When studying the human body is helpful to consider its basic architecture; that is, how its smallest parts are assembled into larger structures. It is convenient to consider the structures of the body in terms of fundamental levels of organization that increase in complexity: subatomic particles, atoms, molecules, organelles, cells, tissues, organs, organ systems and organisms.
Cell: The smallest structural and functional unit of an organism, typically microscopic.
All living cells arise from pre-existing cells by division.
The activity of an organism depends on the total activity of independent cells.
Prokaryote: A simple, mostly single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle. Prokaryotic DNA is in the cell's central part: the nucleoid
- The prefix "pro-" means "before" and the suffix "-karyote" means
nucleus
*Bacteria cells are prokaryotic
Eukaryote: Cells that contain 1) a membrane-bound nucleus; 2) numerous membrane-bound organelles such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others; and 3) several, rod-shaped chromosomes.
- The prefix "eu-" means "true" and the suffix "-karyote" means
nucleus
*Human cells are eukaryotic. The sperm is unique in the human
body, as it is the only cell that contains a flagella to allow for
movement during fertilization
A cell’s plasma membrane defines the boundary of the cell and contains receptors, which are attachment sites for specific substances that interact with the cell. Each receptor is structured to bind with a specific substance.
The plasma membrane can be defined as a fluid mosaic. The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—in which the components are able to flow and change position.
The phospholipids that make of the bulk of the plasma membrane are amphipathic, meaning they contain both hydrophilic and hydrophobic portions.
- Hydrophilic: water loving - the heads of the phospholipids
- Hydrophobic: water fearing - the fatty acid tails of the
phospholipids
The amphipathic nature of the phospholipids results in the bilayer orientating itself so the parts that fear water are not in contact with the water containing cytoplasm or extracellular fluid, while the parts that love water are.
Cytosol: the intracellular fluid within a cell
Cytoplasm = cytosol + organelles
Organelles: Subcellular structure that has one or more specific jobs to perform in the cell, much like an organ does in the body
- Nucleus: Houses the cell’s DNA in the form of chromatin
* DNA is packaged by special proteins called histones to form
chromatin. The chromatin further condenses to form
chromosomes.
* DNA contains genes, a sequence of nucleotides in DNA that
are transcribed to produce RNA and ultimately proteins.
- Rough Endoplasmic Reticulum: Named because the ribosomes attached to its surface, giving it a studded appearance when viewed through an electron microscope. The ribosomes synthesize proteins.
- Smooth Endoplasmic Reticulum: Continuous with the rough endoplasmic reticulum, but has few or no ribosomes on its surface. Its functions include synthesis of carbohydrates, lipids (including phospholipids), and steroid hormones; detoxification of medications and poisons; alcohol metabolism; and storage of calcium ions.
- Golgi Apparatus: A series of flattened membranous sacs where the sorting, tagging, packaging, and distribution of lipids and proteins takes place.
- Lysosomes: The cell’s “garbage disposal.” Digestive enzymes within the lysosomes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles.
- Vesicles and Vacuoles: Membrane-bound sacs that function in storage and transport. Vacuoles are somewhat larger than vesicles.
- Ribosomes: The cellular structures responsible for protein synthesis.
- Mitochondria: Often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule.
- Peroxisomes: Small, round organelles enclosed by single membranes. They carry out oxidation reactions that break down fatty acids and amino acids. They also detoxify many poisons that may enter the body. A byproduct of these oxidation reactions is hydrogen peroxide, H2O2, which is contained within the peroxisomes to prevent the chemical from causing damage to cellular components outside of the organelle.
- Cytoskeleton: A group of fibrous proteins (microtubules, intermediate filaments, microfilaments) that provide structural support for cells. Cytoskeletal components are also critical for cell motility, cell reproduction, and transportation of substances within the cell.
All cells, rather prokaryotic or eukaryotic, have the following:
1 - Cell membrane - cells must be able to control what is
entering and exiting the cell
2 - Cytoplasm - the fluid material that fills the interior of the cell,
where many chemical reactions occur at in the cell
3 - Genetic material - contains the basic code that tells each cell
how to grow, function and reproduce
*Genetic material will be located in the nucleus of eukaryotic
cells and in the nucleoid of prokaryotic cells
4 - Ribosomes - the organelle responsible for coordinating protein
synthesis. All cells must be able to produce proteins
