Week 5: The Nucleus

Question 1

What is the primary function of the nucleus in a cell?

Answer 1

The nucleus is responsible for storing and managing genetic information, and it is involved in processes like transcription and mRNA splicing.

The nucleus is not just a storage place; it is a busy and active site for various cellular processes.

Question 2

How many pairs of chromosomes do humans have?

Answer 2

23 pairs of chromosomes.

This totals approximately 2 meters of DNA per cell.

Question 3

What structure forms when DNA wraps around histones?

Answer 3

Nucleosomes.

Nucleosomes stack to form chromatin.

Question 4

What is the nuclear envelope composed of?

Answer 4

Inner and outer nuclear membranes.

It also includes the perinuclear space.

Question 5

What is the role of the nuclear pores?

Answer 5

They facilitate the transport of molecules between the nucleus and the cytoplasm.

This includes the movement of mRNA and proteins.

Question 6

What are the two types of chromatin and how do they differ?

Answer 6

Euchromatin and heterochromatin.

Euchromatin is less condensed and accessible for transcription, while heterochromatin is highly condensed and not actively transcribed.

Question 7

What is the nucleolus primarily known for?

Answer 7

Ribosome production.

It is the site of synthesis of ribosomal RNA (rRNA) and assembly of ribosomal subunits.

Question 8

Fill in the blank: DNA is replicated during the _______ phase of the cell cycle.

Answer 8

S phase.

Question 9

What are the main DNA repair mechanisms?

Answer 9

• Proofreading activity of DNA polymerase
• Direct repair
• Base Excision Repair (BER)
• Single-strand break repair
• Nucleotide Excision Repair (NER)
• Mismatch Repair (MMR)
• Non-homologous end joining (NHEJ)
• Homologous recombination repair (HR)

These mechanisms protect DNA from damage and mutations.

Question 10

True or False: The nuclear lamina is part of the nucleoskeleton and helps organize chromatin.

Answer 10

True.

Question 11

What is the diameter range of nuclear pores?

Answer 11

50-80 nm.

The length of the pores is approximately 40-70 nm.

Question 12

What types of molecules can diffuse rapidly through nuclear pores?

Answer 12

Small molecules ~9 nm (<5 kDa) such as ions, solutes, and small peptides.

Larger molecules require active transport.

Question 13

What is the significance of the perinuclear space?

Answer 13

It is the space between the inner and outer nuclear membranes.

It is continuous with the endoplasmic reticulum.

Question 14

What are the four types of rRNA produced in the nucleolus?

Answer 14

• 5S
• 5.8S
• 18S
• 28S

These are essential components of ribosomes.

Question 15

How are genes coding for rRNA arranged in the genome?

Answer 15

As tandem repeats.

There are approximately 200 copies of rDNA per nucleus.

Question 16

What is the role of RNA polymerase I in the nucleolus?

Answer 16

It transcribes rDNA to produce rRNA.

This process is crucial for ribosome assembly.

Question 17

What happens to the nuclear lamina during cell division?

Answer 17

It breaks down.

This allows for the reorganization of chromatin.

Question 18

What is the function of the nuclear envelope?

Answer 18

It separates nuclear and cytoplasmic activities and protects the DNA from damage.

It also allows for mRNA processing within the nucleus.

Question 19

What is the structure of the nucleolus?

Answer 19

It is a prominent feature of the nucleus involved in ribosome production.

It is the site of rRNA synthesis and processing.