Study Unit 3

Question 1

What is cell division?

Answer 1

Cell division is the process by which cells make more cells, occurring for cell growth, replacement, healing, and reproduction.

Question 2

What are the types of cell division in prokaryotes and eukaryotes?

Answer 2

Prokaryotes use binary fission, while eukaryotes undergo mitosis and meiosis.

Question 3

Describe the genome differences between eukaryotes and prokaryotes.

Answer 3

Eukaryotes have a large, linear genome found in the nucleus, while prokaryotes have a small, circular genome located in the cytoplasm.

Question 4

What are the two main phases of the eukaryotic cell cycle?

Answer 4

The two main phases are M phase (cell division) and interphase (preparation for division).

Question 5

What are the stages of interphase in the eukaryotic cell cycle?

Answer 5

G1 phase (cell growth), S phase (DNA synthesis), G2 phase (preparation for mitosis), and G0 phase (cell not actively dividing).

Question 6

What was the key finding of Meselson and Stahl’s experiment on DNA replication?

Answer 6

They confirmed that DNA replication is semiconservative, with each new DNA duplex consisting of one old strand and one new strand.

Question 7

In what direction does DNA replication occur?

Answer 7

DNA replication occurs in the 5′ to 3′ direction.

Question 8

What are Okazaki fragments?

Answer 8

Short segments of DNA synthesized on the lagging strand during DNA replication.

Question 9

What role does DNA ligase play in DNA replication?

Answer 9

DNA ligase joins Okazaki fragments together by completing the sugar-phosphate backbone.

Question 10

How do telomeres and telomerase function in eukaryotic cells?

Answer 10

Telomeres protect chromosome ends from shortening during replication, and telomerase extends these ends.

Question 11

What are the main stages of mitosis?

Answer 11

Prophase, prometaphase, metaphase, anaphase, telophase.

Question 12

What occurs during metaphase?

Answer 12

Chromosomes align along a single plane in the middle of the cell.

Question 13

What is the role of cyclins and CDKs in cell cycle regulation?

Answer 13

Cyclins regulate the cell cycle by activating cyclin-dependent kinases (CDKs), which promote cell division.

Question 14

What are the three major cell cycle checkpoints?

Answer 14

DNA damage checkpoint, DNA replication checkpoint, spindle assembly checkpoint.

Question 15

What is apoptosis?

Answer 15

Apoptosis is programmed cell death, crucial for development and maintaining cellular health.

Question 16

Define oncogenes and proto-oncogenes.

Answer 16

Oncogenes are cancer-causing genes, while proto-oncogenes are normal genes that can become oncogenes if mutated.

Question 17

How do tumor suppressor genes function?

Answer 17

They encode proteins that inhibit cell division, preventing uncontrolled cell growth.

Question 18

What is the multiple-mutation model for cancer development?

Answer 18

Most cancers develop from the accumulation of multiple mutations in proto-oncogenes and tumor suppressor genes.

Question 19

What enzymes are involved in DNA replication and what are their functions?

Answer 19

DNA Helicase: Unwinds the DNA double helix.
Single-Strand Binding Proteins (SSBs): Stabilize the unwound DNA.
DNA Primase: Synthesizes RNA primers needed to start replication.
DNA Polymerase: Adds nucleotides to the growing DNA strand and proofreads for errors.
DNA Ligase: Joins Okazaki fragments on the lagging strand.
Topoisomerase: Relieves the tension caused by unwinding of the DNA.

Question 20

Where do the enzymes involved in DNA replication operate in eukaryotic cells?

Answer 20

They operate in the nucleus, where the chromosomal DNA is located.

Question 21

What is the function of the enzyme telomerase?

Answer 21

Telomerase extends the telomeres of chromosomes, compensating for the shortening that occurs during DNA replication.

Question 22

Describe the DNA damage checkpoint and its key regulator.

Answer 22

The DNA damage checkpoint ensures that the cell’s DNA is intact before proceeding with replication. The key regulator is the protein p53, which can halt the cell cycle and initiate DNA repair or apoptosis if the damage is irreparable.

Question 23

What is the DNA replication checkpoint?

Answer 23

This checkpoint ensures that all DNA is replicated before the cell enters mitosis. It prevents the division of cells with incomplete or damaged DNA.

Question 24

Explain the spindle assembly checkpoint.

Answer 24

This checkpoint ensures that all chromosomes are properly attached to the spindle microtubules before anaphase begins, preventing chromosome missegregation.

Question 25

What are point mutations and how can they affect proteins?

Answer 25

Point mutations are changes in a single nucleotide base in the DNA sequence. They can lead to:

Silent Mutations: No change in the protein.
Missense Mutations: A different amino acid is incorporated into the protein.
Nonsense Mutations: A premature stop codon is introduced, truncating the protein.

