Chapter 9: Cell Cycle and Cellular Reproduction

pg. 144

What is the cell cycle?

Ordered set of stages that takes place between the time a eukaryotic cell divides and the time resulting daughter cells also divide?

What are the two portions of the cell cycle?

Interphase - number of stages

Mitotic - when mitosis and cytokinesis occur

What is interphase? How many stages

Most of the cell cycle is spent in this phase. Three stages - G₁, S, G₂

Stages of the cell cycle (G_1, S_, G₂) during which growth and DNA synthesis occur when the nucleus is not actively dividing.

• Performs its usual functions.

• Adult mammalian cells, interphase lasts for about 20 hours, 90%

• Embryonic cells complete in a few hours.

G₁ Stage

“G” stands for growth. This stage is before DNA replication. The cell recovers from the previous division.

Grows in size and increases the number of organelles and gets materials that will be used for DNA synthesis.

Performing their normal functions—talking w/ other cells, secreting substances, and carrying out cellular respiration.

Which cells do not complete the cell cycle?

Nerve and muscle cells. They exit interphase and enter G₀. No preps are made for cell division. Cells can’t leave this stage without proper signals from other cells and parts of the body.

S Stage

Happens after G₁ when DNA synthesis (replication) happens

Each chromosome has one DNA double helix at the beginning.

After replication, each chromosome now has two identical DNA double-helix molecules.

What is a chromatid?

After replication, a chromosome has a pair of sister chromatids, held together at the centromere and each chromatid is has a single DNA helix

What is the definition for sister chromatid?

One of two genetically identical chromosomal units that are the result of DNA replication and are attached to each other at the centromere.

• they remain attached until they are broken apart by mitosis.

G₂ Stage

After S stage.

Completion of DNA replication to the onset of mitosis.

Cell synthesizes the proteins that will help with cell division.

Mitotic Stage

After interphase, the cell enters the M (for mitotic) stage. This cell division includes mitosis (nuclear division) and cyokinesis (division of the cytoplasm).

Daughter chromosomes are distributed by the mitotic spindle to two daughter nuclei. When the division of cytoplasm is complete, two daughter cells are present.

Mitosis

The stage of cellular reproduction in which nuclear division occurs and the process in which a parent nucleus produces two daughter nuclei, each having the same number and kinds of chromosomes as the parent nucleus.

Cytokinesis

Division of the cytoplasm following mitosis or meiosis.

Mitotic Spindle

A complex of microtubules and associated proteins that assist in separating the chromatids during cell division

What is a signal and what are growth factors?

Signal is a molecule that influences the activities of a cell

Growth Factors are signaling proteins received at the plasma membrane (stimulated by a hormone or chemical secreted by one cell, that may stimulate or inhibit growth of another cell or cells).

Cyclin

Protein that cycles in quantity as the cell cycle progress; combines with and activates the kinases that promote the events of the cycle

What is p53?

A signaling protein. In mammalian cells, it stops the cycle at the G₁ when DNA is damaged.

p stands for protein

53 represents its molecular weight in kilodaltons.

p53 attempts to repair DNA but rising levels of p53 can bring apoptosis.

What is RB?

Protein that is responsible for interpreting growth signals and nutrient availability signals.

• Stands for retinoblastoma, a cancer of the retina that happens when the RB gene undergoes a mutation

What is apoptosis?

Programmed cell death.

• involves a cascade of specific cellular events leading to death and destruction of the cell.

What are caspases?

The enzymes that bring about apoptosis are always present in the cell. Held in check by inhibitors but can be released by internal or external signals.

What are somatic cells?

Body cell; excludes cells that undergo meiosis and become sperm or eggs.

• cell division increases and apoptosis decreases the number of somatic cells.

What does a eukaryotic chromosome contain?

single double-helix DNA molecule and it’s composed of more than 50% protein.

What are the five primary types of histone molecules? What are histones responsible for?

H1, H2A, H2B, H3, H4

• Responsible for packaging the DNA so it can fit into a small space.

How is DNA wounded?

• DNA is at the intervals around eight histone molecules (H2A, H2B, H3, H4), looking like a string of beads.

  • Each bead is called a nucleosome and they are joined by linker DNA.

