Biological and Biochemical Foundations of Living Systems: Content Category 2B

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The structure, growth, physiology, and genetics of prokaryotes and viruses

The highly organized assembly of molecules that is the cell represents the fundamental unit of structure, function, and organization in all living organisms. In the hierarchy of biological organization, the cell is the simplest collection of matter capable of carrying out the processes that distinguish living organisms. As such, cells have the ability to undergo metabolism; maintain homeostasis, including ionic gradients; the capacity to grow; move in response to their local environments; respond to stimuli; reproduce; and adapt to their environment in successive generations.

Life at cellular levels arises from structural order and its dynamic modulation. It does so in response to signals, thereby reflecting properties that result from individual and interactive features of molecular assemblies, their compartmentalization, and their interaction with environmental signals at many spatial and temporal scales.

The content in this category covers the classification, structure, growth, physiology, and genetics of prokaryotes, and the characteristics that distinguish them from eukaryotes. Viruses are also covered here.

Topic Level Key:

The abbreviations found in parentheses indicate the course(s) in which undergraduate students at many colleges and universities learn about the topics and associated subtopics. The course abbreviation is:

BIO = two-semester sequence of introductory biology

Please note topics that appear on multiple content lists will be treated differently. Questions will focus on the topics as they are described in the narrative for the content category.

Cell Theory (BIO)

  • History and development

  • Impact on biology

Classification and Structure of Prokaryotic Cells (BIO)

  • Prokaryotic domains

    • Archaea

    • Bacteria

  • Major classifications of bacteria by shape

    • Bacilli (rod-shaped)

    • Spirilli (spiral-shaped)

    • Cocci (spherical)

  • Lack of nuclear membrane and mitotic apparatus

  • Lack of typical eukaryotic organelles

  • Presence of cell wall in bacteria

  • Flagellar propulsion, mechanism

Growth and Physiology of Prokaryotic Cells (BIO)

  • Reproduction by fission

  • High degree of genetic adaptability, acquisition of antibiotic resistance

  • Exponential growth

  • Existence of anaerobic and aerobic variants

  • Parasitic and symbiotic

  • Chemotaxis

Genetics of Prokaryotic Cells (BIO)

  • Existence of plasmids, extragenomic DNA

  • Transformation: incorporation into bacterial genome of DNA fragments from external medium

  • Conjugation

  • Transposons (also present in eukaryotic cells)

Virus Structure (BIO)

  • General structural characteristics (nucleic acid and protein, enveloped and nonenveloped)

  • Lack organelles and nucleus

  • Structural aspects of typical bacteriophage

  • Genomic content — RNA or DNA

  • Size relative to bacteria and eukaryotic cells

Viral Life Cycle (BIO)

  • Self-replicating biological units that must reproduce within specific host cell

  • Generalized phage and animal virus life cycles

    • Attachment to host, penetration of cell membrane or cell wall, and entry of viral genetic material

    • Use of host synthetic mechanism to replicate viral components

    • Self-assembly and release of new viral particles

  • Transduction: transfer of genetic material by viruses

  • Retrovirus life cycle: integration into host DNA, reverse transcriptase, HIV

  • Prions and viroids: subviral particles

Additional Review: Khan Academy MCAT® Collection Tutorials

To support your studies, see the following video tutorials below from the Khan Academy MCAT® Collection. The videos and associated questions were created by the Khan Academy in collaboration with the AAMC and the Robert Wood Johnson Foundation.

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