2 the cell cycle and cell growth, death and differentiation

Question 1

Describe and outline binary fission in prokaryotic cells and the steps in this process

Answer 1

Binary fission: process of reproduction by prokaryotes (archaea and bacteria)

1. Replication of DNA chromosome and cell elongation occurs
2. The two chromosomes migrate to either end of the cell.
3. The cell membrane pinches in two and a septum (a new cell wall) forms along the middle of the cell, which extends and finally breaks in half to form two cells

Question 2

Describe the eukaryotic cell cycle

Answer 2

Cell cycle: series of events of cell growth and reproduction that results in two daughter cells

1. Interphase
2. Mitosis
3. Cytokinesis

Question 3

Describe the characteristics and processes in interphase

Answer 3

Interphase: cell growth and DNA synthesis

1. G1 stage: cell grows, increasing the amount of cell cytosol
   —> quiescent (non-dividing) G0 stage: near the end of G1 stage, cells will either commit to continuing the cell cycle or will drop out and not divide
2. S stage: parent cell replicates its DNA; at the end of the S stage the parent cell contains two identical copies of its original DNA
3. G2 stage: proteins are synthesised and the cell continues to grow in preparation for division

Question 4

Describe the characteristics and processes in mitosis

Answer 4

Mitosis: production of new cells genetically identical to the original cell

1. Prophase: chromosomes condense and become visible, spindle forms and the nuclear membrane breaks down
2. Metaphase: chromosomes line up along the equator of the cell
3. Anaphase: the sister chromatids separate and are pulled to opposite ends of the spindle by the contraction of spindle fibres
4. Telophase: nuclear membranes form around the two sets of chromosomes, forming two nuclei.

Question 5

Describe the characteristics and processes in cytokinesis, including differences b/w plant & animal cells

Answer 5

Cytokinesis: division of the cytoplasm
- new membranes form, enclosing each of the two new cells (and cell walls in the case of plants). these cells then return to interphase and may divide again or enter G0.

Animal cells: the cell membrane is cleaved to form two cells

Plant cells: a cell plate extends from the middle to the sides to complete the separation.

Question 6

Identify different ways the cell cycle is regulated w/ reference to checkpoints

Answer 6

Normal regulation: the rate of production of new cells balances the rate of loss of cells.

G1 checkpoint: makes sure the DNA is not damaged and is ready to undergo replication
—> p53: a gene (found in the nucleus) that makes a protein and plays a key role in controlling cell division and cell death
G2 checkpoint: the replicated DNA of the cell is checked for completeness and lack of damage; if the cell passes this checkpoint, it can then advance to mitosis
M checkpoint: the connection between chromatid and spindle fibres is checked and corrected

Question 7

Summarise differences in the cell cycle in different organisms

Question 8

Define apoptosis and highlight its importance

Answer 8

Apoptosis: programmed death of cells that occurs as a normal and controlled part of an organism’s growth or development

Importance: to rid the body of cells that have been damaged beyond repair

Question 9

Describe the process of apoptosis

Answer 9

1. Cell shrinkage
2. Formation of blebs (protrusions of the cell membrane)
3. Formation of apoptotic bodies
4. Clean-up of apoptotic bodies through phagocytosis (after apoptosis).

Question 10

Outline disruptions that can occur in the cell cycle

Answer 10

Mutations in genes: can cause cancerous cells

Question 11

Describe how malfunctions in apoptosis can lead to deviant cell behaviour w/ reference to cancer

Answer 11

Cancerous cells: excess of cell reproduction, producing masses of cells called tumours
Metastasis: process where malignant tumours spread throughout the body

• Mutations causes the cell cycle to continue in an unregulated manner
• Checkpoints are overridden or fail

Question 12

Differentiation and specialisation in relation to cells and tissue (describe)

Answer 12

Differentiation: the process by which cells, tissues and organs acquire specialised features

Specialisation: the adaptation of something for a specific function

Question 13

Stem cells and their importance (explain & describe)

Answer 13

Stem cells: unspecialised and can differentiate into specialised cells

Importance: ability to differentiate into any cell type and repair damaged tissue — potential treatment for medical conditions

Question 14

Different stem cell potencies (describe)

Answer 14

Totipotent: cells have the potential to give rise to all cell types. E.g. zygote (fertilised egg)

Pluripotent: cells can differentiate into many cell types. E.g. embryonic stem cells

Multipotent: cells have the ability to differentiate into a closely related family of cells. E.g. red blood cell

Unipotent: cells have the ability to produce only cells of their own type. E.g. adult (somatic) muscle stem cells

Question 15

Different sources of stem cells of different potencies (identify)

Answer 15

Embryonic stem cell (ESC): an undifferentiated cell obtained from early embryonic tissue that is capable of differentiating into many cell types

Somatic stem cells: undifferentiated cells obtained from various sources and capable of differentiating into related cell types

Induced pluripotent stem cell (IPSC): a stem cell that has been genetically reprogrammed to return to an undifferentiated embryonic state

Question 16

How stem cells are used in regenerative medicine (explain)

Answer 16

Regenerative medicine: an experimental field of research involving stem cells in medicine that promises the treatment of degenerative conditions and severe trauma injuries

• In stem cell transplants, stem cells replace cells damaged by disease to fight some types of cancer and blood-related diseases