Cell Biology: Anatomy and Physiology 12 Intro

Introduction to Cell Anatomy and Physiology

  • Conceptual Framework: In Anatomy and Physiology 12, the cell is taught as a functioning system analogous to the human body. Just as organs in the body work together, organelles within a cell do not function in isolation.
  • Interdependence of Organelles: Understanding the cell requires knowing how one part interacts with another. Examples include:
    • The nucleus's interaction with the mitochondria.
    • The mitochondria's relationship with the Endoplasmic Reticulum (ER).
    • The ER's coordination with the Golgi apparatus.
  • Organ-Organelle Analogy: This connection is compared to bodily systems where the heart, lungs, digestive system, kidneys, and brain all work in a integrated manner.

The Cell Theory and Modern Technology

  • Traditional Cell Theory: Historically, cell theory encompasses the following principles:
    • Cells are the smallest unit of living things.
    • Life cannot be broken down further than the cellular level.
    • All cells come from preexisting cells.
  • Technological Re-evaluation: Modern technology allows for the creation of new cells using only specific parts of a cell, such as DNA or RNA. While a whole cell might not be necessary, a part of a preexisting cell is still required (e.g., cats come from cats, humans from humans).
  • Sustainability of Life: The cell remains the smallest structure capable of sustaining life independently.

Evolutionary Classification: Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic Cells:
    • Description: Considered the "old school" cells and the first living things (e.g., bacteria).
    • Characteristics: They lack a nucleus and membrane-bound organelles. They are typically unicellular and simplistic in structure.
  • Evolution of Eukaryotes (hypothesis):
    • It is hypothesized that eukaryotic cells originated when several prokaryotic cells began living together.
    • Each prokaryote took on specialized roles: one acting as a manager (nucleus), one breaking down food (mitochondria), and one packaging materials (Golgi).
  • Eukaryotic Cells:
    • Focus: This is the primary cell type studied in Anatomy and Physiology 12, encompassing both plant and animal cells.
    • Characteristics: They contain a nucleus and various membrane-bound organelles (Golgi, mitochondria, RER, SER).
    • Definition of Organelles: Organelles are like "mini-organs," each having a specific task, similar to how the heart beats to flow blood, the lungs manage gas exchange, the stomach digests food, the small intestine absorbs nutrients, and the kidneys filter blood for urine.

The Plasma Membrane (Cell Membrane)

  • Function: Acts as the "skin" of the cell, protecting it from external pathogens. It controls the movement of substances entering and exiting the cell.
  • Metaphor: The membrane functions like a "bouncer" at a club, checking credentials and IDs to determine who is allowed entry based on status or condition.
  • Terminology of Permeability:
    • Permeable: Substances can move in and out freely.
    • Impermeable: Substances are unable to pass through the membrane.
    • Selectively Permeable: The membrane allows certain substances in while blocking others. Examples of substances that move through pores include gases, sweat, and salts.
  • Chemical Composition: The membrane is a phospholipid bilayer composed of:
    • Glycerol-Phosphate Heads: These are polar and hydrophilic ("water-loving"). They face outward toward the aqueous environments (extra-cellular and intra-cellular).
    • Fatty Acid Tails: These are non-polar and hydrophobic ("water-hating"). They face inward toward each other to avoid contact with water.

Mitochondria and Cellular Respiration

  • Function: Known as the "powerhouse of the cell" because it produces ATP (Adenosine Triphosphate).
  • Cellular Respiration Equation:
    • C6H12O6+6O2→6CO2+6H2O+ATPC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}
    • The breath we exhale contains moisture because water is a byproduct of this reaction.
  • Structure:
    • Cristae: The internal folds within the mitochondria where cellular respiration occurs.
    • Matrix: The liquidy internal part of the mitochondria.
    • Visual Identification: Under an electron microscope, they appear as elongated ovals with internal folds (double membrane structure) located away from the nucleus.
  • Biological Classification: ATP is a nucleic acid containing a nitrogen base, though the balanced equation for cellular respiration is a simplified version of the complex process taught in post-secondary or AP Biology.
  • Physiological Distribution: Mitochondria are found in high concentrations in cells requiring significant energy, such as muscles (arms/legs), the heart, and neurons in the brain during action potentials.

