Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
15 Cards in this Set
- Front
- Back
|
What is the problem with packaging DNA?
|
Huge amount of information (DNA) must be condensed into a very small package. But, also needs to be accessible during interphase for transcription/replication.
|
|
|
Solution?
|
Package the DNA in four discreet levels. more compact during mitosis, less when being used to encode proteins.
|
|
|
What's going on with uncoiled proteins?
|
Uncoiled chromatin. They're still attached to histone proteins (still in level 1 packaging).
|
|
|
Level 1 of DNA packaging?
|
Unless the DNA is being read, it always remains wrapped around histomes making nucleosomes.
|
|
|
core of a nucleosome?
|
8 histone proteins (4 pairs). Histones have a large # of positively charged amino acids on their surface... attracts the - charged DNA (the phosphates in DNA give it a negative charge).
|
|
|
How does DNA wrap around the histones?
|
Wraps around the 8 histones twice, and is bound by a 9th histone, called H1.
|
|
|
Level 2?
|
Due to the H1, the layer pushes onto itself, creating a double layer. This is the state that most G0 DNA is found in. Called a coiled coil or 30nm fibre.
|
|
|
Level 3?
|
Happens in prophase and prometaphase. Looped Domains - Loops of 30 nm fibres attached to a protein scaffold in the chromosome during mitosis
|
|
|
Differences in level 3 between G0 cells and mitosis?
|
In a G0 cell the protein scaffold lines the inner surface of nuclear envelop and also some in nucleoplasm.
|
|
|
Level 4?
|
Fully condensed chromosomes. Loops of 30 nm fibres on a protein scaffold make up Looped domains which, when further coiled make up fully condensed chromosome
|
|
|
Differences between euchromatin and heterochromatin?
|
Euch -- The 'accessible' DNA is kept in a less compact form
|
|
|
Do simpler organisms have this divide?
|
No, they have no need. They need all their DNA. A more complex organism (like us), needs to preferentially store things.
|
|
|
How to differentiate euch from hetero in a cell?
|
Euchromatin looks less dense or more light coloured in a cell nucleus.
|
|
|
What does the nuclear lamina do? Nuclear matrix?
|
it's a chromatin organizer.
Matrix: Additional protein 'web' throughout nucleus also organizes. |
|
|
Do prokary (and archea) package DNA similiarly?
|
No. Bacteria has large circular pieces for the genome that is condensed by physical twisting. Space is not as much of an issue for them .
Archea -- Have histosone like proteins, and something like nucleosomes, but nothing as complex, and that's as far as it goes. |
