Cell Biology: Cell Division

• Cell biology is the study of cells, their structure, function, and behavior.
• It encompasses the physiological properties of cells, their interactions, and their environment.
• Cell biology examines both prokaryotic and eukaryotic cells.
• Research in cell biology is related to other fields such as genetics, molecular biology, and biochemistry.
• Understanding cell biology is vital for comprehending tissues, organs, and the overall functioning of living organisms.

Cell Division

• Cell division is the process by which a parent cell divides into two or more daughter cells.
• In eukaryotes, there are two main types of cell division: mitosis and meiosis.
• Mitosis is the division of a somatic cell into two identical daughter cells, crucial for growth, repair, and asexual reproduction.
• Meiosis is the division of a germ cell into four genetically different daughter cells, essential for sexual reproduction, creating gametes (sperm and egg cells).
• In prokaryotes, cell division occurs through binary fission, a simpler process than eukaryotic mitosis or meiosis.
• The cell cycle includes interphase, where the cell grows and replicates its DNA, followed by the mitotic phase (mitosis and cytokinesis) or meiosis.
• Regulation of the cell cycle is critical; disruptions can lead to uncontrolled cell division and diseases like cancer.
• Cytokinesis is the physical process of cell division, where the cytoplasm of a single eukaryotic cell divides to form two daughter cells.
• In animal cells, cytokinesis involves the formation of a cleavage furrow, while in plant cells, a cell plate forms.

Cell Organelles

• Cell organelles are specialized subunits within a cell that perform specific functions.
• They are membrane-bound structures in eukaryotic cells.
• Major cell organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes.
• The nucleus contains the cell's genetic material (DNA) and controls the cell's growth and reproduction.
• Mitochondria are responsible for generating energy through cellular respiration, producing ATP.
• The endoplasmic reticulum (ER) is involved in protein synthesis, folding, and lipid synthesis; it exists in two forms: rough ER (with ribosomes) and smooth ER (without ribosomes).
• The Golgi apparatus processes and packages proteins and lipids synthesized in the ER, directing them to their final destinations.
• Lysosomes contain enzymes that break down cellular waste and debris, as well as ingested substances.
• Peroxisomes are involved in detoxification and lipid metabolism.
• Ribosomes, though not membrane-bound, are essential for protein synthesis; they can be found free in the cytoplasm or attached to the ER.
• The cytoskeleton provides structural support and facilitates cell movement; it includes microtubules, intermediate filaments, and microfilaments.
• Centrioles are involved in cell division in animal cells, organizing the mitotic spindle.
• Vacuoles store water, nutrients, and waste products; they are particularly large in plant cells, helping maintain turgor pressure.
• Chloroplasts (in plant cells) conduct photosynthesis, converting light energy into chemical energy.
• The cell membrane (plasma membrane) is a selectively permeable barrier that controls the movement of substances into and out of the cell.
• The cell wall (in plant, bacteria, fungi) provides additional support and protection.

Nucleus

• The nucleus houses the cell's DNA, organized into chromosomes.
• It is surrounded by a double membrane called the nuclear envelope.
• The nuclear envelope contains pores that regulate the passage of molecules between the nucleus and cytoplasm.
• The nucleolus, located within the nucleus, is the site of ribosome synthesis.
• The nucleus controls cell growth, metabolism, and reproduction.

Mitochondria

• Mitochondria are the powerhouses of the cell, producing ATP through cellular respiration.
• They have a double membrane structure: an outer membrane and a highly folded inner membrane (cristae).
• The cristae increase the surface area for ATP production.
• The mitochondrial matrix contains enzymes, DNA, and ribosomes.
• Mitochondria have their own DNA, suggesting an endosymbiotic origin.

Endoplasmic Reticulum (ER)

• The ER is a network of membranes involved in protein and lipid synthesis.
• Rough ER (RER) is studded with ribosomes and is involved in protein synthesis and modification.
• Smooth ER (SER) lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.
• The ER plays a role in transporting molecules within the cell.

Golgi Apparatus

• The Golgi apparatus processes and packages proteins and lipids.
• It consists of flattened sacs called cisternae.
• Proteins and lipids from the ER pass through the Golgi, where they are modified, sorted, and packaged into vesicles.
• Vesicles transport these molecules to their final destinations, such as the cell membrane or lysosomes.

Lysosomes

• Lysosomes contain hydrolytic enzymes that break down cellular waste and debris.
• They are involved in autophagy (the breakdown of cellular components) and phagocytosis (the engulfment of external particles).
• Lysosomes help maintain cellular cleanliness and recycle cellular components.

Peroxisomes

• Peroxisomes contain enzymes that detoxify harmful substances and metabolize lipids.
• They break down fatty acids and produce hydrogen peroxide as a byproduct, which is then converted into water and oxygen.
• Peroxisomes are important in liver and kidney cells.

Cytoskeleton

• The cytoskeleton is a network of protein filaments that provides structural support and facilitates cell movement.
• It includes microtubules, intermediate filaments, and microfilaments.
• Microtubules are hollow tubes that provide tracks for intracellular transport.
• Intermediate filaments provide mechanical strength and support.
• Microfilaments (actin filaments) are involved in cell movement and muscle contraction.

Cell Membrane

• The cell membrane (plasma membrane) surrounds the cell and controls the movement of substances into and out of the cell.
• It is composed of a phospholipid bilayer with embedded proteins.
• The phospholipid bilayer is selectively permeable, allowing some molecules to pass through while blocking others.
• Membrane proteins perform various functions, such as transporting molecules, acting as receptors, and facilitating cell adhesion.