Saturday, March 10, 2012

Unit 2

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.

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