Unit 1 Notes: The Unity of Life and Course Logistics

Learning Objectives

  • Describe the shared characteristics of living organisms, cells, and the two cell types.
  • Define cell theory and describe why the statement is true: Not all organisms are made up of many cells, and not all cells are the same thing as life.

Course Schedule and Assessments

  • Detailed daily schedule outlines all activities and days when we’re not in class; complete assigned tasks on non-class days (videos, practice questions).
  • Today is August 27, Unit 1, Section 1; plan for intro to evolution on Friday; Labor Day = no class.
  • September 4: homework quiz; quizzes administered online via Canvas; open-notes but better to attempt without notes first, then double-check.
  • Bio connections are in-depth assignments completed and submitted via Gradescope; these count toward the grade.
  • Unit 1 wrap-up in class: in-class activities done in small groups; no internet or notes allowed; group quiz-style activity; in-class submission counts toward grade.
  • Exams: Common hour exams for all three biology sections; exam in-class at ~75 minutes; about 45 questions; more time than a typical class period.
  • DRC accommodations: two options—extra time or a quiet room; a form is available for testing accommodations.
  • Exam preparation: students create a study guide (called a bio buddy) before the exam; one-page front-and-back reference sheet allowed; not a “cheat sheet” since it’s permitted material.
  • Unit review: daily activities and consistent, small study chunks improve retention more than cramming; goal is to build ongoing study habits.
  • Participation/assignment submission: you must create a weekly schedule (Monday–Sunday) for biology tasks, classes, note review, and study time; format can be planner, calendar, fresh document, paper, Excel—whatever works; you may include SI times but remove personal details if desired; submit the schedule on Canvas for participation credit.
  • Canvas/Gradescope linkage note: assignments link to Gradescope; some date displays may show August 26 instead of August 27 due to a date error; I will fix the dates after class; Gradescope submissions may not immediately reflect a completed status in Canvas until grading is done; I will grade the first week’s participation (e.g., 25th) this afternoon; expect a brief delay in Canvas showing completion.

The Unity of Life: What Counts as Life?

  • Today’s focus: what makes living things living, what distinguishes living from non-living matter.
  • Biology as the study of life, but life is not defined by a single simple definition; it’s characterized by a set of features.
  • Organism diversity is huge; three major branches discussed:
    • Bacteria (a large, diverse prokaryotic group, many species are unicellular)
    • Archaea (prokaryotic and single-celled; more closely related to eukaryotes; formerly grouped with bacteria)
    • Eukaryotes (include single-celled and multicellular organisms; examples: yeast, protozoans, fungi, plants, animals)
  • Asgard archaea (e.g., Loki and Thor) are highlighted as particularly closely related to eukaryotes, illustrating deep evolutionary relationships.
  • Core unifying idea: all life shares a common framework despite diversity; this includes DNA and the central dogma, information flow, and other shared features.

DNA and the Central Dogma

  • DNA is the key hereditary material in all living organisms.
  • Central dogma concept: information flows from DNA to RNA to protein. DNA makes RNA (transcription); RNA makes protein (translation); information generally cannot flow back from protein to DNA.
  • Analogy: DNA is a big cookbook stored in the nucleus; transcription copies a specific recipe onto a note card (RNA); translation uses that note card to make a protein.
  • Transcription: copying the DNA sequence into RNA.
  • Translation: reading RNA and assembling a protein from amino acids.
  • In most organisms, proteins carry out most cellular functions; some RNA enzymes exist, but the vast majority of functional output comes from proteins.
  • All known life uses the same four-letter genetic alphabet in DNA (and in RNA with U replacing T): the same genetic code is largely universal across life; there are minor exceptions in some bacteria.
  • The genetic code encodes amino acids via codons (three-nucleotide sequences); most codons map to amino acids in a standard way.
  • Implication: a shared code links all organisms and underpins modern genetics and biotechnology; differences are small but can be biologically meaningful.

The Two Cell Types and Cell Theory

  • Cells are the basic units of life; organisms are composed of one or more cells.
  • Prokaryotic vs. Eukaryotic:
    • Prokaryotic cells (e.g., bacteria, archaea): no nucleus, no prominent internal membranes; generally smaller.
    • Eukaryotic cells: have a nucleus and membrane-bound organelles; can be unicellular (yeast, protozoa) or multicellular (fungi, plants, animals).
  • Cell theory (two core tenets):
    1) All organisms are made of one or more cells.
    2) All cells come from other cells (i.e., cells arise by division; no spontaneous generation under typical conditions).
  • Reproduction ties into inheritance: reproduction involves transmission of DNA and cellular inheritance; growth is a form of cellular reproduction.

