Cell bio lecture 6

What is chromatin structure

À DNA-protein complex made of double helix DNA wrapped around a histone core of 2A,@B,3and4. Histone H1 links beads together making it into a 300nm fibre. A secondary loop happens in mitosis making it a 700nm making the visible karyotype structure. Made of repeating 146 base pairs this is the beads or nucleosome.

Which chromosome elements are responsible for structural maintenance and propagation to maintain chromosomes in nuclei+ steps to this(3)

Telomere:caps chromosome ends protecting degradative enzymes from attacking units in interphase or G phase.

origins of replication: these are initiation points for DNA synthesis during S phase in ur cell.

kinetochore/centromere:nuclear envelope breaks down, chromosomes are separated into daughter cells by the kinetochore.

Rôle of DNA replication fork

Allows DNA replication to happen @same time on two anti parallel DNA strands(one runs 5-3 other 3-5) The fork moves away from the origin of replication making and leading the lagging strands by a continuous and discontinuous process respectively.

Chromosome replication

Starts at origin of replication sites recruit initiation complexes which are throughout the cell.

Toposiomerase and helical unzip the DNA

DNA synthesis goes in both directions from complexes, when those complexes meet up the DNA strands are ligated(joined together) MAking one parental and one newly synthesized strand.

DNA polymerase builds things 5’-3’, the one that works this way is the leading made by DNA Polymerase3.The lagging strand needs proteins like:single-strand binding protein to keep the strands apart and stable, primate adds RNA strands bc polymerase can’t run across to get them all so it needs stepping stones then DNAPolymerase1 translates them into DNA and these fragments are called Okazaki fragments, then they are lighted(glued) together into one big strand.

Histone 1 job and structure

Domains: globular NH2-terminal and COOH-terminal arm. It binds to diffferent regions thru its globular domain, the COOH arm segment reaches out to the specific binding sites of other H1-containing nucleosomes

Chromosomal compaction or condensation

Begins with forming 11-nm chromatin fibre using the DNA helix and core nucleosome proteins.

Then builds 30nm fiber with Histone , . 1 binding, this length of fiber represents a looped chromosome section, these folds result in a 10-fold packing unit of 300nm. (Like a lil pancake stack)

The loops are then arranged in a secondary loop folding it into a 700nm structure

How many chromosomes does a human have, how are they numbered, what is the total number in a human karyotype

22 autosomal, 2 sex chromosomes

Numbered by length

46, XX or 46,XY

Cancer karyotypes

Philadelphia Chromosome: oncogenic translocations, pieces of 2 different non-matching chromosomes break off and swap places.

T(9;22) chromosome translocation:BCR/ABL fusion resulting in CML(chromic myeloid leukemia, cancer in bone marrow)

Bursitis Lymphoma t((8;14) translocation moving the genes that code for proteins that regulate cell growth, c-myc to a new location causing non-Hodgkin lymphoma.

Mouse chromosomes

Acrocentric(centromere is located close to one end opposed to humans who have them in the middle(metacentric). Mice only have 40 chromosomes but have high gene order with humans, sentient meaning a lot of their chromosomes are in the same place as ours.