Cancer Cells

What type of cancer originates from epithelial cells?

Carcinomas

Which cancers arise from supporting tissues like bone and muscle?

Sarcomas

What is the difference between lymphomas and leukemias?

Lymphomas grow as solid masses; leukemias spread in the bloodstream.

What is a tumor?

A mass of cells that divide uncontrollably.

How are benign tumors different from malignant tumors?

Benign tumors stay local and are rarely dangerous; malignant tumors invade and spread.

What type of tumor is capable of metastasis (spreading)?

Malignant tumors

What is anchorage-independent growth?

The ability of cancer cells to grow without being attached to a solid surface.

What does density-dependent inhibition mean?

Normal cells stop dividing when they touch each other, forming a single layer.

Why do cancer cells keep dividing beyond the normal limit?

They produce telomerase to maintain telomere length, preventing cell aging.

What kind of DNA is lost during each round of replication in normal cells?

Telomere DNA

What are the three major steps in the development of cancer?

Initiation → Promotion → Tumor Progression

What are HeLa cells?

Immortalized cancer cells taken from Henrietta Lacks in 1951 that are still used in research today.

What is invasion in cancer?

The direct migration and penetration of cancer cells into neighboring tissues.

What is metastasis?

When cancer cells enter the bloodstream and travel to distant sites, forming new tumors called metastases.

What is the role of angiogenesis in metastasis?

It allows tumors to grow new blood vessels to receive nutrients and oxygen for growth and spreading.

What protein involved in cell adhesion is often defective in cancer cells?

E-cadherin

Name two molecules that increase cancer cell motility.

Chemoattractants and Rho GTPases

What enzymes help cancer cells break through tissues?

Proteases

Name three major causes of cancer.

Carcinogens, radiation, infectious agents

What are polycyclic aromatic hydrocarbons and where are they found?

Carcinogenic chemicals found in cigarette smoke that bind to DNA.

What are pyrimidine dimers?

Abnormal bonds formed between adjacent pyrimidines (usually thymine) in DNA due to UV exposure.

What is an oncogene?

A mutated gene that promotes uncontrolled cell division and survival, contributing to cancer.

How are oncogenes typically formed?

From mutations in proto-oncogenes or introduced by cancer-causing viruses.

What is a proto-oncogene?

A normal gene that, when mutated, can become an oncogene and lead to cancer by promoting cell growth and division.

Name six mechanisms that can convert proto-oncogenes into oncogenes.

1. Growth factors
2. Receptors
3. GTP-binding proteins
4. Protein kinases
5. Transcription factors
6. Apoptosis/cell cycle regulators

Why is a single oncogene not usually enough to cause cancer?

Multiple genetic mutations are generally needed to transform a normal cell into a cancerous one.

What are tumor-suppressor genes?

Genes that inhibit cell division or promote DNA repair/apoptosis; their loss can lead to cancer.

What are the two types of tumor suppressor genes?

Gatekeeper genes (e.g., RB, p53, APC) and caretaker genes (e.g., BRCA1, BRCA2).

Gatekeeper genes

their loss opens the gates to excessive cell proliferation

• RB, p53 and APC

Caretaker genes

involved in DNA repair and chromosome sorting, which maintains genetic stability

• BRCA1 and BRCA2

What is the role of the RB gene?

It prevents cells from passing the G1 restriction point without proper signals, keeping it arrested at G0, controlling proliferation (rapid increase)

What happens if the RB gene is mutated?

Cells divide uncontrollably, which can lead to cancers like retinoblastoma.

How does HPV contribute to cancer through RB inactivation?

It produces the E7 protein, which binds and inactivates Rb, preventing it from halting cell division.

What is the most frequently mutated gene in human cancers?

The p53 tumor suppressor gene.

What does the p53 gene do?

triggers cell cycle arrest and apoptosis

What happens when p53 is disrupted?

cells with DNA damage avoid apoptosis and continue dividing

Which HPV oncogene targets p53 for destruction?

E6 oncogene

What does the APC tumor suppressor gene do?

Encodes a protein that inhibits the Wnt signaling pathway, which regulates cell proliferation.

Mutation of the APC gene is associated with what condition?

Familial adenomatous polyposis, which causes thousands of colon polyps.

How does loss of APC function promote cancer?

It prevents degradation of β-catenin, keeping the Wnt pathway permanently active and stimulating cell proliferation.

• when B-catenin is not destroyed, promotes more cell grit which leads to further growth of tumour

What is a key feature of most cancers regarding genetic changes?

Genetic instability — high mutation rates due to loss of genome maintenance mechanisms.

What are 4 causes of genetic instability in cancer cells?

1. Defects in DNA repair

   1. BRCA1, BRCA2 encode proyeins involved in repair of double stranded breaks

2. Loss of p53, which normally blocks proliferation of damaged cells

3. Errors in chromosome sorting during mitosis

4. Defective spindle attachment proteins