Cell Biology: Cell Membrane and Cytoplasm

Cell Membrane

• Cholesterol molecules maintain the flexibility and functionality of the membrane by ensuring its fluidity, even in varying situations.

Cytoplasm

• The cytoplasm is a viscous colloidal solution that occupies the intracellular space, enveloping the nucleus.
• It consists primarily of water, ions, enzymes, and organelles, and functions as the medium for numerous cellular processes.
• The cytoplasm contains various organelles, including the endoplasmic reticulum, Golgi apparatus, and mitochondria.
• It plays a vital role in intracellular transport, facilitating the movement of molecules throughout the cell via processes such as diffusion and active transport.
• It offers essential support to the cell and aids in preserving its structural integrity.

Nucleus

• The nucleus is the control center of the cell, responsible for regulating cell activity and housing genetic material.
• It is a large, spherical body that contains genetic material in the form of DNA.
• The nucleus is enclosed by a dual-layered membrane known as the nuclear envelope, which is equipped with pores that regulate the transport of chemicals into and out of the nucleus.
• Chromosomes are structures within the nucleus that arrange genetic material in the form of DNA.
• The nucleus contains the cell's genetic information, which contains instructions for protein production and cell activity.

Mitochondria

• Mitochondria are organelles enclosed by two membranes that are present in the majority of eukaryotic cells.
• They have a vital function in cellular respiration, producing energy in the form of ATP.
• Mitochondria possess their own genetic material, referred to as mitochondrial DNA (mtDNA), and have the ability to replicate and synthesize proteins to some extent independently.
• The mitochondria's inner membrane is composed of cristae, which are folded structures that enhance the available surface area for ATP synthesis.
• Enzymes within the mitochondria facilitate a sequence of metabolic activities called the citric acid cycle and oxidative phosphorylation.

Ribosomes

• Ribosomes are small yet powerful organelles present in both prokaryotic and eukaryotic cells, with the primary function of synthesizing proteins.
• Ribosomes are composed of ribosomal RNA (rRNA) and proteins.
• They can be found either freely in the cytoplasm or bound to the endoplasmic reticulum.
• Ribosomes serve as the biological sites where the genetic information contained in messenger RNA (mRNA) is converted into proteins.

Flagella

• Flagella are structures made up of microtubules and surrounded by the cell membrane.
• They have a distinctive waving or spiraling movement that enables the cell to move forward in its surroundings.
• The motion is caused by the synchronized movement of motor proteins along the microtubules inside the flagellum.
• Flagella in unicellular organisms function as a method of propulsion, enabling the organism to navigate towards nourishment or away from detrimental substances.
• Flagella are essential in multicellular organisms for various functions, including fertilization.

Endoplasmic Reticulum

• The endoplasmic reticulum (ER) is an intricate network of membranous tubules and sacs present in eukaryotic cells.
• The ER is divided into two distinct regions: the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER).
• The rough endoplasmic reticulum (RER) is covered with ribosomes on its surface, resulting in a coarse appearance when observed under a microscope.
• The smooth endoplasmic reticulum (SER) is devoid of ribosomes and has a role in synthesizing lipids, detoxifying medicines and poisons, and storing calcium ions.
• Both forms of endoplasmic reticulum (ER) are interconnected, enabling the efficient transportation of chemicals throughout the cell.

Golgi Apparatus

• The Golgi apparatus is an essential organelle present in the majority of eukaryotic cells.
• Structurally, it consists of a sequence of flattened, membrane-bound sacs called cisternae.
• The Golgi apparatus plays a crucial role in the modification, organization, and packaging of proteins and lipids, whether for release outside the cell or for internal usage.
• Glycosylation is a process in which carbohydrates are added to proteins by enzymatic activities occurring within the cisternae, along with other changes.
• The Golgi apparatus also contributes to the production of intricate polysaccharides, which are vital constituents of the cell wall in plants and the extracellular matrix in animals.

Lysosomes

• Lysosomes are created through the process of budding from the Golgi apparatus.
• They are involved in the degradation of cellular waste and foreign substances.

Cytoskeleton

• Microtubules are part of the cytoskeleton, which are the largest filaments and are made up of tubulin subunits organized in a tubular pattern.
• They play a crucial role in numerous cellular functions, such as the segregation of chromosomes during cell division, the transportation of vesicles and organelles along intracellular pathways, and the preservation of cell morphology.
• The cytoskeleton's capacity for swift assembly and disassembly of its constituents enables cells to adjust to their dynamic surroundings.

Centrioles

• Centrioles are cylindrical organelles present in the majority of eukaryotic cells.
• They have a crucial function in cell division and the arrangement of the microtubule network.
• Centrioles play a role in the creation of the mitotic spindle, which is a structure composed of microtubules that separates chromosomes into the daughter cells during cell division.