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Chapter 3: Cell Structure and Function - Vocabulary Flashcards

Chapter 3: Cell Structure and Function (Notes)

Prokaryotes vs. Eukaryotes

  • Two fundamentally different cell types under an umbrella model: prokaryote and eukaryote.
  • Prokaryotes
    • Generally lack a membrane-bound nucleus; DNA is free-floating in the cell (nucleoid region).
    • Examples typically include bacteria.
  • Eukaryotes
    • Possess a nucleus; examples include plants and animals.
    • DNA is housed inside a nuclear envelope; numerous membrane-bound organelles.
  • Quick takeaway: these are the two main camps for cell organization and complexity.

Cell Theory (review tied to the scientific method)

  • Core idea: all organisms are composed of cells; cells are the basic units of structure and function.
  • All cells come from pre-existing cells; there is no spontaneous generation.
  • Connection to Chapter 1: scientific method cycle (hypothesis → experiment → data → conclusion) leads to a theory when results are repeatedly observed.
  • Historical note: maggots on meat were once thought to arise spontaneously from dead meat; it's now known that a fly lays eggs that become larvae. This supports "all cells come from other cells" and disputes spontaneous generation.
  • Implication: no known organism lacks at least one cell; cell theory underpins biology.

Surface Area to Volume Ratio (SA:V) and why cells are small

  • Illustration concept: same volume can have different surface areas; smaller units have a larger surface area relative to volume.
  • Consequences: large surface area relative to volume allows more efficient nutrient uptake and waste removal; shorter diffusion distances shorten energy and time for transport.
  • When a cell is small, it can ship products quickly via exocytosis (concept introduced here; not defined in depth yet).
  • Bottom line: small cells grouped into tissues enable more efficient nutrient/waste exchange and movement of materials.

Prokaryotic Cells: structure and diversity

  • Core traits:
    • No nucleus; DNA is not enclosed by a membrane.
    • Two primary domains: Bacteria and Archaea (archaea = not pronounced with an \'a\', just Archaea).
  • Shared essentials with eukaryotes:
    • Plasma membrane is present in both Bacteria and Archaea.
    • Nucleus is absent in prokaryotes.
      -DNA is present (but not enclosed in a true nucleus).
    • Ribosomes are present (prokaryotic ribosomes are smaller than eukaryotic ones, but still perform protein synthesis).
  • Notable features of prokaryotes (as seen in bacteria):
    • Often unicellular (one cell).
    • Not all bacteria cause disease; many are beneficial (e.g., gut E. coli helps in digestion and vitamin production).
    • Typical bacterial cell components include: DNA, ribosomes, a cell wall, a capsule for adherence, hair-like bristles (pili), and a tail (flagellum) for movement.
  • Example image features to recognize:
    • Hair-like bristles (pili), nucleoid region with DNA, capsule, flagellum, ribosomes.
    • Translation and transcription: DNA is transcribed into RNA, and ribosomes translate RNA into proteins.

Eukaryotic Cells: structure, diversity, and major organelles

  • General features:
    • Highly organized with subcellular compartments (organelles).
    • Possess a nucleus containing DNA.
    • Four major kingdoms within the eukaryotes domain: plants, animals, fungi, and protists (the latter includes a diverse set of mostly unicellular and some multicellular organisms).
  • Shared features across many eukaryotes:
    • Plasma membrane present in all.
    • Nucleus present in all (unlike prokaryotes).
    • Ribosomes present in all.
    • Rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER) are characteristic of eukaryotes (not found in prokaryotes).
    • Golgi apparatus, lysosomes, vacuoles, peroxisomes, mitochondria; chloroplasts in plants/algae.
    • Cytoskeleton, cilia, and flagella; centrioles are animal-cell-specific.
  • Not all eukaryotes have cell walls:
    • Plants, fungi, and some protists have cell walls.
    • Animals lack cell walls.
  • Key universal components to recognize on diagrams:
    • Plasma membrane, nucleus, nucleolus, chromatin (DNA in a more dispersed form).
    • Rough ER (ribosomes studding its surface) and smooth ER.
    • Golgi apparatus; lysosomes; vacuoles; mitochondria; chloroplasts (only in plants and some protists).
    • Cytoskeleton; cilia/flagella; centrioles (animal cells only).
  • Fundamental idea about common cell components:
    • Some structures are universal (plasma membrane, ribosomes, DNA).
    • Others are specific to certain lineages (mitochondria always present in eukaryotes; chloroplasts only in photosynthetic eukaryotes).
  • Baseline conceptual reminder: cells must have a plasma membrane, ribosomes, and DNA; many also have cytoplasm and other organelles depending on cell type.

