Chapter 8

What is cell division?

When two daughter cells that are genetically identical to each other form from the original parent cell

What are chromosomes?

The structures that contain most of the cell’s genetic information in the form of DNA

How many sets of chromosomes do the daughter cells get?

One

How similar are the chromosomes of the daughter cells?

They are identical to the parent cell

What is asexual reproduction?

The creation of genetically identical offspring by a single parent without the participation of a sperm or egg

What is the principle of inheritance in asexual reproduction?

The long parent and each offspring have identical genes

What is sexual reproduction?

A type of cell division that occurs only in the reproductive organs using gametes, eggs, and sperm

What does a gamete give to the daughter cell?

It gives half as many chromosomes as the parent cell, which contain a unique set of genes

What is the difference between asexual and sexual reproduction?

Asexual reproduction is when cell division results in the reproduction of a whole organism, while sexual reproduction uses gametes, sperm, and eggs as well as other organs to reproduce.

What can sexual reproduction do?

Can produce great variation among offspring due to the unique set of genes that daughter cells get

What role does cell division play other than the production of gametes?

Enables sexually reproducing organisms to develop from a single cell into an adult organism

What is a zygote?

A fertilized egg

What happens to cells when an organism is fully grown?

Cell division continues to function in renewal and repair, replacing cells that die from normal wear or accidents

What is the process of cell division in asexual reproducers called?

Mitosis

What is the process of cell division in sexual reproducers called?

Meiosis

What is binary fission?

Cell division in prokaryotes

How is cell division done in prokaryotes?

Most genes are carried on one circular DNA molecule that makes the organism’s single chromosome

How does a prokaryotic chromosome compare to a eukaryotic one?

It is typically much shorter and has fewer genes

What are the steps of binary fission?

First, the chromosome must duplicate and separate, then the cell elongates, and divides into two daughter cells

Where are the genes of a human found in the cell?

In the nucleus

How many chromosome does a human have?

46 (23 unique ones)

What does a eukaryotic chromosome consist of?

One long DNA molecule bearing many genes and proteins attached to DNA

What is chromatin?

The long thin fibers of DNA and protein that would normally be too long to fit in the nucleus

Why do chromosomes have to be coiled and compacted when dividing?

The DNA must be compact into manageable packages to make them more easily transported

Why is DNA and protein attached to the chromosome during cell division?

To maintain the chromosome’s structure and regulate its genes

What are the copies of chromosomes called?

Sister chromatids

How are the sister chromatids connected?

In the middle with the centromere

What happens to chromatids during cell division?

They are split and considered now individual chromosomes identical to the parent. Each chromatid goes to a different daughter cell so that each daughter cell has a complete and identical set of chromosomes.

Why does all life depend on cell division?

Cell division is the basis of reproduction for every organism by allowing it to grow to its adult size and replace damaged cells

What is the cell cycle?

An ordered sequence of events that run from the instant a cell is first formed from a dividing parent cell until its own division into two cells

What stages does the cell cycle have?

Interphase (a growing stage) and mitotic phase (where the cell doubles everything)

What is the cell’s metabolic activity like during interphase?

It is very high as it performs normal functions

How long does interphase last?

For about 90% of the cell cycle

What are the subphases of interphase?

G1, synthesis, and G2 phases

What is the G1 phase?

Cellular contents, including chromosomes are duplicated

What is the S (Synthesis) phase?

Each of the 46 chromatids is duplicated

How long does the s phase last?

About half of interphase

What happens during the G2 phase

The cell checks the duplicated chromosomes for any errors and makes the needed corrections

What happens during the mitotic phase?

The cell physically divides

What are the stages of the mitotic phase?

Mitosis and cytokinesis

What is mitosis

The nucleus and its contents (ESPECIALLY the duplicated chromosomes) dividing and are distributed to the two daughter nuclei

What happens during cytokinesis?

Usually begins before mitosis ends, and cytoplasm is split into two

What does the combination of mitosis and cytokinesis produce?

Two genetically identical daughter cells

Where does mitosis occur?

It is unique to eukaryotes and is the evolutionary solution to the problem of allocating an identical copy of the whole set to two daughter cells

How accurate is mitosis?

It is extremely accurate

What are the stages of mitosis?

Prophase, prometaphase, metaphase, anaphase, and telophase

What is prophase?

In the nucleus, chromatin condenses into tightly coiled chromosomes. In the cytoplasm, mitotic spindles begin to form as microtubules grow out from the centrosomes

What is prometaphase?

Nuclear envelope fragments and disappears. Microtubules extend from the centrosomes into the nuclear region. Some spindle microtubules attach to kinetochores on each sister chromatid. Other microtubules meet those from the opposite poles

What is metaphase?

