Cell Biology (IB)

Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells.

Cell theory

Cell theory

Proposed by Mathias Schleiden, Theodore Schwann, and Rudolf Virchow, it states that all living organisms are composed of cells and their products, the cell is the basic unit of structure and function in living organisms, and all cells arise from pre-existing cells.

Functions of life

The various functions that a cell carries out, including metabolism (sum of all chemical reactions in the body), catabolism (energy-releasing processes that break down complex molecules), anabolism (energy-requiring processes that build complex molecules), and control and regulation of chemical reactions in the body.

Response

An action, behavior, or answer that follows a particular stimulus or situation, which can be voluntary, involuntary, or dependent on conscious control.

Homeostasis

The body's natural ability to maintain internal stability and balance, ensuring that the internal environment remains stable despite external changes.

Growth

One of the essential characteristics of living organisms, occurring at the cellular, tissue, organ, and organismal levels.

Reproduction

The biological process by which new individuals of the same species are produced, ensuring the survival and continuation of the species.

Excretion

The process of eliminating waste products and excess substances from the body.

Nutrition

The process by which organisms obtain and utilize the nutrients and substances necessary for their growth.

Surface and Volume ratio

As a cell grows in size, its surface area-to-volume ratio decreases, affecting the cell's ability to exchange materials with its environment.

Magnification

The process of enlarging an object or image to make it appear larger than its actual size, commonly used in optics and microscopy.

Emergent Properties

Characteristics or behaviors that arise in complex systems but are not evident in their individual components, allowing multicellular organisms to perform functions that unicellular organisms cannot.

Cell Differentiation

The development and maintenance of multicellular organisms, involving the transformation of unspecialized or stem cells into specialized cell types.

Gene Packaging

The organization and compaction of genetic material within the nucleus of eukaryotic cells, involving euchromatin (active genes) and heterochromatin (inactive genes).

Stem cells

Unspecialized, undifferentiated cells with the ability to develop into various specialized cell types, characterized by self-renewal and pluripotency/multipotency.

Stem Cell Therapy

The use of stem cells to treat various diseases, injuries, and medical conditions, based on their ability to self-renew and differentiate into different cell types.

Microscopes

Essential scientific instruments that enable the observation of objects and structures at a microscopic level, revealing details not visible to the naked eye.

Electron Microscopes

These use focused beams of electrons to achieve higher magnification and resolution, including transmission electron microscopes (TEM) and scanning electron microscopes (SEM).

Confocal Microscopes

These use lasers and pinhole apertures to create sharp, three-dimensional images, often used in biological and medical research.

Magnification

The increase in the apparent size of an object achieved by a microscope.

Resolution

The ability to distinguish between closely spaced objects, which is improved by higher magnification and resolution.

Cell Scale

The metric used to measure the size of cells.

Prokaryotes

Primitive, small, and simple organisms that lack a distinct nuclear compartment and membrane-bound organelles.

Bacteria

The primitive organisms that are classified based on shape into four types:cocci (spherical), bacilli (rod-shaped), spirillum (spiral-like), and vibrio (comma-shaped).

Archaebacteria

Special organisms that can survive in extreme habitats such as salty, marshy, and hot spring environments.

Eukaryotes

Advanced and complex organisms that have a distinct nuclear compartment and membrane-bound organelles.

Flagella

Slender whip-like structures used for locomotion in prokaryotic cells.

Pili and Fimbriae

Structures in prokaryotic cells that aid in attachment to substrates.

Cell Wall

Provides structural support and protection against damage in prokaryotic cells.

Cell Membrane

Provides protection and allows the movement of substances in and out of cells in prokaryotic cells.

Ribosome

Responsible for protein synthesis in prokaryotic cells.

Plasmid

Extra-chromosomal DNA in prokaryotic cells that can contain antibiotic resistance genes and be used as a vector for genetic engineering.

Capsule

Protects prokaryotic cells from chemical and dry environments.

Nucleus

Stores the cell's hereditary material, DNA, and coordinates the cell's activities in eukaryotic cells.

Cytoplasm

The contents of the cell located between the plasma membrane and the nuclear membrane in eukaryotic cells.

Mitochondria

Known as the "powerhouse" of the cell, responsible for breaking down sugar molecules to release ATP, the energy currency of cells, and regulating cellular metabolism in eukaryotic cells.

Endoplasmic Reticulum

A structural framework involved in the production and processing of proteins, carbohydrates, and lipids in eukaryotic cells.

Golgi Apparatus

Modifies proteins synthesized by ribosomes and is the site of formation of glycoproteins and glycolipids in eukaryotic cells.

Lysosomes

Contain lytic enzymes and are responsible for intracellular digestion and the destruction of certain organelles during development in eukaryotic cells.

Cytoskeleton

Provides mechanical support, motility, and maintenance of cell shape in eukaryotic cells.

Centrosome and Centriole

Centrioles form the basal body of cilia, flagella, and spindle fibers involved in cell division in animal cells.

Chloroplast

Helps in photosynthesis and is only present in plant cells.

Cell Wall

Maintains cell shape and prevents cell bursting, only present in plant cells.

Plant Cell

A type of eukaryotic cell that has a cell wall, chloroplasts, and lacks centrioles, with a large vacuole located in the center of the cell and a nucleus located at the side of the cell.

Animal Cell

A type of eukaryotic cell that lacks a cell wall and chloroplasts, contains centrioles, has a small vacuole, and has a nucleus located in the center of the cell.

