1. Pima Medical Institute BIO 120
Hole’s Essentials of Human Anatomy & Physiology
Cell Types, Structure, and Function
BIO 120 Lesson 3 - Cells
David Shier, Jackie Butler, Ricki Lewis, Hole’s Essentials of Human Anatomy & Physiology, 10th Ed. CopyrightThe McGraw-Hill Companies, Inc. Created by Dr. Melissa Eisenhauer, Trevecca Nazarene University

2. Introduction:
A. The human body consists of 75 trillion cells that vary considerably in shape and size yet have much in common.
B. Differences in cell shape make different functions possible.
Recipe for a human being: cells, their products, and fluids. A cell, as a unit of life, is a world unto itself. To build a human, trillions of cells connect and interact, forming dynamic tissues, organs, and organ systems.
The estimated 75 trillion cells that make up an adult human body have much in common. Yet cells in different tissues vary considerably in size and shape, and typically, their three-dimensional forms make possible their functions (illustrated in Figure 3.1, slide 2). For instance –
Nerve cells often have long, threadlike extensions that transmit electrical impulses from one part of the body to another.
Epithelial cells that line the inside of the mouth are then, flattened, and tightly packed. This tile-like organization enables the cells to protect those beneath them.
Muscle cells, which pull structures closer together, are slender and rod-like. The precise alignment of the fibers within muscle cells provides the strength to withstand the contraction that moves the structures to which they attach.

3. Cells vary in structure and function
Cell variations in Figure 3.1
A nerve cell’s long extensions enable it to transmit impulses from one body part to another.
The sheet-like organization of epithelial cells enables them to protect underlying cells.
The alignment of contractile proteins within muscle cells enables them to contract, pulling closer together the structures to which they attach.
Figure 3.1

4. A Composite Cell:
A. A composite cell includes many different cell structures.
B. A cell consists of three main parts--the nucleus, the cytoplasm, and the cell membrane.
C. Within the cytoplasm are specialized organelles that perform specific functions for the cell.
Describing a typical cell is impossible because cells vary in size, shape, content, and function. A composite cell includes many known cell structures.
Under a light microscope, a properly applied stain reveals three basic cell parts: the cell membrane that enclosed the cell, the nucleus that houses the genetic material and controls cellular activities, and the cytoplasm that fills out the cell. Within the cytoplasm are specialized structures called organelles, which are suspended in a liquid called cytosol, perform specific functions, which divides the labor of the cell.

5. A composite cell Figure 3.2
A composite cell illustrates the organelles and other structures found in cells. Specialized cells differ in the numbers and types of organelles, reflecting their functions.
Figure 3.2

6. Cell Membrane:
1. The cell membrane regulates the movement of substances in and out of the cell, participates in signal transduction, and helps cells adhere to other cells.
2. General Characteristics
a. The cell membrane is extremely thin and selectively permeable.
b. It has a complex surface with adaptations to increase surface area.
The cell membrane (also called the plasma membrane) is more than a simple boundary surrounding the cellular contents. It is an actively functioning part of the living material. The cell membrane regulates movement of substances in and out of the cell and is the site of much biological activity.
Many of the cell’s actions that enable it to survive and to interact with other cells use a molecular communication process called signal transduction. A series of molecules that are part of the cell membrane form pathways that detect signals from outside the cell and transmit them inward, where yet other molecules orchestrate the cell’s response. The cell membrane also helps cells adhere to certain other cells, which is important in forming tissues.
The cell membrane is extremely thin, flexible, and somewhat elastic. In addition to maintain cell integrity , the cell membrane is selectively permeable, which means that only certain substances can enter or leave the cell. The cell membrane has complex surface features with many outpouchings and infoldings that increase surface area (see Figure 3.2, slide 5).

7. The cell membrane is composed primarily of phospholipids (and some cholesterol), with proteins scattered throughout the lipid bilayer and associated with its surfaces.
Figure 3.3

8. 3. Cell Membrane Structure:
a. The basic framework of the cell membrane consists of a double layer of phospholipids, with fatty acid tails turned inward.
b. Molecules that are soluble in lipids (gases, steroid hormones) can pass through the lipid bilayer.
The cell membrane is composed mainly of lipids and proteins, with few carbohydrates. Its basic framework is a double layer, or bilayer, of phospholipid molecules.
The membrane’s interior is oily because it consists largely of the fatty acid portions of the phospholipid molecules (Figure 3.3). Molecules such as oxygen and carbon dioxide, which are soluble in lipids, can easily pass through this bilayer. However, the bilayer is impermeable to water-soluble molecules, such as amino acids, sugars, proteins, nucleic acids, and various ions.

