Lecture 3 Review

DNA is a double helix with two anti-parallel strands held together by hydrogen bonds between complementary base pairs. The sugar-phosphate backbone runs on the outside, and the base pairs are on the inside.

Adenine (A) always pairs with Thymine (T) and Guanine (G) always pairs with Cytosine (C). These base pairs are held together by hydrogen bonds.

The process by which a DNA molecule is copied, resulting in two identical DNA molecules.

Each new DNA molecule consists of one original strand (template) and one newly synthesized strand.

An enzyme that adds deoxynucleotides to the 3' end of a growing DNA strand during replication.

DNA synthesis can only occur in the 5' to 3' direction. This means that new nucleotides are added to the 3' end of the growing strand.

The original DNA strand that serves as a guide for the synthesis of a new strand during replication.

The building blocks of DNA. They are composed of a deoxyribose sugar, a nitrogenous base, and three phosphate groups.

The lagging strand is synthesized discontinuously, with short Okazaki fragments that are later joined together. This happens because DNA polymerase can only add nucleotides in the 5' to 3' direction, and the lagging strand runs in the opposite direction.

Telomeres are protective caps at the ends of chromosomes that prevent them from shortening during DNA replication. This ensures that essential genetic information is not lost.

A nucleosome is the basic unit of chromatin, consisting of a DNA segment wrapped around a histone octamer (eight histone proteins).

Chromatin is the complex of DNA and proteins that makes up chromosomes. It undergoes various levels of compaction, from "beads-on-a-string" to highly condensed mitotic chromosomes.

In the nucleus, chromosomes occupy specific regions called territories, even though they are not physically separated by membranes.

DNA polymerase is incredibly accurate, making only one error for every 10 million bases it copies. This accuracy is due to its ability to select the correct nucleotide and remove incorrect ones.

Despite its accuracy, DNA polymerase is fast, copying around 100 nucleotides per second. However, even at this speed, copying the entire human genome would take about two years.

DNA replication starts at specific points called 'replication origins'. The human genome has about 20,000 of these, speeding up the process.

During replication, the DNA strands separate, creating a 'replication bubble' with two 'forks' where DNA synthesis occurs.

DNA polymerase needs a free 3'-OH group on the existing DNA strand to add new nucleotides.

Short RNA primers are synthesized by primase, providing the necessary 3'-OH group for DNA polymerase to start copying.

The leading strand of DNA is synthesized continuously, going in the same direction as the replication fork.

The lagging strand is synthesized in fragments called Okazaki fragments, as it moves in the opposite direction of the replication fork.

The lagging strand is synthesized in small segments called Okazaki fragments, which are later joined together.

The lagging strand is synthesized in fragments, leaving a gap at the end of the chromosome that cannot be replicated using traditional DNA synthesis.

A strong chemical bond formed by the sharing of electrons between atoms. It is the typical type of bond between atoms in molecules.

A bond formed by the electrostatic attraction between positively and negatively charged ions, arising from the transfer of electrons between atoms.

A weak non-covalent bond formed between a hydrogen atom covalently linked to an electronegative atom (like oxygen or nitrogen) and an electron pair of another electronegative atom.

Weak, non-covalent interactions arising from temporary fluctuations in electron distribution, creating transient dipoles in molecules.

Non-covalent interactions that drive hydrophobic (water-repelling) parts of molecules to associate with each other, minimizing their contact with water.

The four main types of macromolecules found in cells are:

1. Carbohydrates (polysaccharides) - composed of monosaccharides (sugars)
2. Lipids (fats/oils) - comprised of fatty acids (long hydrocarbon chains)
3. Proteins (polypeptides) - made up of amino acids
4. Nucleic Acids (DNA/RNA) - formed from nucleotides.

A small, simple molecule that serves as a building block for larger polymers. Examples include sugars, amino acids, and nucleotides.

A large molecule composed of multiple repeating subunits (monomers) linked together by covalent bonds.

This process is called condensation or dehydration synthesis. It involves the removal of a water molecule from the monomers as they join together.

DNA is composed of monomers called nucleotides. Each nucleotide consists of three parts: a phosphate group, a sugar (deoxyribose), and a nitrogenous base.

The four nitrogenous bases found in DNA are:

• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)

Nucleotides are linked together in a DNA strand through a phosphodiester linkage. This involves a phosphate group from one nucleotide forming a bond with the sugar of the adjacent nucleotide.

DNA strands have a directionality, meaning they have two distinct ends: 5' end and 3' end. The 5' end is where the phosphate group is attached, while the 3' end consists of a free hydroxyl group on the sugar.

Two DNA strands, running in opposite directions (anti-parallel), interact through base pairing between their nucleotides. Adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C) via hydrogen bonds.

Hydrogen bonds between base pairs are the primary force holding the two strands of DNA together, forming the double helix structure. They are also essential for the accurate replication and transcription of DNA.

DNA serves as the blueprint of life, containing the genetic instructions for an organism's development, functioning, and reproduction. It is transmitted from one generation to the next.