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Biology > 7.1 > Flashcards

7.1 Flashcards

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1
Q

what is eukaryotic DNA always associated with

A

basic (alkaline) and positively charged proteins called histones

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2
Q

what charge is a histone

A

positive

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3
Q

around how many base Paris are in a length of DNA in nucleosome

A

150 base Paris

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4
Q

what is the DNA wrapped around

A

eight histones (four pairs of four different histones)

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5
Q

what is the special histone called

A

H1 special histone

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6
Q

what charge is DNA

A

acidic and negatively charged

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7
Q

how is DNA neutralized

A

by bonding with histones

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8
Q

how and why are nucleosomes linked

A

they have linker DNA as the DNA strand from one nucleosome flows directly into the next nucleosome.

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9
Q

what do nucleosomes form when they are packed together

A

chromatin fibre - which then goes on to supercoil and form chromosomes

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10
Q

why does `DNA recoil

A

to fit the genetic material into the nucleus

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11
Q

what halves DNA supercoil

A

nucleosomes and they ensure appropriate access to it

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12
Q

how does access to the DNA occur

A

when the coils unwind and histones are moved out of the way so that DNA can be copied ro transcribed

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13
Q

what described a eukaryotic chromosome

A

it consists of a single linear molecule fo double stranded DNA plus proteins

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14
Q

What type of cells have DNA associated with histones?

A

eukaryotic cells

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15
Q

what does DNA replication rely on

A

base pairing

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16
Q

how does base pairing allow for stability of the double helix

A
  • hydrogen bonding between purines and the pyrimidines. Two hydrogen bonds occur between A and T whereas three occur between C and G
  • the slightly positive charge on T and the slightly negative charge on A allows for two bases to bond together during complementary base paring
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17
Q

what is a pyrimidine always bonded to in DNA

A

a purine

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18
Q

what are purines

A

guanine and adenine

two rings

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19
Q

what are pyrimidines

A

thymine and cytosine (one ring)

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20
Q

what are important enzymes related to DNA replication

A

helices
DNA gyrase
DNA ligase
DNA polymerase 1 and III

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21
Q

what is the rate of replication

A

approximately 100 nucleotides per second in eukaryotes

can be as high as 1000 nucleotides per second in prokaryotes

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22
Q

how many base pairs are replicated during the S phase of the cell cycle

A

6 billion base pairs

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23
Q

how many base pairs to human genome have per haploid set of chromosomes

A

3 billion

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24
Q

what happens on the leading strand in DNA replication

A

helices binds to the origin of replication and breaks hydrogen bonds between base pairs to wind the DNA double helix.

Single strand binding proteins then bind to the single strands formed to keep them apart of allow time of the DNA sequence to be copied

the strand acts as a template for the replication process.

DNA gyros received the tension on the region ahead caused by helices

as fee nucleoside triphosphate bind to the template, they lose their two extra phosphate groups to generate energy which is used to add the nucleotide to the growing polynucleotide chain.

DNA polymerase III adds DNA nucleotides to the strands and can only add a nucleotide to the 3’ OH group of the deoxyribose.

the DNA polymerase follows the gelicase, separating th strands and adding the DNA nucleotides because no DNA polymerase enzyme can initiate a new DNA on its own. An RNA primer is needed once for this leading strand

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25
Q

what happens on the lagging strand during DNA replication

A

same steps as leading strand, however, because the last nucleotides ends with a 5’ phosphate, the DNA primate has to make short RNA primers, which allow the DNA polymerase III to add DNA nucleotides to the 3’ OH of the RNA primer. Many such primers are made as a scaffold for the DNA polymerase II.

It synthesizes short DNA fragments call Okazaki fragments which are joined together by DNA ligase to form a complete DNA strand. The result is two new strand, both based on the template of the old DNA molecule.

