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Molecular Cell Bio > chapter 6 > Flashcards

chapter 6 Flashcards

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1
Q

The process of DNA synthesis is begun by _ that bind to specific DNA sequences called replication origins.

A

initiator proteins

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2
Q

DNA polymerase is so accurate that it makes only about one error in every _ nucleotide pairs it copies.

A

10^7

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3
Q

when DNA polymerase does make a rare mistake and adds the wrong nucleotide, it can correct the error through an activity called _.

A

proofreading

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4
Q

proofreading mechanism is possible only for DNA polymerases that synthesize DNA exclusively in the _ direction, otherwise, it would be _

A

5’-to-3’
unable to proofread

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5
Q

when a nucleotide is removed from the 5’ end, the remaining strand lacks the necessary chemical group (-_) on the 5’ end for the next nucleotide to be added. Without this group, the polymerase _, so the process is blocked, making it a _ for further synthesis.

A

OH
can’t continue building the DNA
dead end

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6
Q

Thus, for a DNA polymerase to function as a self-correcting enzyme that removes its own polymerization errors as it moves along the DNA, it must proceed only in the _ direction.

A

5’-to-3’

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7
Q

An _ fragment thus serves as a _ for DNA synthesis, and the enzyme that synthesizes the RNA primer is known as _.

A

RNA
primer
primase

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8
Q

Enzymes called DNA _ relieve this ten- sion. A DNA _ produces a transient, single-strand _ in the DNA backbone, which temporarily releases the built-up tension; the enzyme then reseals the _ before falling off the DNA

A

topoisomerases
topoisomerase
nick
nick

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9
Q

purine bases (_)

A

A and G

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10
Q

The rep- lication machine makes approximately one mistake per 10^7 nucleotides synthesized; DNA mismatch repair corrects 99% of these replication errors, increasing the overall accuracy to one mistake in _ nucleotides synthesized.

A

10^9

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11
Q

a _ is especially difficult to repair.

A

double-strand break

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12
Q

double-strand break can be repaired by:

A

nonhomologous end joining
homologous recombination

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13
Q

Homologous recombination most often occurs _ before _

A

shortly after a cell’s DNA has been replicated
cell division

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14
Q

Before a cell divides, it must _.

A

accurately replicate the vast quantity of genetic information carried in its DNA

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15
Q

Because the two strands of a DNA double helix are _, each strand can act as a _ for the synthesis of the other. Thus DNA replication produces _, double-helical DNA molecules, enabling genetic information to be copied and passed on from a cell to its _ and from a parent to its _.

A

complementary
template
two identical
daughter cells
offspring

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16
Q

During replication, the two strands of a DNA double helix are _ at a _ to form two _. DNA _ at each fork produce a new, _ DNA strand on each _.

A

pulled apart
replication origin
Y-shaped replication forks
polymerases
complementary
parental strand

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17
Q

DNA polymerase replicates a DNA template with remarkable _, making only about one error in every _ nucleotides copied. This accuracy is made possible, in part, by a _ process in which the enzyme _.

A

fidelity
_
10^7
_
proofreading
_
corrects its own mistakes as it moves along the DNA

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18
Q

Because DNA polymerase synthesizes new DNA in the _, only the _ at the _ can be synthesized in a _ fashion. On the _, DNA is synthesized in a _ process, producing _ that are later joined together by _.

A

5’-to-3’ direction
leading strand
replication fork
continuous
lagging strand
discontinuous backstitching
short fragments of DNA (Okazaki fragments)
DNA ligase

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19
Q

DNA polymerase is _ of starting a new DNA strand from scratch. Instead, DNA synthesis is _ called _, which makes short lengths of _ that are then elongated by _. These _ are subsequently _ and _.

A

incapable
primed by an RNA polymerase
primase
RNA primers
DNA polymerase
primers
removed
replaced with DNA

20
Q

DNA replication requires the _ that form a _ that _ the double helix and _ the information contained in both DNA strands.

A

cooperation of many proteins
multienzyme replication machine
pries open
copies

21
Q

In eukaryotes, a special enzyme called _ replicates the DNA at the ends of the chromosomes, particularly in rapidly dividing cells.

