3.1 Examining Cell Structure

In your study of anatomy and physiology, you will focus on the structure and function of eukaryotic cells because these are the cells found in the human body. Typically, the largest structure inside a eukaryotic cell is the nucleus, which contains the cell’s DNA and directs all cellular activities.

The cytoplasm is the gel-like cell matrix located outside the nucleus. It consists of a fluid portion, the cytosol, and various structures called organelles. The organelles are divided into two categories: (1) membranous organelles, which are surrounded by a phospholipid membrane, similar in structure to the plasma (cell) membrane. These membrane-bound structures have internal compartments with chemical environments that may be different than the surrounding cytosol; and (2) nonmembranous organelles, which are not surrounded by a membrane and, thus, are in direct contact with the cytosol.

1. Peroxisomes: 
Contain enzymes that neutralize toxins produced by cellular metabolism or taken in fromthe  outside; they also break down fatty acids.

   

2. Lysosomes:    
  are filled with digestive (hydrolytic) enzymes. They digest old, worn- out organelles, and destroy harmful bacteria, viruses, and toxins. 

3. Centrioles:      
are paired with cylindrical structures, arranged at right angles to each other and located at   one the cytoskeleton, form the bases from which the cilia and flagella are produced, and form   the mitotic spindle for mitosis.

4. Microvilli:       
 are tiny, fingerlike extensions that increase the surface area along the cell membrane of cells that absorb substances. They contain bundles of microfilaments that are anchored to the terminal web, a filamentous band that runs just below the cell surface.
5. The Golgi apparatus:
 is a series of flattened membranous sacs, resembling a stack of pancakes. This organelle modifies and packages proteins that are produced by the rough endoplasmic reticulum.
6. The endoplasmic reticulum (ER): 
is a highly folded membranous structure that encloses a network of fluid-filled cavities.
7. The rough endoplasmic reticulum (RER):
is studded with ribosomes (fixed ribosomes), the sites of protein synthesis. It produces proteins that are secreted by the cell, incorporated into the plasma membrane, or used by lysosomes.
8. The smooth endoplasmic reticulum (SER):
which lacks ribosomes, synthesizes lipids and glycogen and detoxifies poisons and various drugs.
9. The nucleolus:  is suspended in a gel-like matrix called the nucleoplasm. It produces ribosomes.
10. Chromatin:
 is composed of complex molecules of DNA and protein. DNA is the genetic material of the cell.
11. The nuclear envelope: 
 is a double membrane that separates nucleoplasm from cytoplasm. It is dotted with numerous nuclear pores that allow the passage of various substances into and out of the nucleus.
12. Free ribosomes produce proteins used for cellular metabolism.
13. Mitochondria:
are bean-shaped structures surrounded by a double membrane. The inner membrane, which contains numerous inward folds, encloses a gel-like material called the matrix. Mitochondria produce
most of the cell’s energy in the form of ATP.
14. The plasma (cell):  membrane is composed of phospholipids, proteins, and carbohydrates and acts as a selectively permeable barrier between the cell and its external environment.
15. The cytoskeleton:  consists of three types of protein filaments—microtubules, intermediate filaments,
and microfilaments. They provide strength and flexibility for the cell and support for the various other organelles.

Cell Structure and Cell Division

 

Learning Outcomes

These Learning Outcomes correspond by number to the laboratory activities in this exercise.

When you complete the activities, you should be able to:

Activity 3.1  Describe the structure and function of the nucleus and major organelles in a eukaryotic cell.

Activity 3.2  Prepare a wet mount of cells derived from your own cheek.

Activity 3.3 Compare and contrast light microscopic and electron microscopic observations of cell structure.

Activity 3.4 Identify and describe the stages of mitosis.

