module 3 - Genomes Flashcards
what is a genome?
the complete set of DNA molecules possessed by an organism
what is the function of DnaA in e.coli
- bind close to the origin of replication
- DNA becomes wound around protein - forces bases to break at replication origin
what is the function of DnaB in e.coli
- forms prepriming complex by attatching to origin
- DnaB acts as helicase
- breaks base pairs so replication fork moves away from origin
what is the primosome?
- complex that makes the RNA primers that initiate replication of the 2 leading strands
- formed by the attatchment of 2 primase enzymes
what happens at the replication fork in e.coli?
- helicase (DnaB) breaks base pairs
- single strand binding proteins protect bare single strands
- DNA topoisomerase unwinds strands
- primase forms primers on leading + lagging strands
- DNA Pol III synthesises DNA
- DNA Pol I and DNA ligase removes primers + joins okazaki fragments
- gamma complex (clamp loader) attatches + detatches DNA Pol III from lagging strand
- beta complex (sliding clamp) holds DNA Pol III to template - allows it to slide
what is the function of the gamma complex?
clamp loader
- attatches + detaches DNA Pol III from lagging strand
what is the function of the beta complex?
sliding clamp
- holds DNA Pol III to the template - allows it to slide
what happens at the replication fork in humans?
- helicase breaks base pairs
- single strand binding proteins protect bare single strands
- DNA topoisomerase unwinds strands
- primase/DNA Pol alpha forms primers on leading + lagging strands
- DNA Pol delta synthesises DNA
- FEN1 + DNA ligase removes primers + joins okazaki fragments
- proliferating cell nuclear antigen (PCNA) sliding clamp that holds DNA Pol delta to the DNA
what shape is the E.Coli genome?
circular
what is a Tus protein?
a protein that allows a replication fork to pass in one direction but not the other
- has a permissive and a non-permissive face
tusks on a boar - can’t get past head on bc tusks face forwards, but can run past from the back
what do Tus proteins bind to?
terminator sequences
what happens as a result of two adjacent Tus proteins?
creates a region where the replication fork gets trapped
- Tus lock domain
- allows replication to stop in circular DNA
what is chromatin?
DNA extracted from the nucleus
- digestion with an endonuclease shows that chromatin is actually a DNA-protein complex
what are histones?
the proteins within chromatin
what are the 5 histone proteins?
H1
H2A
H2B
H3
H4
what is a nucleosome?
- octamer - made up of 8 proteins
- made up of two each of H2A, H2B, H3, and H4
what is the role of histone H1?
linker histone - attatches outside nucleosome
what is a chromatosome?
the composition of a nucleosome + DNA wrapping around it + linker histone on top
why are histones important?
- allows a vast amount of DNA to be packed into nucleosomes and other higher order DNA structures
what is euchromatin?
contains active genes as 30nm fibre (less densely packed)
what is heterochromatin?
contains inactive genes (more densely packed)
what is the difference between constitive and facultative heterochromatin?
Con - contains DNA that is always tightly packed in all cells
Fac - cotains DNA that is tightly packed only in some cells
what is the function of the centromere in a chromosome?
- holds daughter chromosomes together
- contains special histones - CENP-A instead of H3
- attatchment point for microtubules + spindle fibres that pull chromosomes apart
what is the function of telomeres in chromosome?
- telomeres protect the ends from exonuclease attack or from being mistaken for chromosome breaks and being joined together by DNA repair mechanisms
