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

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Chromosome Rosettes of Chromatin Loops

Scaffold protein

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Chromosome Rosettes of Chromatin Loops Chromatin Loop

Chromatin loop

Scaffold protein Scaffold protein

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chromosome Rosettes of Chromatin Loops Chromatin Loop Solenoid

Chromatin loop

Scaffold protein Scaffold protein

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Chromosome Rosettes of Chromatin Loops Chromatin Loop Solenoid

Nucleosome

Histone core

Chromatin loop

Scaffold protein Scaffold protein

DNA

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Chromosome Rosettes of Chromatin Loops Chromatin Loop Solenoid

Nucleosome Histone core

Chromatin loop

Scaffold protein Scaffold protein

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)

17 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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29 Essential Cell Biology (© Garland Science 2010)

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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