BIO 004 · Human Anatomy
Anatomy of the Cell
Block 1 · Module 2: Cell Anatomy
A reference for the cell anatomy video and lab. The cell is the smallest living unit of the body. Every tissue, organ, and system is built from cells, so the structures named here are the foundation for the histology page that follows.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids and the sequence respond to Study and Quiz too, with a Reveal button on each row or step.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the membranous and non-membranous organelles and how cell structure matches cell job.
- Name the three basic regions of a generalized cell and state what each one contains.
- Describe the plasma membrane, distinguish integral from peripheral proteins, and name its surface specializations.
- Identify the membranous and non-membranous organelles and state the job of each.
- Explain how the nucleus stores the genetic material and how the nuclear pores control its traffic.
- Trace the path a product follows through the endomembrane system, from the ER to the cell surface.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
The Generalized Cell
Cells vary widely, but a composite model shows the three regions and the structures common to most body cells.
- Generalized cella composite model showing the features shared by most body cells
- Plasma membranethe outer boundary that encloses the cell and separates it from its surroundings
- Cytoplasmeverything between the plasma membrane and the nucleus, the cytosol plus the organelles
- Nucleusthe control center, usually the largest structure in the cell
The Plasma Membrane
The outer boundary of the cell, and a selective barrier that controls which substances enter and leave. Compare its components by where each one sits and what each one does.
Membrane structure
| Component | Location in the membrane | Role |
|---|---|---|
| Phospholipid bilayer | a double layer of phospholipids, the basic fabric of the membrane | forms the continuous sheet; the fluid mosaic model describes proteins drifting within it |
| Integral proteins | firmly embedded in the bilayer; most span it completely as transmembrane proteins | form the channels, carriers, and receptors |
| Peripheral proteins | attached loosely to one face of the membrane or to integral proteins, not embedded | act as enzymes and brace the cell shape |
| Cholesterol | wedged among the phospholipids | stabilizes the membrane and keeps it fluid |
| Glycocalyx | the fuzzy external coat of glycoproteins and glycolipids | the cell's identity badge, used in recognition and adhesion |
Surface specializations
| Specialization | Description | Function |
|---|---|---|
| Microvilli | finger-like extensions of the cell surface | increase surface area for absorption |
| Cilia | short hair-like extensions | sweep substances across the cell surface |
| Flagellum | a single long extension | propels the cell; the only human example is the sperm tail |
The Nucleus
The control center of the cell. It stores the genetic code and directs the building of proteins.
- Nuclear envelopethe double membrane that encloses the nucleus, its outer membrane is continuous with the rough ER
- Nuclear poresprotein-lined channels through the envelope that regulate traffic both ways, messenger RNA and ribosomal subunits move out while proteins needed inside move in
- Nucleoplasmthe fluid inside the nucleus that suspends the other nuclear structures
- Nucleolusa dense body inside the nucleus where ribosomal subunits are assembled
- Chromatinthe loose, threadlike form of DNA wound on proteins, present when the cell is not dividing
- Chromosomesthe tightly coiled form of chromatin, visible when the cell divides
Cytoplasm and Organelles
The cytoplasm is the cytosol, a gel-like fluid that suspends the organelles, plus the organelles themselves, the small structures that each carry out a specific job. Compare them by structure and function.
Membranous organelles
| Organelle | Structure | Function |
|---|---|---|
| Rough ER | a ribosome-studded membrane network | makes and packages proteins |
| Smooth ER | a tubular membrane network with no ribosomes | makes lipids and stores calcium |
| Golgi apparatus | a stack of flattened membrane sacs | sorts, packages, and ships cell products |
| Lysosomes | membrane sacs of digestive enzymes | break down worn parts and debris |
| Peroxisomes | membrane sacs of enzymes | neutralize toxins and free radicals |
| Mitochondria | double-membraned organelles | produce most of the cell's ATP |
| Vesicles | small membrane sacs | move substances within the cell |
Non-membranous organelles
| Organelle | Structure | Function |
|---|---|---|
| Ribosomes | tiny particles of RNA and protein, free in the cytosol or attached to the rough ER | build proteins |
| Cytoskeleton | an internal protein framework | gives the cell shape and allows movement |
| Microfilaments | the thinnest fibers, made of actin | support the cell surface and enable movement |
| Intermediate filaments | rope-like fibers | resist pulling forces and give the cell strength |
| Microtubules | the thickest fibers, hollow tubes | form tracks for transport inside the cell |
| Centrosome | a region near the nucleus | organizes the microtubules |
| Centrioles | paired rod-shaped structures within the centrosome | organize the spindle during cell division |
The Path Materials Take Through the Cell
The membranous organelles connect into one route, the endomembrane system: the nuclear envelope, the ER, the Golgi apparatus, vesicles, and lysosomes. The numbered path below traces a secreted protein in order, from where it is made to where it leaves the cell. The mechanism belongs to physiology and is not covered here.
- Rough ERthe start of the path, where a new protein is made and enters the endomembrane system
- Transport vesiclebuds from the ER and carries the product to the Golgi apparatus
- Golgi apparatusthe mid-path stop, where the product is sorted, modified, and packaged
- Secretory vesiclethe carrier on the final leg, from the Golgi to the plasma membrane or to a lysosome
- Exocytosisthe exit point, where the vesicle fuses with the plasma membrane and the product leaves the cell
Supporting structures on the route
- Endocytosisthe reverse direction, where material is taken into the cell inside a newly formed vesicle
- Microtubulesthe tracks the vesicles follow between stops on the path
- Nuclear poresthe gateway on the path between the nucleus and the cytoplasm, where messenger RNA exits
Cells Vary With Their Job
No single cell looks like the generalized model. A cell's shape and its mix of organelles match the work it does: structure follows job, and a cell built for a task carries the organelles that task needs. Compare three examples.
| Cell type | Structural adaptation | Why it fits the job |
|---|---|---|
| Muscle cell | long and packed with mitochondria | contraction demands a constant, heavy supply of ATP |
| Red blood cell | loses its nucleus and organelles | frees interior space for oxygen-carrying contents |
| White blood cell | changes shape freely | can squeeze between cells to reach a site of infection |
See also: Histology: The Four Tissue Types, the companion page in this module, where cells are organized into tissues.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Name the three regions of a generalized cell and state what each one contains.
- Trace a secreted protein through the endomembrane system, from where it is made to where it leaves the cell.
- Compare membranous and non-membranous organelles and give two examples of each.
- Explain how the structure of the plasma membrane makes it a selective barrier.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.