Cell structure and types: Prokaryotic vs Eukaryotic

• The cell constitutes the basic structural and functional unit in all known living organisms.
• It represents the smallest unit of an organism considered alive.
• Cells can independently execute all essential life functions.
• Cell biology is the study of cells.

Cell Structure

• A plasma membrane encloses all cells, separating the cell's interior from the external environment.
• Cells contain cytoplasm, the jelly-like substance filling the cell.
• Cells contain DNA as their genetic material.

Types of Cells

• The two primary cell types are prokaryotic and eukaryotic.

Prokaryotic Cells

• Prokaryotic cells are simpler and generally smaller than eukaryotic cells.
• Nucleus and other membrane-bound organelles are absent in prokaryotic cells.
• Prokaryotic cells have DNA located in the cytoplasm within a region termed the nucleoid.
• Bacteria and Archaea exemplify organisms composed of prokaryotic cells.

Eukaryotic Cells

• Eukaryotic cells are more complex and generally larger than prokaryotic cells.
• Eukaryotic cells possess a nucleus housing the cell's DNA.
• Membrane-bound organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus, are present in eukaryotic cells.
• Plants, animals, fungi, and protists are examples of organisms that have eukaryotic cells.

Cell Components and Their Functions

• Key components are the plasma membrane, cytoplasm, nucleus, and various organelles.

Plasma Membrane

• The plasma membrane acts as a selective barrier, regulating substance passage into and out of the cell.
• Its composition includes a phospholipid bilayer with embedded proteins.
• Cell signaling, transport, and maintenance of cell shape are among its functions.

Cytoplasm

• The cytoplasm occupies the region between the plasma membrane and the nucleus.
• Cytosol, a jelly-like substance, and organelles constitute the cytoplasm.
• Many metabolic reactions occur in the cytoplasm.

Nucleus

• The nucleus houses the cell's DNA and governs cell activities.
• A double membrane with pores, known as the nuclear envelope, surrounds it.
• The nucleolus, involved in ribosome production, resides within the nucleus.

Mitochondria

• Mitochondria serve as the cell's powerhouses, producing ATP via cellular respiration.
• Their structure includes a double membrane, with the inner membrane folded into cristae.
• Mitochondria possess their own DNA and ribosomes.

Endoplasmic Reticulum (ER)

• The ER is an extensive membrane network participating in protein and lipid synthesis.
• Two ER types exist: rough ER (with ribosomes) and smooth ER (without ribosomes).
• Protein synthesis and modification are functions of the rough ER, while lipid synthesis and detoxification are functions of the smooth ER.

Golgi Apparatus

• The Golgi apparatus processes and packages proteins and lipids.
• Flattened membranous sacs called cisternae comprise it.
• The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles.

Lysosomes

• Lysosomes are organelles that contain enzymes for breaking down cellular waste and debris.
• They digest old or damaged organelles, along with engulfed viruses and bacteria.
• Programmed cell death (apoptosis) involves lysosomes.

Ribosomes

• Protein synthesis is the function of ribosomes.
• They are present in the cytoplasm and on the rough ER.
• Ribosomes translate mRNA into proteins.

Cell Wall

• Plant cells feature a cell wall, a rigid outer layer providing support and protection.
• Cellulose is the primary component of the cell wall.
• Maintaining cell shape and preventing excessive water uptake are functions of the cell wall.

Chloroplasts

• Plant cells contain chloroplasts, organelles that conduct photosynthesis.
• Chlorophyll, a pigment capturing light energy, is present in chloroplasts.
• Light energy is converted into chemical energy (glucose) by chloroplasts.

Vacuoles

• Vacuoles are large vesicles storing water, nutrients, and waste products.
• Plant cells have a large central vacuole that maintains cell turgor pressure.
• Cell growth, storage, and waste disposal involve vacuoles.

Cell Functions

• Cells perform life-sustaining functions, including:
• Metabolism: Cells execute chemical reactions for energy acquisition and molecule synthesis.
• Growth: Cells increase in size and number through cell division.
• Reproduction: Cells create new cells through cell division.
• Response: Cells react to stimuli from their surroundings.
• Homeostasis: Cells maintain a stable internal environment.

Cell Communication

• Cells communicate via chemical signals.
• Signals can be transmitted by direct contact, local signaling, or long-distance signaling.
• Coordinating cell activities and maintaining homeostasis depend on cell communication.

Cell Division

• The process by which cells produce new cells is cell division.
• Mitosis and meiosis are the two main types of cell division.
• Mitosis yields two identical daughter cells for growth and repair.
• Meiosis yields four genetically different daughter cells for sexual reproduction.