2.6 Cell Division, Cell Diversity, and Cell Differentiation
The cell cycle
Interphase
- Carry out cells' main function
- All processes that occur when cell isn't dividing.
G1 Growth phase
- New cell grows and carries out normal functions - protein synthesis,
respiration.
- Makes proteins for S phase.
- Organelles duplicate.
S Synthesis
- Cells' DNA replicated so that each chromosome double stranded (2 sister
chromatids).
- Energy (ATP) saved up ready for cell division.
G2 Growth phase
- Further cell growth.
- Checks to ensure cell ready for M phase.
Mitosis
Nuclear division.
Cytokinesis
Cytoplasm divided between two daughter cells to finish cycle. Each new cell enters
G1 and resumes normal function.
Checkpoints
- G1/S - Does it have resources and correct size? Is DNA damaged?
- G2/M - Has DNA replicated correctly?
- M - Have chromosomes attached to spindles?
G0
May leave cell cycle temporarily or indefinitely.
○ Apoptosis (cell death)
○ Senescence (cell ageing)
○ Differentiation
Gene: length of DNA that codes for polypeptide or for length of RNA involved in
regulating gene expression.
Centromere: structure in chromosome that holds together two chromatids.
Cell Cycle: sequence of events that take place for cell division to occur, including
growth of cell and replication of genetic material, and then division. Can be split into
four parts: G1, S, G2 (all interphase), and M phases.
Karyotype: photomicrograph of chromosomes in cell.
Somatic Cell: any biological cell other than sperm or egg cells (germ cells). In
humans, these are diploid.
Sister Chromatids: when chromosome has replicated, resulting two identical
chromatids produced are sister chromatids.
Replication: copying of genetic material to create two identical sets of DNA.
Haploid: having only one set of chromosomes; represented by symbol 'n'.
Mitosis: type of nuclear division that produces daughter cells genetically identical to
each other and to parent cell.
Diploid: cell in which nucleus has two complete sets of chromosomes.
Chromatin: mixture of DNA and proteins that form chromosomes found in cells of
Module 2 - Foundations in biology Page 1
, Chromatin: mixture of DNA and proteins that form chromosomes found in cells of
humans and other eukaryotes.
Mitosis
All organisms must produce genetically identical daughter cells by mitosis for
the following reasons:
1. Asexual Reproduction
○ Protoctists - amoeba, paramecium
○ Fungi (yeasts)
○ Plants (strawberry plants have runners)
○ Animals - female sharks in captivity without males (female offspring,
clones); aphids - can produce eggs by mitosis that don't need to be
fertilised
2. Growth
All multicellular organisms grow by producing more genetically identical cells.
3. Tissue Repair
Increased growth of endothelial and smooth muscle cells to repair damaged
blood vessels triggered by chemicals produced by platelets and macrophages
(white blood cells).
Meiosis I and II
Meiosis is process of cell division underlying sexual reproduction.
• Meiosis I introduces genetic variation by dividing cell’s genes in two. Results
in two haploid cells.
• Meiosis II similar to mitosis. Splits each chromosome into two chromatids
and places one in each daughter cell. Results in four haploid gametes.
Module 2 - Foundations in biology Page 2
The cell cycle
Interphase
- Carry out cells' main function
- All processes that occur when cell isn't dividing.
G1 Growth phase
- New cell grows and carries out normal functions - protein synthesis,
respiration.
- Makes proteins for S phase.
- Organelles duplicate.
S Synthesis
- Cells' DNA replicated so that each chromosome double stranded (2 sister
chromatids).
- Energy (ATP) saved up ready for cell division.
G2 Growth phase
- Further cell growth.
- Checks to ensure cell ready for M phase.
Mitosis
Nuclear division.
Cytokinesis
Cytoplasm divided between two daughter cells to finish cycle. Each new cell enters
G1 and resumes normal function.
Checkpoints
- G1/S - Does it have resources and correct size? Is DNA damaged?
- G2/M - Has DNA replicated correctly?
- M - Have chromosomes attached to spindles?
G0
May leave cell cycle temporarily or indefinitely.
○ Apoptosis (cell death)
○ Senescence (cell ageing)
○ Differentiation
Gene: length of DNA that codes for polypeptide or for length of RNA involved in
regulating gene expression.
Centromere: structure in chromosome that holds together two chromatids.
Cell Cycle: sequence of events that take place for cell division to occur, including
growth of cell and replication of genetic material, and then division. Can be split into
four parts: G1, S, G2 (all interphase), and M phases.
Karyotype: photomicrograph of chromosomes in cell.
Somatic Cell: any biological cell other than sperm or egg cells (germ cells). In
humans, these are diploid.
Sister Chromatids: when chromosome has replicated, resulting two identical
chromatids produced are sister chromatids.
Replication: copying of genetic material to create two identical sets of DNA.
Haploid: having only one set of chromosomes; represented by symbol 'n'.
Mitosis: type of nuclear division that produces daughter cells genetically identical to
each other and to parent cell.
Diploid: cell in which nucleus has two complete sets of chromosomes.
Chromatin: mixture of DNA and proteins that form chromosomes found in cells of
Module 2 - Foundations in biology Page 1
, Chromatin: mixture of DNA and proteins that form chromosomes found in cells of
humans and other eukaryotes.
Mitosis
All organisms must produce genetically identical daughter cells by mitosis for
the following reasons:
1. Asexual Reproduction
○ Protoctists - amoeba, paramecium
○ Fungi (yeasts)
○ Plants (strawberry plants have runners)
○ Animals - female sharks in captivity without males (female offspring,
clones); aphids - can produce eggs by mitosis that don't need to be
fertilised
2. Growth
All multicellular organisms grow by producing more genetically identical cells.
3. Tissue Repair
Increased growth of endothelial and smooth muscle cells to repair damaged
blood vessels triggered by chemicals produced by platelets and macrophages
(white blood cells).
Meiosis I and II
Meiosis is process of cell division underlying sexual reproduction.
• Meiosis I introduces genetic variation by dividing cell’s genes in two. Results
in two haploid cells.
• Meiosis II similar to mitosis. Splits each chromosome into two chromatids
and places one in each daughter cell. Results in four haploid gametes.
Module 2 - Foundations in biology Page 2
