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Helicase

Cell Explorer

Every living thing is made of cells. Click the parts of a cell to see what each one does, then test yourself.

Eukaryotic cells divide their work among membrane-bound organelles. Explore what each structure does, how it is built, and what happens when it fails.

Compartmentalization lets eukaryotic cells run incompatible chemistry side by side. Explore organelle function, structure, molecular players and disease mechanisms.

Cell BiologyMolecular BiologyPlant Biology
Schematic animal cellNot to scale. Selected structure: Nucleus.

Structures

Schematic drawing, not to scale. Colors only help tell structures apart; every structure is named in the list.

Nucleus

Stores most of the cell's DNA and controls which genes are used.

What it does

The nucleus is the cell's control room. It holds most of the cell's DNA, the instructions for building and running the cell.

The nucleus stores the chromosomes and is where DNA is copied and genes are transcribed into RNA. A double membrane called the nuclear envelope separates it from the rest of the cell, and nuclear pores control what moves in and out.

The nuclear envelope is a double membrane continuous with the endoplasmic reticulum and perforated by nuclear pore complexes, which control the import of proteins and the export of RNA. Inside, chromatin is packaged with histones, and the nucleolus assembles ribosomal subunits. A meshwork of lamin proteins lines and supports the envelope.

Compare all three reading levels
Beginner
The nucleus is the cell's control room. It holds most of the cell's DNA, the instructions for building and running the cell.
Intermediate
The nucleus stores the chromosomes and is where DNA is copied and genes are transcribed into RNA. A double membrane called the nuclear envelope separates it from the rest of the cell, and nuclear pores control what moves in and out.
Advanced
The nuclear envelope is a double membrane continuous with the endoplasmic reticulum and perforated by nuclear pore complexes, which control the import of proteins and the export of RNA. Inside, chromatin is packaged with histones, and the nucleolus assembles ribosomal subunits. A meshwork of lamin proteins lines and supports the envelope.

Structure

Double membrane (nuclear envelope) with pores, chromatin (DNA wrapped around proteins), a dense nucleolus, and a supporting layer of lamin proteins.

Key molecules

  • DNA
  • Histones
  • RNA polymerase
  • Lamins
  • Nuclear pore proteins

When it goes wrong

Educational summaries, not medical advice.

Research

Researchers study how nuclear pores control traffic between the nucleus and cytoplasm.

Search papers about nuclear pore complex

Landmark papers

Sources for this structure

Cells by the numbers

Estimates of how many cells make up a person once ranged across several orders of magnitude. Careful organ-by-organ counts put an adult at roughly 30 to 37 trillion human cells, and about 90 percent of them belong to the blood-forming (hematopoietic) lineage.Source: Sender et al., 2016Source: Bianconi et al., 2013

The same 2016 analysis estimated about 38 trillion bacteria living in and on a 70 kg reference adult, the same order of magnitude as human cells, replacing the often repeated claim of ten bacteria for every human cell.Source: Sender et al., 2016

Knowledge check

In a typical animal cell, which organelle makes most of the ATP?

Knowledge check

Why does the most common cystic fibrosis variant (delta F508) leave cells without working CFTR channels?

Knowledge check

A lysosomal enzyme never receives its mannose-6-phosphate tag. Where does it most likely end up?

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Sources & further reading

The explanations on this page are our own summaries of these sources. Follow a link to read the original; if anything here disagrees with it, the original wins. How we choose and check sources.

  1. Revised estimates for the number of human and bacteria cells in the body (opens the original in a new tab)

    Sender R, Fuchs S, Milo R (2016). PLOS Biology 14:e1002533.

    About 3.0 × 10^13 human cells and 3.8 × 10^13 bacteria in a 70 kg reference adult.

    Peer-reviewedPrimary research
Show 26 more sources