Lecture 4 Flashcards
Directs all cell activities
Contains DNA
Separated by nuclear membrane
Nucleus
Many nuclei
Multinucleate
No nucleus
Anucleate
Examples of multinucleate
Muscle
Some liver cells
Examples of anucleate
Mature RBC
Three main structures of the nucleus
Nuclear envelope
Nucleoli
Chromatin
Double membran barrier suurpunds nucleus
Outer part continuous with Rough ER
Nuclear envelope
Control entry/exit of molecules
Nuclear pores
Dark-staining bodies in nucleus
1-2 per cell
Site where ribosomes are made
Nucleolus
DNA + Proteins
Chromatin
DNA wrapped around 8 histone proteins
Nucleosome
Allow for compact and orderly packing of long DNA molecules
Histones
Fundamental structural packing units of chromatin
Nucleosomes
Complex of DNA tightly wrapped around basic proteins called histones
Nucleosome
Consist of two tetramic molecules, each having four histone-subunits
Nucleosome Core
Four histone-subunits
H2A
H2B
H3
H4
Coils twice around the histone octamer
DNA helix
External ninth histone added which holds the nucleosome structure together
H1 linker histones
Nucleosome plus one H1-histone
Chromatosome
Nucleosomes are separated one another by a
Linker segments of 20-200 nucleotides pairs
Unfolded chromatin appearance
Beads-on-a-string appearance
Nucleosomes with the aid of histone H1 packed together and wound into a regular coil called
Solenoid
Contains six to eight nucleosomes per turn
Solenoid
A solenoid forms
30nm nucleoprotein fibers
Packaging DNA in nucleosomes and then in solenoid reduce its length by
A factor of about 50
During cell division, chromatin condenses to form
Chromosomes
Between cell divisions (interphase), chromatin exist as a tangle of fibers of
10-30 nm (10-9m) diameter
0.25-2 mm length
The unfolded regions are reffered to as
Euchromatin
More condensed unfolded regions are called
Heterochromatin
Before cell division (Mitosis), the chromatin condense into
Metaphase chromosomes
During this condensation, the DNA packaging factor increase dramatically from
50 to about 7000
Folded and organized with specific non-histone proteins, into subdomains of coiled loops
Nucleoprotein chromatin fibers
Two identical, symmetrical DNA molecules
Chromatids
Made of chromatids
Chromosome
Joined by a centromere which attach them to the mitotic spindle
Chromatids
Each chromosome contains:
2 chromatids
1 centromere
4 telomeres (ends of DNA molecule)
Copying of genetic material
Replication
Process of duplication of the entire genome prior to cell division
DNA Replication
Biological significance of DNA replication
Extreme accuracy of DNA replication
Only occurs during the S phase of the cell cycle
