A Structural components of CELL MEMBRANES

about the cell membrane as the barrier of cell, which is semi-permeable. controls enter and exit of the cell

1. GENERAL BIOLOGY 1 STRUCTURAL COMPONENTS OF THE CELL MEMBRANE

2. LEARNING OBJECTIVES 1. identify the three major constituents of the cell membrane; 2. distinguish the different composition of the cell membrane; 3. explain the importance of the structural components of the cell membrane; 4. explain how the arrangement of molecules provides fluidity to the cell 7/27/2025 2

3. FACT OR BLUFF Direction Tell whether if the following information about the cell membrane during cell division is a fact or bluff. 7/27/2025 Sample Footer Text 3

4. 1. The cell membrane disintegrates during the late phase of mitosis. 2. Cytokinesis, the division of the cytoplasm, happen both in plant and animal cells does not involve the cell membrane. 3. Cytokinesis in animal cells starts with the constriction in the cell membrane during late anaphase or early telophase. 7/27/2025 Sample Footer Text 4

5. 4. The cell membrane forms and create cleavage furrow that grows deeper between the two cells until they pinch off and separate to form two separate daughter cells. 5. In plant cells, cytokinesis involves the formation and insertion of a new cell membrane that separate daughter nuclei after mitosis 7/27/2025 Sample Footer Text 5

6. Identify the different components of the cell membrane using the description given below. Use the appropriate number to locate each molecule. 7/27/2025 Sample Footer Text 6

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8. CELL MEMBRANE Cell Membrane (also known as plasma membrane)  It serves as a barrier, maintaining the internal environment of the cell by keeping its constituents in and unwanted substances out. The membrane is composed primarily of a double layer of phospholipids with embedded proteins. These proteins facilitate the transport of essential nutrients into the cell and the removal of waste products. The cell membrane's semipermeable nature allows selective passage of molecules, maintaining the cell's homeostasis and enabling communication with its environment 7/27/2025 Sample Footer Text 8

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10. STRUCTURAL COMPONENTS OF THE CELL MEMBRANE The cell membrane is composed of three main components: lipids, proteins, and carbohydrates. The ratio of lipids and proteins in the cell membrane is 1:1 or 50% lipids and 50% proteins. Membrane protein in the cell membrane is several times larger than the lipid molecule, but lipid molecules are 50 times more than protein molecules. The ratio is not absolute and varies from membrane to membrane 7/27/2025 Sample Footer Text 10

11. PHOSPHOLIPID BILAYER The fundamental building block of cell membrane is the phospholipid which is an amphipathic molecule, consisting of both hydrophobic and hydrophilic regions. The hydrophilic or “water loving” (polar) region is the globular head containing phosphate group; the hydrophobic or “water-fearing” (nonpolar) regions are their fatty acid tails. 7/27/2025 Sample Footer Text 11

12. PHOSPHOLIPID BILAYER The membrane lipids are organized into a continuous bilayer in which the hydrophobic regions of the phospholipids are shielded from the aqueous environment since it is poorly soluble in water and constitute a barrier impenetrable to almost all substances, while the hydrophilic regions are exposed to high water content region. Proteins are found inserted into this lipid bilayer and are classified into integral proteins and peripheral proteins. 7/27/2025 Sample Footer Text 12

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15. INTEGRAL PROTEIN Integral proteins as their name suggests, integrated into the membrane proteins that penetrate the lipid bilayer. They pass entirely through the lipid bilayer and protrude from both the extracellular and cytoplasmic sides of the cell membrane 7/27/2025 Sample Footer Text 15

16. PERIPHERAL PROTEIN Peripheral proteins are membrane proteins that are associated within the surface of the cell membrane and found either on the cytoplasmic or extracellular side. Unlike integral protein, they do not stick into the hydrophobic core of the membrane and they tend to be more loosely attached. 7/27/2025 Sample Footer Text 16

17. CARBOHYDRATES Carbohydrates are the third major components of the cell membrane. In general they are found on the outside surface of the cells and are bound either in protein forming glycoproteins or to lipids forming glycolipids. These carbohydrates may consist of 2-60 monosaccharide units and can either be straight or branched 7/27/2025 Sample Footer Text 17

18. THE FLUID MOSAIC MODEL The fluid mosaic model describes the cell membrane as several molecules (phospholipid, cholesterol and proteins) that are constantly moving. This movement helps the cell membrane maintains its role as a barrier between the inside and outside of the cell environment. The fluidity of a cell membrane depends on the lipid composition of the membrane, the density of integral proteins, and the temperature. The fatty acids and cholesterol play an important role in the fluidity of the cell me 7/27/2025 Sample Footer Text 18

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20. ROLE OF FATTY ACIDS The structure of the fatty acid tails of the phospholipid is important in determining how fluid is the membrane. Saturated fatty acids have no double bonds, so they are relatively straight while unsaturated fatty acids contain one or more double bond, often resulting in a bend or kink. A long chain of saturated fatty acids have greater interactions among themselves making the cell membrane stiffer. While more unsaturated fatty acids in the lipid tails make the membrane becomes less tightly packed resulting to the increase of the cell membrane fluidity 7/27/2025 Sample Footer Text 20

21. ROLE OF FATTY ACIDS Thus, at cooler temperature the straight tails of saturated fatty acids can pack tightly together, making a dense and fairly rigid cell membrane while unsaturated fatty acid tails cannot pack together as tightly because of the bent structure of the tails making the cell membrane to stay fluid at lower temperature 7/27/2025 Sample Footer Text 21

22. ROLE OF CHOLESTEROL The presence of cholesterol in the membrane makes it possible for the cell membrane to maintain its fluidity across a wide range of temperatures. It helps to minimize the effects of temperature on fluidity. At low temperature, cholesterol increases the fluidity by keeping the phospholipids from packing tightly together while at high temperature, it reduces fluidity. In this way, cholesterol expands the range of the temperatures at which a membrane maintains a functional healthy fluidity 7/27/2025 Sample Footer Text 22

23. ROLE OF CHOLESTEROL The number of cholesterol molecules in the membrane can be as high as the number of phospholipids. A high amount of cholesterol in the phospholipid bilayer makes the cell membrane remains fluid. While having a high density of integral proteins makes the cell membrane have less fluid 7/27/2025 Sample Footer Text 23

24. THE IMPORTANCE OF MEMBRANE FLUIDITY Membrane fluidity provides a perfect compromise between a rigid structure which makes mobility absent and a completely fluid where mechanical support would be lacking. It also allows interactions to take place within the membrane. Because of membrane fluidity, molecules that interact can come together, carry out the necessary reaction, and move apart. 7/27/2025 Sample Footer Text 24

25. THE IMPORTANCE OF MEMBRANE FLUIDITY Basic cellular processes, including cell movement, cell growth, cell division, formation of intercellular junctions, secretion, and endocytosis, depend on the fluidity of the cell membrane. 7/27/2025 Sample Footer Text 25

26. Direction : Answer the following questions. How is phospholipid arranged in the cell membrane? How does the arrangement of different structural components the cell membrane contribute to its fluidity? Aside from cell membrane, where else can you find a bilayer of lipid? 7/28/2025 Sample Footer Text 26