Mitosis: the Cell Cycle!

2 Cell Division All cells are derived from pre- existing cells All cells are derived from pre- existing cells New cells are produced for growth and to replace damaged or old cells New cells are produced for growth and to replace damaged or old cells Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals) Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals)

3 Keeping Cells Identical The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules

4 DNA Replication DNA must be copied or replicated before cell division DNA must be copied or replicated before cell division Each new cell will then have an identical copy of the DNA Each new cell will then have an identical copy of the DNA Original DNA strand Two new, identical DNA strands

5 Identical Daughter Cells Parent Cell Two identical daughter cells

6 Before we start: What is a Chromosome? A threadlike structure of nucleic acids and protein found in the nucleus of most living cells, in the form of genes Before we start: What is a Chromosome? A threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes

7 Prokaryotic Chromosome The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane called a plasmid The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane called a plasmid

8 Eukaryotic Chromosomes Each eukaryotic chromosome is composed of a single, tightly coiled DNA molecule Each eukaryotic chromosome is composed of a single, tightly coiled DNA molecule Chromosomes can’t be clearly seen when cells aren’t dividing and are called chromatin Chromosomes can’t be clearly seen when cells aren’t dividing and are called chromatin Chromatin = Unorganized DNA

9 Compacting DNA into Chromosomes DNA is tightly coiled around proteins called histones

11 Eukaryotic Chromosomes Based on the organism, eukaryotes will have a varying number of chromosomes in their cells. Based on the organism, eukaryotes will have a varying number of chromosomes in their cells. Human body cells have 46 chromosomes Human body cells have 46 chromosomes

12 Karyotype A picture of the chromosomes from a human cell arranged in pairs by size: karyotype A picture of the chromosomes from a human cell arranged in pairs by size: karyotype First 22 pairs are called autosomes First 22 pairs are called autosomes Last pair are the sex chromosomes Last pair are the sex chromosomes XX female or XY male XX female or XY male

13 Boy or Girl? Y - Chromosome X - Chromosome The presence of a Y Chromosome Decides

14 Chromosomes in Dividing Cells Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids

15 The Cell Cycle Mitosis: The creation of two Identical Daughter Cel ls (asexual reproduction) Parent Cell Two identical daughter cells

16 Cell Division in Prokaryotes Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission Single chromosome makes a copy of itself Single chromosome makes a copy of itself Cell wall forms between the chromosomes dividing the cell Cell wall forms between the chromosomes dividing the cell Parent cell 2 identical daughter cells Chromosome replicates Cell splits

Mitosis: Five Phases of the Cell Cycle I - Interphase I - Interphase G 1 - primary growth phase G 1 - primary growth phase S – synthesis; DNA replicated S – synthesis; DNA replicated G 2 - secondary growth phase G 2 - secondary growth phase collectively these 3 stages are called interphase M - mitosis M - mitosis C - cytokinesis C - cytokinesis

Cell Cycle

Interphase - G 1 Stage 1 st growth stage after cell division 1 st growth stage after cell division Cells mature by making more cytoplasm & organelles Cells mature by making more cytoplasm & organelles Cell carries on its normal metabolic activities Cell carries on its normal metabolic activities

Interphase – S Stage Synthesis stage Synthesis stage DNA is copied or replicated DNA is copied or replicated Two identical copies of DNA Original DNA

Interphase – G 2 Stage 2 nd Growth Stage 2 nd Growth Stage Occurs after DNA has been copied Occurs after DNA has been copied All cell structures needed for division are made (e.g. centrioles) All cell structures needed for division are made (e.g. centrioles) Both organelles & proteins are synthesized Both organelles & proteins are synthesized

What’s Happening in Interphase? What the cell looks like Animal Cell What’s occurring

Four Mitotic Stages Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase

Steps in Prophase  DNA coils tightly & becomes visible as chromosomes (chromatin becomes chromosomes)  Nuclear membrane disappears  Nuceolus disappears  Centrioles migrate to poles  Spindle begins to form

Prophase What the cell looks like

Eukaryotic Chromosome

Mitotic Spindle

Metaphase ~ Chromosomes line up in the middle of the cell (equator) ~Spindle fibers play a game of “tug o war” until the chromosomes are perfectly aligned

Metaphase What the cell looks like What’s occurring

Anaphase ~ Spindle fibers shorten and separate sister chromatids. ~ Chromatids move AWAY from each other

Anaphase What the cell looks like What’s occurring

Telophase Sister chromatids at opposite poles Sister chromatids at opposite poles Spindle disassembles Spindle disassembles Nuclear envelope forms around each set of sister chromatids Nuclear envelope forms around each set of sister chromatids Nucleolus reappears Nucleolus reappears CYTOKINESIS occurs CYTOKINESIS occurs Chromosomes reappear as chromatin Chromosomes reappear as chromatin

Telophase

Cytokinesis Means division of the cytoplasm Means division of the cytoplasm Division of cell into two, identical halves called daughter cells Division of cell into two, identical halves called daughter cells In plant cells, cell plate forms at the equator to divide cell In plant cells, cell plate forms at the equator to divide cell In animal cells, cleavage furrow forms to split cell In animal cells, cleavage furrow forms to split cell

Cytokinesis Cleavage furrow in animal cell Cell plate in plant cell

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Controls on Cell Division How is the cell cycle regulated? -Controlled by regulatory proteins -There are 3 checkpoints throughout the cell cycle to make sure -G1 checkpoint -G2 checkpoint -M checkpoint

–The controls on cell growth and division can be turned on and off. –For example, when an injury such as a broken bone occurs, cells are stimulated to divide rapidly and start the healing process. The rate of cell division slows when the healing process nears completion.

The Discovery of Cyclins –Cyclins are a family of proteins that regulate the timing of the cell cycle in eukaryotic cells. –This graph shows how cyclin levels change throughout the cell cycle in fertilized clam eggs.

Regulatory Proteins –Internal regulators: proteins that respond to events inside a cell. They allow the cell cycle to proceed only once certain processes have happened inside the cell. –External regulators: proteins that respond to events outside the cell. They direct cells to speed up or slow down the cell cycle. –Growth factors: external regulators that stimulate the growth and division of cells. They are important during embryonic development and wound healing.

Apoptosis –Apoptosis - programmed cell death. –Apoptosis – helps development by shaping the structure of tissues and organs in plants and animals. For example, the foot of a mouse is shaped the way it is partly because the toes undergo apoptosis during tissue development.

Cancer: Uncontrolled Cell Growth – How do cancer cells differ from other cells? – Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, the cells divide uncontrollably. –They do not pay attention to density dependent inhibition or anchorage inhibition

–Cancer is a disorder in which body cells lose the ability to control cell growth. –Cancer cells divide uncontrollably to form a mass of cells called a tumor.

A benign tumor is noncancerous. It does not spread to surrounding healthy tissue. A malignant tumor is cancerous. invades and destroys surrounding healthy tissue can spread to other parts of the body. The spread of cancer cells is called metastasis. Cancer cells absorb nutrients needed by other cells, block nerve connections, and prevent organs from functioning.

breast cancer Brain cancer

What Causes Cancer? –Cancers are caused by defects in genes that regulate cell growth and division. –Some sources of gene defects are smoking tobacco, radiation exposure, defective genes, and viral infection. –A damaged or defective p53 gene is common in cancer cells. It causes cells to lose the information needed to respond to growth signals.

Cancer cell being attacked by immune system

Treatments for Cancer –Some localized tumors can be removed by surgery. –Many tumors can be treated with targeted radiation. –Chemotherapy is the use of compounds that kill or slow the growth of cancer cells.