Human Chromosome

Question 1

What proteins make up nucleosome?

Answer 1

2x H2A, H2B, H3, H4

Question 2

What is the length of the diameter of the nucleosome bead fiber?

Answer 2

11 nm

Question 3

What forces facilitate winding of DNA around nucleosome?

Answer 3

neg charge from DNA 5’-phosphate groups AND pos charge from Arg/Lys res on histone core proteins

Question 4

What are the 3 types of histone modifications?

Answer 4

1. acetylation
2. methylation
3. phosphorylation

Question 5

Briefly describe mechanism of acetylation

Answer 5

• causes decondensation of chromatin
• neutralizes pos Lys charge
• carried out by histone acetyltransferases (HATs)

Question 6

Briefly describe mechanism of deacetylation

Answer 6

• maintains pos charge of histones
• catalyzed by histone deacetylases (HDACs)
• silences genes

Question 7

State purpose of methylation

Answer 7

• condenses chromatin

Question 8

Phosphorylation

Answer 8

• promotes decondensation
• adds - charged PO4 groups to histones
• negates histone-DNA attraction

Question 9

Regulators of chromatin winding/unwinding? (5)

Answer 9

• SWI/SNF (activators) mediate HAT function to decondense chromatin
• H1/HP1/SCC (repressors) condense DNA thru HDACs

Question 10

Hallmark characteristic of Rett syndrome?

Answer 10

Degeneration of previously met milestones

Question 11

Major symptoms of Rett syndrome?

Answer 11

Regression in communication skills after first 18 months of life + constant hand-wringing

Question 12

Underlying cause of Rett syndrome?

Answer 12

• inactivating mutation in gene MECP2
• normal MECP2 function: recruits HDACs to condense DNA
• inactive MECP2 protein decreases HDAC function –> inappropriate gene expression –> neurodegeneration

Question 13

What is nullisomy?

Answer 13

• Missing pair of homologs (both alleles)

- lethal in embryos

Question 14

What is monosomy?

Answer 14

• one chromosome missing

- embryonic (pre-implantation) lethal if missing chromosome is an autosome

Question 15

What is the only case where monosomy is not lethal?

Answer 15

• Turner syndrome

- female is missing 1 of the 2 X chromosomes (45, XO)

Question 16

What is triploidy?

Answer 16

• cell/nucleus contains 3 entire homologous sets of chromosomes

Question 17

Main difference between symptoms of aneuploidy & chromatin remodeling disorders?

Answer 17

• aneuploidy = very early onset

- CRD = later onset, 1st or 2nd yr of life

Question 18

Major symptoms of Turner syndrome? (5)

Answer 18

• born w/ edema of hands/feet
• webbing (skin folds) in neck
• cardio problems
• slow growth
• underdvp’d sexual dvp’ment

Question 19

How is Turner syndrome treated?

Answer 19

Hormonal therapy, specifically GH & estrogen

Question 20

Most common trisomy?

Answer 20

• Trisomy 16, embryonic lethal

Question 21

What trisomy is Edwards syndrome?

Answer 21

Trisomy 18, similar symptoms to Trisomy 13

Question 22

Symptoms of Trisomy 13 (Patau syndrome)? (5)

Answer 22

• cleft lip/palate
• clenched hands
• polydactyly
• microcephaly
• micrognathia (small lower jaw)

Question 23

Is the term “beads on a string” associated with condensed or decondensed DNA?

Answer 23

Decondensed; 11 nm; euchromatin

Question 24

How does G-banding work?

Answer 24

• stains A-T rich (G-C poor) regions of DNA

- shows unique banding patterns along chromo

Question 25

How does C-banding work?

Answer 25

• visualizes centromere & heterochromatic regions of chromo 1,9,16, & Y
• also visualizes pericentric inversions