theme 4: modules 1 and 2 Flashcards
cell division
continuous process. that allows pre-existing cells to give rise to new cells. this is a regulated process
cell division in prokaryotes
binary fission
-initiated when DNA of bacterial chromosome is attached by proteins to the inside of the plasma membrane
-bacterial replication can then begin along the origin of replication region of the bacterial chromosome
- as chromosome replicates, cells begin to elongate and newly synthesized DNA is also anchored to the plasma membrane
-cell continues to elongate until the 2 attachment sites are at opposite sites of the elongated cell
-when replication is complete, bacterium is 2 times its og size, begins to constrict along the midpoint of the cell
-constriction is accompanied by the synthesis of a new cell membrane and cell wall that will lead to the complete division of the 2 halves to 2 identical daughter cells
cell division in eukrayotes
mitosis (allows for unicellular fertilised egg to develop into a complex multicellular organism)
Stem cells
contained in early embryos - unspecialised cells that can both reproduce indefinitely, and are able to differentiate into specialised cells of one or more types (under appropriate conditions)
Adult stem cells
not able to give rise to all cell types in the organism, able to replace non reproducing specialised cells
ex:
-quiescent (nondividing) satellite stem cells present in the basement membrane of the muscle tissue are able to become “activated” and begin dividing to enable muscle regeneration
-activation of these stem cells leads to proliferation, differentiation, and fusion of muscle precursor cells called myoblasts, which eventually form mature muscle cells that make up muscle fibre (myofibers)
-once myofibers are formed, they are no longer able to divide
Eukaryotic DNA vs prokaryotic
larger, organised into linear chromosomes
-highly condensed into nucleus of cell
2 distinct stages of cell division
- interphase (DNA synthesis, 2 gap-grow phases called G1 and G2)
-cells prepare for cell division, which include the replication (S phase) of DNA in the nucleus, and an overall increase in cell size - M-phase (mitosis and cytokinesis occur)
mitosis occurs in what cells?
somatic cells - living organism
Producing daughter cells that are genetically identical to the parent cell
Functions of mitotic cell division
growth, repair, development
(Animals, Fungi, & Plants complete the Cell Cycle)
4 phases of cell cycle
G1 phase (Interphase).
S phase (Interphase)
G2 phase (Interphase).
Mitotic phase (M phase)
G1 phase:
cell growth and duplication of organelles
S phase:
DNA synthesis (chromosomes are replicated)
G2 phase:
Cell growth & duplication of organelles to build the protein
“machinery”
why do gap phases exist?
Gap phases ensure that the parent cell is large enough in
size & has the required organelles before mitosis occurs, so
that the daughter cells will function normally.
Prophase
In the Nucleus
- Chromatin fibers contract (DNA condenses) by tightly coiling.
- Chromosomes are visible & each consists of two identical sister chromatids joined together at the centromere
In the Cytoplasm
- Mitotic spindle forms.
- Assembly of microtubules begins in the centrosome (animals) and the microtubule organizing centre (plants).
- In animals, the centrioles begin to move apart to opposite sides of nucleus (2 poles).
Prometaphase
- Chromosomes do not appear completely aligned or organized
- Spindle fibers attach to sister chromatids at the kinetochore regions
What are the function of the kinetochore microtubules?
-Assist with the movement of the chromosomes
What are the functions of the nonkinetochore microtubules?
-Forms a cage-like network, which facilitates the activities of the cell cycle components. Assist in elongating the entire cell during anaphase.
Metaphase
-Chromosomes line up along the Metaphase Plate
* Centromeres are aligned on the metaphase plate, which is
located equidistance from the two poles
Anaphase
-Binding proteins between the sister chromatids break down
-Centromeres of sister chromatids disjoin & segregate, this process is called Disjunctional Segregation (split and travel to opposite poles)
-Chromosomes move centromere first (they appear V shaped)
-Cell elongates
Telophase
-Nonkinetochore microtubules further elongate the cell
-Two daughter nuclei form
-Formation of the nuclear envelopes around each set of chromosomes
Cytokinesis
plants: from cell plate
animals: slime molds
fungi: cleavage furrow
cyclins in the cell cycle
proteins that oscillate in concentration during the cell cycle.
-regulates cyclin dependent kinase (CDK) activity
CDK (Cyclin Dependent Kinase)
* protein kinase, which uses ATP
* adds phosphate groups to protein
* induces conformational change
* to be active, it must be attached to cyclin.
checkpoints
G1 (to S): pass is cell size is accurate, nutrients are sufficient, DNA undamaged, intact and suitable for replication
G2 (to M): pass if chromosomes replicated successfully, DNA undamaged, activated MPF present ‘
Metaphase (to anaphase): all chromosomes attached to spindle fibres and aligned at equator
Ori sites
-are the specific points where DNA replication begins
-DNA double helix opens up at the origin to form 2 single strands
replication forks
(Y shaped regions) spread in both
directions from the ori sites.
leading vs lagging strand
Leading Strand
-Continuous synthesis, grows in 5’to 3’ direction, new nucleotides added only to 3’end
Lagging Strand
* Discontinuous synthesis, grows in overall direction of 3’ to 5’
direction, however, note that it is produced by Okazaki fragments that individually grow in 5’to 3’ direction.
Ligase
Catalyzes the formation of phosphodiester bonds joining the new Okazaki fragments in the growing lagging strand
Walther Plemming
discovery that the distinct stages of mitosis could be staged based on chromosomal position and features
-analyzed developing salamander embryos that he have stained to be able to visualize the chromosomes of the dividing cells
-discovered the distinct stages : PPMAT
Tim Hunt (1980)
measured the protein level changes of dividing sea urchin embryos. added radioactively labeled amino acids (methionine) to the sea urchin eggs.
found that most protein bands on the gel became darker as cell division and embryonic development progressed. Band oscillated in intensity - this protein increased and decreased w/each subsequent cell division.
This was due to cyclin nature of this protein - cyclin (suspected that it played some regulatory role on cell cycle progression)
telomerase
specific type of reverse transcriptase
Telomerase is an enzyme that maintains the length of telomeres, the protective caps on the ends of chromosomes. It helps prevent the shortening of telomeres during cell division, which is important for the longevity of cells. Telomerase is often active in cells with high proliferative capacity, such as stem cells, and its reactivation is associated with cancer.
Replication complex (other proteins that participate in DNA replication)?
-DNA helicase: during initiation are able to bind to the parental DNA strands at the origin of replication and initiate the unwinding of the DNA double helix. DNA helicase is able to break the hydrogen bonds between complementary nucleotide base pairs
-Single stranded binding protein: binds to and stabilizes each parental strand until elongation can begin (so they do not rejoin)
-Topoisomerases: able to bind upstream of the replication fork and minimize the torsional strain that is brought about by the unwinding that occurs at the replication fork. Serve as initiator proteins that trigger the process of unwinding at the origin of replication.
DNA polymerase I
DNA polymerase II
I: does most elongation work in prokaryotes
II: enzyme responsible for removing RNA primer after DNA replication and replacing those short sequences w/DNA nucleotides
Replication in prokaryotes
have one origin of replication
-during replication of their circular DNA, the excised primer is replaced by specific DNA nucleotides and these is no gap in the newly synthesized DNA
Replication in Eukaryotes
replacement of the RNA primer with the DNA nucleotides leaves a sugar phosphate backbone of the 3’ end w/a free phosphate backbone
-prevalent among okazaki fragments of the lagging strand
Proofreading mechanism
The proofreading mechanism in DNA is the ability of DNA polymerases to detect and correct errors that occur during the synthesis of a new DNA strand by removing and replacing incorrect nucleotides.
