Chapter 12: Cell Cycle Flashcards
What are the 2 types of reproduction for cells?
Asexual and Sexual
Asexual Reproduction
Purpose is to create genetically identical offspring
Single parent
Can replace cells or an entire organism
Replace an entire organism
Growth of multicellular organisms
Growth of organism from fertilized egg
Repair and replacement of cells
Sexual Reproduction
Involves 2 parents
Results in genetically different organisms
Many chances for variation promoted by nature
How does prokaryotes reproduce?
Binary fission
Binary Fission
- Duplication of chromosome & separation of copies
- Continued elongation of the cell & movement of copies
- Division into 2 daughter cells
What is division is used for multicellular organisms?
Growth
Repair
Reproduction of an organism
What is passed into daughter cell’s ?
Exact copy of genetic material = DNA
Mitosis
Organelles, cytoplasm, cell membrane, enzymes
cytokinesis
What are the stages of mitosis?
Interphase, prophase, pro-metaphase,
Metaphase, anaphase, cytokinesis, telophase
Interphase
About 90% of cell life cycle
Cell doing its “everyday job”
Produce RNA, synthesis proteins/enzymes
Prepares for duplication of triggered
What cells grow and matures and never divide again ?
Brain, nerve and muscle cells
How many phases is interphase divided into ?
3
G1
1st Gap (Growth)
Cell doing its everyday job
Cell grows
1st phase of Interphase
S
DNA Synthesis
Copies chromosomes
Dividing cell replicates DNA
Must separate DNA copies correctly to 2 daughter cells
Human cell duplicate ~ 3 m DNA
Error rate: ~ 1 per 100 million bases
2nd phase of Interphase
G2
2nd Gap Growth
Prepares for division
Cell grows (more)
Produces organelles, proteins, membranes
3rd phase of interphase
How is the nucleus during interphase?
Well defined, DNA loosely packed in long chromatin fibers
Prepares for mitosis
Replicates chromosome
DNA & proteins
Produces proteins & organelles
How is DNA organized?
DNA is organized in chromosomes
Double Helix DNA molecule
Wrapped around histone proteins
like thread on spools
DNA- proteins complex= chromatin
organized into long thin fiber
Condensed further during mitosis
What happens after DNA duplicates?
Chromatin condenses
Coiling & folding to make a smaller package
The Cell Cycle is an ordered sequence events for cell division & consists of what 2 stages ?
Interphase : duplication of cell contents
G1– growth, increase in cytoplasm
S - duplication of chromosomes
G2 - growth, preparation for division
Mitotic Phase : division
Mitosis— division of the nucleus
Cytokinesis— division of cytoplasm
What are the 5 phases of Mitosis
Prophase
Pro metaphase
Metaphase
Anaphase
Telophase
Cytokinesis is well underway by late telophase
Prophase
Chromatin condenses
- visible chromosomes
Chromatids
Centrioles move to opposite poles of cell
Protein fibers cross cell to form mitotics spindle
- microtubules
Actin, myosin
- coordinates movement of chromosomes
Nucleus disappears
Nuclear membrane breaks down
Transition into metaphase
Spindle fibers attach to centromeres
creating kinetochores
microtubules attach at kinetochores
Connect centromeres to centrioles
Chromosomes begin to moving
Metaphase
Chromosomes align along middle of cell
Metaphase plate
Meta= middle
Spindles fibers coordinate movement
Helps to ensure chromosomes separate properly
(So each new nucleus receives only 1 copy of each chromosome)
Anaphase
Sister chromatids separate at kinetochores
Move to opposite poles
Pulled at centromeres
— pulled by motor proteins “walking” along microtubules
actin myosin
Increased production of ATP by mitochondria
Poles move farther apart
Separation of Chromatids
In anaphase, proteins holding together sister chromatids are inactivated
separate to become individual chromosomes
What causes the movement alone the chromosome?
Kinetochores use motor proteins that “walk” chromosome along attached microtubules
Microtubules shortens by dismantling at kinetochore (chromosome) end
Telophase
Chromosomes arrive at poles
Daughter nuclei form
Nucleoli form
Chromosomes disperse
No longer visible under light microscope
Spindle fibers disperse
Cytokinesis begins
— cell division
Cytokinesis in Animals
constriction belt of actin micro filaments around equator of cell
Cleavage furrow forms
Splits cell in two
Like tightening a draw string
Cytokinesis in Plants
Cell plate forms
Vesicles line up at equator
Derived from Golgi
Vesicles fuse to form 2 cell membranes
New cell wall laid down b/tw membranes
New cell wall fuses with existing cell wall
What is the eukaryotic cell cycle regulated by?
