DNA structure and purines

Question 1

chromatin vs chromosome ?

Answer 1

lots of chromatin together y3mel chromosome

Question 2

what is a nucleosome and what appearance does it give ?

Answer 2

8 histone octomers with DNA wrapped twice around it to give it a bead on a string appearance

Question 3

what allows for there to b a closed condensed link between nucleosomes ?

Answer 3

histone H1

Question 4

what charge is there on DNA vs on histones and why ?

Answer 4

DNA is negatively charged due to phosphate groups
histones are positively charged due to lysine and arginine

Question 5

in what phase of cell replication does the formation of DNA and histones happen ?

Answer 5

S phase

Question 6

what is thee difference between heterochromatin and euchromatin?

Answer 6

heterochromatin is highly condensed and is transcriptionally inactive
euchromatin is less condensed and is transcriptionally more active

Question 7

what is DNA methylation ?

Answer 7

adding a methyl group to cytosine
methylation mutes DNA
Makes it more condensed
less available for transcription

Question 8

what type of chromatin is associated with methylation ?

Answer 8

heterochromatin

Question 9

what clinical syndrome is associated with dysregulated DNA methylation ?

Answer 9

fragile X syndrome

Question 10

what is thee difference between histone and DNA methylation ?

Answer 10

histone methylation is reversible
DNA methylation irreversible

Question 11

what does histone methylation lead to the formation of ?

Answer 11

heterochromatin

Question 12

what does histone acetylation do ?

Answer 12

it results in the formation off euchromatin as it removes the histones positive charge and relaxes the DNA coil allowing for more transcription to happen
an acetyl group is added to lysine

Question 13

what does histone deacetylation do ?

Answer 13

does thee opposite off acetylation and deactivates DNA

Question 14

what is the difference between nucleotides and nucleosides ?

Answer 14

nucleotides have a phosphate group nucleosides dont

Question 15

what are the different types of nucleotides and mention the types of each ?

Answer 15

purines and pyrimidines
purines - adenine and guanine, hypoxanthine 2 rings
pyrimidines - thiamine, cytosine 1 ring

Question 16

what controls the melting temperature of DNA ?

Answer 16

the number of CG bonds

Question 17

what are the nitrogen and carbon sources for purine synthesis ?

Answer 17

nitrogen sources are glycine
aspartate
glutamine

the carbon sources
glycine
carbon dioxide
teetrahydrofolate

Question 18

what diseases could benefit from histone deactylase inhibitors ?

Answer 18

huntingtons disease
some cancers show a high expression of histone deacetlyase

Question 19

which base pairs are associated with methylation ?

Answer 19

repeating CG islands
a lack off methylation off CG islands results in triggering an immune response

Question 20

what is the first step of purine de novo synthesis ?

Answer 20

ribose 5 phosphate

Question 21

what are the steps in purine synthesis ?

Answer 21

start off with 5 ribose phosphate
then PRPP
then we get IMP, GMP, AMP

Question 22

what is the clinical significance of histones ?

Answer 22

drug induced lupus - anti histone antibodies
in comparison to classic lupus where there is anti - dsDNA

Question 23

in purine de novo synthesis where does the 5 ribose phosphate come from ?

Answer 23

from the HMP shunt

Question 24

what are the intermediates in purine d novo synthesis ?

Answer 24

IMP
PRPP

Question 25

what drugs intervene with purine synthesis ?

Answer 25

mycophenolate and ribavarin.
6MP

Question 26

what does ribavarin do
and what ennzyme is inhibited by it ?

Answer 26

it is an antiviral that stops the conversion from IMP to GMP
inhibits IMP dehydrogenase

Question 27

what is the mechanism of mycophenolate ?

Answer 27

immunosuppressants that stops the conversion of IMP to GMP
by inhibiting IMP dehydrogenase

Question 28

what are the two fates of purines ?

Answer 28

either be converted into xanthine and excreted in uric acid
or salvages ( reused )

Question 30

how does the salvage process happen ?

Answer 30

the purines are converted back to their monophosphate form in the presence of PRPP

Question 31

in the purine salvage process how is guanine, adenine and hypoxanthine converted back to their monophosphate form ?

Answer 31

guanine and hypoxanthine see HGPRT in combination with PRPP to give MP and GMP
while adenine uses APRT and PRPP to give AMP

Question 32

essentially what is PRPP ?

Answer 32

a nucleotide with no base

Question 33

how does 6MP work ?

Answer 33

mimics the structure of guanine , so HGPT holds on to it and makes a mutant nucleotide

Question 34

what syndrome is associated with a lack off HGPRT enzyme and what happens in this disease?

Answer 34

lesch nyhan syndrome
no purine salvage happens
also called juvenile gout

Question 35

what is the classic presentation of lesch nyhan syndrome ?

Answer 35

young male
motor symptoms
self mutilation
gout
Hyperuricemia
Pissed off
Gout
Red orange crystals in urine
Tense muscles dystonia

Question 36

what drug cannot be given with azathioprine ?

Answer 36

allopurinol both are xanthine oxidase inhibitors

Question 37

what is the clinical association of adenosine deaminase deficiency ?

Answer 37

SCID
severe combined immunodeficiency disease
this happens due to
decrease ADA means mooore dATP
which will inhibit ribonucleotide reductasee (RNR)
decrease thee DNA preccursors which will inhibit thee productiion of lymphocytes

Question 38

what is the form of inheritance inn lesch nyhan syndrome ?

Answer 38

x linked recessive

Question 39

what is histone acetylation catalyzed by ?

Answer 39

HAT