Cell Reproduction/Mitosis

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Cell Reproduction/Mitosis

Chapter 12

What you need to know!

• Mitotic Cell division results in genetically identical daughter cells

• The mitotic phase alternates with interphase in the cell cycle

Overview

I.

Cell Division Overview

II.

The Cell Cycle

III. Mitosis

– nuclear division/cytokinesis

IV. Stages of Mitosis

Cell Division

• Life depends on the ability of cells to reproduce/copy

• Cell Division = 1 cell divides into 2

• Unicellular organisms cell division = reproduction

– Prokaryotes, Protists

– Bacteria = binary fission

Cell Division

Multicellular organisms cell division = growth and development, repair and replace.

– Protists, fungi, plants and animals

2 types of multicellular organism cells:

1. Somatic Cells: Body cells of an organism that do all the daily function of the organism

2. Germ Cells: reproductive cells (eggs and sperm)

Cell Cycle

• G

0

: the cell spends its life working and growing (i.e. breaking down sugars, making

ATP, enzymes)

• Sometimes a cell will prepare to divide

– 1 mother cell 

2 daughter cells

• Interphase

– G

1

(Gap1): Growth, development, organelle production, etc. Cell must enter reproduction (S phase) or not (G

0

)

– S (Synthesis): DNA replication

– G

2

(Gap2): continued growth and preparation for division (centrosomes/centrioles duplicate)

Cell Cycle

• Mitosis (M): nuclear division

• Cytokinesis: division of cytoplasm and cell membrane/cell wall

DNA

• Chromatin: spread out DNAprotein complex. In Eukaryotes the proteins are histones. Human cells have 3 billion base pairs.

• Chromosomes: condensed strands of DNA distinct in number and length for each organism.

One chromosome is made up of

30 to 150 million base pairs.

DNA

• Humans have 46 chromosomes (23 pairs).

• Each chromosome contains a few thousand genes that code for cellular proteins

DNA

• Diploid indicates that our somatic

(body) cells have 23 pairs of chromosomes (2n)

• Haploid indicates that our gametes

(sex cells) have 23 chromosomes (1n or n)

Mitosis: Division of the Nucleus

• Problem: distribution of one exact copy of each of their chromosomes to each new cell.

• Each chromosome contains thousands of genes, each necessary to the proper functioning of the organism.

• Humans have ~120,000 genes spread over 46 chromosomes in each somatic cell.

Mitosis

• During Mitosis all access to the DNA stops as chromatin coils up and condenses into visible chromosomes

• Each replicated chromosome is composed of 2 identical parts (sister chromatids) held together by a centromere.

Mitosis

• Sister chromatids are pulled apart during mitosis, and partitioned into 2 daughter cells

• Result of mitosis & cytokenesis: 2 daughter cells genetically identical to the parent cell.

IV. Stages of Mitosis

• Prophase: Chromosomes condense, centrosomes are pushed apart by growing spindle, nuclear envelope disintegrates

Stages of Mitosis

• Prometaphase: the 2 centromeres of each chromosome attach to one kinetochore spindle fiber; centrosomes move to opposite poles

Kinetochore spindle fiber

Non Kinetochore spindle fiber

Stages of Mitosis

• Metaphase: Chromosomes line up at the metaphase plate (equator); centrosomes are at opposite poles

Stages of Mitosis

• Anaphase: Chromosomes separate due to shortening of kinetochore spindle fibers; cell elongates due to lengthening of non-kinetochore spindle fibers

Non Kinetochore spindle fiber

Kinetochore spindle fiber

Stages of Mitosis

• Telophase: Chromosomes immediately uncoil and resume transcription activities; spindle proteins disassemble; nuclear envelope reassembles

Mitosis Animation

• http://vcell.ndsu.nodak.edu/animations

/mitosis/movie-flash.htm

Cytoskeleton Creates

Chromosome Migration

Spindle fibers are microtubules made of tubulin proteins that are always present in the cytoplasm

Enzymes assemble and disassemble spindle fibers

Centromere region contains

1. Centromere protein clamp, holding the 2 sister chromatids together; deactivated during anaphase

2. Kinetochore motor protein; 1 on each sister chromatid

Kinetochore microtubule

• Several microtubules attach to each kinetochore motor protein

• Motor protein starts moving (walks along the spindle fibers); kinetochore microtubules shorten, pulling chromsomes (at the metaphase plate) apart

– ATP hydrolysis powers the motion

Non Kinetochore Microtubules

• Microtubules lengthen, pushing the two poles apart (cell expands)

Non Kinetochore spindle fiber

Kinetochore spindle fiber

Cytokinesis

Animal:

• Cleavage furrow

– Made by microfilaments (actin fibers)

– A drawstring around the middle of the cell

• Cell pinches off into 2 daughter cells

Mitosis & Cytokinesis in

Plant Cells

• Plants have centrosomes w/out centrioles

• No cleavage furrow

– plant cells cannot separate due to cell wall

• Cell plate grows through divided cell

Duration of the Cell Cycle

• Prokaryotic Cells – 20 minutes

• No DNA/Histone complex + fast DNA replication (500 NT/sec)

• No spindle fibers, no mitosis

• 2 DNA rings are attached to 2 spots of the plasma membrane which grows apart

• 1 plasmid

Duration of the Cell Cycle

• Eukaryotic Cells – 12-48 hrs

• Longest phase of the cell cycle is interphase

• Longest phase of mitosis is prophase

Frequency of Cell Cycles

• Depends on cell type:

Cell type Life span/frequency

Esophagus, epidermis 2-3 days

Small intestine

Large intestine

1-2 days

6 days

Red blood cells

White blood cells

Nerve cells

3 months

Up to 10 years

Lifetime (G

0

)

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