Biology Fundamentals: Microorganisms, Genetics, and GMOs

Microorganisms: Bacteria and Viruses

Bacteria: Key Characteristics

Bacteria are single-celled, prokaryotic microorganisms. They possess ribosomes, typically around 1000nm in size.

Viruses: Key Characteristics

Viruses are non-cellular genetic elements that are obligate intracellular parasites, meaning they must use living cells to reproduce. Their size ranges from approximately 20-300nm.

Viral Structure Explained

A typical viral structure includes:

• Nucleic Acid (Genome): This is the genetic material, which can be either DNA or RNA.
• Capsomeres: Protein subunits that assemble to form the capsid.
• Viral Nucleocapsid: The combined structure of the nucleic acid and its surrounding protein capsid.
• Core Wall (Capsid/Envelope): A protective shell, often referred to as the capsid, which encloses the genetic material. Some viruses also have an outer lipid envelope.

Types of Viruses by Genetic Material

• RNA Viruses: These viruses have RNA as their genetic material. They require host cell machinery to replicate (e.g., Arenaviridae).
• DNA Viruses: These viruses contain DNA as their genetic material. They also utilize host cell machinery for replication (e.g., Herpesviridae).

Understanding the Viral Life Cycle

The viral life cycle typically involves several stages:

1. Entrance: The virus enters the host cell, often by binding to specific attraction proteins on the cell surface, and then injects its viral genetic material (DNA or RNA).
2. Replication & Synthesis: The viral nucleic acid replicates, and new viral protein coats are synthesized using the host cell's machinery.
3. Exit: New viruses are assembled and released from the host cell, often by breaking the cell membrane (lysis).

Viral infections can lead to different outcomes for the host cell:

• Lysogenic Cycle: The viral DNA integrates into the host cell's genome, remaining dormant or in a 'hibernation' state without immediately causing cell lysis.
• Lytic Cycle: The viral replication leads to the rapid production of new viruses, culminating in the lysis (bursting) and death of the host cell.

Studying Viral Dynamics

Dynamic processes of viruses can be studied using:

• In vivo cell studies.
• Immunocytology techniques.

Advanced Virus Tracking Methods

Two primary methods are used for tracking viruses:

1. Genetically Modified DNA: Introducing genetically modified DNA that produces phosphorescent proteins. These proteins mark specific viral structures, allowing their movement to be captured and observed.
2. Chemical Labeling: Direct chemical labeling of viral structures with small dye molecules at different time points throughout the viral life cycle.

Genetically Modified Organisms (GMOs)

What are Genetically Modified Organisms?

Genetically Modified Organisms (GMOs) are organisms whose DNA has been altered through genetic engineering. This process is often undertaken to introduce new traits or enhance existing ones, potentially making the organism less susceptible to harm or more beneficial.

Traditional Methods of Genetic Modification

Historically, genetic modification has been achieved through:

• Selective Breeding: A traditional method, exemplified by Gregor Mendel's work with pea plants, involving the careful selection and cultivation of organisms with desired traits.
• Mutation Breeding: Inducing mutations using chemical agents or radiation to create new variants. This method offers less control over the specific genetic changes.

Modern Techniques for GMO Creation

Modern genetic engineering employs precise techniques, including:

• Gene Gun: A device that shoots microscopic particles coated with DNA into cells.
• Agrobacterium Method: Utilizes the bacterium Agrobacterium tumefaciens to transfer desired genes into plant cells.
• Direct Gene Transfer: Various methods for changing genes, such as in fish, often without the use of bacterial vectors.

Advantages of Genetically Modified Organisms

GMOs offer several potential benefits:

• Increased resistance to pathogens (diseases).
• Tolerance to herbicides, simplifying weed control.
• Improved taste and aesthetic qualities.
• Enhanced nutritional value.

Disadvantages of Genetically Modified Organisms

Concerns associated with GMOs include:

• Potential for cross-pollination with non-GMO crops.
• Uncertain long-term environmental and health effects.
• Potential harm to non-target organisms.

Principles of Heredity and Genetics

Alleles: Fundamental Concepts

Alleles are different versions of a gene, typically found at the same locus on homologous chromosomes, that determine a specific characteristic.

• Heterozygote: An individual possessing two different alleles for a particular trait.
• Homozygote: An individual possessing two identical alleles for a particular trait.
• Phenotype: The observable physical or biochemical characteristics of an organism, resulting from the interaction of its genotype and the environment.
• Genotype: The genetic makeup of an organism, referring to the specific set of alleles it possesses.

Gregor Mendel's Pioneering Work

Gregor Mendel established the basic principles of heredity through his experiments. He chose pea plants for his studies because they were easy to grow, reproduced quickly, exhibited a diversity of easily observable characteristics, yielded numerous results, and could be artificially pollinated.

Exceptions to Mendelian Inheritance

While Mendel's principles are foundational, some inheritance patterns deviate:

• Incomplete Dominance: Occurs when two alleles express their information with equal dominance, resulting in a blended or intermediate phenotype (e.g., a red flower crossed with a white flower produces pink offspring).
• Co-dominance: Both alleles express their information with equal dominance, but both traits are distinctly visible without blending (e.g., in certain blood types, both A and B antigens are expressed).
• Polygenic Inheritance: A single phenotypic trait is influenced by the interaction of multiple different alleles or genes (e.g., human height or skin color).
• Gene Linkage: Alleles located very close to each other on the same chromosome tend to be transmitted together during inheritance, rather than assorting independently.

Chromosomes: Autosomes and Allosomes

• Autosomes: Any chromosome that is not a sex chromosome.
• Allosomes: Sex chromosomes, which determine an individual's biological sex (e.g., X and Y chromosomes in humans).

Inheritance Patterns: Human Blood Types

Human ABO blood types are an example of autosomal inheritance with multiple alleles. The alleles involved are I^A, I^B, and i.

• Type A: Genotypes I^AI^A or I^Ai
• Type B: Genotypes I^BI^B or I^Bi
• Type O: Genotype ii
• Type AB: Genotype I^AI^B (an example of co-dominance)

Mechanisms of Sex Determination

Sex determination can occur through various mechanisms:

• Chromosomal Sex Determination: Sex is determined by specialized sex chromosomes (e.g., XX/XY system in humans, ZW/ZZ system in birds).
• Karyotypic Sex Determination: Refers to the number of chromosome sets (e.g., haploidy vs. diploidy in some insects, where haploid individuals are male and diploid are female).
• Environmental Sex Determination: Sex is determined by external environmental factors, such as temperature during development (e.g., in some reptiles, cooler or warmer temperatures during incubation determine sex).