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Cell Division

Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

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Prokaryotes Heredity information in a prokaryote - stored in DNA –the prokaryotic chromosome -single circle of DNA –DNA replication begins with the unzipping of the double-stranded DNA at a point called the origin of replication a new double helix is formed by adding complementary nucleotides to the exposed DNA strands that have been unzipped the end result of replication is that the cell possess two complete copies of the hereditary information

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Page 1: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Cell Division

Page 2: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Prokaryotes -Have a Simple Cell Cycle• Cell division in prokaryotes takes place in

two stages, which together make up a simple cell cycle

1. copy the DNA this process is called replication

2. split the cell in two to form daughter cells this process is called binary fission

Page 3: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Prokaryotes

• Heredity information in a prokaryote - stored in DNA– the prokaryotic chromosome -single circle of DNA– DNA replication

• begins with the unzipping of the double-stranded DNA at a point called the origin of replication

• a new double helix is formed by adding complementary nucleotides to the exposed DNA strands that have been unzipped

• the end result of replication is that the cell possess two complete copies of the hereditary information

Page 4: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Prokaryotes

• After replication, the cell grows in order to partition the replicated DNA molecules– cell splits into two equal halves– new plasma membrane and cell wall are

added at a point between the partitioned DNA– cell constricts in two to form two daughter

cells• each daughter cell is a complete, living cell with its

own DNA

Page 5: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Figure 9.1 Cell division in prokaryotes

Page 6: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Eukaryotes- Have a Complex Cell Cycle• Eukaryotic cells contain more DNA than

prokaryotic cells and the DNA is also packaged differently– cell division is more complex– DNA in eukaryotic cells is linear and

packaged into a compact chromosome• there is more than one chromosome in a

eukaryotic cell

Page 7: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Eukaryotes

• Eukaryotic cells undergo two different mechanisms to divide up the DNA– mitosis is a cell division mechanism that

occurs in nonreproductive cells• these cells are called somatic cells

– meiosis is a cell division mechanism that occurs in cells that participate in sexual reproduction

• these cells are called germ cells

Page 8: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Eukaryotes

• The eukaryotic cell cycle is divided into distinct phases

– Interphase (G1,S, and G2 phases)

– Mitosis (M phase)

– Cytokinesis (C phase)

Page 9: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Eukaryotic Cell Cycle

Page 10: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Chromosomes• Chromosome number varies among organisms

– most eukaryotes have between 10 and 50 chromosomes in their somatic cells

• Chromosomes are paired in somatic cells– pairs-homologous chromosomes, or homologues– homologues -contain information about the same

traits but the information may vary– diploid cells- cells that have two of each type of

chromosome• one chromosome of each pair is inherited from the mother

and the other is inherited from the father

Page 11: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Chromosomes

Sister chromatids- form when homologous chromosomes replicate– the sister chromatids are joined together by a

structure called a centromere– humans have 23 pairs of homologous

chromosomes• when each chromosome in the pair is replicated,

this makes for a total of 92 chromatids

Page 12: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Figure 9.3 The difference between homologous chromosomes and sister chromatids

Page 13: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

9.3 Chromosomes• A karyotype is an

arrangement of chromosomes

• Chromosomes can be compared based on size, shape, and centromere location

• The karyotype at right shows the 23 pairs of human chromosomes

Figure 9.4 The 46 chromosomes of a human

Page 14: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Chromosomes

• Chromosomes– are comprised of chromatin

• a complex of DNA and protein– the DNA in a chromosome is one very long

double-stranded fiber that extends unbroken for the length of the chromosome

– the DNA is coiled in order to allow it to fit into a small space despite being very long

Page 15: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Chromosomes

• DNA is coiled around proteins called histones– the histones have positive charges to counteract the

negative charges associated with the phosphate groups of the DNA

• The DNA coils around a core of eight histone proteins to form a complex called a nucleosome– the nucleosomes in turn can be coiled together further

to ultimately form a compact chromosome

Page 16: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Figure 9.5 Levels of eukaryotic chromosomal organization

Page 17: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Figure 9.2 How the cell cycle works

Page 18: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Interphase1. The time preparing for cell division2. Cells spend most of their time in this

phase3. DNA is uncoiled in the form of chromatin4. 3 Parts

– A. G1: Growth 1– B. S: Synthesizing DNA– C. G2: Growth 2

Page 19: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Cell

Nucleus

Page 20: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Mitosis

• Prophase–Metaphase

•Anaphase–Telophase

»Cytokinesis

Page 21: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Prophase1. Chromatin condenses and now exist as

chromosomes• Chromosomes are made of two sister

chromatids2. Nuclear membrane and nucleolous break

down3. Spindle forms4. Centrioles move to opposite poles in animal

cells.

