Cell Cycle Flashcards
Cellular reproduction is essential:
– Creates new life
– Produce multi-cellular organisms
– Repair & renew cells
mitosis
- somatic cellular division
- asexual
- results in two genetically identical daughter cells
- 2n→2n
genome
specific genetic makeup of any organism
chromosomes
DNA condensed around histone proteins
somatic cells
body cells except for gametes
chromatin
DNA relaxed inside of the nucleus of a non-dividing cell (“spaghetti”)
sister chromatids
identical chromosomes separated during mitosis into each cell
centromere
- joins sister chromatids together
- region of chromosomes composed of proteins
- spindle fibers attach to kinetochore of centromere
binary fission
asexual prokaryotic replication
- chromosome replication begins. one copy of the origin moves rapidly toward the other end of the cell.
- replication continues. one copy of the origin is now at each end of the cell.
- replication finishes. plasma membrane grows inward and new cell wall is deposited.
- two daughter cells result.
cell cycle
Events between time where cell divides
and rests
• Duration depends on the type of cell
• Muscle & nerve cells will never divide
interphase
the cell grows and prepares for division by producing proteins and cytoplasmic organelles and replicating DNA; 90% of cycle
G1 Phase
first gap - cell growth and organelle manufacture and normal functioning
-most variable in time for different types of cells (fast dividing: short phase, slow dividing: long phase)
S Phase
DNA (chromatin) replication as cell continues to grow
G2 Phase
second gap - cell prepares for division
- centrosomes have duplicated (ea with 2 centrioles)
- 1 or more nucleoli present in nuclear envelope
prophase
- chromatin condense into chromosomes
- nucleoli disappear
- mitotic spindles (spindle apparatus) begin to form
- centrosomes move toward opposite poles
prometaphase
-nuclear envelope fragments
• Microtubules enter middle of cell & begin attaching to chromosomes at kinetochores
• Nonkinetochore spindles interact with each other
metaphase
• Chromosome meet in the middle of the spindle on the metaphase plate
-all sister chromatids are attached to kinetochore microtubules
• Longest phase of
mitosis
anaphase
• Sister chromatids are pulled apart (each is now considered a chromosome)
• Chromosomes move to opposite poles due to microtubules
-nonkinetochore microtubules lengthen, elongating cell
• Shortest phase of mitosis
telophase
– Nuclei begin to reform and nuclear envelopes arise from fragments
– Chromosomes begin to relax
– Mitosis is now complete
cytokinesis
– The division of the cytoplasm
– Now you have two identical daughter cells
cytokinesis in animal cells
A cleavage furrow create a shallow groove in the cell surface using a contractile ring of actin microfilaments
cytokinesis in plant cells
Vesicles from the Golgi body move along microtubules to the middle of the cell to create cell plate
G1 checkpoint
(aka restriction point) this is the most important & if passed usually results in complete cell division
-ensures that all external and internal condition are met for cell division
• If “no go” at this point the cell will enter G0 phase
G2 Checkpoint
determines the cell is appropriately sized & DNA replicated correctly
M Checkpoint
ensures all chromosomes are aligned during metaphase before anaphase
-each chromosome is attached to spindles and centromeres lined at metaphase plate
skipping the M checkpoint would…
aneuploidy (incorrect # of chromosomes) and nondisjunction ex. Down syndrome
cyclin-dependent kinases
– Enzymes that activate proteins by phosphorylating them
– Give the “go” signal at G1 & G2 checkpoints
– Constant amount found in the cell
– aka: cyclin-dependent kinases (Cdks)
cyclins
– Transforms kinases into their active form
– Amount in cell fluctuates during cell cycle
Maturation Promoting factor
Pushes cell past G2 checkpoint and into M phase
– Cyclin accumulates during G2 phase which activates MPF in turn starting mitosis by phosphorylating a variety of proteins in the nucleus causing fragmentation
– Switched off during anaphase by destroying its cyclin so nuclei can re-form during telophase
proto-oncogenes
encode cyclin proteins
tumor suppressor genes
produce proteins that signal cells when environmental conditions and DNA replication are not suitable for cell division and regulate apoptosis
cell cycle control factors: internal
cdks to regulate checkpoints
cell cycle control factors: external
– Proper nutrition and growth factors must be available for division (more important than density)
– Density-dependent inhibition: crowded cells stop dividing
– Anchorage dependence: cells must attach to a substrate in order to divide
cancer
Cancer cells don’t respond to the body’s control of cell division resulting in the excessive dividing of cells
– They don’t need normal signals to stimulate division
– Growth isn’t inhibited by density dependence or anchorage dependence like normal cells
– After 20 to 50 division normal cells die, not cancer cells (ex: HeLa cells)
cancer: transformation
Problem begins with transformation of a normal cell into a cancer cell
– Typically this is caught by your immune system, but if it goes undetected it can create a tumor
cancer: benign tumor
– Cancerous cells stay at original site
cancer: Malignant tumor
– Invasive cells that impair the functioning of one or more organs
– Have abnormal number of chromosomes
– Lose/destroy attachment to neighboring cells which allows for them to travel throughout the body resulting in metastasis
Metastasis
- tumor grows from a single cancer cell
- cancer cells invade neighboring tissue
- cancer cells spread through lymph and blood vessels to other parts of the body
- small percentage of cancer cells survive and establish a new tumor in part of the body
Treatment of Cancer: radiation
damages the DNA in cancer cells (more than normal cells) which are unable to repair the damage
Chemotherapy
treatment of metastasis by using toxic drugs in the circulatory system
– Stops specific parts of the cell cycle to stop division
– Lots of side effects due to drug working on normal cells
G0 Phase
nondividing state
