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

The Miller-Urey Experiment: Origin of Life

The Miller-Urey experiment represents the first demonstration that organic molecules can form spontaneously from simple inorganic substances under simulated early Earth conditions. This groundbreaking experiment provided crucial insights into the chemical origins of life.

In the experiment, a gaseous mixture (simulating Earth's early atmosphere) was introduced into a sealed flask, where water was kept boiling to mimic the primordial ocean. The resulting vapor then underwent condensation. Substances were circulated continuously through the experimental setup, while two electrodes consistently produced electric shocks, simulating lightning.

Crucially, samples were extracted from the apparatus for analysis.... Continue reading "Evolutionary Biology: Miller-Urey, Lamarck, and Natural Selection" »

Levels of Biological Organization

Living matter is organized into distinct levels, categorized as abiotic or biotic:

• Abiotic: Components that do not conform to living matter, such as inert substances.
• Biotic: Components exclusive to living organisms.

Hierarchy of Living Matter

• Subatomic: Particles and atoms.
• Atom: The smallest portion of a chemical element.
• Molecular: Molecules formed by the joining of two or more atoms.
• Macromolecules: Resulting from the binding of many molecules to form a polymer.
• Supramolecular Complexes: Aggregations of macromolecules.
• Subcellular Structures: Union of different supramolecular complexes, resulting in the cell's structure with characteristic functions.
• Cells: Comprised of various organelles and structures. (Biotic Level)

Proteins and Amino Acids

Proteins are formed by a union of linear amino acids (NH2-COOH). There are 20 amino acids that are part of proteins. Nucleobases form a triplet or codon, which determines a particular amino acid. There are 4x4x4 = 64 different triplets; this implies that there are different triplets that encode the same amino acid. The code is degenerate because the combination of 3 letters adds up to 64 possible triplets.

The Genetic Code

The genetic code is the relationship between the sequence of bases in DNA and the ratio of amino acids in protein. There are three special triplets coding for a stop sign:

• TAA
• TAG
• TGA

There is also a triplet (ATG) determining a beginning.

Functions of Proteins

Proteins perform various essential functions:

• Transport

DNA Structure and Function

DNA is a large molecule formed by the union of simpler molecules called nucleotides. They are composed of phosphoric acid, deoxyribose, and a nitrogenous base (adenine (A), guanine (G), cytosine (C), or thymine (T)).

DNA consists of two long chains of nucleotides twisted into a double helix. Adenine joins with Thymine (with double hydrogen bonds), and Guanine joins with Cytosine (with triple hydrogen bonds).

Molecular Tools in Genetics

Cellular enzymes are used to cut and join fragments of DNA within cells. Restriction enzymes are responsible for "cutting" the DNA, and ligases unite the fragments.

Cloning DNA Technology

DNA Cloning Process

Cloning a DNA fragment consists of obtaining billions of identical copies of that... Continue reading "DNA Structure, Genetic Engineering, and Stem Cell Applications" »

The Nervous System

The nervous system is a biological system that enables very complex beings to interact with what surrounds us. We can say that it is a huge network responsible for the collection of internal and external stimuli. It processes these stimuli to generate the response that the decision center (brain) considers optimal.

There are two main divisions:

• Central Nervous System: Consists of the brain and spinal cord.
• Peripheral Nervous System: Includes all the nerves of the body that connect internal and external stimuli to the central nervous system.

Peripheral Nervous System

The peripheral nervous system includes different types of nerves:

• Sensory Nerves: Transmit information from sensory receptors (like those for touch, pain, temperature)

Advances in Stem Cells and Regenerative Medicine

Recent breakthroughs in stem cell research offer immense potential for tissue regeneration, curing diseases like cancer, and even slowing the aging process.

Key Concepts in Cellular Biology and Genetics

• Cloning: The process of creating an exact genetic copy of an organism or cell.
• Embryonic Stem Cells: These remarkable cells possess the ability to reproduce and differentiate into various specialized cells and organs.
• Therapeutic Cloning: A technique where the development of an individual is intentionally halted to obtain stem cells from a very early-stage embryo, known as a blastocyst.
• Totipotent Stem Cells: Cells capable of dividing and differentiating into any cell type required by an organism.
• Pluripotent

Core Terminology in Classical Genetics

• Character (Trait): An inherited attribute of an individual.
• Gene: The fundamental unit of heredity responsible for a character.
• Alleles: The different variations or forms that a gene can take.
• Homozygous: An individual possessing two identical alleles for a specific gene.
• Heterozygous: An individual possessing two different alleles for a specific gene.
• Genotype: The specific set of genes an individual possesses.
• Phenotype: The set of observable, hereditary traits expressed by an individual.

Allelic Expression and Inheritance Patterns

• Dominant Factor (Allele): The allele that is phenotypically expressed in both homozygous and heterozygous individuals.
• Recessive Factor (Allele): The allele whose phenotypic expression

The Origin of the Moon

• Sister. The Moon formed while the Earth did, but the Moon is 100 million years younger, and their densities are different.
• Adopted. Both formed, but the Moon formed in an area farthest from the Sun and would have been attracted to the Earth. This does not explain the difference in age.
• Daughter. A planet similar to Mars collided with the Earth. Part of the star that crashed formed a debris cloud that orbited around the Earth. The union of these materials created the Moon.

Prebiotic Synthesis

Hypotheses in which life would have originated on Earth as a result of a process:

• Formation of simple organic molecules. Radiation caused molecules to react, forming simple organic molecules.
• Formation of complex organic molecules.

DNA Structure and Genetic Information

Genes are the carriers of biological information, found inside every cell. Their precise location was not known until their discovery within chromosomes. The chromosome number in sex cells is half that which exists in other somatic cells. Genes are contained within chromosomes, and each gene is made up of the molecule known as DNA (Deoxyribonucleic Acid).

DNA Replication: Ensuring Genetic Continuity

Each time a cell divides into two, the two resulting cells must receive the same genetic material. For this to happen, it is essential that DNA copies itself, a process known as replication or duplication.

RNA: Types and Functions

RNA (Ribonucleic Acid) is typically single-stranded. In RNA, the sugar deoxyribose... Continue reading "Fundamentals of Genetics: DNA, Genes, and Human Biology" »

HIV and AIDS: An Introduction

AIDS (Acquired Immunodeficiency Syndrome) is caused by infection with the retrovirus HIV. This virus attacks and destroys T4 lymphocytes and macrophages. Affected individuals have a depressed immune system, which can lead to certain types of cancers.

Development of the Disease

HIV is found in the blood and other bodily fluids of infected persons. Transmission to a healthy person can occur through various routes. These include contaminated blood transfusions and sexual intercourse between an infected and healthy individual.

Once HIV enters the blood of a new host, it joins T cells and penetrates inside. There, a large number of viruses are created, ultimately destroying the infected cell.

AIDS: Treatment and Prevention

There... Continue reading "HIV and AIDS: Understanding the Disease and Prevention" »