Cell Structure and Functions PDF

# Cell Structure and Functions ## Major Parts of the Cell - **Plasma Membrane:** Outer covering that separates the cell’s interior from its surrounding environment. - **Cytoplasm:** Consisting of a jelly-like cytosol within the cell in which other cellular components are found. - **Nucleus:** Serv...

# Cell Structure and Functions ## Major Parts of the Cell - **Plasma Membrane:** Outer covering that separates the cell’s interior from its surrounding environment. - **Cytoplasm:** Consisting of a jelly-like cytosol within the cell in which other cellular components are found. - **Nucleus:** Serves as the brain of the cell and directs all of the cell’s activity. ## Plasma Membrane - It encloses and safeguards its organelles from possible harm that foreign materials can inflict on them. - This membrane contains a phospholipid bilayer, integral membrane proteins, cholesterol, a protein channel, cytoskeletal filaments, and peripheral membrane proteins. - It also controls the exchange of essential components and obtains chemical messages from other cells. - The plasma membrane is a mosaic of components—primarily, phospholipids, cholesterol, and proteins —that move freely and fluidly in the plane of the membrane. - The plasma membrane is made of glycerol, two fatty acid tails, and a phosphate-linked head group. Biological membranes usually involve two layers of phospholipids with their tails pointing inward, an arrangement called a phospholipid bilayer. - Cholesterol is another lipid composed of four fused carbon rings, is found alongside phospholipids in the core of the membrane. - Proteins help move large molecules or aid in cell recognition. - Peripheral proteins are attached on the surface (inner or outer). - Integral proteins are embedded completely through the membrane. ## Cytoplasm - It is the entire region of a cell between plasma membrane and nuclear envelope. - The cytoplasm is composed primarily of water, proteins, and salts. - In the cytoplasm, the organelles are suspended in a gel-like solution called cytosol, which is composed of both organic and inorganic compounds. - Cytosol accounts for about 70% of cellular content. It contains a rich supply of macromolecules and smaller organic molecules. - The Cytoplasm also contains enzymes that break down waste and enable metabolic reactions. - It allows for cellular expansion and growth. - Together with cytoskeleton, cytoplasm determines cell shape and accommodates movement for some cell types. ## Nucleus - The nucleus was discovered by Robert Brown in 1833. - It is the most vital part of the cell and dubbed as the "control center". - It directs all of the cell’s activities and determines how a cell should appear and function. - A double layer of nuclear membrane encloses the nucleus to keep it distinct from other cellular components. - Nucleolus serves as the site of ribosomes synthesis. - Nucleus holds chromosomes which carry tightly wrapped and coined DNA. ## The cell organelles: endomembrane system - The endomembrane system is a group of membranes and organelles in eukaryotic cells that works together to modify, package, and transport lipids and proteins. - This system is made up of organelles that are communally linked by structure specific to each of them. - The following organelles make up the endomembrane system: - Endoplasmic Reticulum - Ribosomes - Vacuoles - Golgi Apparatus - Lysosomes - Peroxisomes - Centrosomes ## Endoplasmic reticulum - The Endoplasmic Reticulum(ER) is a series of interconnected membranous sacs and tubules that collectively modifies proteins and synthesized lipids. - These two functions are performed in separate areas of ER; the rough endoplasmic reticulum and smooth endoplasmic reticulum. - The hollow portion of ER tubules is called lumen or cisternal space. - The membrane of the ER, which is a phospholipid bilayer embedded with proteins, is continuous with nuclear envelope. ### Rough endoplasmic reticulum - It has ribosomes on its surface. - It makes membrane proteins and proteins for export out of the cell. - Proteins are made by ribosomes on ER surface. - They are then threaded into the interior of the Rough ER to be modified and transported. ### Smooth endoplasmic reticulum - It incorporates proteins into cisternae and transports synthesized proteins across the cytoplasm, thereby allowing the synthesis of fatty acids and phospholipids. - It is abundant in liver cells, where it detoxifies hydrophobic chemicals. This makes them water-soluble for excretion. ## Ribosomes - Ribosomes are involved in providing a frame for proteins synthesis; hence they are site of protein production. - They are present in both prokaryotic and eukaryotic cells. - Developing muscle cells, skin, and hair cells contain large numbers of free ribosomes. ## Vacuoles - A vacuole is a fluid-filled vesicle enclosed by a membrane. - It has a selectively membrane freely allowing water passage but retaining smaller molecules within it and stores chemicals within the cell. - Vacuoles' ability to break down large molecules makes it comparable with lysosomes in animal cells. Likewise, both organelles thrive in acidic environments. ## Lysosomes - The lysosomes serve as digestion