DNA and Gene Expression

1. The Structure of DNA

a. A twisted ladder, or double helix

b. A spiral staircase composed of two strands of smaller molecules called nucleotides whose bases face each other.

c. In the 1950s Watson and Crick build a model showing DNA’s structure and won the Nobel Prize in 1962

2. Nucleotides have 3 parts:

1. A phosphate group – makes up the sides

2. A Sugar molecule –glue for the sides

3. A base compound- 2 families/ 4 kinds

a. Purines

§ Adenine

§ Guanine

b. Pyrimidines

§ cytosine

§ thymine

3. Base-pairing rules:

§ Adenine forms hydrogen bonds only with Thymine

§ Guanine forms hydrogen bonds only the Cytosine

4. What is meant by complementary strands in a DNA molecule?

§ The sequence of bases on one strand of DNA determines the sequence of base on the other strand of DNA

§ ATTGCAT = TAACGTA

5. List the steps in DNA Replication

a. Replication is when a DNA molecule makes a copy of itself.

A. DNA replication begins when a section of the double helix unzips down the middle, exposing the nucleotide sequence. (Strands of the DNA molecule separate.)

B. An enzyme called DNA polymerase moves along the complementary bases to the exposed nucleotides.

C. Then new nucleotides attach to the strand.

D. A complementary strand is formed for each strand of the original double helix. Each original strand joins its complementary strand to form a DNA molecule resulting in two identical DNA molecules.

E. At the end of replication, there are two identical copies of DNA.

6. Define Gene Expression: the process of making proteins from information in DNA.

a. DNA directs the synthesis of RNA in a process called transcription. RNA directs the synthesis:

A. messenger RNA (mRNA)

1. used in transcription

B. transfer RNA (tRNA)

C. ribosomal RNA (rRNA)

b. Two stages:

A. Transcription : an RNA copy of a gene is made

B. Translocation:

1. DNA makes an RNA copy of its information. The information in the mRNA is used to make a protein translation.

2. 3 different kinds of RNA work to assemble amino acids into a protein molecule.

§ Codon= each nucleotide triplet in mRNA, these code for a specific amino acid. (page 143 book)

§ Genetic code= correspondence between nucleotide triplets in DNA and the amino acids in proteins

§ “Stop” codons= end of amino acid sequence.

§ RNA makes a protein

i. Anti codon= complementary to mRNA codons.

ii. Repressor protein- blocks transcription by preventing the RNA polymerase from marrying along gene.

iii. Inducers= bind to repressor proteins to change its shape so that it no longer fits the DNA and transcription can begin.

7. RNA VS DNA

a. DNA does not build protein. DNA copies the instructions for making a specific protein into a nucleic acid called RNA.

b. DNA and RNA are made of nucleotides.

c. RNA is made of only one strand of nucleotides not two, like DNA.

d. RNA contains 3 of the same bases Adenine, Guanine, and Cytosine. RNA also has a base called Uracil instead of Thymine. Uracil only pairs with Adenine.

e. RNA is chemically similar to DNA except that its sugar, ribose, has an additional oxygen atom, and the base Thymine (T) is replaced by a structurally similar base called Uracil (U).

8. Specialized cells:

a. If every cell has the same DNA why are they not the same?

A. Cells become specialized by gene expression.

B. Cells need the proteins that are important for their specific job.

C. Cells control expression of their genes.

D. Cells regulate when particular genes are transcribed, so they make only needed proteins.

E. Example muscle cells and nerve cells.

9. When does replication take place in the cell cycle?

§ Before cell division, during S phase in Interphase

Links:

DNA

http://www.brooklyn.cuny.edu/bc/ahp/SDPS/SD.PS.polynuc.html

DNA replicates

http://web.ukonline.co.uk/webwise/spinneret/genes/dna.htm

Transcription

http://www.hhmi.org/news/tjian2.html

Forensic Evidence

http://www.forensic-

evidence.com/site/EVID/DNA_Watters.html

chromosomal translocations http://gslc.genetics.utah.edu/units/disorders/karyotype/karyotypeinfo.cfm

Bioethics addressed:

· A couple has one son with Tay-Sachs. In their second pregnancy, prenatal diagnosis indicates that the fetus has Tay-Sachs. The parents choose to abort the fetus.

· Two known carriers of Sickle Cell Anemia decide to have a child.

· Nathaniel Wu should not be hired by IPC due to the presence of the Huntington's gene on his chromosome #4. (BSCS)

· The parents of Baby Doe decide to withhold feeding and medical treatments.

· A husband wishes to remove eggs from his wife's dying body to be fertilized by his sperm in vitro and then implanted into a surrogate mother. Should we allow this request?

· The first cloning of a human embryo has recently occurred. Should the medical community allow the use of this technique?

