How to view tiny parts of DNA? Make them ‘blink’ | Science News for Students

How to view tiny parts of DNA? Make them ‘blink’

By shining light on genetic material, researchers can get nano-features to identify themselves with a brief glow
Feb 22, 2017 — 1:00 pm EST
chromosome flash

A single chromosome, here, has blinked on brightly, after being excited by light. That light being emitted by the genetic tissue makes internal cellular structures visible without the need for fluorescent dyes.

B. DONG ET AL/PNAS 2016

BOSTON, Mass. — A new technique can home in on parts of a cell that are smaller than 10 nanometers (billionths of a meter) in size without damaging the cell. On February 17, Vadim Backman described how he and his group makes cells do this. They take advantage of DNA’s natural ability to “blink” on when hit with the right color of light.

Backman and Hao Zhang work at Northwestern University in Evanston, Ill. Together, the biomedical engineers found a way to make some materials in a cell briefly shine more brightly than if they had been labeled with one of the most powerful fluorescent chemicals. Their trick: They tickle cells with a particular wavelength — or color — of light.

Backman presented the details, here, at the annual meeting of the American Association for the Advancement of Science. This new approach, he argues, can offer views of genetic material and other cellular parts that had been too small to see without dyes or techniques that might destroy them.

DNA and other proteins don’t naturally glow. So to make them show up in the darkness of a cell, scientists use special dyes that glow. They can attach a dye to the desired molecule in a cell, then flash some light on it. This will “excite” the dye, meaning the light will release some of its energy to the dye. Shortly afterward, the dye will fluoresce — releasing that energy again. But the light that the cell now gives off has a slightly different color. Taking a photo of this light can show biologists what was happening at that moment in a cell’s life cycle.

Backman and Zhang can now make cells glow much the same way — but without the dye. They still shine light on the cells. And if they use the right color, certain proteins inside the cell will become “excited.” Later, they too will blink on, emitting a brief, tell-tale glow.

The researchers call their new process SICLON. It’s short for a very long term: spectroscopic (SPEK-troh-SKOP-ik) intrinsic-contrast photon-localization optical nanoscopy (Naa-NOS-ko-pee).

So far, the engineers have used SICLON to peer at the inner walls of microtubules. These are structures that help separate chromosomes as a cell divides. Their technique has made it possible to resolve structures that are a mere 6.2 nanometers across. For comparison, a DNA molecule is around 3 nanometers wide. Backman says his group hopes their new blinking trick will make it possible to one day image how tiny inner structures change as a cell turns cancerous.

Power Words

(for more about Power Words, click here)

annual     Adjective for something that happens in every year. (in botany) A plant that lives only one year, so it usually has a showy flower and produces many seeds.

biomedical     Having to do with medicine and how it interacts with cells or tissues.

biomedical engineer     An expert who uses science and math to find solutions to problems in biology and medicine; for example, they might create medical devices such as artificial knees.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size. Some organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

chemical     A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

chromosome     A single threadlike piece of coiled DNA found in a cell’s nucleus. A chromosome is generally X-shaped in animals and plants. Some segments of DNA in a chromosome are genes. Other segments of DNA in a chromosome are landing pads for proteins. The function of other segments of DNA in chromosomes is still not fully understood by scientists.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

fluorescent     Capable of absorbing and reemitting light. That reemitted light is known as a fluorescence .

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

life cycle     The succession of stages that occur as an organism grows, develops, reproduces — and then eventually ages and dies.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

optical     An adjective that refers to light or vision.

peer     To look into something, searching for details.

photon     A particle representing the smallest possible amount of light or other electromagnetic radiation.

protein     Compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better-known, stand-alone proteins. Medicines frequently work by latching onto proteins.

wavelength     The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

NGSS: 

  • MS-PS4-2
  • MS-LS1-2
  • HS-PS4-1
  • HS-LS1-1

Citation

Meeting: V. Backman. Label-free super-resolution imaging of chromatin structure and dynamics. American Association for the Advancement of Science annual meeting, Boston, February 17, 2017.

Journal: B. Dong et al. Superresolution intrinsic fluorescence imaging of chromatin utilizing native, unmodified nucleic acids for contrast. Proceedings of the National Academy of Sciences. Vol. 113, August 30, 2016, p. 9716. doi: 10.1073/pnas.1602202113.