Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 PDF

Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 WEEK 2 Unit 4: Cell Structure and Function Readings: OpenStax Textbook unit 4 I. Specify the characteristics associated with life and explain why the cell is the basic unit...

Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 WEEK 2 Unit 4: Cell Structure and Function Readings: OpenStax Textbook unit 4 I. Specify the characteristics associated with life and explain why the cell is the basic unit of life. No single characteristic defines life, rather, there is a set of general characteristics which matter must possess before it is considered to be living. In this objective, we will examine these characteristics and consider why they are applied to a cell. First, living organisms exchange materials with their immediate environment. Some materials are taken in and other materials are released. Our cells take in nutrients and respiratory gases, and release wastes, on an ongoing basis. All of our cells absorb needed materials from, and deposit waste materials into, the extracellular fluid. Secondly, living matter can obtain energy from organic molecules. For example, cells take in sugars and metabolize these sugars to obtain cellular energy which can then be used to perform cellular activities. Thirdly, living matter can synthesize complex organic molecules. For example, proteins and fats are only found in living cells or organisms or in situations where living cells have deposited the molecules. The fourth characteristic of living matter is that it can reproduce. The fifth characteristic is that living organisms can respond to stimuli present in the environment. For example, cells and organisms respond to cold temperatures by moving to a warmer environment, or by altering their physiology to make more heat. The cell is considered the basic unit of life because a cell is the simplest structure that possesses all the basic characteristics of living matter. Many of these characteristics are more appropriately assigned to individual cells, rather than the whole organism. II. Describe the levels of structural organization in the body. Cells are the basic structural and functional units in the body. They are composed of chemical substances, organelles, and membranes that are necessary to maintain life. The major chemicals are organic and inorganic molecules. Although cells are the basic unit of life they do not exist independently of each other. Rather, in order to carry out their functions, they are organized together into groups called tissues. A tissue is a group of similar cells and their associated extracellular materials, which have a similar origin and perform special functions. Because the cells perform the same function and have a similar origin and appearance. The tissues in turn are organized into organs. An organ is a structure with a definite form and 1  Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 function composed of two or more tissues. In both cases the organs contain multiple tissue types. Each tissue is in a different location and is different in composition and structure, which reflects the different functions each tissue performs in fulfilling the general function as a whole, which is to digest and store food in the case of the stomach or pump blood throughout the body in the case of the blood vessel. Organs, in turn, are arranged into organ systems, which consist of a group of organs that interact to perform a general function. Finally, all of these organ systems collectively comprise the body as a whole. III. Describe the structure and the functions of major components of a cell. Organelles are structures within cells that have specialized functions. Table 1 summarizes the basic structures and functions of the organelles. a. The cell membrane (plasma membrane) surrounds the cell and its primary functions are to regulate what materials enter and leave the cell, and to allow communication with the extracellular environment. b. The endoplasmic reticulum is a series of interconnected tubes and membranes that extend through the cytoplasm. There are two distinct kinds of endoplasmic reticuli (ER) - the rough ER and the smooth ER. The rough ER possesses membranes studded with attached ribosomes. The rough ER represents a transport system involved in processing and sorting proteins for export to the Golgi apparatus. The rough ER also produces some distinct groups of proteins (see “bound ribosomes” below). The smooth ER is a continuation of the rough ER, but its membranes do not carry any ribosomes. The smooth ER has a number of functions, such as: (i) lipid synthesis, metabolism and transport; (ii) sex steroid hormone synthesis (in certain cells); and (iii) drug detoxification. c. Ribosomes provide the sites where information from the DNA is used to make proteins. There are two types of ribosomes: free ribosomes, which float in the cytoplasm; and attached ribosomes, which are