Botany Lecture - Chapter 4

8/12/2019 Botany Lecture - Chapter 4

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Growth and Division of the cell

Life cycle initiation, growth, and death


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Cell cycle

Cells divide to produce new cells

Cell cycle arrest

Hela cells

Animal cells

Plants


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Reasons that might cause a cell to divide:

growth and complexicityof Multicellular organisms;

replacement of Old anddamaged cells;

Single-celled organismssuch as bacteria divide to

make new, independentorganisms.
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Some cells never stop dividing

1. apical meristems 2. cambia


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The Cell Cycle

2. Brief Division Phase

1. karyokinesis2. cytokinesis

1. Longer growth Phase

resting stage or interphase

G1, S, G2


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G1 Phase

Synthesis ofnucleotide

nucleotides aremonomer of nucleic

acid,

consists of a nitrogenousbases, a sugar, and aphosphate group


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S genes in the nucleus are replicated

Genespolymers of nucleotides

specific sequence of nucleotides

Genome- totality of genes of an organism

Chromosomes- linear sequence of genes


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G2 Phase-

Synthesis of alphaand beta tubulins

Synthesis ofprotein forprocessingchromosomes

Synthesis ofenzymes fornuclear breakdown


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Plant cell in interphase stage


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MITOSIS a duplication

division

nuclear genes are copied, separated

from the other and packed into each

own nucleus


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STAGES OF MITOSIS


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1. Prophase.

Stage of chromosome

shortening and thickening

Events:1. Disappearance of nuclear

membrane

2. Appearance of spindle fibers3. Appearance of chromosomes

4. Chromosomes attachment to

the spindle fibers

Onion root tip cells


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CENTROMERE/KINETOCHORE

FOR MICROTUBULE BINDING


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2. metaphase.

stage of chromosome

alignment

Metaphase plate


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Late metaphase - division of the centromere by

the enzyme separase


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Molecular mechanism of chromosome segregation. At the metaphaseanaphasetransition, APC/CCdc20 ubiquitinates securin. Degradation of securin activates

separase. Separase then cleaves the Scc1 subunit of cohesion, allowing chromosome

segregation. In response to sister-chromatid not properly attached to the mitotic

spindle, the spindle checkpoint promotes the assembly of checkpoint protein

complexes that inhibit the activity of APC/C, leading to the stabilization of securin,

preservation of sister-chromatid cohesion, and a delay in the onset of anaphase

Anaphase promoting complexAPC Checkpoints


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Anaphase

stage of chromosome migration

What moves the chromosomes to opposite poles?


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TELOPHASE

stage of nuclear reconstitution

Major cell activities of this stage

1. Disappearance of thechromosomes

2. Disappearance of spindle fibers

3. Appearance of nuclear

membrane

4. Appearance of nucleolus


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Cytokinesis Division of the cytoplasm .

It is accomplished by formation of cell plate.


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TELOPHASE STAGE IN ONION ROOT TIP


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Lets identify stages ofmitosis..

I think his cellsare immortalNo mitosis???


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Thank you.

Ross D. Vasquez

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Botany Lecture - Chapter 4