A

telomerase

22
Q

The rare copying mistakes that escape _ are dealt with by _, which increase the accuracy of DNA replication to one mistake per _ nucleotides copied.

A

proofreading
mismatch repair proteins
10^9

23
Q

Damage to one of the two DNA strands, caused by _, is repaired by a variety of _ that _ damaged DNA and _. The _ DNA is then resynthesized by a _, using the _ as a template.

A

unavoidable chemical reactions
DNA repair enzymes
recognize
excise a short stretch of the damaged strand
missing
repair DNA polymerase
undamaged strand

24
Q

If both DNA strands are broken, the double-strand break can be rapidly repaired by nonhomologous end joining. Nucleotides are _, _.

A

often lost in the process
altering the DNA sequence at the repair site

25
Q

Homologous recombination can _ repair double-strand breaks (and many other types of DNA damage) using an _ as a template.

A

flawlessly
undamaged homologous double helix

26
Q

Highly accurate DNA replication and DNA repair processes play a key role in protecting us from the _.

A

uncontrolled growth of somatic cells known as cancer

27
Q

each strand of a DNA double helix—labeled here as the _ strand and its complementary _ strand—can serve as a template to specify the sequence of nucleotides in its _.

A

S
S’
complementary strand

28
Q

A DNA double helix is opened at _.

A

replication origins

29
Q

DNA sequences
at replication origins are recognized by _, which _. The exposed single strands can then serve as _ for copying the DNA.

A

initiator proteins
_
locally pull apart the two strands of the double helix
_
templates

30
Q

The _ formed at a replication origin move _.

A

two replication forks
away in opposite directions

31
Q

The particles visible along the DNA are _, structures made of _.

A

nucleosomes
_
DNA and the histone protein complexes around which the DNA is wrapped

32
Q

At each replication fork, the lagging DNA strand is synthesized in _.

A

pieces

33
Q

Because both of the new strands at a replication fork are synthesized in the _ direction, the lagging strand of DNA must be made initially as _, which are later _

A

5’-to-3’
a series of short DNA strands
joined together.

34
Q

To replicate the lagging strand, DNA polymerase uses a _ mechanism: it synthesizes _ (called _ fragments) in the 5􏰀-to-3􏰀 direction and then _.

A

backstitching
_
short pieces of DNA
_
Okazaki
_
moves back along the template strand (toward the fork) before synthesizing the next fragment

35
Q

DNA polymerase contains separate sites for DNA _
and _.

A

synthesis
proofreading

36
Q

When the polymerase adds an incorrect nucleotide, the newly synthesized DNA strand (red ) transiently _ from the template strand (orange), and its _ to allow the incorrect nucleotide to be removed.

A

unpairs
3’ end moves into the editing site (E)

37
Q

DNA polymerases are held on the leading- and lagging-strand templates by _ that allow the polymerases to slide.

A

circular protein clamps

38
Q

On the lagging-strand template, the clamp _.

A

detaches each time the polymerase completes an Okazaki fragment

39
Q

A _ is required to attach a sliding clamp each time a new Okazaki fragment
is synthesized.

A

clamp loader

40
Q

At the head of the fork, a_ unwinds the strands of the parental DNA double helix.

A

DNA helicase

41
Q

_ keep the DNA strands apart to provide access for the primase and polymerase.

A

Single-strand DNA-binding proteins

42
Q

the lagging strand shown in (A) has been _ to bring its DNA polymerase in _ with the leading-strand DNA polymerase. This folding process also brings the _ close to the start site for the _.

A

folded
contact
3’ end of each completed Okazaki fragment
next Okazaki fragment

43
Q

_ relieve the tension that builds up in front of a replication fork.

A

DNA topoisomerases

44
Q

DNA topoisomerases _.

A

relieve the tension that builds up in front of a replication fork

45
Q

As a DNA helicase moves forward, unwinding the DNA double helix, it generates a section of _ DNA ahead of it.

A

overwound

46
Q

Some of this torsional stress
is relieved by additional coiling of the
DNA double helix to form _.

A

supercoils

Molecular Cell Bio (10 decks)

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