Week 4 Day 2

Question 1

Adenine and Guanine are which type of nitrogenous base?

Answer 1

Purines

Question 2

Cytosine, Thymine, and Uracil are which type of nitrogenous base?

Answer 2

Pyrimadines

Question 3

What is a nucleoside compared to a nucleotide?

Answer 3

Nucleosides lack any phosphates.

Question 4

Which amino acid is the major nitrogen donor and carrier in the body?

Answer 4

Glutamine.

Question 5

Where is the purine ring assembled?

Answer 5

On the ribose sugar.

Question 6

Where is the pyrimidine ring synthesized?

Answer 6

In the cytosol, and then attached to the ribos, and then modified to completion.

Question 7

Which enzyme is responsible for the committed step in purine synthesis?

Answer 7

Gln-PRPP amidotransferase.

Question 8

Synthesis of AMP and GMP are regulated by which molecules?

Answer 8

AMP and GMP have a negative feedback with themselves.

Question 9

What energy molecule is used in the synthesis of AMP and GMP?

Answer 9

GTP is used for AMP synthesis and ATP is used for GMP synthesis.
This helps prevent dys-proportionate amounts of either molecule from occurring.

Question 10

What major precursors are used in de novo purine synthesis?

Answer 10

Glutamine and other amino acids.

Folate and derivatives (TH4)

Question 11

The first step in pyrimidine synthesis is carried out by a tri-functional enzyme, carbamoyl phosphate sythetase, what molecule inhibits this enzyme?

Answer 11

UTP

Question 12

UMP synthase deficiency is responsible for a disease known as Orotic aciduria. Why would treatment of oral uracil help treat this disorder?

Answer 12

Uracil inhibits an earlier step in pyrimidine synthesis, thus not allowing oratate to build up in the blood.

Question 13

Why does the purine salvage pathway cause gout?

Answer 13

This is do to increased amounts of adenosine and guanosine being turned into uric acid, which is not highly soluble in blood and crystallizes into joints.

Question 14

What do phosphoribosyltransferases do?

Answer 14

They transfer already made purine rings onto PRPP.

Question 15

How does 5-fluorouracil act as a cancer treatment?

Answer 15

It suicide inhibits thymidilate synthase. Preventing dTMP synthesis.

Question 16

Which molecule shuts down ribonucleotide reductase and why does ADA deficiency cause SCID?

Answer 16

dATP.

ADA deficiency causes a build up of deoxyadenosine, which then leads to a build up of dATP.

Question 17

What is the main function of vit B-12?

Answer 17

The main function of B-12 is to regenerate THF and SAM.

Question 18

How does intrinsic factor allow the absorption of Vit B-12?

Answer 18

IF is recognized by mucosal cells, allowing the uptake of Vit B-12 by those cells and transport into the body.

Question 19

What are the 2 essential reactions that require Vit B-12?

Answer 19

THF regeneration via homocysteine to methionine conversion.

Odd chain fatty acid catabolism.

Question 20

What disorder is caused from Vit B-12 deficiency, why does this disorder develop, and what are the major associated problems with this disorder?

Answer 20

Megaloblastic Anemia.
DNA synthesis is inhibited from lack of THF, this causes the cells to not progress from G2 phase, which causes continued cell growth without division.
These symptoms are seen as large immature RBC (megaloblasts) and anemic symptoms from RBC deficiency and lack of Hb.

Question 21

What disorder is caused from IF deficiency, why does this disorder develop, and what are the major associated problems with this disorder?

Answer 21

Pernicious Anemia.
DNA synthesis is inhibited from lack of THF, this causes the cells to not progress from G2 phase, which causes continued cell growth without division.
These symptoms are seen as large immature RBC (megaloblasts) and anemic symptoms from RBC deficiency and lack of Hb.

Question 22

Why does Vit B-12 deficiency lead to neurological problems?

Answer 22

Demylination occurs from incorporation of methylmalonyl CoA substitutions. This leads to branched chain fatty acid synthesis which disrupts membrane structure.

Question 23

What disorder is caused by folate deficiency?

Answer 23

Neural tube defects

Question 24

What type of inheritance can not be male to male transmission?

Answer 24

Sex linked

Question 25

Which type of disease transmission is generally not multi-generational, except in sibship?

Answer 25

Autosomal Recessive

Question 26

Which disease pattern of inheritance is usually caused by new mutations?

Answer 26

Autosomal Dominant, especially lethal. | Sex-linked can be, but much less commonly.

Question 27

What is incomplete penetrance?

Answer 27

The possibility of having the mutation(s) but not expressing any phenotype.

Question 28

What is incomplete expressivity?

Answer 28

Having the disorder, but having varying degrees of expression of the phenotype. Can be seen as different severity or different clinical features.

Question 29

Don't forget that Bayes' theorem explains the lesser likelihood of having a disease when children don't express the disease.

Answer 29

I mean... Just don't... It might be statistically dumb, but don't.

Question 30

What is Hardy Weinberg Equilibrium?

Answer 30

p + q = 1 | p^2 + 2pq + q^2 = 1

Question 31

If the son, who does not have the disorder, of 2 people who are carriers for B-Thalassemia is having children with his wife, what are the chances their child will have B-Thalassemia, given the frequency for having the disorder in the population is 1/2500? (B-Thalassemia is an autosomal recessive disorder)

Answer 31

He has a 2/3 chance for being a carrier (remember he doesn't have the disorder) His wife has about a 1/25 chance (take the square root of q and multiply by 2 since 1 - q is so small) His child would then have 1/4 chance of inheriting the disorder Therefore the chance is 1/150

Question 32

Why do loss of function mutations usually follow recessive inheritance?

Answer 32

Usually the good copy of the gene can make up for the bad gene. Metabolism diseases are very common for this.

Question 33

Why do x-linked mutations follow dominant inheritance in males, even if the disease is caused by loss of function?

Answer 33

The male only has one copy of the gene, and therefore only needs to acquire one bad copy to lose the full amount of enzyme present in cells.

Question 34

Why do gain of function mutations usually follow dominant inheritance?

Answer 34

Explanations of this aren't great, but it is because the protein is doing something it shouldn't, or being expressed ectopically.

Question 35

Why do dominant negative mutations usually follow dominant inheritance?

Answer 35

The bad gene is interacting and disturbing the good gene.