1Molecular. Chromatin Structure Nucleotides De novo pyrimidine and purine synthesis

Question 1

A researcher adds DNA to a solution with positively and negatively charged ions. With which of the ions does the DNA precipitate (bind to)?

Answer 1

The positively charged ions (DNA is negatively charged)

Question 2

How many subunits make up a nucleosome core? What are the subunits?

Answer 2

Eight; two of each of four histone types (H2A, H2B, H3, and H4)
•

Question 3

A lab researcher induces Barr body (inactive X chromosome) formation. It is transcriptionally inactive. How does this DNA appear on EM?

Answer 3

This is HeteroChromatin, which is Highly Condensed; appears darker and more condensed on EM

Question 4

What is transcriptionally active DNA called?

Answer 4

Euchromatin—it is uncondensed and accessible to replication enzymes

Question 5

How many times does DNA loop around each nucleosome core?

Answer 5

Two times

Question 6

Which nucleotides on the template strand are methylated in DNA replication?

Answer 6

Cytosine and adenine

Question 7

What is the charge of the histone octamers?

Answer 7

Positive, giving the histones affinity for negatively charged DNA

Question 8

Methylation at CpG islands ____ (activates/inactivates) transcription of DNA.

Answer 8

Inactivates (CpG Methylation makes DNA Mute)

Question 9

Predominance of which two amino acids gives histones a positive charge?

Answer 9

Lysine and arginine

Question 10

Histone ____ (methylation/acetylation) relaxes DNA coiling, allowing transcription.

Answer 10

Acetylation (histone Acetylation makes DNActive)

Question 11

An experiment is done to tie nucleosome beads together in a string to stabilize chromatin. Which protein facilitates this process?

Answer 11

Histone H1

Question 12

What allows mismatch repair enzymes to distinguish between old and new DNA strands?

Answer 12

Methylation of the template strand’s cytosine and adenine during DNA replication

Question 13

How many hydrogen bonds are there between adenine and thymine?

Answer 13

Two

Question 14

Which two nucleotides are purines?

Answer 14

Adenine and guanine (purines = PURe As Gold

Question 15

A guanine-cytosine bond is ____ (stronger/weaker) than an adenine-thymine bond.

Answer 15

Guanine-cytosine bond is stronger, as it has three hydrogen bonds—the adenine-thymine bond has only two

Question 16

What are the three pyrimidines?

Answer 16

Cytosine, Uracil, and Thymine (CUT the PY [pie]: PYrimidines)

Question 17

What molecule does deamination of cytosine yield?

Answer 17

Uracil

Question 18

Nucleoside = ____ + (deoxy)ribose

Answer 18

Base

Question 19

In what type of nucleic acid is uracil found?

Answer 19

• RNA

Question 20

What type of bond links nucleotides?

Answer 20

3′–5′ phosphodiester bond

Question 21

In what type of nucleic acid is thymine found?

Answer 21

DNA

Question 22

What nucleotide has a methyl group?

Answer 22

Thymine (thymine has a methyl)

Question 23

____ (Nucleotide/nucleoside) = ____ plus (deoxy)ribose

Answer 23

Nucleoside; base

Question 24

What amino acids are necessary for purine synthesis?

Answer 24

Glycine, Aspartate, Glutamine (GAG)

Question 25

A novel drug blocks purines, which are ____ and _____. Thus metabolic demand for which amino acids will increase?

Answer 25

Adenosine, guanine. Glycine, Aspartate, and Glutamine (GAG) are needed for purine synthesis, so more of these amino acids are needed

Question 26

An oncology patient is treated with 5-fluorouracil and methotrexate. Which parts of the pyrimidine synthesis pathway do these inhibit?

Answer 26

Thymidylate synthase and human dihydrofolate reductase (DHFR), respectively, both of which decrease dihydrofolate reductase availability

Question 27

Trimethoprim (TMP) is a commonly used antibiotic. What mechanism does it target?

Answer 27

Inhibits bacterial dihydrofolate reductase (DHFR)

Question 28

What enzyme converts the ribonucleotide UDP to the deoxyribonucleotide dUDP?

Answer 28

Ribonucleotide reductase

Question 29

Deoxyuridine monophosphate (dUMP) is converted to deoxythymidine monophosphate (dTMP) by which enzyme?

Answer 29

Thymidylate synthase

Question 30

What is the co-factor in the thymidylate synthase reaction (dUMP to dTMP)?

Answer 30

Methylene tetrahydrofolate (methylene THF)

Question 31

Converting carbamoyl phosphate into orotic acid requires ____ as the cofactor.

Answer 31

Aspartate

Question 32

Converting phosphoribosyl pyrophosphate (PRPP) into inosinic acid requires ____, ____, ____, and ____.

Answer 32

Aspartate; glycine; glutamine; tetrahydrofolate (THF)

Question 33

A patient takes 6-mercaptopurine (6-MP) for treatment of her cancer. What is the mechanism of action?

Answer 33

It blocks de novo purine synthesis

Question 34

What enzyme does hydroxyurea inhibit?

Answer 34

Ribonucleotide reductase

Question 35

Three pharmacologic treatments decrease deoxythymidine monophosphate (dTMP) through different mechanisms; what are they?

Answer 35

5-fluorouracil (5-FU) blocks dUMP →dTMP; methotrexate (MTX), and trimethoprim (TMP) both block DHF →THF by inhibiting DHFR

Question 36

What deficiency causes an accumulation of carbamoyl phosphate and, therefore, orotic acid?

Answer 36

Ornithine transcarbamylase deficiency

Question 37

Dihydrofolic acid (DHF) is converted to tetrahydrofolic acid (THF) by what enzyme?

Answer 37

Dihydrofolate reductase (DHFR

Question 38

A patient with colon cancer begins chemotherapy that blocks thymidylate synthase. What drug is used? How will it affect dihydrofolate (DHF)?

Answer 38

5-Fluorouracil (FU); inhibits thymidylate synthase, reducing conversion of dUMP to dTMP and N5N10-methylene THF to DHF = less DHF