1. Read the following article:

In a 300-word essay, discuss how changes in proteins can lead to diseases. 

Unit 2 Audio Lecture



The level of organizations starts with atoms. Atoms represent the basic unit of an element that carries that element’s nucleus. Neutrons (n) carry no charges and are also located in the nucleus of the atom. Electrons (e-) are negatively charged particle that is located in electron shells around the nucleus. The electron shells are also known energy levels in which each of them can carry a designated number of electrons; the first will hold only two electrons; after that, each level can hold up to eight electrons.

118 elements are recognized with unique properties, each of them that allows us to differentiate between them. The atomic number is unique for the element, this represents the total number of protons present in the nucleus of that element, and it should be equal to the number of the electron in orbit, which make the atom balance the charges and carry a zero charge. The second is the atomic mass or weight; this represents everything present in the nucleus, the protons, and the neutrons. There are no two elements that have the same atomic number and atomic mass.

The next method to recognize elements is to use the alphabet to represent them in a chemical formula rather than write the complete name. This uses the first letter in a capital case, but several elements may have the same letter. To avoid confusion, the next letter is used in lower case. For example, for Carbon, we used (C), and for Calcium, it is (Ca), and for Cupper is (Cu).


When the atoms of that element have different atomic mass due to having extra neutrons, the isotopes are not stable and start to emit that entire extra neutron via energy-rich particles known as the alpha, beta, and gamma. The emitting is recognized as radioactivity. Radioactive elements are very beneficial in our life. They have been utilized in many applications, such as medical use in X-ray and CT scans. They are also used in other industries. Carbon has threeunit2mo1.jpg different isotopes, C12, C13, and C14 which are important in carbon coding for fossils’ discovery.

Naturally, element atoms are balanced because of the equality between electrons and protons. Still, they are not stable because the outer electron orbit is not full of electrons; they will seek that stable state and thus be involved in different chemical interactions resulting in compounds. The interactions can be Ionic, Covalent, and Hydrogen attractions. The resulted molecules have different ratios depending on the atoms, a molecule of Oxygen O2 has a ratio of 1:1, and a molecule of glucose C6H12O6 will have a ratio of 1:2:1. A molecule that is composed of different atoms is called a compound.


Atoms that are unstable because the outer shell is not full will start to be active to reach that stable state known as the octet rule. For some atoms to be stable, they have to lose, and others will gain electrons. When an atom gains or loses electrons, it becomes unbalanced in the number of negatively charged electrons to the positively charged proton, and that is recognized as an ion. If the atom loses an electron, it will have a more positive charged proton and thus; become positively charged and called a cation. On the other hand, atoms that gain electrons become negatively charged and will be called an anion. The creations of the action and anion create attraction between different charged atoms creating ionic chemical bonds. For example, let’s look at the sodium atom Na, which has an atomic number of 11, and the Chlorine atom, which has an atomic number of 17. When we distribute the electrons for the Na, we will have 2e in the first orbit, 8e in the second, and only 1e in the outer is a valiance because it is not full. The Na will be looking to lose this electron to be stable, and when that happens, Na becomes a positively charged cation.

On the other hand, looking at Cl, the distribution gives us 2e, 8e, and 7e in the outer orbit. It is also not stable and is looking to gain electrons, making it a negatively charged anion. When the Na cation faces the Cl anion, the attraction between the negative and positive charges will bring them together, creating the ionic bond. The ionic bond happened only between different kinds of atoms.


Organic and inorganic compounds are composed of different elements; organic compounds usually contain hydrogen and Carbon in their structure and are made within living organisms. Organic molecules have functional groups that are unique for each of them, thus creating proteins, carbohydrates, and lipids. All of these compounds are built from very basic units called monomers that are linked together to create larger macromolecules.

Metabolism is the only mechanism that is utilized by living organisms via dehydration and hydrolysis. Anabolic reactions are dehydration reactions when two monomers are linked to a larger level. In the catabolic reactions, the molecule is hydrolysis by the addition of water molecules and breakdown into the basic units.


They are generally called surges; they contain a large number of Carbon and hydrogen with other substances. And are macromolecules with different levels of complexity in the structure. In general, they have a fixed ratio of one Carbon: two hydrogens: and one oxygen in a chemical formula of C6H12O6. They range from Monosaccharides, Disaccharides, and polysaccharides.


At the first carbohydrate level, three different monosaccharides are Glucose, Fructose, and Galactose. The three molecules have the same number of carbon, hydrogen, and oxygen. That way, they are called isomers with differences in structure orientation. Glucose is full that can be used by our body cells and allow us to stay alive. Autotrophs produce all three. 


2nd part is middle workHave You Ever Wondered…

How many cells are in your body? It is estimated that about 30 trillion cells make up the human body, with an equal number and maybe more prokaryotic cells (such as bacteria) which make up the human microbiome. These microscopic organisms are found almost everywhere inside the body, especially in areas with mucus membranes such as the nose, vagina, digestive tract, and even the skin.

