Chapter 8: Cellular Transport and the Cell Cycle



Chapter 8.2, 8.3 and 11.1 Notes

A.Schevers

Section 8. 2 Cell Growth and Reproduction

I. Cell Size Limitations

* Cells come in a wide variety of sizes and shapes.

Ex. Red blood cells only 8 micrometers, nerve cells can reach up to one meter in length.

A. Diffusion limits cell size

* Within the cell, nutrients and wastes move by diffusion.

*Diffusion becomes slow and inefficient as the distances become larger.

B. DNA limits cell size

* Proteins are used throughout the cell to perform critical cell functions.

* There is a limit to how quickly these directions for protein production can be copied.

* In many larger cells there will be more than one nucleus.

C. Surface area-to-volume ratio

1. As a cell’s size increases, it’s volume increases much faster than its surface area.

Ex. Cell has 1 mm sides

Cell has 2 mm sides

2. Because cell size can have a dramatic effect on a cell, cells divide before they become too large to function properly.

II. Cell Reproduction

*Cell division = the process by which new cells are produced from one cell

*Cell division results in two cells that are identical to the original parent cell.

Ex. Old cells on the soles of your feet are being shed and replaced.

A. The discovery of chromosomes

*Chromosomes = cell structures that carry the genetic material that is copied and passed from generation to generation of cells.

1. Early biologists observed that just before cell division, several short stringy structures suddenly appeared in the nucleus.

2. These structures seemed to vanish soon after division of a cell.

1. These structures are called chromosomes.

* Accurate transmission of chromosomes during cell division is critical.

B. The structure of eukaryotic chromosomes.

1. For most of a cell’s lifetime chromosomes exist as chromatin.

*Chromatin = long strands of DNA wrapped around proteins called histones.

1. The chromosomes of a eukaryotic cell undergo changes in shape and structure during the different phases of the cell cycle. (Fig. 8.10 on page 205)

III. The Cell Cycle

*Cell cycle = is the sequence of growth and division of a cell.

1. As a cell proceeds through its cycle, it goes through two general periods.

a. Interphase – period of growth

b. Mitosis – period of division

2. Interphase

a. During interphase a cell grows in size and carries on metabolism.

b. Chromosomes are duplicated in preparation for division.

3. Mitosis

a. Following interphase, a cell enters its period of nuclear division

b. This is the process by which two daughter cells are formed, each containing a complete set of chromosomes.

4. Interphase and Mitosis make up the bulk of the cell cycle.

5. Following mitosis the cytoplasm divides separating the two daughter cells, this is called cytokinesis. (Fig. 8.11, page 206)

IV. Interphase: A Busy Time

1. Interphase is divided into three stages.

a. G1 phase (gap 1) – the cell undergoes intense growth

b. S phase (synthesis) – genetic material copied

c. G2 phase (gap 2) – centrioles, mitochondria or other organelles replicate, cell prepares for division.

V. The Phase of Mitosis

*Although cell division is a continuous process, biologists recognize four distinct phases of mitosis.

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

A. Prophase: The first phase of mitosis (Fig 8.13, pg. 207)

1. The chromatin coils to form visible chromosomes

*Each duplicated chromosome is made up of two halves.

*The two halves are called sister chromosomes, and they are exact copies of each other.

* They are held together by a structure called a centromere, which help scientist identify chromosomes.

2. Nucleus begins to disappear.

3. In animal cells the centrioles begin to migrate to opposite ends of the cell.

4. Spindle fibers begin to appear.

B. Metaphase: The Second stage of Mitosis

1. Doubled chromosomes become attached to the spindle fibers by their centromeres.

2. Chromosomes begin to line up on the midline, or equator.

3. Each sister chromatid is attached to its own spindle fiber.

*this ensures that each new cell receives an identical and complete set of chromosomes.

C. Anaphase: The Third Phase of Mitosis

1. The centromeres split and the sister chromatids are pulled apart to opposite poles of the cell. (Fig. 8.13, pg. 207)

D. Telophase: The Fourth Phase of Mitosis

1. Spindle fibers start to break down, the nucleolus reappears and new nuclear envelope forms around each set of chromosomes.

2. A new membrane begins to form between the two new nuclei.

VI. Cytokinesis

*cytokinesis differs between plants and animals

1. Animal cells – the plasma membrane pinches in and the two new cells are separated.

2. Plants – the cell plate is laid across the cell’s equator, a cell membrane forms around each cell and new cell walls form on each side of the cell plate.

