Bio 1 - DNA Basics

Question 1

Why is it easy for DNA to wrap around histones?

Answer 1

Histones are positively charged due to lots of lysine and argenine, while DNA is negatively charged (lots negatively charged phosphate groups).

Question 2

What ties one nucleosome to another?

Answer 2

Histone H1. The whole structure is chromatin, which packs a lot of DNA.

Question 3

What does deaminacion of cytosine cause?

Answer 3

It turns it into uracil (which is found in RNA). Cytosine is only found in DNA.

Question 4

How many bounds does cytosine-guanine have in DNA? and thymine-adenine?

Answer 4

Three hydrogen bonds in C-G. Two hydrogen bonds in T-A.

Question 5

What five substances do we need to make Purines (adenine and Guanine)?

Answer 5

Glycine, Glutamine, Aspartate. You also need the vitamin Tetrahydrofolate and CO2.

Question 6

What are the Two substances needed to make Pyrimidines (Cytosine, Thymine)?

Answer 6

Aspartate and Carbamoyl phosphate. Making Carbamoyl phosphate requires CO2, glutamine, ATP.

Question 7

What is the enzyme required to make Carbamoyl phosphate?

Answer 7

Carbamoyl phosphate synthetase II (CPS-II). It is the rate limiting step of pyrimidine synthesis.

Question 8

What is the difference between Carbomyl phosphate synthetase (CPS) I and CPS II?

Answer 8

CPS-I is located in mitochondria, is involved in the Urea cycle, and its source of nitrogen is ammonia. CPS-II is located in cytosol, is involved in the Pyrimidine synthesis, and its source of nitrogen is glutamine.

Question 9

What is a nucleosome?

Answer 9

A unit that consists of 8 histones (2 of each: H2A, H2B, H3, H4) and DNA wraps twice around it.

Question 10

What drugs inhibit dyhydropholate reductase in Prokaryotes?

Answer 10

Trimethoprim.

Question 11

What drugs inhibit dyhydropholate reductase in Eukaryotes?

Answer 11

Methotrexate.

Question 12

What is the mechanism of action of 5-fluorouracil?

Answer 12

It inhibits the production of pyrimidine by blocking Thymidylate synthase.

Question 13

What is the mechanism of action of Hydroxyurea?

Answer 13

It inhibits the production of Pyrimidine by blocking Ribonucleotide reductase.

Question 14

What is Orotic Aciduria And what is it’s cause?

Answer 14

Too much orotic acid in the urine, caused by deficiency of UMP synthase enzyme (Autosomal recessive). This deficiency causes the inability to convert orotic acid to UMP.

Question 15

What are the symptoms of Orotic aciduria?

Answer 15

Elevated orotic acid in the urine. No hyperammonemia. Failure to thrive. Megaloblastic anemia (not responsive to B12 or folic acid supplementation because they still need pyrimidine).

Question 16

What is the treatment for orotic aciduria?

Answer 16

Supplemental dietary uridine.

Question 17

What is the rate limiting step of Purine synthesis?

Answer 17

The enzyme glutamine PRPP amidotransferase.

Question 18

What is the mechanism of action of 6-Mercaptopurine?

Answer 18

It inhibits the production of de novo purine synthesis by blocking the rate limiting enzyme glutamine PRPP amiDOtransferase.

Question 19

What is the enzyme that converts IMP to GMP in the de novo purine synthesis pathway?

Answer 19

IMP dehydrogenase.

Question 20

What is the mechanism of action of the drug Mycophenolate?

Answer 20

It inhibits the enzyme IMP dehydrogenase in the Purine synthesis pathway.

Question 21

What enzyme recycles Guanine back to GMP?

Answer 21

HGPRT (hypoxanthine-guanine phosphoribosal transferase).

Question 22

What 2 substances can HGPRT recycle back up in the purine salvage pathway?

Answer 22

It can convert guanine back to GMP. It can convert hypoxanthine back to IMP.

Question 23

What disease is caused when you are deficient in HGPRT?

Answer 23

Lesch-Nyhan syndrome.

Question 24

What are the symptoms of Lesch-Nyhan syndrome? What is the treatment?

Answer 24

Gout. Intellectual disability. Aggressive behavior. Self-mutilation (lip biting). Choreoathetosis. Allopurinol is the treatment.

Question 25

What is the enzyme that converts adenosine to inosine?

Answer 25

Adenosine deaminase.

Question 26

In what disease is adenosine deaminase deficiency involved in?

Answer 26

SCID (severe combined immunodeficiency).

Question 27

What is the classic triad of SCID (severe combined immunodeficiency)?

Answer 27

Severe recurrent infections (candidiasis, pneumocystis pneumonia). Chronic diarrhea. Failure to thrive. Also, No thymic shadow on the newborn on CXR.

Question 28

What is the rate limiting enzyme in purine synthesis? In pyrimide synthesis?

Answer 28

Purine synthesis: Glutamine PRPP amiDOtransferase. Pyrimidine synthesis: Carbomoyl Phosphate Synthetase II.

Question 29

What are the sources of carbons in the formation of purines? What are the carbon sources in pyrimidine synthesis?

Answer 29

In purine synth: Glycine, Tetrahydrofolate, and CO2 provide carbon (glutamine and aspartate provide nitrogen). In pyrimidine synth: Aspartate and CO2 provide carbon (while glutamine provides nitrogen).

Question 30

Which medication Inhibits ribonucleotide reductase?

Answer 30

Hydroxyurea.

Question 31

Which medication Inhibits dihydrofolate reductase?

Answer 31

Trimethoprim, methotrexate.

Question 32

Which medication Inhibits thymidylate synthase?

Answer 32

5-fluorouracil.

Question 33

Which medication inhibits inosine monophosphate dehydrogenase?

Answer 33

Mycophenolate.

Question 34

Which medication inhibits PRPP amidotransferase?

Answer 34

6-mercaptopurine.

Question 35

How many adenine residues are found in a molecule of DNA if one strand contains A=2000, G=500, C=1500, and T=1000?

Answer 35

There is 3000 adenine residues.

Question 36

RFF: A boy w/ self-mutilating behavior, intellectual disability and gout.

Answer 36

Lesch-Nyhan syndrome.

Question 37

RFF: Orotic acid in the urine + elevations in serum ammonia.

Answer 37

OTC deficiency.

Question 38

RFF: Orotic acid in the urine + no elevations in serum ammonia.

Answer 38

Orotic aciduria.

Question 39

RFF: Megaloblastic anemia that does not improve with folate and B12.

Answer 39

Orotic aciduria.