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The Effects of UV Light on Yeast Cell

Respiration

Problem-Ultraviolet light is an inherent risk for many terrestrial organisms.-UV light exposure varies due to altitude, shade, and ozone shield.-What cell activities are compromised by UV exposure?

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Ultraviolet Light- Electromagnetic radiation with a wavelength ranging from 100 nm to 400 nm.- Can cause sun burn, lead skin cancer, increase the appearance of aging, harm eyes, and damage DNA.- To prevent these effects, it is suggested to wear sunglasses, hats, protective clothing, and sun screen.- Sources include the sun, tanning beds, and fluorescent lamps.

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Stressed Cells- UV light can stress cells and interfere with their ability to carry out basic functions.- Oxidative stress is a condition where oxidant production increases, free radicals accumulate, and cellular degeneration occurs.

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Yeast- Unicellular eukaryotic micro-organism in the kingdom Fungi.- Common model organism in the research of modern cell biology.- Similar cell cycle, DNA replication, recombination, cell division, and metabolism to humans.- Saccharomyces cerevisiae (baker’s yeast) is a species of budding yeast and is often used in the food industry.

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Aerobic Cellular Respiration- Set of metabolic reactions.- Includes glycolysis, Kreb’s cycle, and the electron transport chain.- Process in which the cell yields energy in the form of ATP.- Substances such as FADH2, NADH, and CO2 are also yielded.

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Aerobic Cellular Respiration (cont.)

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Effects of Different Isomers of Sugar on Yeast Respiration

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PurposeTo determine if ultraviolet light has an effect on the aerobic cellular respiration of Saccharomyces cerevisiae.

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HypothesesHypothesis:

Ultraviolet light will significantly decrease the cellular respiration of yeast.

Null Hypothesis:Ultraviolet light will have no significant effect on the cellular respiration of yeast.

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Materials- Packs of Red Star® Quick

Rise Yeast- 125 mL Erlenmeyer flasks- Party Express helium

quality balloons (9 in.)- Plastic Weigh boats- Sugar- Plastic tubs- Large plastic bin

- 250 mL graduated cylinders- 250 mL graduated cylinders 11

- Laminar Flow Hood UV Light

- Plastic wrap- Water- Deionized water- Pipettes- Incubator- YEPD agar plates (1%

yeast extract, 2% peptone, 2% dextrose, 1.5% sugar)

- Spreader bars- Sterile dilution fluid (SDF)

Procedure1. 4.00 grams of Red Star® Quick Rise yeast granules were spread into a monolayer on the plastic weigh boats.2. Plastic weigh boats were positioned underneath a Laminar Flow Hood UV Light. The different exposure times for each group were 0 seconds, 30, 90, and 150 seconds.3. UV light was turned on and each group of yeast received its designated exposure before being removed.4. 0.60 grams of sugar (sucrose table sugar) and 30.0 mL of deionized water were added to each Erlenmeyer flask.5. Flasks were swirled to dissolve sugar.6. Yeast samples were transferred into flasks with the water and sugar.

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Procedure (cont.)7. Immediately, Party Express helium quality balloons were affixed to the rims of the flasks.8. Flasks were gently swirled to suspend the yeast.9. The flasks were transferred to a 30 °C water bath and incubated for one hour.10. The displacement of water was used to determine the amount of gas produced.(250 mL graduated cylinders were filled with water and inverted into a half filled tub of water. The nozzle of the balloon was pinched and placed in the inverted graduated cylinder. The air from the balloon was released slowly. The volume of the gas was recorded.)

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Pictures of the Experiment

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Procedure (UV Survivorship)1. 0.2 grams of Red Star® Quick Rise yeast granules were spread into a monolayer on the plastic weigh boats.2. Plastic weigh boats were positioned underneath a Laminar Flow Hood UV Light. The different exposure times for each group were 0, 30, 90, and 150 seconds.3. UV light was turned on and each group of yeast received its designated exposure before being removed.4. Yeast was poured into a tube containing 10 mL sterile dilution fluid (SDF).5. After vortexing, serial dilution was performed to yield a countable number of colonies.

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Procedure (UV Survivorship cont.)

8. Solution from tube was spread out into YEPD plates.9. Plates were incubated for one day.10. Colonies in YEPD plates were counted.

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10 mL SDF

YEPD Plates

100 uL

Weigh Boat

UV Stressed Yeast Survivorship

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UV Stressed Yeast Survivorship (cont.)

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UV Exposure Time Selection- The yeast used in finding the effects of UV light on cellular respiration of yeast were granules.- However, the yeast used in UV light survivorship experiments were suspended in fluid and plated.- The granular form is thought to be more resistant to radiation and thus UV exposure range was increased.

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0 30 90 1500

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40

60

80

100

120 106.2594.25 93.75 88.25

The Effects of UV Light on Yeast Respiration

Time of UV Light Exposure (Seconds)

Am

ou

nt

of

CO

2 (

mL

)

P-Value is 0.013807

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Dunnett’s Test Chart

Exposure Times

T Value Interpretation

30 seconds 2.60 Not Significant

90 seconds 2.73 Significant

150 seconds

3.90 Significant

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The T critical value is 2.68.

Respiration and Survivorship(Relative to the Control)

30 seconds

90 seconds

150 seconds

Cell Respiration 88.7% 88.2% 83.1%

Survivorship 103% 83.0% 20.4%

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ConclusionHypothesis: ACCEPTED

The total amount of cellular respiration that occurred in the ultraviolet light exposed yeast samples was significantly less than the amount in the control. However, this could be because the yeast died and the rate of cell respiration was not affected.

Null Hypothesis: REJECTEDThe total amount of cellular respiration that occurred in the yeast samples was significantly affected by the ultraviolet light.

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InterpretationPuzzle (?)Why did the 150 second exposure cells yield such a large volume of CO2? - The data suggests that (1) the cell respiration increased dramatically in the individual cells for that group, or (2) that the cells were able to survive for the short remaining time of the respiration experiment, but did not survive for the one day toxicity incubation.

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Extensions:- Test the effect UV light has on some of the other functions of an organism.- Investigate the effects UV light has on the cell respiration of other organisms.- Observe yeast cell respiration in other potentially harmful circumstances.- Stress the yeast cells, perform the respiration experiment and immediately perform a Trypan Blue exclusion assay.

Limitations:- Amount of time allowed for the yeast to perform cell respiration.- The temperature conditions during the experiment were not ideal for the respiration.- Amount of trials and different UV exposure times.

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Works CitedNelson, Andrew. "Saccharomyces Cerevisiae." BioWeb Home. Web. 22 Jan.

2011. <http://bioweb.uwlax.edu/bio203/s2007/nelson_andr/>.

Bailey, Regina. "Cellular Respiration." Biology. Sat. 15 Jan. 2011. <http://biology.about.com/od/cellularprocesses/a/cellrespiration.htm>.

"UV Radiation." NASA Advanced Supercomputing (NAS) Division Home Page. Web. 15 Jan. 2011. <http://www.nas.nasa.gov/About/Education/Ozone/radiation.html>.

Zeman, Gary. "Ultraviolet Radiation." Health Physics Society. Web. 23 Jan. 2011. <http://www.hps.org/hpspublications/articles/uv.html>.

Schuster, Tom, Rosalie Van, and Harold Coller. "Yeast Respiration." California State University, Northridge. Web. 27 Jan. 2011. <http://www.csun.edu/scied/2-longitudinal/schuster/index.html>.

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