slots for cellular materials that are due for expiration or are no longer useful. - It is the cell’s reprocessing area, where it hacks chemical bonds of any foreign substance it comes in contact with, in order to recycle with the raw material. - It is dubbed as the cell’s "suicide bags". - These organelles are capable of self-destruction in order to save the rest of the other organelles from being poisoned. - This happens through autophagy, or the natural process of organelle destruction. - Cells take in food by phagocytosis. - Lysosomes digest the food & get rid of wastes. - Example: macrophages. ## Peroxisomes - It is a small, round organelle enclosed by a single membrane, somehow resembles that of a lysosomes. - It is responsible for self-damage and mostly disintegrate proteins, accommodate the breakdown of fatty acids and detoxify many poisons that enter the body. - It also shields the cell from serious damage caused by reactive oxygen species (ROS) molecules. ## Golgi Apparatus - Stacks of flattened sacs. - Have a shipping side (cis face) & a receiving side (trans face). - Receive proteins made by ER. - Transport vesicles with modified proteins pinch off the ends. - A stack of pancakes. - Modify, sort, & package molecules from ER. - For storage OR - Transport out of the cell. ## Centrosome - It comprised of two centrioles or cylindrical structures with a central cavity surrounded by microtubules arranged side by side. - These structures take part in the assembly of spindle fibers at cell division and contribute to the successful outcome of mitosis. - It is found in all eukaryotic cells, assist in arranging microtubules (hollow tubes of proteins) to be utilized for cell division. - They also enable the said microtubules to form part of the cells’ microtubules to form part of the cells’ cytoskeleton. - In this way, cellular shape is maintained, and the cell structure is stabilized. ## Mitochondria - Mitochondria are the sites of cellular respiration, the metabolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars, fats, and other fuels. - The mitochondria are oval-shaped organelles found in most eukaryotic cells. They are considered to be the “powerhouses” of the cell. - Mitochondria are most plentiful in cells that require significant amounts of energy to function, such as liver and muscle cells. - The mitochondria has two membranes that are similar in composition to the cell membrane. - **Outer membrane** — is a selectively permeable membrane that surrounds the mitochondria. - It is the site of attachment for the respiratory assembly of the electron transport chain and ATP Synthase. - It has integral proteins and pores for transporting molecules just like the cell membrane - **Inner membrane** — folds inward (called cristae) to increase surfaces for cellular metabolism. - It contains ribosomes and the DNA of the mitochondria. The inner membrane creates two enclosed spaces within the mitochondria. - Intermembrane space — between the outer membrane and the inner membrane. - Matrix — that is enclosed within the inner membrane. - **ATP** is the major energy currency of the cell that provides the energy for most of the energy-consuming activities of the cell. - **Mechanism** — When the third phosphate group of ATP is removed by hydrolysis, a substantial amount of free energy is released. ## Chloroplast - Chloroplasts, which are found in plants and algae, are the sites of photosynthesis. - This process converts solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water. - Chloroplasts are double membrane-bound organelles and are the sites of photosynthesis. - The chloroplast has a system of three membranes: the outer membrane, the inner membrane, and the thylakoid system. ### Structure of chloroplast - **Outer membrane** — This is a semi-porous membrane and is permeable to small molecules and ions which diffuse easily. - The outer membrane is not permeable to larger proteins. - **Intermembrane Space** — This is usually a thin intermembrane space about 10-20 nanometers and is present between the outer and the inner membrane of the chloroplast. - **Inner membrane** — The inner membrane of the chloroplast forms a border to the stroma. - It regulates passage of materials in and out of the chloroplast. In addition to the regulation activity, fatty acids, and are synthesized in the inner chloroplast membrane. - **Stroma** — This is an alkaline, aqueous fluid that is protein-rich and is present within the inner membrane of the chloroplast. - It is the space outside the thylakoid space. - The chloroplast DNA, chloroplast ribosomes, thylakoid system, starch granules, and other proteins are found floating around the stroma. - **Thylakoid System** — The thylakoid system is suspended in the stroma. It is a collection of membranous sacks called thylakoids. - Thylakoids are small sacks that are interconnected. - The membranes of these thylakoids are the sites for the light reactions of the photosynthesis to take place. The chlorophyll is found in the thylakoids. - The thylakoids are arranged in stacks known as grana. Each granum contains around 10-20 thylakoids. ## Practice: HOMEWORK - Draw and label each part of plant and animal cells in a short bond paper.