General Biology I Module 5 (Week 5) PDF

11 GENERAL BIOLOGY I 1 Quarter st Cell Cycle and Transport Mechanisms (WEEK 5) 1 2 GENERAL BIOLOGY I Content Standards: The learners demonstrate an understanding of Cell Cycle and Transport Mechanisms. Most Essential Learning Competenc...

11 GENERAL BIOLOGY I 1 Quarter st Cell Cycle and Transport Mechanisms (WEEK 5) 1 2 GENERAL BIOLOGY I Content Standards: The learners demonstrate an understanding of Cell Cycle and Transport Mechanisms. Most Essential Learning Competencies: The learners should be able to: 1. Identify disorders and diseases that result from the malfunction of the cell during the cell cycle STEM_BIO11/12Ig-h-10 2. Describe the structural components of the cell membrane STEM_BIO11/12Ig-h-11 3. relate the structure and composition of the cell membrane to its function STEM_BIO11/12Ig-h-12 Lesson Disorders and Diseases from the Malfunction of the Cell 1 Cycle The cell cycle is controlled by a complex series of signaling pathways by which a cell grows, replicates its DNA and divides. As a result of genetic mutations, this regulatory process malfunctions, causing uncontrolled cell proliferation. Errors can occur during meiosis producing gametes with an extra or missing chromosome. The consequences of this following fertilization depend on which chromosomes are affected. Often the embryo is not viable, but some of these errors can lead to trisomy conditions or sex chromosome disorders. Genetic disorders are diseases, syndromes, or other abnormal conditions that are caused by chromosomal alterations or mutations in one or more genes. Genetic disorders are typically present at birth; however, they are different from congenital disorders, which are any disorders, regardless of cause, that are present at birth. Some congenital disorders are not caused by genetic mutations or chromosomal alterations and instead, are caused by problems that arise during embryonic or fetal development or during birth. An example of a nongenetic congenital disorder is fetal alcohol syndrome, a collection of birth defects, including facial anomalies and intellectual disability, caused by maternal alcohol consumption during pregnancy. Cancer is basically a disease of uncontrolled cell division. Its development and progression are usually linked to a series of changes in the activity of cell cycle regulators. For example, inhibitors of the cell cycle keep cells from dividing when conditions aren’t right, so too little activity of these inhibitors can promote cancer. Similarly, positive regulators of cell division can lead to cancer if they are too active. In most cases, these changes in activity are due to mutations in the genes that encode cell cycle regulator proteins. 3  Cancer cells are cells gone wrong — in other words, they no longer respond to many of the signals that control cellular growth and death. Cancer cells originate within tissues and, as they grow and divide, they diverge ever further from normalcy. Over time, these cells become increasingly resistant to the controls that maintain normal tissue — and as a result, they divide more rapidly than their progenitors and become less dependent on signals from other cells. Cancer cells even evade programmed cell death, even though their multiple abnormalities would normally make them prime targets for apoptosis. In the late stages of cancer, cells break through normal tissue boundaries and metastasize (spread) to new sites in the body. DNA, sometimes called a genetic blueprint, contains the hereditary material in nearly all organisms. The improper copying of DNA produces two types of errors, or mutations. Silent mutations have no impact on the DNA sequence, but missense mutations, which alter amino acid sequences, often impact the associated function. Missense mutations can multiply over time, leading to cell cycle disruption and the formation of tumors, which are the product of runaway cell reproduction. Cancer occurs when mutated cells ignore or override the normal "checkpoints" regulating mitosis and begin to reproduce uncontrollably. The process of mitosis generates identical daughter cells by arranging chromosomes into two equal groups. When the process occurs normally, chromosomes attach to string-like spindles and begin to move to the middle of each daughter cell. If chromosomes fail to attach to these spindles, however, a daughter cell might have an extra copy of a chromosome after the cell divides, or it might be missing one. Scientists refer to the condition whereby cells have an incorrect number of chromosomes as aneuploidy. Down syndrome, which is characterized by specific facial features and higher susceptibility to certain diseases