Studied by 46 peopleCell cycle
Progressive stages in specific order -
Gap1 or growth 1 (g1), synthesis (s), Gap2 or growth 2(G2), Mitosis (m), Cytokinesis (c)
Cells either go through continuously or delay indefinitely until it’s needed
Controlled by proteins, mainly enzymes, called kinases and cyclins
Kinase
Enzyme that phosphorylates a protein, activating it.
Specific Kinases activate specific cyclins
S kinase activates S cyclins
M kinases activates M cyclins
Phosphorylate
taking a PO4 Group from ATP, placing it on a protein, energizing it
Cyclins
enzyme that regulate cell cycle by initiating specific phases
S-cyclins begin to accumulate in g1 until a critical level and then activated by S-kinase, starting synthesis
During g2, M-cyclins increase to certain concentration then activated by M-kinase, starting mitosis
Interphase
longest phase of CC, where cell goes through normal cell function while preparing for cell division
3 stages: Gap1, synthesis, Gap 2
Gap 1
Longest phase of interphase and cell cycle
Cell doubles in size and replicates some organelles
S-cyclins accumulate
at the end there is a checkpoint (G1/s checkpoint)
If at checkpoint, s-cyclins are high enough level, synthesis, begins
If checkpoint passed, synthesis must occur
Synthesis
Replication of cell’s genetic info (individual genome) into 2 identical copies
Once S begins, cannot be stopped
When DNA is replicated and condensed into chromatin, G2 begins
Gap 2
Enzymes and structures for Mitosis are synthesized
Mitochondria replicate, chromatin condensed into chromosomes, spindle fibers made of microtubules assemble
M cyclins accumulate to a concentration where they are activated by M-kinases (G2/M Checkpoint). Once checkpoint passed, M must occur
Mitotic Phase
2nd phase of CC; includes mitosis and cytokinesis
Mitosis
distribution of chromosomes into 2 nuclei
Copied DNA has condensed into identical chromosomes, which attach forming sister chromatids
spindle fibers attach to sister chromatids and pull them apart (to opposite ends of cell) into identical chromosomes
identical chromosomes then unravel into chromatin with newly formed nuclei.
mitosis in plant and animal cells are similar, but plants dont use centrioles
Can be separated into stages; Prophase, Metaphase, Anaphase, Telophase
Prophase
the replicated DNA in form of chromatin condenses into chromosomes.
Centrioles (formed during G2) move to opposite poles of cell and form spindle fibers
at same time, nuclear membrane begins to disintegrate
Metaphase
At beginning of this phase (prometaphase), identical chromosomes attach to each other(using centromere), creating sister chromatids.
spindle fibers attach to sister chromatids and sister chromatids move to equator of cell
Anaphase
shortest phase
Spindle fibers contract, pulling sister chromatids apart
Results in 2 identical chromosomes going to opposite poles where centrioles are
Telophase
Once chromosomes reach reach poles of cell, spindle fibers disassemble
Chromosomes are enveloped by a reforming nuclear membrane
once nucleus reforms, chromosomes uncoil into chromatin
Cytokinesis
Means cell movement
actual division of cell membrane that results in 2 cells
process different slightly from plant and animal cells
Animal cell cytokinesis
after telophase, a belt of micro-filaments(formed during metaphase) attaches to cell membrane and contract in a process called furrowing
Causes cell to pinch on itself and form 2 new cells
Plant cell cytokinesis
because plant cells have cell wall that prevents furrowing, their cytokinesis is slightly different
Golgi apparatus of plant cell produces vesicles which travel along cytoskeleten to midpoint between daughter nuclei
vesicles fuse together forming cell plate
membrane of cell plate completes cell membrane of both daughter cells
cell membrane then releases molecules that initiate construction of cell wall
Factors that impact cell devision:
Anchorage dependence and density-dependent inhibition
Anchorage dependence
for most animal cells to divide, they must be in contact to another cell or tissue
Density dependent inhibition
when cells stop dividing because they become too “crowded”
cells stop dividing when they touch other cells
if cell are removed(die) from tissue, cells will divide until cells have been replaced and touch each other
Stem cells
Undifferentiated cells that can replicate and develop into multitude of diverse cells
Embryonic stem cells
undifferentiated cells found in an embryo up to 13-14 days after fertilization.
hypothetically, cells at this stage of development have potential to develop into into any type of cell/tissue within the body
after 13-14 days, cells begin to differ slightly and form 3 germ layers within blastocyst
Pluripotent
Stem cell that has the potential to develop into any cell in the body
Embryonic stem cells are pluripotent
Induced pluripotent
A somatic cell (usually blood or skin) that is genetically modified to behave like an embryonic stem cell
These cells are used for therapeutic purposes and research
Adult stem cells
Possess several different types of stem cells
each type of stem cell can develop into a variety of cells, variations that are somewhat similar to each other
Cancer
genetic disease( usually not hereditary) that causes uncontrolled growth of cells (result of failure in cell division control) into a malignant neoplasm called a tumor.
