Comprehensive Cellular Organelles and Microscopy Notes

Nuclear Envelope

  • Boundary of the nucleus; protective membrane surrounding the nucleus.
  • Nuclear pores are holes in the nuclear envelope that regulate transport between the nucleus and cytoplasm.
  • Function implied: barrier and regulated exchange with cytoplasm.

Centrosome and Centrioles

  • The cell has two centrosomes; each centrosome contains two centrioles.
  • Centrioles are generally invisible until cell division.
  • Centrioles are arranged at a 90° angle to each other.
  • Function: participate in cell division; help segregate genetic material during mitosis (rip chromosomes apart for future daughter cells).

Golgi Apparatus (Golgi complex)

  • Structure: stack of flattened membranous sacs (cisternae), canals, and vesicles; membrane-bound.
  • Looks like a stack of pancakes.
  • Function: process, sort, and deliver proteins and other materials produced in the cell.
  • Acts like the cell’s UPS: receives cargo from the ER, modifies it, labels/tags it, and packages it into vesicles for transport.
  • Vesicles transport materials away from the Golgi to various destinations inside or outside the cell.
  • Vesicle definition: membrane-bound bubble; not to be confused with a vessel (a pipe-like structure).

Vesicles

  • Small membrane-bound bubbles that carry materials using the Golgi or other organelles.
  • Pinched off from the Golgi (as depicted) and used for intracellular or extracellular transport.

Mitochondria

  • Sometimes several mitochondria visible in a cell; may appear as separate bean-shaped organelles.
  • Structure: two membranes (outer and inner); inner membrane folds inward to form cristae; outer membrane is smooth.
  • Cristae: folds of the inner mitochondrial membrane that increase surface area for ATP production.
  • Function: ATP synthesis; powerhouse of the cell; most ATP produced here.
  • Mitochondrial DNA (mtDNA): circular DNA located inside mitochondria; maternally inherited.
  • Morphology: can be sausage-like or bean-shaped; cristae give a folded appearance in cross-section.

Lysosome

  • Lysosome is a membrane-bound vesicle containing powerful digestive enzymes.
  • Function: intracellular digestion; break down waste, damaged organelles, and invading pathogens.
  • Autolysis: self-digestion of the cell when damaged beyond repair; autolysis = self (auto) + lysis (breakdown/destruction).
  • Lysosomes play a key role in maintaining cellular cleanliness and turnover.

Plasma Membrane

  • Also called the cell membrane; boundary of the cell.
  • Functions: physical isolation; regulation of material traffic into and out of the cell; cell–cell recognition and communication; structural support.
  • Important note: plasma membrane is not the same as the cell wall.
  • Mention of future discussion: a more in-depth look at plasma membrane structure and function will occur in a later lesson.

Cytoplasm and Cytosol

  • Cytosol: intracellular fluid; the aqueous component inside the cell.
  • Cytosol is not pure water; it contains many dissolved solutes and resembles a gel.
  • Function of cytosol: site of many metabolic and biochemical reactions; host to many metabolic processes.
  • Note from lecture: cytoplasm and cytosol are discussed to distinguish the gel-like intracellular fluid from the rest of the cytoplasmic components.

Rough Endoplasmic Reticulum (RER)

  • Structure: membranous sacs and tubules studded with ribosomes (giving a rough appearance).
  • Ribosomes on the RER give it a “lumpy” texture.
  • Function: protein synthesis; ribosomes synthesize polypeptides that enter the RER for processing.
  • Proteins synthesized here may undergo modifications and be directed toward destinations inside the cell or outside the cell.
  • RER is continuous with the smooth ER (SER).

Rough Endoplasmic Reticulum vs. Smooth Endoplasmic Reticulum

  • Smooth Endoplasmic Reticulum (SER): lacks ribosomes, appears smooth.
  • Functions of SER:
    • Lipid synthesis (e.g., synthesis of steroids).
    • Detoxification of toxins and drugs (chemical modification of toxic substances).
    • Storage of calcium ions (Ca²⁺), particularly in muscle cells; SER stores calcium in muscle tissue.
  • Relationship: SER follows after RER; both are part of the endomembrane system involved in synthesis and trafficking of cellular products.