like Alzheimer's and leukemia, is one disorder caused by the presence of an extra chromosome. Cell division is a normal process that takes place in all living things. Growth, healing, reproduction and even death are the results of cell division. Several factors cause and affect cell division. Some factors improve health and development while others cause cancer, birth defects, a variety of disorders and even death. Nutrients The nutrients present in the cell affect cell division. Certain nutrients such as vitamins, minerals and antioxidants are able to neutralize some chemicals in the body that cause cells to mutate and divide. Healthy nutrients obtained from consuming fruits and vegetables help to ensure that cells remain healthy and therefore cell division produces health cells. In the case of microorganisms, nutrients are absorbed from their surroundings. Genetics Genetic code regulates cell division. Whether a fetus growing in the womb, a child whose bones are growing or an elderly woman whose bones have begun to break down, the rate and frequency at which cell division occurs is regulated by genetic code. Some people's genetic code causes more cell division than others. For example, one person who grows to be seven feet in height will have more cell division during the growth phase than someone who stops growing at five feet. 4 Chemicals Exposure to toxic chemicals such as pesticides and some cleaning chemicals can cause cell mutation. When cells mutate and then divide the results are multiple mutated and damaged cells. Mutated cells are the cause of illness and disease. Fortunately, there are treatments to kill off cells that were damaged or mutated during cell division. Stress Stress affects cell division. Research shows that extreme stress levels can actually damage cells in the human body. If these cells are damaged yet still undergo cell division, the new cells will also be damaged. This can cause cancer and other diseases. Cancer is unchecked cell growth. Mutations in genes can cause cancer by accelerating cell division rates or inhibiting normal controls on the system, such as cell cycle arrest or programmed cell death. As a mass of cancerous cells grows, it can develop into a tumor. Cancer cells can also invade neighboring tissues and sometimes even break off and travel to other parts of the body, leading to the formation of new tumors at those sites. Lesson Cell Membrane Structure 2 The cell membrane, also known as the plasma membrane, is a double layer of lipids and proteins that surrounds a cell. It separates the cytoplasm (the contents of the cell) from the external environment. It is a feature of all cells, both prokaryotic and eukaryotic. The cell membrane gives the cell its structure and regulates the materials that enter and leave the cell. It is a selectively permeable barrier, meaning it allows some substances to cross, but not others. Like a drawbridge intended to protect a castle and keep out enemies, the cell membrane only allows certain molecules to enter or exit. Structure of the Cell Membrane Phospholipid Bilayer The cell membrane is made up of a phospholipid bilayer. Phospholipids are lipid molecules made up of a phosphate group head and two fatty acid tails. Importantly, the properties of phospholipid molecules allow them to spontaneously form a double-layered membrane. The phosphate group head of a phospholipid is hydrophilic, whereas the phospholipid tail is hydrophobic. This means that the phosphate group is attracted to water, whereas the tail is repelled by water. When in water or an aqueous solution (including inside the body) the hydrophobic heads of phospholipids will orient themselves to be on the inside, as far away from the water as possible. In contrast, the hydrophilic heads will be on the outside, making contact with the water. The result is that a double layer of phospholipids is formed, with the hydrophobic heads clustering together in the 5 center, and the hydrophilic tails forming the outside of the structure. The technical term for this double layer of phospholipids that forms the cell membrane is a phospholipid bilayer. Structure of the cell membrane and its associated components Membrane-Associated Factors In addition to the phospholipid bilayer, the cell membrane also contains lipid molecules, particularly glycolipids and sterols. One important sterol is cholesterol, which regulates the fluidity of the cell membrane in animal cells. When there is less cholesterol, membranes become more fluid, but also more permeable to molecules. The amount of cholesterol in the membrane helps maintain its permeability so that the right amount of molecules can enter the cell at a time. The