Biology Chapter: Human Cell Structure

The Human Cell

• Cells are complex, constantly active, and are the building blocks of the entire body.
• Cells perform specific functions to maintain the body.
• Cytosol is a gel-like substance, primarily water with dissolved and suspended components (e.g., glucose, proteins, amino acids).
• Cytosol is also known as intracellular fluid (ICF) and is the fluid component of cytoplasm.
• The structure and properties of cytosol within cells are not fully understood.

Plasma Membrane

• The plasma membrane is a flexible, semi-permeable barrier that separates a cell's interior from its surroundings.
• The membrane is made of a phospholipid bilayer.
• Certain components within the phospholipid bilayer allow materials to enter and leave the cell.
• Proteins embedded in the membrane perform specific functions, including selective molecule transport and cell-cell recognition.

Organelles

• Listed as organelles (but not all organelles were listed in the text): Nucleus, Plasma membrane, Smooth endoplasmic reticulum, Peroxisome, Lipid bilayer, Mitochondria, Rough endoplasmic reticulum, Lysosome, Golgi complex.

Nucleus

• The nucleus is a large organelle containing genetic information.
• The nucleolus is the largest structure within the nucleus and is involved in ribosome formation and ribosomal RNA synthesis.
• Most cells have at least one nucleus, but some (like mature red blood cells) don't.
• The word "nucleus" is Latin for "little kernel" and its application to cells was first recorded in 1831.

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum (ER) is a network of membrane-enclosed sacs for packaging and transporting materials for cellular growth and related functions.
• The smooth ER extends from the rough ER and synthesizes lipids, steroids, phospholipids, and various metabolic processes.
• The rough ER plays a role in protein packaging and synthesis. The ribosomes on the rough ER are responsible for protein making.

Ribosomes

• Ribosomes contain over 50 proteins and a high concentration of ribosomal RNA (rRNA).
• Ribosomes are responsible for protein synthesis, utilizing proteins for cell function, membrane creation, and other structures.
• Ribosomes can be free-floating in the cytosol, or bound to the rough ER.

Golgi Complex

• The Golgi complex is composed of 3–20 flattened membranous sacs (cisternae).
• It processes proteins produced by the endoplasmic reticulum.
• Enzymes modify the proteins in the sacs of the cisternae.
• Proteins are packaged into transfer vesicles and transported to their destinations within the cell.

Mitochondria

• Mitochondria, or "powerhouses of the cell," are involved in producing ATP (adenosine triphosphate), a vital molecule for energy.
• The amount of mitochondria present in a cell can vary depending on the type of cell and its function, ranging from a few hundred to thousands.
• In the book "A Wind in the Door," mitochondria are depicted as sentient with special structures called "farandolae."

Lysosomes

• Lysosomes contain digestive enzymes that break down substances a cell consumes and recycles waste materials.

Peroxisomes

• Peroxisomes process and neutralize toxins present within a cell.