Class Notes (839,398)
Canada (511,327)
Biology (6,826)
Biology 1001A (1,727)
Dr.Mike (47)
Lecture 8

Lecture 8 IS - Origins of Variation word.doc

3 Pages

Course Code
Biology 1001A

This preview shows page 1. Sign up to view the full 3 pages of the document.
Lecture 8 IS- Origins of Variation Mechanisms that Promote Inheritance of Sameness - Mechanism of proofreading - Mechanism of mßismatch repair Mechanisms that Promote Inheritance of Difference - mutations in DNA may change protein which may change function, which is important for the evolutionary process - Transposition 1. Mechanism of proofreading and likely result of proofreading defects - DNA polymerase rarely make mistakes and their mistakes are usually base- pair mismatches and these errors are usually corrected - proofreading mechanism depends on the ability of DNA polymerases to back up and remove mispaired nucleotides from a DNA strand - the correct pairs allow the hydrogen bonds that stablize the DNA to form - if nucleotide is mismatch, DNA polymerase cannot continue to add nucleotides - If the nucleotide is mismatched, DNA polymerase reverses using built-in de- oxyribonuclease (3’-5’ exonuclease) to remove the incorrect nucleotide - then it keeps going - If proofreading defects there is still mismatch repair 2. Mechanism of mismatch repair - Second round of correction after proofreading - correct base pairs fit together and their dimensions separate the sugar- phosphate backbone chains at a constant distance - mismatched pairs will be too big or too small and so cannot form the hydro- gen bonds and so distort the structure of the DNA helix - provides a recognition site for the enzymes catalyzing mismatched pairs - repair enzymes move along the double helix for distortions and if they en- counter one, they remove a portion of the new chain - they fill in the gap using DNA polymerase - DNA ligase then comes and seals the nucleotide chain into a continuous DNA molecule - this mechanism is also used for correction of alterations in DNA caused by chemicals, and radiation - people with Xeoderma pigmentosum have faulty repair mechanisms and so can develop skin cancer easily - if errors remain in DNA, it is a primary source of mutation - will get carried on in replicated copies - may alter the property of the protein encoded - may alter how organism functions 3. Differences among insertion sequences, transposons and retrotransposons - Transposition: - occur at a low frequency Lecture 8 IS- Origins of Variation - does a cut and past process where the transposable elements leaves it original location and transposes to a new location - or a copy of a transposable element transposes to a new location leaving the original transposable element behind - for most, transposition starts with contact between the transposable element and the target site - makes genetic changes eg, making mutations by transposing into genes and knocking out their functions - Insertion sequences ( a type of transposable elements in bacteria) - simplest - relatively small and contain only genes for their transposition, the gene for transposase (enzyme that catalyzes some of the recombina- tion reactions for inserting or removing the TE from the DNA) - has a short inverted repeat sequence (same DNA sequence running in opposite directions) at each ends of an IS - allows transposase to identify ends of the TE when it catalyzes transposition - Transposon (other type of transposable element in bacteria) - has central region that may include genes that code for antibiotic re
More Less
Unlock Document

Only page 1 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.