Module 8 Lec 8

Question 1

What is heterochromatin and where is it found?

Answer 1

Heterochromatin is darkly stained, highly compacted DNA, usually near centromeres. It remains condensed during interphase.

Question 2

What is constitutive heterochromatin?

Answer 2

Constitutive heterochromatin remains condensed in all cells most of the time, e.g., parts of the Y chromosome.

Question 3

What is euchromatin?

Answer 3

Euchromatin is lightly stained DNA, contains most of the genes, and is less compact.

Question 4

What is a Barr body?

Answer 4

A Barr body is the inactivated X chromosome in female mammals, visible as a dark dot under the microscope.

Question 5

Why is one X chromosome inactivated in female mammals?

Answer 5

One X chromosome is inactivated to balance X chromosome dosage between males (XY) and females (XX).

Question 6

Is the inactivation of the X chromosome random?

Answer 6

Yes, the inactivation of the X chromosome is a random process early in development, resulting in a mosaic of X chromosome activity in females

Question 7

What type of heterochromatin is the Barr body?

Answer 7

The Barr body is an example of facultative heterochromatin, where the inactivated X chromosome can vary between tissues.

Question 8

What precedes gene expression in chromosomal packaging?

Answer 8

Decompaction of chromatin precedes gene expression.

Question 9

What happens to nucleosomes during decompaction?

Answer 9

Nucleosomes unwind in the decompacted area, allowing the initiation of transcription.

Question 10

How do transcription factors help with gene expression?

Answer 10

Transcription factors unwind nucleosomes and dislodge histones at the 5’ end of genes, making the DNA accessible for RNA polymerase.

Question 11

What is the result of nucleosome unwinding at the gene’s 5’ end?

Answer 11

The unwound portion of the DNA is open for interaction with RNA polymerase, which initiates gene expression.

Question 12

What is the meaning of “telos” in Greek?

Answer 12

“Telos” means “end.”

Question 13

What are telomeres?

Answer 13

Telomeres are protective caps at the ends of chromosomes that prevent fusion with other chromosomes.

Question 14

What do telomeres consist of?

Answer 14

Telomeres consist of tandemly repeated DNA and associated proteins.

Question 15

Why is there an “end problem” in linear replication?

Answer 15

The “end problem” occurs because the replication process can’t fully replicate the ends of linear chromosomes, leading to potential loss of genetic information.

Question 16

Why can’t DNA polymerase reconstruct the 5’ end of a DNA strand?

Answer 16

DNA polymerase cannot reconstruct the 5’ end due to the directionality of DNA replication (it can only add nucleotides in the 5’ to 3’ direction).

Question 17

What would happen if chromosomes got shorter after each cell cycle?

Answer 17

If chromosomes got shorter after each cell cycle, genetic information could be lost, leading to potential cell dysfunction or death.

Question 18

What is the “end problem” in DNA replication?

Answer 18

The “end problem” refers to the inability of DNA polymerase to fully replicate the 5’ end of linear chromosomes, leading to potential loss of genetic material after each cell cycle.

Question 19

How does telomerase solve the “end problem”?

Answer 19

Telomerase extends the telomeres by adding repetitive DNA sequences to the 3’ end of the chromosome, preventing the loss of important genetic material.

Question 20

What is the role of the primer in telomere extension?

Answer 20

The primer provides a starting point for DNA polymerase to extend the new strand, allowing the telomeres to be lengthened.

Question 21

What is the function of the “primer extension” in the telomere replication process?

Answer 21

Primer extension allows the telomerase to add DNA repeats to the 3’ end of the chromosome, lengthening the telomere.

Question 22

What happens during the “digestion” step in telomere replication?

Answer 22

The digestion step refers to the removal of the RNA primer once telomere extension is complete, allowing for proper chromosomal integrity.

Question 23

What is the repeat unit in vertebrate telomeres?

Answer 23

The repeat unit in vertebrate telomeres is TTAGGG.

Question 24

How many times are the repeat units in telomeres typically repeated?

Answer 24

The repeat units in telomeres are repeated 250 to 1500 times.

Question 25

What enzyme is responsible for solving the “end problem” in telomeres

Answer 25

The enzyme telomerase (a ribonucleoprotein) is responsible for solving the “end problem” by elongating telomeres.

Question 26

How does telomerase elongate the telomeres?

Answer 26

Telomerase binds to the single-stranded repeat unit and uses its RNA template to elongate the opposite strand.

Question 27

What is the function of RNA in telomerase?

Answer 27

The RNA in telomerase serves as a primer template for elongating the telomere’s DNA strand

Question 28

How does the amount of telomerase affect the lifespan of cell lines?

Answer 28

High levels of telomerase increase the lifespan of cell lines, while low levels lead to telomere shortening and cell death.

Question 29

Which cells express high levels of telomerase?

Answer 29

Germ cells express high levels of telomerase, helping to maintain telomere length across generations.

Question 30

What happens to telomeres in somatic cells with low telomerase activity?

Answer 30

In somatic cells with low telomerase activity, telomeres shorten over time, leading to cell death.

Question 31

How do tumor cells relate to telomerase activity?

Answer 31

Tumor cells often exhibit very high telomerase activity, which helps maintain their telomeres and promotes cell immortality.