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

Common Illnesses and Their Causes

Illnesses Caused by Viruses

Viruses are responsible for a variety of illnesses, some of which are highly contagious. Here are a few examples:

• The Common Cold: A highly contagious illness that causes mild discomfort, increased nasal secretions, congestion, and sneezing. It typically does not cause fever. Transmission occurs through direct contact, but the virus can also spread through the air. Frequent handwashing is crucial for prevention.
• Flu (Influenza): Often confused with the common cold due to its prevalence in winter and similar transmission methods. However, the flu generally causes greater discomfort, including joint pain, and is a more serious illness.
• AIDS (Acquired Immunodeficiency Syndrome): A serious

James Watson: Pioneer of Molecular Biology

James Watson, a U.S. biochemist and geneticist, received the Nobel Prize in Physiology or Medicine in 1962. This prestigious award recognized his groundbreaking work in discovering the double-helix molecular structure of deoxyribonucleic acid (DNA) and its profound significance as a signaling molecule of heredity. Watson also directed the Human Genome Project from 1988 to 1992, resigning to protest the possibility of patenting genes. He is widely considered one of the fathers of modern molecular biology.

Early Life and Education

Watson pursued his studies in his hometown and at Indiana University. In 1947, he obtained the equivalent of a degree in Zoology, and in 1950, he earned his doctorate in Zoology... Continue reading "James Watson: Unraveling the DNA Double Helix" »

Cellular Functions

Cellular functions are basic units of life and conduct nutrition, relationships, and reproduction. Unicellular cells perform all these functions within a single cell, while multicellular organisms have specialized cells.

• Nutrition: Molecular intake from the external environment provides energy to renew cellular structures. This process inside the cell is known as metabolism.
• Relationships: Cells communicate with the outside environment, adapting to changes and maintaining stability.
• Reproduction: New cells are formed from existing ones. In unicellular organisms, this leads to a new being. In multicellular organisms, it replaces dying cells and increases cell numbers during growth. Cells pass their genetic material to their daughter

Item 14. Physical Agents: Thermal Environment

Introduction

Thermal environment refers to environmental conditions including:

• Temperature
• Humidity
• Physical activity

Homeotherms

Homeotherms maintain internal temperature within very narrow ranges.

• Danger: Heat stress
• Heat discomfort
• Comfort
• Discomfort from cold
• Danger: Hypothermia

Thermal Equilibrium

Thermal equilibrium between body and environment involves mechanisms of thermoregulation.

Mechanisms of Thermoregulation

Q = M ± R ± C - E

• Q: Heat generated or heat buildup
• M: Metabolic activity
• R: Radiation exchange
• C: Exchange by convection
• E: Heat lost by evaporation

Radiation Exchange (R)

Heat exchange that originates between two solid bodies in proximity.

Exchange by Convection (C)

Mechanism by which the body exchanges... Continue reading "Thermal Environment: Effects, Regulation, and Comfort" »

Soma Cells: These cells comprise the whole body, excluding the germ cells.

Germ Line: Specialized cells in reproductive organs responsible for producing gametes.

Karyogamy: The fusion of cell nuclei.

Sexual Dimorphism: Morphological differences between males and females of a species.

Fecundity: The ability to produce offspring.

Withers: When two hermaphroditic individuals mate and fertilize each other.

Parthenogenesis: A phenomenon where an unfertilized egg develops into a normal adult.

Receptaculum Seminis: A storage location for sperm after mating.

Spermatophores: Packets containing sperm that are transferred to females.

Segmentation: A series of rapid cell divisions during early embryonic development.

Morula: A solid ball of cells in the early embryo.... Continue reading "Key Concepts in Reproduction and Embryonic Development" »

Chromosomes and the Cell Cycle

Chromosomes undergo distinct changes throughout the cell cycle. Here's a summary of their states:

• Invisible Chromosomes (Chromatin) with One Chromatid: Initially, chromosomes exist as invisible chromatin fibers, each with a single chromatid.
• Formation of a Second Chromatid: A second chromatid is formed, creating a mirror image.
• Invisible Chromosomes (Chromatin) with Two Chromatids: Chromosomes remain as invisible chromatin but now consist of two chromatids.
• Condensation and Visibility: Condensation of the chromatids occurs, making the chromosomes visible.
• Visible Chromosomes with Two Chromatids: Chromosomes are now clearly visible, each composed of two chromatids.
• Separation of Chromatids: The two chromatids separate

Mendel's Laws

Mendel explained the observations made during years of crossing different types of peas in the gardens of a monastery. He collected the general laws of inheritance that later became known as Mendel's laws.

Double Helix DNA

DNA carries the genetic information. DNA is a molecule composed of four simple units, repeated often and combined in different ways (called nucleotides). There are four types of DNA nucleotides: cytosine, guanine, thymine, and adenine. A single DNA molecule is formed by two chains of nucleotides linked and facing each other, with a structure that forms a spiral staircase: a double helix.

Replication of DNA

DNA contains genetic information. When the cell divides, it is capable of making an exact copy of the entire... Continue reading "Mendel's Laws, DNA, Genes, and the Genetic Code" »

Biomolecules and Genetic Information

Biomolecules form long chains, such as in genetic information storage. These chains consist of repeating nucleotides. A nucleotide is composed of a nitrogenous base, a pentose sugar (like am5C), and a phosphate group. A nucleoside is simply a base plus a pentose sugar.

Nitrogenous bases include adenine (A), thymine (T), uracil (U), and guanine (G). Purine bases (A and G) have a two-ring structure, while pyrimidine bases (C, T, and U) have a single-ring structure. These bases contain the genetic code necessary for protein synthesis. Approximately 3000 base pairs are needed to code for a single protein. The human genome contains 46 chromosomes (23 pairs), with 22 pairs being autosomes and one pair being sex... Continue reading "Biomolecules, Genetics, and Chromosomal Variations" »

Factors Affecting Enzyme Activity

pH Effects on Enzyme Function

Enzymes exhibit an optimum pH at which their activity is maximal, characterized by a low K_m (substrate concentration) and maximum velocity. Small variations around this optimum pH value cause a sudden drop in activity. This can be due to the appearance or disappearance of electrostatic forces that alter the spatial structure of the active site, or changes in the charges of the active center and substrate, which affect their binding capacity. If the pH change is very high, the enzyme is denatured and ceases to be functional.

Temperature's Role in Enzyme Kinetics

In general, an increase in temperature increases the rate of chemical reactions. In the case of enzyme-catalyzed reactions,... Continue reading "Enzyme Activity: Factors, Inhibition, and Metabolic Control" »

Fertilization Process

Ovulation occurs about fourteen days before menstruation. The egg released from the Graafian follicle is propelled along the fallopian tube to the uterus, taking over a week for this journey.

The egg can be fertilized for only 24 hours after ovulation while traveling along the fallopian tube.

Intercourse, or the sexual act, is the introduction of the penis into the vagina. At ejaculation, sperm are released inside the vagina.

Unlike the egg, sperm are very fast. They ascend through the vagina, traverse the cervix and uterus, and reach both fallopian tubes in a few hours. They can also survive for three to five days, so if intercourse occurs in the days before ovulation, the probability of pregnancy is very high.

If the egg... Continue reading "Fertilization and Early Pregnancy Stages" »