Cells as basic unit of living organisms - Session 3

Organelles are specialized structures within cells that perform specific functions necessary for the cell's survival and overall operation. Each organelle is typically enclosed within a membrane that separates its contents from the rest of the cell, and has a distinct structure and set of functions. Some examples of organelles include the nucleus which contains the cell's genetic material and mitochondria which produce energy for the cell.

The nucleus is a highly specialized organelle that is found in most eukaryotic cells. It is responsible for containing and protecting the cell's genetic material. The genetic material within the nucleus is made up of DNA and associated proteins. The structure of the nucleus includes a nuclear envelope, which is a double membrane that encloses the contents of the nucleus. The nuclear envelope is perforated by nuclear pores. These pores allow molecules to move in and out of the nucleus.

The nucleolus is a distinct region within the nucleus that is responsible for the production of ribosomes, which are involved in protein synthesis. The DNA within the nucleus is organized into distinct units called genes, which code for the production of specific proteins. Abnormalities in the structure or function of the nucleus can result in a variety of diseases, including cancer, developmental disorders, and genetic disorders.

Mitochondria are organelles found in most eukaryotic cells. They are responsible for generating energy in the form of ATP. ATP stands for adenosine triphosphate. Mitochondria have a unique structure, with an inner and outer membrane and their own DNA. Dysfunction of mitochondria has been linked to a range of diseases, including metabolic disorders and neurodegenerative diseases.

Ribosomes are tiny, complex structures found in all living cells that are responsible for making proteins. They are made up of two parts, the large subunit and small subunit, that come together to create a functional ribosome. Ribosomes can be found in the cytoplasm of the cell, as well as on the rough endoplasmic reticulum, where they are involved in protein synthesis and transport. Ribosomes are essential for the functioning of all living cells and are found in both prokaryotes and eukaryotes. Ribosomes work by decoding the information contained within the messenger RNA molecules. Then they use this information to assemble the amino acids into a specific sequence that will eventually form a protein.

The endoplasmic reticulum is a complex network of membrane-bound tubes and flattened sacs. It is found in eukaryotic cells. There are two types of endoplasmic reticulum. The rough endoplasmic reticulum and the smooth endoplasmic reticulum. The rough endoplasmic reticulum is studded with ribosomes, which synthesize proteins. The newly synthesized proteins are transported into the lumen of the rough endoplasmic reticulum for folding, modification, and transport to other parts of the cell. The smooth endoplasmic reticulum lacks ribosomes and is involved in lipid metabolism, detoxification, and calcium ion storage and release.

The Golgi Apparatus is an important part of eukaryotic cells that acts like a packaging and distribution centre. It takes in proteins and lipids, modifies them, and sends them to their final destination. The Golgi apparatus is made up of a stack of flattened membranes called cisternae. Each cisterna has a specific job in processing and modifying the molecules that come through. The Golgi apparatus is responsible for sorting and packaging proteins and lipids into vesicles, which act like delivery trucks for the cell. Golgi apparatus helps to make some of the complex carbohydrates that are found in the extracellular matrix. Without the Golgi apparatus, the cell wouldn't be able to function properly.

The cytoskeleton is a complex network of protein filaments found in eukaryotic cells. It provides structural support and shape to the cell. There are three main types of filaments in the cytoskeleton. They are microfilaments, intermediate filaments, and microtubules. Microfilaments are the thinnest filaments and are made up of actin protein. They help the cell maintain its shape and are involved in cell movement and division. Intermediate filaments are stronger and provide mechanical support to the cell. They are made up of various proteins depending on the cell type.

Microtubules are the thickest filaments and are made up of tubulin protein. They are involved in many cellular processes, including cell division and intracellular transport. The cytoskeleton is a dynamic structure that can be remodelled in response to various stimuli.

Vacuoles are membrane-bound organelles found in the cells of many organisms. They are primarily responsible for storing and maintaining various substances within the cell. Vacuoles are common in plant cells, where they are involved in maintaining turgor pressure and regulating the pH of a cell. Vacuoles can also act as lysosomes, which breakdown and recycle cellular waste. Animal cells also have vacuoles, but they are smaller and serve different functions.

In some organisms, such as amoebas, vacuoles are used for excretion and waste disposal. Some vacuoles contain pigments that give colour to flowers, fruits, and other parts of plants. Finally, in some species, vacuoles can serve as a defence mechanism by storing toxins or other harmful compounds.

Peroxisomes are small, membrane-bound organelles that are found in eukaryotic cells. They participate in cellular metabolism, particularly in the breakdownwards of fatty acids and the detoxification of harmful substances. Peroxisomes contain enzymes that are involved in the oxidation of various substances, which produces hydrogen peroxide as a byproduct. Enzymes are the protein molecules that speed up the rate of a reaction.

However, peroxisomes also contain an enzyme called catalase, which breaks downwards hydrogen peroxide into water and oxygen. This helps to prevent damage to the cell from the accumulation of hydrogen peroxide. Peroxisomes are especially abundant in the liver and kidney cells. They are involved in the detoxification of drugs and other harmful substances. In some plants, peroxisomes are also involved in photorespiration, a process that helps to reduce the levels of toxic compounds produced during photosynthesis.

Cilia and flagella are slender, hair-like structures found on the surface of many types of cells. They are involved in cell movement and sensing. Both have a similar structure.Cilia are typically shorter and more numerous, while flagella are longer and usually only occur in one or a few copies. Cilia are found on the surface of cells lining the respiratory tract, reproductive system, and apical surface of particular epithelial cells.

Cilia help to move fluids and particles across a surface. Flagella are typically found on cells that need to move themselves, such as sperm cells or particular types of bacteria. Both cilia and flagella participate in important roles in the body, helping to maintain normal physiological function.

ATP is adenosine triphosphate. It participates in energy metabolism in cells. It is often referred to as the energy currency of the cell. ATP is composed of a nitrogenous base which is adenine, a sugar which is ribose, and three phosphate groups. The bonds between the phosphate groups store energy that can be used for cellular work. When one phosphate group is removed from ATP, energy is released, which can be used by the cell for various processes.

The process of removing a phosphate group from ATP is called hydrolysis. ATP is constantly being synthesized and broken downwards in cells, depending on the cell's energy needs. The production of ATP is a complex process that involves several metabolic pathways in cells. The breakdown of glucose during cellular respiration is one of the primary ways that cells generate ATP. In summary, ATP is a key molecule in the cell that provides energy for a wide variety of cellular processes. We shall discuss more about ATP in upcoming lessons.