Interphase, mitosis, and cytokinesis (1)

Question 1

What are the three phases of a cell’s life cycle?

Answer 1

1. Interphase
2. Mitosis
3. Cytokinesis

Question 2

What are the three reasons for cell division? (TAG)

Answer 2

1. Tissue repair
2. Asexual reproduction (simple eukaryotes)
3. Growth

Question 3

What is needed for a cell to divide?

Answer 3

1. Copy DNA: interphase
2. Separation of DNA: anaphase
3. Separation of cell parts: telophase + cytokinesis
4. Split into two cells: cytokinesis

Question 4

Describe the order of mitosis (Penises Make A Tent), what happens during each process, and what is ultimately produced as a result.

Answer 4

1. Prophase: chromatin winds up to become chromosomes, nuclear membrane breaks down, centrioles migrate to opposite poles of the cell, nucleolus disappears, spindle fibres begin to form.
2. Metaphase: sister chromatids line up along the equator, spindles are attached to centromeres.
3. Anaphase: sister chromatids separate and move to opposite sides of the cell.
4. Telophase: chromosomes reach poles, cell membrane (cell plate in plants) begins to form, two cells begin to divide, two nuclear membranes (at poles) and nucleoli (in nucleus) reform, spindle fibres disintegrate, cell elongates for cytokinesis

Two identical daughter cells are produced by mitosis.

Question 5

Wild carrrrrd! Go draw a labelled diagram of interphase and at least two steps of mitosis, and in chronological order too :) make sure not to make it too simple or complex and trip yourself up!

Some important labels (not for all stages):
- Nucleolus
- Centromeres
- Centrioles
- Sister chromatids
- Nuclear membrane
- Spindle fibres
- Cleavage furrow
- Nuclear envelope
- Chromatin

Question 6

What is the formula for the mitotic index?

Answer 6

(P + M + A + T)/(total # of cells) or (# of cells during mitosis)/(total # of cells)

Letters here refer to the number of cells at each stage.

Question 7

Define cytokinesis. What differs about it and mitosis in animal cells vs plant cells?

Answer 7

It is the division of the parental cytoplasm between two daughter cells after mitosis (usually beginning in telophase).

The mitosis process in animal and plant cells differs because plant cells do not have centrioles. The cytokinesis process in animal and plant cells differ because plant cells have a cell wall.

In animal cells:
1. Microfilaments form around the cell center.
2. They constrict, causing the cleavage furrow.
3. The cell is pinched apart apart by the microfilaments and two cells form.

In plant cells:
1. Vesicles form around the cell center.
2. They fuse and a cell plate starts to form.
3. The cell plate finishes forming, creating two separate cells.

Question 8

Describe each stage of interphase, and where it takes place.

Answer 8

G1 (in cytoplasm): the cell grows due to rapid protein synthesis and functions normally. Proteins for DNA synthesis are created. Mitochondria and chloroplasts (for plant cells) are replicated. (GROWTH)

S (in nucleus): DNA amounts double as DNA replication takes place, and genetic material is duplicated (SYNTHESIS)

G2 (in cytoplasm): Protein synthesis produces proteins needed for cell division (e.g. microtubules for spindle fibres). Cell prepares for cell division. (PREPARATION TO DIVIDE)

(Extra note: remember that both G stages take place in the cytoplasm!)

(For what happens during each stage: Ginormous Sized Penis)

Question 9

Wild carrrrrd! Go make sure you can label each part of the cell cycle diagram! (Not the actual intricacies of the stages themselves)

Question 10

Summarize the discovery of cyclin and the type (Hint: it starts with an ‘s’ and it’s not a very scientific word) of discovery that it was

Answer 10

Tim Hunt was studying control of protein synthesis sea urchin eggs, and noticed that during fertilization a certain protein was in high concentration. After fertilization, it dropped, though all other proteins in the cell continued to rise due to rapid cell division. This protein was called cyclin, and this was a serendipitous discovery!

(Serendipitous discoveries are unintentional but fortunate).

Question 11

Describe the cycle of mitotic cyclins during cell division.

Answer 11

When cyclins are accumulated (during G2), the Mitosis Promoting Factor (MPF) is formed, and the cell is signalled to enter mitosis

When the cyclin degrades, MPF is deactivated, and the cell exits mitosis and divides.

Question 12

What factors control cyclin levels?
(Shit Exits Rectum)

Answer 12

1. Cell size (SIZE)
2. Completion of DNA replication (REPLICATION)
3. Cellular environment (ENVIRONMENT)

Question 13

How is cyclin-dependent kinase used in regulating mitosis?

Answer 13

Cyclins bind to enzymes called cyclin-dependent kinases (CDKs) and activate them. The activated CDKs phosphorylate other proteins in the cell. This enables the other proteins to become active and carry out tasks for whatever phase of the cell cycle.

Phosphorylation: to attach phosphate groups to

Question 14

Wild carrrrrd! Go find the cyclin expression cycle and study it until you know which curve is which!

Question 15

How does the mitotic index differ in different cells?

Answer 15

Certain types of cells have a higher mitotic index based on their location and/or function (e.g. root tips divide at a higher rate than root base). Whether the mitotic index is good or bad for the cell depends on the type of tissue.

Question 16

Define cancer in scientific terms.

Answer 16

Cancer is an abnormal growth of cells caused by mutations in gene expression, and leading to cell proliferation. More cells produce than die off. They grow and divide uncontrollably, forming malignant tumors, and often develop the ability to spread around the body.

Question 17

What is the difference between a benign and malignant tumor?

Answer 17

Benign: non-invasive and grows only locally
Malignant: Invasive; invades neighboring tissue and metastasizes.

Metastasis: When cancerous tumors spread from their local site to other areas around the body

Question 18

What is the abundance of division cycles in normal cells, and how is cyclin involved with it?

Answer 18

Normal cells usually undergo a limited number division cycles, depending on limiting factors like space or nutrient levels.
This is regulated by cyclin levels.

Question 19

How does cancer commonly travel?

Answer 19

Through the blood or lymphatic system.

Question 20

Describe oncogenes.

Answer 20

They are mutated genes that contribute to the development of cancer but also help to drive the cell cycle forward.

In their normal state, genes that code for the proteins controlling the cycle are called proto-oncogenes. When they change into oncogenes, their abnormal protein products exhibit increased activity that contributes to tumor growth.

Instead of stopping within a G phase as usual, a tumor cell continues to progress through the following stages of the cell cycle, causing uncontrolled cell division. This can rescue cells from apoptosis.

Question 21

Define tumor suppressor genes and state what happens if they are mutated.

Answer 21

Tumor suppressor genes produce proteins that regulate cell division. When mutated, a tumor suppressor gene cannot function properly, and uncontrolled cell growth may occur. This results in a risk of cancer.

Question 22

Define mutagens and carcinogens, and list two examples of carcinogens.

Answer 22

Mutagens are physical/chemical agents that cause change to genetic material (DNA or RNA).

Carcinogens are mutagens that lead to the development of cancer.

(There are a lot, but diesel exhaust, wood dust, UV radiation, and tobacco smoke are all easy to remember!)

Question 23

Wild carrrrrd! Go annotate a diagram of cyclin regulating mitosis, or at least inspect one closely :)

https://classroom.google.com/c/NDk4MzE3OTM5NTA3/m/NTU0NjM4MjE4NzYy/details