CHROMATIN STRUCTURE AND FUNCTION Flashcards
Chromatin
Organised structure of DNA and protein found in nucleus of eukaryotic cell
It is the stainable material of cell nucleus, consisting of DNA and proteins.
Difference between chromatin and chromosome
Chromatin is less condensed
Chromosome is more condensed
Types of chromatin
Euchromatin -
less condensed
lightly stained
Takes part in DNA replication
Histone acetylation and methylation
Heterochromatin
more condensed
darkly stained
Does not take part in DNA replication
Deacetylation and methylation
MAR
Matrix associated region
Depending on virus, genetic material can be
ssRNA (influenza virus, polio virus)
dsRNA (reoviruses)
ssDNA (paroviruses)
dsDNA (T-2 bacteriophage, Gemini virus)
It may be circular/ linear
Charge of DNA
Negatively charged
Chromosomes in prokaryotes
- just one circular chromosome
- located in nucleoid (since nucleus is lacking)
- DNA is supercoiled and compacted by nucleoid associated protein
- smaller in size
Topoisomerase
Amount and type of supercoiling (+ve or -ve) is controlled by topoisomerase enzymes found in all organisms
Types -
1. Topoisomerase l - reduces number of -ve supercoils in DNA
2. Topoisomerase ll - adds -ve supercoils in DNA
Chromosomes in eukaryotes
- most of them have multiple linear chromosomes
- located in nucleus
- DNA is wound around histone proteins and further compacted by supercoiling and folding
- larger in size
C value
Total amount of DNA in haploid genome of a species is called C value of that species
DNA content of cell during cell cycle
Eukaryotic cell reproduce in cell cycle, which has four phases— G1, S, G2 and M
G1, S and G2 = interphase
M = division phase
Each eukaryotic chromosome, including duplicated, chromosomes with two sister chromatic have one linear dsDNA molecule running throughout the length of chromosome/ each system chromatid.
G0 phase in cell cycle is where cells are alive, but do not replicate.
S phase = synthesis phase, where DNA replication occurs.
State the type of proteins in chromatin
Histones and non-histones
Histones
- most abundant
-Play important role in chromatin packaging
- Basic in nature
- Positively charged
- five main types include H1, H2A, H2B, H3, H4
Non-histones
- acidic in nature
- Includes proteins, important for DNA replication, repair, transcription, and recombination.
What is the least compact form of chromosome packaging?
10nm
Telomere repeat sequence in humans is
TTAGGG
Chromosome packaging
- in chromosome packaging, nucleosome of 8 histone core (2 each of H2A, H2B, H3, H4) are wound by DNA 1.65 times
- individual nucleosome are connected by linker DNA strands
- Nucleosomal DNA is binded by H1 histone and converted into coiled chromatin fibres, which is compacted into chromosome arms. As a result forming a chomatid
Proteins responsible for structural maintenance of chromosomes
Condensin
Enzyme for supercoiling and relaxation of DNA
DNA gyrase
Histones are rich in
Lysine and arginine
Centromere
- located at constricted region of chromosome
- binds sister chromatids together
- ensures correct chromosome segregation during cell division
- defects in centromere can lead to - aneuploidy, chromosomal in stability.
Telomere
- located at ends of chromosome
- Protects chromosomes from degradation and fusion
- stabilises chromosome
- telomeres shorten with age, which may lead to age related disorders
- Required for replication
Gene
- smallest unit of genetic information
- Basic unit of heredity
- Passed from parents to offspring
- Made of DNA sequences
- Located in nucleus, in chromosome, in specific locations
- genes encodes, the information for making proteins necessary for all processes in our body
- genes are located in specific segments of DNA (DNA which is tightly coil around proteins), in chromosome, in nucleus, in cell of the organism.
