Beadle and Tatum



Beadle and Tatum

 

Selected as object for their investigations an organism with very simple structure, a bread mold, Neurospora crassa,

It is able to synthesize its body substances from a very simple culture medium: sugar, salts, and a growth factor.

When cultures of the mold are exposed to X-ray irradiation, mutations - that is, changes in individual genes

Beadle and Tatum succeeded in demonstrating that the body substances are synthesized in the individual cell step by step in long chains of chemical reactions, and that genes control these processes by individually regulating definite steps in the synthesis chain.

This regulation takes place through formation by the gene of special enzymes.

If a gene is damaged, for example through irradiation-induced mutation, the chain is broken, the cell becomes defective - and may possibly be unable to survive

Protein

PKU

 - auto recessive

• PA cannot be converted to Tyrosine

• Tyrosine needed for melanin

• May lead to hyperthyroidism (goiters)

• It is contained in most protein rich foods but good sources are found in dairy products, almonds, avocados, lima beans, peanuts and seeds.

Signs & Symptoms

Newborns affected by PKU usually do not show any signs of the disease at birth. But within the first few weeks of life they begin to show neurologic disturbances such as epilepsy. Children suffering from undiagnosed PKU also may have an unpleasant, musty smell. It has been shown that almost 90% of affected people have blond hair and blue eyes. Signs also include skeletal changessuch as a small head, short stature, and flat feet. PKU sufferers may also have a skin disorder called eczema

 

• Maple Syrup

o Amino Acid defect (similar to PKU)

 

Carbohydrate

• Monosaccharide – 1 sugar unit

o Glucose

o Fructose

o Galactose

Fructose buildup can be seen when there is a switch to solid food in infants

Causes digestive stress

Fructose is a simple (small) sugar that is broken down to provide energy. Fructose can be broken down as follows

|  |enzyme 1  |  |enzyme 2 |  |  |  |

|Fructose |-----------> |A |-----------> | X |----> ----> ----> |complete breakdown in usual way |

There is a rare genetic condition called fructosuria (meaning fructose in the urine) that is caused by a lack of enzyme 1. Fructosuria is inherited in a standard Mendelian fashion. (No sex linkage or other complications.) This condition is relatively benign, but if you eat too much fructose, you get fructose in your urine.

 

Disaccharide 2 sugar units

• Lactose     glucose and galactose

• Sucrose     glucose and fructose

• Maltose    glucose and glucose

Complex sugars

Glycogen

Cellulose 

Lactose cannot be used as an energy source

Needs to be broken down into galactose and glucose via lactase

At birth levels of lactase are high, but may decrease over time (become lactose intolerant)

If galactose cannot be broken down there will be a build up of galactose – phosphate

This can lead to galactosemia (toxic levels of galactose)

Signs and Symptoms

Galactosemia usually causes no symptoms at birth, but jaundice, diarrhea, and vomiting soon develop and the baby fails to gain weight.  If not detected immediately, it results in liver disease, cataracts, mental retardation, and even death

Lipids

Tay Sachs

1 in 350,000

Disease of lysosome function

Auto recessive

People with Tay-Sachs disease lack an enzyme (protein) called hexosaminidase A (hex A) that is necessary for breaking down certain fatty substances in brain and nerve cells.

These fatty substances build up and gradually destroy brain and nerve cells, until the entire central nervous system stops working

First notice by Drs Tay and Sachs (identification of cherry red spots on retina of affected children)

High incidence in Jewish populations of Eastern European descent

Is there any treatment?

Presently there is no treatment for Tay-Sachs.

What is the prognosis?

Even with the best of care, children with Tay-Sachs disease usually die by age 5.

 

 

Nucleic Acids

Lesch Nyhan - X - Linked

Basically a defect in the ability to reuse A,G,T,C

Block in DNA metabolism

Lesch-Nyhan Disease (LND) is a rare and devastating genetic disorder characterized by spasticity, speech impairment, renal disease, varying degrees of cognitive deficit, and the hallmark symptom, compulsive self-injury.

LND is a rare condition that is caused by a defective gene on the X chromosome. The condition can be inherited, or can occur spontaneously via a genetic mutation. Since the defective gene is recessive, females almost never exhibit the disease, but may be carriers.

LND is associated with a nearly complete absence of the enzyme hypoxanthine guanine phosphoribosyl transferase (HGPRTase), which metabolizes hypoxanthine and guanine to uric acid.

By four years of age many of the affected children begin to exhibit the classic manifestation of LND, self-mutilation. The behaviors seem to escalate as the child grows and becomes more physically capable of inflicting self-injury, and he becomes more cognitively capable of conceiving new methods of self-injury. The self-mutilation seen in LND is generally quite severe and can lead to the loss of lips and fingers from biting, visual loss from rubbing the eyes, and any number of other injuries.

It is hypothesized that the self-mutilation is related to neurotransmitter abnormalities, in particular derangements in serotonin or dopamine metabolism.

Is there any treatment?

Treatment for LNS is symptomatic. The drug allopurinol may be used to control excessive amounts of uric acid. Kidney stones may be treated with lithotripsy. There is no standard treatment for the neurological symptoms of LNS. Some symptoms may be relieved with the drugs carbidopa/levodopa, diazepam, phenobarbital, or haloperidol.

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