Molec Cell Chapters 4, 5 & 6 Smartwork

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91 Terms

1
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A mutation that increases the affinity for GTP and a mutation that results in an increase associated with guanine exchange factors are

more active

2
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A mutation that increases the GTPase activity and a mutation that increases the affinity for GDP are

less active

3
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A disulfide bond is a

covalent interaction within the protein

4
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What is true of prion proteins?

  • they are misfolded forms of normal proteins

  • they can spread from one organism to another

5
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What is NOT true of prion proteins?

  • they cannot spread from cell to cell

  • they form unstable protein aggregates

6
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In an alpha helix, hydrogen bonds form between what?

every fourth amino acid

7
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Protein molecules that have a quaternary structure must have two or more of what?

polypeptide chains

8
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What is the definition of a protein-binding site?

any region on a proteins surface that interacts with another molecule through noncovalent bonding

9
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What does the primary structure of a protein refer to?

the linear amino acid sequence of the protein

10
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What do the segments of a transmembrane protein that cross the lipid bilayer usually consist of?

an alpha helix with mostly nonpolar side chains

11
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Generally speaking, what determines the biological activity of a protein?

amino acid sequence

12
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Which part of an amino acid gives it its unique properties?

side chain

13
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What parts of amino acids are involved in a peptide bond?

amino group of one amino acid and side chain of another

14
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Which amino acid is involved in the formation of disulfide bonds?

cysteine

15
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What would happen to the secondary structure of a protein if an alcohol that disrupts hydrogen-bonding were added

  • the beta sheets would unfold, disrupting protein structure

  • the alpha helices would unfold, disrupting protein structure

16
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Both alpha helices and beta sheets:

  • formed by hydrogen-bonding between backbone atoms

  • can be formed by many sequences

17
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Beta sheets only:

  • side chains alternating above and below the structure

  • consists of antiparallel or parallel strands

18
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Alpha helices only:

  • cylindrical structure

  • one full turn every 3.6 amino acids

19
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In a cytosolic folded protein, what orientation and/or interaction do the hydrophobic amino acids tend to have?

  • theyre tucked away inside the protein

  • theyre interacting with other nonpolar amino acids

20
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Enzymes can have both active and regulatory sites. What is the purpose of these sites?

the binding of CTP at a regulatory site on the protein causes decreased production of carbamoyl aspartate

21
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Ras is a

GTP-binding protein involved in cell division (proliferation)

22
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Ras activates

cell signaling pathways that promote cell division

23
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Mutations in the gene that encodes Ras can lead to

cancer

24
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How might mutations in the gene encoding Ras lead to the uncontrolled proliferation characteristic of cancer cells?

they decrease the rate at which Ras hydrolyzes GTP

25
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How does the GTP bound form of a GTP-binding protein switch to a GDP-bound form?

it hydrolyzes GTP, releasing a phosphate

26
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Many proteins are regulated by the binding of

GTP or GDP

27
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Which form is the active state of a protein?

the GTP-bound form

28
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Phosphorylation is the only form of covalent modification that can affect a protein’s activity or location. True or false?

false

29
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Phosphorylation can only take place in the cell nucleus. True or false?

false

30
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The formation of an alpha helix is governed by

hydrogen bonding between atoms that are not in the side chains

31
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What level of protein structure involved the interaction of more than one polypeptide chain into a 3-D structure?

quaternary

32
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A binding site on the surface of a protein interacts specifically with another protein through

many weak noncovalent interactions

33
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Disulfide bonds stabilize protein shape outside the cell by

covalent bonds between cysteines

34
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The function of feedback inhibition of an enzymatic pathway is to

turn off synthesis of a product when it is in abundance

35
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When a ligan binds to an allosteric enzyme’s regulatory site, it changes the activity of that enzyme by

inducing a conformational change

36
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How does phosphorylation of a protein affect its activity?

could increase or decrease activity

37
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How does binding of GTP to a GTP-binding protein affect its activity?

always activates the protein

38
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Chemical modifications like phosphorylation and acetylation of proteins occur on

side chains of amino acids and can affect interaction of proteins with other cell components or structures

39
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Unsequenced DNA is likely part of

euchromatin

40
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Centromeric DNA is likely to be

sequenced in all samples

41
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Which chemical group is at the 3’ end of a DNA strand?

hydroxyl group

42
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Prokaryotes have chromosomes that are

circular in structure

43
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Prokaryotic chromosomes would lack

telomeres, centromeres, and a nucleus

44
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The majority of human DNA does not code for genes. True or false?

true

45
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What histone protein is thought to act as a linker that pulls nucleosomes together into a regular repearing array, resulting in 30nm fiber?