cell membrane also contains many different proteins. Proteins make up about half of the cell membrane. Many of these proteins are transmembrane proteins, which are embedded in the membrane but stick out on both sides (i.e., they span across the entire lipid bilayer). Some of these proteins are receptors, which bind to signal molecules. Others are ion channels, which are the only means of allowing ions into or out of the cell. Scientists use the fluid mosaic model to describe the structure of the cell membrane. The cell membrane has a fluid consistency due to being made up in large part of phospholipids, and because of this, proteins move freely across its surface. The multitude of different proteins and lipids in the cell membrane give it the look of a mosaic. Lesson Cell Membrane Structure and 3 Function The cell membrane is an extremely pliable structure composed primarily of back-to-back phospholipids (a “bilayer”). Cholesterol is also present, which contributes to the fluidity of the membrane, and there are various proteins embedded within the membrane that have a variety of functions. A single phospholipid molecule has a phosphate group on one end, called the “head,” and two side-by-side chains of fatty acids that make up the lipid tails (Figure 1). The phosphate group is negatively charged, making the head polar and hydrophilic—or “water loving.” A hydrophilic molecule (or region of a molecule) is 6 one that is attracted to water. The phosphate heads are thus attracted to the water molecules of both the extracellular and intracellular environments. The lipid tails, on the other hand, are uncharged, or nonpolar, and are hydrophobic—or “water fearing.” A hydrophobic molecule (or region of a molecule) repels and is repelled by water. Some lipid tails consist of saturated fatty acids and some contain unsaturated fatty acids. This combination adds to the fluidity of the tails that are constantly in motion. Phospholipids are thus amphipathic molecules. An amphipathic molecule is one that contains both a hydrophilic and a hydrophobic region. In fact, soap works to remove oil and grease stains because it has amphipathic properties. The hydrophilic portion can dissolve in water while the hydrophobic portion can trap grease in micelles that then can be washed away. Figure 1. Phospholipid Structure. A phospholipid molecule consists of a polar phosphate “head,” which is hydrophilic and a non-polar lipid “tail,” which is hydrophobic. Unsaturated fatty acids result in kinks in the hydrophobic tails. The cell membrane consists of two adjacent layers of phospholipids. The lipid tails of one layer face the lipid tails of the other layer, meeting at the interface of the two layers. The phospholipid heads face outward, one layer exposed to the interior of the cell and one layer exposed to the exterior (Figure 2). Because the phosphate groups are polar and hydrophilic, they are attracted to water in the intracellular fluid. Intracellular fluid (ICF) is the fluid interior of the cell. The phosphate groups are also attracted to the extracellular fluid. 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. Because the lipid tails are hydrophobic, they meet in the inner region of the membrane, excluding watery intracellular and extracellular fluid from this space. The cell membrane has many proteins, as well as other lipids (such as cholesterol), that are associated with the phospholipid bilayer. 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 2. Phospolipid 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. MEMBRANE PROTEINS The lipid bilayer forms the basis of the cell membrane, but it is peppered throughout with various proteins. Two different types of proteins that are commonly associated with the cell membrane are the integral proteins and peripheral protein (Figure 3). As its name suggests, an integral protein is a protein that is embedded in the membrane. A channel protein is an example of an integral protein that selectively allows particular materials, such as certain ions, to pass into or out of the cell. 7  Figure 3. 