What is the initial characteristic of benign tumors?
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They lack the ability to invade or spread to other tissues.
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What is the initial characteristic of benign tumors?
They lack the ability to invade or spread to other tissues.
What happens when mutations occur in the p53 gene?
Non-functional p53 proteins are synthesized.
What process allows tumor cells to spread to other parts of the body?
Metastasis.
What are the consequences of non-functional p53 proteins?
They cannot carry out DNA repair, halt the cell cycle, or induce apoptosis.
How do tumor cells migrate to other sites in the body?
By penetrating blood or lymphatic vessels and circulating through the circulatory system.
What is the effect of accumulated DNA damage in a cell?
It increases the risk for cancer formation.
What is angiogenesis?
The formation of new blood vessels.
What type of mutation in tumor suppressor genes, such as p53, leads to uncontrolled cell division?
Loss of function mutation.
What is one of the key functions of the p53 protein?
To induce apoptosis.
What role do new blood vessels play in tumor development?
They supply nutrients and oxygen to the growing tumor at the new site.
What is a point mutation?
A small change in the base sequence, such as substitution or deletion, in the coding region.
What type of mutation in proto-oncogenes, such as ras, contributes to uncontrolled cell division?
Gain of function mutation.
How does p53 contribute to cell cycle regulation?
By halting the cell cycle in response to DNA damage.
When is a tumor regarded as malignant?
When it gains the ability to invade normal tissues and spread, thus being referred to as cancer.
How can point mutations in the coding region affect proteins?
They may change the 3D conformation of the protein, causing it to become hyperactive.
How is cancer development described in terms of process?
As a multi-step process that includes accumulation of mutations, angiogenesis, and metastasis.
What can errors in DNA replication lead to in cancer cells?
Extra gene copies through gene amplification.
What is the effect of mutations in the regulatory region, such as the promoter?
They may lead to overexpression of the gene, causing overproduction of the normal functional protein.
What are some causative factors that may increase the chances of cancerous growth?
Genetic factors, chemical carcinogens, ionizing radiation, and loss of immunity.
What is a key characteristic of gene amplification?
Selective replication of a region of a chromosome, leading to many copies.
What internal factor increases the chance of cancer cell multiplication in the body?
Loss of immunity.
What is the role of the Myc transcription factor?
It stimulates the transcription of other genes required for cell proliferation.
What does the Ras gene code for?
A G-protein found on cell membranes.
What is the role of mutations in cancer development?
Mutations accumulate over time, leading to changes in cancer cells and the development of malignant tumors.
What happens to genes within the amplified portion of a chromosome?
They can be transcribed to produce normal proteins, leading to overproduction.
What happens when the Myc gene is over-expressed?
It leads to overproduction of the Myc transcription factor, causing enhanced cell proliferation.
How does loss of immunity contribute to cancer risk?
It reduces the body's ability to eliminate infected or transformed cells.
What is the limit on the number of cell divisions for normal cells?
Normal cells have a limit on the number of divisions and undergo apoptosis when they reach that limit.
What triggers the activation of the Ras protein?
The binding of an appropriate growth factor to a receptor.
What are the internal factors that can contribute to cancer?
Loss of immunity, genetic predisposition, and hormones.
In which type of cells is gene amplification commonly observed?
Cancer cells.
What is a genetic predisposition to cancer?
Having a defective copy of a tumor suppressor gene inherited from parents.
What is apoptosis?
Apoptosis is the normal, programmed death of cells.
What is a gain-of-function mutation?
A mutation where cells with the mutant form of the protein gain a new function not present in cells with the normal gene.
What happens when GTP displaces GDP in the Ras protein?
The Ras protein becomes active and passes on the signal to cytoplasmic kinases.
What is the nature of cancer development?
Cancer development is a multi-step process involving the accumulation of mutations.
What external factors are associated with an increased risk of cancer?
Chemical carcinogens, UV radiation, and ionizing radiation.
What is the first step in cancer development?
A single cell in a tissue suffers a mutation in a gene involved in the cell cycle.
What can the amplification of an oncogene lead to?
Deregulated cell growth.
What is the significance of the BRCA1 gene?
Its mutation increases the lifetime risk of breast cancer by 70%.
What role does telomerase play in cancer cells?
Telomerase is activated in cancer cells, allowing them to undergo unlimited cell divisions without triggering apoptosis.
How do most oncogenes arise?
From dominant mutations, where a single copy of the oncogene is sufficient for expression of the trait.
How many independent mutations are typically required for cancer development?
