Unit 9 - Mitosis, Meiosis, & Cell Cycle Flashcards
combos of chromosomes in Meiosis =
2^n where n = haploid #
32F
-gene regulatory protein that binds to promoters of many genes that encode for S-phase re-entry
4 Classes of Cyclins which drive the cell cycle
- G1-Cdk –> helps with passage through the restriction point
- G1/S-Cdk –> commits cells to DNA replication
- S-Cdk –> carries out replication
- M-Cdk –> promotes events of mitosis (MPF)
Advantages of Sexual Reproduction
- allows natural selection against deleterious alleles of genes
- species better equiped to survive environmental changes
Anaphase (Mitosis)
-sister chromatids seperate
Anaphase 1
-homologs begin to seperate
Anaphase 2
-sister chromatids begin to seperate
Apoptosis
- programmed cell death
- getting rid of unwanted cells
- carried out by caspase family of enzymes
- present in all cells as inactive precursors
- all or none signal
- regulated by Bcl-2 family of proteins
Asexual Reproduction
-organism well adapted to its environment can ‘clone’ itself at a rapid rate
Cancer can be a result of…
-failure to respect checkpoints
Chromosomes become visible when…
-cells are about to divide
Cyclin
- regulatory subunit
- levels oscillate throughout the cell cycle
Cyclin-Dependent Kinase (Cdk)
- catalytic subunit
- transfers phosphate from ATP to amino acids on target proteins
- not active unless bound to cyclin partner
- levels not constant
Cytokinesis in Animal Cells
- ring of actin filaments under plasma membrane are involved
- associated with motor proteins (myosin)
Cytokinesis in Plant Cells
- microtubules and proteins define and organize the regions where the new cell membrane and wall form
- vesicles (from Golgi) arrive, carrying polysaccharides & glycoproteins to lay down matrix for the new cell wall
- later cellulose fibres are laid down to complete the wall
Eukaryotic Chromosomes
- multiple linear chromosomes housed in nucleus
- two copies (each) essential for survival
- highly variable in number
- complex packaging of DNA
G1 Phase
- “gap 1”, most of cell’s growth occurs here
- part of interphase
G1/S Checkpoint: Restriction Point
- discovered in yeast
- integration of external and internal signals
- inappropriate ‘start’ signals is often associated with answer cells
G2 Phase
- “gap 2”
- cell completes preparations for mitosis
- chromosomes start to condense
- spindle apparatus starts to form
G2/M Checkpoint
Checking for internal issues
Growth Factors
- growth often coupled with cell division
- signals exist that negatively regulate growth
How can the Cell Cycle be ‘paused’?
- Cdk inhibitors can block entry to S phase
- inbition of activating phosphatase blocks entry to mitosis
- inhibition of APC activation delays exit from mitosis
How can we regulate Cdk activity?
- change the levels of cyclin partner: increase activity = increase cyclin expression
- addition/removal of inhibitory phosphate groups: increase = remove phosphate (activates phosphatase)
- presence/absence of inhibitory protein: increase = Cdk inhibitors not bound to cyclin-Cdk
How do we inactivate Cdk activity?
-targeted destruction of cyclin
Interphase (Mitosis)
- 90% of a proliferating cell’s time
- cell grows by producing proteins & organelles
- copies chromosomes and prepares for cell division
Interphase (Meiosis)
-chromosomes are replicated but remain as chromatin (not condensed)
Leland Hartwell
-START gene, checkpoint concept
M Phase
- mitosis & cytokinesis
- subdivided according to state of chromosomes
- chromosomes finally condensed enough to become visible at prophase
Meiosis
- division of genetic material to produce daughter cells with half hereditary material found in parent cell
- involved in production of gametes
- basis of sexual reproduction & genetic inheritance
Meiosis produces cells which have…
- different combo. of chromosomes
- different complement of genes
- offspring which are genetically distinct from each other and their parents
Metaphase (Mitosis)
-chromosomes migrate to the ‘equator’ of the cell –> metaphase plate
Metaphase 1
-tetrads migrate to the metaphase plate
Metaphase 2
-chromosomes line up
Metazoans
-many cell divisions required to generate new organism from fertilized egg
Mitogens
-push cells past the G1/S restriction point
Mitosis
- division of genetic material that produces daughter cells genetically identical to parent cell
- usually accompanied by cytokinesis
Mitosis vs Meiosis 1 (differences)
Mitosis: homologs line up independently, each cell gets same genes
Meiosis 1: homologs line up in pairs, positioning is random
Mitosis-Promoting Factor (MPF)
- discovered in mammalian cells
- induces mitosis in all eukaryotic cells
- hetero dimeric protein
oncogenes/oncoproteins
-mutated versions of normal genes/proteins involved in driving cell division/proliferation
p53
- detects DNA damage at G1/S checkpoint
- leads to synthesis of inhibitor of G1/S-Cdk and S-Cdk
Prophase 1
- chromosomes condense and nuclear envelope breaks up
- spindle forms and synapsis of homologs occurs
- crossing over of non-sister chromatids, recombo. of genes
Prophase 2
-spindle apparatus forms
Rb (retinoblastoma) protein
- binds to E2F during G1
- blocks transcription of S-phase genes
- blocks cell cycle progression
S Phase
- “Sythesis” phase
- DNA copied here
- chromosomes attached at centromeres, still fully extended
Sexual reproduction involves both…
- haploid cells and
2. diploid cells
Sir Paul Nurse
-cyclin-dependent kinase
Sister chromatids
- replicated homolog
- one chromosomes consisting of 2 sister chromatids
Spindle Checkpoint
Metaphase –> Anaphase
Telophase & Cytokinesis (Mitosis)
- nuclear envelope re-forms
- spindle apparatus disintegrates
Telophase 1 & Cytokinesis
- chromosomes move to the opposite sides of cell
- cell divides
Telophase 2 & Cytokinesis
- chromosomes separate
- cells divide
terminally differentiated
-when cells become highly specialized and can no longer divide
Tim Hunt
-discovery of cyclins (sea urchins)
Tumor Suppressors
- link cell cycle to DNA damage
- proteins that detect DNA damage and initiate events that halt the cell cycle
- typically transcription factors that drive expression of genes that code for proteins which inhibit Cdks
Unicellular
generates complete new organism
what 2 transient cytoskeletal structures are required for cell division in eukaryotes?
- microtubules of the mitotic spindle
- actin and myosin filaments of the contractile ring
What mistakes can occur in meiosis?
-improper distribution of chromosomes to each daughter cell - “non-disjuction” = gametes with abnormal # chromosomes –> “aneuploidy”
When is the cell ready to complete mitosis?
-when all chromosomes are properly attached to spindles
When should a cell divide?
when it receives an external signal
When should a cell undergo mitosis?
- when the DNA is properly replicated
- when no DNA is damaged
where does genetic variability occur in meiosis?
- recombo. during prophase 1
- independent assortment of homologs during meta/ana/telophase of meiosis 1
- independent assortment of chromatids during meta/ana/telophase of meiosis 2