H1

46
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Because nucleosomes play a key role in packaging DNA into chromosomes, they bind to the DNA molecule very tightly, and once they’re assembled, they cannot be moved. True or false?

false

47
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Histone proteins have a high proportion of

positively charged amino acids, which bind tightly to the negatively charged DNA backbone

48
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Nucleosomes are found only in mitotic chromosomes. True or false?

false

49
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Nucleosomes represent the

first and most fundamental level of chromatin packing

50
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Nucleosomes can be seen in

the electron microscope

51
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A nucleosome consists of

DNA wrapped around 8 histone proteins, plus a short segment of linker DNA

52
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Nucleosomes convert a DNA molecule into a

chromatin thread about 1/3 length of the intial DNA

53
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What structure in an interphase eukaryotic cell is the site of ribosomal RNA transcription?

nucleolus

54
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Telomeres cap the ends of

linear chromosomes and prevent them from being recognized by the cell as broken DNA in need of repair

55
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Telomeres contain

repeated nucleotide sequences that are required to replicate the ends of linear chromosomes

56
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What represents the specializede DNA sequence that attaches to microtubules and allows duplicated eukaryotic chromosomes to be separated during M phase?

centromere

57
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What suggests that the large amount of excess “junk” DNA in a genome may serve an important function?

a portion of “junk” DNA is highly conserved in its DNA sequence among many different eukaryotic species

58
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Duplicated chromosomes are

separated during mitosis of the cell cycle

59
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What alteration would prevent proper chromosome segregation during mitosis?

deletion of the centromere sequence

60
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How do chromatin-remodeling complexes work?

they use energy from ATP hydrolysis to alter the arrangement of nucleosomes, rendering certain regions of the DNA more accessible to other proteins

61
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The tails of the core histone protein can be chemically modified by the covalent addition of

  • acetyl groups

  • methyl groups

  • phosphate groups

62
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What is the name given to the most highly condensed form of chromatin?

heterochromatin

63
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When a cell divides, its chromatin structure is completely reset. True or false?

false

64
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Once heterochromatin has been established, it will often spread until it encounters what?

a barrier DNA sequence

65
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Histone tail modifications establish and maintain the different chromatin structures found in heterochromatin and euchromatin. True or false?

true

66
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Chromatin-remodeling complex uses ATP energy to alter chromatin:

may increase or decrease transcription

67
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Histone acetyltransferase adds acetyl groups to histone tails:

increase transcription

68
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Histone deacetylase removes acetyl groups from histone tails:

decrease transcription

69
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Methyltransferases add methyl groups to histone tails:

may increase or decrease transcription

70
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What is a function of the protein component of chromosomes?

it packages the DNA strands

71
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What is the relationship between genome size and organismal complexity?

more complex organisms generally have larger genomes but there are many notable exceptions

72
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Portions of junk sequence DNA are conserved between species and thus may be functional. True or false?

true

73
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What specialized DNA sequences provides an attachment point for the segregation of duplicated chromosomes?

centromeres

74
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What is a function of the nucleolus?

to assemble ribosomal RNA and proteins into ribosomes

75
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How does methylation of histone tails affect the accessibility of DNA?

it can have different effects depending on the location

76
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What region most likely contains the highest density of genes?

euchromatin

77
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What can happen if heterochromatin spreads inappropriately into an area with active genes?

the active genes can become silenced

78
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The double helix in each daughter cell consists of

one parental strand and one newly synthesized strand

79
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What best describes DNA replication?

semiconservative

80
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What kinds of bonds link the two strands of a double helix to each other?

hydrogen

81
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Nucleotides in each strand of DNA are held together by what type of bonds?

phosphodiester

82
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Approximately how often does DNA polymerase make an error during DNA replication?

once per 10 million nucleotides added to the growing DNA chain

83
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When does DNA polymerase perform its editing function on incorrectly incorporated nucleotides?

before adding the next nucleotide in the chain

84
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The error-correcting proofreading activity of DNA polymerase occurs in which direction?

opposite the direction of polymerization

85
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What does depurination refer to?

the loss of A or G bases from DNA

86
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How does ultraviolet radiation in sunlight typically damage DNA?

it causes two adjacent pyrimidine bases to become covalently linked

87
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What type of enzyme removes damaged DNA from the rest of the DNA molecule?

polymerase

88
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In the absence of repair, what would the replication of a double helix containing a mismatch yield?

one DNA molecule with the normal sequence and one DNA molecule with a mutated sequence

89
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What occurs when a cell repairs a double-strand DNA break by the process of nonhomologous end joining?

the DNA sequence at the site of repair is altered by a short deletion

90
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Double-strand breaks can be repaired flawlessly by what?

homologous recombination

91
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The DNA sequence at the site of repair contains a short segment of telomere DNA. True or false?

false