Animal vs. Plant Cells: typical features and differences

  • Animal cells:
    • Plasma membrane; nucleus; chromatin; nucleolus; mitochondria; Golgi; rough and smooth ER; cytoskeleton; centrioles; no cell wall.
  • Plant cells:
    • Similar core organelles as animal cells (plasma membrane, nucleus, ER, Golgi, mitochondria).
    • Additional plant-specific organelles: chloroplasts (site of photosynthesis), central vacuole (water storage and turgor pressure maintenance).
    • Cell wall present (unlike animal cells).
  • Central vacuole vs. chloroplast:
    • Central vacuole stores water; maintains internal pressure; wilted vs crisp leaves relate to vacuole size.
    • Chloroplasts perform photosynthesis; plants and some protists have chloroplasts; chloroplasts contain chlorophyll and are site of light-driven sugar production.
  • Practical takeaway: presence of chloroplasts strongly suggests plant (or rare protist) source; absence of chloroplasts with a cell having a cell wall and chloroplasts? Not typical.

Endomembrane system and protein trafficking

  • Pathway overview (endomembrane system):
    • Nucleus transcribes DNA into RNA.
    • Rough ER synthesizes proteins (ribosomes on RER translate mRNA into polypeptides).
    • Proteins are packaged into vesicles and sent to the Golgi apparatus.
    • Golgi modifies, tags, and sorts proteins for transport to destinations inside or outside the cell.
    • Exocytosis (export of proteins/secreted materials) is a fate of some vesicles.
  • This system explains how proteins are synthesized, processed, and directed to their proper locations.

Energy-related organelles: mitochondria and chloroplasts

  • Mitochondria:
    • Generate ATP energy via cellular respiration.
    • Present in nearly all eukaryotic cells.
  • Chloroplasts:
    • Carry out photosynthesis in plants and some protists; convert light energy to chemical energy (carbohydrates) and release O2.
  • Relationship between photosynthesis and cellular respiration:
    • Photosynthesis (in chloroplasts):6 ext{CO}2 + 6 ext{H}2 ext{O} + ext{light energy}
      ightarrow ext{C}6 ext{H}{12} ext{O}6 + 6 ext{O}2
    • Cellular respiration (in mitochondria): ext{C}6 ext{H}{12} ext{O}6 + 6 ext{O}2
      ightarrow 6 ext{CO}2 + 6 ext{H}2 ext{O} + ext{ATP}
  • Important plant note: plants possess both chloroplasts and mitochondria; they convert sunlight to carbohydrates and then metabolize those carbohydrates to generate energy for growth.
  • Connection to real-world relevance: photosynthesis sustains life by providing oxygen and fixed carbon; respiration releases energy stored in carbohydrates for cellular processes.

The Cytoskeleton: actin filaments, intermediate filaments, and microtubules

  • General role: maintains cell shape, supports movement, and assists transport of organelles; cytoskeleton is dynamic and can remodel (assemble/disassemble).

  • Actin filaments (microfilaments)

    • Located just under the plasma membrane; provide structural support and help form projections like microvilli in intestinal cells, increasing surface area for absorption.
    • Involved in muscle contraction together with myosin proteins; essential for movement and mechanical support.

  • Intermediate filaments

    • So named because they are between actin filaments and microtubules in size.
    • Provide structural support for the nuclear envelope; contribute to cell-cell junctions (e.g., skin cohesiveness); help reinforce hair.