Ribosomes and Protein Synthesis

  • Function: Site of protein synthesis.
  • Components of Protein Synthesis:
    1. Transcription: The first part (occurs in the nucleus).
    2. Translation: The second part, which occurs specifically at the ribosome.
  • Structure: Ribosomes are made of protein and rRNA (ribosomal RNA). They are composed of units that string amino acids together to form proteins.
  • Polyosomes: Clusters of many ribosomes making the same protein simultaneously (e.g., producing large amounts of insulin).
  • Location:
    • Attached to the Rough Endoplasmic Reticulum (RER).
    • Free-floating in the cytoplasm.

The Endoplasmic Reticulum (ER)

  • Rough ER (RER):
    • Appearance: "Rough" due to the presence of ribosomes on its surface.
    • Function: Receives proteins from ribosomes and begins modifying them (adding or taking away components). It is responsible for the initial modification and packaging.
    • Localization: Found in high volumes in the liver (making protein hormones) and the pancreas (making digestive enzymes).
  • Smooth ER (SER):
    • Appearance: Tubular and lacks ribosomes.
    • Functions: Synthesizes and transports lipids and steroids; detoxifies drugs and chemicals.
    • Localization: Found in high volumes in the testes (making testosterone) and ovaries (making estrogen and progesterone) because these are steroid-based hormones. It is also prevalent in the liver for detoxification.
    • Membrane Production: The SER is responsible for making phospholipids, which form vesicles and other organelle membranes.

The Golgi Apparatus and Vesicles

  • Golgi Apparatus:
    • Function: The primary center for protein modification and packaging. It changes the shape of proteins and may add/remove polypeptides before the final product leaves the cell.
    • Identification: Located further from the nucleus than the ER; characterized by surrounding circles (vesicles).
  • Vesicles:
    • Metaphor: Function as "taxi cabs" or storage units.
    • Function: Moving waste, water, and proteins around the cell.
    • Composition: Made of a phospholipid bilayer, which is why they can fuse with other membranes.
  • Lysosomes:
    • Definition: A specialized vesicle produced by the Golgi that contains hydrolytic enzymes.
    • Function: Breaking down (lysis) dead organelles, bacteria, viruses, or large food molecules.
    • Mechanism: They use Hydrolysis (breaking things down by adding water) to degrade proteins, nucleic acids, lipids, and carbohydrates.
    • Process: They fuse with a phagosome (a vesicle containing ingested particles like bacteria) to deliver enzymes for destruction and recycling.
  • Peroxisomes: (Note: Mentioned as an aside) Similar to lysosomes but specifically responsible for breaking down fats.

The Nucleus and Nucleolus

  • The Nucleus:
    • Metaphor: The "brain" of the cell or a "VIP section" in a club.
    • Nuclear Envelope: A double phospholipid bilayer (extra security) that protects the DNA.
    • Nuclear Pores: Selective openings that control the passage of materials between the nucleus and cytoplasm (selectively permeable).
    • Responsibilities: Monitoring internal/external conditions, controlling other organelles, DNA replication, and Transcription.
  • The Nucleolus:
    • Appearance: A dark spot in the center of the nucleus.
    • Function: The site where the rRNA component of ribosomes is produced.
  • Genetic Material: Houses DNA and chromosomes.

Cytoplasm

  • Description: A jelly-like substance (matrix) that fills the cell and gives it shape.
  • Composition: Contains microtubules and microfilaments (cytoskeleton).
  • Function: Provides a medium for organelles to reside in and for vesicles to move along.

Questions & Discussion

  • Question: Why are fatty acid tails facing together in the cell membrane?
  • Response: They are hydrophobic. Since there is water both inside and outside the cell, the hydrophilic heads face the water, while the tails point inward to stay dry.
  • Question: What kind of biological molecule is ATP?
  • Response: It is a nucleic acid.
  • Question: What are the two parts of protein synthesis?
  • Response: Transcription and translation. Translation occurs at the ribosome.
  • Discussion on Organelle Abundance: The instructor prompted students to determine where certain organelles would be found in high concentrations. Examples included mitochondria in active muscles/heart/brain and RER in the pancreas for enzyme production.