Chapter 17
The Mitotic Cell Cycle
Meiosis
Jim's General Idea
Chapter 18
Cancer
Chapter 19
Gregor Mendel's Basic Rules
Maternal Inheritance
Incomplete Dominance and Codominance
Genetics and Inheritance
Chapter 20
The Polymerase Chain Reaction
Transgenic Organisms and Gene Therapy
Chapter 17
The Mitotic Cell cycle
All cells in the human
body divide by mitosis with the exception of gametes (sperm and eggs
formed at the testes and ovaries). All body cells (except gametes)
have 46 chromosomes in the form of 23 pairs of chromosomes. Gametes
have 23 chromosomes. Gametes are haploid. The mitotic cell cycle
generates diploid cells, or cells containing chromosomes that come in
pairs. DNA is duplicated and split between two daughter nuclei, and
the nucleus then divides. Nuclear division (otherwise known as
mitosis) consists of the phases: interphase, prophase, metaphase,
anaphase and telophase followed by cytoplasmic division (or
cytokinesis). Cytokinesis is where the cytoplasm divides, two new
daughter cells form and the process starts over.
During interphase, the
cell grows and synthesizes. Gap 1 (G1) is the long growth period
between cell divisions. Synthesis (S) of DNA for cell division occurs
before Gap 2 (G2), or the last phase of growth before cell division.
Interphase is all about cell growth and the cell’s metabolic
activity.
National High Magnetic Field Laboratory, March 7th 2012
Prophase is the next
phase. Here, the mitotic spindle forms and the centrioles migrate to
the opposite poles in the spindle. Chromatin (multiple chromatids)
condenses into visible chromosomes. The nuclear membrane dissolves
and the metabolic activity decreases.
Nikon Microscopy March 7 2012
During metaphase, the
chromosomes meet at the cell’s equator, forming a single line
between the cell poles.
Visual Photos March 7th, 2012
At anaphase, the
duplicate chromosomes separate and microtubules pull the daughter
chromosomes toward the cell poles.
Visual Photos March 7th 2012
At telophase, the spindle
formed in prophase pulls apart. The nuclear membrane forms and the
chromosomes uncoil and turn back into chromatin.
Visual Photos, March 7th 2012
During cytokinesis, a ring of
filaments forms at the middle of the cell and tightens. A cleavage
furrow forms and two identical daughter cells (diploid cells) form as
the ring pinches them apart.
Meiosis
Gametes, or
haploid cells, are formed in the ovaries and testes in the process of
meiosis. Meiosis reduces chromosome numbers in half, producing
haploid daughter cells.
Meiosis 1
Prophase 1
consists of duplicated homologous chromosomes of a particular gene
that pair up and swap segments in the synapse (process of crossing
over)
In metaphase 1,
homologous pairs of chromosomes line up and a double line of
chromosome pairs forms.
During anaphase
1, the pairs of chromosomes are separated but the duplicated
chromosomes stay intact.
Telphase 1 and
cytokinesis yields two haploid daughter cells but chromosomes are
still in their duplicated state.
APII
Notes Home page, March 7th
2012
Meiosis 2 yields 4
haploid daughter cells. In males, 4 viable, functional sperm from
from each cell. In females, however, unequal cytokenesis during
meiosis yields one egg and three polar bodies from each cell entering
meiosis. Only the egg is viable.
Jim's General Idea
Jim's
General Idea consists of three steps. First is DNA replication, or
the process of copying DNA prior to cell division (making exact
copies of all 46 chromosomes, or 23 pairs)
A gene is a short
segment of DNA, which contains the basic code for protein. Genes are
the smallest unit of DNA.
In replication,
the DNA strands uncoil, or unzip much like a zipper. The DNA
nucleotides are positioned and linked by polymerase. There is a
specific pairing method (such as A-T, C-G) to assure the exact copy.
The centromere holds the duplicate daughter chromosomes together.
There are 2 meters of DNA per cell.
Cell
Sculpt, March 7th,
2012
The cells can
mutate, however. Alterations, really mistakes, in the DNA code, most
frequently during DNA replication cause mutations. These are caused
by chemical and physical forces. Though there can be silent effects
(no effect), most mutations are harmful, resulting in cell death or
cancer. Some can be beneficial as well. Some of these mutations are
repaired by enzymes.
Second is the
transcription process, or the copying of DNA of a gene into mRNA,
which is messenger Ribonucleic Acid. This process occurs within the
nucleus.
The DNA with the
gene region unwinds. RNA polymerase assists in copying base sequence
in RNA nucleotides. A primary transcript is made, including introns
(intervening sequence) and exons (which carry the genetic info). The
introns are edited out and the exons are specified appropriately. A
messenger RNA strand is produced.
The Genetic Code:
In the nucleus of
each cell is a DNA molecule, which is like the reference section for
the whole cell. The code contains 3-letter words, each giving
instructions for one amino acid. The amino acids then are put
together and build polypeptides.
