DNA, RNA And Replication Flashcards
What is DNA?
deoxyribonucleic acid.
Double stranded= double helix.
Long polymer/ polynucleotide
Carries the genetic information which codes for proteins
Relatively simple structure (meant many scientists didn’t believe it carried the genetic code)
What is RNA?
ribonucleic acid.
Single stranded
Short polynucleotide
Transfers genetic code from DNA (nucleus) to ribosomes in the cytoplasm
Ribosome formed from RNA and proteins
In RNA what pairs with adenine
Uracil replaces thymine as a base
Compare DNA and RNA
Double stranded- twisted into a double helix and held together by hydrogen bonds vs single stranded
Deoxyribose sugar vs ribose sugar
A,T,C,G vs A,U,C,G
Long vs relatively short
What are polynucleotides?
When two nucleotides join by condensation
Sugar phosphate backbone
A always pairs with T
C always pairs with G
Antiparallel strands
How does DNA structure relate to its function?
Sugar phosphate backbone = DNA is strong and stable molecule
Many hydrogen bonds = provides strength and rigidity
Hydrogen bonds weak= strands can be easily separated during DNA replication
Double stranded = bases are protected/ replication can be semi conservative
Long molecule/ polymer = can store lots of genetic information
Bases in sequence = information can be stored (codes for amino acid)
How many hydrogen bonds are between A and T?
2
How many hydrogen bonds are between C and G?
3
How is DNA replicated?
by semi-conservative replication. New DNA is made of one original strand and one new strand.
Describe semi-conservative replication
- DNA helicase unwinds separates the two strands of DNA into single strands by breaking the H bonds between the bases
- both strands act as a template
- free DNA nucleotides attach
- by complementary bases pairing (A,T and C,G)
- DNA polymerase joins nucleotides
- H- bonds reform
- DNA replication is semi conservative as new DNA contains one new strand and one original strand.
What effect does the anti parallel nature of DNA have
The nucleotides on each strand are arranged differently. The active site of DNA polymerase has a specific tertiary structure, only substrates with complementary orientation/shape form an enzyme substrate complex.
Also DNA polymerase working on one end of the strand moves in the opposite direction to the DNA polymerase working on the other template
how is each end of DNA strand slightly different in its structure?
One end is called 3’ and one is the 5’. During replication the site of DNA polymerase is only complementary to the 3’ end of the newly forming DNA strand- so the enzyme can only add nucleotides to the strand at the 3’ end so new strand is made in a 5’ to 3’ direction and DNA polymerase moves down the template strand in a 3’ to 5’ direction.
What experiment verified semi conservative replication?
Meselson and Stahls experiment
Describe the Meselson-Stahl experiment
Population cultures in a growth medium containing heavy nitrogen only
When centrifuged only one heavy band is observed
Cells transferred to a medium with only light nitrogen
After one replication the DNA band was intermediate (and twice the thickness)
After two replications in light nitrogen- intermediate and light bands observed .
Proving DNA replication is semi conservative
