Cell Division and Death II

Question 1

name the 2 phases of the cell cycle

Answer 1

• Interphase
  
  • Gap1 (G1)
  • DNA Synthesis (S)
  • Gap2 (G2)
• Mitosis (M)
  
  • Karyokinesis
    
    • Division of nucleus
  • Cytokinesis
    
    • Division of cell cytoplasm

Question 2

describe the centromere

Answer 2

• Centromere
  
  • Constricted region that holds sister chromatids together
  • Centric HC
  • Persists throughout interphase
  • Site of kinetochore formation

Question 3

describe the kinteochore

Answer 3

• Large protein complex (>80 proteins)
• Forms near the centromere
• Attach chromosome to mitotic spindle

Question 4

describe the centrosome

Answer 4

• Microtuble organizing center (MTOC)
  
  • Contains a pair of centrioles
    
    • Position of centrioles determines location of mitotic spindle poles
  • Numerous gamma-tubulin rings
    
    • Nucleating sites for growth of microtubules

Question 5

describe the mitotic spindle

Answer 5

• Mitotic spindle microtubules will attach to each kinteochore as chromosomes are moved apart later

Question 6

describe interphase

Answer 6

• S phase
  
  • replication of DNA
  • replication of centrosome
• G2 to M transition
  
  • centrosomes separate
  • move to opposite poles
  • orientation determines the cell’s plane of division

Question 7

describe prophase

Answer 7

• Beginning of mitosis
• Condensation of replicated chromosomes
• chromatids connected at centromere
• Kinetochores form near centromeres
• Mitotic spindle assembly
• Nucleolus disassembles

Question 8

describe prometaphase

Answer 8

• breakdown of NE
  
  • dissolution of nuclear lamins
• Spindle microtubules bind to kinetochores

Question 9

describe metaphase

Answer 9

• chromosomes align at the equatorial, metaphase plate
  
  • Kinteochore microtubules
    
    • Attach sister chromatids to opposite poles
  • Motor proteins
    
    • Move chromatids into position

Question 10

describe anaphase

Answer 10

• Anaphase promoting complex (APC)
• Sister chromatids separate
  
  • Each pulled to opposite spindle poles
    
    • motor proteins dyneins
  • Anaphase A
    
    • Kinetochore microtubules get shorter
  • Anaphase B
    
    • Overlap microtubules lengthen
    • Spindle poles move apart

Question 11

describe telophase

Answer 11

• Sister chromatids arrive at opposite poles and decondense
• Nuclear envelope reassembly
  
  • Completion of nuclear divions (karyokinesis)
• Assembly of the contractile ring

Question 12

describe cytokinesis

Answer 12

• Division of cytoplasm
  
  • cleavage furrow
  • separation due to the contractile ring
    
    • actin
    • Myosin II
  • Creation of 2 daughter cells
    
    • Genetically identical
    • Diploid (2n)
• Completion of cell cycle

Question 13

name the cyclin and Cdks at each phase of the cell cycle

Answer 13

• G1
  
  • Cyclin D, Cdk4/6
  • Retinoblastoma protein (Rb)
  • p53
• S
  
  • Cyclins E & A
  • Cdk2
• G2
  
  • Cyclin A, Cdk1
• M
  
  • Cyclin B, Cdk1
  • APC

Question 14

describe retinoblastoma protein (Rb) and when it is active/inactive

Answer 14

• Tumor suppressor gene
• Stable G1
  
  • Resting cells
  • Rb active
    
    • Hypophosphorylated Rb binds gene regulatory protein E2F
    • Inhibitor of cell cycle progression
    • Tumor suppressor
• G1 to S progression
  
  • Cycling cells
  • Rb inactive
    
    • ​Hyperphosphorylated Rb due to increased Cyclin D/cdk4/6 activity
    • Dissociates from E2F
    • E2F free to activate gene expression

Question 15

describe regulation between G2 to M

Answer 15

• Cdc25 phosphatase (takes off phosphate)
  