Several different
codons encode each amino acid, but methionine (AUG) is the start
codon in RNA. TAC is the start codon in DNA. The genes can end in
UAA, UAG, or UGA.
Third is
translation, or the process of converting mRNA into one or more
proteins. This process occurs in the cytoplasm at ribosomes. Along
with mRNA, tRNA (transfer RNA), relatively small RNA molecules that
escort amino acids to the ribosomes (site of translation). This
contains sites for mRNA and incoming amino acid-tRNA. It also
contains the enzymes/factors that cayalyze the peptide bond
formation.
Initiator tRNA
(carrying methionine) and ribosomal subunits form an initiation
complex. Next, during elongation, tRNA brings specific amino acids to
developing protein chain, which elongates one amino acid at a time.
During termination, the stop codon terminates the chain and protein
is released.
Chapter 18
Normal
cells have regulatory mechanisms that maintain an appropriate rate of
cell division using an “internal clock”, horomones, inhibitory
signals from nearby cells, and check points. In general, they remain
in one location throughout their entire lifespan.
Signals
from within the cells are called internal cell signals. Cyclins are
present during certain stages of the cell cycle. Destroying cyclin at
the right time is crucial for cell progression.
External
cell signals affect the cell cycle as well. EGF (epidermal growth
factor) stimulates skin near an injury to finish cell cycle and
repair injury. Estrogen stimulates the lining of the uterus to divide
and prepare for the egg. Cells divide about 70 times in culture, then
die. Programmed cell death is called apoptosis.
Apoptosis
is unleashed by internal or external signals, It helps keep the
number of cells at appropriate level. Remaining cell fragments are
engulfed by white blood cells.
Cancer
may result from imbalance due to cell mutation. Cancer is defined as
a disease of the cell cycle in which cellular reproduction occurs
repeatedly without end, so the cells do not die off. Types of cancer
are carcinoma (cancer of the epithelial tissue lining organs),
sarcoma (cancer in the muscle or connective tissue) and leukemia,
which is cancer of the blood (connective tissue).
Cancer
cells lack differentiation. They interfere with body function. They
may divide repeatedly, have abnormal nuclei with abnormal numbers of
chromosomes. They form tumors and do not respond to inhibitory
signals. The cells travel to start new tumors and from new blood
vessels to nourish themselves (metastis). Carcinogenesis is the
development of cancer.
University
of Texas MD Anderson Cancer Center Marc h 7 2012
Tumors,
also known as neoplasm, are a discrete mass of cells resulting from
hyperplasia (a substantial increase in the rate of cell division.)
Benign tumors are non cancerous. They remain in one location, defined
by a single mass.
Cancerous
cells, however are formed by displasia, an abnormal change in cell
structure, considered a precancerous state. Cancerous tumors have
abnormal cell structure and have loss of regulation of cell growth.
Malignant
tumors invade normal tissue and compromises organ functions.
Secondary malignant tumors may develop.
Cancer
develops through mutated or damaged proto-oncogenes, which would
regulate and promote cell growth, differentiation or adhesion,
turning into oncogenes. It could also occur through damage or
deactivation of tumor suppressor genes. Genes in DNA repair during
replication may also be mutated.
Things
that could lead to cancer include viruses such as HPV, Hepatitis B
and C, and HIV. Chemicals in the environment, tobacco, radiation,
dietary factors, and free radicals can also lead to cancer. It is the
job of the immune system, generally to defend against cancer. Cancer
cells may not be recognized as our bodily cells and can be destroyed.
Tumor
Imaging, such as x-rays, PET, MRI, genetic testing and enzyme tests
for cancer makers are now available for detection of cancer. Popular
treatments include surgery and chemotherapy while less popular
treatments include magnetism, photodynamic therapy, immunotherapy,
starving of the cancer and molecular treatments that target
oncogenes.
Skin
cancers include basal cell carcinoma, squamous cell carcinoma, and
melanoma. Basal cell carcinoma (the basal cells are in the base layer
of epithelium) doesn't usually metastasize, but should be removed.
Squamous cell carcinoma metastasizes slowly. The deadliest is
melanoma, metastasizing quickly, can include asymmetry, irregular
shape, variance in color, be greater than 6 mm, and can evolve.
Melanoma is the cancer of the malnocytes, which produce melanin.
Fortunately, it is the least common of the skin cancers.
WebMD,
March 7th
2012
Lung
cancer, usually brought on by smoking, is hard to detect, so it's
usually more advanced when detected. Symptoms are easy to mistake
with bronchitis or pneumonia or just coughing.
Breast
cancer risk factors include genetics. Two different genes (BRCA1 and
BRCA2 or Breast Cancer 1 and 2) and age, such as early onset of
menstruation and late menopause or obesity after. Oral contraceptives
and hormone replacement after menopause also contribute to breast
cancer.
