Mutations Flashcards
What is a mutation?
Changes in the sequence of nucleotide of DNA
Inheritable
Harmful, lethal, helpful or silent
What is a point mutation?
Change in a single base
Most common
Silent missense and nonsense
What are spontaneous mutations?
Errors in normal processes
What are base analogs
Mismatch during replication e.g 5BrDU
What are intercalating agents
Insert extra bases eg ethidium bromide
What do agents that modify nucleotide bases do
Alter H bonding
What are UV mutagenesis
Faulty repair of thymine dimers
What are alkylating agents
Mutagens likely to introduce small changes and major changes
what is an example of base modicfictaion
nitrous acid as it converts adenine so it no longer pairs with thymine and modified adenine pairs with cytosine
what are nucleoside analogs
compounds that resemble bases closely- eg adenine and thymiine nucleoside
what is adenine nucleoside
2-aminopurine is incorportaed into DNA in place of adenine but can pair with cytosine so an AT pair becomes a CG pair
what is thymine nuceloside
5-bromouracil is an anticancer drug as it is mistaken for thymine by cellular enzymes but pairs with cytosine so AT pair becomes a CG pair
what happens when UV light passes through DNA
it becomes abnormal and results in a thymine dimer - the adjacent thymines become crosslinked, forming a thymine dimer and disrupts normal base pairing
what is the difference between endo and exonuclease
endo= cuts DNA
exo= Removes damaged DNA
What is a part of DNA replication
proofreading
what is the error rate for DNA polymerase without proof reading
1 - 1,000,000 nucleotides
what is the error rate for DNA repliaction
DNA polymerase error rate 1 in 10-9 nucleotides
what is the error rate for transcription
RNA polymerase error rate 1 in 10-5 nucleotides
what is the error rate for translation
Translation error rate 1 in 10-4 per codon
what does DNA ligase do
seals the remaining gap by joining old and new DNA (ineffcient repair leads to mutation)
what are the types of mutation
Point= silent , nonsense and missense
Frameshift= insertion or deletion mutation
Chromosomal= duplication deletion and translocation
Repeat expansion= causes Huntington’s and fragile X syndrome
what is a missense mutattion
a DNA chnage that reuslts in different amino acids being encoded at a particular position in the resulting protein. e.g sickle cell anemia
C-G becomes A-T and causes a change in the amino acid sequence and a new protein is released
Explain Missense mutation and antibiotic resistance
Mycobacterium tuberculosis
Chronic lung infection
High fatality rate without treatment
Antibiotic rifampicin very effective
Binds to RNA polymerase
Inhibits transcription
Problem: high rate of point mutation in rpoB
Single base change
Single amino acid change
Reduced drug binding
RESISTANCE
what is a nonsense mutation
stop mutation is a change in DNA that causes a protein to terminate or end its translation earlier than expected e.g protein CFTR leads to CF
What is a silent mutation
no change in the polypeptide - change in the DNA sequence has no effect on the amino acid sequence E.g AAA codes for amino acid lysine and when mutated AAG can code for lys
what is a frameshift mutation
in a gene refers to the insertion r deletion of a nucelotide bases in numbersthat are not multiple of three e.g crohns, CF and types of cancer
Shift in the reading frame and change in protein
What are the codes for GLY
GGU, GGC, GGA and GGG
What is vertical gene transfer
when genes are passed from organism to its offspring. Parent to daughter/offspring and is a part of reproduction
what is horizontal gene transfer
occurs between mature cells and is not a part of reproduction and transfers from donor to recipient. It contributes to genetic diversity- brings organism new functions
what are the 3 major mechanisms of horizontal gene transfer
transformation, conjugation and transduction
what is transformation
genes transferred from one bacterium to another as “naked” DNA
what is conjugation
plasmids transferred 1 bacteria to another via direct contact
what is transduction
DNA transferred from 1 bacteria to another by a virus that infect bacteria (bacteriophage)
what experiement looked into transformation
griffith experiment in 1928
what does Natural transformation require
competence- Some bacteria are naturally competent.
Have DNA uptake proteins in cell membranes
Some competent all the time
Some competent only at specific stages in the growth phase.
Streptococcus pneumoniae, Bacillus subtilis, Haemophilus influenza, Neisseria gonorrhoeae.
Many other bacteria have been shown to contain the genes for natural competence but have never been observed to do so.
what is the lytic phage cycle T4
where phages infect and repidly kill their infected host thereby shaping bacterial population dynamics and assissting in their long term evolution via generlised transduction
what are the phases of T4
Adsorption, penetration, replication, maturation, release and reinfection
0 min= DNA injected
2 min= host DNA degraded
3 min= Phage DNA made
5 min= late RNA made
12 min= heads and tails made
13 min= heads filled
15 min= virions formed
22 min= host cell lysis
What is the lysogenic phage life cycle
DNA is incorporated into the host genome, where it is passed onto subsequent generations. Environmental stressors such as starvation or exposure to toxic chemicals may cause the prophage to excise and enter the lytic cycle
what can phage carry
more than the minimum requirement to replicate themselves.
what is Diphtheria: Corynebacterium diphteriae
Respiratory infection
5-10% fatality rate
Bacterial toxin major virulence factor
Lysogenic Β-phage integrates into the bacterial DNA
Β-phage encodes the characteristic diphtheria toxin
what is Conjugation in Bacteria
Transfer of DNA by contact of two bacterial cells Can transfer plasmid or chromosome
what are plasmids
DNA elements capable of autonomous replication
Generally encode non-essential genes
Useful metabolic activities
Antibiotic resistance
size: 1 – 1000 kb
double stranded DNA
1 to >100 copies / cell
Some are transmissible to other strains
very abundant in nature
300 different plasmids identified in E. coli isolates
what occurs in bacterial conjugation
Large amounts of DNA transferred
up to 200 kb
Some plasmids encode antibiotic resistances
R plasmids
Interspecies transfer possible
Plasmids “evolve” at a very rapid rate!
what are the maintenance genes
ori, rep and inc
what are the transfer genes
tra
what are the Antibiotic Resistance genes
Tet
Sul
Str
Mer
Cat
what happens in R Plasmid Evolution
Plasmids carrying multiple antibiotic resistances identified:mup to 18 different genes on one plasmid and use of one antibiotic selects for 17 other resistances!
Methods of picking up antibiotic resistance:
transposons
site specific recombination (integrons)
homologous recombination
What is insertion
Addition of one or more nucleotides and causes a shift in the reading frame and leads to the synthesis of a different protein or a premature stop codon causeing a loss of function
What is deletion
Removal of one or more nucleotides causing abframshift Protein can be truncated it functional and leads to disorders
