Week 7 DNA Structure and Replication Flashcards
What are the three components of DNA
Phosphate
Deoxyribose sugar - missing an oxygen atom
4 nitrogenous bases - A,G (purines), C,T (pyrimadines)
these three components form the chemical subinit of DNA- deoxynucleotides
Describe the backbone of the strands of DNA
They are made up of alternating phosphate and deoxyribose sugar units - they are linked together by phosphodiester linkages
Describe the purpose of the grooves in DNA
They are recognized for protein binding -Major groove is the deeper groove
Difference between purines and pyrimadines
Purines have a a double ring structure and pyrimadines have a single ring structure
Describe the enzymes and proteins involved in unwinding the DNA double helix
Helicases disrupt hydrogen bonds of the souble helix
single strand DNA binding proteins (SSB) stabilize the onwound DNA and prevent the duplex from reforming
DNA gyrase remove the extra twisting (supercoils)
Topoisomerase relaxes supercoiled DNA by breaking a single DNA strand or both strands
What is the replisome
The replisome is a multiprotein molecular machinery responsible for the replication of DNA.
Describe the assembly of the replisome in bacteria
Begins at the origin of replication
DnaA protein binds to DnaA boxes and the an AT rich region to promote unwinding - forms a single strand DNA bubble and DnaA coat the origin
DnaB helicases bind and slide 5’-3’ to unzip the helix at the replication forks
Now the replisome can come in to start replication
How does DNA polymerase III and I catalyze DNA chain elongation in bacteria
III comes with the replisome - add deoxyribonucleotides the the 3’ end of a growing nucleotide chain - removes two of the three phosphates in the form of pyrophosphate
I - removes mismatched nucleotides 3’-5’ exonuclease activity
5’-3’ exonuclease activity that degrades single stranded DNA or RNA
How is DNA replication semi discontinuous
DNA pol can extend but not start a chain so they need primers
- Can synthesize continuously only in the 5’3’ direction off of the 3’-5’ leading strand
Primase synthesizes short RNA primers in the 5’3’ lagging strand so that DNA pol IIIcan synthesize DNA starting at the 3’ end
DNA pol I removes RNA primers and fills the gaps
DNA ligase connects the Okazaki fragments
During what phase of cell synthesis is DNA replicated in eurkaryotic organisms
the S phase
How does replication begin in eukaryotic DNA?
The origin recognition complex (ORC) binds to the DNA, and recruits Cdc6
This loads a helicase and Cdt 1 (twice), then Cdc6 and Cdt 1 release and replication begins (DNA pol is recruited)
What does telomerase do?
Carries short RNA molecule complementary to 3’ overhang and uses reverse transcriptase activity to elongate 3’ end
RNA and Telomerase can move (translocation) and repeat elongation
This allows for an RNA primer to be sythesized and DNA pol can fill in the gap, the overhang this time is okay to be chopped as it is just a repeat
