First Aid: Biochemistry

Question 1

DNA and histone methylation make DNA _____________.

Answer 1

sterically inaccessible

Question 2

Histone acetylation ________ DNA.

Answer 2

activates

Question 3

Nucleosides have ________.

Answer 3

only sugars (think of the S)

Question 4

Nucleotides have _________.

Answer 4

phosphates (think of the T)

Question 5

Methotrexate inhibits ___________.

Answer 5

dihydrofolate reductase, which is necessary for thymine synthesis

Question 6

Ataxia telangiectasia is a defect of the ___________ pathway.

Answer 6

non-homologous end joining

Question 7

What do RNA polymerases I, II, and III do?

Answer 7

I makes rRNA, II makes mRNA, and III makes tRNA.

Question 8

snRNPs control _______, while miRNA _______.

Answer 8

splicing; decreases translation by degrading mRNA

Question 9

tRNA binds amino acids at the _____ end.

Answer 9

3’

Question 10

tRNA use ______ to charge and _______ to translocate through the rRNA.

Answer 10

ATP; GTP

Question 11

COP I is _______ movement, while COP II is _________; clathrin is ________.

Answer 11

retrograde; anterograde; a trafficker between the trans-Golgi and the membrane

Question 12

What is Menkes disorder?

Answer 12

An X-linked, recessive defect of copper absorption that leads to kinky hair, growth retardation, and hypotonia–connective tissue issues.

Question 13

Marfarns is an _________.

Answer 13

autosomal dominant defect of fibrillin, a glycoprotein that forms sheath around elastin; presents with long limbs and fingers, pectus excavatum, and heart problems

Question 14

Polycystic kidney disease… AR or AD?

Answer 14

Both!

Question 15

FAP…. AR or AD?

Answer 15

AD

Question 16

Hereditary spherocystosis… AR or AD?

Answer 16

AD

Question 17

p53 is shown by _________.

Answer 17

SBLA (sarcoma, breast, leukemia, and adrenal gland cancers)

Question 18

MEN (multiple endocrine neoplasias) is associated with the __________ genes.

Answer 18

MEN1 (for type 1) and RET (for types 2A and 2B)

Question 19

Cystic fibrosis is an __________.

Answer 19

autosomal recessive defect, most commonly of Ph508

Question 20

What are the symptoms of myotonia type 1?

Answer 20

Myotonia (inability to relax muscles), testicular atrophy, frontal balding, and arrhythmia (my tonia, my testicles, my toupee, and my ticker)

Question 21

Duchenne’s results from ________.

Answer 21

frameshift or nonsense mutations in the dystrophin gene

Question 22

What are the trinucleotide repeat disorders?

Answer 22

Huntington, myotonic dystrophy, Friedrich ataxia, and fragile X (try hunting for my fried eggs [X])

Question 23

Atresia is ________.

Answer 23

a disorder in which an orifice or passage that should be open is closed

Question 24

95% of Down syndrome cases result from ___________.

Answer 24

meiotic nondisjunction (the rest are due to Robertsonian translocations)

Question 25

Edwards syndrome is trisomy _____ and Patau syndrome is trisomy _____.

Answer 25

18 (think E = election age); 13 (think Patau = P = puberty age)

Question 26

Histone _____ is on the outside of the nucleosome.

Answer 26

1

H1 is the linker.

Question 27

___________-chromatin is darker on EM.

Answer 27

Hetero

“HeteroChromatin is Highly Condensed”

Question 28

Which kind of chromatin gets expressed?

Answer 28

Euchromatin

“Euchromatin is Expressed”

Question 29

Deamination of ______ makes uracil.

Answer 29

cytosine

Question 30

Methylation of uracil makes _____________.

Answer 30

thymine (hence methotrexate inhibits the formation of thymine from uracil)

Question 31

What enzyme initiates the pyrimidine synthesis pathway?

Answer 31

Carbamoyl phosphate synthase!

Recall that mitochondrial carbamoyl phosphate synthase makes carbamoyl phosphate for exportation into the urea cycle, while cytosolic CPS makes pyrimidines.

Question 32

UMP is made from what precursor?

Answer 32

Orotic acid

Hence, this is why some pyrimidine synthesis disorders can present with elevated orotic acid.

Question 33

HGPRT catalyzes what two reactions?

Answer 33

• Hypoxanthine to IMP
• Guanine to GMP

It’s in the name: hypoxanthine guanine phosphoribiosyltransferase

Question 34

Say a patient with Lesch-Nyhan is allergic to allopurinol. What treatment can you give them?

Answer 34

Febuxostat