DNA Replication

Semiconservative

The replication of a DNA molecule ...

... begins when the two complementary DNA strands are separated. This is usually accomplished by special proteins that unwind the molecule and expose the nucleotide bases.

New complimentary DNA strands are then synthesized by joining together deoxyribonucleotide triphosphates, one at a time, and with the removal of a di-phosphate. Click on the blue dot in the figure above to get a close up of the way in which the bases pair up as the new DNA strand is synthesized.

At the end of the process the cell has made to identical copies of all the biological information contained on the original, parental, DNA molecule, but the two new daughter DNA molecules are "Half old" and "Half new". Half the original DNA molecule is saved, or conserved in the daughter molecules. This is why the process is called semi-conservative.

How Is a Heart Attack Treated?

How Is a Heart Attack Treated?


Early treatment can prevent or limit damage to the heart muscle. Acting fast, at the first symptoms of heart attack, can save your life. Medical personnel can begin diagnosis and treatment even before you get to the hospital.

Certain treatments are usually started right away if a heart attack is suspected, even before the diagnosis is confirmed. These include:

1.Oxygen

2.Aspirin to prevent further blood clotting

3.Nitroglycerin, to reduce the workload on the heart and improve blood flow through the coronary arteries

4.Treatment for chest pain

5.Once the diagnosis of heart attack is confirmed or strongly suspected, treatments to try to restore blood flow to the heart are started as soon as possible. Treatments include medicines and medical procedures.

Medicines :

A number of different kinds of medicines may be used to treat heart attack. They include the following.

Thrombolytic Medicines :

These medicines (also called clot busters) are used to dissolve blood clots that are blocking the coronary arteries. To be most effective, these medicines must be given within 1 hour after the start of heart attack symptoms.

Beta Blockers :

These medicines decrease the workload on your heart. Beta blockers also are used to relieve chest pain or discomfort and to help prevent additional heart attacks. Beta blockers also are used to correct arrhythmias (irregular heartbeats).

Angiotensin-Converting Enzyme (ACE) Inhibitors 

These medicines lower blood pressure and reduce the strain on your heart. They also help slow down further weakening of the heart muscle.

Anticoagulants :

These medicines thin the blood and prevent clots from forming in your arteries.

Antiplatelet Medicines :

These medicines (such as aspirin and clopidogrel) stop platelets (a type of blood cell) from clumping together and forming unwanted clots.

Other Medicines   

Medicines may also be given to relieve pain and anxiety, and to treat arrhythmias, which often occur during a heart attack.

Medical Procedures :

If medicines can’t stop a heart attack, medical procedures—surgical or nonsurgical—may be used. These procedures include the following.

Angioplasty  :

This nonsurgical procedure can be used to open coronary arteries that are blocked by a blood clot. During angioplasty, a catheter (a thin, flexible tube) with a balloon on the end is threaded through a blood vessel to the blocked coronary artery. Then, the balloon is inflated to push the plaque against the wall of the artery. This widens the inside of the artery, restoring blood flow.

During angioplasty, a small mesh tube called a stent may be put in the artery to help keep it open. Some stents are coated with medicines that help prevent the artery from becoming blocked again.
Coronary Artery Bypass Grafting :

Coronary artery bypass grafting is a surgery in which arteries or veins are taken from other areas of your body and sewn in place to bypass (that is, go around) blocked coronary arteries. This provides a new route for blood flow to the heart muscle.

Treatment After You Leave the Hospital :

Most people spend several days in the hospital after a heart attack. When you leave the hospital, treatment doesn’t stop. At home, your treatment may include daily medicines and cardiac rehabilitation (rehab). Your doctor may recommend lifestyle changes, including quitting smoking, losing weight, changing your diet, and increasing your physical activity, to lower your chances of having another heart attack.

Cardiac Rehabilitation

Your doctor may prescribe cardiac rehab to help you recover from a heart attack and to help prevent another heart attack. Almost everyone who has had a heart attack can benefit from rehab. The heart is a muscle, and the right exercise will strengthen it.

But cardiac rehab isn’t only about exercise. It also includes education, counseling, and learning about reducing your risk factors. Rehab will help you learn the best way to take care of yourself after having a heart attack and how to prevent having another one.

The cardiac rehab team may include doctors (your family doctor, a cardiologist, and/or a surgeon), nurses, exercise specialists, physical and occupational therapists, dietitians, and psychologists or other behavioral therapists.

Who Is At Risk for a Heart Attack?

Who Is At Risk for a Heart Attack?


Certain risk factors make it more likely that you will develop coronary artery disease (CAD) and have a heart attack. Some risk factors for heart attack can be controlled, while others can't.

Major risk factors for heart attack that you can control include:

1.Smoking

2.High blood pressure

3.High blood cholesterol

4.Overweight and obesity

5.Physical inactivity

6.Diabetes (high blood sugar)


Risk factors that you can't change include:

1.Age. Risk increases for men older than 45 years and for women older than 55 years (or after menopause).

2.Family history of early CAD. Your risk increases if your father or a brother was diagnosed with CAD before 55 years of age, or if your mother or a sister was diagnosed with CAD before 65 years of age.

Certain CAD risk factors tend to occur together. When they do, it’s called metabolic syndrome. In general, a person with metabolic syndrome is twice as likely to develop heart disease and five times as likely to develop diabetes as someone without metabolic syndrome.