Approximately 4 to 6 independent mutations.
What is the role of active Ras protein in cell signaling?
It activates transcription factors that turn on genes for proteins that stimulate the cell cycle.
What types of mutations can occur in the first step of cancer development?
Gain of function mutation in a proto-oncogene or loss of function mutation in a tumor suppressor gene.
Which oncogene is commonly amplified in a wide range of tumors?
myc oncogene.
What role does estrogen play in cancer?
It is needed for breast tumors to grow in females.
What are telomeres?
Telomeres are non-coding, repetitive sequences at the end of chromosomes that act as buffers for coding sequences.
What is the significance of an oncogene in germ line cells?
It results in an inherited predisposition for tumors in the offspring.
How does the Ras protein turn off the signaling pathway?
By hydrolyzing its bound GTP to GDP, becoming inactive again.
Why is mutation in one proto-oncogene or tumor suppressor gene usually insufficient to cause cancer?
Because all controls at several checkpoints must be inactivated for cancer to be initiated.
What advantage does a mutated cell have over other cells?
A slight growth advantage.
What is insertional mutagenesis?
Insertion of a retrovirus into DNA causing overexpression of a proto-oncogene.
What are chemical carcinogens?
Substances that damage or alter DNA, such as tobacco smoke and benzene.
What happens when telomeres reach a critical length?
The cell undergoes apoptosis once a critical length of the telomere is reached.
What is the consequence of a mutated Ras protein?
It remains constitutively active even in the absence of growth factor.
Is a single oncogene usually sufficient to cause cancer?
No, a single oncogene is usually not sufficient to cause cancer.
What age group is most affected by cancer and why?
Most cancers occur in people over 40 years of age due to the need to inactivate several regulatory genes over decades.
What happens to DNA damage in mutated cells?
It is passed on to all daughter cells produced from these mutated cells.
How does a retrovirus affect a proto-oncogene during infection?
It integrates into the host DNA near the proto-oncogene, leading to overexpression.
How does UV and ionizing radiation affect DNA?
It causes DNA bases to become more reactive and can lead to mutations.
How do normal cells respond to DNA damage?
Normal cells cease to divide and undergo apoptosis when there is DNA damage.
What are the genetic changes required for a cell to become cancerous?
Gain of function mutation in at least one proto-oncogene and loss of function mutations in several tumor suppressor genes.
What genetic changes are associated with the conversion of a proto-oncogene into an oncogene?
A number of genetic changes lead toward cancer.
What can happen over time to descendant cells of a mutated cell?
They may suffer another mutation in another cell cycle regulatory gene.
Why do retroviral sequences lead to overexpression of proto-oncogenes?
They do not respond to environmental signals that normally regulate expression.
What is the main cause of cervical cancer?
Human papillomavirus (HPV) infection.
How do cancer cells behave in response to DNA damage?
Cancer cells continue to divide even when there is significant DNA damage.
What happens to mutations in a cancer-promoting cell?
They are passed to all its descendants.
What is the consequence of further mutations in descendant cells?
It further deregulates the cell cycle of that cell and its descendants.
Which genes are examples of overexpression due to insertional mutagenesis?
c-myc and c-myb genes.
How is HIV associated with cancer risk?
It increases the risk of cancers like lymphoma and Kaposi's sarcoma.
What causes cancer at the genetic level?
Cancer is caused by mutations in genes regulating the cell division cycle, leading to unrestrained cell proliferation.
What are the consequences of accumulated mutations in cancer cells?
Overstimulation of cell growth and division, inability to halt the cell cycle, carry out DNA repair, and initiate apoptosis.
What is the effect of a point mutation in the ras oncogene?
It may cause a change in the 3D conformation of the Ras protein.
How does the rate of mitosis affect DNA damage?
As the rate of mitosis increases, the chances of further DNA damage increases.
What effect does chronic tissue injury have on cancer risk?
It stimulates the rate of mitosis, increasing the chance of mutations.
What evidence supports the multi-step process of cancer development?
Analysis of tumors reveals different degrees of malignancy and accumulation of genetic alterations as tumors progress.
What are the two broad categories of genes involved in cancer?
Proto-oncogenes and tumor suppressor genes.
What is the primary function of tumor suppressor genes in normal cells?
They code for proteins that prevent cell division or lead to cell death (apoptosis).
What ability does the altered Ras protein lose due to mutation?
The ability to hydrolyze GTP to GDP.
What occurs when many mutations accumulate in a cell line?
The growth of the line of clones becomes completely unregulated.
How does chronic inflammation contribute to cancer?
