2.3: Lab Exercise 3- Investigating Cells and Cell Variations

Lab Summary: You have already learned that atoms of elements come together to make molecules and compounds. Those molecules and compounds are then arranged to form cells. Cells are the smallest structural and functional units of all living organisms. In this lab, you will learn the cell organelles and their functions, cell division, and cell transport mechanisms. Additionally, you will explore how variations in anatomical structure affects the functions of some selected cell types seen throughout A&P.

Your objectives for this lab are:

• In a cell model (there are two models for you to explore), you should be able to identify and list the function(s) of
  • Nucleus
  • Nucleolus
  • Plasma membrane/ cell membrane o Cytoplasm
  • Ribosomes
  • Smooth endoplasmic reticulum
  • Rough endoplasmic reticulum
  • Golgi apparatus
  • Vesicles
  • Lysosomes
  • Peroxisomes
  • Mitochondria
  • Centrioles
  • Cytoskeleton filaments
• Compare and contrast specialized cells (red blood cells, neurons, simple squamous cells, teased smooth muscle cells) with a "generalized cell". Be able to relate anatomical differences to physiological/functional differences
• In a whiteish blastula slide, you should be able to identify the following stages of the cell cycle and describe events that occur during these phases
  • Interphase
  • Mitosis
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis
• Describe the functions of the following structures in the process of cell division
  • Chromosome
  • Chromatin
  • Chromatid
  • Centriole
  • Mitotic spindle/ spindle fiber

Background

All living organisms are composed of cells. This is one of the tenets of the Cell Theory, a basic theory of biology, which states that,

• All life is composed of cells
• Cells are the fundamental units which possess all the characteristics of living things
• New cells can only come into existence by the division of previously existing cells

This remarkable fact was first discovered over 300 years ago and continues to be a source of wonder and research today. Cell biology is an extremely active area of study and helps us answer such fundamental questions about how organisms function. Through an understanding of how cells function, we can discover how human ailments, such as cancer and AIDS, can be possibly treated. Throughout your study of A&P, you will continue to explore how different types of cells contribute to homeostasis in humans.

Notice that this scientific concept about life is called a theory. In science, unlike the layman’s definition, the word theory is used for a hypothesis about which there is a large body of convincing evidence.

Activity 3.1: Exploring Cell Membrane Structure

Procedure for Activity 3.1: Use the information and pictures below to learn about the components of the cell membrane and their functions. If a cell membrane model is available, you will also be directed to locate structures in that. You should review the molecular structure and functions of each part of the cell membrane. Why does a cell membrane need to be composed, primarily, of lipids? What would happen if cell membranes were made of water-soluble compounds?

Figure \(\PageIndex{1}\): Cell Membrane The cell membrane of the cell is a phospholipid bilayer containing many different molecular components, including proteins and cholesterol, some with carbohydrate groups attached.

The cell membrane (Figure \(\PageIndex{1}\)) is an extremely pliable structure composed primarily of a double layer of phospholipids (a “bilayer”). The hydrophobic lipid tails of one layer face the hydrophobic lipid tails of the other layer, meeting at the interface of the two layers. The hydrophilic phospholipid heads face outward, one layer exposed to the interior of the cell and one layer exposed to the exterior (Figure \(\PageIndex{2}\)); these border the intracellular and extracellular fluid, respective. Intracellular fluid (ICF) is the fluid interior of the cell (the cytosol). Extracellular fluid (ECF) is the fluid environment outside the enclosure of the cell membrane. Interstitial fluid (IF) is the term given to extracellular fluid not contained within blood vessels. An important feature of the membrane is that it remains fluid; the lipids and proteins in the cell membrane are not rigidly locked in place.

Figure \(\PageIndex{2}\): Phospholipid Bilayer The phospholipid bilayer consists of two adjacent sheets of phospholipids, arranged tail to tail. The hydrophobic tails associate with one another, forming the interior of the membrane. The polar heads contact the fluid inside and outside of the cell.