VII. Results of Mitosis

A. Levels of Organization in multicellular organisms

1. In multicellular organisms cell growth and reproduction result groups of cells that work together as tissue.

2. Tissues organize in various combinations to form organs.

3. Multiple organs that work together form an organ system.

4. All organ systems work together for the survival of the organism.

Section 8.3 Control of the Cell Cycle

I. Normal Control of the Cell Cycle

*some cells divide rapidly, while others divide slowly.

A. Proteins and Enzymes Control the Cell Cycle

1. Cell cycle is controlled by proteins called cyclins and a set of enzymes that attach to the cyclin.

2. Cancer = is a result of uncontrolled cell division.

3. The loss of control may be caused by environmental factors or by changes in enzyme production.

4. Enzyme production is directed by genes, which are segments of DNA.

A. Cancer: A Mistake in the Cell Cycle

1. Currently, scientists consider cancer to be a result of changes in one or more of the genes that aid in controlling the cell cycle.

2. These changes are expressed as cancer when something prompts the damaged genes into action.

3. Cancerous cells form masses of tissue called tumors.

4. In later stages, cancer cells enter the circulatory system and spread throughout the body forming new tumors.

B. The Cause of Cancer

1. It is difficult to pinpoint because both genetic and environmental factors are involved.

Ex. of environmental factors- cigarette smoke, air and water pollution and exposure to ultraviolet radiation

C. Cancer Prevention

1. Healthily diet and not using tobacco are recommended to reduce the risk of cancer.

Chapter 11.1: What is DNA?

* DNA determines an organism’s traits.

* DNA achieves its control by determining the structure of proteins.

* Living things contain proteins, your skin, muscles, and bones all contain proteins.

* All actions, such as eating, running, thinking, depend on proteins called enzymes.

* Within the structure of DNA is the information for life, the complete instructions for manufacturing all the proteins for an organism.

A. DNA as the genetic material

* In the early 1950’s many scientists believed that proteins was he genetic material.

* In, 1952 Hershey and Chase performed experiments using radioactively labeled viruses that infected bacteria.

* These results were convincing evidence that DNA is the genetic material.

B. The structure of nucleotides

* DNA is capable of holding all its information because it is a very long molecule.

*DNA is a polymer made of repeating subunits called nucleotides.

* Nucleotides have three parts.

1. Simple sugar

2. Phosphate group

3. Nitrogenous base

*In DNA there are four possible nitrogenous bases

1. Adenine (A)

2. Guanine (G)

3. Cytosine (C)

4. Thymine (T)

C. The structure of DNA

* In 1953, James Watson and Francis Crick published a letter proposing that DNA is made of two chains of nucleotides held together by nitrogenous bases.

* They stated that the nitrogenous bases of the nucleotides hold the two strands of DNA together with weak hydrogen bonds.

* Adenine on one strand pairs only with thymine on the other strand, and guanine on one strand pairs only with cytosine on the other strand

* Watson and Crick also proposed that DNA is shaped like a ling zipper that is twisted into a coil like a spring, this shaped is called a helix. Because DNA is composed of two strands twisted together, its shape is called a double helix. (Fig. 11.2 pg. 283 & Fig. 11.3 pg 284)

D. The importance of nucleotide sequence.

* The sequence of nucleotides forms the unique genetic information of an organism.

Ex. Nucleotide sequence of A-T-T-G-C carries different information from a sequence of T-G-C-A-T-C.

*The closer the relationship is between two organisms, the more similar their DNA nucleotide sequence will be.

* Scientists use nucleotide sequence to determine evolutionary relationships among organisms.

II. Replication of DNA

* The DNA in chromosomes is copied in a process called DNA

replication.

* Without DNA replication, new cells would have only half the DNA of

parents. Species could not survive.

* All organisms undergo DNA replication. (Fig. 11.4B pg. 285)

A. How DNA replicates

* During replication, each strand serves as a pattern, or template, to make a new DNA molecule.

* Replication begins as an enzyme breaks the hydrogen bonds between bases that hold the two strands together, thus unzipping the DNA.

* As the DNA continues to unzip, nucleotides that are floating free in the surrounding medium are attached to their base pair by hydrogen bonding.

* Another enzyme bonds these nucleotides into a chain.

* This process continues until the entire molecule has been unzipped and replicated.

* Each new strand formed is a complement of one of the original strands.

* The result is the formation of two DNA molecules, each of which is identical to the original DNA molecule. (Fig. 11.5 pg 286-7)

CELL CYCLE

PHASES OF MITOSIS DNA STRUCTURE

DNA REPLICATION

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