Cell Biology Cheat Sheet

The core ideas of Cell Biology distilled into a single, scannable reference — perfect for review or quick lookup.

PiqCue — piqcue.com/cell-biology/cheatsheet

Quick Reference

Cell Theory

The foundational principle of biology stating that all living organisms are composed of cells, the cell is the basic structural and functional unit of life, and all cells arise from pre-existing cells through division. This theory, formulated in the 19th century, unified biology and provided a framework for understanding life at its most fundamental level.

Cell Membrane

A selectively permeable phospholipid bilayer that surrounds every cell, controlling the passage of substances into and out of the cell. It contains embedded proteins that serve as channels, receptors, and enzymes, enabling the cell to interact with its environment and maintain homeostasis.

Mitochondria

Double-membrane-bound organelles often called the powerhouses of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP) through oxidative phosphorylation. Mitochondria possess their own circular DNA and ribosomes, supporting the endosymbiotic theory of their evolutionary origin from ancient bacteria.

DNA Replication

The biological process by which a cell copies its entire genome before cell division, ensuring each daughter cell receives a complete and accurate set of genetic instructions. The process is semiconservative, meaning each new DNA molecule consists of one original strand and one newly synthesized strand.

Mitosis

A type of cell division that produces two genetically identical daughter cells from a single parent cell, used for growth, repair, and asexual reproduction in eukaryotic organisms. It proceeds through defined phases: prophase, metaphase, anaphase, and telophase, followed by cytokinesis.

Meiosis

A specialized form of cell division that reduces the chromosome number by half, producing four genetically unique haploid gametes from a single diploid cell. It involves two successive divisions and incorporates crossing over and independent assortment to generate genetic diversity.

Endoplasmic Reticulum

An extensive network of membrane-enclosed tubules and flattened sacs connected to the nuclear envelope, existing in two forms: rough ER (studded with ribosomes for protein synthesis and processing) and smooth ER (involved in lipid synthesis, detoxification, and calcium storage).

Cell Signaling

The complex system of communication that governs basic cellular activities and coordinates cell actions. Cells detect and respond to chemical signals from their environment through signal transduction pathways, which convert extracellular signals into intracellular responses such as gene expression changes or metabolic adjustments.

Apoptosis

A highly regulated and orderly process of programmed cell death that eliminates damaged, infected, or unnecessary cells without triggering inflammation. It is essential for development, tissue homeostasis, and immune function, and its dysregulation is implicated in cancer and autoimmune diseases.

Stem Cells

Undifferentiated cells with the unique ability to self-renew through mitotic division and to differentiate into specialized cell types. They are classified by potency: totipotent cells can become any cell type including placental tissue, pluripotent cells can form any body cell, and multipotent cells are restricted to certain lineages.

Key Terms at a Glance

Cell:The fundamental structural and functional unit of all living organisms, bounded by a membrane and containing genetic material and the molecular machinery needed for metabolism, growth, and reproduction.

Organelle:A specialized membrane-bound or non-membrane-bound structure within a eukaryotic cell that performs a specific function, such as the nucleus, mitochondria, endoplasmic reticulum, or Golgi apparatus.

Nucleus:The large, membrane-enclosed organelle that contains the cell's chromosomal DNA and controls gene expression, DNA replication, and cell division. It is surrounded by a double-membrane nuclear envelope with nuclear pores.

Chromosome:A structure of tightly coiled DNA wrapped around histone proteins that carries genetic information. Humans have 46 chromosomes (23 pairs), with one set inherited from each parent.

Phospholipid Bilayer:The fundamental structural component of cell membranes, consisting of two layers of phospholipid molecules with hydrophilic heads facing outward and hydrophobic tails facing inward, creating a selectively permeable barrier.

Ribosome:A molecular machine composed of ribosomal RNA and proteins that translates messenger RNA into polypeptide chains (proteins). Ribosomes can be free in the cytoplasm or bound to the rough endoplasmic reticulum.

Golgi Apparatus:A stack of flattened membrane-bound sacs (cisternae) that modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum for transport to their final intracellular or extracellular destinations.

Lysosome:A membrane-bound organelle containing hydrolytic enzymes that digest macromolecules, old cell parts, and microorganisms at an acidic pH. Dysfunction of lysosomes can lead to lysosomal storage diseases.

Cytoskeleton:A dynamic network of protein filaments (microfilaments, intermediate filaments, and microtubules) that gives the cell shape, enables movement, and facilitates intracellular transport and cell division.

Endocytosis:The process by which cells internalize substances from the external environment by engulfing them in vesicles formed from the plasma membrane. Types include phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Exocytosis:The process by which intracellular vesicles fuse with the plasma membrane and release their contents into the extracellular space. It is used for secretion of hormones, neurotransmitters, and waste products.

Chromatin:The complex of DNA and histone proteins found in the nucleus of eukaryotic cells. Chromatin can exist in a loosely packed form (euchromatin, transcriptionally active) or a densely packed form (heterochromatin, largely inactive).

Enzyme:A biological catalyst, typically a protein, that accelerates chemical reactions in the cell by lowering the activation energy. Enzymes are highly specific and are regulated by factors such as temperature, pH, and inhibitors.

ATP (Adenosine Triphosphate):The primary energy carrier molecule in cells, consisting of adenine, ribose, and three phosphate groups. Energy is released when the terminal phosphate bond is hydrolyzed, converting ATP to ADP and inorganic phosphate.

Diffusion:The passive movement of molecules from a region of higher concentration to a region of lower concentration, driven by kinetic energy. No cellular energy is required, and the process continues until equilibrium is reached.

Get study tips in your inbox

We'll send you evidence-based study strategies and new cheat sheets as they're published.

We'll notify you about updates. No spam, unsubscribe anytime.