Based on your understanding of cells and commensalism and parasitism, discuss the possible roles of these prokaryotic cells. 


Case Study

New Parts for Human Bodies

WHEN LUKE MASSELLA WAS 10 YEARS OLD, he faced a very serious health crisis. Complications from a birth defect had left Luke with a bladder that could not fully function, and his dysfunctional bladder was inflicting damage on his kidneys. Without some kind of intervention, Luke’s kidneys would fail, with potentially fatal consequences. With Luke’s health declining rapidly, he underwent an experimental surgery in which his bladder was replaced with a new one. But the new bladder was not a natural organ taken from a cadaver. Instead, Luke’s new bladder was grown in a laboratory, bioengineered just for him.

Luke’s bioengineered bladder was built from his own cells. A team led by Dr. Anthony Atala removed a very small piece of tissue from Luke’s urinary tract. The scientists induced the cells to multiply and then spread the resulting cells over a biodegradable, bladder-shaped mold made largely of the protein collagen. With a thin layer of muscle cells on the outside, and a thin layer of epithelial cells on the inside, the mold was placed in a nutrient broth inside a temperature-controlled “bioreactor,” where further cell proliferation ultimately formed a complete bladder. When the artificial bladder was ready, surgeons used it to replace Luke’s damaged organ.

In the years after his pioneering surgery, Luke went on to become the captain of his high school wrestling team, graduate from college, and begin his career. Meanwhile, Dr. Atala and Bioengineering human organs demonstrates our expanding ability to manipulate cells, the fundamental units of life. What structures make up cells? What new bioengineering techniques involving human or animal cells are being developed and tested?

At a Glance

4.1 What Is the Cell Theory?

4.2 How Do Scientists Visualize Cells?

4.3 What Are the Basic Attributes of Cells?

4.4 What Are the Major Features of Prokaryotic Cells?

4.5 What Are the Major Features of Eukaryotic Cells? 

The discovery of cells in the 1600s was the first step toward understanding their importance. In 1838, the German botanist Matthias Schleiden concluded that cells and substances produced by cells form the basic structure of plants and that plant growth occurs by adding new cells. In 1839, German biologist Theodor Schwann (Schleiden’s friend and collaborator) drew similar conclusions about animal cells. The work of Schleiden and Schwann provided a unifying theory of cells as the fundamental units of life. In 1855, the German physician Rudolf Virchow completed the cell theory—a fundamental concept of biology—by concluding that all cells come from previously existing cells.

The cell theory consists of three principles:

Every organism is made up of one or more cells.

The smallest organisms are single cells, and cells are the functional units of multicellular organisms.

All cells arise from preexisting cells.

Check Your Learning

Can you . . .

trace the historical development of the cell theory?

list the three principles of the cell theory?

4.2 How Do Scientists Visualize Cells?


Although cells form the basis of life, they’re so small that people didn’t realize cells existed until they could actually be seen. In 1665, the English scientist and inventor Robert Hooke aimed his primitive light microscope at an “exceeding thin . . . piece of Cork” and saw “a great many little Boxes,” which he drew with great skill (Figure 4-1a). Hooke called the boxes “cells,” because he thought they resembled the tiny rooms (called cells) occupied by monks in a monastery. Cork comes from the dry outer bark of the cork oak tree, and we now know that he was looking at the nonliving cell walls that surround all plant cells. Hooke wrote that in the living oak and other plants, “These cells [are] fill’d with juices.”

Figure 4-1 Light microscopy yesterday and today

(a) Hooke observed the walls of cork cells through his elegant microscope. (b) Hooke’s contemporary van Leeuwenhoek built a microscope that produced images superior to those of Hooke’s. (c) Modern light microscopes can reveal structures within cells, as seen in this light micrograph of a living, single-celled protist of the genus Paramecium.

Light Microscopes Can View Living Cells

In the 1670s, Dutch microscopist Anton van Leeuwenhoek constructed his own simple microscopes (Figure 4-1b) and observed a previously unknown living world. Although Hooke described Van Leeuwenhoek’s microscopes as “offensive to my eye” because of their primitive appearance, their superior lens

Light Microscopes Can View Living Cells

In the 1670s, Dutch microscopist Anton van Leeuwenhoek constructed his own simple microscopes (Figure 4-1b) and observed a previously unknown living world. Although Hooke described Van Leeuwenhoek’s microscopes as “offensive to my eye” because of their primitive appearance, their superior lenses provided clearer images and higher magnification than did Hooke’s microscope. Van Leeuwenhoek’s descriptions of myriad “animalcules” (mostly single-celled organisms) in rain, pond, and well water were greeted with amazement. Over the years, he described an enormous range of microscopic specimens, including blood cells, sperm cells, and the eggs of aphids and fleas. Observing plaque scraped from his teeth, van Leeuwenhoek saw swarms of cells that we now recognize as bacteria. Disturbed by these animalcules in his mouth, he tried to kill them with vinegar and hot coffee—but with little success.