Page 22: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Chromosome

Sister Chromatids

Centromere

Centriole

Spindle

Page 23: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Metaphase

1. Spindle attaches to centromere (center of the chromosome)

2. Chromosomes line up (in the middle) on the metaphase plate

M= Middle

Page 24: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Metaphase Plate

Page 25: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Anaphase

1. Sister Chromatids separate and move to opposite poles

A = Away

Page 26: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle
Page 27: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Telophase

1. Chromosomes uncoil2. Nuclear membrane and nucleolus reform3. Cytokinesis begins4. Looks like start of prophase (with 2 joined cells)

Page 28: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle
Page 29: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Cytokinesis

1. Cytoplasm and its contents divide into 2 new cells (daughter cells)

A. Animal Cell- Pinching in of cell membrane forming a cleavage furrow

B. Plant cells- Cell Plate forms between 2 cells and turns into a cell wall

Page 30: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

2 New Daughter Cells

Page 31: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Figure 9.7 Cytokinesis

Page 32: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Cell Cycle Control System

Page 33: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

External Regulations

1. Anchorage dependence – cells must be anchored (attached) to something before they will divide (extracellular matrix)

2. Contact inhibition – cells stop dividing when they touch each other

A. Caused by growth factors – proteins secreted by some cells that signal nearby cells to begin dividing

Page 34: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Contact Inhibition

Page 35: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Internal RegulationsCheckpoint – critical point where stop and go-ahead signal can regulate the cell cycle

Signals to checkpoints come from cellular surveillance mechanisms and from signals outside the cell

• G1 checkpoint– this checkpoint makes the decision about whether the cell should divide and enter S– some cells never pass this point and are said to be in G0

• G2 checkpoint– this checkpoint leads to mitosis

• M checkpoint– this checkpoint occurs during metaphase and triggers the exit process of the M phase and entry to

the G1 phase

Cyclins – proteins that help regulate the timing of the cell cycle in eukaryotic cellsCalled cyclins because their concentration rises and falls with the cell cycle

Page 36: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Figure 9.9 Control of the cell cycle

Page 37: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

CANCERA breakdown in the control of the cell

cycle leads to CANCER!!!!!The cells:• Do not exhibit contact inhibition

– Make more cells even when no more are needed• “Immortal” – divide indefinitely if supplied

with proper nutrients (HeLa cells - 1951)• Caused by transformation of single cell

Page 38: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

What Is Cancer?

• Cancer is a growth disorder of cells– begins when apparently normal cells grow

uncontrollably and spread to other parts of the body– growing cluster of cells called a tumor

• benign tumors are surrounded by a healthy layer of cells (also known as encapsulated) and do not spread to other areas

• malignant tumors are not encapsulated and are invasive– cells from malignant tumors leave and spread to different areas

of the body to form new tumors» these cells are called metastases

Page 39: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Lung Cancer

Figure 9.11 Lung cancer cells (300x)

Page 40: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

What Is Cancer?

• Cancer is caused by a gene disorder in somatic tissue in which damaged genes fail to properly control the cell cycle– mutations cause damage to genes

• may result from chemical or environmental exposure, such as UV rays

– viral exposure may also alter DNA

Page 41: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

What Is Cancer?

• There are two general classes of genes that are usually involved in cancer– proto-oncogenes

• these genes encode proteins that stimulate cell division• mutations to these genes can cause cells to divide

excessively– when mutated, these genes become oncogenes

– tumor-suppressor genes• these genes normally turn off cell division in healthy cells• when mutated, these genes allow uncontrolled cell division

Page 42: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Cancer and Control of the Cell Cycle

• Cancer results from damaged genes failing to control cell division– one such gene, p53, affects the G1 checkpoint

• its normal action is to detect abnormal DNA– it prevents cell division of a cell with damaged DNA until

the DNA is repaired or directs the cell to be destroyed if the damage cannot be fixed

• if this gene itself becomes damaged, it will allow damaged cells to divide unchecked

Page 43: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

Figure 9.12 Cell division and p53 protein

Page 44: Cell Division. Prokaryotes -Have a Simple Cell Cycle Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle

What causes loss of cell cycle control and leads to cancer?