9. Cell Membrane Structure: (continued)
c. Embedded cholesterol molecules strengthen the membrane and help make the membrane less permeable to water-soluble substances.
d. Many types of proteins are found in the cell membrane, including transmembrane proteins and peripheral membrane proteins.
Cholesterol molecules embedded in the cell membrane’s interior help make the membrane less permeable to water-soluble substances, while stabilizing the membrane with their rigid structure.
A cell membrane includes a few types of lipid molecules, but many kinds of proteins, which provide special functions.
Membrane proteins are classified according to their positions. Membrane-spanning (transmembrane) proteins extend through the lipid bilayer and my protrude from one or both faces. Peripheral membrane proteins associate mostly with one side of the bilayer.

10. Cell Membrane Structure: (continued)
e. Membrane proteins perform a variety of functions and vary in shape.
f. Some proteins function as receptors on the cell surface, starting signal transduction.
g. Other proteins aid the passage of molecules and ions.
Membrane proteins have a variety of functions, some form receptors on the cell surface that bind incoming hormones or growth factors, starting signal transduction. Other proteins transport ions or molecules across the cell membrane. Membrane proteins form selective channels that allow only particular ions to enter or leave. In nerve cells, for example, such selective channels control movement of sodium and potassium ions.

11. Cell Membrane Structure: (continued)
h. Proteins protruding into the cell anchor supportive rods and tubules.
i. Still other proteins have carbohydrates attached (glycoproteins); these complexes are used in cell identification. Membrane proteins called cellular adhesion molecules (CAMs) help determine one cell’s interactions with others.
Proteins that extend inward from the inner face of the cell membrane anchor it to the protein rods and tubules that support the cell from within. Proteins that extend from the outer surface of the cell membrane mark the cell as part of a particular tissue or organ in a particular person. This identification as self is important for the functioning of the immune system.
Many of these proteins are attached to carbohydrates, forming glycoproteins. Another type of protein on a cell’s surface is a cellular adhesion molecule (CAM), which guides a cell’s interactions with other cells. For example, a series of CAMs helps a white blood cell move to the site of an injury, such as a splinter in the skin.

12. networks of membranes and organelles.
Cytoplasm:
1. The cytoplasm consists of a clear liquid (cytosol), a supportive cytoskeleton, and
networks of membranes and organelles.
a. Endoplasmic reticulum is made up of membranes, flattened sacs, and vesicles, and provides a tubular transport system inside the cell.
i. With ribosomes, endoplasmic reticulum (ER) is rough ER, and functions in protein synthesis.
ii. Without ribosomes, it is smooth ER, and functions in lipid synthesis.
The cytoplasm is the gel-like material in which organelles are suspended—it makes up most of as cell’s volume. Through a light microscope, cytoplasm usually appears as a clear jelly with specks scattered throughout. Through an electr5on microscope, with its greater magnification, the cytoplasm contains networks of membranes and organelles suspended in the clear liquid cytosol. Cystoplasm also includes abundant protein rods and tubules that form a framework, or cytoskeleton, meaning “cell skeleton”.
Cell activities occur mainly in the cytoplasm, where nutrients are received, processed, and used. The following organelles have specific functions in carrying out these activities:
a) Endoplasmic reticulum provides a vast tubular network that transports molecules from one cell part to another. The ER participates in the synthesis of protein and lipid molecules. These molecules may leave the cell as secretions or be used within the cell for such functions as producing new ER or cell membrane as the cell grows. The ER’s outer membrane is studded with many tiny, spherical structures called ribosomes, which give the ER a textured appearance when viewed with an electron microscope (see Figure 3.4 a, b).

