Biology: Cell Structure and Function

Cell Structure and Function

• Cells are the basic units of life, and all living organisms are composed of one or more cells.
• Cells exhibit a remarkable diversity in their shapes and sizes, reflecting their specialized functions.
• Cell structures perform specific functions essential for maintaining life.
• Prokaryotic cells (bacteria and archaea) are simpler, lacking a nucleus and other membrane-bound organelles.
• Eukaryotic cells (plants, animals, fungi, and protists) are complex, possessing a nucleus and a variety of membrane-bound organelles.

Cell Membrane

• The cell membrane, also known as the plasma membrane, is a selectively permeable barrier that encloses the cell's contents.
• It is primarily composed of a phospholipid bilayer interspersed with proteins and cholesterol.
• The phospholipid bilayer provides a hydrophobic barrier that regulates the passage of substances into and out of the cell.
• Membrane proteins play crucial roles in transport, enzymatic activity, cell signaling, and cell adhesion.
• Different kinds of transport mechanisms across the membrane include passive transport (e.g. diffusion, osmosis) and active transport (requiring energy).

Cytoplasm

• The cytoplasm is the jelly-like substance that fills the cell and surrounds the nucleus.
• It contains various organelles – specialized structures that carry out specific functions within the cell.
• Cytosol, the liquid component of cytoplasm, contains water, dissolved ions, small molecules, and macromolecules.
• Cytoskeleton – a network of protein fibers (microfilaments, intermediate filaments, microtubules) in the cytoplasm which gives shape to the cell, and enables movement.

Nucleus

• The nucleus is the control center of the cell, containing the cell's genetic material (DNA).
• It is enclosed by a double membrane, the nuclear envelope, with pores that regulate the passage of substances between the nucleus and cytoplasm.
• Within the nucleus is the nucleolus, a region involved in ribosome biogenesis.
• The DNA in the nucleus is organized into tightly coiled structures called chromosomes.

Organelles

• Mitochondria are the "powerhouses" of the cell, generating ATP (energy) through cellular respiration.
• Ribosomes are responsible for protein synthesis.
• Endoplasmic reticulum (ER) is a network of membranes involved in protein synthesis, folding, and transport.
• Golgi apparatus modifies, sorts, and packages proteins.
• Lysosomes contain digestive enzymes, breaking down waste and cellular debris.
• Vacuoles, primarily in plant cells, store water, nutrients, and waste products.
• Peroxisomes contain enzymes that detoxify harmful substances.
• Chloroplasts (only in plants) are responsible for photosynthesis converting light energy into chemical energy.

Cell Division

• Cell division is a fundamental process enabling growth, repair, and reproduction in organisms.
• Two main types of cell division are mitosis (for somatic cells) and meiosis (for gametes).
• Mitosis results in two genetically identical daughter cells from a single parent cell.
• Meiosis results in four genetically diverse daughter cells (gametes) from a single parent cell.

Cell Communication

• Cells communicate with each other through various mechanisms, including direct contact, signaling molecules, and receptor proteins.
• These interactions are essential for coordinating cellular activities and maintaining homeostasis.