DNA Replication

Question 1

What sugar is found in DNA?

Answer 1

Deoxyribose.

Question 2

What type of bond are formed between nucleotides?

Answer 2

Phosphodiester bonds.

Question 3

What type of bond holds complementary bases together?

Answer 3

Hydrogen bonds.

Question 4

What does antiparallel mean in DNA?

Answer 4

The two strands run in opposite 5’→3’ directions.

Question 5

Why is directionality important?

Answer 5

It determines how enzymes replicate or transcribe the DNA.

Question 6

What makes DNA compact?

Answer 6

Supercoiling and histone packing in chromosomes (Seen partly with gene regulation mechanisms)

Question 7

Which bases are purines?

Answer 7

Adenine and guanine.

Question 8

How does DNA allow for error correction?

Answer 8

Complementary base pairing enables proofreading.

Question 9

What is the shape of DNA?

Answer 9

A right-handed double helix.

Question 10

What is Chargaff’s rule?

Answer 10

%A = %T and %C = %G.

Question 10

Why does C-G pairing make DNA more stable?

Answer 10

More hydrogen bonds provide stronger bonding.

Question 11

What ensures the consistency of the DNA helix?

Answer 11

Base pairing with one purine and one pyrimidine.

Question 12

If A = 20% in a molecule of DNA, what % is G?

Answer 12

30%.

Question 13

Which regions of DNA are more stable?

Answer 13

C-G-rich regions.

Question 14

Why is complementarity important for replication?

Answer 14

It allows each strand to serve as a template for more efficient replication and for repair.

Question 15

Can base-pairing occur in RNA?

Answer 15

Yes, but A pairs with U instead of T.

Question 16

Who conducted the experiment on DNA replication?

Answer 16

Meselson and Stahl.

Question 17

What did the first generation of replication show?

Answer 17

Intermediate density DNA.

Question 18

What did the second generation show?

Answer 18

Light and intermediate DNA.

Question 19

What model was supported?

Answer 19

Semiconservative replication.

Question 20

What is conservative replication?

Answer 20

Entire parental strand is conserved; daughter is entirely new.

Question 21

What is dispersive replication?

Answer 21

DNA is mixed, with old and new parts in both strands.

Question 22

Why was intermediate density crucial?

Answer 22

It proved one strand was old, one new.

Question 23

Where does replication begin?

Answer 23

At origins of replication.

Question 24

What enzyme unwinds DNA?

Answer 24

Helicase.

Question 25

What prevents supercoiling/bending of the DNA during replication?

Answer 25

Topoisomerase.

Question 26

What stabilizes open DNA strands?

Answer 26

Single-strand binding proteins.

Question 27

What enzyme synthesizes DNA?

Answer 27

DNA polymerase III.

Question 27

What lays down RNA primers?

Answer 27

Primase.

Question 28

In what direction does DNA synthesis occur?

Answer 28

5' to 3'.

Question 29

What removes RNA primers?

Answer 29

DNA polymerase I.

Question 30

What connects Okazaki fragments?

Answer 30

DNA ligase.

Question 31

What is the lagging strand?

Answer 31

Strand synthesized discontinuously away from the fork.

Question 31

Why is DNA replication uneven?

Answer 31

DNA polymerase only works 5'→3', but strands are antiparallel.

Question 32

What is the leading strand?

Answer 32

Strand synthesized continuously toward the fork. oving in opposite directions.

Question 33

What are Okazaki fragments?

Answer 33

Short DNA segments on the lagging strand.

Question 33

Why does lagging strand need more primers?

Answer 33

Each fragment requires a new primer.

Question 34

What enzyme seals Okazaki fragments?

Answer 34

DNA ligase.

Question 35

Which enzyme replaces RNA primers?

Answer 35

DNA polymerase I.

Question 35

Why can’t DNA polymerase start synthesis directly?

Answer 35

It needs a 3' OH from a primer.

Question 36

Which strand needs primase more frequently?

Answer 36

The lagging strand.

Question 37

What is a replication bubble?

Answer 37

A region where DNA has been opened for replication with two forks moving in opposite directions.

Question 38

What are telomeres?

Answer 38

Telomeres are repetitive DNA sequences at the ends of chromosomes that protect coding DNA.

Question 39

Why do telomeres shorten during DNA replication?

Answer 39

Because the lagging strand cannot be fully replicated at the 3' end due to primer removal.

Question 40

What happens when telomeres become too short?

Answer 40

Cells enter senescence and stop dividing.

Question 41

What is the Hayflick limit?

Answer 41

The estimated number of times a human cell can divide before senescence (about 50-60 times).

Question 42

What is telomerase?

Answer 42

An enzyme with an RNA template that extends the 3' end of DNA, allowing replication of telomeres.

