Question

Cell Question

Describe the structure and function of each of the following: lysosomes, peroxisomes, vacuoles, mitochondria, chloroplasts, plastids, internal cell membranes, centrosome, microtubules, centromeres, ribosomes, smooth and rough endoplasmic reticulum, and Golgi bodies.

Answer 1

Lysosomes - Lysosomes are vacuoles, which contain digestive and destructive membranes. These are used to kill the bacteria or virus in WBC, while in tadpole-tail cells they kill the cell by separation of the tail from the main body. They help in cellular digestion involved in apoptosis, which is the process of programmed cell death.

Peroxisomes -It is a small organelle present in the cytoplasm of many cells, which contains the reducing enzyme catalase and some oxidases. They perform a variety of metabolic processes and as a by-product, produce hydrogen peroxide. They use peroxase enzyme to break down this hydrogen peroxide into water and oxygen.

Vacuoles - Vacuoles are cellular storage places. They consist of a lipid bilayers, which act as a selectively permeable barrier to regulate movement of materials into and out of the compartment. They have a variety of purposes, storing food, water, or waste products, or immune functions such as contains dangerous materials. They maintain the turgor pressure.

Mitochondria - Mitochondria are the organelles, which are responsible for the metabolism of cell. They synthetizes ATP through a protein known as ATP synthase. Mitochondria have a double membrane. An outer membrane and a folded inner membrane. The internal membrane, known as the cristae is invaginated , act as to maximize surface area enabling it to hold more ATP synthases. They have matrix inside the inner membrane. They are powerhouse of the cell which is present in the eukaryotic organisms.

Chloroplasts - They are bounded by a double membrane, which includes an outer membrane and inner membrane. The double membrane encloses the semifluid stroma, which contains enzymes and thylakoids. The thylakoids are disklike sacs structures. Chlorophyll and the other pigments, which capture solar energy are located in the thylakoid membrane, and the enzymes synthesize carbohydrates are present in outside the thylakoid in the fluid of the stroma. They can grow and pinch in two, reproducing themselves. They are mobile and move around the cell along tracks of the cytoskeleton. Chloroplasts use solar energy to sythesize carbohydrates.

Plastids - The plastid is a double-membrane organelle found in the cells of plants, algae, and some other eukaryotic organisms. They are the site of manufacture and storage of important chemical compounds used by the cell. They often contain pigments used in photosynthesis and the types of pigments in a plastid determine the color of cell.

They differentiate into several forms, which depend upon types of function they play in the cell.

Chloroplasts are green plastids. They help in the process of photosynthesis;

Chromoplasts are coloured plastids. They help in pigment synthesis and storage.

Leucoplasts are colourless plastids. They help in monoterpene synthesis and storage.

Internal cell membranes - The membrane is composed of a phospholipid bilayer in which proteins are embedded such as integral proteins or peripheral proteins. The two sides of the plasma membrane are not identical. The hydrophobic tails of phospholipids make up the interior of the membrane and the hydrophilic polar heads face the outside and inside of the cell. In the animal plasma membrane is found also cholesterol, which helps modify the fluidity of the membrane. It is differentially permeable. Small, noncharged molecules can freely cross the membrane .It provides protection and shape to the cell.

Centrosome - Centrosomes are structures found inside of cells. They are made from two centrioles. Centrioles are microtubule rings. Two centrioles are surrounded by an amorphous mass of protein known as the pericentriolar material (PCM). The PCM contains proteins responsible for microtubule nucleation and anchoring, which includes γ-tubulin, pericentrin and ninein. It acts as the main microtubule organizing center (MTOC) of the animal cell and regulator of cell-cycle progression. It provides structure for the cell. It pulls chromatids apart during the process of cell division.

Microtubules - It is a microscopic tubular structure present in numbers in the cytoplasm of cells. They are the largest cytoskeletal filaments in cells. They are made out of subunits called tubulin. Each tubulin subunit is made up of one alpha and one beta tubulin that are attached to each othe. They also serve a transportation function. They are the routes upon which organelles move through the cell. They give support to the cell. They move vesicles, granules, organelles like mitochondria, and chromosomes via special attachment proteins. They also serve a cytoskeleton role.

Centromeres - The centromere is the specialized DNA sequence of a chromosome, which links a pair of sister chromatids. During mitosis, spindle fibers attach to the centromere by the help of the kinetochore. It determines kinetochore formation and sister chromatid cohesion. They interact with spindle microtubules to ensure the segregation of chromatids during the process of mitosis and of homologous chromosomes in meiosis. They hold the two sister chromatids together until it's time for them to separate during anaphase.

Ribosomes - Ribosomes are responsible for protein synthesis. They are comprised of interacting protein and nucleic acid chains. They consist a large and a small subunit. The small subunit functions to attach to the mRNA strand and hold it in place during translation, while the large subunit holds and manufactures the growing polypeptide chain.

Smooth and rough endoplasmic reticulum - The endoplasmic reticulum consists of a complicated system of membranous cannes and sacules. It is physically continuous with the nuclear envelope. It forms vesicles, which transport molecules to other parts of the cell, notably the Golgi apparatus. The ER membrane separates the internal compartment of the ER, known as the ER lumen (cavity) or cisternal space, from the cytosol. And because the ER membrane is continuous with the nuclear envelope, the space between the two membranes of the envelope is continuous with the lumen of the ER.

Smooth ER act as transport for various things, the RNA from the nucleus to the ribosomes. Smooth ER appears smooth in texture, because of lack of ribosomes. Smooth ER plays an important role in lipid emulsification and digestion in the cell.

Rough ER are rough because of the ribosomes embedded in them. The rough ER takes the protein to the Golgi apparatus to be packaged into vacuoles.

Golgi bodies - They sort the modified molecules and packaged them into vesicles, which depart from the outer face. They are stack of flattened saccules. They consists of layers of lipid membrane stacked one one top of another, with a cis face and a trans face. One side of the stack (cis) is directed toward the ER, and the other side (trans) is directed toward the plasma membrane. They modify these substances and move through its saccules. They act as packaging center for the cell, which attach to various cell products to direct them to their respective locations and packaging the products into vacuoles to ensure delivery.