attached to the membranes of the endoplasmic reticulum. Attached ribosomes are also sometimes called “bound” or “fixed” ribosomes. Free ribosomes produce proteins that are used immediately in the cytosol of the cell. Attached ribosomes produce three distinct groups of proteins: (i) proteins to be exported out of the cell; (ii) cell membrane proteins; and (iii) proteins to be used inside membranous organelles. d. The Golgi apparatus (Golgi complex) consists of a stack of flattened membranous sacs. The function of the Golgi apparatus is to take the proteins 2 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 made by bound ribosomes and modify, concentrate, package, and ship the proteins to their final destinations (outside the cell, in the cell membrane, or inside membrane-bound organelles). e. Lysosomes are small sacs bounded by a single membrane. They contain enzymes which can digest all the different types of organic molecules found inside of cells. Lysosomes perform a number of functions including: (i) the breakdown of bacteria, viruses, and toxins brought into the cell by phagocytosis; (ii) the breakdown old organelles, activating the release of stored molecules; and (iii) autolysis (apoptosis), which is the self-destruction of injured or dying cells. f. Mitochondria are generally bean-shaped structures; although their shape may change. They are surrounded by very distinctive double membranes, with the inner membrane being highly folded. Mitochondria are the sites of cellular respiration-a process which breaks down glucose and produces adenosine triphosphate (ATP) for the cells to use as an energy source. The number of mitochondria per cell may vary widely, from about 100 to several thousand. g. Vesicles (vacuoles) are membrane bound sacs that may contain food particles, other solids or liquids. Vesicles function in storing, importing or exporting materials. The nucleus houses the DNA, which contains the information required to make proteins. By determining which proteins will be made, the nucleus regulates all cellular activities. Most cells possess a single nucleus although larger cells (like skeletal muscle cells) may possess several nuclei, and one type of cell (red blood cells) does not have a nucleus. h. The nuclear envelope is a double membrane with pores that regulate the passage of material into and out of the nucleus (Figure 3.26 Marieb & Hoehn 11th ed.; Figure 4.6 OpenStax). i. chromosomes When a cell prepares to divide, the chromatin in the nucleus coils and condenses to form short, rod- like structures called chromosomes. As the nucleus disappears, chromosomes appear, and vice versa. Chromosomes carry genes which transmit genetic information from one generation to the next (Figure 3.27 Marieb & Hoehn 11th ed.; Figure 4.6 OpenStax). j. nucleolus Inside the nucleus are normally one or two darker regions called the nucleolus, or nucleoli, respectively. The function of the nucleoli is to produce the basic subunits of ribosomes. The ribosomal subunits are then transferred to the cytoplasm, and ribosomes are assembled in the cytoplasm (Figure 3.26 Marieb & Hoehn 11th ed.; Figure 4.6 OpenStax). IV. Define metabolism, and distinguish between anabolism and catabolism. Cell metabolism is the sum total of all the chemical processes that go on in a cell and these chemical processes can be divided into two types-anabolic reactions and catabolic reactions. Anabolic reactions are building up processes, as when complex molecules are built up from simpler building block molecules. Catabolic reactions are break down processes, as when complex molecules are broken down into simpler building block molecules. So the sum total of all anabolism and all catabolism is metabolism. A distinguishing feature between anabolism and catabolism is that, in anabolic reactions, energy is utilized whereas in catabolic reactions, energy is released. For example, when glucose is 3 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 broken down, energy is released. However, energy is used when starch is made from glucose subunits. V. Describe the cellular processes involved in the growth of the human body from a fertilized egg to an adult. A number of basic cellular changes occur as an individual grows from a fertilized egg. The most important process is cell division. All of the trillions of cells in our bodies arose through cell reproduction starting from a single fertilized egg. Once cells divide, they grow and increase in size. For example, nerve cells first appear as relatively small cells but then they elongate to become extremely long cells. Similarly, muscle cells grow to become extremely long cells as muscles are formed. Very early in life, cells in different parts of the body specialize and take on particular structures and functions. Some embryonic cells become liver cells; other cells become nerve cells, and so on. Cells develop along different pathways as different sets of genes are activated in different cells early