Lecture 3 Flashcards
How are errors in DNA repaired during replication?
-can be repaired on spot, DNA polymerase III can go backwards and cut the incorrect bases (exonuclease) function the proteins of the replication complex excise the incorrect nucleotides -some people don’t have this ability exoderma (the huge growths on skin etc.)
How are errors in DNA repaired after replication?
mismatch repair:- when misread in replication or paired wrongly -mismatch repair proteins excise the wrong sequence plus some adjacent nucleotides, DNA polymerase I adds the correct nucleotides and ligase repairs the nicks. -if environmental damage to the sequence- enzymes can repair it in the same way excision repair: damage response -a nucleotide in DNA is damaged -the excision repair proteins excise the damaged nucleotide and some adjacent ones -DNA polymerase I adds correct nucleotides by 5’- 3’replication of the short strand
Describe PCR!
-add DNA sequence to be amplified, 4 deoxyribonucleotide triphosphates (carrying the bases), deoxyribose, enzyme and 2 primers complementary to 3’ends of both strands -heat up to 95 C to separate DNA strands (hydrogen bonds break) -cool down to 60-65 C then the primers bind need to know the end of the added sequence so you can design the primer(must be complementary to the end sequence)-need primer for the lagging strand -can amplify regions of up to 2000 bases (2kb) -so sensitive you can use primers with the whole human genome and amplify a specific sequence -sequence of DNA can be amplified millions of times after several cycles of PCR
Why is the temperature in PCR an issue?
Normally enzymes in DNA replication denature at 37 C. So here an enzyme from a bacterium living in hot springs is added Taq polymerase (type of DNA polymerase III of bacterium Thermus aquaticus) this adds the bases to the template DNA
Is chromosome number constant during organism’s lifetime?
-yes
What is aneuploidy?
extra chromosomes but not a set! -Eg. trisomy 2N+1, monosomy 2N-1 -happens in meiosis, non-disjunction at Anaphase I or Anaphase II (or both)
What is klinefelter syndrome?
XXY -all males sort of… -extra chromosome X (bad, some genes 3x-messes it up) -varying severity of retardation -many die before the age of 5 (usually heart failure) -the ones who survive, in their 40s- Alzheimer like disease (get amyloid deposits in brain as chromosome 21 is an amyloid precursor) -enlarged tongue -males: enlarged breasts, small penis, slow learner, infertile
What is euploidy?
extra sets (adding or taking sets), polyploidy, triploidy 3N, tetraploid 4N -can tolerate more sex chromosomes but not autosomes -polyploidy(more than 2 sets) often in agriculture -triploid bananas (3N) tetraploid grapes (4N) – reproduce vegetatively -triploid: three of each type of chromosome, humans- 69 3N- odd numbers of polyploidy usually result in death
What are the effects of polyploidy in some animals?
: reproduction is then parthenogenic (without fertilization) - lizards, salamanders - triploid oysters do not spawn (spawning females unpalatable)
What is the effect of triploidy in humans?
human triploidy leads to death in-utero or soon after birth, not uncommon, very common cause of miscarriages (especially older mothers)
What are the 5 ways of preventing human aneuploidy that are used in pregnancy?
-pre-implantation diagnosis -ultrasound -triple test of maternal blood -chorionic villus sampling -amniocentesis
What is pre-implantation diagnosis (PID)?
when IVF treatment : take out a single totipotent cell from an embryo before implantation
What is ultrasound?
8-10 weeks and second at 20 weeks that can pick up gross abnormalities and then further testing
What is the triple test of maternal blood?
measures 3 compounds(eg. protein= indication of open spinal chord, skull) which give an indication of possible abnormalities (around the time of first ultrasound)
What is chorionic villus sampling?
10- 12 weeks, chorion is a tissue that has the same genetic make up as the fetus, more invasive, guided by ultrasound