    • The string folds into a zigzag structure, making the DNA strand shorter. (H1 mediates this process)

Euchromatin

Chromatin with a lower level of compaction and therefore accessible for transcription

• may be accessed by RNA polymerase to promote transcription

Heterochromatin

Highly compacted chromatin that is not accessible for transcription.

• dark-stained fibers within the nucleus of the cell. highly compacted form of chromosome

• considered inactive chromatin, because the genes contained are infrequently transcribed

Which is easier to move about during cell division?

Compact chromosomes are easier to move than extended chromatin.

What happens before cell division?

a protein scaffold helps further condense the chromosome into a form that is characteristic of metaphase chromosomes

When a eukaryotic cell is not undergoing division…

the DNA and associated proteins are structured as euchromatin, looking like a tangled mass of thin thread

Before mitosis begins…

chromatin becomes highly coiled and condensed, and it is easy to see the individual chromosomes

diploid and haploid and examples

Diploid (2n) Cell condition in which two of each type of chromosome are present

• most somatic cells of animals are diploid.

Haploid (n) contains only one chromosome of each kind.

• The gametes of animals (egg and sperm) are examples of haploid cells.

Centromere and kinetochores?

• Constriction where sister chromatids of a chromosome are held together.

• An assembly of proteins that attaches to the centromere of a chromosome during mitosis.

Each daughter chromosome has

only one double-helix molecule…

Centrosome and centrioles?

• Central microtubule-organizing center of cells. In animal cells, it contains two centrioles

• Cell structure, existing in pairs, that occurs in the centrosome and may help organize a mitotic spindle for chromosome movement during animal cell division. not in plant cells.

What are the phases of mitosis?

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Prophase

First phase of mitosis; characterized by the condensation of the chromatin; chromosomes are visible, but scattered in the nucleus.

Prometaphase

Second phase of mitosis; chromosomes are condensed but not fully aligned at the metaphase plate.

Metaphase

Third phase of mitosis; chromosomes are aligned at the metaphase plate. Straight line across the middle of the cell

• Several nonattached spindle fibers, called polar spindle fibers, reach beyond the metaphase plate and overlap

Anaphase

Fourth phase of mitosis; chromosomes move toward the poles of the spindle.

• the two sister chromatids of each duplicated chromosome separate at the centromere, giving rise to two daughter chromosomes.

Telophase

Final phase of mitosis; daughter cells are located at each pole.

• Each daughter nucleus contains the same number and kinds of chromosomes as the original parent cell. Remnants of the polar spindle fibers are still visible between the two nuclei.

What happens when mitosis occurs but cytokinesis doesn’t occur?

Multinucleated cell.

Cleavage Furrow

Indentation in the plasma membrane of animal cells during cell division; formation marks the start of cytokinesis.

Cytokinesis in plant cells involve

the building of new cell walls between the daughter cells.

Cell Plate

Structure across a dividing plant cell that signals the location of new plasma membranes and cell walls

Therapeutic and Reproductive Cloning

• Used to create mature cells of various cell types. Facilitates study of specialization of cells and provides cells and tissue to treat human illnesses.

• Used to create an organism that is genetically identical to the original individual.

Angiogenesis

Formation of new blood vessels; rapid angiogenesis is a characteristic of cancer cells.

Proto-oncogenes

Gene that promotes the cell cycle and prevents apoptosis; may become an oncogene through mutation.

Tumor suppressor genes

Gene that codes for a protein that ordinarily suppresses the cell cycle; inactivity due to a mutation can lead to a tumor

• prevents cells from dividing uncontrollably by indirectly or directly inhibiting the cell cycle

Oncogenes

Cancer-causing gene formed by a mutation in a proto-oncogene; codes for proteins that stimulate the cell cycle and inhibit apoptosis.

Telomere

Tip of the end of a chromosome that shortens with each cell division and may thereby regulate the number of times a cell can divide

Asexual Reproduction

Cell division may be used to produce two individuals from a single parent. Common on prokaryotes and some protistans. Chromosomes are duplicated

Binary Fission

Splitting of a parent cell into two daughter cells; serves as an asexual form of reproduction in bacteria.

Both binary fission and mitosis

ensure that each daughter cell is genetically identical to the parent cell.

Single-celled organisms are…

Prokaryotes (bacteria and archaea), protists (many algae and protozoans), and some fungi (yeasts)

Multicellular organisms are….

In plants, animals, and multicellular fungi (molds and mushrooms),