in development. The development of specific and distinctive features in cells is called cell differentiation. Specialized cells are arranged, according to function, into tissues and subsequently organs, organ systems and finally a complete human being. VI. Define cell specialization and describe its importance to an organism. All cells have a similar structure early in development. Initially the human body begins as a single cell, a fertilized egg. This cell divides many times, producing thousands of cells. The process continues until eventually a whole new individual is produced. At first the cells are identical. However, they eventually divide unevenly, producing a size difference, and then take on different shapes. Cell specialization is defined as the tendency of a particular cell type to have a special shape or structure which is related to the special functions the cell carries out. This process of cell specialization at first occurs during embryonic and fetal development, but continues throughout life as certain specialized cells are produced by other non-specialized cells which are dividing. The importance of cell specialization is that it increases the efficiency of the body. The same cell type cannot be expected to perform all of the body’s various functions efficiently. Different shapes and internal structure are better suited to carry out different functions. Having different cell types for different functions allows for a greater speed of activity and a greater effectiveness in performing the various activities. This will be further illustrated in the next objective. VII. Describe the general characteristics of each of the following cell types and relate their characteristics to their functions: nerve cell, muscle cell, red blood cell (erythrocyte), white blood cell (leukocyte). These four cell types are shown in Figure 1. Notice how they are markedly different from each other in size and appearance. 4 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 Skeletal muscle Smooth muscle Erythrocyte Leucocyte Neuron Figure 1. Examples of Different Cell Types The cell on the far left is a nerve cell (Figure 1A). The function of a nerve cell is to conduct an electrical impulse from one part of the body to another part. It acts as a communication line. Notice that the cell has numerous processes around its body. These processes will receive impulses from another cell - either a receptor or another nerve cell. The longer process extending below will then relay the impulse somewhere else. Such a cell structure is well suited for receiving and transmitting impulses. The next pair of cells consists of a striated muscle cell and a smooth muscle cell (Figure 1B & C). A muscle is designed to pull on a bone or to collapse a tube or sac. In order to create such a movement a muscle cell is elongated, allowing a maximum amount of movement when the cell contracts. Shown in Figure 1D is a red blood cell (erythrocyte). The cell on the left is viewed from the top surface, and the one on the right is viewed from the side. The shading in the center of the cell on the left is not a nucleus, but rather demonstrates the depressed center of the cell, giving it a doughnut shaped appearance (without the hole). A major feature of the mature red blood cell is the lack of a nucleus (notice that the other cell types illustrated here each have nuclei). This suggests that the red blood cell has a reduced metabolism and as a result, it uses little oxygen. The function of the red blood cell is to carry oxygen to different parts of the body and it is important that it does not use up much of the oxygen it must deliver. The shape of the red blood cell (flattened) also increases its surface area 5 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 relative to its volume, which allows for a greater movement of gases across its surface. Finally, the cell on the far right is a white blood cell (leucocyte; Figure 1E), in particular one which ingests foreign materials. It is large, which allows it to surround and ingest bacteria. It also has a flexible shape which is related to its role in engulfing bacteria. Unit 5: Cell Biology: Membrane Transport Readings: OpenStax Textbook unit 5 I. Describe the “fluid mosaic” model of membrane structure including the membrane components. The Singer-Nicholson model is also known as the fluid mosaic model of the cell membrane (see pp. 64-65 Marieb and Hoehn 11th ed.; Figure 5.3 OpenStax). The backbone of the membrane is formed by two layers of phospholipid molecules arranged to form a bilayer. Proteins are inserted into the lipid bilayer. The proteins are divided into two categories, integral proteins and peripheral proteins, based on the way they associate with the membrane. Integral membrane proteins penetrate directly within the lipid bilayer, either completely spanning the membrane or being partially embedded in the membrane. Those integral proteins that span the membrane, or the transmembrane