Ch 12 the cell cycle

Draw the appearance of the two daughter cells

(see answer key)

Somatic cells

-all body cells except reproductive cells -each contain 46 chromosomes made up of 2 sets of 23 -one set inherited from each parent

One copy of a duplicated chromosomes is called a_____

chromatid

The complex of DNA and protein that makes up eukaryotic chromosomes is called

chromatin

Cyclin-dependent protein kinases are called

Cdks

Centromere

-the central region joining sister chromatids

Telophase

-part of the cell cycle that includes mitosis and cytokinesis

Draw and label a duplicated chromosome, include the sister chromatids and centromere.

(see document)

Metaphase plate

-plane midway between the two poles of a dividing nucleus

Mitotic phase

-part of the cell cycle that includes prophase, prometaphase, metaphase, anaphase, and telophase

Human gametes contain

-23 chromosomes

Human somatic cells contain

-46 choromosomes

How is the cell cycle regulated?

-A molecular cell‐cycle control system, under the direction of the genome (nuclear DNA,) drives the cell cycle.

Cyclin-dependent kinases

-Cdks -Protein kinases - enzymes that activate or inactivate proteins by phosphorylating them (serine, threonine, tyrosine‐ all with hydroxyl groups.) -Particular protein kinases give the "go‐ahead" signals at the G1 and G2 checkpoints - Present at constant concentration throughout the cell cycle but are inactive much of the time -Must be attached to cyclin in order to be active

Cyclin

-Cell cycle regulatory protein whose concentration fluctuates cyclically with the cell cycle

Surveillance Mechanisms

-Cellular surveillance mechanisms (e.g., is there damage to the DNA that needs to be repaired before entering S phase; is everything ready to begin M phase; is everything complete before completing cytokinesis?) ̶ signals from outside the cell (e.g., is there room for or the need for another cell?)

Compare and contrast mitosis and cytokinesis

-Cytokinesis is the process of dividing a cell in two. It is often described as division of the cytoplasm. -Mitosis is nuclear division. It is the highly ordered process that ensures that the genetic material (DNA) of the parent cell is distributed in such a way that each daughter-cell receives an exact copy. -Mitosis is the division and distribution of the nuclear material. -Cytokinesis (cell movment) is the division of the cytoplasm into 2 new cells. Cytokinesis is not considered a part of mitosis.

Taxol is an anti-cancer drug that acts by stabilizing microtubules. What effect would you expect taxol to have on cell division? Explain your reasoning. Why would taxol be an effective therapeutic agent for cancer?

-Kinetochore microtubule disassembly is necessary to "pull" the sister chromatids to opposite poles -during anaphase of mitosis. If this process is blocked, the cell can't continue with the cell cycle and will eventually die. -Most cells in our bodies are not actively dividing so they are not affected. -Cancer cells are actively dividing (going through the cell cycle) so they are affected. -Blood cells and the cells lining our intestinal tract are two cell types in our bodies that are actively dividing and these will be affected (explaining the side-effects of nausea and anemia experienced during chemotherapy).

Do cancer cells exhibit either density‐ dependent inhibition or anchorage dependence?

-NO -do not heed normal signals that regulate the cell cycle -divide excessively and invade other tissues

Genome

-a cell's endowment of DNA, its genetic information

Cell cycle control system

-a cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle -checkpoint in cell cycle is a control point where stop and go-ahead signals can regulate the cycle -Animal cells have built‐in stop signals so that the cycle is halted unless the proper go‐ahead signal is received.

