Mitosis and Meiosis Flashcards
Describe interphase of mitosis
- 90% of cell life cycle, cell divides, grows, carries out functions
- G1 phase: organelle replicates, cell grows, carries out functions (5-6 hrs)
- G2 phase: chromosomes duplicates (DNA synthesis) (10-12hrs)
- G3: growth, finish organelle replication, prepare to divide
describe prophase of mitosis
- chromatin fibers condense, now visible
- replicated DNA now identical sister chromatids
- mitotic spindle fibers form
- microtubules organizing centers move to opposite poles
- nucleolus membrane breaking apart
describe metaphase of mitosis
- microtubules at opposite poles
- chromosomes with centromeres line up down the middle
- spindle fibers of microtubules attach to centromeres
- checkpoint occurs
describe anaphase of mitosis
- adhesive proteins break and sister chromatids separate: move towards poles
- cell begins to elongate, both ends with equal amount of DNA
- occurs quick (fast stage) and looks like “V’s”
describe telophase of mitosis
- chromatids reach poles, now chromosomes which condense
- nuclear membrane reforms, 2 daughter nuclei form, cleavage furrow visible (begin cytokinesis with is division of cells)
- begin interphase again
outline the differences between cytokinesis in plants and animals
Plants:
- vesicles move to equator to fuse and merge to form membrane
- pectins and other substances deposited by exocytosis between membrane to form cell wall
Animals:
- plasma membrane pulled towards equator to form cleavage furrow
- actin and myosin proteins provide pull
- when cleavage reaches. middle, cells pinched apart
how are cancer tumors related to the cell cycle?
- group of cells that can form at any time in the body
- benign (no spread) or malignant (can detach or spread)
- carcinogens are cancer causing agents: like viruses, x-rays, UV, chemicals
- mutations are changes to DNA, but most do not cause cancer, some affect control of cell cycle (oncogenes)
- cancer can result if cell division goes unchecked
what do cyclins do?
- group of proteins that help control cell cycle
- bind to cyclin-dependent kinases, which then add phosphate to other proteins to trigger action
- 4 types of cyclins in the human body
- levels will rise and fall, next phase begin when cyclin level is high
what are the phases and events of meiosis generally?
- 2 phase processes to produce cells with 1/2 the needed DNA for gamete cells
- 1 diploid –> 2 haploid –> 4 haploid
- prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II
- in the first phases, there are homologous pairs
- difference is in prophase I: crossing over occurs
how does independent assortment lead to variation in gametes?
- the placement of homologous pairs does not influence the placement of others
- occurs in metaphase 1 of meiosis
- allows for large variation in DNA
how does crossing over lead to a large variation in gametes?
- during prophase I
- homologous chromosomes become connected by protein structure called synapsis
- 2 homologous proteins lined up together are bivalent
- during crossing over, chromatids break at the same spot cross over, and fuse with non-sister chromatid (connection point called chiasma)
- this adds infinite genetic variation in gamete cells, segment from 1 parent can be swapped with segment from another parent
how does nondisjunction during meiosis lead to individuals with chromosomal differences? (aneuploidy)
- chromosomes do not separate correctly during meiosis (anaphase I and II)
- can lead to an extra or missing chromosome in sperm or egg
- sometimes chromosomes break and there is a partial chromosome
- often trisomy 21 (XXY, XYY, or XXX) or monosomy 21 (X)