proteins, play an important role as transport proteins. Some transport proteins have a hydrophilic channel through which certain molecules or atomic ions pass to cross the membrane. Others move their “passengers” across the membrane by changing their conformation (see Objective 4). In both cases, transport proteins are specific for the substances they translocate. Peripheral membrane proteins are not inserted into the lipid bilayer, but are associated with the inner or outer surfaces of the membrane. The outer surface of the plasma membrane also has a glycocalyx. The glycocalyx is a sugar coating formed by short or long chains of sugars attached to proteins (which are then called glycoproteins and proteoglycans) as well as sugars attached to lipids (which are then called glycolipids). The glycocalyx helps protect the cell from mechanical and chemical damage and also plays an important role in cell to cell recognition. It is like a fingerprint and helps cells recognize other cells of the same kind to form tissues and to reject foreign cells. In many ways, a cell’s glycocalyx serves as its “identification”. For example, people who have the same blood type (A, B, AB, or O) all have a particular array of glycoproteins on the surface of their red blood cells. II. Describe how the structure of the cell membrane affects membrane permeability. The hydrophobic interior of the phospholipid bilayer is a barrier to most hydrophilic molecules. Lipid bilayers are generally impermeable to ions and charged molecules, no matter how small. On the other hand, they are permeable to hydrophobic molecules. The rate at which molecules diffuse across the membrane varies depending on the molecule’s size and solubility properties. The smaller the molecule and the more hydrophobic or nonpolar the molecule is, the faster it will diffuse across the membrane. S m a l l hydrophobic molecules such as molecular oxygen and carbon dioxide can rapidly diffuse across the lipid bilayer. Larger 6 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 uncharged molecules (such as glucose), because of its size, hardly diffuses at all through the lipid bilayer. Water moves through the lipid bilyayer via specific protein channels called aquaporins. In order for cells to take up nutrients and get rid of wastes, cell membranes must allow the passage of many molecules which will not diffuse across the lipid bilayer. The way these molecules cross the membrane is through specialized transport proteins. Transport proteins function in various ways, and two major classes of membrane transport proteins can be distinguished: carrier proteins and channel proteins. Carrier proteins bind to the molecule they are transporting on one side of the membrane and physically transport them to the other side. Channel proteins form tiny hydrophilic pores through which solutes can move. These physical characteristics of the membrane, that is, both the presence of the lipid bilayer as well as the specific transport proteins make it selectively permeable (semipermeable). III. Describe the following passive processes: diffusion, facilitated diffusion and osmosis. Explain the function of each in a cell. A solution is a mixture of a solvent and a solute (or solutes). A solute is simply a substance that dissolves in a solvent, while a solvent is the substance into which the solute dissolves. For example, if salt is added to water, the salt dissolves. In this example, water is the solvent, and salt is the solute. In cells, water is always the solvent. The water inside a living cell contains many dissolved materials including sugars and proteins. Water outside a cell also contains various solutes. Diffusion is defined as the movement of solute molecules from an area of high solute concentration to an area of lower solute concentration. In gases, liquids, or solids, molecules move about at random. They do so because they possess internal kinetic energy and they move on their own. Consequently, molecules move in all possible directions until they become evenly distributed in a given space. Even though the solute molecules are moving in all directions, the net flow is from an area of high solute concentration to an area of low solute concentration. See also Figures 3.5 & 3.6 in Marieb and Hoehn (11th ed.; Figure 5.4 OpenStax). Diffusion occurs within a solution, but diffusion is also very important in transporting solutes across the cell membrane. In this case, the solute must travel through a selectively permeable cell membrane. The semipermeable nature of a membrane is due to its structure. As mentioned in section 2, charged molecules or larger polar molecules cannot diffuse through the bilipid layer. Instead, they are transported by facilitated diffusion, with the assistance of carrier or channel proteins in the cell membrane which allow the movement of solute from an area of high solute concentration to an area of low solute concentration. For example, as illustrated in Figure 3.6b