2Molecular . Purine salvage deficiencies Genetic code features Dna Replication

Question 1

What is the end product of guanosine and adenosine degradation?

Answer 1

Uric acid, which is renally excreted eventually

Question 2

What enzyme catalyzes the conversions of both guanine to guanylic acid (GMP) and hypoxanthine to inosinic acid (IMP)?

Answer 2

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)

Question 3

What enzyme in the purine salvage pathway catalyzes both the conversions of hypoxanthine into xanthine and of xanthine into uric acid?

Answer 3

Xanthine oxidase

Question 4

Lesch-Nyhan syndrome is the result of an absence of what enzyme?

Answer 4

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) (He’s Got Purine Recovery Trouble)

Question 5

What enzyme catalyzes the formation of adenylic acid from adenine?

Answer 5

• Adenine phosphoribosyltransferase (APRT)

Question 6

What type of inheritance does phosphoribosyltransferase demonstrate?

Answer 6

X-linked recessive

Question 7

To a deficiency of which purine salvage enzyme may severe combined immunodeficiency (SCID) be due? What is the inheritance pattern?

Answer 7

Adenosine deaminase (ADA), which converts adenosine into inosine; autosomal recessive

Question 8

A child with intellectual disability, gout, and choreoathetosis self-mutilates. How would you treat him?

Answer 8

This is Lesch-Nyhan syndrome, treated with allopurinol or (second line) febuxostat

Question 9

A child with intellectual disability, gout, and choreoathetosis self-mutilates. Activity of which two enzymatic pathways is increased?

Answer 9

Uric acid production (xanthine oxidase) and de novo purine synthesis (phosphoribosyl-pyrophosphate)

Question 10

What is the classic presentation of Lesch-Nyhan syndrome?

Answer 10

HGPRT: Hyperuricemia, Gout Pissed off (e.g., aggression), Retardation (intellectual disability), dysTonia

Question 11

Through which mechanism does the drug allopurinol act?

Answer 11

Blocks xanthine oxidase (XO), thereby inhibiting conversion of hypoxanthine to xanthine

Question 12

What are the only codons that code for tryptophan and methionine?

Answer 12

UGG (tryptophan) and AUG (methionine)

Question 13

How is the genetic code unambiguous and yet redundant?

Answer 13

Whereas each codon specifies a single amino acid (unambiguous), an amino acid can be coded for by multiple codons (redundant

Question 14

Feedback inhibition of which enzyme occurs because of ATP and dATP accumulation in severe combined immunodeficiency?

Answer 14

Ribonucleotide reductase

Question 15

What does a commaless, nonoverlapping genetic code entail?

Answer 15

The entire genome is read from a fixed starting point as a continuous string of bases
exeption some viruses

Question 16

Typically the genetic code is considered universal (i.e., conserved throughout evolution). What is one noteworthy exception to this rule?

Answer 16

Human mitochondrial DNA, which is not conserved

Question 17

What is the purpose of DNA topoisomerase’s creation of a break in the DNA helix?

Answer 17

Relaxes supercoils; helps unwind DNA for proper replication

Question 18

In DNA replication, prokaryotes have ____ (multiple/one) origin(s) of replication, whereas eukaryotes have ____ (multiple/one) origin(s).

Answer 18

One; multiple

Question 19

What enzyme has 3′-to-5′ exonuclease activity in prokaryotic DNA replication?

Answer 19

DNA polymerase III has 3′–to–5′ exonuclease activity for proofreading

Question 20

What enzyme elongates the leading strand of DNA synthesis by building on an RNA primer?

Answer 20

DNA polymerase III

Question 21

What does DNA polymerase III require to initiate replication?

Answer 21

An RNA primer, created by primase

Question 22

What enzyme degrades the RNA primer and replaces it with DNA during prokaryotic DNA replication?

Answer 22

DNA polymerase I

Question 23

To which end of the newly synthesized DNA molecule does DNA polymerase III add the next deoxynucleotide?

Answer 23

The 3′ end—this is 5′–to–3′ synthesis

Question 24

When does DNA polymerase III stop adding deoxynucleotides to the 3′ end?

Answer 24

When it reaches the primer of the preceding fragment

Question 25

A patient is treated with an antibiotic that inhibits DNA gyrase (prokaryotic topoisomerase II). What antibiotic is this?

Answer 25

Fluoroquinolone

Question 26

The discontinuous DNA segments formed on the lagging strand are called ____. They are later joined together by ____.

Answer 26

Okazaki fragments; DNA ligase, which creates phosphodiester bond within a strand of double-stranded DNA

Question 27

DNA polymerases I and III are ____ (prokaryotic/eukaryotic) enzymes.

Answer 27

Prokaryotic

Question 28

What enzyme has 5′-to-3′ exonuclease activity?

Answer 28

DNA polymerase I (removes RNA primer)

Question 29

The Y-shaped region where leading and lagging strands are synthesized is called what?

Answer 29

The replication fork

Question 30

Patients with progeria lack telomerase. What would be seen in their cells following replication?

Answer 30

Loss of genetic material with each replication from the 3′ end of the chromosomes

Question 31

This enzyme unwinds the DNA template at the replication fork.

Answer 31

Helicase

Question 32

A patient has a condition in which DNA strands reanneal too quickly during replication. What proteins is he likely missing?

Answer 32

Single-stranded binding proteins

Question 33

In a test, an enzyme is used to add DNA to chromosomal 3′-ends to prevent loss of genetic material with duplication. Name the enzyme.

Answer 33

Telomerase