13. Cytoplasm: (continued)
b. Ribosomes are found with ER and are scattered throughout the cytoplasm. They are composed of protein and RNA and provide a structural support for the RNA molecules that come together in protein synthesis.
b) Ribosomes are composed of protein and RNA molecules. Ribosomes provide a structural support on which amino acids are strung together to form proteins. Clusters of ribosomes in the cytoplasm, called polysomes, enable a cell to quickly manufacture proteins required in large amounts. All ribosomes are composed of protein and RNA molecules. Ribosomes provide enzymatic activity as well as a structural support for the RNA molecules that comes together as the cell links amino acids to form proteins. The ER’s outer membrane is studded with many tiny, spherical structures called ribosomes, which give the ER a textured appearance when viewed with an electron microscope (see Figure 3.4 a, b).

14. Figure 3.4 The Endoplasmic Reticulum (ER)
The endoplasmic reticulum is the site of protein and lipid synthesis, and serves as a transport system.
(b) Rough ER is dotted with ribosomes
(c) smooth ER lacks ribosomes
Figure 3.4
The Endoplasmic Reticulum (ER)

15. Cytoplasm (continued)
c. The Golgi apparatus is composed of flattened sacs, and refines, packages, modifies, and delivers proteins.
i. Vesicles formed on ER travel to the Golgi apparatus which modifies their contents chemically.
ii. The vesicle may then move to the cell membrane and secrete its contents to the outside.
iii. Vesicles form a “delivery service,” carrying chemicals throughout the cell (vesicle trafficking).
Golgi apparatus consists of a stack of about six flattened, membranous sacs whose membranes are continuous with the endoplasmic reticulum. This functions to refine and "package" the proteins synthesized by the ribosomes associated with the endoplasmic reticulum.

16. The Golgi apparatus processes secretions
a) A transmission electron micrograph of a Golgi apparatus (48,500x)
b) The Golgi apparatus consists of membranous sacs that continually receive vesicles from the endoplasmic reticulum (ER) and produce vesicles that enclose secretions.
Figure 3.5

17. Cytoplasm (continued)
d. Mitochondria are the powerhouses of the cell and contain enzymes needed for aerobic respiration.
i. The inner membrane of the mitochondrion is folded into cristae which hold the enzymes needed in energy transformations to make ATP.
ii. Very active cells contain thousands of mitochondria.
Mitochondrion are elongated fluid filled sacs. The membrane surrounding a mitochondrion has an inner and outer layer. The inner layer is folded extensively to form partitions called cristae. In the cristae are enzymes that control some of the chemical reactions by which energy is released from organic substances. The cristae function in transforming this energy into a chemical form that is usable by various cell parts. Mitochondria are the major sites of chemical reactions that capture and store this energy within the chemical bonds of adenosine triphosphate (ATP), a chemical form that the cell can easily use.

18. Figure 3.6 A mitochondrion is a major site of energy reactions.
a. A transmission electron micrograph of a mitochondrion (28,000x)
b. Cristae partition this saclike organelle.
Figure 3.6

19. Cytoplasm (continued)
e. Lysosomes are the "garbage disposals" of the cell and contain digestive enzymes to break up old cell components and bacteria.
f. Peroxisomes contain enzymes that function in the synthesis of bile acids, breakdown of lipids, degradation of rare biochemicals, and detoxification of alcohol.
Lysosome are tiny, membranous sacs that contain powerful enzymes that are capable of breaking down molecules of nutrients or foreign particles that enter cells. These also function in the destruction of worn cellular parts. Lysosomes digest worn cellular parts or substances that enter cells.
Peroxisomes—these membranous sacs are abundant in liver and kidney cells. They house enzymes that catalyze (speed) a variety of biochemical reactions, including synthesis of bile acid (used to digest fats); detoxification of hydrogen peroxide, a by-product of metabolism; breakdown of certain lipids and rate biochemicals; and detoxification of alcohol.

