Why do cells divide?
- Growth and development
- Tissue renewal
- Maintain surface area:volume ratio
Types of cellular division
Types of asexual cellular division
Type of sexual reproduction
How much DNA in your cells?
- 2 m of DNA per cell
- Approximately 3 billion base pairs
What kind of chromosomes do prokaryotes have?
Single circular chromosomes
What kind of chromosomes do eukaryotes have?
- Linear chromosomes
- Cells often contain two copies of each chromosome (homologous chromosomes)
What are the subunits (nucleotide) of DNA are composed of?
A nitrogenous base (A,T,C,G), sugar, and phosphate group
- Long strand of DNA wrapped around proteins (histones)
- Chromatin make up chromosomes
Parts of a chromosome structure
Condensed region of chromosome
- Region of repetitive DNA sequences at end of chromosome
- -These acts as buffers
- -Tells the cell to stop dividing
Disc-shaped protein that spindle fibers attach to
What do chromosomes do before they divide?
- They are duplicated
- They create sister chromatids
- Helf together at centromere
When are the sister chromatids are pulled apart?
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
Eukaryotic Cell Cycle Steps
Steps in interphase
- G2Cells spend 90% of their time in interphase
Gap 1 (G1)
- Cellular contents, excluding the chromosomes are duplicated
- Growth, protein synthesis, organelle synthesis
- -normal function
- -protein synthesis
- Each of the 46 chromosomes is duplicated by the cell
- DNA is duplicated
Gap 2 (G2)
- The cell "double checks" the duplicated chromosomes for error, making any needed repairsGrowth, synthesis of microtubules, cell cycle checkpoints
Best description of interphase portion of the cell cycle
During interphase, a cell is metabolically active
Two joined copies of a replicated chromosome are called
- 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)
- 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
Vinblastine is a chemotherapeutic drug because it interferes with microtubule formation, its effectiveness must be related to?
Disruption of mitotic spindle formation
- Chromosomes begin to condense
- Spindle apparatus (MTOC) begins to form
- -"machine" responsible for pulling apart the chromatids
- -composed of microtubules and other proteins
- Nuclear envelope disassembles
- Spindle fibers attach to kinetochores
- 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
- Is where the chromosomes line up in the center of the cell
- It's not a physical structure like the equator
What phase is the shape of chromosome an X
- 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
What marks the beginning of anaphase?
Cohesion that holds the sister chromatids together are cleaved by enzymes
Which does not occur during mitosis?
E) replication of the DNA
- Reversal of prophase events
- Nuclear envelopes reform around DNA
- Chromosomes unfold back into chromatin
- Division of cytoplasm
- Not a part of mitosis
- -begins during telophase
What happens in animals during cytokinesis?
Cleavage furrow pinches off separated nuclei
What happens in plants during cytokinesis?
- New cell wall is formed
- Golgi-derived vesicles bring material to middle
- -Fuse to form cell plate
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
What are the two main regulatory molecules of the cell cycle clock?
- Cyclin-dependent kinases (cdks)
Is a regulatory protein who's levels fluctuate cyclically
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
What is a protein synthesized at specific times during the cell cycle that associates with a kinase to form a catalytically active complex?
What step comes before the M phase-promoting factor?
G2 checkpoint (G2 to M)
M phase-promoting factor (MPF)
- Promoting mitosis
- Protein dimmer consisting of cyclin and cdk
Cells get past cell-cycle checkpoints by..
Cdks bound to cyclins to phosphorylating other proteins
- "Restriction point"- most important in mammals
- If cell receives:
- -Green light it continues to S phase
- -Red light it exits cell cycle, enters G0
What factors does the G1 checkpoint consider?
- Is the cell big enough
- Are conditions favorable
- Is there any DNA damage, etc?
What comes before the anaphase promoting complex (APC)?
M phase checkpoint (metaphase to anaphase)
Anaphase promoting complex (APC)
Complex of 11-13 proteins that marks cell cycle proteins for degradation
How does the MPF protein complex turn itself off?
Activating a process that destroys cyclin components
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
What is the genome made up of?
All the genes on the chromosomes and all of the chromosomes together
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
What does the M phase check for in a cell? What happens if they aren't there?
- Targets include:
- -Proteins involved in mitotic spindle formation
- -Lamins (proteins involved in nuclear envelope assembly/breakdown)
- If these aren't found, the cell cycle will halt
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
What is within mitosis and happens from metaphase to anaphase?
Anaphase promoting complex
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
Same chromosomes (one from mom and dad)
Only form after replication
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
What comes from mitosis?
- 2 daughter cells
- Makes identical sister cells
- Somatic cells (body cells not germ cells)
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
- Makes 4 daughter cells with half chromosomes to make gametes
- n= 23 pairs of chromosomes
- Germ cells