KH8

Question 1

What’s a chromosome?

Answer 1

Independent linear DNA molecules that constitute the genome of a species.

Question 2

What’s chromatin?

Answer 2

DNA/protein complex (DNA doesn’t exist “naked”). Essentially condensed DNA.

DNA < Nucleosome < Chromatin < Topological domains/Boundary elements < Chromosome

Question 3

What’s the difference between interphase and metaphase?

Answer 3

Metaphase: most condensed form
Interphase: chromosome replication and transcription (actually functions)

Question 4

What are histones?

Answer 4

These beads that allow DNA to wrap around. (Nucleosomes are histones octamers)

Question 5

What’s polytene chromosome?

Answer 5

Large chromosomes with thousands of DNA strands. They contain puffs (decondensation) at which transcription occurs. (Doesn’t occur in humans and most animals)

Question 6

True or False? “Polytene chromosomes contain parallel identical chromatids”

Answer 6

True. Due to not allowing cell division. All connected at the telomere and centromere.

Question 7

What are sister chromatids?

Answer 7

Identical molecules resulting from DNA replication of a template strand.

Question 8

What is a karyotype?

Answer 8

It’s the chromosome complement of a species, its genetic luggage. Number, shape, size are different from species to species (even sex-specific).

Question 9

What’s chromosome painting?

Answer 9

Recognition of certain sequences during the study of karyotypes (requires in situ hybridization)

Question 10

What’s special about chromosomes at the metaphase?

Answer 10

Most condensed, allows to read karyotype. Twice the genetic material present.

Question 11

What are translocations (when referring to chromosomes)?

Answer 11

Rearrangements (breaks) due to chromosomes breaking and rejoining incorrectly. It happens during somatic (non-sex) cell cycles and lead to mutations.

Question 12

True or False? “Translocation only occurs in somatic cells”

Answer 12

False. Germ-line chromosomes can switch genes around but it’s rarely passed on to new generations. (When it does happen, it contributes to evolution.)

Question 13

What are the three structures forming chromosomes?

Answer 13

ORI // Centromere // 2 telomeres

Question 14

True or False? “Plasmid of bacterial origin can help non-bacterial cells produce new or missing proteins (without any help)”

Answer 14

False. The bacterial ORI aren’t picked up by other species. Therefore, the plasmid and its contents can’t be used.

Question 15

How can one go about making bacterial plasmids useful for other species?

Answer 15

Introduce a non-bacterial ORI (one of the specific species you’re studying) into the plasmid. However, this isn’t enough to bring a significant change (very little cells end up with the plasmid).

Question 16

What can we add to a bacterial plasmid (already containing a specific ORI) to increase its efficiency in the host cells?

Answer 16

Add a centromeric sequence (from the host). Allows for good segregation during mitosis.

Question 17

Other than condensed chromosome alignment, what else happens at the metaphase?

Answer 17

Spindle microtubules attach onto the kinetochore (centromere).

Question 18

Describe the centromere-spindle linking process.

Answer 18

CENP-A (histone) recruits CBF3 which recruits Ndc80 which attaches to microtubules. From there, the connection goes from lateral (next to each other) to end-on (front-back).

Question 19

True or False? “Plasmids with specific ORI and CEN can work in both circular and linear DNAs”

Answer 19

False. They work well in circular ones but they lack the stability given by telomeres to be linear.

Question 20

What are the functions of telomeres?

Answer 20

Protect from exonuclease // Prevent end-to-end fusion // solves shortening of chromosomes after replication

Question 21

What’s the biological solution to DNA getting shorter (due to the lagging strand missing pieces)?

Answer 21

Telomerase: polymerase that extends telomeres. Restores length.

Question 22

How does telomerase function?

Answer 22

Telomeres repeat the same DNA sequences. // Telomerase has reverse transcriptase activity (complementary RNA to telomeres repeat sequence) // As telomere extends, the RNA slips (jumps) to a later point and keeps synthesizing. // This gives more template for RNA primer to latch onto.

Question 23

True or False? “Living beings missing telomerase are okay for 3 generations before fecundity declines”

Answer 23

True

Question 24

True or False? “All cells have telomerase activity”

Answer 24

False. Germ and stem cells only. Somatic cells are fine with their starting telomere length.