Notes, summaries, assignments, exams, and exercises for Biology for Baccalaureate

DNA: The Molecule of Life

DNA (Deoxyribonucleic Acid) is the biomolecule responsible for carrying genetic information. A core component of chromosomes and found within the nuclei of eukaryotic cells, DNA belongs to the nucleic acid family. DNA is formed from nucleotides, each composed of a monosaccharide, a phosphoric acid, and a nucleobase. DNA consists of four types of nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G). DNA comprises two chains of nucleotides coiled together, forming the double helix. Adenine pairs with thymine, and cytosine pairs with guanine. The sequence refers to the order in which nucleotides are arranged. DNA duplication or replication is the process where a cell makes an exact copy of its DNA to share...

Nonspecific Immune Defense Mechanisms

Nonspecific mechanisms include the inflammatory response, activation of the complement system, and the action of interferon. These mechanisms are highly effective, and few foreign elements bypass this control. However, when a pathogen escapes, specific mechanisms are activated, namely the cellular immune response and the humoral immune response.

The Inflammatory Response

This mechanism activates when the skin or mucous membranes are injured. The symptoms of inflammation are easily recognizable:

• Redness
• Swelling
• Local pain
• Fever

Why do these symptoms occur? The redness of a wound is caused by an increase in blood flow to the area. This increase is due to the release of pyrogenic substances, such as histamine, by...

First Meiotic Division (Meiosis I or Reduction Division)

It is so named because it reduces by half the number of chromosomes in the initial cell. That is, it starts with a diploid cell, the meiocyte, and produces two haploid cells.

Phases of Meiosis I

The first meiotic division is subdivided into four phases: Prophase I, Metaphase I, Anaphase I, and Telophase I.

Prophase I

It is the longest stage, which can last for months or even years. At the end of Prophase I, the nuclear envelope disintegrates along with the nucleolus, and the mitotic spindle structure forms, similar to mitotic prophase. However, two events unique to meiosis occur: crossing-over and genetic recombination.

To facilitate study, Prophase I is subdivided, in turn, into five stages:...

Mendelian Heredity

Gregor Mendel's experiments on pea plants revealed that inheritance is transmitted through heredity, following simple statistical norms.

Mendelian Inheritance

These are the rules governing the transmission of characteristics from one generation to the next.

1st Law (Uniformity)

In the first generation, all offspring are identical if one of the parents is homozygous dominant and the other is homozygous recessive.

2nd Law (Segregation)

Hereditary factors separate during gamete formation, leading to new combinations.

3rd Law (Independent Assortment)

Characters are transmitted independently, as long as the genes are located on different chromosomes.

Post-Mendelian Heredity

Mendel's laws were extended to animals, and it was later discovered...

DNA Replication: A Detailed Explanation

DNA replication is a fundamental process in all living organisms. It ensures the accurate duplication of the genome before cell division. This process involves several key steps and enzymes.

1. Unwinding the DNA Helix

The first step involves unwinding and opening the DNA helix. This process, also known as DNA despiralization, separates the two DNA strands. Specific enzymes, including helicases, attach to the DNA strands and unwind them. Topoisomerases prevent the formation of knots during this unwinding process.

Replication begins at specific points of origin. In prokaryotes, there is typically one point of origin, while eukaryotes have multiple origins due to their larger DNA content. Helicases break the...

Central Dogma

The Central Dogma concept illustrates the mechanisms and expression of genetic inheritance. The DNA molecule contains useful biological information that is stably transmitted. The process involves DNA replication without variation from cell to cell and generation to generation, with simple mechanisms for the translation of messages. Occasional variations may occur, reflecting the biological needs of organic evolution, leading to the production of new genotypes on which natural selection can act. DNA structure allows for mutation and recombination.

Cloning

Cloning is the process of obtaining one or more individuals from a somatic cell or a nucleus from another individual, so that the cloned individuals are identical or nearly identical...

The Double Helix of DNA

Deoxyribonucleic acid (DNA) is a molecule composed of simpler molecules: a pentose sugar called deoxyribose, phosphoric acid, and four nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

DNA is formed by two antiparallel strands of DNA. This double chain is held together by hydrogen bonds that are established between their nucleobases. This forms the characteristic double helix structure of DNA.

Its function is to carry the genetic information encoded in a living organism and it has the ability to replicate itself.

DNA Replication

The information contained in DNA encodes all the bases, the basic pattern of inheritance of each species. It contains all the information that needs to be transmitted intact...

Gametogenesis: The Formation of Gametes

Gametogenesis is the process of gamete formation, through which haploid gametes originate from undifferentiated diploid cells via a meiotic process. This process can be either spermatogenesis or oogenesis.

Specifically, spermatogenesis is the formation of male gametes (sperm), and oogenesis is the formation of female gametes (eggs).

Spermatogenesis Stages

• Propagation: Germ cells originate by mitosis from other germ cells (spermatogonia).
• Growth: Enlarged spermatogonia transform into first-order spermatocytes (2n).
• Maturation: Meiosis occurs. Each first-order spermatocyte (2n) undergoes the first meiotic division, leading to two second-order spermatocytes (n). In the second meiotic division, these will form

Asexual Reproduction in Animals

This is a reproductive process in which new individuals arise from the somatic cells of a single parent. It is common in less evolved animals.

Budding

This consists of the formation of a multicellular outgrowth (bud) on the parent animal's body. Later, these buds may separate to form an independent adult, or they may remain attached, giving rise to colonies, as seen in corals.

Fragmentation (Excision)

The parent body divides into two or more parts, each capable of regenerating into a new animal. Fragmentation can be:

• Longitudinal: Division occurs parallel to the main body axis.
• Transverse: Division occurs perpendicular to the main body axis.

Strobilation

This is a form of multiple transverse fragmentation found in some...

Endocrine Pharmacology Study Roadmap

🔹 1. Thyroid Physiology & Pathophysiology

🔸 Physiology

• TRH (hypothalamus) → stimulates TSH (anterior pituitary) → stimulates T3/T4 release (thyroid)

• T3 = active, T4 = prohormone

• Feedback loop: T3/T4 inhibit TRH and TSH

• T3/T4 actions:

  • ↑ Metabolic rate, heart rate, cardiac output

  • ↑ Oxygen consumption, lipolysis, glucose metabolism

  • CNS effects (mood), reproductive effects

🔸 Synthesis

• Iodide uptake → oxidation to iodine → binds to thyroglobulin → forms MIT/DIT → forms T3/T4

🔸 Disorders

• Hypothyroidism: Hashimoto's thyroiditis, iodine deficiency, thyroidectomy, myxedema coma

• Hyperthyroidism: Graves' disease, toxic adenoma, thyroid storm

🔹 2. Thyroid Pharmacology

🔸 For Hypothyroidism

• Levothyroxine