Prokaryotic Cell

A primitive cell that is generally small in size, lacks a nucleus, has a single circular chromosome, and lacks membrane-bound organelles.

Eukaryotic Cell

A true nucleus-containing cell that is generally larger in size, has a nucleus, lacks plasmids, has a nucleolus, and contains membrane-bound organelles.

Cell Membrane

The outermost layer in animals and the second most layer after the cell wall in plants, composed of a phospholipid bilayer with embedded proteins.

Lipid Bilayer

The main component of the cell membrane, composed of phosphoglycerides, sphingolipids, and sterols, forming a two-dimensional fluid structure.

Membrane Proteins

Responsible for performing most of the membrane's specific tasks, they are amphiphilic and can be transmembrane proteins, located entirely in the cytosol, or peripheral membrane proteins.

Carbohydrates

Oligostructures of glycolipids and glycoproteins on the outer surface of the plasma membrane involved in cell-to-cell recognition mechanisms.

Selective Permeability

Membranes are selectively permeable, allowing certain substances to pass while restricting others, determined by factors such as molecular size, charge, and lipid solubility.

Passive Transport

Occurs without the input of energy, primarily through diffusion, which can be simple diffusion or facilitated diffusion.

Active Transport

Requires the expenditure of energy, usually ATP, to move molecules against their concentration gradient, can be primary active transport or secondary active transport.

Endocytosis

The process by which cells engulf substances from the extracellular environment by forming vesicles.

Exocytosis

The process by which vesicles fuse with the membrane, releasing their contents into the extracellular space.

Membrane Potential

The voltage difference across the cell membrane, usually maintained by ion concentration gradients and crucial for cellular functions.

Transporters

Integral membrane proteins that facilitate the movement of specific molecules across the membrane through active or passive mechanisms.

Symport

The transport of two different molecules in the same direction.

Antiport

The transport of two different molecules in opposite directions.

Uniport

The transport of a single molecule or ion.

Ion Channels

Specialized membrane proteins that allow the selective passage of ions across the cell membrane.

Voltage-gated ion channels

These channels open or close in response to changes in the membrane potential.

Ligand-gated ion channels

These channels open or close in response to the binding of specific molecules (ligands) to the channel.

Mechanically-gated ion channels

These channels open or close in response to mechanical stimuli such as pressure or stretch.

Leak channels

These channels are always open, allowing a small and constant flow of ions across the membrane.

Ion Selectivity

Ion channels exhibit selectivity for specific ions based on their size, charge, and hydration.

Conductance

The ability of an ion channel to allow the flow of ions.

Permeability

The measure of the ease with which ions can pass through a channel.

Resting Membrane Potential

The electrical potential difference across the cell membrane when the cell is at rest.

Action Potentials

Rapid and transient changes in the membrane potential that allow for long-range communication in excitable cells.

Depolarization

A change in the membrane potential towards a more positive value.

Repolarization

The process of returning the membrane potential back to its resting state after depolarization.

Refractory Period

A period during which the membrane is temporarily unresponsive to further depolarization stimuli.

Saltatory Conduction

The jumping of action potentials from one node of Ranvier to the next in myelinated neurons.

Synaptic Transmission

The release of neurotransmitters from the presynaptic neuron, which then bind to receptors on the postsynaptic neuron.

Abiogenesis

The scientific theory proposing the natural, non-biological origin of life from simple organic compounds.

Biogenesis

The concept that living organisms can only arise from pre-existing living organisms.

Cell Cycle

The highly regulated process that ensures proper cell growth, DNA replication, and cell division.

Interphase

The longest phase of the cell cycle where the cell grows, carries out its normal functions, and replicates its DNA.

Mitotic Phase

The phase of the cell cycle involving the actual division of the cell into two daughter cells.

Cytokinesis

The final stage of the cell cycle where the cytoplasm divides and two daughter cells are formed.

Cell-Cycle Control System

A complex network of molecular checkpoints and regulatory mechanisms that ensure the orderly progression of the cell cycle.

Meiosis

A specialized form of cell division that occurs in sexually reproducing organisms, resulting in the production of gametes.

Meiosis I

The first division of meiosis, involving the pairing and separation of homologous chromosomes.

Meiosis II

The second division of meiosis, similar to mitosis, where the sister chromatids of each chromosome separate.

Crossing Over

The exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis I.

Anaphase I

The stage of meiosis I where homologous chromosomes separate and move towards opposite poles of the cell.

Telophase I

The stage of meiosis I where chromosomes arrive at the poles, start decondensing, and nuclear envelopes may form around each group of chromosomes.

Meiosis II

The second division of meiosis, similar to a mitotic division, consisting of prophase II, metaphase II, anaphase II, and telophase II.

Prophase II

The stage of meiosis II where chromosomes condense and the nuclear envelope disintegrates.

Metaphase II

The stage of meiosis II where individual chromosomes line up along the equator of the cell, without homologous pairs.

Anaphase II

The stage of meiosis II characterized by the separation of sister chromatids, with each chromatid being pulled towards opposite poles of the cell.

Telophase II

The stage of meiosis II where chromosomes arrive at the poles, start decondensing, and nuclear envelopes may form around each set of chromosomes.

Cytokinesis

The process of dividing the cytoplasm, resulting in the formation of two haploid daughter cells in meiosis I and four haploid daughter cells in meiosis II.

Haploid

Having a single set of chromosomes, as in the daughter cells produced at the end of meiosis II.

Genetic diversity

The result of meiosis II, where the four haploid daughter cells are genetically distinct from one another and the parent cell.