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BIOLOGY 1A03 > T4M2 > Flashcards

T4M2 Flashcards

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1
Q

DNA is the macromolecule that determines

A

the characteristics of the cell

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2
Q

We know DNA molecule exists in a helical structure with purines paired with pyrimidines along the entire DNA helix based on work by

A

Francis Crick, James Watson and Rosalind Franklin

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3
Q

Watson and Crick concluded their 1953
Nature paper that proposes the structure of DNA with the statement

A

“It has not escaped our notice
that the specific pairing we have postulated
immediately suggests a copying mechanism for
genetic material.”

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4
Q

Watson and Crick proposed that

A

DNA consists of a pair of template chains which are complementary to each other, and that prior to replication, the hydrogen bonds are broken between these complementary strands, which allows for unwinding and separation

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5
Q

Watson and Crick believed that

A

when a cell copies its DNA, that each strand serves as a template for the ordering of new nucleotides (according to the base-pairing rules) into a new complementary strand.

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6
Q

Matthew Meselson and Franklin Stahl conclusively demonstrated

A

DNA replicates in a semiconservative manner

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7
Q

In the late 1950s, Meselson and Stahl

A
  • cultured E. coli bacterial cells for many generations in a medium that contained the nucleotide precursors with the radioactively labelled heavy isotope of nitrogen
    (15N).
  • they transferred the bacteria into a medium that contained 14N, the lighter isotope.
  • every new strand of replicated DNA would be built containing 14N rather than the 15N isotopes.
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8
Q

Meselsen and Stahl identified that

A

DNA from bacteria that had been growing in the media containing the 15N isotope had only one distinct band

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9
Q

It was found that following rounds of replication of DNA and cell division in media containing fluorescent nucleotides

A

the chromosomes of eukaryotic cells could contain hybrid and fully labelled nucleotides

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10
Q

DNA replication begins in

A

the S-phase of the cell cycle at specific regions along DNA called the origins of replication

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11
Q

Replication in prokaryotes begins at

A

a single origin of replication, after which replication continues around the circular chromosome from this one initiation site

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12
Q

During DNA replication, the template strand is copied

A

from the 3’ end to the 5’ end and produces a daughter strand that elongates in a 5’ to 3’ direction

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13
Q

During the process of DNA replication, each
incoming complementary nucleotide engages in

A

a hydrogen bond with the nucleotide on the
template strand and interacts with the 3’ hydroxyl of the existing polymer that is forming on the new daughter strand

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14
Q

A phosphodiester bond forms between

A

the growing daughter strand and the
new incoming nucleotide, allowing it to become
part of the DNA molecule backbone on the
daughter strand (and in the process producing a pyrophosphate)

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15
Q

The unwinding of the DNA double helix results in

A

the separation of the parental strands at regions called replication forks within the origins of replication

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16
Q

The initiation of replication requires that

A

a short stretch of an RNA molecule or a
primer (that is usually 5-10 nucleotides long) be
synthesized and base pair with the template DNA strands

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17
Q

Why is the primer is required?

A

The enzymatic machinery that elongates a new
daughter strand can only do so from an existing
piece of DNA or RNA

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18
Q

As elongation progresses, the polymerization of each newly replicated daughter strand is

A

catalyzed by the DNA polymerase enzyme in a 5’ to 3’ direction

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19
Q

Polymerase enzyme

A

synthesizes a replicated DNA strand from the primers that anneal to the template strand

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20
Q

Leading strand

A

Replication of one daughter strand is continuous from the primer

21
Q

How many primers are required on the leading strand?

A

1

22
Q

Antiparallel parent strand

A

discontinuous (or fragmented) replication occur. The produced daughter strand is referred to as the lagging strand.

