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Dr. Azhar Chishti Department of Medical Biochemistry Dr. Azhar Chishti.

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Presentation on theme: "Dr. Azhar Chishti Department of Medical Biochemistry Dr. Azhar Chishti."— Presentation transcript:

1 Dr. Azhar Chishti Department of Medical Biochemistry Dr. Azhar Chishti

2 LECTURE OUTLINES 1. Southern Blotting: 1. History 2. Main use 3. Advantages 4. Probes 5. Hybridization 6. Procedure 7. Steps 8. Methods of Transfer 9. Example of application of SB for the diagnosis of diseases (SCA) 2. Northern Blotting: 1. History 2. Definition 3. Basic steps 4. Applications 3. Western Blotting: 1. WB: Definition 2. Applications & Advantages 3. WB: An overview 4. Direction of transfer 5. Factors Affecting Transfer Efficiency 6. WB procedure, briefly 7. WB Detection methods 8. Examples of used substrates 9. WB procedure, illustrated 10. Comparison between SB & WB (Similarities & Differences)

3 Dr. Azhar Chishti OBJECTIVES To understand the basic concept of blotting techniques (Southern, northern, western) To know the main applications and advantages of each of the main types of blotting techniques To be familiar with the steps (in brief) for performing a blotting procedure To understand the major similarities & differences between different blotting techniques To be introduced to an example of applying a blotting technique in diagnosis of diseases (SCA)



6 Blotting: History Southern Blotting is named after its inventor, the British biologist Edwin Southern (1975) Other blotting methods (i.e. western blot, WB, northern blot, NB) that employ similar principles, but using protein or RNA, have later been named in reference to Edwin Southern's name.

7 SOUTHERN BLOTTING ? Experimental procedure DNA is extracted from cells, leukocytes. DNA is cleaved into many fragments by restriction enzyme (BamH1, EcoR1 etc) Dr. Azhar Chishti

8 The resulting fragments are separated on the basis of size by electrophoresis. The large fragments move more slowly than the smaller fragments. The lengths of the fragments are compared with band of relative standard fragments of known size. Dr. Azhar Chishti

9 The DNA fragments are denatured and transferred to nitrocellulose membrane (NYTRAN) for analysis. DNA represents the individual's entire genome, the enzymic digest contains a million or more fragments. The gene of interest is on only one of these pieces of DNA. Dr. Azhar Chishti

10 DNA segments were visualized by a nonspecific technique, they would appear as an unresolved blur of overlapping bands. To avoid this, the last step in Southern blotting uses a probe to identify the DNA fragments of interest. Dr. Azhar Chishti

11 Southern blot analysis depend on the specific restriction endonuclease The probe used to visualize the restriction fragments. Dr. Azhar Chishti

12 Labeled material to detect a target. For DNA: 20-30 nucleotides, complementary to a region in the gene Methods of labeling: Non-radioactive e.g. Biotin Radioactive e.g. 32 P Sensitive Relatively cheap Hazardous You should follow the radioactive waste disposal regulations. Sensitive Relatively expensive Target DNA Probe Biotin Avidin * Target DNA Probe * Probes

13 Dr. Azhar Chishti The binding between ss labeled probe to a complementary nucleotide sequence on the target DNA. Degree of hybridization depends on method of probe labeling (radioacitve or non-radioactive system e.g. biotin-avidin. Hybridization

14 Detection of mutations The presence of a mutation affecting a restriction site causes the pattern of bands to differ from those seen with a normal gene. A change in one nucleotide may alter the nucleotide sequence so that the restriction endonuclease fails to recognize and cleave at that site (for example, in Figure, person 2 lacks a restriction site present in person 1). Dr. Azhar Chishti


16 1- DNA extraction 2- DNA cleavage (RE) 3- DNA Electrophoresis (based on size) - + 4- DNA Denature, Transfer, blocking, 5- Hybridization e.g. with 32 P- labeled probe 6- Detection

17 Dr. Azhar Chishti Steps Digestion of genomic DNA (w/ one RE) DNA fragments Size-separation of the fragments (standard agarose gel electrophoresis) In situ denaturation of the DNA fragments (by incubation @ temp) Transfer of denatured DNA fragments into a solid support (nylon or nitrocellulose). Hybridization of the immobilized DNA to a labeled probe (DNA, RNA) Detection of the bands complementary to the probe (e.g. by autoradiography) Estimation of the size & number of the bands generated after digestion of the genomic DNA w/ different RE placing the target DNA within a context of restriction sites)

18 METHODS OF TRANSFER Downward Capillary Transfer Upward Capillary Transfer Simultaneous Transfer to Two Membranes Electrophoretic Transfer Vacuum Transfer

19 Dr. Azhar Chishti Example of Transfer Upward Capillary Transfer Weight Glass Plate Whatman 3MM paper Gel Paper towels Membrane (nylon or nitrocellulose) Whatman 3MM paper Transfer buffer

20 Dr. Azhar Chishti Buffer drawn from a reservoir passes through the gel into a stack of paper towels DNA eluted from the gel by the moving stream of buffer is deposited onto a membrane weight tight connection

21 Dr. Azhar Chishti Example of Application of SB in diagnosis of mutation in globin gene

22 Dr. Azhar Chishti Example of Application of SB in diagnosis of mutation in globin gene

23 Dr. Azhar Chishti Northern Blotting Northern Hybridization A northern blot is a method routinely used in molecular biology for detection of a specific RNA sequence in RNA samples. The method was first described in the seventies (Alwine et al. 1977, 1979) It is still being improved (Kroczek 1993), with the basic steps remaining the same

24 Dr. Azhar Chishti Basis Steps of NB 1. Isolation of intact mRNA 2. Separation of RNA according to size (through a denaturing agarose gel e.g. with Glyoxal/formamide) Transfer of the RNA to a solid support Fixation of the RNA to the solid matrix Hybridization of the immobilized RNA to probes complementary to the sequences of interest Removal of probe molecules that are nonspecifically bound to the solid matrix Detection, capture, & analysis of an image of the specifically bound probe molecules.

