genetic engineering i restriction enzymes and gel electrophoresis
Post on 19-Dec-2015
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How are changes made to DNA
• Genetic engineering: Scientists use their knowledge of the structure of DNA and its chemical properties to study and change DNA molecules
• Different techniques are used to:- Cut DNA into smaller pieces- Identify the sequence of bases in a DNA molecule- extract DNA from cells- Make unlimited copies of DNA
The tools of molecular biology
• Cutting DNA: restriction enzymes are used to cut DNA into smaller pieces
• Separating different length of DNA: gel electrophoresis is used to separate different fragments of DNA by their size
Restriction Enzymes
• Naturally found in different types of bacteria:- Bacteria use restriction enzymes to protect
themselves from foreign DNA injected by viruses
• Function: Restriction enzymes cut DNA at specific sequences, they are also called “ molecular scissors”
Restriction Enzymes• There are 2 types of bonds found in DNA:1. Covalent bonds : found inbetween
nucleotides within a single strand2. Hydrogen bonds: found inbetween the 2
strands
Restriction Enzymes• Restriction enzymes cut the covalent bonds of
DNA molecules at specific sequences called restriction site:
• 5’ GAATTC 3’ 3’ CTTAAG 5’• Remember: DNA is composed of anti-parallel
strands• Palindrome sequence: a sequence that is the
same whether read 5’ to 3’ on one strand or 5’ to 3’ on the complementary strand
• Some English palindromes: Dad, racecar, nurses run
Do you notice anything interesting about the sequence of the two strands?
• When restriction enzymes cut they produce either:
- Sticky ends:
- Blunt ends:
Restriction Enzymes
Gel electrophoresis
• Gel electrophoresis separates molecules on the basis of their charge and size:
- DNA molecules are negatively charged- Different sized DNA fragments are placed in a gel made
of agarose (a sugar found in seaweed)- Electricity is applied to the gel- DNA fragments will move across the gel at a speed
dependent on their size: the longer DNA fragments will move slowerthe shorter DNA fragments will move faster
Applications for restriction enzymes and gel electrophoresis
1. Evolutionary study: Comparing DNA samples from different organisms to measure evolutionary relationships
–
+
DNA
1 32 4 5 1 2 3 4 5
turtle snake rat squirrel fruitfly
2. Medical diagnostic: Comparing normal alleles to disease alleles:e.g. test for Huntington's disease
chromosome with disease-causing allele 2
chromosomewith normal allele 1
–
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allele 1allele 2
DNA
Applications for restriction enzymes and gel electrophoresis
3. Forensics: comparing DNA samples from a crime scene with suspects & victim
–
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S1
DNA
S2 S3 Vsuspects crime
scene sample
Application for restriction enzyme and gel electrophoresis
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