Human Chromosome

Question 1

What are the histone octamer core proteins?

Answer 1

8 total

Two each of H2A, H2B, H3, H4

Question 2

How does DNA wrap around the nucleosome?

Answer 2

~250 bp wraps twice around this core, including a linker/spacer region

Question 3

What interactions are involved in DNA wrapping around the nucleosome?

Answer 3

Electrostatic (negative DNA phosphates and positive histone Arg & Lys)

Question 4

What is the most open and thus transcriptionally active form of compaction?

Answer 4

11nm nucleosome chromatin fiber, aka “beads on a string”

Question 5

Formation of the 30nm transcriptionally silent fiberBe

Answer 5

Beads on a string wraps such that 6 nucleosomes arrange in a zigzag formation, twisting into the 30nm fiber

Question 6

In the interphase nucleus, which is dark and which is light - hetero vs euchromatin

Answer 6

Heterochromatin is dark (transcriptionally silent)

Euchromatin is light (transcriptionally active)

Question 7

Acetylation by ____ has what effect on chromosome compaction?

Answer 7

Acetylation by histone acetyltransferases (HATs) causes unwinding because the acetylation neutralizes the electrostatic stability

Question 8

Methylation on chromosome compaction

Answer 8

Methylation prevents acetylation, thus promoting condensation

Question 9

Deacetylation by ___ has what effect on chromosome compaction?

Answer 9

Deacetylation by HDACs maintains electrostatic stability, resulting in condensation.

Question 10

HIstone phosphorylation on chromosome compaction

Answer 10

Phosphorylation adds negative charges to the histones, which would cause unwinding from the negative DNA.

Question 11

Underlying cause of Rett Syndrome (neurodegenerative)

Answer 11

Mutation in MECP2, which binds methylated DNA in the brain to recruit HDACs and suppress gene expression.

Inactivating MECP2 causes a more open chromatin structure –> inappropriate gene expression –> neurodegenerative symptoms

Question 12

G-banding

Answer 12

Stains A-T rich DNA, showing unique banding patterns

Question 13

Metaphasic spread allows

Answer 13

Karyotyping of chromosomes, searching for gross aberrant chromosomal structures, diagnostic for a disease

Question 14

C-banding

Answer 14

Visualizes centromere and heterochromatic regions of chromosomes 1, 9, 16, and Y. Useful for visualizing pericentric inversions

Question 15

Euploidy

Answer 15

Normal complement of allelic chromosomes:

46 chromosomes: 22 autosomal chromosome pairs, one pair of sex chromosomes

Question 16

Types of aneuploidy

Answer 16

• Nullisomy: missing pair of homologs (both alleles)
• Monosomy: one chromosome is missing
  
  • Partial monosomy: missing chromosome only partially deleted
• Triploidy: three entire homologous sets of chromosomes
• Tetraploidy

Question 17

Differenc ein deteciton between aneuploidy and chromatin remodeling (like Rett’s)

Answer 17

Aneuploidy has early onset detection, even embryonic lethality; birth can come with clear developmental and/or neurological abnormalities.

Chromatin remodeling abnormalities has late onset (1st or 2nd yr) with progressive and/or neurodegenerative symptoms that get worse over time

Question 18

If the missing chromosome in monosomy is an autosome, then ____

Answer 18

usually embryonic lethal, with the exception of Turner’s syndrome (45,XO)

Question 19

Turner syndrome

Answer 19

45, XO

Female is missing oen of her two X chromosomes, resulting in edema, webbing, cardiovascular problems, slow growth, underdeveloped sexual development.

Question 20

Trisomy of sex chromosomes…

Answer 20

minor problems (because we already have X-chromosome inactivation and the Y chromosome doesnt do anything anyway)

Question 21

Trisomy 13 (Patau Syndrome)

Answer 21

Physical abnormalities - cleft lip/palate, clenched hands, polydactyly, microcephaly, micrognathia

Question 22

Trisomy 16

Answer 22

Embyronic lethal in the first trimester; most common trisomy

Question 23

Trisomy 18 (Edwards syndrome)

Answer 23

Same physical abnormalities as trisomy 13; more common in females

Question 24

Trisomy 21 (Down’s)

Answer 24

Single msot common cause of birth defects; can range form mild to severe