MPF

-a cyclin Cdk complex that triggers the cell's passage past the G2 chcekpoint into the M phase (M-phase promoting factor)

Mitosis

-a process of nuclear division that conserves chromosome number by equally allocating replicated chromosomes to each of two daughter nuclei

Binary fission

-bacterial cell division

Interphase

-chromosome duplication and growth phase of the cell cycle -part of the cell cycle that includes G1, S, and G2 phases

Density-dependent inhibition

-contact inhibition; a phenomenon in which crowded cells stop dividing

Cdk

-cyclin dependent (active only when bound to cyclin protein kinase)

Cytokenisis

-division of the cell cytoplasm to form two daughter cells

Mitotic spindle

-fibers of microtubules and associated proteins that guide assortment of chromosomes during mitosis and meiosis

Evolution of mitosis

-given that prokaryotes preceded eukaryotes on Earth, we might hypothesize that mitosis evolved from simpler prokaryotic mechanisms of cell replication -as eukaryotes evolved, along with their larger genomes and nuclear envelopes, the ancestral process of binary fision, somehow gave rise to mitosis -fig 12.13 page 237 show some variations on cell division in different groups of organisms -possible intermediate stage are suggested by two unusual types of nuclear division found today in certain unicellular eukaryotes---dinoflagellates, diatoms, and some yeasts -thought to be cases where ancestral mechanisms have remained relatively unchanged over evolutionary time -nuclear envelope remains intact in both types...contrast to what happens to most eukaryotic cells

Functions of Cell division

-growth and development -tissue renewal

Internal and external signals at checkpoints in the cell cycle

-growth factor (external) -nutrient levels (external) - PDGF (platelet‐derived growth factor) (external) -density-dependent inhibition...crowded cells stop dividing once a single layer of cells is formed in the inner surface of culture container -anchorage dependence

Cancers

-malignant tumors ̶ Usually arise from a single transformed cell (transformation: process that converts a normal cell to a cancer cell)

MPF continued

-mpf causes phosphorylation of various proteins of nuclear lamina -during anaphase, MPF helps switch itself off by initiating a process that leads to destruction of its own cyclin

Chromatid

-one copy of a duplicated chromosome

Do prokaryotes undergo mitosis?

-prokaryotes (bacteria and archae) can undergo a type of reproduction in which the cell grows to roughly double its size and divides to form two cells -binary fission

Growth factor

-protein released by certain cells that stimulates other cells to divide -researches have discovered more than 50 growth factors -different cell types respond specifically to different growth factors or combinations of growth factors

PDGF

-released by blood platelets ̶ required for growth and replication of fibroblasts (connective tissue cells) ̶ contributes to repair following a tissue injury

Chromosomes

-replication and distribution of so much DNA is manageable because the DNA molecules are packaged into these structures -consist of one very long, linear DNA molecule associated with many proteins

Meiosis

-reproduction -a 2 stage type of cell division that equally allocates chromosomes to gametes such that each receives half the chromosome number of the original cell

Gametes

-reproductive cells -sperm and eggs -have half as many chromosomes as somatic cells -one set of 23 chromosomes in humans

G1 checkpoint

-restriction point in animal cells -is most important

Cell plate

-structure formed in the middle of plant cells during cytokinesis by the coalescence of vesicles derived from the Golgi apparatus

Kinetochore

-structure of proteins and specific section of DNA at the centromere and chormosomes

Telomeres

-tandomly repetitive DNA sequence at the end of eukaryotic chromosomes

Chromatin

-the entire complex of DNA and proteins that is building material of chromosomes

Cleavage furrow

-the first sign of cytokinesis; a shallow groove in the cell surface near the old metaphase plate

Anchorage dependence

-to divide, animal cell smust be attached to a substratum such as the inside of a culture jar or extracellular matrix of a tissue

Describe the replication of prokaryote chromosome

1. chromosome replication begins. Soon after, one copy of the origin moves rapidly toward the other end of the cell by a mechanism not fully understood yet 2. replication continues. One copy of the origin is now at each end of the cell. Meanwhile, the cell elongates 3. replication finishes. The plasma membrane grows inward, and a new cell wall is deposited 4. two daughter cells result

A chicken has 78 chromosomes in its somatic cells. How many chromosomes did the chicken inherit from each parent? How many chromosomes are in each of the chicken's gametes? How many chromosomes will be in each somatic cell of the chicken's offspring?

39; 39; 78

How many chromosomes will each daughter cell have?

4

How many chromosomes?

4

How many chromatids are shown in this cell?