Other Common Signs and Symptoms :

Other common signs and symptoms that a person can have during a heart attack include:


1.Upper body discomfort in one or both arms, the back, neck, jaw, or stomach

2.Shortness of breath may often occur with or before chest discomfort

3.Nausea (feeling sick to your stomach), vomiting, lightheadedness or fainting, or breaking out in a cold sweat

Not everyone having a heart attack experiences the typical symptoms. If you’ve already had a heart attack, your symptoms may not be the same for another one. The more signs and symptoms you have, the more likely it is that you’re having a heart attack.

Act Fast


Sometimes the signs and symptoms of a heart attack happen suddenly, but they can also develop slowly, over hours, days, and even weeks before a heart attack occurs.

Know the warning signs of a heart attack so you can act fast to get treatment for yourself or someone else. The sooner you get emergency help, the less damage there will be to your heart.

Don’t drive yourself or anyone else to the hospital. Call an ambulance so that medical personnel can begin life-saving treatment on the way to the emergency room.


 

Control of Genes

Control of Genes


Even simple organisms such as bacteria have as many as 3000 genes, producing protein products such as enzymes, cell wall components, building proteins, ribosomal proteins and many others. During a typical cell cycle a bacterial cell may have to make energy releasing proteins all the time, DNA synthesis proteins only during DNA replication, sugar digesting enzymes when it encounters sugar in its environment, and cell wall proteins only when it is about to grow and enlarge. Different proteins are needed at different times, some constantly but many only at specialized moments in the life of the bacterial cell. It would be both wastefull and inefficient to make all proteins continuously. The cell, therefore, needs some method of controling when and where these many different proteins are made

Bacterial Genes

Francois Jacob and Jacques Monod were the first scientists to successfuly investigate how cells control the production of proteins. They used bacteria (because of their simplicity) and developed a model of how these types of cells regulate their genes in response to changes in their environment. Bacteria are opportunists and respond quickly to new sources of food or the presence of dangerous chemicals. Their method of genetic regulation allows them to adapt very rapidly to to what is going on around them.

Jacob and Monod studied how bacteria respond to the sudden appearance of a sugar (called Lactose) in their growth medium. To digest this sugar the cells must make an enzyme called Beta-galactosidease. Since Lacatose sugar is rare, and not always available, it would be wasteful to make this specialized enzyme when it was not needed, so most bacterial cells do not make it until needed.


These scientists discovered that the sudden appearance of Lactose sugar cause the bacterial cells to turn on transcription (making mRNA) of the gene for the enzyme. This type of control of a gene is called transcriptional control, and turned out to be one of the major ways all cells control their genes and the production of proteins.

Gene Regulation

Gene Regulation

The Operon

The Operon

 

Four regions of DNA control the production of a protein such as the enzyme Beta-galactosidease;

 

•        a structural gene that holds the codons for the amino acid sequence found in the enzyme.
•        an operator region right in front of the structural gene.
•        a promotor region where the RNA making enzyme will bind to the DNA.
•        a regulator gene which has a role in controling the transcription from the structural gene.

 

The combined region of the operator and structural gene is called an operon.

Summary :

Many genes are ....


... normally blocked by the action of a repressor protein. This prevents the RNA polymerase enzyme from binding to the gene and transcribing the structural gene. Such genes are induced by the arrival of an inducer molecule which binds to the repressor protein and rendering it inactive. This allows transcription from the structural gene and the production of a protein.

Other genes are normally active and able to be constantly transcribed, because the repressor protein is produced in an inactive form. On the arrival and binding of the corepressor molecule the complex can act as a functional repressor and block the structural gene by binding at the operator site.

These genes are therefore either inducible or repressible.



 

What Is a Heart Attack?

What Is a Heart Attack?


A heart attack occurs when blood flow to a section of heart muscle becomes blocked. If the flow of blood isn’t restored quickly, the section of heart muscle becomes damaged from lack of oxygen and begins to die.

Heart attack is a leading killer of both men and women in the United States. But fortunately, today there are excellent treatments for heart attack that can save lives and prevent disabilities. Treatment is most effective when started within 1 hour of the beginning of symptoms. If you think you or someone you’re with is having a heart attack, call 9–1–1 right away.

Heart Attack Symptoms and Warning Signs

A blockage in the heart's arteries may reduce or completely cut off the blood supply to a portion of the heart. This can cause a blood clot to form and totally stop blood flow in a coronary artery, resulting in a heart attack (also called an acute myocardial infarction or MI).


Irreversible injury to the heart muscle usually occurs if medical help is not received promptly. Unfortunately, it is common for people to dismiss heart attack symptoms.

What are the warning signs of a heart attack?

The American Heart Association and other medical experts say the body likely will send one or more of these warning signals of a heart attack:

1.Uncomfortable pressure, fullness, squeezing or pain in the center of the chest lasting more than a few minutes.

2.Pain spreading to the shoulders, neck or arms. The pain may be mild to intense. It may feel like pressure, tightness, burning, or heavy weight. It may be located in the chest, upper abdomen, neck, jaw, or inside the arms or shoulders.

3.Chest discomfort with lightheadedness, fainting, sweating, nausea or shortness of breath.

4.Anxiety, nervousness and/or cold, sweaty skin.

5.Paleness or pallor.

6.Increased or irregular heart rate.

7.Feeling of impending doom.

Not all of these signs occur in every attack. Sometimes they go away and return. If some occur, get help fast. IF YOU NOTICE ONE OR MORE OF THESE SIGNS IN YOURSELF OR OTHERS, DON'T WAIT. CALL EMERGENCY MEDICAL SERVICES (9-1-1) RIGHT AWAY! In the event of cardiopulmonary arrest (no breathing or pulse), call 9-1-1 and begin cardiopulmonary resuscitation (CPR) immediately.