyribose or a ribose sugar and a base together

Question 7

phosphate group

Answer 7

consists of a phosphorus atom bonded to four oxygen atoms

frequently carry a negative charge, which makes DNA acidic

Question 8

phosphodiester linkages

Answer 8

strong covalent bonds that link the 5’-phosphate group of one nucleotide to the 3’-hydroxyl group of the next nucleotide

Question 9

polynucleotide strand

Answer 9

a series of nucleotides linked in phosphodiester linkages

Question 10

5’ end

Answer 10

a free phosphate group (meaning that it’s unattached on one side) is attached to the 5’-carbon atom of the sugar in the nucleotide

Question 11

3’ end

Answer 11

the other end has a free OH group attached to the 3’-carbon atom of the sugar

Question 12

antiparallel

Answer 12

the two polynucleotide strands run in the opposite directions; the 5’ end of one strand is opposite the 3’ end of the other strand

Question 13

complementary DNA strands

Answer 13

the two polynucleotide strands of a DNA molecule are therefore not identical; provides for efficient and accurate DNA replication

Question 14

transcription

Answer 14

the information is transferred from DNA to RNA, information remains in the language of nucleic acids

Question 15

translation

Answer 15

the information must be translated from the language of nucleotides into the language of amino acids
info passes from RNA to protein

Question 16

replication

Answer 16

information passes from one DNA molecule to other DNA molecules

Question 17

reverse transcription

Answer 17

transfer from RNA to DNA

Question 18

RNA replication

Answer 18

some RNA viruses transfer information from RNA to RNA

Question 19

supercoiling

Answer 19

a type of DNA structure which takes place when the DNA helix is subjected to strain by being overwound or underwound

Question 20

relaxed state

Answer 20

a stretch of 100 bp of DNA would assume about 10 complete turns

Question 21

positive supercoiling

Answer 21

molecules that are overrotated

Question 22

negative supercoiling

Answer 22

underrotated molecules

Question 23

topoisomerases

Answer 23

supercoiling relies on enzymes that add or remove rotations from the DNA helix by temporarily breaking the nucleotide strands, rotating the ends around each other, and then rejoining the broken ends

Question 24

two advantages for DNA being negatively supercoiled

Answer 24

1) makes the separation of the two strands of DNA easier during replication and transcription
2) the supercoiled DNA can be packed into a smaller space than can relaxed DNA

Question 25

nucleoid

Answer 25

bacterial cell DNA appears as a distinct clump which is confined to a definite region of the cytoplasm

Question 26

chromatin

Answer 26

the combination of DNA and protein

Question 27

two basic types of chromatin

Answer 27

euchromatin and heterochromatin

Question 28

euchromatin

Answer 28

undergoes the normal process of condensation and decondensation in the cell cycle

Question 29

heterochromatin

Answer 29

remains in a highly condensed state throughout the cell cycle, even during interphase
most of the centromere is made up of this

Question 30

histones

Answer 30

most abundant proteins in chromatin

small, positively charged proteins of five major types: H1, H2A, H2B, H3, and H4

Question 31

nucleosome

Answer 31

the repeating core of protein and DNA produced by digestion with nuclease enzymes is the simplest level of chromatin structure

Question 32

linker DNA

Answer 32

nucleosomes are located at regular intervals along the DNA molecule and are separated from one another by this, which varies in size among cell types; in most cells, it comprises from about 30 to 40 bp

Question 33

epigenetic changes or epigenetics

Answer 33

alterations of chromatin structure that are passed on to descendant cells or individuals

Question 34

telomeric sequences

Answer 34

usually repeated units of a series of adenine or thymine nucleotides followed by several guanine nucleotides

Question 35

shelterin

Answer 35

a multiprotein complex binds to telomeres and protects the ends of the DNA from being inadvertently repaired as a double-strand break in the DNA

Question 36

repetitive DNA

Answer 36

exist in many copies

Question 37

deoxyribonucleotides

Answer 37

DNA nucleotides are properly known as this

Question 38

ribonucleotides

Answer 38

equivalent RNA nucleotides are this

Question 39

central dogma

Answer 39

states that genetic information passes from DNA to protein in a one-way information pathway

Question 40

nonhistone chromosomal proteins

Answer 40

a heterogeneous assortment, also found in eukaryotic chromosomes
also called chromosome scaffold proteins

Question 41

core DNA

Answer 41

DNA wrapped around the core particle (histone octamer)

Question 42

10-nm fiber

Answer 42

electron micrographs of DNA in its least condensed state

Question 43

solenoid structure

Answer 43

6-8 nucleosomes per turn and histones H1 stabilizing

Question 44

300-nm fiber

Answer 44

interphase chromosomes have variably sized loops of 30-nm fibers that form this

Question 45

metaphase chromatin

Answer 45

compacted 250-fold; condensed chromatin 1400-nm

Question 46

radial loop scaffold model

Answer 46

nonhistone proteins anchor chromatin loops (20 to 100 kb) to MARs (matrix attachment regions)