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Terms in this set (81)
How do prokaryotes divide?
By prokaryotic fission
What are the steps to prokaryotic fission?
1. A single circular chromosome binds to cell membrane
2. DNA replicates in both directions around circle
3. Cell divides by adding to the cell membrane
Where is DNA carried?
In the nuclear membrane
When is DNA replicated?
Prior to nuclear division in interphase
What are the 2 parts to cell division and what cell part do they divide?
Mitosis-divide the nucleus
Cytokinesis- divide cytoplasm
What is needed in order to divide the cell?
Microtubules, microfilaments, motor proteins, and ATP
What are the 2 types of eukaryotic nuclear division?
Mitosis and meiosis
What does mitosis produce?
Clones (daughter cells)
What does unicellular organisms do mitosis for?
What does multicellular organisms do mitosis for?
-asexual reproduction (budding)
What does meiosis produce?
-chromosome number cuts in half
Why do cells do meiosis?
For sexual reproduction
What is a somatic cell?
Normal diploid body cell
What is a diploid cell?
Has 2 copies of each chromosome
What is a haploid cell?
Has 1 copy of each chromosome
What is a chromosome?
Naturally occurring segment of DNA and associated proteins
What is a genome?
All of a cells DNA
How many chromosomes do humans have?
46 (2 of each type)
What are the steps to mitotic spindle formation?
1. Tubulin subunits in centrosome begin to assemble into microtubules
2. Microtubules grow toward the center to form spindle fibers
3. Short microtubules form a radial array called an aster
4. Centrioles present in animals but not needed
What are kinetochores?
Proteins located at the centromere and they are the attachment site for some microtubules of spindle
What do mitotic spindles include?
Centrosomes, spindle microtubules, and aster
What happens in prophase?
-centrosomes begin producing microtubules and move towards opposite polls
-chromosomes condense into chromatids
What happens in pro-metaphase?
-nuclear envelope breaks down
-microtubules attach to kinetochores
-polar microtubules overlap at the equator
What happens in metaphase?
-chromosomes lined up at equator
-pulled by kinetochore microtubules
-chromosomes line up single file, one sister chromatid on each side
-centrosomes reach poles
What happens in anaphase?
-cohesin proteins cleaved (cut) by separase enzymes
-separated sister chromatids move toward opposite polls
-kinetochore microtubules shrink as they depolymerize (undo the polymer) at centrosome
-motor proteins drag chromatids along shrinking microtubules toward poles
-cell elongates as motor proteins push polar microtubules past each other
What happens in telophase?
-begins when chromatids reach poles
-nuclear envelope reforms
-chromosomes decondense into chromatin
What are some characteristics of cytokinesis?
-begins before mitosis is complete
-different in plant and animal cells
-does not always take place
How do animal cells do cytokinesis?
Contractile ring mechanism
What are the steps to the contractile ring mechanism?
1. A band of microfilaments of the cell cortex contract
2. Indention forms cleavage furrow
3.ring contracts until cell membrane is pinched in 2
How does the cell tighten the ring in the contractile ring mechanism?
Myosin motor proteins move actin filaments past each other
How do plant cells do cytokinesis?
Cell plate formation
What happens during cell plate formation in plant cells?
-vesicles containing cell wall components move from the golgi to the equator
-merging vesicle membranes form new cell membrane
-cell wall components assembled in the center of merging vesicles form the new primary cell wall
What are characteristics of the primary cell wall?
Flexible, stretchy, allows growth
Where is the secondary wall located and what are characteristics of it?
Located inside the primary cell wall
-solid, inflexible, support wall
What are the 3 sub phases of interphase?
1. G1-Gap 1
3. G2-Gap 2
What happens during G1 of interphase?
The cell grows (max size based on the SA:V ratio)
-cell performs its function for the body
-some cells may never leave G1 (ex: nerve cells)
What happens during synthesis of interphase?
The entire genome is synthesized by semi-conservative replication
-growth and cell function continue
What happens during G2 of interphase?
Cell grows and prepares to divide
-duplicates centrosomes and centrioles (not required, but present in animals)
What is the cell cycle controlled by?
What are checkpoints?
