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

Elements Involved

In order to perform the transcription of DNA into cells, the following elements are required:

• Original DNA to serve as a template to be copied.
• RNA polymerase: synthesizes RNA from a DNA template.
• Ribonucleotide triphosphates to perform the copy.
• Poly-A polymerase, small nuclear ribonucleoprotein, RNA ligase.

Transcription Mechanism

As in replication, there are differences between prokaryotes and eukaryotes. The main differences are the existence of multiple RNA polymerases in eukaryotes and, above all, the need to produce a "mature" form of some RNAs due to the existence of introns. The process is divided into three stages:

• Initiation: The RNA polymerase binds to a region of DNA prior to the DNA that is to be transcribed. It then

The Journey of Childbirth and Lactation

Understanding Childbirth

Stages of Labor and Delivery

Childbirth begins with labor, typically lasting around 12 hours, characterized by frequent uterine contractions that move the fetus towards the dilating cervix. If the amniotic sac ruptures, amniotic fluid exits through the vagina. The baby then passes through the cervix and vagina during birth, after which the umbilical cord is cut. The process concludes with the expulsion of the placenta and other membranes.

Hormonal Regulation of Childbirth

• Progesterone: This hormone remains in the uterus, maintaining pregnancy conditions, particularly by relaxing uterine walls and keeping the cervix closed.
• Estrogens: During pregnancy, estrogens stimulate the growth

Understanding Immune System Components

Lymphoid Organs: Sites of Immune Activity

Lymphoid organs are specialized sites where immune system cells concentrate and function. They are classified into two main types:

• Primary Lymphoid Organs: These are the sites where lymphocytes mature. Stem cell precursors originate in the bone marrow. T lymphocytes mature in the thymus, while B lymphocytes mature in the bone marrow (or the Bursa of Fabricius in birds).
• Secondary Lymphoid Organs: These are the locations where mature lymphocytes accumulate, encounter antigens, and initiate adaptive immune responses. Examples include the spleen (which filters blood), lymph nodes (which filter lymph), and various lymphoepithelial structures (like tonsils and Peyer's patches)

The Skeletal System: Bones and Structure

Axial Skeleton

Vertebral Column

The vertebral column, or spine, holds the skull, attaches to the ribs, protects the spinal cord, and allows for the insertion of a large number of muscles. It consists of:

• Cervical vertebrae
• Thoracic vertebrae
• Lumbar vertebrae
• Sacrum
• Coccyx

Thoracic Cage

The thoracic cage includes the ribs and sternum.

• Ribs:
  • True ribs (first 7 pairs) join directly to the sternum.
  • False ribs (next 3 pairs) join the sternum indirectly via cartilage.
  • Floating ribs (last 2 pairs) do not join the sternum.
• Sternum: Composed of 3 parts:
  • Manubrium
  • Body
  • Xiphoid process

Appendicular Skeleton

The appendicular skeleton comprises the bones of the limbs and their girdles.

• Upper Extremities:
  • Girdle: Clavicles and scapulae
  • Arm:

Methods for Measuring Water Content in Meat

The CRA (water free of meat) can be measured by:

1. Compression between two plates.
2. Centrifugation (e.g., using centrifuge tubes with meat diluted in saline, centrifuged on a glass plate at 70 °C for 30 minutes, or using centrifugal filter paper).
3. Capillarity (where free water is absorbed, and capillary air moves in a graduated U-shaped column).

Dry Fermented Sausage Composition

Dry fermented sausage is a mixture of meat, fat, salt, starter cultures, and spices.

Objectives of Fermentation

The primary objectives include:

• Developing desirable taste and odor.
• Achieving a controlled, low drop in pH.
• Removing the antagonistic effects of undesirable microorganisms.

Starter Cultures

Requirements for Starter Cultures

1. Ability

Lamarckism: Key Principles

Jean-Baptiste Lamarck proposed a theory of evolution based on the following principles:

• There is a gradual progression from simpler organisms to more complex forms.
• The mechanism by which gradual changes occur is adaptation to the environment through the use and disuse of certain organs.
• The exercise of an organ produces its development and perfection.
• Inherited acquired characteristics can easily be adapted to environmental conditions.

Darwinism: The Theory of Natural Selection

The Voyage of the HMS Beagle

Charles Darwin embarked on the HMS Beagle for a trip around the world. His mission on board consisted of collecting exotic plants and animals. The trip lasted 5 years, and by the end, Darwin found evidence of the variability... Continue reading "Darwinism vs. Lamarckism: Understanding Evolutionary Theory" »

Cellular Motion Structures

Cells can move using either changes in the viscosity of the cytoplasm (pseudopods) or by means of flagella and cilia.

• Pseudopods: These are cytoplasm elongations produced by changes in cytoplasm viscosity, which, in turn, are due to changes in proteins of the cytoskeleton.
• Cilia and Flagella: These are mobile organelles attached to the cell membrane. They consist of a basal corpuscle and a string-like structure that projects out of the cell, composed of the cell membrane and a series of microtubules.
• The Centrosome: This organelle is constituted by two small cylinders positioned perpendicular to each other. Each cylinder is called a centriole, which is made up of nine sets of three microtubules. The centrosome controls

The Organs of Speech

The Lungs

The lungs hold air when we breathe in. We enlarge the chest cavity (in part by lowering the diaphragm). This, in turn, expands the lungs, and air rushes in to fill the vacuum. Breathing out involves the opposite procedure. The chest is contracted, and air is squeezed out of the lungs, passing through the two bronchi (or bronchial tubes), then through the windpipe (more technically the trachea), and finally emerging in the throat.

The Larynx

Before the air reaches the throat, it has to pass through one of the most important speech organs: the larynx. It is at this point that the first possibilities occur for modifying the airstream and generating sound.

The larynx can conveniently be thought of as an irregularly shaped... Continue reading "The Organs of Speech and Sound Production" »

Animal Respiration Methods

1. Cutaneous Respiration (Skin)

Many small, less active multicellular animals respire through their skin. This is possible because the ratio between body surface area and body mass is very large. In larger, more active animals, it is sometimes a complementary method. This occurs in amphibians, where cutaneous respiration supplements lung respiration. In amphibians, gas exchange can be performed through the skin because it is well-vascularized and has large glands that keep it very moist. In some fish, skin breathing can occur via the oral mucosa, intestine, swim bladder, or the epidermis of the fins.

2. Gill Respiration

This is characteristic of aquatic animals. In this type of breathing, gas exchange takes place in the... Continue reading "Animal Respiration Methods Explained" »

Understanding the Human Genome

The study of the human genome involves understanding the complete set of DNA molecules organized into 23 chromosomes. To fully comprehend the information it contains, we must know the sequence of its bases. This knowledge has been instrumental in identifying the human genome. To grasp its immense scale, imagine a library 18 stories high. Current research focuses on deciphering the function of individual genes and how they interact to govern the organization and functioning of the human body.

Benefits of Human Genome Knowledge

Knowing the human genome offers significant advantages. Primarily, it accelerates the identification of disease-causing genes and helps identify individuals who are carriers of diseases. Understanding... Continue reading "Decoding the Human Genome: DNA, Disease, and Future Health" »