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Quiz about Bodily Defences Against Cancer

Bodily Defences Against Cancer Quiz

Cancer is primarily a genetic disease caused by the accumulation of mutations. This quiz looks at the numerous mechanisms the body uses to prevent and repair such mutations and thus form a defensive system against cancer progression.

A multiple-choice quiz by doublemm. Estimated time: 6 mins.

Author
doublemm

Time
6 mins

Type
Multiple Choice

Quiz #
360,003

Updated
Dec 03 21

# Qns
10

Difficulty
Tough

Avg Score
6 / 10

Plays
425

Awards
Top 20% Quiz

One at a Time - Single Page - Timed Game

Question 1 of 10

1. Mutation can occur during DNA replication, which is performed by an enzyme called DNA polymerase. This enzyme is not 100% efficient (hence the mutations), but it does have a built in ability to degrade DNA that it has synthesised and which contains a mutation. What is this ability called? Hint

Double-checking

Spell-checking

Revision

Proof-reading

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Question 2 of 10

2. Mutations to DNA that are not corrected by DNA polymerase may be targeted by a set of proteins that detect incorrectly paired DNA nucleotides and induce the degradation of this DNA segment. What is this process known as? Hint

Mismatch repair

De-pairing machinery

Point mutation analysis

Base purging

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Question 3 of 10

3. As well as mispairings in DNA, more serious events can occur during DNA replication - namely breaks in the DNA backbone. This can lead to the loss of entire sections of chromosome and so must be repaired when they do occur. What term is given to the repair mechanism which uses undamaged DNA as a template to "rescue" broken DNA? Hint

The "we're all in it together" mechanism

DNA loaning

Homology-directed repair

The "helping hand" mechanism

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Question 4 of 10

4. As well as mechanisms to reverse DNA damage and thus reduce the risk of cancer-development, the human body also employs several preventative measures. These include the use of vitamin C, vitamin E, and superoxide dismutase to reduce the amount of DNA-damaging agents. What name is given to these particular damaging agents that arise from cellular respiration? Hint

Non-nitrogenous compounds

Explosive silicates

Reactive oxygen species

Deleterious carbon compounds

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Question 5 of 10

5. After replication has occurred, DNA exists in cells and is exposed to mutagens from the environment. One such mechanism to correct damage is the nucleotide excision repair (NER) mechanism, which often targets damaged sites known as thymine-dimers. Which mutagen, often associated with the ozone layer, causes these thymine-dimers? Hint

Ultraviolet light

Heterocyclic amines

X-rays

Polycyclic aromatic hydrocarbons

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Question 6 of 10

6. Similar, though not identical, to nucleotide excision is base excision repair (BER). This process removes nucleotides that have undergone deamination. What is meant by deamination? Hint

The removal of an amine group from the nucleotide base

The gain of an amine group by the nucleotide base

The removal of an amido group from the DNA backbone

The gain of an amido group by the DNA backbone

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Question 7 of 10

7. Alkylating agents are substances which damage DNA and so increase the chance of cancer formation. How do these agents damage DNA? Hint

They form bulky adducts with nucleotides

They cleave the DNA backbone

They promote DNA degrading enzymes

They induce apoptosis

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Question 8 of 10

8. When DNA breakages occur, the cell may resort to joining the break and tolerating the loss of the DNA in between. The proper name for this process is called non-homologous end-joining, but what term is also used to describe it? Hint

Quick and dirty repair

Loose and fast repair

Rapid and sticky repair

Cut and paste repair

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Question 9 of 10

9. It is thought by many that stem cells are the cells which accumulate damage and become cancerous. These cells are therefore afforded extra protection to prevent the development of cancer. Which of the following is NOT a quality of stem cells which leads to protection from mutations/cancer? Hint

They have extra DNA repair machinery

They rarely divide

They are kept in protected areas of the body

They readily die upon sustaining damage

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Question 10 of 10

10. As discussed, there are several ways by which the human body can prevent and repair damage to the DNA, thus protecting from diseases such as cancer which rely on such mutations. The final line of defence of cells which acquire extensive damage is to undergo apoptosis (programmed cell death). What benefit does this action offer? Hint

It releases toxic material which also kills surrounding damaged cells

It prevents these mutations being passed on to daughter cells

It induces DNA repair mechanisms

It "mops up" carcinogenic compounds

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Quiz Answer Key and Fun Facts

Answer: Proof-reading

DNA polymerase is said to have a 5'-3' polymerase ability, meaning that it synthesises DNA starting at the 5' end and works towards the 3' end. If an error occurs, the progression of DNA polymerase halts and it moves backwards, degrading the DNA that it has just synthesised. This is done by DNA polymerase's 3'-5' exonuclease ability.

