DNA & DNA Replication

Question 1

What are the 3 parts of a nucleotide?

Answer 1

1.) a phosphate group
2.) a deoxyribose sugar
3.) a nitrogenous base

Question 2

What are the names of carbons in deoxyribose & what attaches to them?

Answer 2

one prime (1’) - base attaches
three prime (3’) - hydroxyl group (OH) group, where nucleotides are added
five prime (5’) - phosphate group attaches

Question 3

What kind of bond connects nucleotides in a strand?

Answer 3

A phosphodiester bond between the 3′ OH and 5′ phosphate of adjacent nucleotides

Question 4

What is meant by the “polarity” of DNA?

Answer 4

DNA strands run in opposite directions — one 5′ → 3′, the other 3′ → 5′

Question 5

Why is DNA’s backbone negatively charged?

Answer 5

Because of the negatively charged phosphate groups

Question 6

What are the two types of nitrogenous bases?

Answer 6

Purines (A, G) with two rings and pyrimidines (C, T, U) with one ring

Question 7

Which base is found in RNA but not in DNA?

Answer 7

Uracil (U), which replaces thymine (T)

Question 8

What specific base pairings occur in DNA?

Answer 8

A–T (2 hydrogen bonds), G–C (3 hydrogen bonds)

Question 9

What is DNA replication?

Answer 9

The process of copying the entire genome so each daughter cell receives identical DNA.

Question 10

What model describes how DNA replicates?

Answer 10

The semiconservative model — each new DNA molecule has one old and one new strand.

Question 11

What direction does DNA synthesis occur in?

Answer 11

5′ → 3′

Question 12

What serves as the template for new DNA synthesis?

Answer 12

The original (parental) DNA strand

Question 13

What prevents the separated DNA strands from rejoining?

Answer 13

Single-strand binding proteins (SSBs)

Question 14

What enzyme relieves strain caused by unwinding ahead of the fork?

Answer 14

Topoisomerase

Question 15

Why is a primer needed for DNA replication?

Answer 15

Because DNA polymerase cannot start synthesis without an existing 3′-OH group

Question 16

What enzyme creates & lays down RNA primers for DNA synthesis?

Answer 16

Primase

Question 17

Which enzyme adds new nucleotides during replication

Answer 17

DNA polymerase

Question 18

How does the leading strand differ from the lagging strand?

Answer 18

Leading strand is synthesized continuously; lagging strand is synthesized in short Okazaki fragments.

Question 19

What enzyme joins Okazaki fragments together?

Answer 19

DNA ligase

Question 20

What enzyme removes RNA primers and replaces them with DNA?

Answer 20

RNase H (or DNA polymerase I in bacteria)

Question 21

What is the replication fork?

Answer 21

The Y-shaped region where DNA is unwound and new strands are synthesized

Question 22

What is the replisome?

Answer 22

A large protein complex that carries out DNA replication at the fork

Question 23

What ensures that DNA replication is very accurate?

Answer 23

Proofreading by DNA polymerases and complementary base pairing

Question 24

How many origins of replication do eukaryotic chromosomes have?

Answer 24

Many — to allow replication to occur efficiently across large genomes

Question 25

What ensures that each origin of replication fires only once per cell cycle?

Answer 25

Tight regulation of initiation proteins

Question 26

Why do linear chromosomes pose a problem for DNA replication?

Answer 26

DNA polymerase can’t fully replicate the 5′ ends, leading to chromosome shortening

Question 27

How does telomerase work?

Answer 27

It carries its own RNA template and adds repeating DNA sequences to the ends of chromosomes

Question 28

What are the three key principles of DNA replication?

Answer 28

1.) Semiconservative (each new molecule has one old + one new strand) 2.) Directional (5′ → 3′ synthesis) 3.) Template-dependent (base pairing ensures accuracy)

Question 29

What are telomeres?

Answer 29

Repetitive, noncoding DNA sequences at chromosome ends that protect genes.

Question 30

What is telomerase?

Answer 30

An enzyme that extends telomeres to prevent chromosome shortening, contains both RNA and protein

Question 31

What strand does telomerase extend?

Answer 31

The parental strand (3′ end)

Question 32

What is the purpose of PCR & what components are required?

Answer 32

To artificially replicate (amplify) a specific DNA region Need: DNA template, primers, DNA polymerase, dNTPs, buffer, Mg²⁺ ions

Question 32

Where does DNA replication begin in cells?

Answer 32

At the origin of replication (ori)

Question 33

In what direction is the template DNA read?

Answer 33

3′ → 5′ direction

Question 34

What is the difference between PCR and DNA replication in cells?

Answer 34

PCR: artificial, uses heat + defined primers. Cells: natural, use helicase + primase, copies entire genome

Question 35

What is the role of dNTPs in DNA replication?

Answer 35

Building blocks of DNA and energy source for synthesis