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Cell division and cancer 9/9
• What is heredity and how is this indicated by ones
karyotype?
• How do we pass our genetic heritage on to the next
generation?
• When is genetic information NOT passed on to the next
generation?
• How much time does it take for a cell to “divide”?
• How do somatic cells divide in the body?
• How do we form the egg and sperm?
• Why do we get cancer?
• What do we do to treat cancer?
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Practice
Quiz:
If one strand of DNA has Adenine at a position, which base would be at the
same position on the complimentary strand?
• What part of what organelle contains DNA that is being used to produce
mRNA AT THE GREATEST rate?
• _____RNA carries the information (codons), ____RNA carries anticodons
and amino acids, and ____RNA is found inside the ______which either
associates with the endoplasmic reticulum or floats freely in the cytosol.
• If your body was cut such that you could see two thumbs and the left and
right medial malleolus, what plane of dissection would you have used?
Practice Quiz
• 1) What process of cellular division is used to produce
gametes?
• Meiosis Osmosis Mitosis Secondary active transport
• 2) Cells reproduce their DNA during what very short stage of
division? Why is it a “short” stage?
• Gap-1 S-Phase Gap-2 Mitotic Phase
• 3) The newly formed chromosomes held in a spindle, split
evenly to two opposite poles during what stage of mitosis?
• Prophase Metaphase Anaphase Telophase
• 4) Which term refers to a cell that is not an egg or sperm?
• Gamete Somatic
Phenotype
Genotype
• 5) What does DNA abbreviate? Why is DNA more chemically
stable than RNA?
Complimentary binding of bases on two complimentary
nucleotides (GC and AT) across the DNA double helix of two
single strands of complimentary DNA.
Heredity is the passage of genetic
characteristics to offspring.
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What are genes?
What are genetic loci?
What are traits?
What are alleles?
Alleles can be Dominate vs Recessive
• What is penetrance?
Polygenetic Trait: several genes responsible for one trait
Pleiotropic Gene: one gene responsible for several traits
• Sex-linked traits:
– Why are men more likely to get a sex linked genetic disorder?
– Consider hemophilia and the X-chromosome
Why are children born to older parents more likely to be born with
genetic abnormalities?
Most human cells have 46 chromosomes: a
karyotype lets us see these chromosomes visually.
• Humans have 46 chromosomes= 23 pairs
• Each chromosome of a pair is a homologous chromosome
– (one strand of dsDNA X 2)
• We have 22 autologous chromosomes
• We have one sex-chromosome
– It is either two X-chromosomes
– Or a X and a Y chromosome
Genotype: what we could become based on our genes
– There are about 35,000 genes found human DNA
– Each “gene” can make one or several proteins
• When we “express“ genes we make their protein products
Phenotype: what genes are expressed as a “trait”
• What you “look” like is based on what genes you express.
• Expression determines the proteins in your body
Which modification in DNA can be passed on to future
generation of your cells and of your body?
Two primary cell types: Somatic cells and Gametes
Mutations in somatic cells cannot be passed on to your children.
Cancer is typically a change in somatic cells
– The risk for cancer can be hereditary, but the cancer itself is
not.
– Each diploid “somatic” cell contains 46 chromosomes (23n)
“Gametes” are the Egg (oocytes) and Sperm (spermatozoa):
– Each haploid gamete contains half of your chromosomal set
(23+23=46 chromosomes)
– Mutations in the DNA of your gametes is passed on to all cells
of next body or your children (if mutation is not fatal)
– Advantageous mutations here give the body advantages,,,,,
• this drives the theory of evolution.
– Advantageous mutations may be inherited by future
generations!
– Fatal mutations “usually” do not get passed on….”usually”.
How do cells divide in the body and in the gonads?
There are two types of cell:
1) Somatic: 46 chromosomes with 23 pairs (types)
2) Gamete: 23 chromosomes with 23 types (no pairs)
(Your mom gave you 23 and your dad gave you 23)
Somatic Cells: Create identical duplicate cells, each with a
diploid set of chromosomes.
Over 99% of cell divisions are somatic!
The testicles and ovaries can produce non-identical cells
(gametes) each with a haploid number of chromosomes
– This type of cell division is very rare but required for
human reproduction
Gametes represent only a tiny percentage of the total cells
found in the body.
Diploid and Haploid cells are formed using two different ways:
Mitosis or Meiosis
Four Phases of the Cell Cycle Occur During
Interphase and Lead to Mitosis (Cell Division)
Also See Page 1052
G1-Gap One Phase: most cells spend most of the time doing
nothing but living.
S-Phase: cell replicates its DNA (Why is time short?)
– dsDNA (1X2)X46 dsDNA
– Identical copies bound by a centromere
– This is “expensive” and not done unless cell “Plans” to
divide!
G2-Gap Two Phase: cell must make special proteins required to
split sisters, cytoplasm, and plasma membrane (Why is this
time short?)
Now we enter the short Mitotic Phase where the nuclear
membrane dissolves and cell division physically occurs!
Cancer cells cannot prevent entry into the S-phase, once a cell
enters S-phase, it tends to divide rather rapidly.
Diploid somatic cells replicate by a process called “Mitosis”
Stages: Interphase>Prophase>Metaphase>Anaphase>
Somatic cells spend most of the time in the interphase stage!
>Metaphase>Anaphase>Telophase>Interphase (46n >46n)
Gametes (Egg and Sperm) are formed in the ovaries or testicles by a
specialized cell division called: Meiosis (See pg 1052). This creates two
non-identical “haploid” cells with 23 chromosomes (not 46 chromosomes)
This uses the same: prophase>metaphase>anaphase>telophase steps,
except that the centromere does not dissolve during the first division!
In the second phase of meiosis, the centromere dissolves and the
identical chromatids split! This happens just before they are needed
for reproduction.
What Causes Cancer in somatic cells?
• Genetic heredity: what we can become.
• Misconceptions about heredity:
– Mutagens/Carcinogens cause neoplasm– Teratogens change human development– Tendency (risk) of a disorder can be hereditaryAny changes in the DNA base sequence may modify proteins
that are produced!
Cell cycles alter severity of change:
– Mitosis vs. Meiosis  Non-Heritable vs. Heritable
Any abnormal growth is a neoplasm or “tumor”
Non-heritable growths can be “Benign” or “Malignant”
Ultimately “cancer” is related to a loss in cellular
function/control that can spread!
Changes in DNA cause changes in regulatory proteins and a
loss in control over cell division.
Oncogenes make proteins that regulate cell division.
Damage to an oncogene can change cell division.
Examples: ras and erbB2…..Why are oncogenes important?
Cancer cellslose control of cell division and form neoplasms
Cancer cellstend to dedifferentiate:
--Cells lose their cellular identity and get large
– When they do this they lose the ability to stick to neighbors
– They may “metastasize?
How do we treat cancer?
Tricks: What do cancer cells need to survive and divide? Why are
these items targets for treatment?
– Treatment Targets: DNA replication, Transcription,
Translation, oncogenes, tumor suppressor genes.
– Why does chemotherapy make the whole body sick?
– Why are there often chemotherapy “side effects?
– What tissues are most sensitive to “side effects” of
chemotherapy.
What is “cancer remission”: Why can’t we be sure (“Cured”)?