Chapter 6: Cell Division Flashcards
cell division
- functions in reproduction, repair, and growth
- mitosis produces two genetically identical daughter cells known as clones with 2n
- meiosis results in haploid cells (n)
chromosome
highly coiled and condensed strand of DNA
structure of chromosome
-two SISTER chromatids (copies) joined by a centromere
kinetochore
protein on centromere that attaches the chromatid to the mitotic spindle during cell division
cell cycle
regular sequence of growth and division
timing and rate of cell division
- affects the normal development, depending on the cell
- if not controlled by kinases allosteric interactions, can lead to cancer
ratio of surface area to volume
- as cell grows, the volume grows faster than the surface area of cell membrane, which affects the exchange of nutrients and waste products
- determinant of when cell divides
capacity of the nucleus
- need enough genetic information to provide nutrients for the cell
- determines when cell divides
phases of the cell cycle
- interphase
- mitosis
- cytokinesis
interphase
- chromatin is not condensed
- nucleus contains one or more nucleoli
- centrosome with 2 centrioles in cytoplamsm of animal cells
- plants lack centrosomes, but have MTOC (microtubule organizing centers)
1. G1 phase: intense growth and biochemical activity
2. G1 checkpoint (restriction point in animals): cell checks to ensure that enough DNA, nutrients, etc. are present in order to commit to division
3. S phase: synthesis (replication) of DNA, duplication of centrosome
4. G2 phase: cell continues to prepare for cell division
5. G2 checkpoint: is DNA replicated properly?
6. G2-M transition: centrosomes separate from each other
mitosis
- actual dividing of the nucleus
1. prophase
2. metaphase
3. anaphase
4. telophase
prophase
- nuclear membrane disintegrates
- strands of chromosomes condense
- nucleolus disappears
- mitotic spindle begins to form in the cytoplasm, extending from one centrosome to the other
metaphase
- chromosomes line up in single file on the metaphase plate
- centrosomes are already on the opposite poles of the cell
- spindle fibers run from centrosomes to kinetochores in the centromere
- M-spindle checkpoint: chromosomes are attached to kinetochores and are lined up on the metaphase plate
anaphase
-centromeres of each chromosome separate because spindle fibers pull apart sister chromatids
telophase
- chromosomes cluster at the opposite ends of the cell
- nuclear membrane begins reforming
- supercoiled chromosomes begin to uncondense
- once 2 individual nuclei form, mitosis is completed
cytokinesis
- dividing of the cytoplasm
- animal: cleavage furrow due to actin and myosin m microfilaments pinching the cytoplasm
- plant: cell plate forms so that daughter cells don’t separate from each other, but rather form a new cell wall and middle lamella (sticks cells together)
characteristics of normal cells
- contact inhibition (density dependent inhibition): cells grow and divide until they become to crowded and enter G0 phase
- anchorage dependence: division will only occur if cell is attached to surface
cancer cells
-uncontrollable cell growth
meiosis
- generates genetic diversity that natural selection and evolution act upon
- produces haploid gametes by dividing the nucleus 2x
- genetic material is randomly separated and recombined
sexual reproduction
joining of 2 haploid cells
meiosis I (AKA reduction division)
process by which homologous chromosomes separate
- interphase (copying DNA)
- prophase I
- metaphse I
- anaphase I
- telophase I
- cytokinesis I
prophase I
- chromosomes pair up with homologue into a tetrad by synapsis
- crossing over: exchange genetic material
- chiasmata: visible result of crossing over
metaphase I
- double file: homologous chromosomes lined up along metaphase plate
- spindle fibers are attached to centromere of each pair of homologues
anaphase I
-separation of homologous chromosomes by spindle fibers
telophase I
-homologous pairs continue to separate until each pole has halpoid number of chromosomes, but the same number of chromatids
cytokinesis I
-usually occurs with telophase
meiosis II
- functionally the same as mitosis, including the same steps
- chromosome number remains haploid (no duplication before separation)
- anaphase II: separate chromosomes into chromatids, leading to each cell gaining haploid cells
independent assortment of chromosomes
homologous chromosomes separate depending on the random way they align on the metaphase plate
crossing over
produces recombinant chromsomes that combine genes from both parents in an individual
random fertilization
sperm fertilizes egg randomly
protein kinases
- common in cell signal transduction
- controls cell cycle timing
- catalyze phosphorylation of target proteins that regulate the cell cycle
cyclin-dependent kinases
-activated by binding with cyclin, which exposes the active site of the CDK and activates the molecule
-example of allosteric inhibition
-regulate cell cycle at specific checkpoints
-cyclins synthesized in response to molecular signals, including growth factors
growth factor –> cyclin synthesis –> CDK activation –> cell cycle
apoptosis
- programmed cell death of infected, damaged, or old cells
- cell components are chopped up and packaged in vesicles where they are engulfed by scavenger cells
- embryonic development, prevent cancerous cells
- plant cells: defense mechanism in fungus and bacteria by leaving no tissue that can spread infection
- mammals: signals from different sources (inside or outside cell) trigger pathways involving caspases (enzymes) to carry out apoptosis
- evolved early in the evolution of eukaryotic cells
