Cellular reproduction depends on the cell cycle

• “All cells come from preexisting cells.”

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• Cell cycle:

– Interphase, G1 or G0, S – DNA synthesis, G2 – preparation for division, M-phase/division, and cytokinesis

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8.1 Cellular reproduction depends on the cell cycle

8-4 Figure 8.1C

The Cell Cycle and Chromosomes

A. The cell cycle can be divided into two main parts: 1) Interphase and 2) Cell division

1. Cells spend most of their lives in interphase—growing (G1), S phase, and G2 (preparing for division).

http://www.cellsalive.com/cell_cycle.htm

The Cell Cycle and Chromosomes

a. Cells that do not “plan” on dividing go into a stalled state called G0 (gap 0)-example-brain neurons & muscle cells

Some cells will stay in G0 until they need to divide-example-white blood cells

http://www.cellsalive.com/cell_cycle.htm

The Cell Cycle and Chromosomes

b. Cells replicate/copy their DNA during S phase (DNA synthesis). Why? Duplicate DNA is needed because the cell nucleus is divided and each new cell needs a complete set.

The Cell Cycle and Chromosomes c. G2 –Cells prepare for division 1-by growing more 2- by repairing DNA damaged during replication/S phase. 3-Producing proteins that control when the cell enters mitosis. 4-IF the cell has too much damaged DNA or isn’t functioning correctly, it will be “killed” off (apoptosis) by a protein called p53—division will never occur in these cells.

http://www.bioinformatics.org/p53/introduction.html

Loose chromosomes

• During interphase and early prophase notice-DNA forms long stranded chromosomes, but still is not in condensed chromosome form. Why?

• It would be much harder to correct DNA duplication errors if it was condensed and wrapped around histones and protein synthesis could not occur during G2.

Extremely condensed and shortened during later mitosis stages

2. Cell Division is an important function performed by cells after their “growth or G1 and G2” phases

-Permits growth and repair -Is necessary for the zygote (fertilized egg) to develop into

a newborn

For example, skin cells need to divide frequently to provide a protective layer

for our body.

B. Draw and label the cell cycle (be sure to include the two main parts: interphase and cell division):

II. DNA and Chromosomes-After Gap 1 and S phase of interphase, DNA forms

chromosomes

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II. DNA and Chromosomes A. In prokaryotic cells, DNA is located in the cytoplasm.

1. Most prokaryotes have a single DNA molecule/chromosome containing most of the cell’s genetic information.

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2. Prokaryotes have “extra” circular pieces of DNA called “plasmids”. Fill in the term plasmid in your bacterial cell diagram on your notes.

tic cells also have “extra” circular pieces of DNA called “plasmids” that function and replicate independent of the cell’s main DNA or may become a part of the main DNA. Label the “plasmid DNA” on the prokaryote diagram:

II. DNA and Chromosomes

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B. A picture of chromosomes during meiosis is called a karyotype. A karyotype can be used to determine genetic abnormalities.

II. DNA and Chromosomes C. Many eukaryotes have 1000

times the amount of DNA as prokaryotes. 1. Eukaryotic DNA is stored as

chromatin in the nucleus. DNA chromatin forms chromosomes during cell division.

2. The number of chromosomes varies widely from one species to another.

II. DNA and Chromosomes C. Many eukaryotes have 1000 times the amount of

DNA as prokaryotes. 3. Most species have 2 sets of chromosomes-one

from each parent (humans have 23 pairs for a total of 46 chromosomes).

a. Species with 2 genders (humans) have 2 sex chromosomes that don’t match (X,Y). So, the total matching homologous pairs for humans is really only 22.

b. The chromosomes that are homologous are called autosomes. Humans have 44 autosomal chromosomes and 2 sex chromosomes.