Marieb and Hoehn (11 th ed.; Figure 5.5 OpenStax), glucose is moved into a cell via facilitated diffusion. Glucose combines with 7 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 the carrier molecule in the membrane, and then the carrier molecule changes shape and carries glucose across the membrane. The glucose is then deposited on the other side of the membrane. In this example, it is interesting to note that facilitated diffusion for glucose is accelerated by the action of insulin, a hormone which lowers blood sugar levels. Facilitated diffusion is similar to simple diffusion in that it does not require an expenditure of energy by the cell and that it moves materials along a concentration gradient. However, it differs from simple diffusion in that it transports molecules which cannot pass through the lipid bilayer, and requires a carrier or a channel molecule to cross a semipermeable membrane. Osmosis refers to the diffusion of solvent (water). Osmosis is defined as the passive movement of water molecules through a semipermeable membrane from an area of high water concentration to an area of low water concentration; or alternatively, from an area of low solute concentration to an area of high solute concentration. Osmosis occurs when there is a difference in the concentration of water (solvent) on either side of a semipermeable membrane. Water will move from an area of low solute concentration (i.e. an area where water is in high concentration) to an area of high solute concentration (i.e. where water is in low concentration). See Figures 3.6d & 3.7 Marieb and Hoehn 11th ed.; Figure 5.6 OpenStax). Osmosis does not require any input of energy by the cell. However, it does require a membrane which is selectively permeable (i.e. the membrane must be permeable to water, but not to the solute). Water moves through the lipid bilayer via specific protein channels called aquaporins. IV. Describe and explain the effects of placing red blood cells in hypertonic, hypotonic and isotonic solutions, respectively. See Figure 3.8 Marieb & Hoehn,11th ed.; Figure 5.7 OpenStax). If an erythrocyte is placed in water containing low concentration of solutes (a hypotonic solution), water moves into the cell by osmosis. Water pressure builds up inside the cell, and it may burst if too much water enters the cell. Cell bursting in this manner is called lysis, and in erythrocytes it is specifically referred to as hemolysis. Osmosis can also produce the opposite effect and cause too much water to leave a cell. If a cell is placed in a solution containing a high concentration of solutes which cannot cross the membrane (a hypertonic solution), water moves from the inside of the cell to the outside. The erythrocyte dehydrates and shrinks. This process of dehydration (water loss) is termed crenation in red blood cells. For erythrocytes placed in water containing the same concentration of solutes inside and outside the cells (an isotonic solution), the water molecules diffuse across the cell membranes at an equal rate, but in opposite directions. Therefore the cells stay the same size since there is not net gain or loss of water. V. Describe the following active processes: primary and secondary active transport, endocyotsis ( phagocytosis, pinocytosis), and exocyotsis. Explain the function of each in a cell. 8 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 Active transport is defined as the movement of solute molecules through a protein pump from an area of low solute concentration to an area of high solute concentration. See Focus Figure 3.2 p 74 & Figure 3.9 in Marieb and Hoehn (11th ed.). Active transport differs from diffusion in several ways. One way is in the direction of movement of solute molecules. In active transport, solute molecules move from an area of low solute concentration to an area of high solute concentration. Recall that in diffusion, solute molecules move in the opposite direction. In diffusion, solute molecules move from an area of high solute concentration to an area of low solute concentration. A second difference is that active transport requires cellular energy whereas diffusion does not require cellular energy. A third difference is that active transport requires a protein pump, whereas diffusion does not. Phagocytosis is an active process by which a cell can take in large pieces of solid material, including in some cases, other cells. In phagocytosis, the cell membrane flows around a large piece of material and engulfs it. The membrane surrounding the material then pinches off on the inside and forms a vesicle which travels through the cytoplasm. Phagocytosis is used by some body cells to engulf and digest bacteria and dead cells. Phagocytosis is illustrated in Figure 3.11a Marieb and Hoehn,11th ed.; Figure 5.9 OpenStax). While relatively few cells use phagocytosis, pinocytosis is a routine activity of most cells. In pinocytosis, part of the cell membrane is drawn into the cell with the extracellular