DNA Structure and Replication Quiz

DNA Structure and Replication

• A cell's DNA is composed of two sets of chromosomes: a maternal set (n = 3) and a paternal set (n = 3), with a total of 2n = 6 chromosomes.
• Each chromosome consists of two sister chromatids joined at the centromere.

DNA Replication

• DNA replication is a biological process that occurs in all living organisms, copying their DNA, and is the basis for biological inheritance.
• The process starts with one double-stranded DNA molecule producing two identical copies of the molecule.
• DNA replication occurs during the S phase of the cell cycle.
• It is a semiconservative process, resulting in a double-stranded molecule that synthesizes to produce two new double-stranded molecules, each containing one original strand and one new strand.

Origins of Replication

• Replication begins at specific sites on the DNA molecule called origins of replication.
• Origins are specific sequences of bases.
• Mammalian DNA has many origins.

Replication Fork

• The replication fork is a structure that forms within the nucleus during DNA replication.
• It is created by helicases, which break the hydrogen bonds holding the two DNA strands together.

Chargaff Rule

• The Chargaff Rule states that A = T and G = C, which is a base ratio.

Watson-Crick Model of DNA Structure

• The Watson-Crick model describes the structure of DNA as a double helix, where one complete turn is 10 base pairs, and the space between base pairs is 0.34 nm.
• The spatial relationship between the two strands creates a major (wide) groove and a minor (narrow) groove.
• The bases in these grooves are exposed and interact with proteins or other molecules.
• The phosphate backbone has a negative charge, facilitating the binding of specific proteins.
• The model explains how genetic information is stored in the sequence of bases, which have a high coding capacity.
• The model also explains how DNA is copied, and how mutations occur.

DNA Denaturation and Renaturation

• DNA denaturation is the process by which the double strands separate into single strands, disrupting the hydrogen bonds between the paired bases.
• This can be achieved through acidic or alkaline pH, or heating.
• Complementary DNA strands can reform the double helix under appropriate conditions.

Nucleotides Structure

• Nucleotides are formed by covalent bonding of the phosphate, base, and sugar.
• The N-glycosidic bond and phosphate ester bond are key components of nucleotide structure.

Nucleotides Nomenclature

• Deoxyribonucleotides are formed by covalent bonding of the phosphate, base, and sugar.
• Deoxyadenosine (nucleoside) can be phosphorylated to form deoxyadenosine monophosphate (dAMP), diphosphate (dADP), and triphosphate (dATP).

Polynucleotides

• Nucleotides are covalently linked via 3'→5' phosphodiester bonds to form polynucleotides chains.
• The resulting chain has polarity, with a 5'-end and a 3'-end that are not linked to other nucleotides, resulting in a chain with 5'→3' direction.
• DNA has two polynucleotides chains, while RNA has only one.

The Watson-Crick Model of DNA Structure

• According to the Watson-Crick model, DNA is composed of two polynucleotide chains running in opposite directions (antiparallel), one chain running in the 5'→3' direction and the other in the 3'→5' direction.
• The two chains are twisted (coiled) around each other in a right-handed double helix.
• The hydrophilic deoxyribose-phosphate backbone of each chain is on the outside, while the hydrophobic bases are stacked inside, paired by hydrogen bonds.
• The overall structure resembles a twisted ladder.
• Base pairing is highly specific: A pairs with T by two hydrogen bonds, and C pairs with G by three bonds.

Test your knowledge on the structure and replication of DNA, including chromosomes, sister chromatids, and the biological process of DNA replication.