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By the end of this section, you will be able to:
  • Describe how cancer is caused by uncontrolled cell growth
  • Understand how proto-oncogenes are normal cell genes that, when mutated, become oncogenes
  • Describe how tumor suppressors function
  • Explain how mutant tumor suppressors cause cancer

Cancer comprises many different diseases caused by a common mechanism: uncontrolled cell growth. Despite the redundancy and overlapping levels of cell cycle control, errors do occur. One of the critical processes monitored by the cell cycle checkpoint surveillance mechanism is the proper replication of DNA during the S phase. Even when all of the cell cycle controls are fully functional, a small percentage of replication errors (mutations) will be passed on to the daughter cells. If changes to the DNA nucleotide sequence occur within a coding portion of a gene and are not corrected, a gene mutation results. All cancers start when a gene mutation gives rise to a faulty protein that plays a key role in cell reproduction. The change in the cell that results from the malformed protein may be minor: perhaps a slight delay in the binding of Cdk to cyclin or an Rb protein that detaches from its target DNA while still phosphorylated. Even minor mistakes, however, may allow subsequent mistakes to occur more readily. Over and over, small uncorrected errors are passed from the parent cell to the daughter cells and amplified as each generation produces more non-functional proteins from uncorrected DNA damage. Eventually, the pace of the cell cycle speeds up as the effectiveness of the control and repair mechanisms decreases. Uncontrolled growth of the mutated cells outpaces the growth of normal cells in the area, and a tumor (“-oma”) can result.

Proto-oncogenes

The genes that code for the positive cell cycle regulators are called proto-oncogenes . Proto-oncogenes are normal genes that, when mutated in certain ways, become oncogenes , genes that cause a cell to become cancerous. Consider what might happen to the cell cycle in a cell with a recently acquired oncogene. In most instances, the alteration of the DNA sequence will result in a less functional (or non-functional) protein. The result is detrimental to the cell and will likely prevent the cell from completing the cell cycle; however, the organism is not harmed because the mutation will not be carried forward. If a cell cannot reproduce, the mutation is not propagated and the damage is minimal. Occasionally, however, a gene mutation causes a change that increases the activity of a positive regulator. For example, a mutation that allows Cdk to be activated without being partnered with cyclin could push the cell cycle past a checkpoint before all of the required conditions are met. If the resulting daughter cells are too damaged to undergo further cell divisions, the mutation would not be propagated and no harm would come to the organism. However, if the atypical daughter cells are able to undergo further cell divisions, subsequent generations of cells will probably accumulate even more mutations, some possibly in additional genes that regulate the cell cycle.

Questions & Answers

why drinking excess alcohol causes thirst and dehydration
uwikuzo Reply
what is reproduction
smart Reply
it is d act of bringing young ones to life
Oyebanji
to ensure survival of a species🚴‍♀️
Michelle
what is a genotype
Collins
what is hazardous
smart
a cell is the smallest unit of a living thing. so we all have cell
smart
It is the formation of a zygote resulting from the fusion of the sperm cell with the ovum.Thus,this results in the production of new species which are genetically dissimilar from their parent cells.
Pallavi
what is size of cell
Mohd Reply
what is size of Hart
Mohd
nanometers=um sign thingie
Michelle
microns=nanometers
Michelle
monomers and polymers of nucleic acids?
Jyrl Reply
dna and rna involvement
Michelle
give me the elements of the soil
Iguma Reply
Air, water, organic matter, inorganic matter
Tshwano
soil water humus air
Veronicah
yap
Beloved
silica, iron
Patience
potassium, sulfur, calcium, carbon
Michelle
what is cell
iyaji Reply
A cell is a smallest fundamental unit of a living organisms.
Kem
the basic structural and functional unit of life
Patience
what is size of cell
Mohd
all things are made up of.....all things cannot exist without pre-exisiting cells...check out the 16th ce tury to learn more about microscope use and cells. i will give a hint: Mr. L.
Michelle
we are all made of cells
Michelle
Nutrition - sensitive intervention
Therowda Reply
what does the sori In fern mean
arhin Reply
biology is the study .exactly what is life?
Jerry
i'm sorry , the study of life
Jerry
how can U identify a person through his blood
Frankyx Reply
through genetic fingerprinting where specific DNA sequences in a person genome can be identified.
Pallavi
by help of genetics and DNA test
Meerbadini
can it also be detected using an RNA test
Frankyx
environmental biology
Ojesola Reply
what is phytoplankton
Ojesola
What is anabolism
Treasure Reply
the break down of substance
Aunty
how many teeth has an adult person
TSEGAY Reply
36
Treasure
32
Favour
32
Kamaluddeen
32 teeth
Meerbadini
32
OLAMIDE
32 (or 36 including the wisdom teeth)
Hailey
32
Sani
26?🤓
Michelle
what is homoestastis
Ayo Reply
hypothalamus negative feedback vs. postive feedback systems.
Michelle
it is the maintenance of a steady internal environment.it is controlled largely by the brain especially the hypothalamus.
Oyebanji
What is a cell
Eric Reply
A cell is the building block of all organisms
Millicent
yes it is , it also helps in functions .
Joezman
cell is structural & functional unit of oraganisms
Meerbadini
it is a building blocks of a living organism
Joezman
it is the basic unit of life in living organisms
Nabwonso
it is the basic unite of life in living organisms
Nabwonso
it is the fundamental unit of life
Adewoye
it is the structural and functional unit of life
Ojesola
Why cells are classify as living and non living things
Millicent Reply
due to such as virus which acts as a living cell inside the cell of an organisms and out side of cell in form of crystals
Meerbadini
because there are living cells which performs complex processes such as reproduction and metabolism then there are dead cells like the top most part of the epidermis or the bark
irish
because there are living cells which performs complex function such as reproduction and metabolism
David
cause otherwise you could call fire alive
Marissa

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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