Cell Division, Diversity and Differentiation Flashcards
Draw the cell cycle and label it
Interphase - G1 - S - G2 M phase - prophase - metaphase - anaphase - telophase Checkpoints - G1/S restriction checkpoint - G2/M - half way through M - early G1
What are the purpose of checkpoints and what do they ensure?
- prevent uncontrolled division that would lead to tumours
- detect and repair damaged DNA (UV)
- cycle cannot be reversed
- DNA is replicated only once in each cycle
Describe G0 phase
- resting phase triggered by early G1 at restriction point, by a chemical checkpoint
- cells undergo apoptosis, differentiation or senescence
- epithelial cells in gut don’t have this phase and neurons remain in this phase for a long time
Describe G1 phase
- G1 checkpoint control mechanism ensures that the cell is ready to enter S and begin DNA synthesis
- cells grow and increase in size
- transcription of genes to make RNA occurs
- organelles duplicate
- biosynthesis like protein synthesis and making enzymes needed for DNA replication - p53 tumour suppressor gene helps control this phase
Describe S phase
- specific sequence to the replication of genes (housekeeping genes which are active in all types of cells replicated first)
- it is committed when it enters
- DNA replicates
- each one has sister chromatids - rapid phase, exposed DNA base pairs are more susceptible to mutagenic agents (reduces chances of mutations)
Describe G2 phase
- special chemicals ensure that the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and formation of spindle
- cells grow
Describe M phase
- checkpoint chemical triggers condensation of chromatin, half way through metaphase ChP ensures that cell is ready to complete mitosis
- cell growth stops
- prophase, metaphase, anaphase, telophase, cytokinesis
What is the significance of mitosis?
- asexual reproduction
- growth
- tissue repair
Describe prophase and include a drawing
- 2 identical sister chromatids now shorten and thicken
- nuclear envelope breaks down
- centriole divides and moves to opposite poles
- cytoskeleton threads form spindle between centrioles
Describe metaphase and include a drawing
- chromatids attach to the spindle threads at the equator region
- attach by their centromeres
Describe anaphase and include a drawing
- centromeres splits
- motor proteins walk along tubulin threads pull them in opposite directions to poles
- (v shape centromere go first)
Describe telophase and include a drawing
- reach poles
- new nuclear envelope forms
- contains two nuclei genetically identical
Describe cytokinesis
- splits in 2
- plasma membrane folds inwards and nips in the cytoplasm
- end plate forms where equator of spindle was new plasma membrane and cellulose wall either side of end plate
- 2 daughter cells genetically identical to each other and parent
What is the significance of meiosis?
- increases genetic variation which increases chance of survival when environment changes some will have characteristics
- makes haploid cells so when two gamete nuclei fuse fertilisation a diploid zygote is produced
What are homologous chromosomes?
23 maternal and 23 paternal chromosomes form matching pairs
Describe prophase 1
- chromatin condenses and chromosomes supercoils
- nuclear envelope breaks down and spindle threads form from centriole
- chromosomes go into homologous pairs (each pair = 2 chromatids)
- crossing over occurs non sister chromatids wrap around, swap sections
Describe metaphase 1
- pairs still crossed over attach to equator of spindle by centromere
- independent assortment
Describe anaphase 1
- members of each homologous chromosomes pulled apart by motor proteins drag along spindle threads
- centromeres don’t divide
- crossed over areas separate
Describe telophase 1
- two nuclear envelopes form around each set then divides by cytokinesis (interphase chromosomes uncoil) 2 chromatids
- plants anaphase 1 to prophase 2
Describe prophase 2
- nuclear envelope breaks down
- chromosomes coil and condense
- spindles form
Describe metaphase 2
- chromosomes attach to equator of spindle
2. chromatids randomly arranged
Describe anaphase 2
- centromeres divide
- chromatids of each chromosomes pulled apart by motor proteins drag opposite poles
- randomly segregated
Describe telophase 2
- nuclear envelope form around 4 haploid nuclei
- animals: 2 cells divide give 4 haploid cells
- plants: tetrad of 4 haploid
How meiosis produces genetic variation?
- crossing over in P1 shuffles alleles
- independent assortment in A1 random distribution of maternal and paternal chromosomes
- independent assortment of chromatids A2 random distribution material
- haploid undergo random fusion with gametes from another organism