Question

4. Describe the structure and cellular activity of each organelle: ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, cytoskeleton, centrosome, and centrioles.

5. Explain the structure of glycosomes and lipid droplets.

6. Describe the role of each of the three parts of the nucleus in the control of cellular activities: the nuclear envelope, the nucleolus, and chromatin.

7. List the phases of the cell life cycle, and describe a key event of each phase.

8. Name specific cell types, and relate their overall shape to their specific functions. 9. Compare theories of cell differentiation and aging.

Answer 1

Ans 4)

Ribosome – They are cellular organelles which consists of RNA and proteins and helps in synthesis of the proteins. They helps in translating the mRNA into amino acid sequence to produce polypeptide. It is a complex which is made of RNA and proteins and consists of two subunits. The mRNA binds to the smaller subunit and the amino acid are added in the large subunit. The ribosomes are made in the nucleolus and they are exported into the cytoplasm with help of nuclear pore. They are basic organelles for the production and synthesis of proteins.

Endoplasmic Reticulum – The ER is divided into rough ER and smooth ER. The rough ER consists of ribosomes on its surface which give it the rough appearance. It consists of interconnected network of cisternae which are flattened membrane sac. The main function of the RER is the production of the proteins on the ribosomes and its storage. The main function of the SER is it helps in lipid synthesis. The smooth ER also is responsible for production of some enzymes which helps in detoxification.

Golgi apparatus – This relates to the structure of ER and it plays a major role in modification, sorting and packing of the proteins. They help in delivering the proteins to their target destination by sorting. It consists of series of flattened disks called cisternae and it has a cis and trans facing Golgi network. The proteins which are produced in ER are packaged within vesicle and fuse with Golgi apparatus. The Golgi helps in modifying, sorting and sending the proteins to their destination.

Lysosome – They have a single outer lysosomal membrane and it has an internal acidic environment. Its main role is to digest the unwanted part of the cells as well as the cellular debris. They consists of hydrolytic enzymes which helps in breakdown of unwanted cellular debris.

Peroxisome – They are cellular organelle which are surrounded by a single membrane with a diameter of 0.5 micrometer. They have enzymes like hydrogen peroxide, oxidase and catalase inside it. They are scavenging organelle which helps in lipid metabolism and it helps in converting the reactive oxygen species into safe molecules. They help in breakdown of long fatty acid chain with help of beta oxidation process.

Mitochondria – They are membrane bound organelle which is the main site for the production of the energy molecule ATP. It has double membrane which is the outer and inner membrane and they are made of proteins and phospholipid layer. The space between the inner and outer membrane is called as intermembrane space. The outer membrane consists of porins which allows free movement of molecules that are less than 5000 daltons and is also permeable to ATP, ADP, ions etc. The inner membrane is permeable to oxygen, water and carbon dioxide. The inner membrane of the mitochondria where the ATP is produced.

Cytokeleton – It is the network of filament and tubules which helps in giving cellular shape and integrity to the cell. The main function is it helps in giving shape to the cell and it also helps with the process of cell division, cell signaling and helps in molecular transport. There are three main types of cytoskeleton which are microtubules, intermediate filaments and microfilaments.

Centrosome – They help in cell division process and they are mostly associated during the prophase. During the cell division process, it helps in maintaining the chromosome number. When the DNA replication takes place, centrosome split into two and they attach to opposite nucleus pole. They helps in connecting to the spindle fibers and help in pulling the chromosomes to opposite end for equal number to be present in both daughter cells.

Centrioles – They are found close to the nucleus and have microtubular wall. They are cylindrical in shape with diameter of 150 – 250 nm and length of 300 – 350 mm. They help in the formation of spindle apparatus and helps in cell division process.