Beadle Tatum Experiment WS PDF

Preview

Summary

Notes...

Description

SBI4U1/3/6

Beadle and Tatum’s One Gene One Enzyme Hypothesis

Molecular Genetics

http://www.dnalc.org/view/16360-Animation-16-One-gene-makes-one-protein-.html http://wps.prenhall.com/wps/media/objects/1552/1589869/web_tut/21_04/21_04_01a.swf

Background Bread mold Neurospora crassa is a simple organism that has a short life cycle. Other than water and oxygen, the mold spores require access to only a few biological substances to live and grow: salts, sugar and vitamin biotin. Thus this assumes that mold can synthesize all the other vitamins and other nutrients (e.g. amino acids) on their own. Type of medium Complete (enriched) Minimal

Supplemented

Description of medium

Content of medium

Contains everything that any cell could possibly need to survive. Contains just the minimal nutrients essential for growth. A minimal media where one nutrient has been added to test whether the nutrient is essential to survival.

Experiment 1 Part A - Selection: Isolating mutated spores 1. Subjected mold (spores) to x-ray. X-rays will damage DNA producing mutants. 2. Grew spores on complete medium (first row of test tubes). 3. Transferred spores to minimal medium (second row of test tubes). Result: Spores grew in both media in 298 test tubes. On the 299th test tube, spores only grew in the complete medium and not in the minimal medium.

Questions A. With spores that could grow in both the complete and minimal media, was their DNA damaged by x-rays? Explain your answer.

B. What conclusion would you make when the spores grew in the complete medium but didn’t grow in the minimal medium?

C. As a scientist, what would you test next with the spores that grew in the complete medium but not in the minimal medium?

Part B - Supplementation: Identifying the missing nutrient 4. Took the mutated spore and transferred it into minimal medium that was supplemented with one additional nutrient. a. What did they observe? b. What does this imply? 5. Took the mutated spore and transferred it into minimal medium that was supplemented with one specific type of vitamin. a. What did they observe? b. What does this imply?

Questions D. How do these results support Archibald Garrod’s hypothesis that inherited disease is due to an inability to make an enzyme?

Experiment 2 Beadle and Tatum continued to mutate spores. Using their method of selection and supplementation they isolated many different types of mutants. Genetic mutations affect metabolic pathways, and they confirmed the synthesis pathway for many vitamins and amino acids. For example, the amino acid arginine is synthesized in a step -wise process catalyzed by enzymes. Their most famous experiment found in most senior biology textbooks is their arginine metabolic pathway mutants. The result from this experiment is below. Each mutant was grown in minimal medium with various supplements. Positive sign (+) means spores grew. Negative sign (-) means spores did not grow. Supplement None Arginine Precursor Citrulline Ornithine

Arginine mutant X + + +

Arginine mutant Y + -

Arginine mutant Z + + -

Each of the supplements are part of the arginine production pathway. Thus the supplements are all substrates in an enzymatic reaction that eventually lead to the production of arginine. The pathway is linear, and the catalysis of one substrate results in a product that becomes the substrate for the next reaction. Given the results, determine where each supplement falls in the arginine pathway by filling in the boxes below with the correct supplement (substrate).

→

→

→

Arginine

Since the mutation is due to a change in the genetic information which affects enzyme function, each mutant should affect one of the enzymatic reactions (substrate → product). Determine which mutant is affecting each of the enzymatic reaction by writing the mutant letter (X, Y, Z) above each arrow.

Questions E. Why do you think Beadle and Tatum’s conclusion is now famously summarized as “One gene, one enzyme”?

F. Given what we know today, the “One gene, one enzyme” hypothesis is inaccurate. Provide an example from your understanding of DNA that would suggest how genes might not result in an enzyme.

G. People have tried to come up with a more accurate statement but they all have flaws since there are always exceptions. Describe an exception for each of the summary statements below. Note: You might not be able to complete this question until after the translation lesson. “One gene, one protein” “One gene, one polypeptide”

Practice A hypothetical metabolic pathway begins with a precursor, ends with a product called Biolazine and has 3 intermediate substrates and 4 enzymes. Number the intermediate substrates 1-3, and label the enzymes A-D (above the arrow).

Precursor →

→

→

Questions (based on above practice question) H. Suppose a mutation made the gene for enzyme C non-functional. What molecule would accumulate in the affected cells?

I.

Suppose an individual has a mutation in the gene that codes for enzyme B. Giving which substrate would allow this individual to produce Biolazine?

J.

Suppose an individual with a mutation can survive if given substrate 3 in their diet. But they die even if given the precursor, substrate 1 and substrate 2. Which enzyme in the pathway is affected by this mutation?

K. Suppose an individual with a mutation can survive when given Biolazine, substrate 1, substrate 2, or substrate 3, but cannot survive when given minimal medium that contains the precursor. Which enzyme in the pathway is affected by this mutation?

→ Biolazine...