Answer: Mismatch repair

Mismatch repair is performed primarily by two proteins - MSH2 and MLH1. MSH2 scans the DNA for mismatches - e.g. when A is paired with C or when G is paired with T. MLH1 then scans for the nearest nick in the DNA (which is indicative of newly synthesised DNA). Once the mismatch and the nick have been detected, the DNA in between these two sites is degraded and DNA polymerase can have another go at replicating the DNA correctly. Mutations affecting this repair mechanism lead to increased levels of mutation elsewhere and are seen in several cancers, in particular in the colon.

Answer: Homology-directed repair

Homology-directed repair refers to the process in which a set of proteins detects DNA breaks during replication and uses adjacent, undamaged DNA as a template so that the synthesis of the broken strand can be completed. The importance of this process in cancer is seen by the fact that proteins which mediate this process often become mutated, predisposing people to cancer.

For example, BRCA2 is one such protein involved in this reparative process and its mutation is one of the leading causes of hereditary breast cancer.

Answer: Reactive oxygen species

An example of reactive oxygen species is hydroxyl radicals. The damaging effects of radicals form the logic behind the push to increase the amount of antioxidants in our diets, though the benefits of this remain contentious (readers are referred to the excellent book "Oxygen" by Nick Lane for more information).

Answer: Ultraviolet light

UV light causes covalent bonds to form between adjacent nucleotides in the DNA. They usually occur between thymine nucleotides, and less regularly between cytosine nucleotides. The NER machinery consists of several proteins in a complex involved in detecting these dimers and cleaving the DNA either side of the damage, allowing it to be removed and replaced. Faulty NER is linked to disorders such as xeroderma pigmentosa, which predisposes sufferers to skin cancers.

6. Similar, though not identical, to nucleotide excision is base excision repair (BER). This process removes nucleotides that have undergone deamination. What is meant by deamination?

Answer: The removal of an amine group from the nucleotide base

Deamination occurs randomly in the genome and can result in point mutations which can lead to changes which contribute to cancer. Deamination is detected by enzymes which remove the damaged nucleotide base, and then cleave the DNA backbone, allowing the damaged site to be removed and replaced.

7. Alkylating agents are substances which damage DNA and so increase the chance of cancer formation. How do these agents damage DNA?

Answer: They form bulky adducts with nucleotides

Alkylating agents are electrophilic compounds which form bulky adducts with nucleotide bases, causing steric perturbation and increasing the chance of mutation accumulation and DNA damage. Such agents are targeted by bodily defence compounds such as GST, and can be removed from DNA by AlkB enzymes, which oxidise them.

Answer: Quick and dirty repair

As mentioned earlier, homology-directed repair uses undamaged DNA on its sister chromatid as a template to complete replication after DNA breakage occurs. However, when no undamaged template exists, non-homologous end-joining occurs. This results in a loss of some genetic material at the site of breakage.

This action is taken since much of the DNA is non-coding and so the chance of the lost DNA being part of a coding gene is relatively low.

Answer: They have extra DNA repair machinery

Stem cells tend to be kept out of the way of damaging extracellular agents and carcinogens. For example, stem cells can be found in crypts in the intestine and in the bone marrow. The rarity with which stem cells divide also protects from the accumulation of mutations, since, as mentioned earlier, DNA replication is error-prone. Finally, DNA repair mechanisms are also error-prone and so stem cells remove this risk by inducing apoptosis upon sustaining damage rather than attempting to correct the damage.

Answer: It prevents these mutations being passed on to daughter cells

When a cell acquires damage, the cell cycle of growth and division is halted and DNA repair mechanisms are employed. Sometimes, extensive damage cannot be repaired and the cell induces apoptosis, meaning that any damage acquired is not passed on.

Source: Author doublemm

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