Exam 1: Lecture 3 Flashcards Preview

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Flashcards in Exam 1: Lecture 3 Deck (18):
1

Somatic Cell Cycle

-3 periods: interphase, mitosis, and cytokinesis

2

Interphase

-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

Mitosis

-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

Cytokinesis (What happens after)

-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

S phase

-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

Prophase

-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

Metaphase

-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

Anaphase

-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

Telophase

-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

Cytokinesis (Process)

-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

Embryonic Oscillator

-cell oscillates between S and M phases without intervening growth phases
-allows for rapid cell division without overall increase in the organisms size

12

Endocycle

-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

Meiosis

-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

Meiosis vs. Mitosis

-meiosis produces 1N
-mitosis produces 2N
-recombination only happens in meiosis

15

Errors in Meiosis and Mitosis

-can occur during spermatogenisis and oogenesis more common in oogenesis because they're halted in meiosis I for several decades

16

Turner Syndrome

-affects females
-X and no other sex chromosome

17

Klinefelter Syndrom

-affects males
-XXY

18

Down Syndrome

-affects males and females
-3 copies of chromosomes 21