Table of Contents
Cell Reproduction and
Differentiation
The Cell Cycle
DNA
Replication
Transcription
Cell Reproduction
Meiosis
Cell Reproduction is Regulated
Environmental Impact on Cell
Differentiation
Reproductive Cloning
Therapeutic Cloning
Cancer
Tumors
How Cells Become Cancer
Early Detection and Diagnosis
Treatment for Cancer
Top 10 Types of Cancer
Preventing Cancer
Genetics
Genetic Inheritance
Causes of Phenotype
X and Y Chromosomes
Separation of Chromosomes
Inherited Genetic Disorders
Genes and Behavior
DNA Technology
and Genetic Engineering
DNA Sequencing
DNA Cloning
Genetic Engineering
Gene Therapy
Works Cited
Cells are reproduced by splitting in half. Cells
reproducing are what allow living things to grow. They also reproduce to
replace cells that have died or are damaged.
The
Cell Cycle
The cell
cycle has 2 stages. They are the interphase and mitotic phase.
§ Interphase
is the stage when the cell is growing for a long period of time and DNA is
copied. There are 3 sub phases of interphase.
· G1
Phase is the first stage. The cell has a large growth period.
· S
Phase is the second stage. S stands for syntheses of DNA. The cell grows at a
slower rate.
· G2
Phase is the last stage. The cell is getting ready to divide. It still
grows but at a slow rate.
§ Mitotic
Phase is when the DNA is split in two and the nucleus divides and the cytoplasm
divides. The two new cells are called daughter cells.
A cell cycle takes 18-24
hours in mammals. The Mitotic Phase is the shortest process and takes 30-45
minutes. When the cells no longer need to reproduce they stop dividing and
enter a stage called G0. Some cells can come out of this stage and begin
to divide again if necessary and some cannot.
DNA
DNA is a “double stranded string of nucleotides
intertwined in a helical shape.”(pg. 407) The DNA is bound together into an
arrangement called a chromosome. There are 46 different chromosomes in humans.
Chromosomes organize the DNA in the nucleus. They have proteins called
histones. Chromosomes can be seen by microscope right before the nucleus
divides. Mitochondria also have a small amount of DNA. These are not made into
chromosome and have about 37 genes. Genes are segments of DNA that have the
code for a protein. The 46 chromosomes have around 20,000 genes. Every cell needs
to have the exact same set of DNA. DNA is duplicated each time a cell is
divided.
Replication
Replication is the
processes a cell goes through in which its DNA is duplicated so that the two new
cells have identical genes. The first step in this process is that the double
strands in the helix come apart and are then copied so that the new strand is
the exact same as the original. When the strands separate, it happens in more
than one spot so the replication does not take too long. Enzymes attach themselves
along the strands and then take a piece of them apart which creates a
replication bubble. The new strands start to form from these bubbles. When the
strands are done being replicated they remain attached at the centromere where
they remain until mitosis. Mutations may occur when mistakes are made during
the replication process. Mutations may also occur from chemicals or physical
injury. If these mutations are not fixed before replication they could be
passed on. If the damage is too much, it may not be able to be fixed. Mutations
are corrected by DNA repair enzymes. These enzymes work by identifying damage,
taking out the damaged nucleotide, putting a new nucleotide in its spot, and
then reconnecting it to the DNA. Genes are in charge of DNA repair. If the gene
or code is damage in charge of repairing DNA is damaged, it will not be able to
make repairs.  |
| (Britannica) |
Transcription
Transcription is the process in which DNA code is changed
into a single strand of mRNA. This process is a lot like replication. Some
differences in the processes are:
v Only
one gene is unwound from instead of the whole molecule.
v Only
one strand of DNA has the genetic code for the synthesis of RNA.
v One
of the base pairs of RNA is different, it uses uracil instead of thymine.
v RNA
uses ribose instead of deoxyribose for its sugar group.
 |
| (Chemis) |
When transcription has been completed, the RNA comes off
the DNA strand and the 2 strands of DNA are rejoined. There are at least three
types of RNA which all have a job to do so that proteins can be produced. mRNA
has the directions for new proteins. Transfer RNA has the code for one amino
acid and anticodon which is the base triplet that matches a sequence to a
codon. tRNAs job is to catch amino acids and take them to the correct spot on
the mRNA. Ribosome RNA is two subunits and proteins. Its job is to make the
mRNA and the tRNA stay in the correct spot while the amino acids are joined
together. Translation is done in three steps. The first step is initiation in
which tRNA attaches to the ribosome subunits and to mRNA molecule. The next
step is elongation in which the amino acids chain grows longer one amino acid
at a time. The third step is termination is when the process is over and the
chain breaks off from the mRNA.