1. Soldiers’ sperm offers biological insurance policy

http://www.msnbc.com/news/874893.asp?0si=-

2. On Human Cloning: Three Views

http://www.pbs.org/wgbh/nova/baby/cloning.html

3. A Way to Choose a Baby's Gender

http://www.cbsnews.com/stories/2002/11/06/earlyshow/contributors/emilysenay/main528404.shtml

4. Babys by design

http://abcnews.go.com/sections/GMA/GoodMorningAmerica/GMA021226_DesignerBabies.html

5. Do we turn the aging gene off?

http://web.mit.edu/newsoffice/nr/2000/guarente.html

6. Sex test in the Olympics?

http://www.pfc.org.uk/news/1999/olympic.htm

Amniocentesis and the Genetics Revolution

What we are learning about our genetic makeup will change medicine forever. Scientists participating in the Human Genome Project, which began in 1990, have produced a working draft of the 3 billion "letters" (chemical building blocks) that make up human genetic material. Their goal is to identify all 30,000 of our genes and learn what they do, including genes that cause disease.

What does this mean for you and your family? Doctors may soon be able to predict who is at risk for many genetic diseases, and provide treatment to prevent some of them. The number of genetic tests readily available should increase rapidly, as more disease-causing genes are identified.

In the 1980s and 1990s, scientists discovered numerous disease-causing genes, including those associated with fragile X syndrome (the most common inherited form of mental retardation), cystic fibrosis, certain heart defects, familial breast and colon cancers, and many more. These discoveries led to improvements in diagnosis and genetic counseling for these diseases and, in some cases, improvements in treatment. New and better drugs for genetic diseases will be developed, based on information about how disease-causing genes work. Treatment will increasingly be tailored to the individual because tests will show which drugs will work best for you. Gene therapy, which aims to cure a genetic disease by replacing or changing a disease-causing gene in certain cells of the body, should become available for some diseases. For you and your family, this could mean a healthier future.

Genetics and You
Now that you're pregnant, your biggest concern is probably your baby's health. Most parents-to-be swear they don't care whether they have a boy or a girl, fair- or raven-haired, just as long as the baby is healthy.

Still, who can resist fantasizing about how your baby will look? Will she have Daddy's curly hair, Mom's big blue eyes? In the past, these characteristics would have been more or less a surprise at birth but each day, we learn more about genetic traits ranging from looks to personality to health.

Many characteristics are determined at conception. Egg and sperm each "donate" 23 chromosomes, and the resultant 46 chromosomes form our genetic blueprint. Some pairs of genes contain one dominant and one recessive gene. For example, if your partner has curly hair and you have straight hair, your baby is likely to have curly hair because this trait tends to be dominant. Other gene pairs act together to determine a characteristic. This is the case with eye color. Two brown-eyed parents, for example, can have a child with any eye color. So your beautiful baby will be truly unique, and she may or may not resemble either of her parents.

Just as harmless traits like curly hair can run in families, so, too, can more harmful conditions. Over 4,000 birth defects have been identified. They occur in one of every 28 births. Sometimes, an abnormal gene can cause or contribute to the occurrence of a birth defect or genetic disease. In other cases, a birth defect can be caused by environmental factors such as alcohol abuse or infections. Often birth defects seem to reflect a combination of both heredity and environment. If one of these conditions runs in your family, you may be worried about passing it on to your baby. A genetic counselor can help determine the risk of this occurring.

What Is Genetic Counseling?
Genetic counseling helps people to identify and understand what particular traits they may pass on to their children and the likelihood that they will do so. A genetic counselor is a trained health care professional who works with a person or family who may be at risk for an inherited disease or an abnormal pregnancy outcome. Genetic counselors are experienced in helping families understand birth defects, risk, and how inheritance works.

If you go to see a genetic counselor, he or she will want to know about your family's medical history. It's okay if you don't know the answers to all the questions. The counselor may suggest blood tests, physical exams, or prenatal tests to help put together a picture of how your family's health may affect your children. For example, blood tests can determine if you and your partner are "carriers" of genes that can cause an inherited disease in your baby. In many cases, a genetic counselor can reassure you that the risk to your baby is lower than you feared.

Anyone who has unanswered questions about diseases or traits in their family should consider genetic counseling. Those who might be especially interested include:

Women who are pregnant or planning to be pregnant after age 35. The risk of Down syndrome and related chromosomal disorders increases with age.
Couples who already have a child with mental retardation, an inherited disorder or a birth defect.
Couples whose infant has a genetic disease diagnosed by routine newborn screening.
Women who have had three or more miscarriages or babies who died in infancy.
Men or women who are concerned that their job, lifestyle or medical history may pose a risk to a current or future pregnancy. Concerns might include exposure to radiation, medications, chemicals, infections or drugs.
Couples who would like testing or more information about genetic defects that occur frequently in their ethnic group. Examples include Tay-Sachs disease (a fatal central nervous system disease) in couples of Eastern European Jewish ancestry; thalassemia (severe anemia) in those of Mediterranean and Southeast Asian ancestry; sickle cell disease (a blood disorder) in African Americans; and cystic fibrosis (a serious disorder affecting lungs and other organs) in couples of northern European background.
Couples who are first cousins or other close blood relatives.
Pregnant women who, based on ultrasound tests or blood tests, have been told their pregnancy may be at increased risk for complications or birth defects.

