Showing posts with label Biochemistry. Show all posts
Showing posts with label Biochemistry. Show all posts

Tuesday, June 3, 2014

Competitive, uncompetitive and non competitive enzyme inhibitors


(A) Enzyme–substrate complex; 
(B) a competitive inhibitor binds at the active site and thus prevents the substrate from binding; 
(C) an uncompetitive inhibitor binds only to the enzyme–substrate complex; 
(D) a noncompetitive inhibitor does not prevent the substrate from binding.

Sunday, August 5, 2012

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Insulin - Structure

Insulin is a protein hormone. It was the first protein to be shown to have a precisely defined amino acid sequence. This work was done by Federick Sanger in 1953. 
As shown above in two colours, the insulin molecule consists of 2 peptide chains. 
a) The blue coloured chain is the A chain. It has 21 amino acids and a sisulphide bond within itself. 
b) The yellow colour represents the B chain. It is larger with 30 amino acids. 
Both chains are connected by 2 disulphide bridges. 
Porcine and bovine insulins differ from human insulin at 1 and 3 positions of the amino acids respectively. 

Friday, January 20, 2012

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Sickle cell disease - Electrophoresis


Above is an electrophoresis of a patient suspected to have sickle cell disease. A blood sample was taken from him and the erythrocytes were separated. After lysis of the RBCs, hemoglobin was released and it was run on a polyacryamide gel.
Electrophoresis was carried out and Western blot was performed to located the hemoglobin.

The principle of electrophoresis is that the the more negatively charged particles move towards the positive pole and vice versa. In the case of sickle cell disease, glutamate is substituted by valine at the 6th position of the beta chain. This removes a negative charge from the chain and thus in the electric field the mutated chain will not move as far towards the positive pole as does the non-mutated chain.

The interpretation is as follows:
1) X is a band that represents the mutated HbS.
2) Y is the normal Hb.
3) 1 is a carrier of HbS i.e. having one normal and one mutated chain.
4) 2 is a person who does not carry any mutant alleles.
5) 3 is a person having the disease i.e. two mutant alleles.

Sunday, October 9, 2011

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Molecular biology - central dogma



The central dogma for molecular biology refers to the flow of information from DNA to RNA to proteins.


Nucleic acids are required for the storage and expression of genetic information. There are two chemically distinct types of nucleic acids:
1) deoxyribonucleic acid (DNA) and
2) ribonucleic acid (RNA).

DNA is the store of genetic information and is present not only in chromosomes in the nucleus of eukaryotic organisms, but also in mitochondria and the chloroplasts of plants. Prokaryotic cells, which lack nuclei, have a single chromosome, but may also contain nonchromosomal DNA in the form of plasmids.

The genetic information found in DNA is copied and transmitted to daughter cells through DNA replication. The DNA contained in a fertilized egg encodes the information that directs the development of an organism. This development may involve the production of billions of cells. Each cell is specialized, expressing only those functions that are required for it to perform its role in maintaining the organism. Therefore, DNA must be able to not only replicate precisely each time a cell divides, but also to have the information that it contains be selectively expressed.

Transcription (RNA synthesis) is the first stage in the expression of genetic information. Next, the code contained in the nucleotide sequence of messenger RNA molecules is translated. There is protein synthesis and thus completing gene expression.

Tuesday, September 20, 2011

Gene cloning - steps and applications


Application:
1) Production of recombinant proteins like factor VIII, insulin and tissue plasminogen activator,
2) Transgenic organisms also called as genetically modified organisms like herbicide resistant crops,
3) Gene therapy to correct a genetic disorder or an acquired disease, though there has only been limited success in this field till now.

Thursday, June 16, 2011

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Polymerase chain reaction - PCR


Polymerase chain reaction is a test tube method to amplify a selected DNA sequence. The advantage is that millions of copies can be made within hours. The steps in one cycle of synthesis include:
1) Primer construction
2) Denaturation of DNA
3) Annealing of primers to single stranded DNA
4) Extension of the chain.

This technique can be used for:
1) forensic analysis of DNA even from a single strand of hair, single drop of blood/semen.
2) detection of viral DNA sequence e.g. of HIV even at very early stage of infection when only a small number of cells are harbouring the virus.
3) prenatal diagnosis and detection of cystic fibrosis.

Most recently, it has been found to be very useful in the screening of CMV in neonates. PCR assays of both liquid and dried saliva are highly sensitive and specific to detect cytomegalovirus in neonates.