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Alex's Genetics > Lecture 18b > Flashcards

Lecture 18b Flashcards

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Biology 101 flashcards
1
Q

Define Cancer.

A

A bunch of multi-factorial and polygenic disorders with uncontrolled cell proliferation.

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2
Q

How many different types of cancer are there?

A

Over 100 types

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3
Q

What is Transformation?

A

The process of converting a normal cell into a malignant cell.

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4
Q

What is the incidence of cancer?

A

Around 1 million Americans are diagnosed with cancer each year.

About 500,000 will die from the disease.

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5
Q

What percentage of cancers are due to inherited predisposition?

A

5-10%

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6
Q

What do 90-95% of cancers result from?

A

A small subset of these come from spontaneous mutations and viruses.

However, at least 80% of cancers are related to exposure to mutagens, which alter the structure and expression of genes.

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7
Q

Define a Carcinogen.

A

An environmental agent/mutagen that causes cancer.

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8
Q

Generally, speaking describe the progression of cancer.

A

Benign Tumor –> Malignant Tumor –> Metastatic Tumor

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9
Q

Describe a Benign Tumor.

A

It is NOT cancer. It consists of cells that are proliferating when they are not supposed to be, however, they respect their boundaries and are not able to invade neighboring tissues (don’t keep dividing).

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10
Q

How does a Benign Tumor become a Malignant Tumor?

A

One of the benign tumor cells gains the ability to move past its boundaries. It needs to secrete enzymes that weaken the junctions making up the cells’ boundary.

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11
Q

Describe a Malignant Tumor.

A

It IS cancer. It consists of cells that are proliferating and are able to invade neighboring tissue.

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12
Q

Describe a Metastatic Tumor.

A

It consists of cancerous cells that can migrate to other parts of the body and establish secondary (aka metastatic) tumors.

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13
Q

How does a Metastatic Tumor migrate?

A

It goes into the bloodstream or other surrounding bodily fluids.

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14
Q

Define an Oncogene.

A

This is a gene whose activity has the potential to cause cancer when over-active or over-expressed.

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15
Q

In tumor cells, how do oncogenes appear?

A

The oncogenes are often mutated or expressed at high levels in tumor cells.

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16
Q

Who showed that oncogenes are over-active normal genes? What did they call these genes?

A

J. Michael Bishop and Harold Varmus.

They called these over-active normal genes “proto-oncogenes”.

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17
Q

Name the 3 ways that proto-oncogenes can turn into oncogenes.

A
  1. The oncogene may be over-expressed.
  2. The oncogene may produce an over-active / mutant protein.
  3. The oncogene may be expressed in a cell type where it is not normally expressed.
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18
Q

What are 2 ways in which an oncogene can be overexpressed?

A

1) A translocation may cause the proto-oncogene to be over-expressed.
2) A viral or transposable element integration may cause the gene to be over-expressed if it acts as an enhancer or external promotor.

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19
Q

A protooncogene is _____________ or ______________ in a large proportion of human cancers.

A

amplified or duplicated

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20
Q

What type of mutation alters the amino acid sequence of the Ras protein? What does this result in?

A

A missense mutation.

The Ras protein is always active then.

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21
Q

What do most oncogenes encode?

A

Most of them encode proteins that function in cell growth signaling pathways, however, not all of them do.

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22
Q

What is EGF?

A

A 53-amino acid peptide hormone.

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23
Q

Name 5 well-known oncogenes.

A

Ras, Raf, MYC, Jun, and Fos are all well-known oncogenes.

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24
Q

What are the 2 things that missense mutations that convert normal ras into an oncogenic ras do?

A

Either decrease the GTPase activity of the Ras protein
Or
Increase the rate of exchange of bound GDP for GTP.

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25
Q

What does the Ras protein do?

A

It takes GTP and hydrolyses it into GDP. When there is GDP bound to the Ras protein, it no longer hydrolyses GTP.

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26
Q

When a missense mutation occurs at the Ras protein, what is the result?

A

There are greater amounts of the active Ras/GTP complex, and the Ras protein constantly stays in the active state, producing a benign tumor.

27
Q

Many human cancers are associated with the ___________ of particular oncogenes that are unstable.

A

Amplification

28
Q

What is Amplification?

A

When there are many more copies of a gene.

29
Q

What does amplification of N-myc result in?

A

Neuroblastoma.

Side note: Having even 1 extra copy (not necessarily amplification) of myc will predispose to cancer.

30
Q

What does amplification of erbB-2 result in?

A

Breast carcinomas

31
Q

Specific types of ____________ ______________ have been identified in certain types of tumors.

A

chromosomal translocations

32
Q

What is an example of a chromosomal translocation that has been identified in certain types of tumors? What does it do?

A

The Philadelphia chromosome puts the proto-oncogene abl under the control of the bcr promoter, which is active in white blood cells, leading to leukemia.

33
Q

Generally speaking, what is abl?

A

A proto-oncogene.

34
Q

Generally speaking, what is bcr?

A

A gene normally expressed in white blood cells.

35
Q

What does the fusion of bcr and abl cause?

A

Abnormal expression of it in white blood cells, which causes chronic myelogenous leukemia.

This 1 mutation is sufficient enough to cause cancer.

36
Q

T/F: Generally, only 1 mutation is sufficient enough to cause cancer.