Cholesterol makes up ~40% of the cell membrane and up to 90% of the cell’s cholesterol is contained within the membrane. Functionally, cholesterol aids in fluidity and stability of the membrane. Functionally, cholesterol aids in fluidity and stability of the membrane. The cholesterol gathers into "rafts," which were thought to serve as platforms from which other signaling molecules might operate. (https://pubs.acs.org/doi/10.1021/ar500260t) Along with his colleagues, Wonhwa Cho, Professor of Chemistry at the University of Illinois, also determined that cholesterol directly interacts with many membrane proteins, which seem necessary for the proper functioning of these proteins. (https://medicalxpress.com/news/2012-12-cholesterol-key-proteins-cell.html )

Membrane proteins are embedded within the membrane and have a variety of functions. An integral protein (also called intrinsic proteins) is a protein that is embedded in the membrane. Examples of integral proteins include channel proteins, enzymes, receptors, ligands, and parts of the glycoproteins that compose the glycocalyx. Peripheral proteins (also called extrinsic proteins) are typically found on the inner-facing or outer-facing surfaces of the lipid bilayer but can also be attached to the internal or external surface of an integral protein. Examples of peripheral proteins include enzymes, support proteins on the surfaces of cell membranes, and cell junctions (such as gap junction structures). Membrane protein functions are summarized below.

• Transport proteins: selectively allow particular materials, such as certain ions (ex. the sodium- potassium pump for Na+ and K+), or molecules (ex. aquaporins for water), to pass into or out of the cell
• Enzymes: catalyze (speed up) chemical reactions
• Receptors: type of recognition protein that can selectively bind a specific molecule outside the cell, which then begins a chemical reaction within the cell
• Attachment points for cytoskeleton: anchors for the proteins of the cytoskeleton, so they are stable
• Cell recognition proteins: serve to mark a cell’s identity so that it can be recognized by other cells (such as the glycoproteins that determine blood types or the glycocalyx that serves as the cell’s “name tag”)

Activity 3.2 Procedure: Investigating Eukaryotic Cell Structures in Models

1. Use the information in Table 3.4 and Figure 3.3 below to learn about the parts of the cell (organelles) and their functions. Your review should include exploring the molecular structure and functions of each organelle shown below.

2. Using cell model, Table 3.4 and Figure 3.3, locate each of the organelles listed in Table 3.4. Practice enough until you can name each part on the cell model and describe its function without using your notes.

Figure \(\PageIndex{3}\): Prototypical Human Cell While this image is not indicative of any one particular human cell, it is a prototypical example of a cell containing the primary organelles and internal structures.

Table \(\PageIndex{1}\): CELL ORGANELLES AND THEIR FUNCTIONS (some organelles are not visible on models)