8

A particular cell has half as much DNA as some other cells in a mitotically active tissue. The cell in question is most likely in a.G1 b. G2 c. Prophase d. Metaphase e. Anaphase

A

In the cells of some organisms, mitosis occurs without cytokinesis. This will result in a. cells with more than one nucleus b. cells that are unusually small c. cells lacking nuclei d. destruction of chromosomes e. cell cycles lacking an S phase

A

Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to a. disruption of mitotic spindle formation b. inhibition of regulatory protein phosphorylation c. suppression of cyclin production d. myosin denaturation and inhibition of cleavage furrow formation e. inhibition of DNA synthesis

A

What is the difference between a haploid cell and a diploid cell?

A haploid cell has only one set of chromosomes. A diploid cell has two sets of chromosomes. In humans, the somatic cells are diploid, and the gametes are haploid.

What are kinetochores?

A structure of proteins associated with specific sections of chromosomal DNA at each centromere.

Cancer cell division

Are "immortal" in cell culture ̶ Normal cells divide only 20‐50 times in culture and then stop dividing ("age", enter G0). ̶ Cancer cells can keep dividing in culture indefinitely as long as they are provided with the proper nutrients.

Through a microscope, you can see a cell plate beginning to develop across the middle of a cell and nuclei forming on either side of the cell plate. This cell is most likely a. an animal cell in the process of cytokinesis b. a plant cell in the process of cytokinesis c. an animal cell in the S phase of cell cycle d. a bacterial cell dividing e. a plant cell in the metaphase

B

Which of the following does NOT occur during mitosis? a. condensation of chromosomes b. replication of the DNA c. separation of sister chromatids d. spindle formation e. separation of the spindle poles

B

One difference between cancer cells and normal cells is that cancer cells a. are unable to synthesize DNA b. are arrested at the S phase of the cycle c. continue to divide even when they are tightly packed together d. cannot function properly because they are affected by density-dependent inhibition e. are always in the M phase of the cycle

C

The decline of MPF activity at the end of mitosis is due to a. the destruction of the protein kinase Cdk b. decreased synthesis of Cdk c. the degradation of cyclin d. the accumulation of cyclin e. synthesis of DNA

C

Prophase

Chromatin fibers become more tightly coiled, condensing into chromosomes. The nucleoli disappear. The mitotic spindle begins to form. The centromeres move away from each other.

The drug cytochalasin B blocks the function of actin. Which of the following aspects of the animal cell cycle would be most disrupted by cytochalasin B? a. spindle formation b. spindle attachment to kinetochores c. DNA synthesis d. cell elongation during anaphase e. cleavage furrow formation and cytokinesis

E

During which stages of the cell cycle does a chromosome consist of two identical chromatids?

From the end of S phase in interphase through the end of metaphase in mitosis

• Most cells in an adult human are in...?

G0

Checkpoints located in

G1, G2, and M

A cyclin complex that triggers the cell's passage past the G2 checkpoint into the M phase is known as _____

M-phase promoting factor or MPF

Describe what happens in each phase of cell cycle

MITOTIC PHASE (M): includes both mitosis and cytokinesis, usually the shortest part of the cell cycle. INTERPHASE: often accounts for about 90% of the cell cycle. During interphase, a cell that is about to divide grows and copies its chromosomes in preparation for cell division. Interphase can be divided into subphases: the G1 Phase, the S Phase and the G2 Phase. G1 PHASE: A cell grows, first gap S PHASE: continues to grow as it copies its chromosomes, synthesis. G2 PHASE: grows more as it completes preparations for cell division, second gap. M PHASE: cell divides.

MPF..how does it relate to the cell cycle?

MPF (maturation promoting factor, "M‐phase promoting factor") • First cyclin‐Cdk complex discovered • Triggers cell's passage past G2 checkpoint into M phas -peaks of MPF activity correspond to peaks of cyclin concentration -MPF acts directly as a kinase and indirectly by activating other kinases

Cell cycle regulation continued

Mitosis doesn't continue unchecked in a normal plant or animal. • Skin cells continue to divide throughout life. • Blood cells continue to divide throughout life. • Liver cells can divide ("regenerating liver") when necessary. • Nerve cells and muscle cells don't divide in a mature human

Cyclin

So‐called because of its cyclical fluctuating concentration in the cell -Activity of a Cdk rises and falls with the changes in concentration of its cyclin partner

If "go-ahead signal is not received...

