Notes, abstracts, papers, exams and problems of Biology

Respiratory System

The respiratory system is formed by the ducts through which air circulates, and by small cavities called alveoli, which are capable of entering the bloodstream. At the same time, blood circulates CO2 through the tubes of the respiratory system.

Upper Respiratory Tract

• Nose and nostrils: Two cavities located in the center of the face. Function: To warm and moisten the air.
• Pharynx: Connects the mouth with the larynx and nasal passages. It also communicates through the auditory tube. It forms part of the respiratory and digestive tracts.
• Larynx: Formed by cartilage and bone, it connects the pharynx with the trachea. It contains the vocal cords, which vibrate with airflow to produce the voice.

Lower Respiratory Tract

• Trachea: A tube

Cell Adhesion Molecules (CAMs): Types and Functions

Structurally, there are five families of CAMs: Cadherins, Immunoglobulin superfamily, Integrins, Selectins, and Proteoglycans.

Cadherins

Cadherins are monomeric molecules, which are receptors that bind *homophilically* (to identical cadherins) or *heterotypically* (to different cadherins) expressed on cells for cell-cell contact. Their action is calcium and temperature-dependent. A cell can express more than one type of cadherin. At least twelve types are known, but the most studied are:

• E-cadherin: Present in epithelia of various tissues, such as liver and kidney.
• N-cadherin: Found in neural tissue and heart muscle.
• P-cadherin: Found in the placenta.

Cadherins allow cell adhesion and maintenance... Continue reading "Cell Adhesion Molecules: Types and Functions" »

Touch

The skin is the largest organ of our body, composed of two layers:

• Epidermis: The outer layer is formed by epithelial tissue. The outer cells are dead and continuously shed as flakes and dandruff.
• Dermis: The inner layer, formed by connective tissue, provides elasticity to the skin. The dermis contains numerous blood vessels and tactile receptors.

Smell

The inside of the nostrils is lined by a mucosa called the pituitary gland. Two regions can be distinguished:

• Red pituitary: Occupies the lower part, has several blood vessels that warm the incoming air.
• Yellow pituitary: Occupies the upper part, contains numerous olfactory receptors.

Taste

At the top of the tongue are numerous projections called taste papillae. These contain sensitive cells (chemoreceptors)... Continue reading "Human Sensory and Locomotor Systems: Functions & Health" »

Fundamentals of Genetics and Chromosomes

In humans, there are 46 chromosomes, occurring in 23 pairs. The diploid number refers to the total number of chromosomes in each body cell of a plant or animal.

Key Genetic Terms

• Gene: A length of DNA that is the code for making a specific protein molecule. Genes are always located in the same position on a chromosome.
• Allele: Different versions of the same gene.
  • A dominant allele is expressed and affects the appearance (phenotype) of the individual.
  • A recessive allele is only expressed if two copies are present or if the dominant allele is absent.
• Genotype: The specific combination of alleles an organism possesses for a trait.
  • Homozygous: Having two identical alleles for a trait (e.g., TT or tt).
  • Heterozygous:

DNA Replication

The process of DNA duplication, which allows identical genetic information to be shared between cellular daughters, consists of the following:

• The two strands of the double helix are separated.
• Free nucleotides can join the DNA nucleotides through their complementary bases. Only the nucleotides A can be combined with T, and C with G.
• The new nucleotides bind and form new DNA chains.
• Each of the two DNA chains serves as a template to create new strands.

Protein Synthesis

Proteins are formed by the joining of smaller molecules called amino acids. There are over 20 types of amino acids in different proteins. The order in which amino acids bind determines the type of protein.

Each cell produces thousands of proteins in its ribosomes, using... Continue reading "DNA Replication, Protein Synthesis, and Gene Therapy" »

Special Types of Cell Division

• Budding: Casts asymmetric cytoplasmic material; the daughter cell emerges as a bud from one side of the mother, such as in yeast or sponges.
• Sporulation: Several successive mitoses occur without cytokinesis; multinucleate cells are formed, for example, in fungi and protozoa.

Meiosis

To condense, look better.

Meiosis I

Stages of Prophase I

It is the most complex stage, with five sub-phases:

1. Leptotene: Chromosomes condense to become visible by light microscopy. Each is composed of two chromatids.
2. Zygotene: Homologous chromosomes pair up until they are completely aligned along their length. This pairing is called synapsis and occurs through a protein structure called the synaptonemal complex.
3. Pachytene: Crossover (chromatid