Cell
Reproduction
The nucleus splitting in two is called mitosis. There are
different phases that make up the mitotic cycle. Prophase is when the copied
chromosomes are first able to be seen. During this phase the tubular part of
the cytoskeleton is broken down and the put back together. This is called the
mitotic spindle and will cause the two sets of DNA to separate. The next phase
is called metaphase. During this phase the copied chromosomes line up in the
middle of the cell. The cells appear to be resting during this phase. Next is
anaphase during which the DNA molecules come apart and go to different sides of
the cell. The last phase is telophase. When the chromosomes are at both ends of
the cells the mitotic spindle breaks apart and nuclear membranes surround the
chromosomes. After mitosis the cell enters a process called cytokinesis which
results in two daughter cells being made. Diploid cells have 46 chromosomes
from 23 pairs of chromosomes. Haploid cells have one set of 23 chromosomes and
are found in sperm and eggs and are made by meiosis. When fertilization happens
the cell will then have 46 chromosomes and be a diploid cell.
Meiosis
Meiosis I and meiosis II are the two events of nuclear
and cell division for meiosis. This begins just like mitosis then during prophase;
the copied homologous chromosomes come together and trade parts of DNA, called
crossing-over. The homologous pairs of chromosomes are then taken from each
other. During meiosis II the copied chromosomes are arranged and the sister
chromatids are detached from each other. The haploid daughter cells are not the
same due to the crossing-over. Meiosis is different is males and females. In
males it makes four sperm that are the same size but has different genetics. In
females meiosis II isn’t finished unless the egg is fertilized by the sperm.
Cell
Reproduction is Regulated
Cells divide at different rates. They have internal
controls that let it know if it needs to divide. There are check points during
the replication process that the cell goes through. There are also things
outside of the cell that tells it to divide or not. If certain hormones or
nutrients are not there the cell will stop at a checkpoint.
Environmental
Impact on Cell Differentiation
Differentiation is how a cell changes so it is no longer
the exact same as its parent or sister cell. A fertilized egg is a large cell.
When the egg starts to divide, it becomes two cells, then four, eight and then
sixteen. During this time the cells do not grow. As they divide they actually
get smaller. When they get to around sixteen or thirty two cells, some cells
are exposed to things that others are not. For example, cells on the outside are
exposed to fluids while the ones on the inside are not. Things that can affect
a fetus gene include cigarette smoke, alcohol, medications, illegal drugs,
chemicals, and radiation.
Reproductive
Cloning
There are two ways that reproductive cloning is done.
Embryo splitting is one of them. This is done by splitting the cells when they
have divided to eight. At this time they have not yet differentiated and are
still identical. After they are split they are placed into different surrogate
mothers. All eight will be clones of each other. The second way reproductive
cloning is done is called somatic cell nuclear transfer. This is done by taking
an egg from a donor and removing the nucleus. A somatic cell is taken from the
animal that is going to be cloned and put in the egg. An electric current is to
blend the two cells together. The egg is placed into a surrogate mother.
Therapeutic
Cloning
Therapeutic cloning is when cells are cloned with the
purpose of treating medical issues in humans. There is still a lot that needs
to be learned about cell differentiation before this becomes a realistic
treatment for humans.
Cancer
Cancer is a disease that is caused by cell division and
differentiation. Healthy cells have mechanisms that keep their rate of division
at a good rate. Healthy cells usually stay in the same location. There are
certain times when cells divide faster than usual and it is normal such as
during pregnancy.
Tumors
 |
| (National Cancer Institute) |
When the rate of cell division is increased it is called
hyperplasia. These cells will develop into a mass called a tumor. Tumors may be
benign or cancerous. Benign tumors do not pose a health risk unless they grow
so big they crowd the healthy cells. Some Benign tumors such as moles have the
potential to develop into cancer.
How
Cells Become Cancer
Cells that turn into cancer also have a structural
change.
· The
nucleus grows larger
· There
is not as much cytoplasm
· They
no longer have a special function and structure.
When the structure changes into something that is not
normal for the cell, it is called dysplasia. Dysplasia can be called
precancerous because the cells are acting in ways that may lead to cancer. If
the tumor is all in one place it is called in situ cancer and doctors are
usually able to remove the entire tumor through surgery. When the cancer spread
to other organs or regions it is called metastasis. This happens when cancer
cells fall off of the tumor and move through the body by blood or lymph. These
tumors are referred to as malignant tumors.
