Biochemistry Of Cancer

Question 1

What is cancer?

Answer 1

Cancer falls under a group of diseases called tumors
Tumors are abnormal new growth of tissues and there 2 types
Benign and malignant tumors.
Benign tumors are slow growing and have distinct borders

Question 2

What are the characteristics of malignant tumors?

Answer 2

• proliferate rapidly,
• diminished growth control and cell death (Apoptosis)
• invade local tissue
• -increased genome mutation.
• spread to other tissues( metastasis)

Question 3

State the phases of the cell cycle

Answer 3

Interphase,
Mitotic phase
Quiescent phase/G0 Phase

Question 4

Describe the intephase of the cell cycle

Answer 4

The cell spends most its time in this phase. Made up of the G1 , S and G2 stages: this is the phase of the growth of the cell and carrying out its metabolic function
G1 STAGE is metabolically active, synthesizing RNA and proteins. Before the cell enters the next stage, there is G1 check point for damaged DNA and Rb and p53 proteins are involved.
S STAGE this is the stage when the cell wants to divide and involves DNA replication.
G2 STAGE this is the stage of further growth and DNA repair before entering the mitotic phase.
There is a key check point between G2 and M Phase for repair of DNA.

Question 5

What is the mitotic phase?

Answer 5

This is the stage for nuclear and cell division. After the Mitotic phase, the cell goes into the Interphase to start the cycle all over again.

Question 6

What is the quiescent phase

Answer 6

G0 PHASE: This is also known as the resting phase. Some cells will enter the INTERPHASE to the G1 stage while other cells will die Apoptosis:- A programmed cell death

Question 7

Explain how the cell cycle is regulated

Answer 7

The cell cycle is regulated to prevent uncontrolled cell division and the following are some of the ways it is done:
1. The cyclin dependent kinases(CDKs) phosphorylates proteins and controls the entry of the cells into each phase of the cell cycle. The CDKs determines whether the cell progresses to the next phase/stage or not.
2. Key check points between G1 and S stages and between G2 stage and Mitotic phase to ensure that the damaged DNA or misaligned DNA are repaired
3. There are Tumour Supressor genes that encode the production of tumor suppressor proteins that regulate the growth and replication of cells called p53 proteins. There is also a Rb(retinoblastoma) tumor suppressor protein

Question 8

Briefly describe oncogenesis

Answer 8

Abnormal cell replication can lead to developmnet of cancer called Oncogenesis
Most cancers arise from a single starting cell that has escaped from the normal growth controls and has also failed to undergo programmed death. It is a gradual multi -step process involving many generations of cells.
The cancer cells become genetically transformed cells with features of malignancy (Excessive growth, invasiveness, metastasis)

Question 9

State the genes that regulate normal cell growth

Answer 9

Growth-regulating proto-oncogenes
Tumor suppressor genes
Genes regulating Apoptosis
DNA repair genes

Question 10

Explain what proto-oncogenes are

Answer 10

Proto- oncogenes are normal genes that regulate cell division.
Proto-oncogenes code for growth factors, receptors, transcription factors, and other proteins involved in cell proliferation
Proto-oncogens are responsible for normal cell growth but when they get mutated by various mechanisms, they get transformed into cancer-causing oncogenes.

Question 11

Which mechanisms are involved in the conversion of proto-oncogenes to oncogenes?

Answer 11

Conversion of proto-oncogenes into oncogenes occurs through various mechanisms including
-promoter insertion
- enhancer insertion,
-chromosome translocation,
- gene amplification,(duplication of DNA segment)
- point mutations.

Question 12

What are tumor supressor genes?

Answer 12

Tumor suppressor genes are also known as anti-oncogenes. They inhibit cell proliferation e.g. Retinoblastoma gene AND p53 gene.

Question 13

Describe the retinoblastoma gene

Answer 13

RETINOBLASTOMA GENE was the first discovered tumor suppressor gene.
Has a role in cell cycle regulation, controls progression of the cell from G1 to S phase
It produces Rb protein which regulates cell cycle.
Once the gene undergoes mutations, cell proliferations becomes uncontrolled.
RETINOBLASTOMA GENE IS THE MOST MUTATED GENE FOUND IN CANCERS.

Question 14

Describe the p53 gene

Answer 14

p53 GENE was discovered later in 1979, is located in almost all normal tissues
It is involved in regulation of the cell cycle between G1 and S stages . It is also involved in DNA repair and apoptosis.
Once it gets mutated, the cell loses the ability of the following: i)the cell cycle regulation
ii) DNA repair and
iii) apoptosis leading to cancer formation.

Question 15

What are the consequences of p53 gene mutation?

Answer 15

Once it gets mutated, the cell loses the ability of the following: i)the cell cycle regulation
ii) DNA repair and
iii) apoptosis leading to cancer formation

Question 16

Explain the effect of alteration in genes regulating apoptosis

Answer 16

APOPTOSIS is programmed cell death
When DNA damage is irreparable, p53 gene induces BCL-2 genes (suicide genes) which activate apoptosis.
When there is a mutation in p53 gene, it can no longer induce apoptosis and the cells with the damaged genes proliferate this ultimately leads to transformation of cells into malignant cells.

Question 17

What does a defect in DNA repair genes result in?

Answer 17

When there is damage or mutation in the genes responsible for DNA repair machinery, the cells with damaged DNA proliferate and ultimately leads to development of malignancy.

Question 18

Briefly state the HALLMARK of the molecular basis of cancer

Answer 18

The HALLMARK of the molecular basis of cancer is as follows:
1. There is DNA damage which leads to various types of mutations.
2. There is mutation of genes that control cell division or cell death.
3. The factors involved in causing mutation hence leading to carcinogenesis are referred to as carcinogens.
4. Carcinogens can be due to chemical, physical, biological injury.