Lecture 2 strobel: mutations, mutagens and dna damage repair part 2 Flashcards
(42 cards)
What are mutagens?
chemical or physical agents that induce mutations
What do mutagens do?
alter DNA in different ways
What do chemical mutagens contain?
base modifiers, base analogs and intercalating agents
What are base modifiers?
they are chemical mutagens that covalently modify the structure of a nucleotides base
What do base modifiers do?
can disrupt pairing by alkylating bases
What are base analogs?
modified nucleotides that fool DNA polymerase and become incorporated into DNA during replication
* incorporation of base analogs can distort DNA structure
* some tautomerize at a high rate
What are intercalating agents?
they can be inserted into the DNA double helix between bases
* they directly interfere with DNA replication and it distorts the structure of the double helix
What are some examples of physical mutagens?
X-rays, gamma rays, ionizing radiation and UV light
What are induced mutations considered?
base modifiers
What is an example of a base analog?
5-bromouridine
What are some examples of base modifiers used during induced mutations?
nitrous acid and alkylating agents
What does nitrous acid do and how are humans exposed to it?
- it replaces amino groups with keto groups (oxidative deamination)
- it is formed in our stomach from nitrates that are used in smoked/cured meats
What do alkylating agents do?
covalently add ethyl or methyl groups to bases
What base does 5-bromouridine look like and what does it do?
- thymine
- it tautomerizes from the keto to the enol form at a high rate
What are the two general classes of radiation?
ionizing and non-ionizing radiation
List the characteristics of ionizing radiation.
- includes x-rays and gamma rays
- has short wavelength and high energy
- can penetrate biological tissues
- produces free radicals
- can cause: deletions, oxidized bases, single strand nicks in DNA, crosslinking and double strand breaks in DNA
Wat are the characteristics of non-ionizing radiation?
- has a longer wavelength and lower energy than ionizing radiation
- its less penetrating but can still cause skin damage
What are some examples of non-ionizing radiation sources?
sunlight, germicidal lamp and UV LED sample irradiator
What can UV Light cause the formation of?
a DNA lesion called a thymine dimer
Why do thymine dimers occur?
adjacent thymine bases become covalently linked, causing errors during DNA Replication
What test do we use to tell if an agent is a mutagen?
the Ames Test
What is the Ames Test?
a method foe assessing the mutagenicity of a physical or chemical agent
What is the strategy for the Ames Test?
start with a salmonella strain that requires histidine to grow
* then expose the salmonella to a suspected mutagen
* if the agent is a mutagen it may cause reversion mutation that restores the ability to synthesize histidine
What happens during direct repair?
an enzyme recognizes DNA dame=age and directly converts the damaged nucleotides back to the correct form