Failure of cell division control is failure of gene p53
gene p53 codes for construction of a protein that checks for mutation to a cell’s DNA at G1/S checkpoint.
Normally, if dmg to a cell’s DNA is detected, p53’s protein will pause cell cycle and repair dmg
Gene p53= tumor supressing gene
Other genes associated with cell cycle can also mutate leading to cancer
Mutations of these genes occur generally after birth due to replicative mutation or mutation caused by a carcinogen.
Cancer mutation is not inherited, so not considered hereditary even though it is a mutation to DNA.
Causes different diseases and is classified by the tissue it affects
Cell size
Cells are microscopic. Human cells are 10-100 microns
Cell sizes are limited by amount of material that can enter and leave the cell
Rate that substances diffuse is affected by many factors, including surface area
As cells increase n size, its volume increases at a larger factor than SA
If size of cell is doubled in diameter, SA is increased by a factor of 4 while volume increases by a factor of 8.
larger cell = more chem rxns required to maintain, meaning more substances must enter the cell
Rxns also produce metabolic waste that needs to be removed
Therefore there comes a point when the SA of the cell cannot allow enough substances into the cell to maintain the chem rxns that sustain life and dies.
Also, if not enough SA to allow waste to exit, the waste accumulates and poisions the cell
So, cells must be small to function and must replicate to maintain their small size
Prokaryotes
Lacks nucleus and membrane-bound organelles
Possess ribosomes (for protein synthesis) that are smaller and slightly different than Eukaryotes ribosomes.
DNA is a double helix that floats in cytoplasm
very small(1-15 microns)
found in domains archaea and bacteria
Unicellular but can form colonies making them appear multicellular
Eukaryotes
has nucleus and membrane-bound organelles that perform specific functions which allows Euks to function more complexly than Proks
Found in domain Eukarya
Hypothesized that they came from 2 symbiotic archaea organisims
Genetic basis of cancer
Cancer is result of uncontrolled cell cycle, causing uncontrolled cytokinesis
Cell division of cancer cells is very rapid, so cells divide before they mature and can function properly
Cancer cells are immature, do not function properly, and reproduce uncontrollably
Because of mutation to gene that code for proteins that control cell cycle
mutations occur after birth, not hereditary
Tumor-suppressing gene
every cell’s DNA contains genes(instruction for construction of a protein) that code for proteins/enzymes which inhibit cell division
these genes code fo proteins/enzymes that help prevent uncontrolled cell growth: they repair dmged DNA
When these genes mutate, chance for uncontrolled cell division and other cancerous genes increases
Oncogene
mutated version of the gene that codes for enzymes that regulate cell cycle, constantly manufacturing proteins/enzymes that initiate/stimulate uncontrolled cell division
proto-oncogene
normal genes that promotes and regulate cell cycle. When these genes mutate, they become oncogenes
Causes of cancer
genetic mutation of cells
mutations occur after birth, so not hereditary
Tumor suppressing genes(genes that inhibit cell cycle) or proto-oncogenes (cells that promote cell cycle) mutate, resulting in unregulated cell cycle creating cancerous (malformed, immature with mutated DNA) cells
Cancer cells ignore anchorage dependence and density-dependent inhibition
Cancer cells function improperly and replicate at a faster rate
Generally 3 causes: Carcinogens, viruses, replicative mutations
Carcinogens
Cancer causing agents that cause mutation to cell’s DNA(tumor suppressing genes or proto-oncogenes) or kill cells
Dead cells need to be replaced, so more cell division must occur, increasing chances of replicative mutations
2 major groups: Radiation and Chemicals
Viruses
Viruses insert fragment of DNA into genetic material of cells they infect.
This DNA can compromise or mutate the proto-oncogenes of the cell
Replicative mutations
majority of mutations of genetic material (both beneficial and harmful) occur during S-phase when DNA is replicated for cell division
During this replication, mutations could occur to tumor suppressing genes or proto-oncogenes, causing them to be ineffective
Neoplasms
new, abnormal in size and growth rate, mass of cells
Form in part bc cancer cells ignore Density dependent inhibition and anchorage dependence.
Referred to as tumors
2 types, benign and malignant
Benign Tumors
mass of cells (neoplasms) that has same composition of cells of surrounding tissue
Benign cell division is slightly faster than normal
Surrounded by connective tissue so they do not spread away from neo plasm
because rate of cell division is only slightly faster, they grow relatively slowly
Malignant tumors
neoplasms where DNA has mutated and differ from cells in surrounding tissue
Cells resemble immature(undifferentiated) cells
Cell division is a lot faster than normal, so growth of tumor is uncontrolled and disorderly
Neoplasm breaks out of surrounding tissue and spread
Malignancies classified by tissue they started in
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