EXPLAINER: How do cells know when they’re fully grown?

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Scientists unlock the key to cell size regulation – and it’s all in the DNA.

How do cells regulate their size? UK researchers have answered this long-standing question in biology. Turns out, they use their DNA content as an internal scale to check how big they are.

Use this explainer resource to investigate how cells regulate their size. This resource is best suited to Year 8 and 10 Biology students looking for applications of learning about cells and their features.

A short video is included to help with explanations.

Word count / Video Length: 512 / 1:22 mins

Cells marked in green are about to enter DNA replication, whilst the magenta marker shows accumulation of KRP4, which is part of the mechanism that regulates cell size. Credit: John Innes Centre

Cells are the building blocks of life, and like life itself they come in all shapes and sizes. Most eukaryotic cells range between one and 100 micrometres, while neurons, for example, are thin cells that reach up to several centimetres long. Eggs are actually single cells – ostrich eggs are the biggest of all, spanning up to 13 centimetres in diameter.

Each type of cell has a characteristic size that it reaches before it divides into two daughter cells to reproduce. Biologists have long wondered how cells know when they have reached this threshold.

In a new study published in Science, researchers from the John Innes Centre in the UK set out to answer the question of “how do cells regulate their size?”  by looking at the growing tips of plants, where new meristem cells are created to make leaves, flowers and stems.

Following the growth and division of these cells over time, the team found that although cells might start life with different sizes, they all reached a consistent size by the time they were ready to replicate their DNA and split into two.

A series of cells showing the mitosis division of eukaryotic cells. Credit: Wikimedia Commons

Delving deeper, the researchers found that regardless of initial size, each cell is born with the same amount of the KRP4 protein. This protein’s role is to delay the start of DNA replication. This means that if a cell is born too small, the protein will delay the DNA replication for longer and give the cell time to catch up and grow to the right size – and vice versa for cells born too big.

To make sure every cell starts off with the same amount of KRP4, this protein hitches a ride on the DNA when a cell splits into two, and any excess KRP4 not bound to the DNA is destroyed by another protein called FBL17. This means the identical newborn cells inherit equal amounts of KRP4.

“It has been suggested for a long time that DNA could be used as a scale for cell size, but it was unclear how cells could read the scale and use the information,” explains co-author of the study, Robert Sablowski.

How, he asks, can a cell know how much it has grown when most of its components increase at the same rate, so can’t be as a fixed comparison?

“One exception is DNA, which exists in the cell in a discrete amount – its amount precisely doubles before cell division, but it does not vary with cell growth,” Sablowski explains.

How do cells regulate their size? “The key is to use the DNA as a template to accumulate the right amount of a protein, which then needs to be diluted before the cell divides. It’s exciting to come across such a simple solution to a long-standing problem.”

Watch the explainer video below:

This article was initially published on Cosmos. Read the original article here.

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Years: 8 and 10


The Body

Additional: Careers, Technology.

Concepts (South Australia):

Biological Sciences – Form and Function


8 & 10
Learning Connections

Student Skill Summary

Australian Curriculum Connections - Version 8.4

Sub StrandYear LevelKey IdeaConcept - ACConcept - SAContent TopicContent CodeContent Descriptor
Biological Sciences10Form and functionDiversity and Evolution | Structure and FunctionDiversity and Evolution | Form and FunctionDNA, Genetics and HereditaryACSSU184Transmission of heritable characteristics from one generation to the next involves DNA and genes
ACSSU149Cells are the basic units of living things; they have specialised structures and functions
ACSSU150Multi-cellular organisms contain systems of organs carrying out specialised functions that enable them to survive and reproduce
Sub StrandYear LevelContent TopicContent CodeContent Descriptor
Nature and Development of Science8Scientific Knowledge Changes Our Understanding of the WorldACSHE134Scientific knowledge has changed peoples’ understanding of the world and is refined as new evidence becomes available
10Refinement of Scientific Understanding, Models and Theories EvolvesACSHE191Scientific understanding, including models and theories, is contestable and is refined over time through a process of review by the scientific community
10Advancements in Scientific Understanding Rely on Technological AdvancementsACSHE192Advances in scientific understanding often rely on technological advances and are often linked to scientific discoveries
Use and Influence of Science8Use of Science Understanding and Skills in OccupationsACSHE136People use science understanding and skills in their occupations and these have influenced the development of practices in areas of human activity