Placements where the cell cycle stops and makes sure certain criteria is met in order to continue the cell cycle
How do cells signal that the criteria has been met at the checkpoints?
They make checkpoint proteins called cyclins
What do cyclins activate?
Cyclin Dependent Kinases (CDKs)
What do CDKs do?
Signal the cell to move on to the next step in the cell cycle
How is cyclin produced?
-when all criteria of a checkpoint is met the specific checkpoint gene for the checkpoint is activated
-the checkpoint gene contains the instructions for making one specific checkpoint protein (cyclin)
-production of that particular cyclin activates a specific CDK which sets up a chain of reactions that lets the cell cycle pass that checkpoint and continue the cell cycle
-cyclin breaks down after one use and levels of that type of cyclin drop
What happens to CDK levels?
They remain constant
What are cell cycles controlled by?
Changing levels of cyclins
What is kinase?
A group of enzymes that phosphorylate proteins (activate them)
When are CDKs activated?
When they are attached to cyclin
Do different versions of cyclin activate different CDKs?
What does activating the specific protein that goes with the CDK do?
It sets off a transduction cascade that tranduces the signal to proceed to the next checkpoint
What happens to animal cells if they are not signaled by growth factors?
They stay in G1 or G0
What are checkpoints regulated by?
What happens if the G1 checkpoint requirements are met?
They cell cycle is initiated and the cell will divide
What does the G1 checkpoint check for?
What happens if all requirements for the G2 checkpoint are met?
The cell will then go into metaphase
What does the G2 checkpoint check for?
-if the DNA replication is complete
What does the M-spindle checkpoint check for?
Chromosome attachment to the spindle
What are growth factors?
Protein signal molecules that are released by cells to signal nearby cells to divide
How do growth factors move throughout the cell?
They diffuse through intercellular fluids
What do growth factors do?
They bind to cell membrane receptors on the target cell and the transduction of signal causes cyclin production
What do cyclin activate?
What are growth factors an example of?
What is an example of a growth factor?
Platelet-derived growth factor (PDGF)
What does released PDGF by the platelet cause?
Fibroblast (wound repair) cells to divide
How do fibroblasts divide?
1. PDGF binds to receptor on fibroblast
2. Signal transduction pathway initiated
3. Cell passes G1 checkpoint and starts to divide
What is M-phase Promoting Factor (MDF)?
A CDK-cyclin complex
What are the steps for MPF?
-checkpoint gene for MPF cyclin is activated
-MPF cyclin levels build up and build MPF levels
-high enough concentration of MPF allows cell to move from G2 into M phase
-MPF concentration reduced in anaphase by breakdown of cyclin causing MPF to revert to inactive CDK
What do Cyclin Dependent Kinase Inhibitors (CKI) do?
Stop the CDK enzymes from working
What is an example of a CKI and what does it stop?
CKI p21- stops CDK2 from working, thus stopping the transition from G1 to S phase
When is the CKI inhibitor molecule p21 active?
When the tumor suppressor gene p53 is transcribed or copied
What is cell division limited by?
1. Density-dependent inhibition cells that are crowded stop dividing
2. Anchorage dependency- cell must be anchored to extra-cellular matrix of a tissue to divide
What are cancer cells not inhibited by?
Density or anchorage
What DONT cancer cells do?
-stop dividing when out of growth factors
-follow signals of checkpoint genes
-self-destruct by apoptosis
What does uncontrolled cell division result from?
The failure of more than one checkpoint protein gene, which causes non-functional checkpoint proteins
How did cancer cells originate?
1 cell undergoes transformation (damage to DNA) and the transformed cell avoids immune system (avoids apoptosis, ignores regular cell cycle signals, and leads to uncontrolled cell division)
Do benign tumors spread?
No-the cell stays anchored
What happens when malignment tumor cells are spread?
What is metastasis?
The spread of cancer cells
What does uncontrolled cell division cause?
Tumors which may cause cancer
What are characteristics of cancer cells?
-they have mutation of check point genes
-change in chromosome number/structure
-abnormal/irregular cell membrane
~lacks attachment proteins
~damaged signal/receptor proteins
-secrete signal molecules that encourage blood vessel growth
How can cancer be treated?
-radiation for localized tumor
-Chemotherapy-poisons most damaging to dividing cells
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