M3 GENOMES Flashcards
What is a genome?
A genome is the complete set of DNA molecules possessed by an organism
How many origin of replication do BACTERIA contain?
1
How many org8isins of REPLICATION do eukaryotic cells contain?
Multiple
How many base pairs is the human genome made of?
3200 Million base pairs (Mb)
In how many linear molecules is the human GENOME split into?
24
How may base pairs is the SHORTEST linear DNA molecule?
48 Mb
How many base pairs is the longest DNA linear molecules in human?
250 Mb
How many base pairs is E.coli DNA?
4.64 Mb
Where does replication generally begin?
At ORIGIN of replication
How is replication INITIATED in E.coli and Humans?
- DnaA protein binds to DNA close to origin of replication point
- DNA then avvolges/surrounds DnaA protein, causing stretching at origin hence breaking of base pairs
- DNA origin is AT rich which allows easier separation of the strands
- Dna B protein binds to exposed strands, forming PREPRIMERS region
- DnaB is a helicase which breaks more base pairs moving replication fork forwards
- PRIMASE then binds do DNA forming rna primers
- which will eventually start replication
- and then each even occurs in a different way at replication fork in E.coli and Humans
DNA in E.coli is circular and replication from origin of replication occurs in both ways, what prevents replication going in circles?
TERMINATING sequences that allow binding of TUS proteins
What feature of the protein involved in termination of replication ensures that it is not continued in circle in E.coli?
- Tus protein have a permissive and non permissive side, which prevent the furthering of the replication fork.
How does DNA in human terminate?
- replication forks just merge into each other, stopping each other as human DNA is linear.
In HUMAN DNA how much does DNA each replication fork copy>
150 Kb
What is chromatin?
DNA + protein histones
What type of histones protein is the chromatin structure made out of?
H1, H2A, H2B, H3, H4
What does a nucleosome consist of?
- Nucleosomes consist of 1 DNA lenght coiled around a histone
- Each nucleosome consists of 8 histone proteins
- 2 of each: H2A, H2B, H3, H4
- nucleosomes are linked together by Linker DNA
- Linker DNA is supported by histone proteins H1 which also links each nucleosome together
What is essentially the job of histone protein and 30 nm fibres?
to reduce size/lenght of the DNA
What do 30 nm fibres do to DNA?
They futher reduce size of DNA,.
The 30nm fibre is the DNA in its interphase state. The DNA is wrapped around the histone complex and then is twisted into a solenoid structure, the 30 nm fibre
What are the 3 levels that DNA in chromatin is arranged in?
- DNA wraps around histone proteins, forming nucleosomes and the so-called beads on a string structure
- Multiple histones wrap into a 30- nanometer fiber consisting of nucleosome arrays in their most compact form
- Higher-level DNA supercoiling of the 30-nm fiber produces the metaphase chromosome (during mitosis and meiosis).
What is Euchromatin?
Euchromatin = (light areas) ,contains active genes probably as 30 nm fibre
What is heterochromatin and what does it subdivide into?
-contains inactive genes more densely packed shown by the fact is darker in the picture
Heterochromatin subdivides in:
* Constitutive heterochromatin contains DNA that is always tightly packed - in all cells
* Facultative heterochromatin contains DNA that is tightly packed only in some cells, meaning that in some cells heterochromatin can be used to transcribe
Which is normally transcribed Euchromatin or heterochromatin?
Euchromatin as it contains active genes
