IB Biology: Viruses, Cell Origins, and Cell Structure

Vocabulary practice flashcards covering viral structure and replication cycles, prebiotic synthesis, the origins of cells and LUCA, the endosymbiotic theory, and multicellular cell differentiation.

Bacteriophage Anatomy

A complex virus structure characterized by a head containing genetic material, a neck, and a tail that attaches to a host cell to inject viral genome.

Retrovirus Structure

A viral architecture consisting of an outer lipid envelope embedded with glycoproteins, a protein capsid, internal genetic material, and reverse transcriptase enzymes.

Capsid

The protective protein shell that encloses the viral genetic material ($\text{DNA}$ or $\text{RNA}$).

Viral Envelope

An outer protective layer surrounding some viruses that adds protection and flexibility to the viral particle.

Reverse Transcriptase

A specialized viral enzyme present in retroviruses that synthesizes $\text{DNA}$ from a viral $\text{RNA}$ template.

Novel Coronavirus (SARS-CoV-2)

A coronavirus family member causing respiratory disease containing $1$ $\text{RNA}$ strand that encodes $4$ proteins, does not integrate into the host genome, and possesses proof-reading enzymes.

Influenza Virus (Flu A + B)

A respiratory virus family containing $8$ $\text{RNA}$ strands encoding between $8$ and $11$ proteins based on reading frame, which does not integrate into host genomic $\text{DNA}$ and lacks proof-reading enzymes.

Human Immunodeficiency Virus (HIV)

A retrovirus contracted through bodily fluids that attacks the immune system, containing $2$ identical $\text{RNA}$ strands encoding $15$ proteins, integrates into the host genome, and lacks proof-reading enzymes.

Antigenic Drift

Gradual mutations and changes in viral proteins over time that render the virus unrecognizable to the host immune system.

Antigenic Shift

A genetic event where two viruses exchange genetic material, resulting in the formation of a completely new viral strand.

Lytic Cycle

A viral reproduction pathway composed of entry and uncoating, replication of the viral genome, transcription and capsid synthesis, followed by self-assembly of new viral particles and cell lysis.

Lysogenic Cycle

A viral life cycle in which phage $\text{DNA}$ circularizes and integrates into the bacterial chromosome as a prophage, passively replicating alongside host cell divisions without causing immediate lysis.

Prophage

The latent form of a bacteriophage genome integrated directly into the host bacterial chromosome during the lysogenic cycle.

Prebiotic Earth Conditions

Early Earth atmospheric conditions featuring a lack of oxygen, abundant lightning, high UV radiation, elevated temperatures, and atmospheric gases including hydrogen, $CO_2$, methane, ammonia, and water vapor that provided energy for synthesizing organic compounds.

Cellular Metabolism

The chemical reactions occurring inside a cell that break down molecules to release energy required to maintain life and survival.

Spontaneous Generation

The disproven hypothesis stating that living, complex organisms can form naturally and spontaneously from non-living or inanimate matter.

Pasteur's Experiments

Nineteenth-century scientific demonstrations conducted by Louis Pasteur that disproved spontaneous generation by proving life only arises from pre-existing life through reproduction.

Miller-Urey Experiment

A laboratory simulation of prebiotic Earth conditions demonstrating that electrical discharges simulating lightning through methane, hydrogen, ammonia, and water vapor can synthesize amino acids and fatty acids.

Vesicle Coalescence

The spontaneous assembly of fatty acids into spherical bilayers upon mixing with water, driven by hydrophobic interactions of fatty acid tails in environments like hydrothermal vents and tidal pools.

Protocell

A primitive prebiotic entity hypothesized to have formed when self-replicating genetic material became entrapped inside a spherical phospholipid or fatty acid vesicle.

RNA World Hypothesis

The hypothesis proposing that $\text{RNA}$ served as the original genetic material due to its ability to store genetic information, self-replicate, mutate, and act as catalytic enzymes in prebiotic synthesis.

Last Universal Common Ancestor (LUCA)

The most recent common ancestor from which all extant living organisms on Earth originated, evidenced by a universal genetic code and shared genes.

Molecular Clock / Molecular Rocks

A method comparing mutation differences between species to estimate divergence timelines, which indicates that LUCA lived approximately $4\text{ billion}$ years ago.

Hydrothermal Vents

Deep-sea vents rich in hydrogen, $CO_2$, and methane where conditions facilitate the prebiotic synthesis of organic molecules, proteins, nucleotides, and fatty acid vesicles.

Endosymbiotic Theory

The evolutionary model stating that eukaryotic cells originated when an ancestral prokaryote engulfed an aerobic prokaryote (evolving into mitochondria) and subsequently engulfed a photosynthetic prokaryote (evolving into chloroplasts).

Cell Differentiation

The process whereby undifferentiated stem cells specialize into distinct cell types, tissues, and organs with specialized physiological functions.

Stem Cells

Undifferentiated cells capable of continuous self-renewal and division that hold the potential to develop into any specialized cell type.

Epigenetic Regulation

Modifications such as $\text{DNA}$ methylation and histone modifications that control stable patterns of gene expression in cell differentiation without altering the underlying $\text{DNA}$ sequence.

Evolution of Multicellularity

The evolutionary transition from unicellular life to cellular cooperation and differentiation, leading to diverse body forms, specialized adaptations, and increased organismal complexity.