20. Cytoplasm (continued)
g. Microfilaments and microtubules are thin, threadlike structures that serve as the cytoskeleton of the cell.
i. Microfilaments, made of actin, cause various cellular movements.
ii. Microtubules, made of the globular protein tubulin, are attached in a
spiral to form a long tube.
Microfilaments are tiny rods of protein arranged in meshworks or bundles that function to cause various kinds of cellular motility (movement). In the muscle cells, for example, microfilaments aggregate (massed into a dense cluster) to form myofibrils, which help these cells contract.
Microtubules are long, slender tubes that have a diameter two or three times greater than microfilaments. Microtubules are composed of molecules of a globular protein called tubulin, attached in a spiral to form a long tube.
(see Figure 3.7, slide 21)

21. Components of the cytoskeleton: Microtubules & Microfilaments
Components of the cytoskeleton. Microtubules built of tubulin and microfilaments built of actin help maintain the shape of a cell by forming a cytoskeleton within the cytoplasm. A cell’s shape is critical to its function.
Figure 3.7

22. Cytoplasm (continued.
h. The centrosome is a structure made up of two hollow cylinders called centrioles that function in the separation of chromosomes during cell division.
i. Cilia and flagella are motile extensions from the cell; shorter cilia are abundant on the free surfaces of certain epithelial cells (respiratory linings, for example), and a lengthy flagellum can be found on sperm cells.
j. Vesicles form from part of the cell membrane or the Golgi and store materials.
The centrosome is located in the cytoplasm near the Golgi apparatus and nucleus, these are nonmembranous and consist of two hollow cylinders called centrioles (see slide 23). These function in cell reproduction by distributing chromosomes to new cells during cell division (mitosis).
Cilia are short, motile extensions of the surfaces of some cells. There are many of these and they have a wavelike motion. This action serves to move fluids, such as mucus, over the surface of certain tissues, including those that form the inner linings of the respiratory tubes (see Figure 3.9a, bottom of slide 23).
Flagella are long, whiplike motile processes that extend outward from the surface of other cells. These have a whiplike motion that generally is used for movement, like the tail on a sperm cell. The tail of a sperm cell is a flagellum that enables this motile cell to “swim” and is the only example of a flagellum in humans (see Figure 3.9b, bottom of slide 23).
Vesicles are membranous sacs formed by part of the cell membrane folding inward and pinching off. As a result, a tiny, bubblelike vesicle, containing some liquid or solid material formerly outside the cell, appears in the cytoplasm. The Golgi apparatus and ER also form vesicles that play a role in secretion (see Figure 3.4, slide 5).

23. Figure 3.8, p. 58
At the top of slide 23 is the Centrioles – a) transmission electron micrograph of the two centrioles in a centrosome (120,000x). b) the centrioles lie at right angels to one another. These structures participate in apportioning the chromosomes of a dividing cell into two cells.
At the bottom of slide 23 we find cilia and flagella, which provide movement.
Cilia are common on the surfaces of certain cells, including those that form the inner lining of respiratory tubes.
Flagella form the tails of these human sperm cells, enabling them to “swim”.
Figure 3.9, p. 59

24. b. Chromatin consists of loosely coiled fibers of protein and DNA.
Cell Nucleus:
1. The fairly large nucleus is bounded by a double-layered nuclear membrane containing relatively large nuclear pores that allow the passage of certain substances.
a. The nucleolus is composed of RNA and protein and is the site of ribosome production.
b. Chromatin consists of loosely coiled fibers of protein and DNA.
The nucleus houses the genetic material (DNA), which direct all cell activities (figures 3.2 slide 5, and 3.10 slide 25). It is a large, roughly spherical structure enclosed in a double-layered nuclear envelope, which consists of inner and outer lipid bilayer membranes. The nuclear envelope has protein-lines channels called nuclear pores that allow certain molecules to exit the nucleus. A nuclear pore is not just a hole, but a complex opening formed from 100 or so types of proteins.
The nucleolus (“little nucleus”) is a small, dense body composed largely of RNA and protein. Ribosomes form in the nucleolus, and then migrate through nuclear pores to the cytoplasm.
Cromatin consists of loosely coiled fibers composed of DNA molecules and protein that contain information for synthesizing proteins. These become chromosomes during cell division (mitosis). When the cell begins to divide, chromatin fibers coil rightly, and individual chromosomes become visible when stained and viewed under a light microscope.

25. Figure 3.10 The nucleus is the genetic headquarters of the cell.
the nuclear envelope is selectively permeable and allows certain substances to pass between the nucleus and the cytoplasm. Nuclear pores are more complex than depicted here.
transmission electron micrograph of a cell nucleus (7,500x). It contains a nucleolus and masses of chromatin.
Figure 3.10

26. Structures and Functions of Cell Parts
Table 3.1 summarizes the structures an functions of organelles.

27. What’s Next?
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