Introduction to the Respiratory System

The ventral wall of the foregut forms a groove, which then develops into a pouch called the laryngotracheal diverticulum. This diverticulum eventually gives rise to the larynx, trachea, and lung buds.

The laryngotracheal diverticulum divides into two parts. The distal end forms the right and left lung buds, which will develop into the bronchi and lungs. The undivided part becomes the trachea, and the opening of the diverticulum forms the larynx.

A condition where there is a connection between the trachea and esophagus, often accompanied by a blockage in the esophagus. This can occur due to incomplete separation of the trachea and esophagus during development.

The respiratory system is divided into two main parts: the upper respiratory tract (nose, nasal cavity, pharynx) and the lower respiratory tract (larynx, trachea, bronchi, lungs).

The development of the lungs progresses through four distinct stages: embryonic, pseudoglandular, canalicular, and saccular. Each stage is characterized by specific structural changes and advancements in branching and vascularization.

The first stage of lung development, occurring from 5 to 16 weeks of gestation. At this stage, the lung buds branch and form primitive airways resembling glands.

The second stage of lung development, occurring from 16 to 25 weeks of gestation. During this stage, the airways continue to branch and differentiate into terminal bronchioles and respiratory bronchioles. The terminal bronchioles end in small, saccular structures called terminal sacs.

The third stage of lung development, occurring from 26 weeks of gestation to birth. Alveolar tissue is rapidly forming, with the appearance of more developed capillaries and thin-walled alveoli. This stage allows for significant gas exchange development.

The final stage of lung development, beginning at birth and continuing until approximately 8 years of age. At this stage, the alveoli mature and expand, increasing the surface area for gas exchange.

Cells found in the terminal sacs of the lungs during the Canalicular Stage. These cells are responsible for producing surfactant, a substance that helps reduce surface tension in the alveoli, enabling them to expand properly for breathing.

A condition that occurs in premature infants, where the lungs lack sufficient surfactant. This deficiency leads to difficulty inflating the alveoli and can cause respiratory distress.

A substance produced by type II alveolar cells in the terminal sac stage. Surfactant reduces the surface tension within the alveoli, allowing the lungs to expand properly and preventing them from collapsing during exhalation.

These bronchioles branch out from the terminal bronchioles and are responsible for distributing air into the terminal sacs during the Canalicular and Terminal sac stages.

DNA and RNA are the fundamental building blocks of life, carrying genetic information. They are composed of smaller units called nucleotides.

A nucleotide is a molecule consisting of three parts: a nitrogen-containing base, a five-carbon sugar, and one or more phosphate groups.

There are two main types of sugars in nucleotides. DNA uses deoxyribose, while RNA uses ribose.

Nucleotide bases are categorized into two groups: purines and pyrimidines. Purines are adenine (A) and guanine (G), while pyrimidines are cytosine (C), thymine (T) (only in DNA), and uracil (U) (only in RNA).

The bond that joins a base to a sugar is called a glycosidic bond. It connects the 1' carbon of the sugar to the nitrogen atom of the base.

A nucleoside consists of a base and a sugar. When a phosphate group is added to a nucleoside, it becomes a nucleotide.

Nucleotides play numerous roles in the body, including energy storage (ATP) and participating in signaling pathways.

Chemical modifications made to RNA after its synthesis. These changes often occur in directly functional RNAs and are usually permanent, not regulatory.

A type of RNA modification that involves replacing the ribose sugar with a morpholine ring and the phosphodiester bonds with non-ionic phosphorodiamidate groups.

The hydroxyl group (OH) on the 2' carbon of the ribose sugar in RNA plays a crucial role in RNA structure and function.

The 2' OH in ribose helps facilitate a reaction that can break phosphodiester bonds, which links nucleotides together in RNA.

RNA molecules, especially directly functional RNAs, often require chemical modifications after synthesis.

Modifications to tRNA are often conserved across different species, highlighting their vital importance for tRNA function.

Approximately ~10% of the 75 nucleotides in tRNA are modified.

Modifications to RNA are usually permanent and are not regulatory.

Chemical modifications in RNA molecules often reflect their crucial functional roles.

Closed circular DNA can be twisted upon itself. The number of bases per turn changes, causing it to coil into a compact structure.

Supercoiling can be positive or negative, depending on the direction of DNA twisting.

Clockwise winding of DNA separates the strands, resulting in negative supercoiling.

Counterclockwise winding of DNA compacts the strands, resulting in positive supercoiling.

Supercoiling can be released by cutting one of the DNA strands.

DNA and RNA are polymers of nucleotides. They are joined by a phosphodiester bond between the 3' hydroxyl of one sugar and the phosphate attached to the 5' hydroxyl of the next.

Nucleic acid strands have directionality. One end has an exposed 3' hydroxyl, the other has a 5' phosphate. They are always written in the 5' to 3' direction.

The repetitive sugar-phosphate backbone forms the structural foundation of DNA and RNA, while the attached bases are the variable components that carry genetic information.

Chargaff's Rule states that the amount of adenine (A) always equals thymine (T) and cytosine (C) always equals guanine (G) in double-stranded DNA. Furthermore, the total purines (A + G) equal the total pyrimidines (C + T).

Two DNA strands associate via non-covalent hydrogen bonds to form double-stranded DNA. A pairs with T with 2 hydrogen bonds, and C pairs with G with 3 hydrogen bonds.

The sequence of one DNA strand dictates the sequence of the other strand. They are complementary to one another and run antiparallel, meaning their 5' ends face opposite directions.

The Watson-Crick model is a double helix structure with the hydrophobic bases clustered in the center and the hydrophilic sugar-phosphate backbone on the outside. The base pairs form a stack in the interior of the helix.

Rosalind Franklin's X-ray diffraction images of DNA were crucial in determining its double helix structure, although she did not receive adequate recognition at the time.

The Watson-Crick model explained the structure of DNA and laid the foundation for understanding how genetic information is stored and transmitted.

In 1962, James Watson, Francis Crick, and Maurice Wilkins received the Nobel Prize in Physiology or Medicine for their work on the structure of DNA.

Van der Waals interactions between stacked nitrogenous bases in DNA provide stability to the helix structure, contributing to the overall stability of DNA.

DNA, the genetic material in most living organisms, has a double helix structure that is maintained by hydrogen bonds between complementary base pairs (A-T and G-C) and van der Waals interactions in base stacking.

The width of A-T and G-C base pairs are approximately the same, resulting in a consistent diameter of the DNA helix, around 20 Å.

B-DNA, the most common form of DNA, has a helical structure that repeats every 10.5 base pairs, with a distance of 3.4 Å between each pair.

B-DNA has a major groove (13 Å) and a minor groove (9 Å) , which serve as binding sites for proteins that interact with DNA.

Regions of DNA with a high proportion of A-T base pairs tend to be more flexible, as the weaker hydrogen bonds between A and T allow for more bending compared to G-C base pairs.

A-DNA is a right-handed helix, but it has 11 base pairs per turn, resulting in grooves that are more evenly sized compared to B-DNA. This conformation can occur due to the binding of specific proteins to DNA.

Z-DNA, left-handed helix, can be induced by factors like cytosine methylation, torsional stress, or high salt concentrations.

Eukaryotic DNA is organized into linear chromosomes, often found within the nucleus, while prokaryotic DNA is typically circular, located in the cytoplasm.

DNA packaging in eukaryotes involves wrapping DNA around histone proteins, forming nucleosomes that are further organized into chromatin fibers and ultimately into chromosomes.