Biochemistry Molecular

Question 1

What is the Chromatin structure?

Answer 1

DNA exists in the condensed, chromatin form
i n order to fit i nto the nucleus. Negatively
charged DNA loops twice around positively
charged h istone octamer to form nucleosome
“bead.” H istones are rich in the amino acids
lysine and argin i ne. Hl ties nucleosome beads
together in a string.
In mitosis, DNA condenses to form
chromosomes.

Question 2

What is Heterochromatin?

Answer 2

Condensed, transcriptionally inactive, sterically
inaccessible.

Question 3

What is Euchromatin?

Answer 3

Less condensed, transcriptionally active,
sterically accessible.

Question 4

what is DNA methylation?

Answer 4

Template strand cytosine and adenine are
methylated i n DNA repl ication , wh ich allows
m ismatch repair enzymes to distinguish
between old and new strands in prokaryotes.

Question 5

What is Histone methylation?

Answer 5

Inactivates transcription of DNA.

Methylation makes DNA Mute.

Question 6

What is Histone acetylation?

Answer 6

Relaxes DNA coiling, allowing for transcription.

Question 7

Which are the nucleotides?

Study Key

Answer 7

• *PUR**i nes (A, G )-2 rings.adenine guanine
• *PY**rimidines (C, T, U ) -1 ring. citosine,thymine,Uracil

Pure As Gold

CUT the PY

Question 8

What is this?

Answer 8

Chromatin structure, Hl tying nucleosome beads

together in a string.

Question 9

What are nucleotides?

Answer 9

Any of a group of molecules that, when linked together, form the building blocks of DNA or RNA: composed of a phosphate group, the bases adenine, cytosine, guanine, and thymine, and a pentose sugar, in RNA the thymine base being replaced by uracil.

Question 10

Special caracteristics of Guanine, Thymine and Uracil?

Answer 10

Guanine has a ketone . Thymine has a methyl .
Deamination of cytosine makes uracil. Uracil found in RNA; thymine in DNA.

Question 11

What nucleotides do we see in DNA?

Answer 11

A,G,C,T

Adenine,Guanine,Cystosine and Thymine.

Question 12

What nucleotides do we see in RNA?

Answer 12

A,G,C,U

Adenine, Guanine,Cytosine, and Uracil

Question 13

What is the difference in structure between Adenine and Guanine?

Answer 13

The process of deamination, the removal of the amino group

Question 14

What is the enzyme that removes the amino group from adenine called?

Answer 14

adenosine deaminase

Question 15

What does the deficiency of adenosine deaminase cause?

Answer 15

severe combined imunodeficiency (autosomal recesive)

Question 16

What is the difference between Cytosine, Uracil and Thymine?

Answer 16

Guanine has a ketone . Thymine has a methyl .
Deamination of cytosine makes uracil.

Question 17

The methylation of uracil to thymine is catalyized by which enzyme?

Answer 17

Thymidylate synthase

Question 18

What can inhibit thymidylate synthase?

Answer 18

5 fluorouracil (5 FU)

Question 19

What is the difference between nucleosides and nucleotides?

Answer 19

A nucleoside is a nitrogen base + sugar

A nucleotide is a nitrogen base + sugar + phosphate

Question 20

What carbon in the sugar of the nucleotide helps diferentiate from DNA or RNA?

Answer 20

the 2 prime which either makes it deoxy if its absent or a ribose if its present

Question 21

What aminoacids are necessary for purine synthesis?

Answer 21

GAG

Glycine, Aspartate, and Glutamine.

Question 22

What does ribonucleotide reductase do?

Answer 22

Ribonucleotides are synthesized first and
are converted to deoxyribonucleotides by
ribonucleotide reductase

Question 23

What blocks de novo purine synthesis?

Answer 23

6-mercaptopurine (6-MP)

Question 24

What inhibits dihydrofolate reductase?

Answer 24

Methotrexate ( MTX)

Question 25

What inhibits bacterial dihydrofolate reductase

Answer 25

Trimethoprim (TMP)

Question 26

What is Orotic aciduria?

Answer 26

Inability to convert orotic acid to UMP (de novo pyrimidine synthesis pathway) because of defect in
 UMP synthase (a bifunctional enzyme).

Autosomal recessive.

Question 27

What can one expect to find in Ortic aciduria?

Answer 27

increase orotic acid in urine, megaloblastic anemia (does not improve with administration of vitamin B12
or folic acid), failure to thrive. No hyperammonemia (vs. OTC deficiency- increase orotic acid with
hyperammonemia).

Question 28

What is the treatment of Ortic aciduria?

Answer 28

Oral uridine administration.

Question 29

What happens in Adenosine deaminase deficiency?

Answer 29

Excess ATP and dATP imbalances nucleotide
pool via feedback inh ibition of ribonucleotide
reductase which prevents DNA synthesis and thus
decrease in lymphocyte count. One of the major causes
of SCID. Autosomal recessive.

1st di sease to be treated by experimental human
gene therapy.

Question 30

What is Lesch-Nyhan syndrome?

Answer 30

Defective purine salvage owing to absence of
HGPRT, which converts hypoxanthine to IMP
and guanine to GMP. Results in excess uric
acid production and de novo purine synthesis.
X-linked recessive.

Question 31

What are the clinical finding in Lesch-Nyhan syndrome?

Answer 31

retardation , self-mutilation,
aggression, hyperuricemia, gout,
choreoathetosis.

Question 32

What bond holds nucleotidesfrom the same strand together in DNA?

Answer 32

Phosodiester bond (PDE)

Question 33

What 2 properties does the dsDNA have?

Answer 33

1. -Complementary (A-T) (G-C)
2. -Antiparallel

Question 34

What bonds hold the dsDNA together?

Answer 34

3 hidrogen bonds(G-C)

2 hidrogen bonds (A-T)

Question 35

What does chargaffs rule say?

Answer 35

that the %A= %T(%U) and that the %G= %C only in dsDNA

Question 36

How many bases do we usually find in a turn of DNA?

Answer 36

10 bases per turn

Question 37

What is DNA denaturation?

Answer 37

The denaturation of nucleic acids such as DNA due to high temperatures is the separation of a double strand into two single strands, which occurs when the hydrogen bonds between the strands are broken. This may occur during polymerase chain reaction.

Question 38

What is DNA renaturation?

Answer 38

The reformation of double stranded DNA from thermally denatured DNA. The rate of reassociation depends upon the degree of repetition and is slowest for unique sequences