cell growth, differentiation & cancer

Question 1

binary fission

Answer 1

process through which prokaryotes divide

Question 2

eukaryotic chromosomes

Answer 2

• Are linear in shape
• Have a constriction called the centromere
• Have a kinetochore which forms a part of the centromere
• Have ends called telomeres.
• Appear as a pair of strands when about to divide.
• Each strand = chromatid.
• Are a single stranded except when about to divide.

Question 3

kinetochore

Answer 3

a patch of protein where the spindle attaches which forms a part of the centromere

Question 4

centromere

Answer 4

Have a constriction called the centromere where spindle fibres attach before cell division occurs

Question 5

cell cycle

Answer 5

• ell division of eukaryotic cells is more complicated than in prokaryotes
• have checking systems to make sure replication of chromosomes and construction of new cells is performed accurately
  -defective cells destroyed

Question 6

mitosis

Answer 6

involves four phases of nuclear division and is followed immediately by division of the cytoplasm during cytokinesis.

Question 7

G1 phase

Answer 7

• Cell grows
• Organelles & proteins synthesized
• Contains the first checkpoint
• Cell is checked to ensure that it is ready to divide.
• Environmental conditions are assessed to ensure that they are suitable for division to take place.
  (Note: G stand for gap – a gap in the cycle of division.)

Question 8

S phase

Answer 8

• New chromosomes are synthesised in a process called DNA replication
• Chromosomes become double stranded
• Chromosomes are still loosely wound and are invisible even under a light microscope.
• centriole is duplicated in animal cells.

Question 9

G2 phase

Answer 9

• At the end of the G2 phase is another checkpoint.
  Checks are for:
• Cell size
• DNA replication
  If DNA damage is found:
• either repaired
• cell is forced to undergo apoptosis
  -if fine = cell divides

Question 10

prophase

Answer 10

• Chromosomes condense and appear
• Mitotic spindle begins to form
• In animal cells the spindle attaches to the centrioles at one end.
• Nucleolus disappears
• Nuclear membrane breaks down
• Some chromosomes become attached to the spindle

Question 11

metaphase

Answer 11

• All chromosomes attached to the spindle
• spindle attaches to the chromosomes at kinetochore
• Chromosomes line up across the equator
• division check occurs to ensure that the chromosomes are attached to the spindle and lined up correctly.

Question 12

anaphase

Answer 12

• Sister chromatids separate to either end of the cell
• cell starts to elongate
• cytoskeleton and a group of proteins which can move along the cytoskeleton, facilitate these movements.

Question 13

telophase

Answer 13

• chromosomes start to decondense.
• loosely wound form
• disappear from view.
• spindle breaks down and a nuclear membrane forms around each set of chromosomes.
• Nucleoli become visible in each nucleus.

Question 14

cytokinesis (not apart of mitosis)

Answer 14

• formation of the new nuclear membranes.
• begins during either anaphase or telophase.
• ends after mitosis is completed.
• In animals the plasma membrane pinches in and separates the cytoplasm
• In plants a cell plateforms down the middle of the cell
• The cell plate is the start of a new cell wall.
• New plasma membranes are also present around the cells.

Question 15

apoptosis

Answer 15

• the process that leads to the destruction of cells through an orderly process.
• Cells undergo apoptosis if they have finished their useful life
• Have DNA damage
• Have mitochondrial damage

Question 16

necrosis

Answer 16

• the death of cells in a disorderly manner.
• occurs as a result of mechanical damage (eg: a cut) or as a result of infection
• Necrosis results in inflammation and an immune response.

Question 17

capsases

Answer 17

• an enzyme
  the breakdown of:
• DNA into fragments
• The membrane proteins
  = The cytoskeleton which allows the plasma membrane to protrude
• Proteins in the cytosol
• Organelles
• Once apoptosis has begun, it cannot be stopped, and the cell will die.

Question 18

intrinsic pathway

Answer 18

• Damage occurs to the mitochondria resulting in the escape of cytochrome c, a respiratory protein, into the cytosol.
• Cytochrome c activates a caspase cascade.

Question 19

extrinsic pathway

Answer 19

• message is received by a receptor on the outside of the cell (called a death receptor)
• often from an immune system cell.
• messenger triggers the activation of the caspase cascade inside the cell.

Question 20

steps of apoptosis

Answer 20

• The cell separates from other cells
• Cytoskeleton collapses
  The cell shrinks
• Organelles, including the nucleus, breaks down
• Plasma membrane forms blebs.
• Blebs separate from the cell, taking cell contents with them.
• Apoptotic bodies are phagocytosed by white blood cells (mostly macrophages).

Question 21

too much apoptosis

Answer 21

• Leads to fewer cells than is required for a healthy body.
• leads to degenerative diseases such as Alzheimer’s disease (loss of neurons due to excessive apoptosis), Parkinson’s disease and motor neuron disease (MND).

Question 22

too little apoptosis

Answer 22

• Means that more cells occur in the body than usual.
• This can lead to syndactyly (webbing between fingers and toes caused by cells that usually apoptose during development)
• Also can result in cancer.

Question 23

causes of cancer

Answer 23

• Mutations in the protein, p53 which normally initiates apoptosis at the G1 checkpoint if irreparable DNA damage is found.
• Mutations which cause defective caspases
• Mutations which stop the formation of apoptotic bodies
• Mutations which stop the cell accepting external messages to undergo apoptosis
• Mutations which cause over-production of proteins that normally keep healthy cells from apoptosis, so the unhealthy cell cannot suicide.

Question 24

tumor suppressor genes

Answer 24

Code for proteins that:
- Slow or stop cell division
- Repair DNA damage or errors
- Cause cells to undergo apoptosis
Reduced activity of these genes can result in cancer

Question 25

proto-oncogenes

Answer 25

Code for proteins that: - Stimulate cell division - Inhibit differentiation - Regulate programmed cell death Increased activity of these genes can result in cancer

Question 26

mutagens

Answer 26

Cause genetic changes Include: - many chemicals in cigarettes - ionizing radiation - X-rays - UV light If they result in cancer they are known as carcinogens.

Question 27

teratogens

Answer 27

Cause problems in foetal development Include: - some hormones - some antibiotics - oral anti-coagulants - thyroid drugs - drugs and alcohol

Question 28

stem cells

Answer 28

3 types: - totipotent (least differentiated - pluripotent - multipotent (most differentiated) - most flexible of the cells is the zygote which is the fertilised egg. - newly formed zygote can become any cell type. - After 5 days the cell bundle is a blastocyst - some cells are beginning to specialise (differentiate)

Question 29

adult stem cells

Answer 29

- Are multipotent - Can sometimes be induced into an earlier stage of potency - Less likely to be rejected by the immune system - Require more manipulation because they are not naturally pluripotent, - the more manipulation the greater the chance of something going wrong.

Question 29

embryonic stem cells

Answer 29

- Are pluripotent so can become most cell types - Many people have moral objections to embryonically derived stem cells - Organs made of non-self cells are likely to result in an immune response & possible rejection