Lecture VIII: Mitosis and the Cell Cycle

Question 1

Why do living organisms need cell division?

Answer 1

Reproduction: creating a new organism (offspring)

Growth and Development: Get bigger and mature into an adult.

Replace old and damaged cells to maintain healthy tissues.

Question 2

Two types of cell division (eukaryotic cells):

Answer 2

Mitosis: responsible for growth, development and replacement of old and damaged cells in multicellular eukaryotes as well as asexual reproduction in unicellular eukaryotes and a few multicellular ones.

Meiosis: responsible for creating gametes (sperm and eggs) for sexual reproduction.

Question 3

What is Mitosis?

Answer 3

Unicellular eukaryotes, most protists and some fungi, can create clones of themselves through mitotic cell division.

A paramecium replicates its DNA and then divides into 2 genetically identical daughter cells.

Question 4

What is chromatine and chromosomes?

Answer 4

Chromosomes
= DNA during cell division
 chromatin tightly coiled around proteins

Chromatin
= DNA when cell is not dividing
 long thin threads

Question 5

Somatic cells vs. Gametes?

Answer 5

Somatic Cells
- All of the cells that make up the tissues of our bodies (ex. Muscle, bone, fat…)
Have 46 chromosomes (Two sets of 23 unique chromosomes, one set from each parent)

Gametes (sex cells)
- Specialized reproductive cells, eggs and sperm
Have only 23 chromosomes (all unique in kind)

Question 6

What is a gene? What is a locus?

Answer 6

A gene is a section of DNA on a chromosome that determines a specific characteristic in the organism (e.g hair colour, height, nose shape etc…) through protein synthesis.
The exact location on the chromosome that the gene resides. The locus for a gene does not change. For example the locus for the flower colour gene will be on the same chromosome and in the same position for all plants of that species.

Question 7

Karyotype:

Answer 7

An organized profile of an organism’s chromosomes.

Question 8

Autosomal Chromosomes (Autosomes)

Answer 8

All chromosomes that are not related to sex determination are autosomal chromosomes.
Humans have 22 pairs of autosomes.

Question 9

Sex Chromosomes

Answer 9

Chromosomes involved in sex determination

In humans, males have 2 different sex chromosomes (XY) where as females have 2 of the same sex chromosome (XX)

Question 10

What is conception?

Answer 10

Fertilization of an egg by a sperm.
One sperm cell enters the egg cell and their nuclei fuse together forming one nucleus containing both sets of chromosomes.

This new cell is called a Zygote.
sperm has 23 chromosomes, egg has 23, the zygote will have 46.

Question 11

What type of cells undergo mitosis?

Answer 11

Stem cells.\
Example: Basal epithelial cells (a type of stem cell) undergo repeated mitotic cell divisions to replace cells that get sloughed off on the surface of our skin.
Whereas, neurons in the brain will never undergo a mitotic cell division.

Question 12

The cell cycle phases?

Answer 12

Whereas, neurons in the brain will never undergo a mitotic cell division.

Interphase: (95% time, cell grows and DNA is replicated)
long phase
Cell growth
DNA replication

Mitotic Phase: (5% of time, division to 2 identical daughter cells)
Short phase
Division of replicated chromosomes equally into 2 daughter cells.

Question 13

3 Stages of Interphase?

Answer 13

3 distinct stages:

Growth 1 (G1)
Synthesis (S)
Growth 2 (G2)

Question 14

Growth 1 (G1)

Answer 14

Begins as soon as daughter cells are formed.

period of active growth

cell increases in size

extensive synthesis of new organelles (normal metabolism), eventually reaches mature size for cell type.
Cells that will not divide complete this stage of the cell cycle and then stop in G0.

Question 15

Synthesis (S)

Answer 15

During the synthesis stage an exact copy of each chromosome is made.

The new copy of each chromosome remains attached to the original and is now called a replicated chromosome.
(goes from a stick to an X shape, but keep in mind that in this stage, it is in chromatin (mess) form)

Question 16

Centromere?

Answer 16

The identical copies of a chromosome remain attached at a midpoint called the centromere.

Question 17

Sister chromatid vs. chromatid vs. non- sister

Answer 17

Each copy of a chromosome is now referred to as a chromatid. Chromatids attached by a centromere are identical and are called sister chromatids.
Chromatids not attached by a centromere (on different replicated chromosomes) are called non-sister chromatids.