fluid and dissolved molecules to form a pocket in the cell membrane. The pocket transforms into a small vesicle and is transported into the cell interior, where it releases materials needed by the cell. Pinocytosis is illustrated in Figure 3.11b of Marieb and Hoehn (11th ed.; Figure 5.9 OpenStax). Pinocytosis differes from phagocytosis by the mechanism by which material is brought into the cell and also on a matter of scale: Phagocytosis deals with larger objects (e.g. cell debris, bacteria), while pinocytosis much smaller molecules (e.g. protein molecules). In relation to the processes described in objectives 8 and 9, it should be noted that the terms phagocytosis and pinocytosis are both processes of cellular ingestion by which material external to the cell is brought into the cell. The general term for these processes is endocytosis. Material may be transported out of the cell by the process of exocytosis, which is essentially a process of cellular excretion or secretion which occurs when vesicles fuse to the outer membrane and release material to the outside of the cell. a) Diffusion is a process which allows cells to obtain or release a variety of materials. For example, when air enters into the lungs, oxygen dissolves in the water on the inner surfaces of the lungs. Then, oxygen diffuses into cells lining the lungs, and eventually diffuses further into the blood. The movement of dissolved gases into and out of the blood is based on diffusion. Diffusion is effective in situations where materials must be moved along a concentration gradient that is from high concentration to low concentration of the solute. b) Facilitated diffusion is essential in allowing the movement charged and large solute molecules 9 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 along a concentration gradient across the cell membrane. (For example, the transmission of a nerve impulse depends, in part, on the opening of sodium channels which allow for the diffusion of sodium into the cell) c) Osmosis is the movement of water and is primarily important in maintaining the proper pressure within cells. In humans osmosis is important in allowing us to move water into, and out of, cells. Because osmosis is a passive process, it is not directly regulated by the cell. However, osmosis is indirectly regulated by the cell as it controls the solute concentrations by active transport. For example, if a cell increases its concentration of Na+ by active transport, then more water will flow into that cell by osmosis. d) Active transport is important because cells may require nutrients (such as sugars and salts) to be maintained at different concentrations inside the cell than is normally present outside the cell, or to counteract the effects of diffusion. Consequently, the cell must expend energy to maintain solute concentration differences on either side of the membrane. Table 1 shows the concentrations of some ions and molecules found in both the extracellular and intracellular fluids. Notice that sodium ions (Na+) are 13 times more concentrated in the extracellular fluid than in the intracellular fluid. The cell must expend energy to export sodium ions which enter by diffusion in order to maintain this concentration difference. Potassium ions (K+), on the other hand, are much more concentrated inside the cell than outside, and active transport must be used to bring this ion into the cell, even though potassium ions might be moving out by diffusion. The cell membrane is impermeable to sodium ions but “leaky” to potassium ions. Active transport is very important in maintaining the concentrations of solutes necessary for normal physiology to occur and to regulate osmosis. e) Phagocytosis is important in humans as it is used to destroy unwanted materials or organisms. For example, white blood cells can engulf bacteria and digest them within the cell as a mechanism for counteracting infections. f) Pinocytosis is a mechanism by which cells can take in larger dissolved molecules. To summarize, cells utilize three active processes to pass materials through the cell membrane. The differences between these processes are predominately the size of the materials brought into the cell. In active transport, ions and small molecules are moved; in pinocytosis, large molecules dissolved in fluid such as proteins are carried through the membrane in solution, and in phagocytosis large pieces of material or whole cells are moved through the membrane. A summary of transport processes is presented in Figure 1. This summary is divided into active and passive processes. See also Tables 3.2 & 3.3 in Marieb and Hoehn (11th ed.). Figure 1. Summary of Methods of Acquisition of Materials by the Cell. 10 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 2 Fall 2024 Acquisition is by: Active processes (cellular Passive processes energy required) (cellular energy not required) Osmosis Diffusion Facilitated Phagocytosis Active Pinocytosis Diffusion Transport 11 12