Ribosomes

  • Composition: made of ribosomal RNA (rRNA).
  • Two main locations in the cell:
    • Attached to the outer surface of the rough ER (RER).
    • Free-floating in the cytosol.
  • Functions:
    • Protein synthesis.
  • Difference between the two ribosome populations:
    • Attached ribosomes synthesize proteins destined for export or secretion, or for insertion into membranes.
    • Free ribosomes synthesize proteins that function inside the cytosol or within organelles.

Peroxisome (labeling note from the lecture)

  • In the lecture, there was uncertainty about a labeled structure: it could be a peroxisome or a storage vesicle.
  • Practical takeaway: one slide included a potential peroxisome label, but the observed content may resemble a lysosome or storage vesicle.
  • General peroxisome function (not explicitly stated in this transcript): breakdown of fatty acids and detoxification of reactive oxygen species; contains enzymes such as catalase.

Cytoplasm (summary note from the session)

  • The instructor emphasized identifying components within the cytoplasm and understanding their roles within the cell’s internal environment.

Microscopy and Lab Instructions (Light Compound Microscope)

  • The session referenced a light compound microscope used for classroom study.
  • Students were instructed to locate and name the parts of the microscope using a labeled diagram on page 37, and to read care and use instructions on page 75.
  • Task guidance:
    • Recognize and understand the parts and their functions.
    • Decide whether to use labels during the exercise or to try labeling without them.
    • Do not affix labels to the glass surfaces of the microscope to avoid difficult cleaning.
  • Group work: students should continue working in groups, taking one microscope per group, with considerations for partner placement.
  • Practical tip: when removing the plastic cover, fold it and set it aside to save workspace.

Connections to Broader Concepts

  • Endomembrane system: ER (rough and smooth), Golgi, vesicles, lysosomes are part of a coordinated pathway for protein and lipid processing and trafficking.
  • Mitochondria as energy generators and genetic heritage: mtDNA provides maternal lineage information and contributes to ATP production.
  • Nuclear envelope and nuclear pores: regulate exchange of material between nucleus and cytoplasm, enabling transcription and translation processes to connect.
  • Lysosome autolysis as a quality-control/degenerative mechanism: prevents damaged cells from persisting and potentially harming the organism.
  • Ribosome localization determines protein destiny: rough ER yields secreted/membrane proteins; free ribosomes yield cytosolic or organelle-targeted proteins.

Quick Reference: Key Terms and Concepts

  • Nuclear envelope: boundary of the nucleus; contains nuclear pores.
  • Nuclear pores: holes regulating transport between nucleus and cytoplasm.
  • Centrosome: organelle organizing center for microtubules; consists of two centrioles; two centrosomes per cell; important during cell division.
  • Centriole: two per centrosome; oriented at 90° to each other.
  • Golgi apparatus: processing, sorting, and shipping center; packages materials into vesicles for transport.
  • Vesicle: membrane-bound bubble used for transport.
  • Mitochondrion: powerhouse; ATP synthesis; two membranes with cristae; contains mtDNA; variable in number.
  • Cristae: folds of the inner mitochondrial membrane increasing surface area.
  • Lysosome: intracellular digestion; autolysis.
  • Plasma membrane: boundary of the cell; regulates traffic; mediates communication and recognition.
  • Cytosol: intracellular fluid; gel-like due to solutes; site of many metabolic reactions.
  • Rough endoplasmic reticulum (RER): ribosome-studded; protein synthesis and processing.
  • Smooth endoplasmic reticulum (SER): lipid synthesis; detoxification; calcium storage.
  • Ribosome: RNA-protein complex; two locations (RER and cytosol); site of protein synthesis; ribosomes on RER vs free ribosomes determine protein destination.
  • Peroxisome: potential label in the lecture; see discussion notes for context; general role in fatty acid metabolism and detoxification.

Relevant Equations and Notation

  • Angle between centrioles: 90^ omo
  • Note: In this transcript, the angle is described as 90 degrees; represented here as 90^ deg (rendered as 90^\circ in proper LaTeX).