Cell Structure and Function

• The cell is the fundamental unit of life that all living organisms are built from.
• All cells share common features like a plasma membrane, cytosol, chromosomes, and ribosomes.

Types of Cells

• Prokaryotic cells lack a nucleus, housing their DNA in a nucleoid region.
• Prokaryotic cells do not have membrane-bound organelles.
• Eukaryotic cells have a nucleus where their DNA is stored within a membranous envelope.
• Eukaryotic cells contain membrane-bound organelles.
• Eukaryotic cells have cytoplasm between the plasma membrane and nucleus.

Cell Size and Compartmentalization

• Cells are small to maintain a high surface area-to-volume ratio, which is essential for efficient nutrient absorption and waste removal.
• A large volume reduces the surface area-to-volume ratio.
• Cell compartmentalization allows for specific functions to be carried out in distinct areas within the cell.

Cell Membranes

• The plasma membrane is a selective barrier controlling the movement of substances in and out of the cell.
• The plasma membrane is composed of a phospholipid bilayer, proteins, and cholesterol.

Cytoplasm

• Cytoplasm occupies the region between the plasma membrane and the nucleus.
• The cytosol is a fluid within the cytoplasm.
• Organelles are suspended in the cytosol, and the cytoplasm is in constant motion.

Nucleus

• The nucleus houses the cell's DNA organized into chromosomes.
• A double membrane known as the nuclear envelope surrounds the nucleus, separating it from the cytoplasm.
• Nuclear pores in the nuclear envelope regulate the movement of molecules into and out of the nucleus.
• The nucleolus, found within the nucleus, is the site of ribosomal RNA (rRNA) synthesis, where ribosome subunits are made.

Ribosomes

• Ribosomes consist of rRNA and proteins.
• Ribosomes conduct protein synthesis in the cytosol (free ribosomes) and on the rough ER.
• Free ribosomes produce proteins that function within the cytoplasm.
• Ribosomes on the rough ER typically synthesize proteins for export or insertion into membranes.

Endomembrane System

• The endomembrane system comprises membranes within and around eukaryotic cells.
• Components include the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, and the plasma membrane.

Endoplasmic Reticulum (ER)

• The ER is continuous with the nuclear envelope.
• There are two types of ER: smooth and rough.
• Smooth ER lacks ribosomes and primarily synthesizes lipids and steroids, and stores calcium.
• Rough ER has ribosomes on its surface, which synthesize proteins destined to leave the cell.
• Rough ER produces glycoproteins (proteins with carbohydrates attached).
• Rough ER distributes products via transport vesicles.
• Rough ER contributes to membrane and lysosome production.

Golgi Apparatus

• The Golgi apparatus consists of flattened membrane sacs called cisternae.
• The Golgi apparatus modifies products from the ER.
• The Golgi apparatus synthesizes polysaccharides.
• The Golgi apparatus sorts materials into transport vesicles.

Lysosomes

• Lysosomes are digestive compartments (primarily in animal cells).
• Lysosomes are membrane-bound sacs containing enzymes for macromolecule digestion.
• Lysosomes break down materials through processes like phagocytosis, where the cell engulfs another cell, forming a food vacuole.
• Lysosomes conduct autophagy, digesting the cell's own organelles to recycle components.

Vacuoles

• Vacuoles are membrane-bound sacs used for storage.
• Food vacuoles are formed during phagocytosis.
• Contractile vacuoles, found in protists, pump out excess water.
• Central vacuoles, present only in plant cells, store organic compounds, water, and waste.

Mitochondria and Chloroplasts

• Both mitochondria and chloroplasts have double membranes.
• Both are involved in energy production.
• Both contain their own circular DNA.
• Both possess their own ribosomes.

Exploration of cell structures and functions, including prokaryotic vs. eukaryotic cells. Importance of cell size and compartmentalization for efficient operation. Discussion of the plasma membrane as a selective barrier.