VCE Biology Unit 1 Chapter 2 Jacaranda Nature of Biology
Why cells undergo cell replication:
Growth: Needs more cells, cells cannot become larger because size is limited
Repair: The replacement of old and damaged cells is important to prevent diseases
Procreation: Some species rely on cell replication to survive
Binary fission: Cell multiplication for prokaryotes
Step 1: The circular DNA chromosome replicates and the cell elongates
Step 2: The two circular chromosomes move to each side of the cell
Step 3: The cell membrane splits into two, a new cell wall (called a septum) forms and breaks in the middle to form two daughter cells
Eukaryotic Cell cycle: The sequence of events of cell growth and reproduction for two daughter cells to form
Interphase: period of DNA replication
Gap 1 (G1) stage: Growth occurs which leads to an increased amount cytosol. Proteins are created. The mitochondria divides. If the cell does not go through this stage, it will be in the G0 or resting phase.
Synthesis (S) Stage: The parent cell’s DNA is replicated and it will have two identical DNA copies.
Gap 2 (G2) Stage: Further cell growth to prepare for cell division. More proteins are synthesised and the cell doubles in size.
Mitosis: The organisation and separation of chromosomes
Prophase: Chromosomes condense → visible as double stranded structures. The spindle forms + nuclear membrane breaks down
Metaphase: Double stranded chromosomes line up at the cell’s equator
Anaphase: Sister chromatids separate and are pulled to opposite sides of the spindle
Telophase: Nuclear membrane forms around each group of single-stranded chromosomes → chromosomes decondense
Cytokinesis: The cytoplasm divides, forming new membranes and enclosing the daughter cells
Animal cells during cytokinesis: Cytoplasm between two nuclei becomes narrow → cell membrane pinches to separate nuclei + cytoplasm into two new daughter cells
Plant cells during cytokinesis: Cell plate forms between chromosome groups → develops into one cell wall for each new cell
Regulation of Cell Cycle:
G1 checkpoint: DNA is checked to be damaged or incomplete → if so, enters G0 stage to be destroyed
If it passes G1 it proceeds to the S stage and the DNA replicates
G2 checkpoint: Replicated DNA is examined for completeness and lack of damage
Advances to mitosis stage afterwards
M checkpoint: Ensures sister chromatids are attached to the correct microtubules of the spindle
Programmed Cell Death
Apoptosis: Programmed cell death as a regular part of an organism’s development
Cells at the end of their natural life
Damaged or diseased cells
Excessive cells
Cell Differentiation
Cell differentiation: cells become specialised for a specific function
Stem cells: Undifferentiated cells that can differentiate into organ or tissue specific cells
Self renewable: Maintains stem cell pull
Differentiation: Replacement of dead + damaged cells
Embryonic stem cells: Can differentiate into many different cell types
Found in the cells of embryos from zygote to blastocyst stage
Adult tissue stem cells: Undifferentiated cells that can differentiate into related cell types
Found in the eye’s surface, brain, skin, breast, intestine, testicles, muscles, bone marrow
AKA somatic stem cells
eg. Blood stem cell found in bone marrow can differentiate into only specialised blood cell types - red blood cells, white blood cells, platelets
Potency: Cell’s ability to differentiate into various cell types
Totipotent stem cells: Can become any cell type or another embryo
Pluripotent stem cells: Differentiate into any of the three germ layers - endoderm, mesoderm, ectoderm (blastocyst cells)
Multipotent stem cells: Give rise to multiple cell types that are related to the family of cells. Ex. Blood stem cells becoming platelets or white blood cells
Oligopotent stem cells: Differentiate into a few cell types. Ex. Adult lymphoid cells
Unipotent: Differentiate into one cell type in a certain tissue repeatedly. Ex. skin epidermal stem cells
Why cells undergo cell replication:
Growth: Needs more cells, cells cannot become larger because size is limited
Repair: The replacement of old and damaged cells is important to prevent diseases
Procreation: Some species rely on cell replication to survive
Binary fission: Cell multiplication for prokaryotes
Step 1: The circular DNA chromosome replicates and the cell elongates
Step 2: The two circular chromosomes move to each side of the cell
Step 3: The cell membrane splits into two, a new cell wall (called a septum) forms and breaks in the middle to form two daughter cells
Eukaryotic Cell cycle: The sequence of events of cell growth and reproduction for two daughter cells to form
Interphase: period of DNA replication
Gap 1 (G1) stage: Growth occurs which leads to an increased amount cytosol. Proteins are created. The mitochondria divides. If the cell does not go through this stage, it will be in the G0 or resting phase.
Synthesis (S) Stage: The parent cell’s DNA is replicated and it will have two identical DNA copies.
Gap 2 (G2) Stage: Further cell growth to prepare for cell division. More proteins are synthesised and the cell doubles in size.
Mitosis: The organisation and separation of chromosomes
Prophase: Chromosomes condense → visible as double stranded structures. The spindle forms + nuclear membrane breaks down
Metaphase: Double stranded chromosomes line up at the cell’s equator
Anaphase: Sister chromatids separate and are pulled to opposite sides of the spindle
Telophase: Nuclear membrane forms around each group of single-stranded chromosomes → chromosomes decondense
Cytokinesis: The cytoplasm divides, forming new membranes and enclosing the daughter cells
Animal cells during cytokinesis: Cytoplasm between two nuclei becomes narrow → cell membrane pinches to separate nuclei + cytoplasm into two new daughter cells
Plant cells during cytokinesis: Cell plate forms between chromosome groups → develops into one cell wall for each new cell
Regulation of Cell Cycle:
G1 checkpoint: DNA is checked to be damaged or incomplete → if so, enters G0 stage to be destroyed
If it passes G1 it proceeds to the S stage and the DNA replicates
G2 checkpoint: Replicated DNA is examined for completeness and lack of damage
Advances to mitosis stage afterwards
M checkpoint: Ensures sister chromatids are attached to the correct microtubules of the spindle
Programmed Cell Death
Apoptosis: Programmed cell death as a regular part of an organism’s development
Cells at the end of their natural life
Damaged or diseased cells
Excessive cells
Cell Differentiation
Cell differentiation: cells become specialised for a specific function
Stem cells: Undifferentiated cells that can differentiate into organ or tissue specific cells
Self renewable: Maintains stem cell pull
Differentiation: Replacement of dead + damaged cells
Embryonic stem cells: Can differentiate into many different cell types
Found in the cells of embryos from zygote to blastocyst stage
Adult tissue stem cells: Undifferentiated cells that can differentiate into related cell types
Found in the eye’s surface, brain, skin, breast, intestine, testicles, muscles, bone marrow
AKA somatic stem cells
eg. Blood stem cell found in bone marrow can differentiate into only specialised blood cell types - red blood cells, white blood cells, platelets
Potency: Cell’s ability to differentiate into various cell types
Totipotent stem cells: Can become any cell type or another embryo
Pluripotent stem cells: Differentiate into any of the three germ layers - endoderm, mesoderm, ectoderm (blastocyst cells)
Multipotent stem cells: Give rise to multiple cell types that are related to the family of cells. Ex. Blood stem cells becoming platelets or white blood cells
Oligopotent stem cells: Differentiate into a few cell types. Ex. Adult lymphoid cells
Unipotent: Differentiate into one cell type in a certain tissue repeatedly. Ex. skin epidermal stem cells
