Overview of DNA Replication and Chromosome Structure Flashcards
Does DNA replication follow a conservative mechanism or a semiconservative mechanism?
SEMICONSERVATIVE MECHANISM
What can be noticed in origins of replication of a genome?
They are A - T rich regions, because this base pairing is easier to separate due to its smaller quantity of hydrogen bonds.
What unwinds DNA in DNA replication?
HELICASES
What is a primer?
Specialized RNA polymerase composed of about 12 nucleotides.
Why is yeast often used in experiments?
Because yeast, which is a unicellular organism, is very easy to manipulate it because you can transform it just like a bacteria with a plasmid, yet it is still a eukaryote.
What is replicated first: euchromatin or heterochromatin?
EUCHROMATIN, because it is already opened.
During what cell cycle phase does chromatin decondense?
INTERPHASE (G1, S, G2)
What are Histones?
They are NUCLEAR PROTEINS which have the task of COMPACTING and ORGANIZING chromosomal DNA.
Rich in POSITIVELY CHARGED AMINO ACIDS, which interact with the negatively charged phosphate groups in DNA
What is Chromatin?
The COMPLEX OF HISTONES AND DNA.
- About half DNA and half protein (majorly histones) by mass.
What are centromeres and telomeres?
Specialized chromosome regions that contain few genes.
Are centromeres and telomeres Euchromatin or Heterochromatin?
HETEROCHROMATIN
What is a Barr Body?
It is a highly proteinaceous heterochromatic blob that is the INACTIVATED X CHROMOSOME IN FEMALES.
What can the Barr Body be used for?
- It can be used to test for SUPER MALES and KLINEFELTER’S SYNDROME by buccal smear.
- It can be used to TEST FOR AUTHENTICITY OF GENDER, which is what they did in the Olympics back in the days.
Who made the discovery of the Barr body?
MURRAY BARR
What is the major chromatin protein?
HISTONES
In what physiological conditions is chromatin in its fibre form?
When it is isolated under physiological ionic conditions (150 mM KCl, 4 mM MgCl2).
In what conditions is chromatin in its “string on a bed”/extended form?
When it is isolated under low ionic conditions, no Mg2+.
What are the “beads” in the “beads on a string” model of chromatin?
NUCLEOSOMES
What is a Nucleosome made of?
- PROTEIN CORE HISTONE OCTAMER (2 x H2A, 2 x H2B, 2 x H3, 2 x H4)
- 147 BASE PAIRS OF DNA
What is necessary to the formation of a Histone?
HAND SHAKE DOMAIN (without it, you die)
What are 3 of the PTMs (Post Translational Modifications) of histone tails and what do they do?
- METHYLATION of lysine or arginine (mono, di- or tri-methylation):
Forms a binding site for CHROMODOMAINS (closes up chromatin / heterochromatin) - ACETYLATION of lysine:
Forms a binding site for BROMODOMAINS (opens up chromatin / euchromatin) - PHOSPHORYLATION of serine or threonine
How do histone tail modifications affect nucleosome behaviour?
- Modifications can AFFECT THE CHARGE on the histone and its ELECTROSTATIC INTERACTIONS with DNA.
- Modifications can RECRUIT SPECIFIC PROTEINS that alter nucleosome structure and function
What is a Nucleosome?
It is the PRIMARY STRUCTURAL UNIT OF CHROMATIN.
What are the 2 types of histone tails?
N and C TERMINAL TAILS
In what type of histones are found the C terminal tails?
H2A and H2B
What are pre-replicative complexes?
A bunch of protein that seed the ability to replicate once they are loaded onto origins of replication, which are A-T rich regions.
What can DNA microarrays tell you?
It tells you…
- WHERE origins of replication are located
- That they are moving BIDIRECTIONALLY
- How QUICKLY they are doing that overtime.
Name one well known bromodomain.
TFIID