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26
Q

what is the leading strand

A

the strand of DNA that is being replicated continuously in the 5’ to 3’ prime direction by continuous polymerization at the 3 growing tip

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27
Q

what is the lagging strand

A

the strand of DNA that is replicated discontinuously in small fragments in the 5 to 3 prime direction away from the replication fork

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28
Q

what are RNA primers

A

short RNA chains of about 10 bases used as a starting point for DNA replication by DNA polymerase III

synthesised by DNA primase

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29
Q

what makes RNA primers

A

DNA primases

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30
Q

what direction does DNA replication always go

A

5’ to 3’ prime direction

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31
Q

what is the role of helicase

A

unwinds the double helix and breaks hydrogen bonds between base pairs

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32
Q

what can helices cause on the DNA molecule

A

supercoiling and tension in the region ahead

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33
Q

what relieves the tension and supercoiling in the region ahead during replication

A

DNA gyrase

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34
Q

what is the role of DNA gyros

A

it moves in advance to helices to relieve tension of the strand ahead

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35
Q

what is the role of the free nucleoside triphosphate

A

they bind to the template and lose their two extra phosphate groups to generate energy, which is used to add the nucleotide to the growing polynucleotide chain

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36
Q

what do single strand binding proteins do

A

they bind to the single strands formed to keep them apart whilst replication takes palce

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37
Q

what do free nucleoside triphosphate lose

A

two extra phosphate groups

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38
Q

what are the two extra phosphate groups used for from free nucleoside phosphates

A

generate energy used to add nucleotides to the chain

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39
Q

what is the role of DNA polymerase III

A

the enzyme that adds DNA nucleotides to the strands and can only add a nucleotide to the 3’OH group of thedeoxyribose

40
Q

what is the role of DNA polymerase in replication

A

the enzyme joins individual nucleotides to produce a new strand of DNA

41
Q

what can a DNA polymerase enzyme not do

A

initiate a new DNA on its own

42
Q

what helps a DNA polymerase enzyme complete its role

A

RNA primers

43
Q

what makes RNA primers

A

DNA primase

44
Q

what are RNA primers later replaced with

A

short DNA segments

45
Q

what do RNA dimers allow for

A

allows the DNA polymerase III to add DNA nucleotides to the 3 OH f the RNA primer

46
Q

what does DNA polymerase III synthesis

A

short DNA fragments

47
Q

what are the short DNA fragments called

A

Okazaki fragments

48
Q

what joins Okazaki fragments together

A

DNA ligase to forma a complete DNA strand

49
Q

when do chromosomes form

A

around the time cells divide

50
Q

what does DNA polymerase I do

A

replace RNA primers with short DNA fragments

51
Q

what components make an Okazaki fragment

A

RNA primer, DNA fragment

52
Q

what end of there rowing strand can DNA polymerase III only join new nucleotides

A

the 3’ end

53
Q

how much of the human genome does non coding DNA account for

A

98%

54
Q

what is non coding DNA

A

DNA sequences within a genome that no not consist of the information to make a protein

55
Q

what are non coding DNA never represented in

A

in amino acid sequences of expressed proteins

56
Q

what are regions of DNA that do not code for proteins

A

regulators of gene expression

introns

telomeres

genes for tRNAs

57
Q

what is the role fo regulators of gene expression

A

DNA sequences that regulate gene expression, such as promotes that occur before genes and act as a binding point for the RNA polymerase enzymes that catalyst the transcription process.

58
Q

what is the role of introns

A

DNA base sequences that are removed at the end of transcription, they do not contribute to the amino acid sequence of the polypeptide made form the gene.

59
Q

what is the role of telomeres

A

repetitive sequences that protect the ends of the chromosome. telomeres help ensure that DNA is replicated correctly. With every cell division, short stretches of DNA are lost from the telomeres

60
Q

what is the role of gene for tRNAs

A

these genes code for RNA molecules that do not get translated into proteins but instead fold to form tRNA molecules that play an important role in translation

61
Q

what is a tandem repeat

A

a sequence of two or more DNA base pairs that is repeated in such a way that the repeats lie end to end on the chromosomes

62
Q

what are tandem repeats usually

A

non-coding but they may be present in some protein coding regions

63
Q

where are tandem repeats located

A

at a single genetic locus in which the number of repeated DNA segments varies from individual to individual

64
Q

what can tandem repeats be used for

A

identification in DNA fingerprinting

DNA profiles

65
Q

give an example of a tandem repeat

A

GTACTAGA’CTA’‘CTA’‘CTA”CTA’‘CTA’CTGGTG

five tandem repeats

66
Q

what steps does DNA profiling involve

A
  • collection of samples and extraction of DNA
  • amplification of the DNA region containing tandem repeats by PCR
  • separation of the DNA fragments using gel electrophoresis
67
Q

When DNA profiling is used to analyse the DNA of individuals, which parts of the DNA are used?