Testing for Genetic Disorders
During pregnancy, prenatal tests can diagnose or—far more likely—rule out Down syndrome and other chromosomal errors, hundreds of genetic disorders, and other conditions that may not be genetic, such as heart defects. Your health care provider may recommend one or more tests including blood tests, ultrasound, amniocentesis, and chorionic villus sampling. Fortunately, about 95 percent of women who undergo these tests learn that their baby does not have the disorder for which he or she was tested.

Gene Disorder Chromosome Maps

http://k-12.pisd.edu/currInst/science/Genetic/Chromosome-Maps.htm

Way cool surgery:

http://www.waycoolsurgery.com/surgery/prep.shtml

DNA from the Beginning

http://www.dnaftb.org/dnaftb/1/concept/index.html

C. How DNA is copied

Before a cell can divide, it must replicate its DNA
It does this by "unzipping at one end breaking the bond between the two strands
As the enzyme, DNA Polymerase, begins to copy the bases, it makes sure that all original Thymines have new Adenines added, New cytosines with old Guanines etc.
Using an old strand to make a new strand is called semiconservative replication
This type of replication preserves the way that the bases are constructed
There is old and new strand together. A copy and an original
Sometimes the wrong base is added which if not caught by DNA ligase and replaced with a correct base by DNA polymerase, a mutation may occur
When all is finished, a new strand is produced from an old strand and two complete DNA molecules remain

II. How proteins are made

A. The transfer of genetic information

Dna is used as a blueprint to make a similar nucleic acid called RNA
Rna then is used to direct the production of a protein
Gene expression is the productionof proteins from the DNA
Gene expression takes place in two steps, Transcription and translation
Three different kinds of RNA are used to code for amino acids which accumulate to make proteins
DNA cannot leave the nucleus os messengers (RNA) have to carry the code to the sites of proteins synthesis
RNA is similar to DNA with three exceptions,

a. RNA uses the sugar Ribose, instead of Deoxyribose

b. RNA is single stranded, DNA is double stranded

c. RNA uses the base Uracil instead of the base Thymine\

8. RNA occurs in three different forms

a. Messenger RNA carries the code from the Nucleus to the Ribosome

b. Transfer RNA carries specific amino acids to the sites of proteins synthesis

c. Ribosomal RNA actually make up the ribosomes which ahave two parts. A larger subunit and a small subunit.

B. How DNA makes RNA

A section of the DNA opens up when RNA polymerase binds to the promoter region
The DNA begins to unwind, exposing the interior of the DNA molecule
RNA polymerase moves along the DNA molecule, placing complimentary bases to the DNA in a chain
The process will continues until a stiop sign called a stop codon is reached
The newly transcribed RNA molecule leaves the nucleus through a nuclear pore and into the cytoplasm it goes.
Once the RNA polymerase stops transcription, it releases the DNA and it winds back up

C. The genetic code

The genetic code is read in sequence of three bases at a time called a codon
The codon of the RNA molecule is the Code for the Protein
Amino acids need to be chained together to make a protein
The codons ultimately code for Amino acids.
The transfer RNA has a match for the code on one side (anticodon) and attached to the top of the Transfer RNA is an amino acid
U,C, G, and A are the bases found in mRNA
There are 64 different codons that can be made from these 4 letters
There are only 20 different amino acids so some tRNA will carry the same amino acids as other tRNA
At the beginning of each mRNA is a codon that codes for an amino acid,
As the mRNS is locked into place, The codon on the mRNA is read and the corresponding anticodon is located
The anticodon is aligned with the codon at the ribosome and the RNA molecule will be advanced one spot
The Next codon is read, the appropriate anitcodon is found and brought to the ribosome
As the second codon and anticodon are lined up, a peptide bond forms between the first and second amino acid forming a peptide chain
This goes on and on until a stop codon is found, at which point there is not amino acid for and the synthesis of a protein is terminated
From the time the mRNA is locked into a ribosome, the process of transcription has taken place

III. Regulating Gene Expression

A. Switching genes on and off

Depending on the needs of the cell, a gene can be turned on or off as needed
Those that are turned off are done so until the protein that they code for are needed
Genes are turned off because a special protein called a repressor protein is attached to the front of the particular gene
Another protein called an inducer protein must bind to the repressor protein to remove it from the gene
At this point the DNA can be expressed (transcription and translation can then occur)