• 4. Cells with a copy of chromosomes from each parent are called Diploid or 2n – Pairs of chromosomes – The diploid number of chromosomes for humans is 46

• Haploid or n cells only contain half from each parent – Unpaired chromosomes – The haploid number of chromosomes for humans is 23

D. Chromosome Structure 1. Eukaryotic chromosomes contain DNA and protein, tightly packed

together to form chromatin.

a. Chromatin consists of DNA tightly coiled around proteins called histones.

b. DNA and histone molecules form nucleosomes.

c. Nucleosomes pack together, forming a thick fiber.

d. Each cell contains about 2 meters worth of DNA, a single person as enough DNA to stretch from the Earth to the Sun more than 400 times. (150 billion meters)

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Chromatin vs. Chromosome

Chromosomes

Tightly packaged/condensed DNA

Condensed form only during cell division after replication

DNA is not being used for protein synthesis

Chromatin

Unwound DNA

Found throughout interphase of cell cycle

DNA is being used for protein synthesis (strands are more accessible)

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8.3 Mitosis has a set series of phases

PMAT-memorize an mnemonic Please make me a taco

• Mitosis phases:

– Prophase

– Metaphase

– Anaphase

– Telophase

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Figure 8.3A 8-21

Figure 8.3A continued

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Cytokinesis: Division of Cytoplasm

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8.4 Cytokinesis follows mitosis

• Cytokinesis – division of cytoplasm

– Follows mitosis in most cells

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Cell Cycle Control and Cancer

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8.5 Cell cycle control depends on checkpoints

• In order for the body to remain healthy, the cell cycle must be controlled.

• G1, S, G2, and M stages occur in order and only when the previous stage has been successfully completed.

• Checkpoints can delay the cycle until all is well. – G1 checkpoint

• Apoptosis (programmed cell death) may be signaled.

– G2 checkpoint

– M checkpoint

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Figure 8.5 8-27

• Development of cancer – Mutations (DNA changes) due to environmental

assaults can result in abnormal growth of cells and eventually cancer.

– Any tissue with a high rate of cell division is more susceptible to carcinogenesis (development of cancer).

– Characteristics of cancer cells: • Lack differentiation • Have abnormal nuclei • Form tumors • Undergo angiogenesis and metastasis

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8.6 Cancer cells are distinctly abnormal

8-29 Figure 8.6

HOW BIOLOGY IMPACTS OUR LIVES

8C Protective Behaviors and Diet Help Prevent Cancer

• Protective behaviors: – Don’t smoke.

– Use sunscreen.

– Avoid radiation.

– Be tested for cancer.

– Be aware of occupational hazards.

– Carefully consider hormonal therapy.

• Right diet: – Increase consumption of foods rich in vitamins A and C.

– Limit consumption of salt-cured, smoked, or nitrite-cured foods.

– Include vegetables from the cabbage family in the diet.

– Be moderate in the consumption of alcohol.

– Maintain a healthy weight.

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Connecting the Concepts: Chapter 8

• All cells receive DNA from preexisting cells through the process of cell division.

• The cell cycle has checkpoints that determine if the DNA is normal and capable of functioning properly.

• Mitosis is part of the cell cycle, and there are negative consequences if the cell cycle comes out of synchronization.

• Separation of the chromatids during mitosis ensures that daughter nuclei have the same number of chromosomes as the parent cell.

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Cell Cycle and Chromosomes Name that species!

Instructions: Groups of two students will be assigned a random species. You will need to find the answers from ch. 5.2 (p. 138-139) and ch. 6.1 (p. 168) and from the species information provided on your handout.

1. What are chromosomes and how many does your species have (notes and p. 138)?

2. Explain Fig. 5-5 in terms of size---when is DNA most visible? Arrange the DNA descriptions from least visible to most visible (there are 5 headings/descriptions to arrange).

3. Is your species a eukaryotic organism or prokaryote? If it is a prokaryote, how is the DNA/chromosome different from eukaryotes? (p. 556)

4. Draw and label an example chromosome of your species (see figure 5.5)

5. 6.1 (p. 168) What are sex chromosomes and How many sex chromosomes do most organisms have?

6. What are autosomes and how many does your organism have?

7. What are homologous chromosomes and how many does your organism have?

8. What is the difference between diploid and haploid cells? Which cells of most organisms are diploid? Which are haploid? Why?

9. Be ready to present your findings.