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Why do cells divide?
- Reproduction
- Growth and development
- Tissue renewal
- Maintain surface area:volume ratio
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Types of cellular division
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Types of asexual cellular division
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Type of sexual reproduction
Meiosis
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How much DNA in your cells?
- 2 m of DNA per cell
- Approximately 3 billion base pairs
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What kind of chromosomes do prokaryotes have?
Single circular chromosomes
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What kind of chromosomes do eukaryotes have?
- Linear chromosomes
- Cells often contain two copies of each chromosome (homologous chromosomes)
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What are the subunits (nucleotide) of DNA are composed of?
A nitrogenous base (A,T,C,G), sugar, and phosphate group
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Chromosomes
- Long strand of DNA wrapped around proteins (histones)
- Chromatin make up chromosomes
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Parts of a chromosome structure
- Centromere
- Telomere
- Kinetochore
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Centromere
Condensed region of chromosome
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Telomere
- Region of repetitive DNA sequences at end of chromosome
- -These acts as buffers
- -Tells the cell to stop dividing
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Kinetochore
Disc-shaped protein that spindle fibers attach to
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What do chromosomes do before they divide?
- They are duplicated
- They create sister chromatids
- Helf together at centromere
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When are the sister chromatids are pulled apart?
Mitosis
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Bacterial Binary Fission
- A form of asexual reproduction
- This happens quickly because there's not as much information and it's easy to get them into the two halves of the cell
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Eukaryotic Cell Cycle Steps
- Mitosis
- Cytokinesis
- Interphase
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Steps in interphase
- G1
- S
- G2Cells spend 90% of their time in interphase
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Gap 1 (G1)
- Cellular contents, excluding the chromosomes are duplicated
- Growth, protein synthesis, organelle synthesis
- -normal function
- -protein synthesis
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Synthesis (S)
- Each of the 46 chromosomes is duplicated by the cell
- DNA is duplicated
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Gap 2 (G2)
- The cell "double checks" the duplicated chromosomes for error, making any needed repairsGrowth, synthesis of microtubules, cell cycle checkpoints
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Best description of interphase portion of the cell cycle
During interphase, a cell is metabolically active
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Two joined copies of a replicated chromosome are called
Sister chromatids
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G0
- Quiescent or "resting" state, cells not preparing to divide but are metabolically active
- -Majority of cells in the human body are here
- -Some cells can be called back (i.e. liver cells)
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Mitosis
- Nuclear division
- Followed by cytokinesis (division of organelles and cytoplasm)
- Produces 2 identical daughter cells
- Typically divided into 5 phases
- This is a continuous process
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Vinblastine is a chemotherapeutic drug because it interferes with microtubule formation, its effectiveness must be related to?
Disruption of mitotic spindle formation
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Prophase
- Chromosomes begin to condense
- Spindle apparatus (MTOC) begins to form
- -"machine" responsible for pulling apart the chromatids
- -composed of microtubules and other proteins
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Prometaphase
- Nuclear envelope disassembles
- Spindle fibers attach to kinetochores
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Metaphase
- Chromosomes align along the metaphase plate
- -occurs because of tug-of-way between the two poles
- -This is important because you want all of the chromosomes in both parts of the cell split
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Metaphase plate
- Is where the chromosomes line up in the center of the cell
- It's not a physical structure like the equator
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What phase is the shape of chromosome an X
Metaphase
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Anaphase
- Sister chromatids are cut apart
- -Cohesion that hold them together cleaved by enzymes
- Sister chromosomes can be pulled to opposite poles
- -Movement achieved through shortening of microtubules
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What marks the beginning of anaphase?
Cohesion that holds the sister chromatids together are cleaved by enzymes
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Which does not occur during mitosis?
C) replication of the DNA
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Telophase
- Reversal of prophase events
- Nuclear envelopes reform around DNA
- Chromosomes unfold back into chromatin
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Cytokinesis
- Division of cytoplasm
- Not a part of mitosis
- -begins during telophase
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What happens in animals during cytokinesis?