  • Microtubules

    • Hollow tubes made of tubulin; provide rigid scaffolding.
    • Centrioles act as a hub for microtubule assembly/disassembly during cell division; radiate microtubules and guide chromosome movement.
    • Form basal structures for cilia and flagella (e.g., sperm tail in humans) and structure those cellular appendages in airways (cilia in trachea/bronchi).

  • Centrioles and cell division:

    • Centrioles help organize microtubules during chromosome movement in mitosis/meiosis.

Evolution of Eukaryotic Cells and the Endosymbiotic Theory

  • Fossil record suggests the first cells were prokaryotic; no clear early eukaryotic fossils in the earliest layers.
  • Biochemical data indicate archaea are more closely related to eukaryotes than bacteria; eukaryotes likely evolved in stages from prokaryotes.
  • Endosymbiotic theory (endosymbiosis): mitochondria and chloroplasts originated as free-living bacteria/cyanobacteria that were engulfed by a host cell and became endosymbionts.
  • Supporting evidence for endosymbiosis:
    • Mitochondria and chloroplasts are similar in size and structure to bacteria outside the cell.
    • They are bounded by a double membrane, consistent with engulfment.
    • They contain their own genetic material (DNA) separate from nuclear DNA.
    • They have their own ribosomes and can synthesize some of their own proteins, independent of the host nuclear genome.
    • Their replication by binary fission (splitting) resembles bacterial division rather than eukaryotic mitosis.
    • RNA-based sequences point to prokaryotic origins for these organelles.
  • Diagrammatic idea: a prokaryotic cell engulfs another prokaryote (mitochondrion) and then a cyanobacterium (chloroplast) becomes a photosynthetic endosymbiont; double membranes arise from the engulfing vesicle.
  • Caution about sources and interpretation:
    • The discussion around endosymbiosis is ongoing; evaluate sources carefully for biases.
    • Recognize that science involves weighing multiple lines of evidence; there are debates and alternative explanations.
    • Use credible sources and read critically when contributing to discussions.

Connecting to broader themes and exam-style takeaways

  • If you observe a structure like mitochondria under a microscope, you can infer you are looking at a eukaryotic cell (since mitochondria are eukaryotic-specific organelles).
  • The presence or absence of cell walls, chloroplasts, and a nucleus helps distinguish plant, animal, fungal, protist, and bacterial cells in practice.
  • The endomembrane system explains how the cell processes and ships proteins: nucleus → rough ER → Golgi → vesicles → destination or secretion.
  • The cytoskeleton underpins cell shape, organization, and movement, and it supports specialized structures and tissues (e.g., intestinal microvilli, muscle contraction, hair, and neuronal processes).
  • The SA:V concept reinforces why cells stay small and why tissues are often organized from many small cells rather than a few large ones.
  • The evolutionary perspective (prokaryotes → eukaryotes; endosymbiosis) connects cellular structure to the history of life and to modern genetic evidence.

Quick reference reminders

  • DNA, ribosomes, plasma membrane are common to all cells; nucleus and organelles are hallmarks of eukaryotes.
  • Plant cells vs. animal cells differences: chloroplasts and central vacuole vs. lack of cell wall and chloroplasts in animals.
  • Endomembrane system and energy organelles (mitochondria/chloroplasts) are central to cellular metabolism and energy flow.
  • Actin filaments, intermediate filaments, and microtubules together form the cytoskeleton and enable structure, transport, and movement.
  • Endosymbiotic theory provides a framework for understanding how mitochondria and chloroplasts evolved and why they carry their own DNA.

Optional discussion prompts (to explore in class or on a board)

  • Do you agree with the endosymbiotic theory? What evidence most strongly supports or contests it?
  • How does the SA:V ratio influence cell size in different tissues (e.g., neurons vs. intestinal cells)?
  • What are the practical implications of cell theory for medical advances and biotechnology?
  • How do archaea differ from bacteria, and why might archaea be more closely related to eukaryotes on the tree of life?
  • In what ways could misinterpretations of the fossil record or gene sequence data affect our understanding of early life evolution?