Lecture 16 - Structure and Replication of DNA

Question 1

What is DNA? What are the three main components of its functional unit?

Answer 1

Deoxyribonucleic acid is a double-stranded, polypeptide molecule. It is made up of nucleotide molecules, each made up of a deoxyribose sugar, a phosphate group, and a nitrogenous base.

Question 2

A deoxyribose sugar have five carbons, each numbers in a particular order. To which end is the phosphate group connected to?

Answer 2

5’ end

Question 3

Nitrogenous bases are categorized into two groups. What are they and mention its members.

Answer 3

Purine - Adenine and Guanine

Pyrimidine – Thymine and Cytosine

Question 4

What are the pairs of nitrogenous bases?

Answer 4

A-T and G-C (3 hydrogen bonds)

Question 5

Genes are mostly locate din chromosomes. Prokaryotic chromosome are found in _______. Eukaryotic chromosomes are found in the ________.

Answer 5

cytosol, nucleus

Question 6

Chromosome consists of ______ and ______. Together, they form _______ which is the unfolded form of chromosomes.

Answer 6

DNA, protein (histones), chromatin

Question 7

DNA is packaged with proteins called _____ to form the _______ (the basic unit of chromatin).

Answer 7

histones, nucleosome

Question 8

(Extra) The _______ clamps the DNA double helix to a core of ___ histone molecules.

Answer 8

Histone H1, 8

Question 9

Differ between euchromatin and heterochromatin in the context of epigenetic event.

Answer 9

Euchromatin is loosely coiled DNA that is transcriptionally active. Heterochromatin is tightly packed DNA that is transcriptionally inactive.

Methylation of promoters (epigenetic event) may convert euchromatin to heterochromatin.

Question 10

DNA replication occurs during the _____ stage of the cell cycle.

Answer 10

Synthesis

Question 11

DNA replication in eukaryotes and prokaryotes start at the _______.

Answer 11

Origin of Replication

Question 12

Describe function of helicase.

Answer 12

separates strands of DNA (anti-parallel)

Question 13

Once the DNA strand is separated, considering the unstable nature of ssDNA, which compounds help separate the strands apart?

Answer 13

the enzyme topoisomerase relieves supercoiling of single-stranded DNA, while single-stranded binding proteins keep the strands apart

Question 14

Differ the function of DNA polymerase I and III.

Answer 14

DNA polymerase III is responsible for DNA replication by adding complement bases to the template (requiring a short double-stranded region to start).

DNA Polymerase I replaces RNA primers with DNA sequences.

Question 15

DNA Polymerase III can only read DNA from ___ to ____. Hence, bases are added from the ____ to the ___.

Answer 15

3’ –> 5’ end

5’–>3’ end

Question 16

Explain the concept of a leading and lagging strand.

Answer 16

The leading strand is the strand of DNA which is being synthesized in the same direction as the growing replication fork.

The lagging strand is the strand of DNA which is being synthesized in the opposite direction as the growing replication fork.

Question 17

Short sequences forms on lagging strands are called ______.

Answer 17

Okazaki fragments

Question 18

Differ between prokaryotic and eukaryotic replication.

Answer 18

Longer Okazaki fragments and faster rate of base addition in prokaryotes, eukaryotes have various types of DNA polymerase, eukaryotic DNA replication also involves the replication, disassembly, and assembly at the replication fork

Question 19

Chromosomes require three elements to function. Mention all of them and explain.

Answer 19

Telomeres: structural stability, replication

Centromeres: essential for segregation during cell division

Origo: replication start point

Question 20

What are telomeres? What are their importance in the context of DNA replication?

Answer 20

Telomeres are repeated sequence at the ends of chromosomes. It acts as a buffer to the degradation of functional gene sequence in the gene sequence by looping or recruiting protective protein.

Question 21

How does degradation of chromosome occur? In which strand?

Answer 21

During lagging strand replication, sometimes there is a overhang, where there is not enough base sequence for primer placement and DNA replication. The overhang therefore is not replicated and is degraded.

Question 22

How does telomerase lead to the concept of immortal cells?

Answer 22

Enzyme telomerase extends the lagging strand, allowing DNA polymerase to complete replication. This extension of the telomeres can occur indefinitely and in theory lead to immortal cells.

Question 23

(Bonus) Explain how high levels of telomerase in cells may not be beneficial to an individual.

Answer 23

Damaged cells which normally would degrade faster would be repeated continuously, increasing risk in the error in the metabolic pathway.

Cancer cells have high levels of telomerase, allowing its capability of unlimited self-renewal.