Structure Name	Function(s) & Structural Information
Cell membrane	Controls entry and exit of substances from the cell; aids in helping the cell identify itself to molecules and other cells; See also Activity 1
Nucleus	Stores and protects DNA; site of transcription of mRNA
Chromatin	Thin, loosely coiled “threads” of DNA wound around histone proteins; condense during prophase of the cell cycle at which point their called chromosomes
Nucleolus	Synthesizes rRNA; performs some ribosome assembly
Nuclear envelope	Lipid-bilayer that surround and protect contents and processes of the nucleus
Cytoplasm	Gel-like watery matrix of the cell; site of anaerobic cell respiration and other chemical reactions (such as the bicarbonate buffering system); stores molecules (such as glucose); cushions and contains organelles; composed of ~50% water Note: Cytosol is only the gel-like watery matrix plus
Smooth ER	Stores calcium in muscle cells (where it is called sarcoplasmic reticulum); manufactures phospholipids; synthesizes proteins for secretion; in liver cells, performs lipid and cholesterol manufacturing
Rough ER	Synthesizes and modifies proteins destined for the cell membrane or for export from the cell; glycosylation of protein is one form of modification
Golgi apparatus/ Golgi complex/ Golgi body	Sort, modify, package (in vesicles), and distribute lipids and proteins
Lysosome	Uses hydrolytic enzymes to degrade worn-out organelles, glycogen, bone matrix, and harmful items (such as poisons or bacteria)
Peroxisome	Use enzymes to detoxify the cell of some medications, alcohol, cancer causing agents, and pesticides (in liver and kidney cells, enzymes within peroxisomes serve to transfer hydrogen atoms from various molecules to oxygen, producing hydrogen peroxide (H2O2), allowing them to neutralize poisons such as alcohol)
Mitochondria	Site of aerobic cell respiration to produce ATP
Centriole	Produces microfilament spindle fibers used in mitosis
Ribosome	Site of protein synthesis; composed of proteins and rRNA
Cytoskeleton	Complex thread-like network throughout the cell consisting of three different kinds of protein-based filaments: microfilaments, intermediate filaments, and microtubules; provide structural support for cells, create “tracks” for movement of substances and organelles within cells, allow the cell to morph and recoil its shape without tearing.
Cilia	Short, hair-like projections that are anchored to the cell membrane; their constant, rhythmic beatings move substances, such as mucus out of the respiratory tract or ova through the Fallopian tubes
Flagellum	Long, whip-like projection that is anchored to the cell membrane; provides locomotion for sperm through spiral motions of its motor proteins
Microvilli	Fan-foldings of the cell membrane that increase surface area for absorption (ex. of nutrients during digestion) and secretion (ex. of ions during urine formation)
Vesicle	Membrane-bound sac for storage of nutrients, wastes, and substances made in the cell or for exocytosis of substances

Activity 3.3: Examining Variations in Cell Structures and Shapes

In this activity, you will examine different cell types to learn about anatomical variations that allow for proper functioning of each cell. Look on the following page for weblinks to give you an idea of what these cells should look like.

Procedure for Activity 3.3:

1. Obtain each of the following slides: red blood cell / RBC, neuron, teased smooth muscle cell, sperm, cheek cell (simple squamous cell

2. For each slide, follow Steps A—D and fill in the information in Table 3.5

   1. View each slide using the objective lens indicated.
   2. Draw a good representation of your observations.
   3. While observing the cells on each slide, make notes about the variations you see in cell structure or shape.
   4. Estimate the size of your cells, using your field diameters from the microscope lab.

Table \(\PageIndex{2}\): Variations in Cell Structure and Function

Cell Type and Total Magnification	Observations (include how structure relates to function; note unique features not seen in other cells)	Estimated Cell Size (in mm and μm)
RBC (Draw using 100X objective) Total Magnification: _____x		______mm ______ μm
Neuron (Draw using 4 or 10X objective) Total Magnification: _____x		______mm ______ μm
Teased Smooth Muscle (Draw using 10X objective Total Magnification: _____x		______mm ______ μm
Sperm (Draw using 100X objective) Total Magnification: _____x		______mm ______ μm
Cheek Cell (Draw using 40X objective) Total Magnification: _____x		______mm ______ μm

Reference for slides:

Red Blood Cells: https://tse2.mm.bing.net/th?id=OIP.wc-IhyExYZX2ZAJfGk1- PQHaFS&pid=Api&P=0&w=214&h=154 

Neuron: https://s-media-cache-ak0.pinimg.com/736x/fe/e8/2a/fee82aa59111b6acda65319330fb7ae9.jpg

Teased Smooth Muscle: https://tse4.mm.bing.net/th?id=OIP .OFV8zRSAkuqT7YV0mUHwSQHaFw&pid=Api&P=0&w=196&h=154

Sperm: https://tse4.mm.bing.net/th?id=OIP .IUhReEKURrPIxFUGAeM5mgHaFi&pid=Api&P=0&w=213&h=160

Cheek Cells: https://tse2.mm.bing.net/th?id=OIP .qhUkjhrgNp1zYm3m5en4yQHaFw&pid=Api&P=0&w=197&h=154

Questions to Consider for Cell Variations:

1. Red blood cells (RBCs) are anucleate as adults; anucleate means that RBCs lack a nucleus when they are mature cells. How does this prevent them from undergoing mitosis?
2. Red blood cells also make ~250 million hemoglobin molecules before they mature; hemoglobin is a quarternary protein. What types of organelles would be found in large numbers in an RBC and why?
3. Why are sperm the only cell in humans’ normal structure that has a flagellum? What might happen if skin cells had flagella?
4. Given the functions of sperm and smooth muscle cells, would you expect them to have large numbers of mitochondria? Explain.
5. Epithelial tissues often create barriers or compose membranes intended for rapid cell transport. Why do you think cheek cells are flat, almost pancake-shaped, structures instead of spherical cells? Why do you think the nucleus is relatively large as compared to the nucleus of other cells you’ve observed in this lab?
6. Why do you think the neurons you observed show long cytoplasmic processes? Hypothesize about how do these long processes aid in efficiently conveying electrical information over long distances. You may want to consider phone lines as an analogy.

Activity 3.4: Examining Phases of the Cell Cycle in Histology Slides

In this activity, you will examine a histology slide and locate the cells in interphase, prophase, metaphase, anaphase, and telophase. Use the pictures and information in Figure 3.6 to learn about the key events that occur in each phase and use that information to locate representations of these phases in your slide. For this activity, you will be using whitefish blastulas. A blastula is group of cells formed during early embryonic development. We will be using the blastulas of a non-specific type of white fish.

You may also use these websites for help in locating the cell cycle stages in a slide:

• http://bio.sunyorange.edu/updated2/ap.HTML/0%20MITOSIS.htm
• https://undergraduate.vetmed.wsu.edu/courses/vph-308/histology/lab-1-histology-cells-and-organelles/white-fish-blastula-slide-wsu_3_092b

Procedure for Activity 3.4:

1. Obtain a slide of whitefish blastulas. View the slide using the 40x and/or 100x objective.

2. Search through the blastula cells and locate two (2) of each phase: interphase, prophase, metaphase, and anaphase. As you work, have a fellow classmate and/or your instructor verify your accuracy.

Activity 3.5: Modeling Phases of Mitosis in Histology Slides

In this activity, you will model the phases of mitosis to provide you with a hands-on experience with the chromosome movement during the cell cycle. The modeling of interphase is not included in this activity.

Procedure for Activity 3.5:

1. Obtain 6 chenille sticks (otherwise known as pipe cleaners)
   1. a.You need 2 each of 3 different colors, ex. 2 red, 2 yellow, 2 purple
2. Model Prophase, Metaphase, Anaphase, and Telophase:
   • a. Construct a model of the chromosomes in the nucleus for a cell with a diploid number of 3.
   • b. You will model prophase, metaphase, anaphase, and telophase. Take a picture of each of the 4 phases you modeled.
     • i. You can twist the chenille sticks together at their centers to represent the joining of them at the centromere.
3. When you’re done, have your instructor look at the 4 pictures to verify your accuracy.

Figure \(\PageIndex{4}\): Cell Division: Mitosis Followed by Cytokinesis The stages of mitosis oversee the separation of identical genetic material (chromosomes) into two new nuclei, followed by the division of the cytoplasm (cytokinesis).

Additional Learning Resources:

• Watch this video for cell model #1: https://youtu.be/Pl4vA35FfXA

• Watch this video for cell model #2: https://www.youtube.com/watch?v=MKUzCNjNTVw

• Practice labeling the cell models using this document: Cell Models Labeling Practice.pdf (found in the Canvas Module containing the electronic copy of the SLM)

• Watch this video for the whitefish blastula slide: http://youtu.be/42IkhVM7YKA?hd=1

• Watch this video to learn about comparisons/contrasts between specialized cells (RBCs, neurons, simple squamous cells, and sperm): https://www.youtube.com/watch?v=ESIX4P-mnNQ

• Play this interactive osmosis simulation: https://nhpbs.pbslearningmedia.org/resource/arct15-sci-osmosis/osmosis/