Question 43

In which types of cells is telomerase active?

Answer 43

Stem cells, germ cells, and some cancer cells.

Question 44

Why is telomerase activity limited in most somatic cells?

Answer 44

To limit uncontrolled cell division and reduce cancer risk.

Question 45

What is the RNA component of telomerase used for?

Answer 45

It acts as a template to add telomere sequences to the DNA strand.

Question 46

How does telomerase affect the Hayflick limit?

Answer 46

It extends telomere length, allowing more rounds of replication.

Question 47

What is the consequence of telomere dysfunction?

Answer 47

Genome instability and activation of DNA damage responses.

Question 48

What is a spontaneous mutation?

Answer 48

A mutation that arises without an external factor, due to DNA replication errors or chemical changes.

Question 49

How often does DNA polymerase make a mistake?

Answer 49

About once every 100,000 bases.

Question 50

What is a tautomeric shift?

Answer 50

A temporary change in base structure that leads to incorrect base pairing.

Question 51

What is deamination?

Answer 51

The removal of an amino group from a base (e.g., cytosine becomes uracil).

Question 52

What is depurination?

Answer 52

The loss of a purine base (adenine or guanine) from the DNA.

Question 53

What is replication slippage?

Answer 53

Misalignment of the DNA strands during replication, causing insertions or deletions.

Question 54

Are all spontaneous mutations harmful?

Answer 54

Not necessarily; some are silent, and others can even be beneficial.

Question 55

How do these mutations become permanent?

Answer 55

If not repaired before the next round of replication, the change is inherited.

Question 56

What determines an organism’s mutation rate?

Answer 56

The fidelity of its DNA polymerases and efficiency of its repair systems.

Question 57

What is DNA proofreading?

Answer 57

The ability of DNA polymerase to remove incorrect nucleotides during replication.

Question 58

What enzyme activity allows DNA polymerase to proofread?

Answer 58

3' to 5' exonuclease activity.

Question 59

What does mismatch repair (MMR) do?

Answer 59

It detects and corrects base mismatches after replication.

Question 60

What is base excision repair (BER)?

Answer 60

It removes and replaces damaged or incorrect single bases.

Question 61

What is nucleotide excision repair (NER)?

Answer 61

It removes damaged sections of DNA including multiple bases, such as thymine dimers.

Question 61

What causes thymine dimers?

Answer 61

UV radiation.

Question 62

What is direct repair?

Answer 62

A mechanism where the damage is chemically reversed without removing the base.

Question 63

What enzyme begins mismatch repair?

Answer 63

A nuclease that cuts out the mismatch-containing DNA segment.

Question 64

What replaces the excised DNA in repair?

Answer 64

DNA polymerase synthesizes new DNA using the correct strand as a template.

Question 65

What does PCR stand for?

Answer 65

Polymerase Chain Reaction.

Question 66

What enzyme is used in PCR?

Answer 66

Taq polymerase.

Question 67

Why is Taq polymerase used?

Answer 67

It can withstand high temperatures needed for denaturation.

Question 68

What are the three steps in a PCR cycle?

Answer 68

Denaturation, annealing, and extension.

Question 69

What are PCR primers?

Answer 69

Short DNA sequences that flank the target region to be amplified.

Question 70

How many primers are used per PCR reaction?

Answer 70

Two: a forward and a reverse primer.

Question 71

Why is DNA denatured during

Answer 71

PCR? To separate the two strands so primers can bind.

Question 72

In which direction does Taq polymerase synthesize DNA?

Answer 72

5' to 3'.

Question 73

Name two applications of PCR.

Answer 73

Forensic DNA profiling, pathogen detection, genotyping, sequencing, etc.

Question 74

How does PCR amplification work?

Answer 74

It doubles the amount of DNA each cycle.

Question 75

What is the formula to calculate DNA after n cycles?

Answer 75

N = M × 2ⁿ

Question 76

How many DNA copies after 10 cycles from one molecule?

Answer 76

1 024 copies.

Question 77

How many copies after 20 cycles from one molecule?

Answer 77

About 1 million copies (220 = 1 048 576).

Question 78

What if you start with 5 molecules and do 10 cycles?

Answer 78

5 × 1 024 = 5 120 copies.

Question 79

What happens if you increase the number of cycles?

Answer 79

The DNA quantity increases exponentially.

Question 80

Why is PCR useful for small DNA samples?

Answer 80

It amplifies even tiny amounts to detectable levels.

Question 81

What are amplicons?

Answer 81

The DNA fragments generated by PCR.

Question 82

What does exponential growth mean in PCR?

Answer 82

Each cycle doubles the existing DNA amount.

Question 83

Why is PCR useful for small DNA samples?

Answer 83

It amplifies even tiny amounts to detectable levels.