2. DNA Replication

Question 1

DNA

Answer 1

• Deoxyribonucleic acid
• Two linked strands that wind around to create a double helix. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T). In RNA, uracil (U) is substituted for thymine (T).
• complementary base-pairing is crucial for DNA replication and transcription.

Question 2

DNA Structure

Answer 2

• Each cell contains 46 chromosomes
• 3 billion bases
• ~ 30,000 genes that code for specific proteins

Question 3

Chromatid

Answer 3

one of the two identical halves of a chromosome that has been replicated in preparation for cell division. The two “sister” chromatids are joined by a centromere.where spindle fibres will attach in mitosis

Question 4

Chromatin

Answer 4

Chromatin refers to a mixture of DNA and proteins that form the chromosomes found in the cells of humans and other complex organisms.

Question 5

Diploid and Haploid

Answer 5

Question 6

Homologous chromosomes

Answer 6

Question 7

Nucleotide

Answer 7

Question 8

Genes and Alleles

Answer 8

Gene is defined as a section of DNA that encodes for a certain trait. An allele is defined as a variant form of a gene. It determines an organism’s genotype. There are dominant allele or recessive alleles. A locus is the position on a chromosome where a gene is found.

Question 9

Karyotype

Answer 9

An individual’s complete set of chromosomes

Question 10

Why does DNA Replicate

Answer 10

Replication is an essential process that occurs before mitosis, whenever a cell divides, the two new daughter cells must contain the same genetic information, or DNA, as the parent cell

Question 11

Process of DNA Replication

Answer 11

1. Replication starts at a specific sequence on the DNA molecule.
2. DNA helicase (enzyme) unwinds and unzips DNA, breaking the hydrogen bonds that join the base pairs, and forming two separate strands.
3. The new DNA is built up from the four nucleotides (A, C, G and T) that are abundant in the nucleoplasm.
4. These nucleotides attach themselves to the bases on the old strands by complementary base pairing.
5. DNA polymerase joins new nucleotides to each other by strong covalent bonds, forming the phosphate-sugar backbone.
6. A winding enzyme winds the new strands up to form double helices.
7. The two new molecules are identical to the old molecule.

Question 12

Direction of DNA Replication

Answer 12

5′-to-3′ direction

Question 13

Leading Strand

Answer 13

In DNA replication, the leading strand is the strand of DNA along which the new strand is synthesized continuously, in the same direction as the fork.

Question 14

Lagging Strand

Answer 14

In DNA replication, the lagging strand is the strand of DNA along which the new strand is synthesized discontinuously, in fragments.

Question 15

Okazaki Fragments

Answer 15

Okazaki fragments are the short fragments of DNA that are synthesized discontinuously along the lagging strand during DNA replication.

Question 16

DNA Ligase

Answer 16

DNA ligase is an enzyme that can join okazaki fragments by forming a bond between the gaps in the sugar–phosphate backbone of DNA.

Question 17

Semiconservative Replication

Answer 17

Semiconservative replication describes the mechanism of DNA replication in all living cells, in which each new DNA molecule is composed of one original strand of DNA and one newly synthesized strand of DNA.

Question 18

Somatic v Gamete

Answer 18

Somatic (body) cells contain two full sets of chromosomes, making them diploid cells (2n). Gametes are reproductive cells (egg and sperm), they are haploid (n), containing only one set of chromosomes