Cleavage furrow pinches off separated nuclei
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What happens in plants during cytokinesis?
- New cell wall is formed
- Golgi-derived vesicles bring material to middle
- -Fuse to form cell plate
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How is the cell cycle regulated?
- Tight regulation is crucial for normal growth and development
- Controlled by a system of signaling molecules which trigger and coordinate the events of the cell cycle
- Multiple checkpoints make sure the cell is ready to proceed to the next step
- -M-phase checkpoints
- -G1 checkpoint
- -G2 checkpoint
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What are the two main regulatory molecules of the cell cycle clock?
- Cyclins
- Cyclin-dependent kinases (cdks)
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Cyclins
Is a regulatory protein who's levels fluctuate cyclically
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Cyclin-dependent kinases (cdks)
- Catalyzes phosphorylation (adds a phosphate) of other proteins to start M phase
- Present at constant concentrations but usually inactive
- Active by attaching to cyclins
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What is a protein synthesized at specific times during the cell cycle that associates with a kinase to form a catalytically active complex?
Cyclin
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What step comes before the M phase-promoting factor?
G2 checkpoint (G2 to M)
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M phase-promoting factor (MPF)
- Promoting mitosis
- Protein dimmer consisting of cyclin and cdk
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Cells get past cell-cycle checkpoints by..
Cdks bound to cyclins to phosphorylating other proteins
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G1 Checkpoint
- "Restriction point"- most important in mammals
- If cell receives:
- -Green light it continues to S phase
- -Red light it exits cell cycle, enters G0
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What factors does the G1 checkpoint consider?
- Is the cell big enough
- Are conditions favorable
- Is there any DNA damage, etc?
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What comes before the anaphase promoting complex (APC)?
M phase checkpoint (metaphase to anaphase)
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Anaphase promoting complex (APC)
Complex of 11-13 proteins that marks cell cycle proteins for degradation
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How does the MPF protein complex turn itself off?
Activating a process that destroys cyclin components
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External factors for cell regulation
- Growth factors- platelet-derived growth factor (PDGF)
- Density- dependent inhibition
- Anchorage dependence
- -cells won't divide if it's not anchored to anything
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What is the genome made up of?
All the genes on the chromosomes and all of the chromosomes together
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When are CDK's activated?
- When they attach to cyclins which then allows the check point to occur
- Referred to M phase promoting factor when CDK is bound to cyclins
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What does the M phase check for in a cell? What happens if they aren't there?
- Targets include:
- -Condensins
- -Proteins involved in mitotic spindle formation
- -Lamins (proteins involved in nuclear envelope assembly/breakdown)
- If these aren't found, the cell cycle will halt
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What do cells do if they need to divide again?
- If the cell needs to divide again, it goes through the checkpoints starting at G1
- If not, it goes to G0 where it will no longer reproduce
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What is within mitosis and happens from metaphase to anaphase?
Anaphase promoting complex
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What happens in the anaphase promoting complex?
- If the checkpoint detects an error then it degrade the APC stopping anaphase from occurring
- APC degrades the securin which is what allows the sister chromatids to separate
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Homogenous chromosomes
Same chromosomes (one from mom and dad)
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Sister chromatids
Only form after replication
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Difference during Prophase I in meiosis and mitosis
- Meiosis has tetrads and crossing over where mitosis just has a line of chromosomes
- The difference is meiosis has tetrads splitting and mitosis has chromosomes splitting
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What comes from mitosis?
- 2 daughter cells
- Makes identical sister cells
- Somatic cells (body cells not germ cells)
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Same characteristics between meiosis and mitosis
- 2 n= diploid (46 chromosomes)
- -both start with this
- 4 n= polyploid
- -both replicate
- Have sister chromatids and homologous chromosomes
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Meiosis
- Makes 4 daughter cells with half chromosomes to make gametes
- n= 23 pairs of chromosomes
- Germ cells
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