Question 26

What are insertions and deletions (indels) and their potential impacts?

Answer 26

Insertions and deletions are the addition or loss of nucleotides in the DNA sequence. They can cause:

Frameshift Mutations: Altering the reading frame of the gene, potentially resulting in a nonfunctional protein.

Question 27

What are the two main types of chromosomal mutations?

Answer 27

Structural Mutations: Changes in the structure of chromosomes, such as deletions, duplications, inversions, and translocations.
Numerical Mutations: Changes in the number of chromosomes, such as aneuploidy (e.g., Down syndrome, which involves an extra chromosome 21).

Question 28

What is a proto-oncogene and how can it become an oncogene?

Answer 28

A proto-oncogene is a normal gene that promotes cell growth and division. It can become an oncogene through mutations or increased expression, leading to uncontrolled cell proliferation and cancer.

Question 29

What is the role of tumor suppressor genes in the cell cycle?

Answer 29

Tumor suppressor genes encode proteins that regulate the cell cycle, repair DNA damage, and initiate apoptosis. Mutations in these genes can lead to loss of function and contribute to cancer development.

Question 30

How do Bax and Bcl-2 proteins regulate apoptosis?

Answer 30

Bax promotes apoptosis by forming dimers that trigger cell death, while Bcl-2 inhibits apoptosis by binding to Bax and preventing it from forming dimers. The balance between these proteins determines cell survival or death.

Question 31

What type of mutation causes cystic fibrosis and what are its effects?

Answer 31

Cystic fibrosis is caused by a deletion mutation in the CFTR gene, specifically the deletion of three nucleotides leading to the loss of phenylalanine at position 508 (ΔF508). This mutation results in defective chloride ion transport, leading to thick mucus in the lungs and digestive tract.

Question 32

What mutation leads to sickle cell anemia and what are its consequences?

Answer 32

Sickle cell anemia is caused by a missense mutation in the HBB gene, where a single nucleotide change (A to T) leads to the substitution of valine for glutamic acid at position 6 of the beta-globin chain (E6V). This mutation causes red blood cells to become rigid and sickle-shaped, leading to blockages in blood vessels and reduced oxygen delivery to tissues.

Question 33

How is Huntington’s disease caused by mutations?

Answer 33

Huntington’s disease is caused by a trinucleotide repeat expansion mutation in the HTT gene. The normal gene has 10-35 repeats of the CAG sequence, while affected individuals have more than 36 repeats, leading to the production of an abnormal huntingtin protein, which causes neurodegeneration.

Question 34

Describe the mutation responsible for Duchenne muscular dystrophy.

Answer 34

Duchenne muscular dystrophy is caused by various mutations in the DMD gene, often large deletions, duplications, or nonsense mutations. These mutations result in the absence or severe reduction of dystrophin, a protein crucial for muscle fiber integrity, leading to progressive muscle weakness and degeneration.

Question 35

What is the genetic basis of Down syndrome?

Answer 35

Down syndrome is caused by a numerical mutation known as trisomy 21, where there is an extra copy of chromosome 21. This results in developmental delays, intellectual disability, and various physical abnormalities.

Question 36

What type of mutation leads to Hemophilia A and how does it affect individuals?

Answer 36

Hemophilia A is typically caused by an inversion mutation or a point mutation in the F8 gene, which encodes the clotting factor VIII. The lack or dysfunction of factor VIII leads to impaired blood clotting, resulting in prolonged bleeding.

Question 37

How do mutations in the BRCA1 and BRCA2 genes increase cancer risk?

Answer 37

Mutations in BRCA1 and BRCA2, which are tumor suppressor genes, lead to a loss of their function in repairing DNA damage. This increases the risk of developing breast and ovarian cancers due to the accumulation of genetic mutations.

Question 38

What mutation causes Tay-Sachs disease and what are its effects?

Answer 38

Tay-Sachs disease is caused by a point mutation or small insertion in the HEXA gene, which leads to a deficiency in the enzyme hexosaminidase A. This enzyme deficiency results in the accumulation of GM2 ganglioside in neurons, causing neurodegeneration and early childhood death.

Question 39

What is the genetic cause of Marfan syndrome and its symptoms?

Answer 39

Marfan syndrome is usually caused by a missense or nonsense mutation in the FBN1 gene, which encodes fibrillin-1. This results in defective connective tissue, leading to symptoms such as tall stature, long limbs, cardiovascular problems, and skeletal abnormalities.

Question 40

What type of mutation leads to Neurofibromatosis type 1 (NF1)?

Answer 40

Neurofibromatosis type 1 is caused by various mutations, including point mutations, deletions, and insertions in the NF1 gene. These mutations lead to the loss of function of neurofibromin, a tumor suppressor, causing the formation of benign and malignant tumors along nerves.