DNA : the material of inheritance Flashcards
Lecture 2 - Mari Knight
“living thing”
a living thing should have
- metabolism
- hereditary replication
metabolism
a coordinated system of chemical reactions contributing to its maintanence system, a system that imports energy to maintain order
hereditary replication
a system of copying in which the new structure resembles the old
discovery of DNA
Miescher 1869
- discover ‘nuclein’ (component of cell)
Griffith 1928
- bacterial transformation
Griffith’s experiment : transformation
- s strain and r strain
- tested on a mouse
- bacteria are capable of transferring genetic information through a process known as transformation
Chargaff’s Rule
Adenine = Thymine
Guanune = Cytosine
A + T ≠ G + C
DNA is a double helix
James Watson & Francis Crick (1953)
- had potential to encode for amino acids, the building blocks of proteins
- mutations could bring about significant differences in proteins
- could be easily copied due to the complemantary nature of the 2 strands
DNA : basic structure
Nucelotide = phosphate + sugar + base DNA = phospate + deoxyribose sugar + nitrogenous base
bases:
- Thymine
- Cytosine
- Guanine
- Adenine
A always binds with T ( 2 hydrogen bonds )
G always binds with C ( 3 hydrogen bonds )
Pyrimidines
Cytosine and Thymine
( 6 carbon ring )
to remember : py : cy : thy
Purines
Guanine and Adenine
6 carbon ring + 5 carbon ring
DNA : anti-parallel structure
2 strands of DNA running anti-parallel to each other
one strand runs in a 5’ to 3’ direction and the other runs in a 3’ to 5’ direction.
- 5 prime end = free phosphate
- 3 prime end = free sugar
each strand is complimentary to the other
semiconservitive replication
DNA replication is semiconservative
produce two copies that each contained one of the original strands of DNA and one new strand
Each strand of the original molecule remains intact and serves as the template for the synthesis of a complementary strand
DNA : replication
occurs simultaneously at several points along the DNA strand ( replication bubbles )
DNA replication mediated by:
- helicase
- RNA primase
- DNA polymerase
Replication Bubbles
an unwound and open region of DNA where DNA replication occurs
- eventually will join up
- rapid replication
DNA : properties
to sustain life DNA must be able to :
- be replicated
A) for cell generation : Mitosis
B) for reproduction : Meiosis - be repaired
- be expressed and regulated
Mutagens
a natural or human-made agent (physical or chemical) which can alter the structure or sequence of DNA
e.g. UV light, nitrous acid, ethidium bromide
replication errors
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.
the final error rate in replication is < 1 per billion nucelotides
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 struvcture recognised
decreases error rate to ~ 1 per 10^9
primary structure ( proteins )
the sequence of a chain of amino acids
secondry structure ( proteins )
occurs when the sequence of amino acids are linked by hydrogen bonds
alpha helix
beta pleated sheet
tertiary structure
coiled/folded further. more bonds form between different parts, including hydrogen bonds and ionic bonds. disulfide bridges form when two cysteine
quaternary structure ( proteins )
protein consisting of ore than one amino acid chain
