7.4 - 7.5

Question 1

what are nucleosomes

Answer 1

~147 bp of DNA wound around octamer protein core containing copies of histones H2A, H2B, H3, H4

Question 2

how does DNA attach to nucleosome

Answer 2

histone octamer surface has positive charges that hold the negatively charged DNA

Question 3

what is the difference between heterochromatin and euchromatin

Answer 3

euchromatin is loose, not coiled and ready for transcription initiation

heterochromatin is tightly coiled, very condensed and not easily reached by transcription factors

Question 4

what are SMC and what do they do

Answer 4

structural maintenance of chromosome (SMC) proteins hold bases of chromatin loops together

Question 5

what are histone tails and what is their importance

Answer 5

histone tails are positively charged sequences of amino acids that can be modified that drive chromatin folding

histone tails regulate chromatin structure and corresponding chromatin transcription activity

Question 6

what happens to lysine in the histone tails

Answer 6

it is either acetylated or deacetylated

Question 7

what happens when lysine is deacetylated

Answer 7

the chromatin condenses and transcription is inhibited

Question 8

what happens when lysine is acetylated

Answer 8

the chromatin is less condensed and open for transcription

Question 9

how does tail get deacetylated

Answer 9

histone deacetylase

Question 10

how does tail get acetylated

Answer 10

histone acetyltransferase

Question 11

nontranscribed genes are __________ susceptible to DNase I digestion than active genes. why?

Answer 11

LESS!!!!
DNase I can not access tightly coiled chromatin

Question 12

what are histone markers?

Answer 12

modifications to the chromatin that are always associated with certain chromatin

Question 13

what is an example of a histone marker

Answer 13

heterochromatin lysine 9 always being tri-methylated

Question 14

what starts the formation of heterochromatin

Answer 14

binding of HP1 to histone H3 tri-methylated at lysine 9

Question 15

what does HP1 do in heterochromatin formation

Answer 15

binds to the tri-methyl at lysine 9 + brings others and they all bind and then condense the chromatin

they are like groupies because they chase after the lysine and then bring all their friends

Question 16

what does H3K9 methyl transferase do

Answer 16

adds methyl groups to lysine

Question 17

how is heterochromatin formed (for dummies)

Answer 17

deacetylation + tri-methylation at lysine 9 and so on calls HP1 chromodomain and friends to bind and coil up the chromatin

Question 18

what does bromodomain do

Answer 18

recognizes acetylated histone tails and binds to hem and then calls transcription factors to come and start transcription

Question 19

what is the difference between chromodomain and bromodomain

Answer 19

chromodomain: associated with chromatin condensation + repressing of transcription

bromodomain: associated with decondensation of chromatin + activation of transcription

Question 20

what is chromosome painting used for

Answer 20

identifying and mapping chromosomal translocations

Question 21

what does telomerase do

Answer 21

adds telomeric sequences (DNA sequences on the END of telomeres) to prevent shortening of chromosomes during DNA replication

Question 22

why is telomerase needed

Answer 22

standard DNA replication leads to the loss of DNA at the 5’ end of each strand of linear DNA molecule

Question 23

what is the centromere

Answer 23

region that allows the spindle to attach

Question 24

what are kinetochores

Answer 24

the glue that holds the spindle to the chromosome’s centromere