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. Another important group of integral proteins are cell recognition proteins, which serve to mark a cell’s identity so that it can be recognized by other cells. A receptor is a type of recognition protein that can selectively bind a specific molecule outside the cell, and this binding induces a chemical reaction within the cell. A ligand is the specific molecule that binds to and activates a receptor. Some integral proteins serve dual roles as both a receptor and an ion channel. One example of a receptor-ligand interaction is the receptors on nerve cells that bind neurotransmitters, such as dopamine. When a dopamine molecule binds to a dopamine receptor protein, a channel within the transmembrane protein opens to allow certain ions to flow into the cell. Some integral membrane proteins are glycoproteins. A glycoprotein is a protein that has carbohydrate molecules attached, which extend into the extracellular matrix. The attached carbohydrate tags on glycoproteins aid in cell recognition. The carbohydrates that extend from membrane proteins and even from some membrane lipids collectively form the glycocalyx. The glycocalyx is a fuzzy- appearing coating around the cell formed from glycoproteins and other carbohydrates attached to the cell membrane. The glycocalyx can have various roles. For example, it may have molecules that allow the cell to bind to another cell, it may contain receptors for hormones, or it might have enzymes to break down nutrients. The glycocalyces found in a person’s body are products of that person’s genetic makeup. They give each of the individual’s trillions of cells the “identity” of belonging in the person’s body. This identity is the primary way that a person’s immune defense cells “know” not to attack the person’s own body cells, but it also is the reason organs donated by another person might be rejected. Peripheral proteins are typically found on the inner or outer surface of the lipid bilayer but can also be attached to the internal or external surface of an integral protein. These proteins typically perform a specific function for the cell. Some peripheral proteins on the surface of intestinal cells, for example, act as digestive enzymes to break down nutrients to sizes that can pass through the cells and into the bloodstream. WHAT I HAVE LEARNED Multiple Choice. Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper. 1. This component of the cell membrane provides stability and flexibility for the structure. a. glycoprotein c. cholesterol 8  b. glycoplipid d. protein channel 2. The cell membrane is composed of a ___________ a. Phospholipid bilayer c. carbohydrate bilayer b. single layer of phospholipids d. single layer of carbohydrates 3. What is the name of the transport protein that is embedded through the entire cell membrane. This transport protein allows for movement of larger molecules in and out of the cell. a. Integral Proteins c. Glycoproteins b. Peripheral Proteins d. Phosphate Proteins 4. True or False: Large molecules, such as glucose, can easily pass through the cell membrane without any help... a. True: They pass right through. b. False: They need a protein channel. 5. The cell membrane is __________ which means it allows some molecules in and keeps other molecules out. a. Homeostasis c. non-selective permeable b. Selectively permeable d. all of the above Prepared: Teresa Eliezel B. Collong Teacher III Hideo B. Kobayashi Special Science Teacher I Jennifer M. Pagdanganan Teacher III Checked: Rosita A. Elopre Master Teacher I Noted: Ma. Victoria C. Vivo Ed.D Principal IV 9  SUMMATIVE ASSESMENT – GENERAL BIOLOGY I MODULE 5 Test I. Fill in the Blanks. Write your answers in the spaces/blanks provided. For Modulars kindly preprare a separate sheet of paper and white your answer. (15pts) 1. Name two function of the cell membrane. (2pts.) 2. The cell membrance contains _________ molecules that are embedded in the lipid bilayer. 3. Why do scientists call the membrane a “mosaic”? (2pts.) 4. Label the image by writing the letter corresponding to your answer. (3pts.) a. Lipid bilayer b. Protein channel c. Carbohydrate chains 1. What three types of organism have cell walls?. (3pts.) 2. What is the main function of the cell wall? 3. What are plant cell walls made of? 5. One of the most important functions of the cell mebrane is to _____________ movement of dissolved ________________ from the liquid on one side of the membrane to the liquuid on the other. (2pts.) Test II. Answer the following questions (2pts each) 1. Describe the fluid – mosaic membrane model proposed by Singer and Nicolson. 2. Sketch a generic phospholipid. Identify the position of the hydrophobic and hydrophilic regions. 3. What components of the cell membrane contribute to the fluid quality of the cell membrane? 4. Explain how composition of the membrane may affect fluidity of the membrane. 5. How are integral proteins different from peripheral proteins? 10  6. Match the Structure with the correct letter from the diagram. (10 pts) ______Cholesterol ______Hydrophobic end of phospholipids ______Cytoskeleton ______Integral Protein ______Glycolipid ______Lipid Bilayer ______Glycoprotein ______Oligosaccharides ______Peripheral Protein ______Hydrophilic end of phospholipids 11