Ch09_Part1

Chapter 9

•  Bacteria divide by binary fission

•  Somatic cells divide by mitosis

•  Sex cells (gametes) are the result of meiosis

Part-1: Proliferation

•  More than one in number

•  Linear chromosomes

•  Highly condensed

•  High degree of compaction

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Chromosome


Chromosome Rosettes of Chromatin Loops

Scaffold protein


Chromosome Rosettes of Chromatin Loops Chromatin Loop

Chromatin loop

Scaffold protein Scaffold protein


Chromosome Rosettes of Chromatin Loops Chromatin Loop Solenoid

Chromatin loop




Nucleosome

Histone core

Chromatin loop


DNA



Nucleosome Histone core

Chromatin loop


DNA

DNA Double Helix (duplex)

•  Orderly arrangement of chromosomes

•  Diploid (2n) number is 46 •  23 pairs of chromosomes

•  Each set is a homologous pair

•  Haploid (n) number is 23

•  Before replication, each chromosome composed of single DNA molecule

•  After replication, each chromosome composed of two DNA molecules (now called “chromatids”)

Homologous chromosomes Homologous chromosomes

chromatids chromatids

Replication

16 Essential Cell Biology (© Garland Science 2010)


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The eukaryotic cell cycle has 5 main phases:

1. G1 (gap phase 1)

2. S (synthesis)

3. G2 (gap phase 2)

4. M (mitosis)

5. C (cytokinesis)

interphase

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•  During interphase, cells •  Engage in metabolic activities

•  Prepare for the next cell division

•  G1,S and G2

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!  The cell gathers nutrients, carries out its regular metabolic roles, and performs its normal function. ! Commits to divide.

!  Some cells never divide; they stay in G1, called Go phase.

! Cell prepares for DNA replication.

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! DNA replication occurs.

!  Each DNA is associated with histone proteins and is called chromatin.

! At the end of S phase,

! duplicated DNA molecules stay attached.

! chromatids are formed.

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Chromosomes must be replicated before cell division.

-Replicated chromsomes are connected to each other at their kinetochores

-cohesin – complex of proteins holding replicated chromosomes together

-sister chromatids: 2 copies of the chromosome within the replicated chromosome

Homologous chromosomes Homologous chromosomes

Sister chromatids

Sister chromatids

Centromere

Replication

Kinetochore

Kinetochores

Cohesin proteins Centromere

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During G2 the chromosomes undergo condensation, becoming tightly coiled.

Centrioles (microtubule-organizing centers) replicate and one centriole moves to each pole.

Final preparations are made for cell division.

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Figure 18-15 Essential Cell Biology (© Garland Science 2010)

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CELL CYCLE

Animal cell _______

DNA replication ______

Plant cell _____

Cytoplasmic division ____

Primary growth stage ______

Additional growth stage ____

__________

Division of the nucleus ______

Package sister chromatids _______

Sister chromatids

align ______

Sister chromatids separate ______

Form daughter nuclei ______

•  Chromatin

•  Chromatid

•  Chromosome

•  Genome

•  Centromere

•  Kinetochore

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•  Cells gather information about themselves and their environment for this decision

•  Cell cycle checkpoints – time points in the cell cell cycle •  Cells evaluate their genetic health, their

location in the body and the body�s need for more cells.

Essential Cell Biology (© Garland Science 2010)

Essential Cell Biology (© Garland Science 2010)

•  Several proteins function as checkpoint regulators

•  Two classes of genes that encode checkpoint proteins:

• Proto-oncogenes

•  Tumor-suppressor genes

•  Balance of these two proteins decides fate of cell cycle

•  A tumor suppressor protein - p53

•  Functions at the G1-S and G2-M checkpoints

•  Tries to repair damaged DNA; if not possible, cell is killed

•  Mutations in p53 gene often lead to cancer

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Ch09_Part1