  • Removes inhibitory phosphorylation of CDK1
  • Proto-oncogene
• CDK1 can then bind cyclin B
• Cyclin B - CDK1 complex activates mitosis

Question 16

describe p53

Answer 16

• Tumor suppressor gene
• Mutations in TP53 found in at least 50% of human cancers
• p53 protein
  
  • transcription factor, regulates >100 genes
• Dual role
  
  • Regulating cell cycle
    
    • Stimulates transcription of Cdk inhibitory proteins (CDKIs)
  • Initiation of apoptosis

Question 17

describe APC

Answer 17

• Anaphase promoting complex activation
  
  • makes sure separation of sister chromatids
    
    • degradation of securin
    • activation of separase
    • cleavage of cohesin complexes
    • pulls sister chromatids apart
  • Degradation of M-phase cyclin B

Question 18

define proto-oncogenes and oncogenes

Answer 18

• Proto-oncogenes
  
  • Genes whose protein products control cell growth, proliferation and differentiation
  • Normal regulatory molecules
• Oncogenes
  
  • Mutated proto-oncogenes

Question 19

describe the funciton of telomerase

Answer 19

• An enzyme complex that elongatest telomere sequences in chromosomal DNA
• Most somatic cells lack telomerase
  
  • As a result, when cells divide, telomeres shrink
  • After many division, telomeres cease to function
  • p53 activated and cell cycle arrest; cell senescence
• Some cancer cells are able to reactivate telomerase

Question 20

describe meiosis I

Answer 20

• separation of homologous chromosomes
• reduction division
• chromosome number reduced from 2n to 1n
• DNA content reduced from 4d to 2d

Question 21

describe meiosis II

Answer 21

• Separation of sister chromatids
• Equatorial division
• DNA content reduced from 2d to 1d

Question 22

list and the 5 phases of prophase 1

Answer 22

1. liptotene
2. zygotene
3. pachytene
4. diplotene
5. diakinesis

Question 23

describe liptotene

Answer 23

• Leptotene
  
  • Characterized by chromatin condensation
  • Sister chromatids condense & connect to each other
  • Pairing of homologous maternal/paternal chromosomes begins

Question 24

describe zygotene

Answer 24

• Zygotene
  
  • Synapsis
    
    • Close association of homologous chromosomes
    • Involves formation of a Syanptonemal Complex
      
      • Binds chromosomes together

Question 25

describe pachytene

Answer 25

• Pachytene
  
  • Synaptonemal complex complete
  • Crossing over
    
    • Transposition of DNA strands between 2 different chromosomes

Question 26

describe diplotene

Answer 26

• The synaptonemal complex begins to break down
• Homologous chromosomes begin to separate
• Newly formed junctions between chromosomes (chiasmata) may be apparent
  
  • Chiasmata indicate crossover may have occurred
• Sister chromatids remain closely associated

Question 27

describe diakinesis

Answer 27

• Homologous chromosomes condense
• Nucleolus disappears
• Nuclear envelope disintegrates

Question 28

describe metaphase I

Answer 28

• Homologous chromosomes randomly align at the equatorial plane
  
  • Still connected via chiasmata
• Spindle microtubules attach to kintechores of the sister chromatids

Question 29

describe anaphase I

Answer 29

• Sister chromatids held together at centromere
• Homologous maternal/paternal chromosomes pulled to opposite poles
  
  • Random assortment
  • Increases genetic diversity

Question 30

describe aneuploidy

Answer 30

• Abnormal number of chromosomes in a cell
• Nondisjunction during mitosis or meiosis
  
  • A chromosome may fail to separate during anaphase
  • Trisomy
    
    • Gain of extra chromosome
  • Monosomy
    
    • Loss of 1 chromosome
  • Nullisomy
    
    • Loss of both chromosomes

Question 31

describe polyploidy

Answer 31

• Whole sets of extra chromosomes
• Triploids (3n)
• tetraploids (4n)