Mitotic spindle is fully formed. Chromosomes align in the middle. Kinetochores of sister chromatids are facing the opposite poles of the spindle

What is anaphase?

The chromosomes are pulled away from each other by the mitotic spindles to each side of the cells

What is telophase?

New nuclei form around chromosomes at each pole. Chromosomes uncoil into chromatin. The mitotic spindle disappears

What is the mitotic spindle?

A football shaped structure of microtubule fibers and associated proteins that guides the separation of the two daughter chromosomes

What happens with cytokinesis and telophase?

They usually overlap with one another

How does cytokinesis occur in animal cells?

It happens by cleavage

What is a cleavage furrow?

A shallow groove in the cell surface of an animal cell

What is at the site of the furrow?

A cytoplasm ring made of microfilaments that, when interacting with myosin, contract

What happens when the cytoplasm ring contracts?

The parent cell divides

Why is cytoplasm different in plant cells?

They possess stiff walls that prevent contraction

What happens during telophase in plant cells?

The vesicles containing the cell wall collect in the middle of the parent cell, then fuse to form a cell plate. When the plate grows outward, it will fuse with the plasma membrane and split the cell in half.

What is anchorage dependence?

Animal cells must be in contact with a solid surface to divide

What is density dependent inhibition?

A phenomenon in which crowded cells stop dividing

What is responsible for inhibiting cell division?

Physical contact between cells

What is another factor that can influence the rate of cell growth?

Chemical factors, like if an essential nutrient is not available for the cell

What are growth factors?

Certain proteins that are necessary for mammals to experience cell division

What is the importance of proper cell division?

Diseases like cancer can start forming

What do growth factors do for the cell?

They regulate and promote cell division

What is the cell cycle control system?

A set of molecules that both triggers and coordinates key events in the cell cycle

How does a stage like anaphase begin?

A protein of the cell cycle control system must trigger anaphase to begin

What are the checkpoints of the cell cycle?

The G1, M, and G2 subphase checkpoint

What happens during the checkpoints?

Intercellular signals detected by the control system tell the it whether key cellular processes have been completed

What does the G1 checkpoint do?

It is the most important, as it makes sure that the s phase can begin.

What happens without the G1 phase?

The cell will switch to a permanent nondividing state called the G0 phase

What is the G1 checkpoint?

Favorable conditions & DNA damage; allows entry into S phase

What is the G2 checkpoint?

Favorable conditions & errors in DNA replication; allows entry into Mitosis

What is the M checkpoint?

Anchorage of spindle assembly to chromosomes prior to anaphase; allows entry into Cytokinesis

How do checkpoints work?

A growth factor is binded to a receptor to trigger a signal transduction pathway, which conveys the message.

When does cancer begin?

When a cell has altered proteins

What is a tumor?

When an invading cell evades destruction from the body’s immune system and forms a mass of abnormally growing cells

What is a benign tumor?

A tumor that remains at its original site

What is a malignant tumor?

A mass of abnormally reproducing cells that spread to neighboring tissues

When is a person said to have cancer?

When they have a malignant tumor

What is metastasis?

The spread of cancer beyond its original site

How are cancer cells able to reproduce so quickly?

They might have defective cell cycles or no growth factors

How can tumors be treated?

There could be a surgery, or high energy radiation, or chemotherapy

What is chemotherapy?

IV drugs are administered which disrupt specific steps of the cell cycle

How can localized tumors be removed?

Surgically

How must metastatic tumors be treated?

Chemotherapy

What is immunotherapy?

Where the immune system is taught to recognize the cancer as foreign and attack it

How can one personalize cancer treatment?

By sequencing the DNA of tumor cells and tailoring treatment based upon the tumor’s specific genetic profile

What is a somatic cell?

A human cell that has 46 chromosomes

How many chromosomes does a somatic cell have?

23 unique sets of chromosomes

What do sister chromatids have in common?

Length, centromere position, and staining pattern

What are homologous chromosomes?

Two chromosomes of a matching pair, because each chromosome carries genes controlling the same inherited characters

How do homologous chromosomes compare to each other?

The gene for a specific trait may be located in the same place, but each chromosome may possess different versions of it

What affects a person’s appearance?

The sequence of genes, whether identical or different

What is an exception to homologous chromosomes?

X and Y chromosomes

What are X and Y chromosomes?

Sex chromosomes that differ in their genes and determine an individual’s sex (Only on in each person)

What are chromosomes other than sex chromosomes called?

Autosomes

What is locus?

When each chromosome of a homologous pair carry genes for the same characteristics at the same place

What are locus made of?

Each chromatid from each chromosome was inherited from either the mother or the father