Cell Division

Question 1

why is cell replication important?

Answer 1

Restoring nucleus-to-cytoplasm ratio
Too much cytoplasm for the nucleus to control so must divide.

Growth and Development
Organisms grow in size by getting more cells.

Tissue maintenance and repair
Cells become damaged or die and need to be replaced.

Question 2

what is mitosis?

Answer 2

division of nucleus into two daughter nuclei .

Question 3

what is cytokenisis?

Answer 3

division of cytoplasm and organelles.

Question 4

is meiosis replication?

Answer 4

Meiosis is not cell replication because daughter cells are different from each other and from the parent cell. Needed in sexual reproduction.

Question 5

how do cells replicate in prokaryotes? why is it quicker?

Answer 5

Binary fission
Before it has just one DNA molecule.
(and 3) DNA molecule is duplicated within the nucleoid.
(and 4) cell almost doubles in size.
Two DNA molecules are pulled to separate poles as the cell grows.
A new cell wall and membrane form between the separating chromosomes, dividing the cell.
Less organelles and chromosomes

Question 6

what is the interphase? when does it happen? what happens? how long? are chromosomes visible?

Answer 6

First stage.
Begins immediately after cell division.
Grows larger, copies chromosomes in preparation.
Grows by producing proteins and organelles.
Interphase lasts much longer than mitosis (about 2 hours).
Interphase can be weeks or years in longer developing cells.
Chromosomes are bot visible.

Question 7

what is the G1 stage?

Answer 7

Daughter cell is quite small.
Carries out everyday functioning and grows.
Increases numbers of organelles.

Question 8

what is the G0 stage?

Answer 8

Resting phase.
Carry out normal functioning.
Temporary and ends when cell reenters G1 phase.
Some like RBC are always in G0 phase and never replicate.

Question 9

what is the S phase?

Answer 9

Synthesis of chromosomes.
Each strand of replicated chromosome is called a chromotid.
The amount of DNA in the cell doubles.
Number of chromosomes remains the same.

Question 10

what is the G2 Phase?

Answer 10

Another stage of growth and energy acquisition.

Prepares for division by creating proteins etc.

Question 11

in terms of the cell cycle, what is mitosis? what are the stages?

Answer 11

Division of the nucleus. PMAT

Question 12

what is prophase? what happens?

Answer 12

Chromosomes condense (shorten and thicken) and become visible.
Each chromosome is two chromatids held by a centromere.
Centrioles (replicated during interphase) move to opposite sides of the cell and from poles.
Spindle begins to form.
Nuclear membrane breaks down.
Centromeres attach to spindle.

Question 13

what is the metaphase?

Answer 13

Centromeres attack to spindle.
Aligned at middle of cell.
Chromosomes are visible.

Question 14

what is the anaphase?

Answer 14

Spindle pull centromere apart.

Chromatids are pulled to opposite poles.

Question 15

what is the telophase?

Answer 15

Nuclear membrane reforms around two sets of chromosomes.

Spindle disappears, chromosomes become longer and thinner.

Question 16

what is cytokinesis? what happens in plants?

Answer 16

Cytoplasm divides and nuclei separate.
Plasma membrane move inwards, pinching cells apart.
In plant cells a cell plate is put in first.
In some cells cytokinesis does not occur and the cell is large and has many nuclei- coenocyte.

Question 17

why does cell division need to be controlled?

Answer 17

Without control, there would be too many cells.

Question 18

what is a mutation? what happens if a mutation is detected? what determine when the cell cycle stops? when are these checkpoints?

Answer 18

Mutation: genetic abnormality.
If mutation occurs the cell needs to be repaired or the cycle stopped.
Regulatory proteins (part of the internal regulation system) determine when the cell cycle stops.
This is known as cycle control system.
These proteins are at G1, G2 and metaphase.

Question 19

what happens in the G1 checkpoint? when?

Answer 19

Towards end of G1.
Checks that there are adequate resources for the cell to divide, the cell is large enough and that the DNA is not damaged.

Question 20

what is the G2 checkpoint? when does it happen?

Answer 20

End of G2.
Checked for resources and cell size.
DNA is checked to have replicated without mistakes or damage.

Question 21

what is the M checkpoint? what happens?

Answer 21

End of metaphase.
known as spindle checkpoint.
Checks that spindle fines have connected correctly and aligned at the equator.

Question 22

what are external cell cycle controls?

Answer 22

Signals from outside: contact inhibition (crowding), molecules called mitogens which stimulate division (hormones etc.), some can bring cells back to resting (G1), environmental conditions (pH).

Question 23

how is DNA repaired?

Answer 23

Enzymes detect and repair damage to DNA.

Run along DNA and check.

Question 24

why might a cell need to die?

Answer 24

Cells may be only needed temporarily or be damaged.

When DNA is damaged, a cell cannot function.

Question 25

what is apoptosis? what happens? why does it happen?

Answer 25

Programmed death.
Enzymes are activated that cause death.
Cell shrinks and separates from adjoining cells.
Cell surface buds to form apoptotic bodies which have cytoplasm, organelles and chromatin.
Phagocytic cells remove these.
Make sure only good cells divide.

Question 26

what is necrosis? why might this happen?

Answer 26

Accidental cell death.

Physical damage or lack of oxygen or lysis.

Question 27

what are limited mitotic divisions? how does this work?

Answer 27

A control that counts the number of divisions that have occurred in a line of cells.
Cells usually die after a certain number of divisions.
Seem to do this by losing a small amount of DNA from the tips of chromosomes (telomeres) after each division.
After about 50, there are no tips left and they stop dividing or enter apoptosis.

Question 28

what is uncontrolled cell division? what happens in an embryo or in an adult? what are the three types?

Answer 28

In an embryo: be abnormal and usually abort.
In a mature organism: a neoplasm may form.
Neoplasm: abnormal growth of tissue that usually forms a mass (tumour).
Three types:
benign: do not spread or become cancer. Divide uncontrollably but not as fast as malignant. Grows in a capsule that contains it.
Potentially malignant: form localised masses that invade and transform into cancer.
Malignant: form masses and invade tissues and transform into cancer. Breaks out of capsule.

Question 29

what are genetic factors that control cell division?

Answer 29

Genes code for enzymes that regulate.

Mutations in genes stop this.

Question 30

what are Proto-oncogenes? what do they do? what can mutations do to them? types?

Answer 30

Normal genes involved in regulation of cell division.
Stimulate cell growth.
mutations cause oncogenes which induce uncontrolled divisions- neoplasms. tumour-suppressor genes and inherited genes

Question 31

what are tumour suppressor genes?

Answer 31

Genes that code for proteins involved in the slowing of cell division, repair of DNA or apoptosis.
if changed uncontrolled divisions may occur.

Question 32

what inherited genes?

Answer 32

Genetic predisposition for cancer.

Receive oncogene or mutated tumour-suppressor gene.

Question 33

what are environmental factors that can cause disruptions?

Answer 33

Chemical
Tabacco.
Chemicals in air pollution.

Physical
X-rays
UV light

Biological
Some viruses.

Question 34

what happens when the immune system becomes weak?

Answer 34

Detects and destroys abnormal cells including those replicating uncontrollably.
If weakened, they may not be detected and destroyed.