Cancer develops when these two things happen at the same
time:
· Cells
divide and grow in an abnormal way
· Cells
change so that they are able to break off from connecting cells
There are different types of genes that tell the cell
what to do.
v Structural
genes are in charge of the proteins that are needed for the cell to grow,
divide, differentiate and adhere.
v Regulatory
genes are in charge of proteins that initiate or stop the expression of
structural genes. There are two types.
Ø Proto-oncogenes
help cells to grow, divide, differentiate or adhere.
§ Proto-oncogenes
that are damaged and may lead to cancer are called oncogenes.
 |
| (National Cancer Institute) |
· There
needs to be more than one oncogene for cancer to occur.
Ø Tumor
suppressor genes stop out of control cell growth, division, differentiate, or
adhesion.
§ When
these genes become damaged it may lead to cancer.
Mutator genes help repair DNA during replication. It is
possible that as these genes mutate they develop errors that may lead to
cancer.
There are many different things that may contribute to
cancer developing.
v Age
is a very important consideration in the development of cancer.
v A
family history of cancer makes you more likely to develop it.
v There
are certain types of viruses that may lead to cancer.
v There
are certain types of bacteria that may lead to cancer.
v Chemicals
that are used in our environments may lead to cancer.
v Tobacco,
both cigarettes and smokeless lead to cancer.
v Radiation,
which is found both in nature and manmade things, can lead to cancer.
v An
unhealthy diet may lead to cancer.
A
healthy immune system is necessary to help prevent cancer.
Early
Detection and Diagnosis
Tests such as MRI and PET are able to give doctors very
good images of places such as tissues that may not be seen on an x-ray. Genetic
testing can let people know if they have a mutated gene. Enzyme tests that look
for the enzyme telomerase can help detect cancer.
Treatment
for Cancer
The most common treatment is surgery, radiation and
chemotherapy. There may be one, two or all three of these done depending on
what type of cancer it is. There are also side effects with these. Radiation
also damages healthy cells but they are usually able to recover but some will
not. Surgery and radiation may miss some cells that have metastasized so the
cancer may come back at later date. Chemotherapy is a chemical that is given
that kills cancer cells. It also kills and damages some normal cells. There are
a lot of side effects such as nausea, vomiting, hair loss and anemia. New
treatments are being developed which will only kill the cancer cells without
damaging the healthy cells. One of these ways is magnetism. This is when a
magnet pulls metallic beads which contain chemotherapy drugs into the tumor.
Another way is photodynamic therapy which uses light sensitive drugs and
lasers. A third way is immunotherapy which tries to strengthen the immune
system. Stopping angiogenesis is another way. This works by stopping blood
vessel growth so that the tumors cannot grow anymore. Gene therapy and
molecular planning are yet another way to combat cancer.
Top
10 Types of Cancer
· Skin
Cancer
· Lung
Cancer
· Breast
Cancer
· Prostate
Cancer
· Colon
and Rectum Cancer
· Lymphoma
Cancer
· Bladder
Cancer
· Kidney
Cancer
· Cancer
of the Uterus
· Leukemia
Preventing
Cancer
Most cancers that are not skin cancer could be prevented
by not smoking and eating a healthy diet. Include cruciferous vegetables such
as broccoli, cauliflower and kale in your diet. Research is showing that the
sulforaphane that is found in these and other cruciferous vegetable can help
prevent cancer. (University)
And most skin cancers could be prevented by avoiding the sun. Knowing your family’s
history of cancer is important and so is knowing your body so you can recognize
lumps or changes in your skin. Drink alcohol only in moderation and stay
informed. There are new studies suggesting that hormone therapy may be related
to breast cancer and that when women stop hormone therapy their chances of
developing new breast cancer are reduced. (Science Daily)
Genetics
Genetics are genes you inherit from your parents. They
are parts of DNA that have a code for making protein. Humans have around 22,000
genes which are found on 23 pairs of chromosomes. The 23 chromosomes are made
up of 22 pairs of autosome and a pair of sex chromosomes. One pair of autosomes
and one sex chromosome is inherited from each parent. There can be slight
changes in the autosomes due to the DNA sequence not being exactly the same.
This type of gene is referred to as alleles. If the pair of alleles is
identical then they are called homozygous. If the pair of alleles is not
identical that is called heterozygous. All of your alleles together are named
your genotype which helps control your phenotype which is your characteristics.
Genetic
Inheritance
 |
| (How Children Inherit Cockayne Syndrome) |
A Punnett Square shows all of the possible ways genotypes
may be passed down by the parents to their children.
