Topic 1B

Question 1

nucleotide

Answer 1

a constituent of nucleic acids, consisting of a 5-carbon sugar, a nitrogen-containing base, and one or more phosphate groups

Question 2

explain the purposes and components of a nucleotide:

Answer 2

the 5-carbon sugars and phosphate forms the backbone of the molecule, the nitrogen base sticks out and gives each nucleotide its chemical identity

Question 3

deoxyribose

Answer 3

the sugar in DNA

Question 4

what happens to the hydroxyl group at cellular pH (7)?

Answer 4

the free hydroxyl groups become negatively charged by losing a proton (the two oxygen atoms have a negative charge)

Question 5

purines

Answer 5

double-ring structures

Question 6

pyrimidines

Answer 6

single-ring structures

Question 7

what are the purines?

Answer 7

adenine (A) and guanine (G)

Question 8

what are the pyrimidines?

Answer 8

thymine (T) and cytosine (C)

Question 9

nucleoside

Answer 9

a molecule consisting of a 5-carbon sugar and a base

Question 10

what are the nitrogen containing bases?

Answer 10

A, G, (purines) and T, C, (pyrimidines)

Question 11

what molecule is used to form nucleotide polymers (DNA, RNA)?

Answer 11

nucleoside triphosphate (nucleosides-sugar+base and three phosphate groups)

Question 12

phosphodiester bond

Answer 12

a bond that forms when a phosphate group in one nucleotide is covalently joined to the sugar unit in another nucleotide. Phosphodiester bonds are relatively stable and form the backbone of a DNA strand

Question 13

polarity

Answer 13

an asymmetry such that one end of a structure differs from the other- caused in a strand of DNA by the phosphodiester linkages

Question 14

5’ end

Answer 14

the end of a nucleic acid strand containing a free 5’ phosphate group (top)

Question 15

3’ end

Answer 15

the end of a nucleic acid strand that carries a free 3’ hydroxyl (bottom)

Question 16

in the double helix model, where are the components of the nucleotides located?

Answer 16

the sugar-phosphate backbones point wind outwards with the bases pointing inward

Question 17

major groove

Answer 17

the larger of two uneven grooves on the outside of a DNA duplex

Question 18

minor groove

Answer 18

the smaller of two unequal grooves to the outside of a DNA duplex

Question 19

why are the grooves important?

Answer 19

proteins that interact with DNA often recognize a particular sequence of bases by making contact with the bases via either/both the major/minor grooves

Question 20

antiparallel

Answer 20

oriented in opposite directions; the strands in a DNA duplex are antiparallel

Question 21

complementary

Answer 21

describes the relationship of purine and pyrimidine bases, in which the base A pairs only with T and G pairs only with C

Question 22

what explains the specificity of complementary base pairs?

Answer 22

hydrogen bonds (A-T has 2) and (G-C has 3)

Question 23

what contributes to the stability of the DNA double helix

Answer 23

the total number of hydrogen bonds between base pairs and base stacking

Question 24

base stacking

Answer 24

stabilizing hydrophobic interactions between bases in the same strand of DNA

Question 25

brief explanation for how replication of DNA occurs:

Answer 25

strands unwind and each strand serves as a "parent" or template to create daughter strands

Question 26

supercoil

Answer 26

a coil of coils; a circular molecule of DNA can coil upon itself to form a supercoil-seen in prokaryotes

Question 27

topoisomerase

Answer 27

any one of a class of enzymes that regulates the supercoiling of DNA by cleaving one or both strands of the DNA double helix, and later repairing the break

Question 28

how are DNA molecules shaped in eukaryotic cells?

Answer 28

linearly

Question 29

chromosome

Answer 29

in eukaryotes, the physical structure in which DNA in the nucleus is packaged

Question 30

chromatin

Answer 30

a complex of DNA, RNA, and proteins (histones) that gives chromosomes their structure; chromatin fibres are either 30 nm in diameter or, in a relaxed state, 10 nm

Question 31

evolutionarily conserved

Answer 31

characteristics that persist relatively unchanged through diversification of a group of organisms and therefore remain similar in related species

Question 32

why do histone proteins (found in all eukaryotes) interact with double-stranded DNA without regard to sequence?

Answer 32

because the proteins are evolutionarily conserved

Question 33

the more distantly related two organisms that share conserved sequences...

Answer 33

the more highly conserved the sequence is

Question 34

the genomes of ALL organisms are ______ relative to the size of the cell

Answer 34

large

Question 35

describe bacterial genomes:

Answer 35

circular, the DNA double helix is under-wound (fewer turns in going around the circle)-caused by topoisomerase II

Question 36

topoisomerase II

Answer 36

an enzyme that breaks a DNA double helix, rotates the ends, and seals the break

Question 37

what does under-winding create on the DNA molecule

Answer 37

strain (relieved by formation of supercoils)

Question 38

what are supercoils that result from under-winding called?

Answer 38

negative supercoils

Question 39

what are supercoils that result from over-winding called?

Answer 39

positive supercoils

Question 40

what kind of supercoils form in DNA in most organisms?

Answer 40

negative supercoils

Question 41

nucleoid

Answer 41

in prokaryotes, a cell structure with multiple loops formed from supercoils of DNA

Question 42

how is DNA packaged in eukaryotes?

Answer 42

the linear DNA forms a single chromosome which is packaged with histone proteins into a complex called chromatin

Question 43

nucleosome

Answer 43

a beadlike repeating unit of histone proteins wrapped with DNA making up the 10-nm chromatin fibre

Question 44

how many histone proteins are in a nucleosome

Answer 44

8 (2 of each-H2A, H2B, H3, and H4)

Question 45

describe the components of a histone protein:

Answer 45

amino acids:lysine and arginine, with positive charges

Question 46

10-nm fibre

Answer 46

a relaxed 30-nm chromatin fibre, the state of the chromatin fibre in regions of the nucleus where transcription is currently taking place

Question 47

30-nm fibre

Answer 47

a chromosomal conformation created by the folding of the nucleosome fibre of DNA and histones

Question 48

chromosome condensation

Answer 48

the progressive coiling of the chromatin fibre, an active, energy-consuming process requiring the participation of several types of proteins

Question 49

scaffold

Answer 49

a supporting protein structure in a metaphase chromosome-how DNA spreads out without histones

Question 50

homologous chromosomes

Answer 50

pairs of chromosomes, matching in size and appearance, that carry the same set of genes; one of each pair was received from the mother, the other from the father

Question 51

at what stage are chromosomes in chromosome paintings?

Answer 51

metaphase of mitosis

Question 52

karyotype

Answer 52

a standard arrangement of chromosomes, showing the number and shapes of the chromosomes representative of a species

Question 53

Since the DNA in each pair of homologous chromosomes is different from that in any other pair of homologous chromosomes....

Answer 53

a particular labeled DNA fragment hybridizes (marks) only with the two homologs of one chromosomes

Question 54

what is the relationship between chromosome number and genome size?

Answer 54

there is no relationship

Question 55

because each type of organelle has its own DNA, this means that...

Answer 55

eukaryotic cells will have multiple genomes

Question 56

nuclear genome

Answer 56

in eukaryotic cells, the DNA in the chromosomes

Question 57

mitochondrial genome

Answer 57

in eukaryotic cells, the DNA in the mitochondria

Question 58

chloroplast genome

Answer 58

in photosynthetic eukaryotes, the genome of the chloroplast

Question 59

how is organelle DNA packaged?

Answer 59

as a nucleoid rather than a chromosome (similar to bacterial ancestors)-difference between structures of mitochondria/chloroplast nucleoid