Cell Biology Overview

Cell Biology

• Cells are the fundamental units of all living things, primarily composed of carbon, oxygen, hydrogen, and nitrogen.
• Cells, as individual units, work together to form tissues and organs, enabling coordinated functions.
• New cells form through cell division and differentiation, responding to internal and external changes within the body.
• Human cells are categorized by size, shape, and function.
• There are two main cell types: germ cells (sperm and oocytes) and somatic cells (all other cells).
• Germ cells transmit genetic information to offspring, while somatic cells, including skeletal, muscle, blood, organ and tissue cells, ensure diverse functions within the organism.
• Somatic cells are diploid (46 chromosomes in humans), while germ cells are haploid (23 chromosomes in humans).
• Mutations in somatic cells don't affect offspring, but mutations in germ cells can be passed to the next generation.
• Red blood cells (erythrocytes) carry oxygen and dispose of carbon dioxide.
• White blood cells (leukocytes) defend against pathogens.
• Blood cells comprise various types like neutrophils, eosinophils, basophils, monocytes, and lymphocytes.

Plasma Membrane

• The plasma membrane forms a barrier between the inside (intracellular fluid) and outside (extracellular fluid) of a cell.
• It's a flexible membrane composed primarily of a phospholipid bilayer with embedded proteins.
• Phospholipids have hydrophobic tails (water-fearing) and hydrophilic heads (water-loving), spontaneously organizing into a bilayer in water.
• The membrane allows for the passage of small molecules (oxygen, carbon dioxide, water) while regulating the passage of larger molecules (amino acids, sugars).
• Membrane proteins perform various functions like transportation of molecules across the membrane.

Membrane Proteins

• Membrane proteins are crucial components of cell membranes.
• They are categorized as intrinsic (permanently embedded) and extrinsic (loosely attached).
• Intrinsic proteins often span the membrane, forming channels or assisting with the movement of ions and molecules across the membrane; these include transmembrane proteins.
• Extrinsic proteins, also known as peripheral proteins, are located on the surface and interact with other proteins or membrane components, frequently participating in signaling processes.

Transport Across a Cell Membrane

• Substances move across membranes through passive transport (no energy required) or active transport (requires energy).
• Passive transport includes diffusion, which substances move down a concentration gradient.
• Active transport involves moving substances against a concentration gradient, often requiring energy (ATP).
• Other transport mechanisms include facilitated diffusion and vesicular transport (bulk transport).
• Vesicular transport includes endocytosis (materials move into the cell) and exocytosis (materials move out of the cell), transporting large substances or materials.

Endocytosis

• It's an active transport mechanism that moves materials into a cell.
• Phagocytosis ("cell eating") engulfs large particles.
• Pinocytosis ("cell drinking") takes in small amounts of extracellular fluid.
• Receptor-mediated endocytosis captures specific target molecules using receptor proteins on the cell surface.

Exocytosis

• It's an active transport process for moving materials out of the cell.
• Materials are enclosed in vesicles that fuse with the plasma membrane, releasing their contents outside.

Transcytosis

• It's a combination of endocytosis and exocytosis.
• Active transport that takes materials across the cell via vesicles.

Cytoplasm

• The cytoplasm encompasses everything within a cell's membrane except the nucleus.
• Cytosol (the intracellular fluid) is a fluid medium for cellular activities.
• Cytoplasm involves a network of organelles.

Nucleus

• The nucleus is the control center of the cell and contains most of the genetic material (DNA).
• It is surrounded by a double membrane called the nuclear envelope.
• Nucleolus, a dense region within the nucleus, is crucial for ribosome production.
• Chromatin consists of DNA organized with proteins into a complex structure to be stored efficiently.

DNA & RNA

• DNA carries genetic instructions for making proteins.
• RNA is involved in the protein synthesis process.
• RNA acts as a messenger to transmit information from DNA in the nucleus to ribosomes in the cytoplasm.

Cell Cycle

• Cells divide to produce new cells via a complex process called the cell cycle
• Interphase involves growth, DNA replication, and routine cellular functions.
• Mitosis is the process of nuclear division resulting in two genetically identical daughter cells.
• Cytokinesis is the division of the cytoplasm following mitosis.
• Meiosis involves two rounds of division, producing four genetically diverse haploid daughter cells, essential for sexual reproduction.

Mitochondria

• Mitochondria are often called the powerhouse of the cell, a primary site for cellular respiration.

Cell Organelles

• Various organelles (compartments) have specific functions within the cell.
• Organelles include the Endoplasmic Reticulum (smooth and rough), Golgi apparatus, lysosomes, centrioles, vacuoles, and vesicles.