(How Children Inherit Cockayne
Syndrom)
In the 1850s, Gregor Mendel, an Austrian monk, discovered
through his research with yellow and green peas that traits can skip
generations and then return. The allele that is inherited is random so there isn’t
a sure way to know what traits will be passed down. Mendel thought that the
reason this would happen is because one of the genes was dominant and the other
was recessive and the dominant gene would be the one shown. The same is true
for humans. Most of the time recessive alleles don’t really matter in regards
to health but in some case they do. Cystic Fibrosis is from recessive alleles
that is missing a critical protein. When referring to dominant and recessive
alleles, dominant does not have anything to do with how often it is found, it
is talking about how it interacts with recessive alleles.
 |
| (South Caldwell High) |
To the right is a Punnett Square when looking at two traits to
see what traits a child could inherit from their parents.
There are other ways alleles work. One of these is
Incomplete Dominance. The result is phenotype that is in between the homozygous
phenotypes. Another is Co dominance. This is when both the alleles work the
same and there is not a dominant one.
Causes
of Phenotype
A lot of traits are caused by many genes not just one.
This is called polygenic inheritance. Examples of polygenic inheritance are:
Ø Eye
Color
Ø Height
Ø Body
Size
Ø Body
Shape
Most people will be similar to their parents but there is
a chance they a child could inherit genes that will cause them to look
different from their parents. Phenotypes are also impacted by environment. Diet
can have a huge effect on height and body size. There are some diseases that
are genetic but most of the time we only a low increased risk of contacting
that disease. Controlling environmental factors that we can such as diet will
help avoid contacting the disease. Alleles that are linked near each other may
be inherited together, affecting the phenotype.
X
and Y Chromosomes
X and Y chromosomes control what sex a child will be.
Females have XX chromosomes and males have XY, making the child’s sex dependent
on what chromosome is inherited from the male. There are some diseases that are
linked to the X chromosome and they are more common in males than females
because they do not have the extra, dominant X chromosome.
Separation
of Chromosomes
Chromosomes that have a copy must break into two cells.
When they break apart into two cells they don’t always come apart correctly.
This is called nondisjunction. Sometimes they don’t break into two like they
should. In rare instances, during meiosis, the chromosome may be lost when it
breaks off, which is called deletion, or may fasten on to a chromosome where it
shouldn’t, which is called translocation. When this happens the cells most
likely just die and are replaced by new cells. Sometimes things go wrong when
the cell breaks off during mitosis. Usually the sperm, egg or embryo will not survive
if the chromosome is not as it should be. There are some cases where the fetus
will be born and live. The usual result when this happens is the child will be
born with Down syndrome. 95% of Down syndrome is the result of having 3
duplicates of chromosome 21. Some other disorders are Edwards syndrome and
Patau syndrome. Nondisjunction can also occur with the sex chromosomes. The
following are the four ways this is usually seen.
Ø Jacob
syndrome-XYY-males have an extra Y chromosome-may be tall-may have learning
difficulties.
Ø Klinefelter
syndrome-XXY-males have an extra X chromosome-they are tall-they also may have
learning difficulties-may have breasts-they are sterile.
Ø Trisomy-X
syndrome-XXX-females have an extra X chromosome-may be mildly mentally
retarded.
Ø Turner
syndrome-XO-females with one X chromosome instead of two-short with small
breasts-sterile-short life expectancy.
When deletion occurs the result is usually miscarriage
but sometimes the fetus survives and is born. One type is cri-du-chat syndrome
which happens when there is deletion from chromosome 5. This syndrome results
in mental and physical retardation. In some cases, translocation can result in
a bigger risk of developing some cancers.
Inherited
Genetic Disorders
Inherited genetic disorders are brought about if two
abnormal alleles are inherited. Some inherited diseases, such as heart disease,
are caused by more than one gene. Phenylketonuria is an inherited genetic
disease that causes a person to not be able to make an enzyme that metabolizes
amino acid. Tay-Sachs disease is also an enzyme disease from a gene on
chromosome 15. People with this disease are not able to metabolize
sphingolipid. Huntington disease is also an inherited genetic disease that
causes nerve degeneration which will lead to death.
Genes
and Behavior
Genes code for
proteins not for behaviors. Some gene codes may influence certain behaviors or
moods but they are not the reason someone acts on them. There is not a certain gene that causes depression, happiness,
aggression, anxiety or other moods and behaviors.
DNA
Technology and Genetic Engineering
DNA technology has to do with taking DNA apart and
putting it back together in a different way which makes new molecules of DNA
that had never been made before. Genetic engineering is when the genetic makeup
of something is changed.