Since the pioneering efforts of early microscopists, biologists, physicists, and engineers have collaborated to develop a variety of advanced microscopes to view cells and their components. Light microscopes use lenses made of glass or quartz to bend, focus, and transmit light rays that have passed through or bounced off a specimen. The resolving power (the smallest structure distinguishable under ideal conditions) of modern light microscopes is generally about 200 nanometers (see Figure 4-3). This is sufficient to see most prokaryotic cells, some structu

Figure 4-2 Electron microscopy

Many of today’s electron microscopes produce both transmission electron micrographs (TEMs) and scanning electron micrographs (SEMs). An SEM image of pollen grains is visible on the computer screen of the electron microscope pictured. All colors in the electron micrographs (SEMs or TEMs) have been added artificially.

Figure 4-2 Think Critically

Tap to view

Scanning electron microscopes bounce electrons off specimens that are dry and hard or that have been covered with an ultrathin coating of metal such as gold. Scanning electron microscopes can be used to view the three-dimensional surface details of structures that range in size from entire small insects down to cells and their components, with a maximum resolution of about 1.5 nanometers.

Check Your Learning

Can you . . .

explain how light microscopes and electron microscopes differ?

describe the difference between transmission electron microscopes and scanning electron microscopes?

4.3 What Are the Basic Attributes of Cells?


All living things are composed of cells, which fall into two types: prokaryotic and eukaryotic. In eukaryotic cells, the genetic material is contained within a membrane-enclosed nucleus, but in prokaryotic cells it is not. The single cells of bacteria and archaea, the simplest forms of life, are prokaryotic. Eukaryotic cells are more complex and make up the bodies of animals, plants, fungi, and protists.

Cells Are Small

Most cells are very small, ranging from about 1 to 100 micrometers (?m; millionths of a meter) in diameter (Figure 4-3). Why are most cells so small? Because they exchange nutrients and wastes with their external environment via diffusion (see Chapter 5). Diffusion—a key process by which molecules dissolved in fluids move—is relatively slow, so all parts of the cell must remain close to the external environment to have ready access to necessary materials and the ability to get rid of wastes. Thus, cells have a very small diameter.

Figure 4-3 Relative sizes

Dimensions encountered in biology range from about 100 meters (the height of the tallest redwood trees) to a few nanometers (nm; the diameter of many large molecules).

Figure 4-3

All Cells Share Common Features

All cells are descended from an ancestor that arose about 3.5 billion years ago. As a result of this common ancestry, all cells share some important features.

The Plasma Membrane Encloses the Cell and Allows Interactions Between the Cell and Its Environment

Each cell is surrounded by an extremely thin membrane called the plasma membrane (Figure 4-4). The plasma membrane consists of proteins embedded in a double layer, or bilayer, of phospholipids.

The phospholipid and protein components of plasma membranes play very different roles. The phospholipid bilayer helps isolate the cell from its surroundings, allowing the cell to maintain essential differences in the concentrations of materials inside and out. In contrast, the huge variety of proteins within the bilayer facilitate communication between the cell and its environment. For example, channel proteins allow specific molecules or ions to pass into or out of the cell (see Figure 4-4). Other proteins embedded in the membrane act as receptor proteins that bind to messenger molecules such as hormones or neurotransmitters, and initiate a cell’s response to the message.

All Cells Contain Cytoplasm

The cytoplasm consists of all the fluid and structures that lie inside the plasma membrane but outside of the nucleus (see Figure 4-6 and 4-7). The fluid portion of the cytoplasm, called the cytosol, contains water, salts, and an assortment of organic molecules, including proteins, lipids, carbohydrates, sugars, amino acids, and nucleotides. Most of a cell’s metabolic activities—the biochemical reactions that support life—occur in the cytoplasm.

The cytoskeleton consists of a variety of protein filaments within the cytoplasm. These filaments provide support, transport structures within the cell, and allow cells to move and change shape. The cytoskeleton also plays a key role in cell division (see chapter 9).

All Cells Use DNA As Hereditary Instructions and RNA to Guide Construction of Cell Parts

The genetic material in all cells consists of deoxyribonucleic acid (DNA) that encodes an inherited set of instructions in segments called genes. Genes store the instructions for making all the parts of a cell and for producing new cells (see Chapter 12). DNA genes are copied to ribonucleic acid (RNA), which is chemically similar to DNA and helps construct proteins based on the genetic instructions. The proteins are constructed on ribosomes, cellular “workbenches” composed of a specialized type of RNA called ribosomal RNA.