A

short tandem repeats

68
Q

what is DNA sequencing

A

the method used for deducing the precise order of nucleotides within a DNA molecule.

69
Q

what can DNA sequencing be used for

A

DNA profiling

paternity suits

forensics

70
Q

what is the Dideoxycytidine’s chain termination method

A

based on the fact that DNA polymerase needs a 3 OH group of the preceding nucleotide to add another nucleotide to the DNA strand. If a dideoxycytidine’s nucleotide is added to the mixture and this nucleotide is built into the growing DNA strand, no further nucleotides can be added and the react stops

71
Q

what is a dideoxycytidine’s nucleotide

A

a normal nucleotide but lacking the oxygen atom at the 3’OH group

72
Q

what method do DNA sequencers use

A

the Dideoxycytidine’s chain termination method along with fluorescent dye to the four dideoxynucleotides so that the base present when replication stops can be recognized.

73
Q

what does dNTP stand for

A

deoxyribose nucleotide triphosphate

74
Q

what does ddNTP stand for

A

dideoxyribose nucleotide trisphosphate

75
Q

Why might a laboratory be using dideoxynucleotides?

A

to sequence DNA gragments

76
Q

what is base sequencing

A

a process that allows the precise order of bases in a DNA strand to be determined

77
Q

what is the main purpose of base sequencing

A

to determine the order of nitrogen bases in a sample of DNA

78
Q

What did Franklin develop

A

a better camera fro the X ray diffraction detectors which enabled her to analyse DNA crystals.

79
Q

Who carried out X-ray diffraction experiments leading to the determination that DNA was a helical molecule?

A

Rosalind Franklin

80
Q

what was Rosalind able to do by using X ray data

A

she was able to determine the distance between base pairs in a DNA molecule and able to determine the size of one turn of the helix within the DNA molecule

81
Q

What type of observation was made from Rosalind Franklin’s X-ray diffraction data?

A

structural details of DNA’s physical shape

82
Q

what did scientists use to wonder about genetic material

A

whether it was protein or DNA

83
Q

what did Hershey and Chase convince scientists

A

that it was DNA and not protein that made up the genetic material

84
Q

what dd Hershey and Chase use in their experiments

A

they used a T2 bacteriophage, which is a virus that infects bacterial cells, it injects its DNA into the bacterial cell while its protein coats stays on the outside

85
Q

what did Hershey and chase use to label the DNA

A

radioactive phosphorus

86
Q

what did Hershey and Chase use to label the protein

A

SUlfur

87
Q

steps of Hershey and Chase experiment for the DNA

A

bacteria and virus are cultured together, radioactive viral DNA enters bacterium

agitation in blender dislodges viruses, radioactivity stays inside the bacterium

centrifugation separates the viruses from bacteria and allows investigator to detect the location of the radioactivity

viruses are liquids and not radioactive whereas bacteria are in sediment and are now radioactive

88
Q

steps of Hershey and Chase for the radioactive protein

A

bacteria and virus are cultured together with the radioactive protein

agitation in the blender dislodges viruses, radioactivity stays outside the bacterium

centrifugation separates viruses from bacteria and allows investigator to detect location of radioactivity

viruses in liquid are radioactive

bacteria in sediment are not radioactive

89
Q

what did Hershey and chase discover

A

when bacteriophages contain radioactive phosphorus, all infected cells because radioactive

however when they were infected with bacteriophages labelled with radioactive sulfur,the virus coats removed and there was almost no radioactivity detected in the infected cells

90
Q

what does DNA contain a lot of

A

phosphate

91
Q

what does proteins contain a lot of

A

sulfure

92
Q

what happens during the formation of Okazaki fragments

A

DNA polymerase III adds nucleotides in the 5’ to 3’ prime direction

93
Q

What is different about the nucleotide used in Sangers strategy

A

they are normal DNA nucleotides but lack the 3’ OH group

94
Q

what did Hershey and Chase do to the phage

A

the phages protein coat was labelled using the radioactive isotope 35S

95
Q

The DNA of telomeres has been found to be highly conserved throughout the evolution of eukaryotes (this means not many changes/mutations have been seen). What does this most probably mean?

A

that the critical function of telomeres must be maintained

Biology (51 decks)

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