DNA
Sequencing
 |
| (Kimball) |
Biologists first place millions of single strand DNA into
a test tube. Next they put small single strand DNA primers into the test tube.
The primer is where the new strand of DNA starts and will be complementary to
the strand that is being sequenced. Then a combination of four nucleotides that
are found in DNA and a combination of four nucleotides that have been altered
are added. When the altered nucleotides are added, synthesis is halted. Then
the strands are placed in gel and go through gel electrophoresis. This process
creates an electrical field and makes the DNA move through the gel. A laser
reads the labels as they move out of the gel and arranges them by size. This shows
the sequence of DNA.
DNA
Cloning
When DNA is cut, spliced and copied, it is called
recombinant DNA technology. This is done so that DNA can be moved from one
thing to another and is usually used to put certain genes into a bacteria so
that protein can be made. Special components are needed for recombinant DNA
technology. Restgriction enzymes are one. They cut the DNA from any source
resulting in two short single strands. DNA ligases are also needed for
recombinant DNA technology. This enzyme joins DNA pieces back together after
they have been cut. Plasmids are also needed. Plasmids are DNA that is in
bacteria and are needed for bacteria to reproduce. DNA can be cloned from a
small portion through polymerase chain reaction. This is not a good way to
clone genes and proteins because the clones do not have regulatory genes and
their proteins. Polymerase chain reaction is done by unwinding the DNA strands
with heat then mixing them with primers, nucleotides and DNA polymerase. The
end result is duplicated DNA strands. DNA fingerprinting is how someone can be
identified from a small piece of DNA. This is done by cloning a small amount of
DNA by polymerase chain reaction. This is used to determine paternity and
identify individuals.
Genetic
Engineering
Genetic engineering creates transgenic organisms, which
is an organism that has genes from a different species. This is used to create
transgenic bacteria, transgenic plants, and transgenic animals. Transgenic
bacteria include insulin, human growth hormone, erythropoietin, tissue
plasminogen activator and human blood clotting factor VIII. Some vaccines are
made from transgenic bacteria. It is harder to make transgenic plants than it
is to make transgenic bacteria. Recombinant DNA can be added by shocking the
plant cells with a high voltage or inserting the recombinant DNA into the plant
cells at a very fast rate. Transgenic plants that have been made include tomato
plants that do not freeze, tomatoes that have a longer shelf life, crops that
resist insects and herbicides. Some transgenic plants grow faster and bigger
and a golden rice was made that has very large amounts of vitamin A. Transgenic
plants may also be used to make edible vaccinations. Transgenic animals are
more difficult to make than transgenic plants. To make a transgenic animal, DNA
would most likely be inserted into a fertilized egg. Bovine growth hormone has
been placed in cows, pigs and sheep. This is done so that animals will grow
faster and larger so food production is increased. Transgenic animals are also
used to study some diseases such as Alzheimer’s.
 |
| (Genetic Engineering, Pesticides and Your Health) |
Gene
Therapy
Gene therapy is when human genes are put into human cells
with the intent to treat a disease. There are still a lot of things that are in
the way of making this a reality. As challenging as transgenic animals are to
make it would be even more difficult to fix genetic disorders in humans. It is
very hard to get the recombinant DNA to the correct cells. If disease could be
corrected through gene therapy it could still be passed down to that person’s
children. If genetic diseases were able to be cured in people who would die
before reproducing, we might actually create more genetic diseases. Gene
therapy may be done my inserting the protein that can prevent the disease
through a vector. One type of vector is a retrovirus. One way this is done is
by taking the cells from a person and putting it with the gene and then putting
it back in the person. Another way is by placing the gene in a person, into the
tissue you want it to go to if possible. There has been some success with gene
therapy treating severe combined immunodeficiency disease. Researchers are
trying ways to treat cystic fibrosis and some cancers with gene therapy.
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Chemis. DNA Sequencing. 1999. 2 March 2012
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DNA Sequencing. n.d. 26 February 2012
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Genetic Engineering, Pesticides and Your Health. 2010. 3 March 2012
<http://www.taees.org/wp-content/uploads/2011/09/genetic-engineering.jpg>.
How Children Inherit Cockayne Syndrom. n.d. 26 February 2012
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Johnson, Michael. Human Biology. Pearson
Education, 2012.
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<http://home.comcast.net/~john.kimball1/BiologyPages/D/DNA_sequence.gif>.
National Cancer Institute. Web-Books.com. n.d.
22 February 2012
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