It generates DNA-damaging oxidizing agents in the cell.
How many genes are thought to exist in the human genome?
Approximately 30,000 genes.
What actions can tumor suppressor proteins carry out if growth conditions are not met?
Halt the cell cycle, carry out DNA repair, and induce cell death (apoptosis).
What is the result of the altered Ras protein being constitutively active?
It continuously delivers signals for cell growth and division, leading to uncontrolled cell division.
What may result from the uncontrolled proliferation of cells?
The formation of tumors.
What is the impact of chronic hepatitis B viral infection on cancer risk?
It leads to a 100-fold increase in liver cancer risk.
What is the consequence of mutations in tumor suppressor genes?
They result in a loss of function, preventing the inhibition of cell growth.
In which cancers has the mutant ras oncogene been identified?
Pancreas (90%), colon (50%), lung (30%), thyroid (50%), bladder (6%), ovarian (15%), breast, skin, liver, kidney, and some leukemias.
How are mutations in tumor suppressor genes typically inherited?
They are usually recessive, requiring both copies of the normal alleles to be mutated for expression.
What does chromosomal rearrangement involve?
The breakage and re-joining of DNA (translocation).
What is loss of heterozygosity in the context of tumor suppressor genes?
It refers to the disruption of the remaining normal allele after one allele has undergone mutation.
What can chromosomal rearrangement result in?
A hyperactive fusion protein or over-production of a normal protein.
What causes chronic myeloid leukemia (CML)?
An exchange in a small section between chromosomes 9 and 22, resulting in a mutant Bcr-Abl gene.
What role does the p53 tumor suppressor gene play in cancer prevention?
It activates DNA repair proteins, holds the cell cycle at the G1 checkpoint, and can initiate apoptosis if DNA damage is irreparable.
What are proto-oncogenes?
Genes that normally trigger cell division when appropriate.
What does the abnormal Bcr-Abl protein do?
It is a constitutively active tyrosine kinase that causes myelocytes to grow and multiply uncontrollably.
What happens to cells with one normal and one mutated allele of a tumor suppressor gene?
They behave normally until other mechanisms cause the loss of the normal allele.
What happens when proto-oncogenes are activated at the wrong time or place?
They function as oncogenes, which can lead to cancer.
What is the role of p53 in maintaining genetic stability?
It activates DNA repair proteins when DNA has sustained damage.
What do oncogenes code for?
Proteins that lead to overstimulation of cell growth and division.
What checkpoint does p53 hold the cell cycle at upon recognizing DNA damage?
The G1 checkpoint.
What is an example of a growth factor coded by proto-oncogenes?
Platelet-derived growth factor (PDGF).
What is the role of PDGF?
Stimulates proliferation of connective tissue cells at the site of injury for wound healing.
What is a characteristic of gliomas?
They have an over-expression of growth factors and receptors in undifferentiated cells.
What is the function of the receptor for epidermal growth factor?
It is a receptor tyrosine kinase that can become constitutively active when mutated.
What is the role of the Ras protein?
It is associated with the cytoplasmic surface of a membrane receptor and regulates cell signaling.
What happens to the Ras protein when it is mutated?
It remains active and continues to send stimulatory signals, leading to more cell division.
What is the function of Src protein?
It catalyzes the addition of phosphate groups onto other proteins, promoting cell survival and proliferation.
In what percentage of tumors from colon, liver, lung, breast, and pancreas is Src protein over-expressed?
About 50%.
What is a key characteristic of cancer cells compared to normal cells?
Cancer cells divide excessively without control and have escaped from cell cycle control.
What happens to normal cells when growth factor synthesis is inhibited?
Normal cells stop dividing.
Do cancer cells require growth factors to divide?
No, cancer cells have lost the need for growth factors and divide regardless of their presence.
What is contact inhibition?
Contact inhibition is the process where normal cells cease division upon contact with other cells.
How do cancer cells behave in relation to contact inhibition?
Cancer cells lose contact inhibition and continue to grow even after touching other cells.
What is the role of tumor suppressor genes like p53 in cancer development?
Loss of function mutations in tumor suppressor genes like p53 lead to uncontrolled cell division.
What is the effect of gain of function mutations in proto-oncogenes like ras?
Gain of function mutations in proto-oncogenes like ras result in uncontrolled cell division.
How many times can a normal cell divide in culture?
A normal cell can divide only 20 to 50 times.
What happens to cancer cells in terms of nutrient supply?
Cancer cells are considered 'immortal' if they have a continued supply of nutrients.