Question 18

Growth 2 (G2)

Answer 18

The cell continues to grow.
The cell prepares for the mitotic phase by replicating the centrosome.
Spindle fibers also begin to form.

At the end of the G2 stage of Interphase the cell has:

Replicated chromosomes
Two centrosomes
Spindle fibers forming

Question 19

Steps of the mitotic phase

Answer 19

There are 2 steps in the mitotic phase:

Mitosis
  Division of the replicated chromosomes
  Occurs in 4 distinct stages:
    Prophase
    Metaphase
    Anaphase
    Telophase

Cytokinesis
Division of the cytoplasm into 2 identical
daughter cells.

Question 20

Prophase

Answer 20

Chromatin condenses into chromosomes.
Centrosomes migrate to opposite ends (poles) of the cell.
Nuclear envelope breaks down.
Spindle fibers extend out from the cetrosomes into the middle of the cell where the chromosomes are and attach to their centromeres.

Question 21

Metaphase

Answer 21

Replicated chromosomes align on the cell’s midline (metaphase plate) with one sister chromatid on either side.

Each replicated chromosome is attached at their centromere (kinetochore proteins) by spindle fibers which extend from both centrosomes.

Question 22

Anaphase

Answer 22

Spindle fibers pull the sister chromatids apart at their centromeres.
Sister chromatids are pulled to opposite poles of the cell.
The cell elongates.
At the end of Anaphase, each pole has 1 copy of every chromosome that existed in the parent cell.

Question 23

Telophase

Answer 23

Chromosomes amass at each pole and begin to loosen.
Nuclear membranes form around each group of chromosomes.
Spindle fibers break down.

Question 24

Cytokinesis

Answer 24

Last step of the mitotic phase
Cytokinesis is the division of the original cell into two daughter cells. Occurs at the same time as telophase.
Basically, the parent cell pinches around it’s midline until 2 new cells are made.

Question 25

Cytokinesis In plant cells

Answer 25

Daughter cells are separated by the growth of a cell plate in between them that becomes the new cell wall.

Question 26

Binary Fission?

Answer 26

Binary Fission: Cell Division resulting in 2 organisms(a form of Asexual Reproduction)

Binary fission by single celled eukaryotic organisms uses the process of mitosis.

Binary fission by prokaryotes (Bacteria and archaea) does not involved mitosis.

The single loop of DNA is replicated from a starting point (origin) in both directions moving toward opposite ends of the cell.
   The cell elongates during DNA replication.
   The plasma membrane pinches in the middle to separate the 2 daughter cells.

Question 27

Cell Cycle Regulation?

Answer 27

The cell cycle is very tightly controlled.

At specific times, the cell checks itself to make an assessment if everything is OK. This is a CHECKPOINT.

If everything looks OK, the cycle continues to the next stage.

Question 28

What is Apoptosis

Answer 28

If a cell does not pass a checkpoint, and the problem cannot be fixed, it will undergo apoptosis.

Apoptosis is programmed cell death.

Question 29

What is the Purpose of Checkpoints?

Answer 29

Without the cell checkpoints:

Damaged cells would continue to be replicated; these cells would most likely have impaired function.

Cells that have damaged genes that regulate the timing of cell division can develop into cancer. Cancer cells grow and divide excessively.

Question 30

What is cancer and what causes it?

Answer 30

A disease in which body cells escape the control methods that normally regulate cell growth and division.

Mutations:
changes in the DNA sequence from what is normal. Cancer causing mutations occur in genes that control rate of cell growth and division.
Due to:
Errors during DNA replication
Exposure to environmental mutagens such as radiation, chemicals and certain viruses

Question 31

What is a tumor?

What are the two types of tumors?

Answer 31

An abnormal growth of cells.
Not all tumors are considered cancer.

1.Benign Tumors
Non-cancerous
Remain localized
May be removed
Not usually life threatening

2.Malignant Tumors
Cancerous. Invades body tissues and often affects the functioning of organs.
Can spread to other areas of the body (metastasis)
May be removed or treated with radiation or chemotherapy.
Often life threatening

Question 32

What is metastasis?

Answer 32

The release of cancerous cells into the blood stream or lymph from the primary tumor. From there they can invade new tissues of the body.
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