Prostate
cancer is most common in men after 50. Diagnosis would include a
rectal exam and a blood test for PS (prostate specific antigen).
Treatment includes surgery, radiation therapy, and hormones.
Symptoms
of colon and rectal cancer include blood in stool and rectal
bleeding. Risk factors can include obesity, smoking, family history,
low fiber diets, high fat diets and others. Screening tests can
detect it early.
Chapter 19
Chromosomes
are structures within the nucleus composed of DNA and protein. Humans
have 22 pairs of homologous chromosomes (or autosomes) and one pair
of sex chromosomes for gender. Homologous chromosomes look alike in
shape, pattern and size, but are not identical. One member of each
pair of chromosomes is inherited from each parent.
Alleles are alternate forms of genes from mutation. Homologous chromosomes might have different alleles of genes. There are two different types of alleles: dominant and recessive. Dominant alleles mask or suppress the expression of its complimentary allele. Recessive alleles will not be expressed next to dominant alleles, contrary to dominant alleles which are always expressive. Recessive alleles are heterozygous. They will only be expressed if the individual is homozygous for the recessive allele. Homozygous chromosomes contain two identical alleles while heterozygous chromosomes have two different alleles.
Alleles are alternate forms of genes from mutation. Homologous chromosomes might have different alleles of genes. There are two different types of alleles: dominant and recessive. Dominant alleles mask or suppress the expression of its complimentary allele. Recessive alleles will not be expressed next to dominant alleles, contrary to dominant alleles which are always expressive. Recessive alleles are heterozygous. They will only be expressed if the individual is homozygous for the recessive allele. Homozygous chromosomes contain two identical alleles while heterozygous chromosomes have two different alleles.
Genotypes
(set of alleles) are the base of phenotypes, the observable traits
such as hair and eye color, etc. Phenotypes are determined by
inheritated alleles and the environment.
The
Punnet square can predict inheritance using the parent phenotypes and
four combinations of their genotypes.
Gregor
Mendel's Basic Rules
Gregor
Mendel worked with pea plants in the 1850s to determine genetics and
inheritance rules. His Law of Segregation states that gametes carry
one allele of each gene. His Law of independent assortment states
that genes for different traits are separated in meiosis. This law
only applies if two genes are on different chromosomes.
Maternal
inheritance
Mitochondria
convert molecules into energy within the cell. They also contain some
DNA. Only females can pass on mitochrondrial mutations to their
offspring because eggs contribute mitochondria to the embryo.
Incomplete
Dominance and Codominance
In
incomplete dominance, the heterozygous phenotype is intermediate
between that of either zygote. For example, wavy hair is the product
of a parent with straight hair and a parent with curly hair.
Codominance-
both alleles are expressed. For example, in ABO blood types, the A
and B genes are codominant.
Genetics
and Inheritance
Polygenetic inheritance is the inheritance of
phenotypic traits that depend on genes such as eye and skin color,
height and shape, etc.
Sex
chromosomes are the 23rd
pair of chromosomes. X and Y carry different genes. Males have and X
and Y chromosome while females have two X chromosomes. Males carry
half of each X and Y gamete and determine the sex of their offspring.
Sex-linked Interitance:
Males express the disease more than females, but is
passed onto the male offspring through the mother (fathers cannot
pass the gene). These can include hemophilia, duchenne muscular
dystropy and color blindness.
Failure of homologous chromosomes or sisster chromatids
separating during meiosis can lead to downs syndrome, or trisomy 21.
It can also lead to alterations of the sex chromosome, such as
trisomy-X syndrome, turner syndrome, etc. Alterations in the
chromosomes can lead to other syndroms, such as cri-du-chat syndrome
(when a piece of a chromosome breaks off). This is known as a
deletion. A translocation happens when the broken piece attaches to
another chromosome.
Chapter
20
Biotechnology is the technical application of biological
knowledge for human purposes. Genetic engineering is the manipulation
of genetic makeup of cells or organisms.
The
Polymerase Chain Reaction (PCR)
The Polymerase Chain Reaction is used to amplify DNA
to make millions of copies. Heating and cooling allows the reaction
to happen rapidly.
During DNA fingerprinting, the DNA gets amplified by
PCR, then gets cut with restriction enzymes. Then it is separated by
gel electgrophoresis by size. The enzymes will cut the molecules
where the sequences between individuals are not the same.
Transgenic
Organisms and Gene Therapy
Transgenic Organisms have been developed with good
intentions. For example, transgenic bacteria produce insulin, human
growth horomone, vaccines, etc. The plants, which resist freezing,
synthesize horomones among other functions. Though much more
difficult to introduce DNA into animal cells, animals have been used
in research and can produce milk from which “pharm” drugs can be
produced.
SCID, or sever combine immunodeficiency is an immune
disorder in which the T-lymphocytes have the inability to recognize
specific proteins with their receptors. Gene has helped this. therapy