Check Your Learning

Can you . . .

describe the structure and features shared by all cells?

distinguish prokaryotic from eukaryotic cells?

explain why cells are small?

Case Study Continued

New Parts for Human Bodies

Why was Luke Massella’s artificial bladder considered a scientific breakthrough? One reason is that the patient’s own cells were used to grow the new body part, so his immune system was unlikely to reject the cells. The plasma membranes of the cells in a body bear glycoprotein molecules that are unique to each individual. These distinctive glycoproteins allow a person’s immune system to rec

4.4 What Are the Major Features of Prokaryotic Cells?


Prokaryotic cells have a relatively simple internal structure and are generally less than 5 micrometers in diameter (in comparison, eukaryotic cells range from 10 to 100 micrometers in diameter). Prokaryotes also lack the complex internal membrane-enclosed structures that are the most prominent features of eukaryotic cells.

Prokaryotes are unicellular (consist of a single prokaryotic cell) and make up two of life’s domains: Archaea and Bacteria. Many archaea inhabit extreme environments, such as hot springs and cow stomachs, but they are also found in more familiar locales, such as soil and oceans. In this chapter, we focus mainly on the more well-known bacteria as representative prokaryotic cells (Figure 4-5).

Figure 4-5 Prokaryotic cells

Prokaryotes come in different shapes, including (a) rod-shaped, (b) spiral-shaped, and (c) spherical. Internal structures are revealed in the TEMs

internal membranes where photosynthesis occurs, as shown in (e).

Figure 4-5

Prokaryotic Cells Have Specialized Cytoplasmic Structures

The cytoplasm of a typical prokaryotic cell contains several specialized structures. A distinct region called the nucleoid (meaning “like a nucleus”; see Figure 4-5a) contains a single circular chromosome that consists of a long, coiled strand of DNA. Unlike the nucleus of a eukaryotic cell, the nucleoid is not separated from the cytoplasm by a membrane. In addition to the DNA in the nucleoid, most prokaryotic cells also contain small rings of DNA called plasmids. Plasmids usually carry genes that give the cell particular properties; for example, some disease-causing bacteria have plasmids that encode proteins that deactivate antibiotics. Bacterial cytoplasm also includes ribosomes, where proteins are synthesized, as well as food granules that store energy-rich molecules such as glycogen. Prokaryotes also contain an extensive cytoskeleton that functions in cell division and helps regulate the shape of the cell.

Prokaryotic Cells Have Distinctive Surface Features

Nearly all prokaryotic cells are surrounded by a cell wall, which is a relatively stiff covering that the cell secretes around itself. The cell wall provides protection and helps the prokaryotic cell maintain its shape, which may be rod-like, spiral, or spherical (see Figure 4-5a, b, c). Bacterial cell walls are composed of peptidoglycan, a polymer in which short peptides link chains

4.5 What Are the Major Features of Eukaryotic Cells?


Eukaryotic cells make up the bodies of organisms in the domain Eukarya: animals, plants, protists, and fungi. As you might imagine, these cells are extremely diverse. The cells that form the bodies of unicellular protists can perform all the activities necessary for independent life. In contrast, each cell in the body of a multicellular organism is specialized to perform a specific function and generally cannot live independently. Here, we focus on plant and animal cells.

Unlike prokaryotic cells, eukaryotic cells contain organelles (“little organs”), membrane-enclosed structures specialized for a particular function. Organelles contribute to the complexity of eukaryotic cells. Figure 4-6 illustrates a generalized plant cell, and Figure 4-7 illustrates a generalized animal cell, each with some distinctive structures. Plant cells have cell walls, central vacuoles, and plastids (including chloroplasts), which are absent in animal cells, and animal cells have centrioles, lysosomes, cilia, and flagella, which are not found in the most common plant cells. Table 4-1 summarizes the principal features of plant, animal, and prokaryotic cells.

Figure 4-6 A generalized plant cell

Figure 4-6

Table 4-1 Functions and Distribution of Cell Structures

Table 4-1

Extracellular Structures Surround Animal and Plant Cells

The plasma membrane, which is only about two molecules thick and has the consistency of viscous oil, would be torn apart in the absence of reinforcing structures. For animal cells, the reinforcing structure is a complex extracellular matrix (ECM), secreted by the cell. The ECM includes an array of supporting and adhesive proteins embedded in a 58gel composed of polysaccharides that are linked together by proteins (Figure 4-8). In addition to structural support, the ECM provides biochemical support functions, such as those provided by proteins called growth factors, which promote cell survival and growth. The ECM also binds adjacent cells to one another, transmits molecular signals between cells, and guides cells as they migrate and differentiate (become a particular type of cell) during development. It anchors cells and provides a supporting framework within tissues; for example, a stiff ECM forms the scaffolding for bone and cartilage.