The cell enter G0 ("exits" the cell cycle; non dividing state)

Is the cell diploid or haploid? How do you know?

The cell is diploid. There are two larger chromosomes that are exactly the same size and shape so we can assume that they are homologues and there are two smaller chromosomes that are exactly the same size and shape so we can assume that they are homologues. Thus, this cell is diploid and has four chromosomes (2n = 4).

At what stage of the cell cycle is the cell shown (question 3 of critical thinking worksheet)

The cell is in metaphase of the mitotic (M) phase. The chromosomes have been duplicated (sister chromatids are shown), condensed, and lined up at the metaphase plate.

What is the mitotic spindle composed of, and what is its function?

The structure consists of fibers made of microtubules and associated proteins. Its function is to organize the chromosomes using microtubules and centrosomes.

A particular cell in a mtitotically active tissue has half as much DNA as most of the surrounding cells. This particular cell is most likely in which stage of the cell cycle? In what stages of the cell cycle are most of the surrounding cells?

The surrounding cells have duplicated (doubled) their DNA so are past S phase of interphase -have not yet completed cytokinesis of mitotic phase (where the amount of DNA in a cell would be halved). -Thus, the surrounding cells are either in G2 or in M phase prior to completion of M phase. -The particular cell must be in G1 (prior to replication/duplication in S phase).

How are sister chromatids held together?

They are held together by the centromere. It's condensed DNA and very important in cell division

Describe the movement of the chromosomes through the stages of mitosis.

They move towards the poles rather than the poles toward the chromosomes

Can cells be called back into the cell cycle?

Yes, some can be called back by environmental cues (e.g., growth factors released during injury)

Tumor

abnormal growth of tissue

Metaphase

centrosomes are now at opposite poles of cell the chromosomes convene at the metaphase plate for each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles

The phenomenon in which crowded cells stop dividing is called

contact inhibition or density-dependent inhibition

A process of nuclear division that conserves chromosome number by equally allocating replicated chromosomes to each of two daughter cells is called

mitosis

The human genome is described as n=23, where n is the number of chromosomes in our genmore. Since we are diploid organisms, our somatic cells have 2n or 46 chromosomes and our gametes are haploid and have 23 chromosomes. What would the n be for the cell shown (on critical thinking worksheet)?

n=23

Prometaphase

nuclear envelope fragments microtubules extending from each centrosome can now invade nuclear area chromosomes have become even more condensed each of the two chromatids of each chromosome now has a kinetochore some of the microtubules attach to the kinetochores nonkinetochore microtubules interact with those from opposite pole of the spindle

Draw one eukaryotic chromosome as it would appear during interphase, during each of the stages of mitosis, and during cytokinesis. Also, draw and label the nuclear envelope and any microtubules attached to the chromosomes

see A-11 of book

In the light micrograph on page 245 of dividing cells near the tip of an onion root, identify a cell in each of the following phases: prophase, prometaphase, metaphase, anaphase and telophase.

see book

Benign tumor:

self‐contained, noncancerous growths that do not spread to other tissues (are not metastatic) and are not invasive. May cause problems by growing and interfering with function of neighboring organs

Anaphase

shortest stage of mitosis begins when cohesion proteins are cleaved two liberated daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten cell elongates as the nonkinetochore microtubules lengthen by the end of anaphase, the two ends of the cell have equivalent and complete collection of chromosomes

If "go-ahead" signal is received...

the cell will divide

Telophase

two daughter nuclei form in the cell nuclear envelopes arise from fragments of parent cell's nuclear envelope and other portions of endomembrane system nucleoli reappear chromosomes become less condensed remaining spindle microtubules are depolymerized mitosis, is now complete

Nutrient levels

‐ cells in culture fail to divide if an essential nutrient is omitted

Evidence for cytoplasmic molecular signals in cell‐ cycle regulation:

• Fusion of a cell in S phase with a cell in G1 • The G1 cell nucleus immediately entered S phase