Molecular control system, the frequency of cell division varies w/ the type of cell
The cell cycle differences result from regulation at molecular level
How is the control of cell signaling communicated
Cell signaling
Coordination of Cell Division
A multicellular organism needs to coordinate cell division across different tissues & organs
Critical for normal growth, development & maintenance
Coordinate timing of cell division Coordinate rates of cell division Not all cells can have the cell cycle
Frequency of Cell Division
Embryo
Cell cycle< 20 minutes
Skin Cells
Divide frequently throughout life
12-24 hours
Liver cells
Retain ability to divide, but keep it in reserves
Divide once every year or two
Mature nerve & muscle cells
Do not divide at all after maturity
Permanently in G0
Cell Cycle Control System
The sequential events of the cell cycle are direct by cell cycle control system
Regulated by internal and external controls
The clock has specific checkpoints where the cell cycle stops until the go-ahead signal is received
Checkpoint Control System
G1/S
Can DNA synthesis begin?
G2/M
Has DNA synthesis been completed correctly?
Spindle Checkout
Are all chromosomes attached to spindle
Can sister chromatids separate correctly
G1/S checkpoint
Most critical
Primary decision point
“Restriction point”
If cell receives “Go” signal it divides
Internal signals: cell growth (size), cell nutrient
External signals: “growth factors”
If cell does not receive signal, it exits cycle & switches to G0 phase
non/dividing, working state
G0 phase
Non-dividing, differentiated state
Most human cells in G0 phase
Go- Ahead Signals
Protein signals that promote cell growth & division
—internal signals
“Promoting factors”
—external signals
“growth factors”
Primary mechanism of control
— phosphorylation
Kinase enzymes
either activates or inactivates cell signals
Cell Cycle Signals
Cell Cycle controls
cyclins
Regulatory proteins
Levels cycle in the cell
Cdks
Cyclin-dependent kinase
Phosphorylates cellular proteins
activates or inactivates proteins
Cdk- cyclin complex (MPF maturation promoting factor)
Triggers passage through different stages of cell cycle
The activity of cyclins and Cdks fluctuates during cell cycle
External Signals
Growth factors
Coordination b/tw cells
Proteins signals released by body cells that stimulate other cells to divide
Density- dependent inhibition
Crowed cells stop dividing
Each cells binds a bit of growth factor
Not enough activator left to trigger division in any one cell.
Anchorage dependence
To divide cells must attached to a substrate
“Touch sensor” receptors
Platelet Derived Growth Factor
made by platelets in blood clots
Binding of PDGF to cell receptors stimulates cell division in connective tissue
heal wounds
Growth Factors & Cancer
Growth factor can create cancers
—Porto-oncogenes
Normally activates cell division
growth factor genes
becomes oncogenes (cancer/causing) when mutated
If switched “On “ can cause cancer
Ex: RAS(Activates. Cyclins).
Tumor-Suppressor Genes
Normally inhibits cell division
If switched “OFF” can cause cancer
Ex: p53
Cancer & Cell Growth
Cancer is essentially a failure of cell division control
— unrestrained, uncontrolled cell growth
What control is lost
Lose checkpoint stops
Gene p53 plays key role in G1/S restriction point
p53 proteins halts cell division if it detects damaged DNA
4 options
stimulates repair enzymes to fix DNA
Forces cell into G0 resting stage
Keeps cell in G1 arrest
Cause apoptosis of damaged cell
All cancers have to shut down p53 activity
What are the 6 key mutations that have to occur for a cell to develop cancer
Unlimited growth
— turn on growth promoter genes
Ignore Checkpoint
— turn off tumor suppressor genes (p53)
Escape Apoptosis
— turn off suicide genes
Immortality = unlimited divisions
— turn on chromosomes maintenance genes
Promotes blood vessels growth
— turn on blood vessels growth genes
Overcome anchor & density dependence
— turn off touch-sensor gene
What can trigger mutations in cells ?
UV radiation
Chemical exposure
Radiation exposure.
Heat
Cigarette smoke
Pollution
Age
Genetics
Tumors
Mass of abnormal cells
Benign Tumor
Abnormal cells remain at original site as a lump.
— p53 has halted cell divisions
Most do not cause serious problems & can be removed by surgery
Malignant Tumor
Cells leave original site
Lose attachment to nearby cells Carried by blood & lymph system to other tissues Starts more rumors= metastasis
Metastasis: development of secondary malignants growth away from primary site
Impair functions of organs throughout body
