Nucleic Acids and Proteins Flashcards
Degrade DNA molecules by breaking the phosphodiester bonds that link one nucleotide to the next in a DNA strand.
nucleases
Two kinds of nucleases
Exonuclease
Endonuclease
Nucleases vary in
Specificity
May be specific for DNA or RNA, such as DNases or RNases, respectively, or even be specific for a DNA/RNA hybrid, such as RNase H, which cleaves the RNA strand of a DNA-RNA hybrid. Therefore, its specificity varies dramatically.
nucleases
Remove nucleotides one at a time from the end of a DNA molecule
Exonuclease
May either attack a polynucleotide chain from the 5’ end and hydrolyze 5’ to 3’ or attack from the 3’ end and hydrolyze 3’ to 5’
Exonuclease
When a nuclease hydrolyzes an ________________ bond in a ________________ linkage, it will have specificity for either of the two ester bonds, generating either 5’ nucleotides or 3’ nucleotides
ester; phosphodiester
Nucleases may be specific for single strand nucleotide chain, double-helix stands, or both.
Strand preference
An exonuclease that can remove nucleotides from both strands of a double-stranded molecule
Bal31
An enzyme that degrades just one strand of a double-stranded molecule, leaving single-stranded DNA as the product
Exonuclease III
Can hydrolyze internal bonds within a polynucleotide chain (break in the middle)
Endonuclease
Can attack the phosphodiester bond from the 5’ end or from the 3’ end of the linkage
Endonuclease
________________ endonuclease only cleaves single strands, whereas ________________ cuts both single- and doublestranded
S1; deoxyribonuclease I (DNase I)
Recognize a specific nucleotide sequence and cleave the DNA molecules internally
Restriction endonucleases
More commonly used in the lab
Restriction endonucleases
3 classes of restriction endonucleases are distinguished by
mode of action
Class of restriction endonuclease that are rather complex and have only a limited role in practical biotechnology applications.
Type I and Type III
Class of restriction endonucleases which are the cutting enzymes that are so important in laboratory and clinical analysis.
Type II
Type II restriction endonuclease is important because these sites (2) are the same.
recognition site
cleavage site
Length of recognition/cutting sites
4 to 8 bp
This means reading the same forward and backward on complementary strands
inverse palindromic
Different sources of Type II restriction
Isoschizomers
Neoschizomers
Isocaudomers
Q1: recognize and cut DNA at the same site
Q2: produce the same nucleotide extensions but have different recognition sites
Q3: recognize and bind to the same sequence of DNA but cleave at different positions
Isoschizomers;
Isocaudomers;
Neoschizomers
Isoschizomers species
BspEI from a Bacillus species
AccIII from Acinetobacter calcoaceticus
Neoschizomers species
NarI from Nocardia argentinensis
SfoI from Serratia fonticola
Isocaudomers species
NcoI from Nocardia corallina
PagI from Pseudomonas alcaligenes
represents a linear sequence of the sites at which particular restriction enzymes find their targets
Restriction map
Before sequencing a large stretch of DNA, this is done to locate the cutting site and examine sizes of fragments
Preliminary mapping
Q1: Restriction digest can be performed in a ________________ in the presence of all necessary components
Q2: what are these components
microcentrifuge tube;
template DNA, restriction enzyme, Mg2+
Q1: A restriction digest results in a number of ________________
Q2: the sizes of which depend on the
DNA fragments;
positions of the recognition sequences
Used to analyze restriction digested DNA fragments
gel electrophoresis
separated based on their size
A specific DNA region can be analyzed by
Southern blot
Enzymes that synthesize a new strand of DNA complementary to an existing DNA or RNA template
Polymerases
Types of polymerases
- DNA Polymerase I
- Klenow Fragment
- Taq DNA polymerase
- Reverse Transcriptase
Prepared from E. coli which an example of an enzyme with a dual activity
DNA polymerase I
DNA polymerase I activities (2)
DNA polymerization
DNA degradation
This treatment of DNA polymerase I produces two polypeptides
Mild proteolytic treatment
The large fragment produced by mild proteolytic treatment of DNA polymerase I which has the polymerase 3’ to 5’ exonuclease activity
Klenow fragment
A Klenow fragment can synthesize a complementary DNA strand on a single-stranded template also known as a ________________ region.
nick
Major application of Klenow fragment
Perform DNA end-filling or DNA sequencing
Bacterium of Taq DNA polymerase
Thermus aquaticus