Notes, abstracts, papers, exams and problems of Biology

Immunological Terms

• Vector Transmission: A DNA molecule used to transfer a particular gene or a specific DNA sequence to another cell.
• Reservoir: A deposit, such as a straight one developed by surgeons, once the rectum has been removed due to disease.
• Phagocyte: A cell capable of surrounding, engulfing, and digesting microorganisms, foreign matter, old cells, and cellular debris, which it covers with its pseudopodia and then digests in the cytoplasm.
• Lymphocyte: A type of leukocyte (white blood cell) included within the agranulocytes.
• Antigen: Antigens are usually proteins or polysaccharides.
• Antibody: Antibodies are glycoproteins of the gamma globulin type. The soluble form can be found in the blood or other bodily fluids of vertebrates.

Infectious

Reproduction and Growth

The hypothalamus is responsible for synthesizing sex steroids. The whole process is triggered by environmental sexual stimuli. Hormones are similar. There are invertebrate males and females.

Growth in vertebrates is dependent on growth hormone released by the adenohypophysis.

The exoskeleton of crustaceans limits their growth. In this case, the juvenile hormone (JH) is synthesized at a low rate to allow the organ to synthesize molting hormone (ecdysone) at higher concentrations for the molt to take place. This happens when they reach sexual maturity and to allow copulation, once the old exoskeleton is clear (allows gonadal development). Once removed, large amounts of JH are re-synthesized to build a new exoskeleton. Regeneration... Continue reading "Animal Reproduction, Growth, and Activity: Key Factors" »

Living Organisms: An Introduction

What Defines a Living Being?

A living being, formed by one or more cells, carries out vital operations, including:

• Nutrition: The set of processes by which living things obtain or exchange matter and energy with the environment.
• Relationships: The ability of living beings to perceive changes in the environment and respond to them in the most suitable way for their survival.
• Reproduction: The ability to produce offspring that develop and maintain the characteristics of their parents over time.

Types of Organisms

Unicellular Beings

These organisms consist of a single cell that performs all vital functions. Their shape is highly variable and adapted to their lifestyle.

Colonies

Colonies are groupings of single-celled organisms... Continue reading "Understanding Living Organisms: Cells, Tissues, and Organs" »

Bacteriophage Replication

The duplication of a bacteriophage is known as the lytic cycle and can be grouped into different stages:

1. Attachment
2. Entry
3. Replication
4. Assembly
5. Lysis and Release

The time required for viral multiplication is 30 to 35 minutes.

Retroviruses

Retroviruses are a type of virus present only in eukaryotic cells. Retroviruses have RNA as genetic material and within their capsid, they also bear a molecule of the reverse transcriptase enzyme that is able to catalyze the transformation of their messenger RNA molecules into DNA. In a later stage, the viral genome, DNA copied and called provirus, is integrated into the cell's DNA and can be transmitted to the descendants of the same when it divides. The next stage, which can occur after a... Continue reading "Bacteriophage and Eukaryotic Virus Replication: Stages and Structures" »

Organelles

An organelle is a small, specialized structure within a cell that performs a specific function. Examples include mitochondria and lysosomes.

Functions of the Cell or Plasma Membrane

1. This structure surrounds the cell, separating it from the external environment.
2. It forms a barrier that allows the cell to incorporate water and nutrients and remove metabolic waste.

Ribosomes

Ribosomes are organelles formed by the combination of different proteins and RNA (ribonucleic acid).

The Golgi apparatus is an organelle that receives immature proteins from the rough endoplasmic reticulum (RER) and releases vesicles containing mature proteins.

• RE: Endoplasmic reticulum
• PER: Ribosomes that have completed the synthesis of a protein

Location and Structure of

Chromosome Structure: A Detailed Explanation

A chromosome consists of two parallel, elongated, rod-shaped subunits called chromatids. The chromatids are not equally thick throughout their length because they contain chromomeres, which are condensed fragments of chromatin.

Chromomere size varies, but the thickness of the chromatid is roughly constant, between 0.25 and 2 micrometers.

Primary Constriction (Centromere)

A structure called the primary constriction, or centromere, divides the chromatid into two arms, which may be of equal or different lengths. This distinction allows for chromosome classification:

• Metacentric chromosome: Central centromere and arms of equal length.
• Submetacentric chromosome: Centromere shifted upward, resulting in upper

The Endosymbiotic Theory

The endosymbiotic theory, proposed by Lynn Margulis in 1967, suggests that eukaryotic cells originated from a primitive cell engulfing other prokaryotic cells, establishing an endosymbiotic relationship. This theory explains the origin of mitochondria and chloroplasts, which resemble bacteria in size and reproduce by division. Crucially, both possess their own DNA and ribosomes, similar to prokaryotes. The acquisition of these bacterial precursors provided eukaryotic cells with aerobic respiration (mitochondria) and photosynthetic capabilities (chloroplasts). This symbiosis offered the prokaryotes a secure environment and food, while their DNA became partially incorporated into the host cell's DNA.

Origin of Eukaryotic

Antidepressants

Tricyclic Antidepressants (TCAs) have a core of condensed 3-rings, a side chain, and amine ends. The introduction of oxygen and nitrogen in the core and the branched side chain are associated with antidepressant action, and the introduction of halogens increases this action. These drugs are well absorbed orally but have low bioavailability. They can also be administered intramuscularly. They tend to bind to plasma proteins and are easily metabolized. TCAs are typically administered twice a day.

Adverse Reactions:

• Cardiovascular: Hypotension, palpitations, tachycardia.
• Anticholinergic: Dry mouth, constipation, urinary retention, nasal congestion, blurred vision (glaucoma).
• Neurological: Confusion, hallucinations, tremors of the hand

Overview of the Nervous System

Cervical Plexus

Supplies the skin of the neck and a deep one that supplies most of the muscles of the neck and the diaphragm muscle.

Brachial Plexus

Three primary trunks:

• 1^st primary trunk: C5-C6
• 2^nd primary trunk: C7
• 3^rd primary trunk: C8-T1

Three secondary trunks:

• External anterior trunk
• Internal anterior trunk
• Posterior trunk

Lumbar Plexus

Gives side branches to the psoas muscle.

Terminal branches:

• Obturator nerve, which serves the thigh.
• Femoral nerve, which extends the knee (quadriceps).

The innervation of this plexus territory does not pass the knee.

Sacral Plexus

Gives collateral branches to the muscles of the hip.

Delivers a single terminal branch, the thickest nerve, called the sciatic nerve.

Innervates the hamstrings and... Continue reading "Overview of the Nervous System Development" »