BEFORE YOU BEGIN, CONSIDER THIS

The term cell was first used in 1665 when Robert Hooke was examining a thin slice of cork for a demonstration at the Royal Society of London. He observed evenly spaced rows of boxes that reminded him of the “cells,” or living quarters, for monks in a monastery. Hooke did not actually observe living cells because the cork tissue was dead. All that remained was the cell wall, a structure found in plant cells and bacteria. With the advent of the first microscope in 1673, Anton van Leeuwenhoek was the first to identify living cells. However, significant advances in cell biology did not occur until the first part of the 19th century, when microscopes with stronger magnification and resolving power were developed.
At the beginning of the 19th century, medical studies on the human body paved the way for the development
of what is known as the cell theory. It was during this time that a fundamental understanding of cell structure and function began to emerge. Gradually, the work of various scientists contributed to the modern cell theory, which includes the following concepts:

• Cells are the structural building blocks of all living organisms.
• All cells arise from preexisting cells.
• The cell is the basic unit of life.
• In a multicellular organism, each cell maintains its own metabolism, independent of other cells, yet individual cells depend on other cells for survival.
• The activities of all cells in an organism are essential and highly coordinated. 

Different cell types vary greatly in size, shape, and function; consider, for example, the differences in a muscle cell and a nerve cell. And yet, the cell theory tells us that all the cells in our bodies derive from a single cell: the fertilized ovum that forms when the cell nuclei of egg and sperm unite. This means that despite their variability, all the cells in your body have the same genetic makeup. Consider how this can be possible.

Cell Structure and Cell Division

Examining Cell Structure

1. Peroxisomes: 
Contain enzymes that neutralize toxins produced by cellular metabolism or taken in fromthe  outside; they also break down fatty acids.

2. Lysosomes:    
  are filled with digestive (hydrolytic) enzymes. They digest old, worn- out organelles, and destroy harmful bacteria, viruses, and toxins. 

3. Centrioles:      
are paired with cylindrical structures, arranged at right angles to each other and located at   one the cytoskeleton, form the bases from which the cilia and flagella are produced, and form   the mitotic spindle for mitosis.

4. Microvilli:       
 are tiny, fingerlike extensions that increase the surface area along the cell membrane of cells that absorb substances. They contain bundles of microfilaments that are anchored to the terminal web, a filamentous band that runs just below the cell surface.
5. The Golgi apparatus:
 is a series of flattened membranous sacs, resembling a stack of pancakes. This organelle modifies and packages proteins that are produced by the rough endoplasmic reticulum.
6. The endoplasmic reticulum (ER): 
is a highly folded membranous structure that encloses a network of fluid-filled cavities.
7. The rough endoplasmic reticulum (RER):
is studded with ribosomes (fixed ribosomes), the sites of protein synthesis. It produces proteins that are secreted by the cell, incorporated into the plasma membrane, or used by lysosomes.
8. The smooth endoplasmic reticulum (SER):
which lacks ribosomes, synthesizes lipids and glycogen and detoxifies poisons and various drugs.
9. The nucleolus:  is suspended in a gel-like matrix called the nucleoplasm. It produces ribosomes.
10. Chromatin:
 is composed of complex molecules of DNA and protein. DNA is the genetic material of the cell.
11. The nuclear envelope: 
 is a double membrane that separates nucleoplasm from cytoplasm. It is dotted with numerous nuclear pores that allow the passage of various substances into and out of the nucleus.
12. Free ribosomes produce proteins used for cellular metabolism.
13. Mitochondria:
are bean-shaped structures surrounded by a double membrane. The inner membrane, which contains numerous inward folds, encloses a gel-like material called the matrix. Mitochondria produce
most of the cell’s energy in the form of ATP.
14. The plasma (cell):  membrane is composed of phospholipids, proteins, and carbohydrates and acts as a selectively permeable barrier between the cell and its external environment.
15. The cytoskeleton:  consists of three types of protein filaments—microtubules, intermediate filaments,
and microfilaments. They provide strength and flexibility for the cell and support for the various other organelles.

NOTE: 

Laboratory Supplies

• Eukaryotic cell model
• Compound light microscopes
• Microscope slides
• Coverslips
• Toothpicks
• 10% methylene blue stain
• Prepared microscope slides of cheek cells
• Prepared microscope slides of various structures
• Electron micrographs of various cell structures
• Prepared slides of whitefish blastula
• Coloring pencils

This is our continuous lesson: 

Activity 3.1  : http://www.worldbeautiful.ga/2016/01/blog-post.html

Activity 3.2 

Activity 3.3

Activity 3.4