25 Applications Study of gene expression in eukaryotic cells: To measure the amount & size of RNAs transcribed from eukaryotic genes To estimate the abundance of RNAs Therefore, it is crucially important to equalize the amounts of RNA loaded into lanes of gels Dr. Azhar Chishti

26 Examples of methods to equalize the amounts of RNA loaded into lanes of gels OD 260 Use of housekeeping gene (endogenous constitutively- expressed gene): Normalizing samples according to their content of mRNAs of this housekeeping gene

27 Dr. Azhar Chishti Western Blotting Immunoblotting = electrophoretic transfer of proteins from gels to membranes

28 Dr. Azhar Chishti WB: Definition Blotting is the transfer of separated proteins from the gel matrix into a membrane, e.g., nitrocellulose membrane, using electro- or vacuum-based transfer techniques. Towbin H, et al (1979). "Electrophoretic transfer of proteins from polyacrylamide gels to nitrocellulose sheets: procedure and some applications.". Proc Natl Acad Sci U S A. 76 (9): 4350–4354

29 Dr. Azhar Chishti Applications & Advantages Applications: To determine the molecular weight of a protein (identification) To measure relative amounts (quantitation) of the protein present in complex mixtures of proteins that are not radiolabeled (unlike immunoprecipitation) Advantages: WB is highly sensitive technique As little as 1-5 ng of an average-sized protein can be detected by WB

30 Western blotting The main steps of blotting technique in a chronological order will be as follows: Blocking Probing with the specific antibody(ies) Wash Detection Washing X-ray (Gel Documentation System) Dr. Azhar Chishti

31 Electrophoretic Transfer: An Overview Important Issue: Where to put the gel and the membrane relative to the electroblotting transfer electrodes?

32 Dr. Azhar Chishti Direction of Transfer Perpendicularly from the direction of travel of proteins through the separating gel Gel Membrane Probe with specific Ab

33 Dr. Azhar Chishti Factors Affecting Transfer Efficiency 1. The Composition of the gel 2. Whether there is complete contact of the gel with the membrane 3. The position of the electrodes 4. The transfer time 5. The size & composition of proteins 6. The field strength 7. The presence of detergents

34 Dr. Azhar Chishti WB Procedure; Briefly… 1 2 3 4

35 Dr. Azhar Chishti Direct Detection Method

36 Dr. Azhar Chishti Indirect Detection Method

37 Dr. Azhar Chishti WB: examples of used substrates

38 Chemiluminescent substrates Dr. Azhar Chishti

39 Enhanced ChemiFluoresenct (ECF) WB Detection Dr. Azhar Chishti


41 Steps of WB Dr. Azhar Chishti

42 Steps of WB Dr. Azhar Chishti

43 Steps of WB Why to block? To increase sensitivity To prevent nonspecific signal Dr. Azhar Chishti

44 Blocking of Blot Several measures should be followed to decrease the nonspecific reactions to a minimum, i.e., increasing the signal to noise ratio. Blocking step is the incubation of the membrane with solution containing BSA or fat-free milk or casein for a sufficient time with shaking. Dr. Azhar Chishti

45 Steps of WB For Direct Transfer, choices are: Dr. Azhar Chishti

46 Primary Antibody labeling The immobilized proteins on the surface of the membrane can be detected using a specific, labeled antibody. Labeling of the antibody can be performed using a radioactive or non- radioactive method. Dr. Azhar Chishti

47 Primary Antibody probing The blot is first incubated with a primary antibody followed by the addition of a labeled secondary antibody that has species specificity for the primary one. For example, probing of the membrane using mouse primary antibody and anti- mouse secondary antibody. Dr. Azhar Chishti

48 Steps of WB Dr. Azhar Chishti

49 Steps of WB Dr. Azhar Chishti

50 Detection and interpretation A prestained MW standard is included in a separate lane during electrophoresis to allow the identification of the MW of the target protein. Similar to the analysis of electrophoresis results on a gel, the data on the membrane can be quantitatively analyzed using gel documentation system. Dr. Azhar Chishti

51 Detection and interpretation (continue) Quantification of a specific protein band can be achieved by densitometry and integrating the areas under the peaks. Several gel documentation systems are commercially available that can be useful for analysis of results from the gel or membranes. Dr. Azhar Chishti

52 Comparison between WB & SB. Similarities: Electrophoretically separated components (proteins in WB & DNA in SB), are transferred from a gel to a solid support and probed with reagents that are specific for particular sequences of AA (WB) or nucleotides (SB). Dr. Azhar Chishti

53 Comparison between WB & SB, Contnd… Differences: The critical difference between SB & WB is: the nature of the probes Probes usually are Ab(s) that react specifically with Ag-ic determinants ( epitopes ) displayed by the target protein NA probes hybridize with a specificity & rate that can be predicted by simple equations, In WB In SB Dr. Azhar Chishti

54 References Lippincott, Illustrated review of Biochemistry, 4th edition Molecular Cloning: A Laboratory Manual, J Sambrook, EF Fritsch, T Maniatis Catalogues of some commercial companies Dr. Azhar Chishti


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