T4M2

Question 1

DNA is the macromolecule that determines

Answer 1

the characteristics of the cell

Question 2

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

Answer 2

Francis Crick, James Watson and Rosalind Franklin

Question 3

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

Answer 3

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

Question 4

Watson and Crick proposed that

Answer 4

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

Question 5

Watson and Crick believed that

Answer 5

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.

Question 6

Matthew Meselson and Franklin Stahl conclusively demonstrated

Answer 6

DNA replicates in a semiconservative manner

Question 7

In the late 1950s, Meselson and Stahl

Answer 7

• 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.

Question 8

Meselsen and Stahl identified that

Answer 8

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

Question 9

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

Answer 9

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

Question 10

DNA replication begins in

Answer 10

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

Question 11

Replication in prokaryotes begins at

Answer 11

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

Question 12

During DNA replication, the template strand is copied

Answer 12

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

Question 13

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

Answer 13

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

Question 14

A phosphodiester bond forms between

Answer 14

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)

Question 15

The unwinding of the DNA double helix results in

Answer 15

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

Question 16

The initiation of replication requires that

Answer 16

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

Question 17

Why is the primer is required?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

Polymerase enzyme

Answer 19

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

Question 20

Leading strand

Answer 20

Replication of one daughter strand is continuous from the primer

Question 21

How many primers are required on the leading strand?

Answer 21

1

Question 22

Antiparallel parent strand

Answer 22

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

Question 23

DNA polymerase can only add nucleotides to

Answer 23

3’ end of a polymerizing DNA molecule

Question 24

Okazaki fragments

Answer 24

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

Question 25

Okazaki fragments named after

Answer 25

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

Question 26

Each Okazaki fragment on the lagging strand is formed by

Answer 26

separate primers

Question 27

After DNA polymerase forms an Okazaki fragment

Answer 27

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

Question 28

During initiation, DNA helicase enzymes are able to

Answer 28

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

Question 29

Topoisomerases

Answer 29

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

Question 30

Topoisomerases initiator proteins trigger

Answer 30

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.

Question 31

RNA primase

Answer 31

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

Question 32

Which DNA polymerase does most of the elongation work?

Answer 32

DNA polymerase III in prokaryotes

Question 33

DNA polymerase I

Answer 33

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

Question 34

Each new fragment of the lagging strand cannot be replicated until

Answer 34

enough of the template DNA is revealed at the replication fork

Question 35

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

Answer 35

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

Question 36

In eukaryotes replacement of the RNA primer with DNA nucleotides leaves

Answer 36

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

Question 37

DNA ligase

Answer 37

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

Question 38

Errors in DNA replication can occur

Answer 38

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

Question 39

Innate proofreading mechanism

Answer 39

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

Question 40

Prokaryotic and eukaryotic cells share many common features during replication including

Answer 40

- 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.

Question 41

The ends of linear eukaryotic chromosomes contain regions called

Answer 41

telomeres

Question 42

telomeres

Answer 42

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

Question 43

Human telomeres

Answer 43

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

Question 44

G-T rich sequences

Answer 44

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

Question 45

Telomeres become shorter during

Answer 45

successive rounds of replication

Question 46

Telomere shortening does not occur in

Answer 46

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

Question 47

Telomerase

Answer 47

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.

Question 48

The RNA template of the telomerase role

Answer 48

elongating the linear chromosomes of stem cells and germ cells

Question 49

To elongate telomere regions

Answer 49

- 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.