23
Q

DNA polymerase can only add nucleotides to

A

3’ end of a polymerizing DNA molecule

24
Q

Okazaki fragments

A

polymerase replicate the DNA in a direction that
is away from the replication fork. The end result
of replication and production of the lagging strand is that the lagging strand will contain segments or fragments of DNA

25
Q

Okazaki fragments named after

A

Reiji Okazaki, the scientist who discovered them in E. coli

26
Q

Each Okazaki fragment on the lagging strand is formed by

A

separate primers

27
Q

After DNA polymerase forms an Okazaki fragment

A

another DNA polymerase is able to replace the RNA primer sequences of all daughter strands with DNA nucleotides

28
Q

During initiation, DNA helicase enzymes are able to

A

bind to the parental DNA strands at the origin of replication and initiate the unwinding of the DNA double helix by break the hydrogen bonds between complementary nucleotide base pairs

29
Q

Topoisomerases

A

are able to bind upstream of the replication fork and minimize the torsional strain that is brought about from the unwinding that occurs at the replication fork

30
Q

Topoisomerases initiator proteins trigger

A

the process of unwinding at the origin of replication
- the process of primer synthesis will follow and marks the beginning of the synthesis of the new daughter DNA molecules.

31
Q

RNA primase

A

synthesizes the short RNA stretches of nucleotides which are complementary to the parental strands from which DNA polymerase can then elongate from

32
Q

Which DNA polymerase does most of the elongation work?

A

DNA polymerase III in prokaryotes

33
Q

DNA polymerase I

A

removing the RNA primer after DNA replication and replacing those short sequences with DNA nucleotides

34
Q

Each new fragment of the lagging strand cannot be replicated until

A

enough of the template DNA is revealed at the replication fork

35
Q

Since prokaryotes have one origin of replication, during the replication of their circular DNA

A

the excised primer is replaced by specific
DNA nucleotides and there is no gap in the newly synthesized DNA

36
Q

In eukaryotes replacement of the RNA primer with DNA nucleotides leaves

A

a sugar phosphate backbone at the 3’ end with a free phosphate (prevalent along the Okazaki
fragments of the lagging strand)

37
Q

DNA ligase

A

is able to join the 3’ end of a fragment to an adjacent DNA nucleotide by catalyzing the phosphodiester bond formation along this region of the DNA backbone and as a result, joining adjacent replicated Okazaki fragments together

38
Q

Errors in DNA replication can occur

A

during the initial pairing between incoming nucleotides and those of the template
strand

39
Q

Innate proofreading mechanism

A

During DNA replication, DNA polymerases are able to proofread each added nucleotide relative to the template strand
- as each DNA nucleotide is added to the growing daughter strand. If an incorrect nucleotide pairing is detected, DNA polymerase removes the incorrect nucleotide, the
correct nucleotide is added, and then replication can continue by the DNA polymerase

40
Q

Prokaryotic and eukaryotic cells share many common features during replication including

A
  • both require a primer for initiation of replication to occur
  • elongation is always in a 5’ to 3’ direction, and
    specialized proteins are utilized within a
    replication complex which allows for the
    replication of daughter strands from parental DNA template strands
  • a leading strand and lagging strand.
41
Q

The ends of linear eukaryotic chromosomes
contain regions called

A

telomeres

42
Q

telomeres

A

special nucleotides sequences that are mainly
made up of repetitions of one short nucleotide
sequence

43
Q

Human telomeres

A

contain the characteristic six-nucleotide
sequence TTAGGG repeated between hundreds
to thousands of times, leading to many tandem repeats of G-T rich sequences

44
Q

G-T rich sequences

A

non-coding repetitive sequence of nucleotides serves as a buffer zone so that coding genes within chromosomes are protected

45
Q

Telomeres become shorter during

A

successive rounds of replication

46
Q

Telomere shortening does not occur in

A

gametes or in stem cells, they have a special telomerase enzyme which catalyzes the lengthening of telomeres in these eukaryotic cells.

47
Q

Telomerase

A

a specific type of reverse transcriptase, enzyme is able to synthesize DNA from an RNA template. In fact, the telomerase itself is a ribonucleoprotein that contains the RNA template as part of the complex itself.

48
Q

The RNA template of the telomerase role

A

elongating the linear chromosomes of stem cells and germ cells

49
Q

To elongate telomere regions

A
  • telomerase binds to the tail of the telomere and subsequently catalyzes the extension of the template strand by adding telomere repeats.
  • Once telomerase has extended the template DNA strand, primase, DNA polymerase and ligase are able to go back and complete the daughter strand replication from the remainder of the template strand.

BIOLOGY 1A03 (24 decks)

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