A

False! Often times, there needs to be several mutations to cause cancer. However, there are some circumstances in which only 1 mutation can be sufficient enough to cause cancer.

37
Q

Define a Tumor Suppressor Gene.

A

This is a gene that normally prevents cancer, but when it loses its function, it promotes cancer.

38
Q

How many types of Tumor Suppressors are there?

A

3: Type 1, Type 2, and Type 3.

39
Q

Describe Type 1 Tumor Suppressors.

A

These repress genes that promote cell proliferation and/or survival.
Ex: Rb and PTEN.

40
Q

Describe Type 2 Tumor Suppressors.

A

These are the most common that we see mutated. They encode proteins that function in the DNA damage response.

41
Q

What does p53 do? What type of tumor suppressor is it?

A

p53 senses DNA damage. If it senses damage, proteins arrest the cell cycle in response to DNA damage until the damage is repaired. Then, they allow the cell cycle to continue.

It is a Type 2 tumor suppressor.

42
Q

Describe Type 3 Tumor Suppressors.

A

These are DNA repair proteins. As mutations in these genes increase, mutation rate and cancer risk also increase.

Ex: Mutations in HNPCC, BRCA1, and BRCA2.

43
Q

T/F: Mutations in both copies of a tumor suppressor gene is not bad because it will just create a null allele.

A

False! It is really bad, because the mutations will accumulate.

44
Q

What are the 3 most common genes that are mutated in familial predisposition to cancer?

A

HNPCC, BRCA1, and BRCA2 (breast cancer).

45
Q

What does Rb (Type 1 tumor suppressor) normally do?

A

Rb binds E2F, which inactivates the E2F transcription factor that promotes cell division.

When Rb is phosphorylated by cyclin-dependent kinases, E2F dissociates and binds to a gene, causing transcription.

46
Q

What are Target Genes?

A

Genes required for cell cycle progression.

47
Q

What happens when both copies of the Rb protein are defective?

A

The Rb is unable to bind the E2F transcription factor, so the E2F protein is always active and this leads to uncontrolled cell division.

48
Q

Define Genome Maintenance.

A

The mechanisms that prevent mutations or prevent mutant cells from surviving or dividing (cell cycle).

49
Q

What do genome maintenance mechanisms detect?

A

These proteins detect abnormalities such as DNA breaks and improperly segregated chromosomes.

50
Q

Define Checkpoint Proteins.

A

Proteins that check the integrity of the genome and prevent cells from progressing past a certain point of the cell cycle if there is damage.

51
Q

T/F: There is only 1 checkpoint in the cell cycle of human cells.

A

False! There are several checkpoints in the cell cycle of human cells.

52
Q

What happens after damage is repaired? What happens if the damage cannot be repaired?

A

If the damage is repaired, the cell cycle continues.

If the damage cannot be repaired, the cell should undergo programmed cell death (apoptosis) to remove the threat it poses for the greater good of the organisms produced.

53
Q

Both the __ and __ checkpoints involve proteins that can sense DNA damage.

A

G1 and G2

54
Q

What is the M checkpoint monitored by?

A

Monitored by proteins that can sense if a chromosome is not correctly attached to the spindle apparatus.

55
Q

The ___ tumor suppressor is “the guardian of the genome” and is ________ in most human tumors.

It is also the most studied.

A

p53, mutated

56
Q

Generally speaking, what is p53 and what 3 things can it do?

A

p53 functions as a transcription factor. It can:

1) Activate genes that promote DNA repair (if can be repaired).
2) Activate genes that arrest cell division and may generally repress other genes that are required for cell division (if can be repaired).
3) Activate genes that promote apoptosis (if DNA damage level is too high).

57
Q

Define Apoptosis.

A

This is programmed cell death in which the cell undergoes cell shrinkage, chromatin condensation, and DNA degradation resulting ultimately in cell death.

58
Q

What are Caspases? What are these sometimes referred to as?

A

These are proteases that make cells commit suicide by apoptosis.

These are sometimes referred to as the cell’s executioners.

59
Q

In ________________, the cell is broken down into small vesicles. What happens to these vesicles?

A

Apoptosis.

These vesicles are eventually phagocytosized by cells of the immune system.

60
Q

What are the 3 main ways in which the function of tumor-suppressor genes can be lost?

A

1) A mutation occurs in the tumor-suppressor gene itself.
2) Repressive chromatin
3) Aneuploidy

61
Q

Describe how a mutation in the tumor-suppressor gene itself could cause loss of function.

A

The promoter could be inactivated or an early stop codon could be introduced in the coding sequence.

62
Q

Define Aneuploidy.

A

This is when a cell does NOT have a normal chromosome number. This may contribute to the progression of cancer if the lost chromosome carries one or more tumor-suppressor genes.

63
Q

What do karyotypes of cancer cells look like?

A

They tend to appear abnormal with fusions of chromosomes, duplications, and deletions. They look aneuploidy.

64
Q

Describe the 3 ways in which some viruses can cause cancer.

A

1) Some viruses carry an oncogene that becomes expressed in the infected cell.
2) Some viruses can insert their DNA into the genome near proto-oncogenes, which can convert them into oncogenes (because the proto-oncogene will be over-expressed).
3) Viruses that insert their DNA into the genome can also cause cancer by inserting in a tumor suppressor gene and disrupting the tumor suppressor genes.

Alex's Genetics (38 decks)

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