DNA Flashcards
What is life?
*Be able to regulate their internal environment to maintain a constant state, converting energy generated from non-living material into cellular components (i.e. a metabolism)
*Be capable of multiplication/growth
*Show variation in form between individuals
*Be able to adapt/change in response to their environment
*heredity (pass on to generation)
What was Griffith’s experiment that led to understanding DNA and what did Avery, Macleod & McCarty do?
He was working with streptococcal bacteria (respiratory diseases) some strains are lethal some are not.
S-strains are lethal to mice whereas R strains don’t kill mice.
Griffith noticed that if you heat kill S-strain bacteria and you inject them into the mouse, it lives proving live cells kill mice but if you inject the mice with non-lethal R-strain and the lysed S-strain you reinstate that lethal property of the S-strain which kills the mice.
What this shows is transformation of the strains from non-lethal to lethal.
Later Avery, Macleod & McCarty did further experiment where they destroyed different constituents of the S-strain bacteria cells and when they specifically destroyed the DNA the mouse lived
What was Chargaff’s Rule?
Adenine = Thymine
Guanine = Cytosine
A+T not equal G+C
What did Maurice Wilkins & Rosalind Franklin find out about DNA?
They used X-ray diffraction and found that DNA has helical properties with 2 periodicities, a major and a minor.
What did James Watson & Francis Crick propose about the structure: of DNA?
*It Had the potential to simply encode for amino acids, the building blocks of proteins
*Small changes (mutations) could thus bring about significant differences in proteins
*Could feasibly be easily copied due to the complementary nature of the 2 strands.
Which bases are purines and pyrimidines
pyrimidines =(cytosine and thymine)
purines = (guanine and adenine)
How does DNA replicate?
semiconservatively
50 bases per second
Replication occurs simultaneously at several points along the DNA strand. Replication ‘bubbles’ eventually join up.
Mediated by helicase, RNA primase and DNA polymerase
How many base pairs long is human DNA?
3 billion base pairs
What are some of the substances that are known to cause mutations in the DNA?
Mutagens
UV light, nitrous acid, ethidium bromide, mustard gas
How many replication errors of DNA polymerase occur in DNA?
size of the average eukaryotic genome is 10^9 - 10^10 bases – error rate of initial DNA polymerase during replication is ~ 1 per 10^5 bases.
Final error rate in replication is < 1 per billion nucleotides.
How are errors recognised in DNA?
*DNA proofreading = Corrects errors during replication. Orientation to the hydroxyl group is incorrect.
Decreases error rate to ~ 1 per 10^7
*Mismatch repair = Corrects errors after replication is complete. Deformity in secondary structure recognised.
Decreases error rate to ~ 1 per 10^9
What era was the material of inheritance known to be contained within the nucleus ?
From the 19th century, but DNA was not confirmed as the molecule of inheritance until the 1940s/50s.
What direction DNA read in?
5’ to 3’ direction
