# Cell Biology 101: Cells, DNA and Genetics Explained

This page is a map of the basics. Each section below covers one part of introductory cell biology in the order most courses teach it, with a link to a full guide for every topic. If you are new to biology, read the sections top to bottom. If you are revising for a test, jump to the topic you need.

## Key Takeaways

- Every living thing is made of one or more cells, and every cell comes from an existing cell. That is cell theory, and the rest of biology builds on it.
- Organelles split the work of a eukaryotic cell: the nucleus stores DNA, ribosomes make proteins, and mitochondria and chloroplasts handle energy.
- DNA carries genetic information. Cells copy it before they divide, transcribe it into RNA, and translate that RNA into protein.
- Genetics and evolution explain how traits pass from parents to offspring and how populations change over generations.

## 1. What a Cell Is

- [The 3 parts of cell theory](/blog/guides/3-parts-of-cell-theory-explained-simply): the three statements every biology course starts with, and who proposed them.
- [Levels of organization](/blog/careers/levels-of-organization-biology): how cells build tissues, organs, organ systems and organisms.
- [Animal vs plant cells](/blog/guides/animal-vs-plant-cell-key-differences-compared): the cell wall, chloroplasts and large central vacuole that set plant cells apart.
- [Parts of a plant cell](/blog/guides/label-a-plant-cell-diagram-and-parts-explained): each structure and what it does.

## 2. Organelles and Their Jobs

- [Cell organelles](/blog/guides/cell-organelles): an overview of the structures inside a eukaryotic cell.
- [Nucleus vs nucleolus](/blog/guides/nucleus-function-roles-of-nucleus-and-nucleolus): where DNA is stored and where ribosomes are assembled.
- [Ribosomes](/knowledge/molecular-biology/ribosome-definition): the machines that build proteins.
- [Endoplasmic reticulum](/blog/guides/endoplasmic-reticulum-cell-function): rough ER for protein folding, smooth ER for lipids.
- [Lysosomes](/knowledge/molecular-biology/what-does-a-lysosome-do-function-and-enzymes): the cell's digestive compartment.
- [Vacuoles](/blog/guides/job-of-vacuole-functions-in-plant-and-animal-cells): storage and turgor pressure in plant and animal cells.
- [Chloroplasts](/blog/guides/chloroplast-function-role-in-photosynthesis): where photosynthesis happens.
- [Cytoplasm](/blog/guides/cytoplasm-role-functions-in-cell-biology): the fluid and structures between the membrane and the nucleus.

## 3. The Cell Membrane and Transport

- [Cell membrane function](/blog/guides/cell-membrane-function-biology): how the membrane controls what enters and leaves.
- [The fluid mosaic model](/blog/guides/fluid-mosaic-model-definition-and-key-components): the standard picture of membrane structure.
- [Passive transport](/blog/guides/passive-transport-diffusion-osmosis-and-types): diffusion, facilitated diffusion and osmosis.
- [Active transport and the sodium-potassium pump](/blog/guides/sodium-potassium-pump-active-transport-explained): moving molecules against a gradient with ATP.

## 4. Energy: Respiration and Photosynthesis

- [Cellular respiration](/knowledge/molecular-biology/what-is-cellular-respiration-stages-and-atp-yield): the stages and how much ATP each one makes.
- [Glycolysis](/knowledge/molecular-biology/glycolysis-pathway-steps-and-where-it-occurs): the first stage, in the cytoplasm.
- [Light-dependent reactions](/blog/guides/light-dependent-reactions-photosynthesis-explained): how chloroplasts capture light energy.
- [Photosynthesis diagram](/blog/guides/photosynthesis-diagram-light-and-dark-reactions): the light and dark reactions side by side.

## 5. Cell Division

- [Prophase and the stages of mitosis](/blog/guides/mitosis-prophase-stages-and-key-events): what happens to chromosomes at each step.
- Each phase in detail: [interphase](/blog/guides/interphase), [metaphase](/blog/guides/metaphase), [anaphase](/blog/guides/anaphase), [telophase](/blog/guides/telophase) and [cytokinesis](/blog/guides/cytokinesis).
- [Chromatid vs chromosome](/blog/guides/sister-chromatid-vs-chromosome-key-differences): how to count each before and after replication.
- [Cell cycle checkpoints](/knowledge/diagnostics/emerging-tech/cell-cycle-checkpoints-a-guide-to-g1-g2-and-m-phase-regulation): how the cell checks itself at G1, G2 and M.

## 6. DNA and How It Is Copied

- [What is DNA?](/blog/guides/what-is-dna): its meaning, structure and function.
- [Nucleotide diagram](/knowledge/molecular-biology/nucleotide-diagram): the phosphate, sugar and base that make up each unit.
- [The double helix](/knowledge/molecular-biology/describe-a-double-helix): how two strands pair and twist.
- [DNA vs RNA](/blog/guides/dna-vs-rna-structure): structural and functional differences.
- [Semiconservative replication](/knowledge/molecular-biology/semiconservative-replication): why each new DNA molecule keeps one old strand.
- [The replication fork](/blog/guides/dna-replication-fork): the leading and lagging strands.

## 7. From Gene to Protein

- [Transcription](/knowledge/molecular-biology/transcription-explained): copying a gene from DNA into RNA.
- [Where transcription takes place](/knowledge/molecular-biology/where-does-transcription-occur-cell-locations): nucleus in eukaryotes, cytoplasm in prokaryotes.
- [Translation](/blog/careers/translation-biology-def): reading mRNA to build a protein.
- [Protein synthesis](/blog/guides/protein-synthesis-diagram-labeled): transcription and translation as one process.

## 8. Genetics and Evolution

- [Alleles](/blog/guides/allele-biology-definition): the different versions of a gene.
- [How to use a Punnett square](/blog/research-skills/how-to-use-a-punnett-square), or try the [Punnett square calculator](/tools/punnett-square-calculator).
- [Mutations](/blog/guides/biology-definition-of-mutation): changes in DNA sequence and their effects.
- [Natural selection](/blog/guides/natural-selection-biology): how heritable traits that help survival become more common.
- [Gene flow vs genetic drift](/blog/guides/gene-flow-vs-genetic-drift): two other forces that change allele frequencies.

## Frequently Asked Questions

### What should I learn first in cell biology?

Start with cell theory and the parts of a cell, then the membrane, then energy, division, DNA and genetics. Each topic depends on the one before it, which is why the sections above follow that order.

### What is the difference between prokaryotic and eukaryotic cells?

Eukaryotic cells keep their DNA inside a nucleus and have membrane-bound organelles. Prokaryotic cells, such as bacteria, have no nucleus and no membrane-bound organelles, and their DNA sits in a region of the cytoplasm called the nucleoid.

## References and Further Reading

<a id="ref-1"></a>[<a href="#ref-1">1</a>] Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. [NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK21054/)

<a id="ref-2"></a>[<a href="#ref-2">2</a>] Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. [NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK9839/)