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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
what happens on the lagging strand during DNA replication
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.
26
what is the leading strand
the strand of DNA that is being replicated continuously in the 5' to 3' prime direction by continuous polymerization at the 3 growing tip
27
what is the lagging strand
the strand of DNA that is replicated discontinuously in small fragments in the 5 to 3 prime direction away from the replication fork
28
what are RNA primers
short RNA chains of about 10 bases used as a starting point for DNA replication by DNA polymerase III synthesised by DNA primase
29
what makes RNA primers
DNA primases
30
what direction does DNA replication always go
5' to 3' prime direction
31
what is the role of helicase
unwinds the double helix and breaks hydrogen bonds between base pairs
32
what can helices cause on the DNA molecule
supercoiling and tension in the region ahead
33
what relieves the tension and supercoiling in the region ahead during replication
DNA gyrase
34
what is the role of DNA gyros
it moves in advance to helices to relieve tension of the strand ahead
35
what is the role of the free nucleoside triphosphate
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
36
what do single strand binding proteins do
they bind to the single strands formed to keep them apart whilst replication takes palce
37
what do free nucleoside triphosphate lose
two extra phosphate groups
38
what are the two extra phosphate groups used for from free nucleoside phosphates
generate energy used to add nucleotides to the chain
39
what is the role of DNA polymerase III
the enzyme that adds DNA nucleotides to the strands and can only add a nucleotide to the 3'OH group of thedeoxyribose
40
what is the role of DNA polymerase in replication
the enzyme joins individual nucleotides to produce a new strand of DNA
41
what can a DNA polymerase enzyme not do
initiate a new DNA on its own
42
what helps a DNA polymerase enzyme complete its role
RNA primers
43
what makes RNA primers
DNA primase
44
what are RNA primers later replaced with
short DNA segments
45
what do RNA dimers allow for
allows the DNA polymerase III to add DNA nucleotides to the 3 OH f the RNA primer
46
what does DNA polymerase III synthesis
short DNA fragments
47
what are the short DNA fragments called
Okazaki fragments
48
what joins Okazaki fragments together
DNA ligase to forma a complete DNA strand
49
when do chromosomes form
around the time cells divide
50
what does DNA polymerase I do
replace RNA primers with short DNA fragments
51
what components make an Okazaki fragment
RNA primer, DNA fragment
52
what end of there rowing strand can DNA polymerase III only join new nucleotides
the 3' end
53
how much of the human genome does non coding DNA account for
98%
54
what is non coding DNA
DNA sequences within a genome that no not consist of the information to make a protein
55
what are non coding DNA never represented in
in amino acid sequences of expressed proteins
56
what are regions of DNA that do not code for proteins
regulators of gene expression introns telomeres genes for tRNAs
57
what is the role fo regulators of gene expression
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
what is the role of introns
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
what is the role of telomeres
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
what is the role of gene for tRNAs
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
what is a tandem repeat
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
what are tandem repeats usually
non-coding but they may be present in some protein coding regions
63
where are tandem repeats located
at a single genetic locus in which the number of repeated DNA segments varies from individual to individual
64
what can tandem repeats be used for
identification in DNA fingerprinting DNA profiles
65
give an example of a tandem repeat
GTACTAGA'CTA''CTA''CTA"CTA''CTA'CTGGTG five tandem repeats
66
what steps does DNA profiling involve
- 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
When DNA profiling is used to analyse the DNA of individuals, which parts of the DNA are used?
short tandem repeats
68
what is DNA sequencing
the method used for deducing the precise order of nucleotides within a DNA molecule.
69
what can DNA sequencing be used for
DNA profiling paternity suits forensics
70
what is the Dideoxycytidine's chain termination method
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
what is a dideoxycytidine's nucleotide
a normal nucleotide but lacking the oxygen atom at the 3'OH group
72
what method do DNA sequencers use
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
what does dNTP stand for
deoxyribose nucleotide triphosphate
74
what does ddNTP stand for
dideoxyribose nucleotide trisphosphate
75
Why might a laboratory be using dideoxynucleotides?
to sequence DNA gragments
76
what is base sequencing
a process that allows the precise order of bases in a DNA strand to be determined
77
what is the main purpose of base sequencing
to determine the order of nitrogen bases in a sample of DNA
78
What did Franklin develop
a better camera fro the X ray diffraction detectors which enabled her to analyse DNA crystals.
79
Who carried out X-ray diffraction experiments leading to the determination that DNA was a helical molecule?
Rosalind Franklin
80
what was Rosalind able to do by using X ray data
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
What type of observation was made from Rosalind Franklin's X-ray diffraction data?
structural details of DNA's physical shape
82
what did scientists use to wonder about genetic material
whether it was protein or DNA
83
what did Hershey and Chase convince scientists
that it was DNA and not protein that made up the genetic material
84
what dd Hershey and Chase use in their experiments
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
what did Hershey and chase use to label the DNA
radioactive phosphorus
86
what did Hershey and Chase use to label the protein
SUlfur
87
steps of Hershey and Chase experiment for the DNA
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
steps of Hershey and Chase for the radioactive protein
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
what did Hershey and chase discover
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
what does DNA contain a lot of
phosphate
91
what does proteins contain a lot of
sulfure
92
what happens during the formation of Okazaki fragments
DNA polymerase III adds nucleotides in the 5' to 3' prime direction
93
What is different about the nucleotide used in Sangers strategy
they are normal DNA nucleotides but lack the 3' OH group
94
what did Hershey and Chase do to the phage
the phages protein coat was labelled using the radioactive isotope 35S
95
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?
that the critical function of telomeres must be maintained

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