Notes, summaries, assignments, exams, and problems for Biology

Punctuated Equilibrium

The fossil record, while incomplete, reveals periods of stability punctuated by the sudden appearance of new species. These species often remain unchanged for extended periods before disappearing abruptly. In 1972, Gould and Eldredge proposed punctuated equilibrium to explain these sudden shifts, suggesting that not all evolutionary changes are gradual. Periods of stasis, where species remain unchanged, alternate with short bursts of rapid change (speciation), during which new species emerge from existing ones.

Gradualism vs. Punctuated Equilibrium

Gradualism

Species evolve along a single lineage, transforming slowly and continuously through small changes over long periods. The entire population transforms, not just isolated... Continue reading "Evolution: Gradualism vs. Punctuated Equilibrium" »

DNA Replication Process

DNA replicates just before cell division, ensuring daughter cells inherit the same genetic information as the stem cell. Genetic information is transmitted via genes. In general, each DNA strand serves as a template. Specific enzymes, known as DNA polymerases, join nucleotides one by one. A new chain is formed that is complementary to the template and identical to the chain that was previously attached to it. This process results in two double-stranded DNA molecules.

On occasion, errors occur during DNA replication that give rise to mutations. Some mutations can lead to certain types of diseases. The extraordinary importance of base complementarity allows DNA strands to be copied from a stem cell to a daughter cell, and... Continue reading "DNA Replication, Gene Expression, and Recombinant DNA" »

The Circulatory System: Heart, Blood, and Vessels

The circulatory system is a vital network responsible for transporting blood throughout the body, delivering essential substances to cells, and removing waste products. It primarily consists of the heart, blood vessels, and blood.

Blood Composition

Blood is a complex fluid composed of two main parts:

• Plasma: The liquid component, primarily water, containing dissolved salts, proteins, lipids, glucose, and urea.
• Blood Cells: Various types of cells suspended in the plasma.

Blood Cells

The main types of blood cells include:

• Red Blood Cells (Erythrocytes): The most abundant cells, non-nucleated, containing the red pigment hemoglobin, which is crucial for transporting oxygen (O2).
• White Blood Cells (Leukocytes)

Prokaryotes and Eukaryotes

Prokaryotes are small, simple cells with their genetic material dispersed throughout the cytoplasm. Eukaryotes are larger, more complex cells with their genetic material contained within a structure called the nucleus, separated from the cytoplasm by a membrane called the nuclear membrane.

• Animal Cell: Found in protozoa and animals.
• Plant Cell: Found in algae and plants.

Photosynthesis

Photosynthesis is the process by which organisms synthesize energy-rich organic molecules, such as glucose, from inorganic substances lacking energy. Sunlight provides the necessary energy. Photosynthesis occurs in leaves and green stems and takes place within chloroplasts.

Formula: H₂O + CO₂ + sunlight = Mineral salts = Glucose + O₂

Cellular

Cellular Digestion: Monomers, Polymers, and Enzymes

Cells may absorb simple molecules (monomers). Monomers are scarce in nature. Typically, there are large molecules (polymers), where hundreds or thousands of simple molecules are joined together, forming foods. Digestion is a process where digestive enzymes break down the bonds between monomers, releasing free monomers. Digestive enzymes are specific to each polymer.

For example, amylase breaks down the links between glucose molecules in starch. Lipase separates fatty acids from glycerol in fats. Proteases break the links between amino acids in proteins, releasing them. The digestive system is essentially a tube. Food undergoes a series of transformations during its journey.

These actions are... Continue reading "Cellular Digestion: Monomers, Polymers, and Digestive Enzymes" »

Regulation of Gene Expression

Cells do not continuously synthesize proteins, which could result in metabolic chaos. There must be a regulation. Jacob and Monod devised a model for gene regulation in bacteria called Operon. An operon is a set of genes on the chromosome, fairly close together, that encode proteins involved in related metabolic processes. In each operon, there are two classes of genes:

• Structural genes

  (z, A) that code for the synthesis of proteins in a given process.

• Regulator gene

  (I) that codes for the synthesis of a repressor protein, which controls the expression of structural genes.

There are also two regions close to these genes whose base sequences influence regulation:

• The promoter (P)

  Next to the structural genes, this is the

The Human Heart: Anatomy and Function

The heart is an organ about the size of a fist, located in the center of the chest, slightly to the left. It is comprised of two atria and two ventricles. Blood enters the atria through the veins and is driven out of the ventricles through the arteries. The heart has valves that force the blood to circulate in one direction.

The Heartbeat

The beating of the heart is the most noticeable manifestation of its activity. The frequency with which the heart beats varies according to the body's needs. Every heartbeat follows a set of phenomena that constitute a cardiac cycle:

• Atrial systole: The atria contract and push blood into the ventricles.
• Ventricular systole: The ventricles contract, and blood leaves through

Genetic Engineering: Understanding the Building Blocks

Genetic engineering relies on our knowledge of the genetic code, gene regulation mechanisms, transcription, translation, and reduction. Automated sequencing techniques, restriction enzymes, and a set of other tools allow us to split and join DNA fragments. These fragments, when combined with other macromolecular carrier DNA, enable the transfer of genetic information between organisms. These are called recombinant DNA molecules.

Key Processes in Genetic Engineering

• DNA Transformation: A cell undergoes a genetic change resulting from the entry of a foreign DNA molecule into its core.
• Transduction: The process of transferring genetic information (e.g., in bacteria) without direct contact, often

Endocrine System

We are formed by a series of glands, whose main characteristic is the production of substances called hormones. These hormones, usually discharged into the blood, perform a variety of functions. They regulate the growth, development, and function of many tissues and coordinate the body's metabolic processes. The most important function is to maintain homeostasis. Some of these glands are:

Hypophysis

A small gland housed at the base of the skull in the center of the sphenoid bone (sella turcica). It produces growth hormone and antidiuretic hormone.

Thyroid

A gland in the neck, at the height of the first tracheal rings. It regulates the growth and maturation of tissues.

Parathyroid

There are four glands located in the back of the thyroid.... Continue reading "Endocrine and Urinary Systems: Functions and Anatomy" »

Genetic Fingerprint

Genetic fingerprinting is a technique capable of distinguishing and identifying individuals through individual peculiarities in their own DNA.

Mutations

Mutations are alterations in the genetic information of cells that may occur spontaneously in any cell of a living being. Their consequences can be negative, neutral, or harmless, but also advantageous or beneficial.

Gene Mutations

Gene mutations are mutations affecting the nucleotides of DNA.

Chromosomal or Genomic Mutations

Chromosomal or genomic mutations affect chromosome number or structure. They are due to errors in the processes of meiosis. When they affect the whole chromosome, it is called genomics.

Biotechnology

Biotechnology consists of a set of techniques or processes... Continue reading "Genetic Fingerprinting, Mutations, and Biotechnology" »