Exam 1: Lecture 3 Flashcards
1
Q
Somatic Cell Cycle
A
-3 periods: interphase, mitosis, and cytokinesis
2
Q
Interphase
A
- G1 phase and G2 phase characterized by cell growth, nutrient accumulation, and organelle duplication.
- S phase is when DNA replication occurs
- the cell is preoccupied with nutrient accumulation, protein and membrane synthesis, organelle duplication as well as a physical increase in size.
3
Q
Mitosis
A
- M phase: prophase, anaphase, metaphase, telophase
- 2 daughter cells identical to parent cell
- cellular goal is to produce two daughter cells that are not only identical to each other but also identical to mother cell in terms of DNA and cytoplasmic contents
4
Q
Cytokinesis (What happens after)
A
- final period when daughter cells separate completely
- after each daughter cell faced with decision to re-enter the cell cycle or exit
- if it exits (G0) phase, will go into a quiescent state or will terminally differentiate.
- if it goes into quiescent state it can re-enter cell cycle, cannot if differentiates
5
Q
S phase
A
- each chromosome is decondensed thereby allowing replication enzymes access to genomic DNA
- replication will initiate at hundreds or thousands of discrete locations called “replication origins”
- a single origin is used in bacteria, three are used in archaea while hundreds or thousands are used in higher eukaryotes
6
Q
Prophase
A
- replicated DNA will begin to re-condense into more discrete structures
- involves complex interactions with protein complexes called histones
- each duplicated chromosome will contain two identical sister chromatids that are joined together at the centromere
- The nuclear envelope will break down as the cell prepares to segregate chromosomes
- in the cytoplasm the mitotic spindle (centrosome and microtubule networks) will begin to
- two centrosomes will migrate to opposite poles of the cell and will be linked to the plasma membrane by astral microtubules
- spindle microtubules will link the centrosomes to the kinetochores of each chromosome
7
Q
Metaphase
A
- the condensed chromosomes will line up along one axis of the cell halfway between the two spindle poles
- a cell will not continue on to anaphase until all cells are attached properly to spindle microtubules and lined up at the metaphase plate
- mechanisms that monitor this event are collectively called the “spindle assembly checkpoint” or “mitotic checkpoint”
- Failure of the spindle assembly checkpoint to be engaged by the cell can result in aneuploidy and has been implicated in tumor formation and the onset of cancer
8
Q
Anaphase
A
- After successful engagement of the spindle assembly checkpoint the sister chromatids from each chromosome are pulled apart by the mitotic spindle apparatus
- chromatids move to opposite ends of cell
- spindle pole with have acquired a set of chromosomes that is eqivalent to what parental cell had prior to S phase
- cells transition into anaphase a relatively large set of mitotic proteins that participated in spindle assembly, sister chromatid attachment and chromosome movement, must be degraded
- Anaphase Promoting Complex (APC) is a multi-protein molecular machine that targets these factors for degradation. Similar types of machinery degrade suites of proteins at the M/G1 transition as well
- must get rid of all dividing proteins so cell doesn’t try dividing again
9
Q
Telophase
A
- each set of chromosomes has completed its migration to the spindle pole
- nuclear envelope begins to re-form around each set of chromosomes and the nucleolus reappears
- cytoplasm and membrane of daughter cells remain attached by midbody
- centrioles/centrosomes duplicate so each daughter cell has a pair
10
Q
Cytokinesis (Process)
A
- characterized by the final separation of the two daughter cell membranes and cytoplasm
- accomplished by contraction of a bundle of aligned actin filaments and myosins
- contractile ring forms in a plane that is perpendicular o that of spindle assembly
11
Q
Embryonic Oscillator
A
- cell oscillates between S and M phases without intervening growth phases
- allows for rapid cell division without overall increase in the organisms size
12
Q
Endocycle
A
- cells oscillate beteen the S and G1 phases
- results in polyploid cell
- i.e. leaves of most plants as are cells that line the gut of most organisms
- cells that must secrete large volumes of enzymes such as the salivary glands and liver cells
- do this to have many more copies of certain genes
- -cell constantly duplicating DNA then growing a bit
13
Q
Meiosis
A
- diploid stem cells in the gonad undergo two meiotic divisions to yield 4 haploid gametes
- During the earliest stages of the first meiotic division all chromosomes are duplicated, so for a brief period of time a human cell in meiosis I will have 46 duplicated chromosomes and 92 chromatids (homologues separated)
- During the second meiotic division DNA is not replicated (sister chromatids separated)
14
Q
Meiosis vs. Mitosis
A
- meiosis produces 1N
- mitosis produces 2N
- recombination only happens in meiosis
15
Q
Errors in Meiosis and Mitosis
A
-can occur during spermatogenisis and oogenesis more common in oogenesis because they’re halted in meiosis I for several decades
