2.6 Cell division, diversity and differentiation Flashcards
What is the name for programmed cell death
Apoptosis
What is the name for cell aging?
Senescence
What are the 3 stages of interphase?
G1
S
G2
What happens in G1? (4)
growth transcription organelles duplicate protein synthesis (e.g. enzymes needed for DNA replication in S phase) p53 tumour supressor gene
What is the purpose of checkpoints in the cell cycle? (2)
prevent uncontrolled division
repair damage to DNA
What may happen in G0?
apoptosis/ scenescence
What happens in S phase?
DNA replicates
What happens in G2
cells grow
Describe mitosis
• The chromosomes that replicated in S phase of interphase (so now have two identical sister chromatids) shorten and thicken as the DNA supercoils
• Nuclear envelope breaks down
• Centriole (usually found in centrosome) divides into two daughter centrioles that move to opposite poles of cell
• Tubulin (microtubules) threads form spindle (in plants spindle made of cytoplasm)
METAPHASE- chromosomes attach
• The pairs of chromatids attach to spindle by centromeres
ANAPHASE- chromatids spit up
• Centromere of each pair of chromatids splits
• Motor proteins walking along the threads pull each sister chromatid of a pair towards opposite poles
• Because the centromere goes first, chromatids (now called chromosomes) make V shape
TELOPHASE
• Separated chromosomes reach poles
• New nuclear envelope forms around each set of chromosomes
• Now cell contains two sets of identical DNA
Describe meiosis
PROPHASE 1
-Nuclear envelope breaks down
-Chromatin condenses + chromosome supercoils
-Spindle fibres form from the centriole
-Chromosomes come together in homologous pairs
-Crossing over occurs and shuffles alleles
METAPHASE 1
-The homologous chromosomes line up at equator
-Spindle thread attaches to their centromeres
-Independent assortment occurs
ANAPHASE 1
-Chromosomes pulled apart by motor proteins walking along tubulin threads
-Centromeres do not divide, each chromosome is now made of 2 sister chromatids
-The crossed over areas separate so there’s recombination of genes
TELOPHASE 1
-Two new nuclear envelopes form around each set of chromosomes (in most animal cells; but in plant cells they go straight to prophase 2)
PROPHASE 2
-If nuclear envelopes have reformed, they break down again now
-Chromosomes coil and condense, each now consisting of 2 chromatids, no longer identical due to crossing over in prophase 1
-Spindles form
METAPHASE 2
-Chromosomes attach by centromere to equator of spindle
-Randomly arranged
ANAPHASE 2
-Centromeres divide
-Chromatids pulled apart by motor proteins that drag them across the tubulin threads
-Chromatids are therefore randomly segregated
TELOPHASE 2
-Nuclear envelopes form around each of the 4 haploid nuclei
-Animal= two cells now divide to give 4 haploid cells
-Plants- a tetrad of four haploid cells is formed
What are the four main types of human tissue
muscle
epithelial
nervous
connective
what is the role of mitosis? (3)
produce genetically identical cells
growth
repair
whats the name of the centre bit of a chromosome?
centromere
Why does S phase need to be rapid?
rapid because exposed DNA bases are more susceptable to mutations, so reduces chance of mutation
name the type of cell division that occurs in asexual reproduction
mitosis