Core Characteristics of Life (Mnemonic and Details)

  • The mnemonic emphasizes six (plus related concepts) core features:
    • DNA: all living things contain DNA as genetic material.
    • Evolution: populations evolve over time; life is organized and changes through evolutionary processes.
    • Cells: all living organisms are cellular, and cells come from existing cells.
    • Reproduction: organisms or their species have the capacity to reproduce.
    • Energy use: all organisms acquire and use energy to maintain order and carry out life processes; two common energy pathways are:
    • Photosynthesis (light energy converted to chemical energy);
    • Chemotrophy/chemoheterotrophy (energy obtained from chemical compounds and/or from consuming other organisms).
    • Response to environment (homeostasis): organisms respond to environmental changes to maintain internal stability and function; this includes physiological responses (e.g., temperature) and behavioral strategies.
  • Entropy and order: living systems maintain order by consuming energy; entropy tends to increase in the universe, but organisms locally decrease entropy by extracting energy and using it to build and repair order; overall balance aligns with thermodynamic principles.

Reproduction, Growth, and Energy Acquisition

  • Reproduction: essential for the persistence of a species; individual organisms may not always reproduce, but species must be capable of reproduction.
  • Growth: a form of cellular reproduction and development; requires energy and genetic information.
  • Energy acquisition and use: without energy, organisms cannot maintain their internal order; energy sources include photosynthesis and consumption of other organisms; diverse strategies exist across life, especially among deep-sea bacteria and soil microbes.

Homeostasis and Environmental Response

  • Homeostasis: maintaining a relatively stable internal state for key variables (e.g., temperature, oxygen levels); not all variables are held constant with the same stringency (e.g., oxygen tends to be tightly regulated in the blood, CO₂ is sensed and adjusted via breathing).
  • Examples of temperature regulation:
    • Opossums show broader acceptable temperature ranges, adjusting via body processes (shivering or sweating) and behavior.
    • Reptiles regulate temperature mainly by behavioral means (basking, moving in and out of sun).
  • Environmental responsiveness is a hallmark of life and interacts with energy management and homeostatic control.

Practical and Real-World Connections

  • Real-world relevance: understanding DNA-to-protein flow underpins genetics, biotechnology, medicine, and evolutionary biology.
  • Acknowledgement of exceptions: while the genetic code is largely universal, some bacteria show slight deviations; the concept is a powerful unifying theme rather than a rigid rule.
  • The unity/diversity of life helps explain why model organisms like yeast (single-celled eukaryotes) are used in research and why studying bacteria and archaea informs our understanding of more complex life.
  • Ethical and philosophical discussion: the definition of life is not straightforward; this has implications for fields like synthetic biology, astrobiology, and debates about the boundaries of life.

Study and Exam Preparation: Practical Details

  • Open-note quizzes: use notes as a tool, but attempt without notes first to gauge recall and understanding.
  • In-class group work: collaboration is encouraged for unit wrap-up activities; no external internet or notes during those tasks.
  • Studying strategy: short, daily study sessions outperform long cram sessions; build a habit of daily engagement with the material.
  • Bio buddies / study guides: students prepare a one-page front-and-back study sheet before the exam; this serves as a personal reference to key topics and difficult points; this is a permitted resource, not a penalty.
  • Important submission notes: dates in Canvas/Gradescope may require date corrections; follow instructor updates and wait for posted corrections before submitting; grading for the first participation tasks may occur after class and be reflected in Canvas accordingly.

Links to Future Lectures and Topics

  • Unit 2 and Unit 3 will expand on DNA structure and function, transcription/translation mechanics, and the genetic code in more depth.
  • Expect deeper exploration of molecular biology, genomes, and protein synthesis, building on the central dogma introduced here.

Summary of Key Points to Remember

  • Life is best understood as a set of shared characteristics rather than a single strict definition:
    • DNA exists in all life forms; central dogma governs information flow from DNA to RNA to protein.
    • All life uses the same basic genetic code with a four-letter alphabet in DNA (A, T, C, G) and RNA (A, U, C, G).
    • Organisms can be unicellular or multicellular; cells come from existing cells; energy acquisition and usage are essential; life responds to the environment and maintains homeostasis.
  • The unity of life is reflected in the shared DNA-based machinery and the universality of core processes, even as life diverges into bacteria, archaea, and eukaryotes with wide diversity in form and habit.