ANSC327 Genetics Exam 1

where are genes stored?

genes are stored in the chromosomes located in the nucleus

describe the findings of Frederick Griffith’s experiment in 1928:

Griffith discovered that non-virulent bacteria (R-strain) could transform into virulent forms (S-strain) when exposed to heat-killed virulent strains, suggesting that physical traits can be passed from one cell to another, giving the first hint that DNA was the genetic material, and that genetic transformation was possible. His experiment used streptococcus pneumonia.

outline the steps of Griffith’s experiment:

1. living S (smooth) cells injected into a mouse kills the mouse. Can isolate live S colonies from dead mouse tissue.

2. Living R (rough) cells injected into a mouse do not kill it. Heat-killed S cells injected into a mouse do not kill

3. Living R cells are mixed with heat-killed S cells and injected, the mouse dies, and live S cells are recovered. Can isolate colonies of both R and S cells.

   Thus, the R cells “transformed” the heat-killed S cells.

describe the findings of Avery, MacLeod, and McCarthy’s experiment in 1944:

Avery, MacLeod, and McCarty demonstrated that DNA is the transforming principle by showing that only DNA extracted from heat-killed S-strain bacteria could transform R-strain bacteria into virulent S-strain. Their work provided strong evidence that the “transforming material” was DNA, not protein, and is the genetic material responsible for heredity.

outline the steps of Avery, MacLeod, and McCarthy’s experiment:

1. Heat-killed S-cells in a test tube were added to a culture of R-cells; isolating both S and R cell colonies on an agar medium. This proved that the transforming material was not degraded by heat.

2. Protease and RNAse (enzymes) were added to a test tube of heat killed S cells, then added to a culture of R cells. Colonies of R and S cells were both isolated proving that the transforming material was not destroyed by protease or RNAse, meaning that it was not likely to be protein or RNA.

3. Step 2 was repeated but with DNAse. When the cells were plated, only R colonies grew—proving that the transforming material was destroyed by DNAse, and thus was likely DNA.

describe the findings of Hershey and Chase’s experiment in 1952:

Hershey and Chase used bacteriophages to prove that DNA material was transferred to progeny while protein material was not. They labeled DNA with phosphorus-32 and protein with sulfur-35. After infection, only phosphorus-32 was found in the bacterial cells, indicating that DNA, not protein, was the genetic material.

outline the steps of Hershey & Chase’s experiment:

Part 1 (DNA):

1. Infect E. coli with nonradioactive T2 phage (virus).

2. E. coli cells grown on a medium containing 32-P (labels DNA).

3. Phages reproduce inside E. coli cells; progeny are labeled with 32-P.

4. DNA-labeled progeny phage is used to infect nonlabelled E. coli cell.

5. After infection, kitchen blender is used to remove attached phage capsule (head).

6. Phages reproduce, E. coli lysis; released progeny contain some 32-P labeled DNA from parental phage.

Part 2 (Protein):

1. Same steps for Part 1, but this time use 35-S (labels protein). Progeny phages contain almost no 35-S labeled protein, proving that DNA is the transferring material and not protein.

explain what Chargaff’s rule is and how it contributed to the structure of DNA:

Chargaff found that A=T and G=C, contributing to Watson and Crick’s proposal that DNA is in a double helix in which the 4 bases are paired accordingly: adenine (A) with thymine (T), and guanine (G) with cytosine (C).

DNA has repeating distances of ____, ____, and ____.

0.34nm, 2nm, and 3.4nm (Wilkins & Franklin)

semi-conservative DNA model

each new DNA ladder has one old side (the original) and one new side with a mixture of DNA (what actually happens)

conservative DNA model

one all-old ladder and one all-new ladder (proven wrong)

dispersive DNA model

each new ladder is a mix of old and new pieces (proven wrong)

what did the Meselson-Stahl experiment prove?

their experiment proved that DNA replicated semi-conservatively

outline the steps of the Meselson-Stahl experiment:

1. Control: E. coli grown for many generations in a ¹⁴N medium. DNA was then extracted from the cells and centrifuged. The result was one thick band at the top of the test tube. Each strand of DNA contained ¹⁴N (¹⁴N¹⁴N).

2. E. coli is grown in a ¹⁵N medium (more dense than ¹⁴N). The result was one thick band at the bottom of the test tube (¹⁵N¹⁵N).

3. Then, ¹⁵N cells transferred to ¹⁴N medium. Cells replicate once to produce first generation of daughter cells. DNA was extracted from the daughter cells and was centrifuged. The result was one thick band in the center of the test tube (¹⁵N¹⁴N).

4. Cells replicate for a second time in the ¹⁴N medium. The DNA of their progeny was centrifuged. The result was one thinner band at the top (¹⁴N¹⁴N) and one thinner band around the middle (¹⁵N¹⁴N). This confirms the prediction of semi-conservative replication.

first discovered hereditary disease caused by defective genes

alkaptonuria

alkaptonuria is caused by a defective enzyme in the pathway important for the breakdown of ______. this defect leads to an accumulation of ______ that turns the urine black upon oxidation

phenylalanine, homogentisic acid

those with PKU cannot have _____ due to the fact it contains phenylalanine

aspartame

explain how a PKU metabolite can be dangerous to infants and fetuses

Aspartame, a common ingredient in diet soda, is a dipeptide of phenylalanine and aspartic acid. Consumption of aspartame would increase phenylalanine levels, which would increase the buildup of homogentisic acid or other compounds in the chain of phenylalanine breakdown

explain what stop/start codons are

the “go” and “end” signals for protein synthesis, where cells build proteins based on DNA instructions (translating mRNA into proteins)

what are the 3 “stop” codons

UAA, UAG, UGA

what is the “start” codon

AUG

polar uncharged amino acids

Some Times Cats Try A Growl
1. S - Serine
2. T - Threonine
3. C - Cysteine
4. T - Tyrosine
5. A - Asparagine
6. G - Glumatic

polar charged amino acids

A Good Lawyer Aims High
1. A - Aspartic acid
2. G - Glutamic acid
3. L - Lysine
4. A - Arginine
5. H - Histidine

non-polar amino acids

Go And Take Vital Part In Promoting Mother Language
1. G - Glycine
2. A - Alanine
3. T - Tryptophan
4. V - Valine
5. P - Proline
6. I - Isoleucine
7. P - Phenyl alanine
8. M - Methionine
9. L - Leucine

explain why an M1V mutation in the PAH enzyme is so problematic

mutation in the first codon that turned methionine into valine. this changes the AUG to a GUG, which results in no PAH being produced

is an M1V mutation or a R40W mutation worse?

M1V, since no protein can be produced at all. R408W mutation changes arginine to tryptophan in codon 408, the protein translated but looks like a Trp instead of an Arg, so only 3% of the activity of a normal enzyme.

define pleiotropy

a single gene affecting multiple traits

give an example of pleiotropy

i. melanin synthesis and PKU - in the absence of PAH, the conversion of phenylalanine to tyrosine is blocked. Tyrosine is a precursor to melanin.

ii. 40% of cats with blue eyes are deaf. among cats with white fur and blue eyes, about 40% are born death. the reason is that pigment cells derived from the neural crest migrate to various tissues including hair follicles, the eyes, and the middle ear, where