the completion of this chapter, the student will be able to:
1.Describe the basic structure, including the main components of a composite cell.
2.Characterize each individual organelle’s structure and function.
3.Distinguish between active and passive membrane transport.
4.Identify the stages of cell division.
5.Associate abnormal cell division and cancer.
Case Study Introduction
Erica is a 43-year-old female who has lived in South Florida since her parents migrated from Scandinavia when she was five years old. Erica is an avid scuba diver and loves outdoor sports. After college, she moved to Key West and opened up her own business renting motor boats, jet skis, and scuba gear.
Over the years, Erica has enjoyed growing her business and using her free time to enjoy the sun. One calm, sunny morning, while applying tanning oil to her skin, she noticed a small bump on the side of her left upper arm. Concerned, she called and scheduled an appointment to see her primary care doctor, Dr. Sanderson.
In the office, Dr. Sanderson obtained a history of Erica’s present condition, as well as a full medical, family, surgical, and social history. Dr. Sanderson then proceeded with a focused physical exam. Erica’s vital signs were all within normal limits with no remarkable findings.
Dr. Sanderson reported a 3 mm × 2 mm lesion on the lateral aspect of the patient’s left arm, just inferior to the deltoid muscle. The lesion was raised, dark brown in color, and had an irregular border. Dr. Sanderson decided to do an in-office biopsy and send it to the pathology lab. Erica was then educated on the health risks of repeated, long-term sun exposure and its effects of damaging skin cells. Erica was given a brochure with instructions on how to protect her skin while outdoors. She was also advised to limit sun exposure, and to apply a high SPF sun block product if she must go out in the sun. Erica was scheduled to return to the office in one week, when the results of the biopsy will be available.
■Introduction
Cytology, or the study of cells, was first established in 1665 by Robert Hooke1 (who actually coined the term cell), when he observed some plant substance under a microscope. He found that it resembled a miniature monastery cell, as they both had many sectioned compartments.
Since that time, numerous scientists have studied plant and animal specimens, all of whom have arrived to the same conclusion: all living specimens consist of cells. Therefore, the smallest structural unit of all living things is the cell. The cell, the smallest unit of life, capable of sustaining itself, must be composed of at least one cell.
A unicellular organism, such as bacteria and protozoa are the simplest forms of life. Human beings are multicellular organisms and are consequently much more complex forms of life. The human being is the result of trillions of cells functioning together in order to materialize into the complex structure that is the human body.
Cell biology, as it’s commonly referred to in today’s academic curricula, is the scientific study of the anatomy, physiology, and chemistry of a cell.
■About the Cell
Cells in the human body can be defined by type:
•Static or differentiated
•Expanding or undifferentiated
•Stem cells (responsible for the renewal of cells that can also differentiate or become different kinds of cells)
Undifferentiated cells have the ability to regrow or regenerate, while differentiated or static cells cannot. Once they reach their ‘peak’, they age and die.
A muscle cell is a type of differentiated or static cell.
Skin cells, which can expand, are a type of undifferentiated cell.
Hair is a perfect example of a type of stem cell. Hair cells die and are replaced on a regular basis.
Over 250 different cells are found in the human body. The shape of a cell is based on its specific function. For example:
•Skin (epithelial) cells are flat, much like floor tiles that form an effective barrier against bacteria.
•Skeletal muscle cells are oblong.
•Fat cells are ovoid or round.
•Microphage cells have tendril-like ‘fingers’ protruding from its center which act much like feelers that seek out and capturing damaged or diseased cells or bacteria for consumption/destruction.
Before investigating its intricate structure and function, it is sensible to first learn and know the basic components of a cell. Four main structural components make up a cell: The cell membrane, cytoplasm, organelles, and the nucleus.
Figure 2-1 Cell organelle.
We will consider each component in order to fully explore and appreciate their individual structures and functions.
Basic components of a cell
All cells in the human body have three major parts2:
•Plasma membrane
•Cytoplasm
•Organelles
The cell (plasma) membrane
The cell membrane, or plasma membrane as its sometimes, called, is a physical barrier that separates the internal components of a cell from the cell’s outside environment.
A membrane, by definition, must have two characteristics – it must be pliable, and it must be permeable. Pliability allows the cell to maintain its structural integrity while adapting to the stress of its outside environment.
Permeability allows certain substances to enter and/or leave the cell while preventing others from doing the same; a unique feature of a cell’s plasma membrane, termed selective permeability. For a closer look at how the cell membrane functions, we must examine its structure more closely.
Figure 2-2 Cellular anatomy.
According to the fluid mosaic model proposed by S.J. Singer and G.L. Nicolson in 1972,3 biological properties of the cell membrane can be appreciated as a semi-fluid that allows the movement of lipids, the binding of intrinsic protein molecules, and selective permeability. This arrangement is possible due to the unique phospholipid bilayer composition of the cell’s membrane.
The phospholipid bilayer is essentially two layers of phosphate-containing fat molecules forming a fluid framework, with the addition of another molecule called cholesterol, which helps stabilize the phospholipid molecules. The phospholipid bilayer also contains two types of protein molecules:
•integral
