Unit 6 cell growth and regulation
Summary of Cell Growth and Regulation
This content provides a comprehensive overview of cell size, the cell cycle, mechanisms regulating
cell growth, and disorders related to cell growth. It explains why cells remain small, how they grow
and divide, the phases of the cell cycle, regulatory proteins involved, and consequences when
regulation fails.
Cell Size and Its Importance
● Cells are small to maintain a high surface area to volume ratio, which is critical for efficient
transport of substances in and out of the cell.
● As a cell grows larger, the DNA becomes overloaded because it must manage more cellular
functions, and transport across the membrane becomes less efficient.
● Surface area to volume ratio decreases as cell size increases, limiting the cell’s ability to
sustain itself if it becomes too large.
Variation in Cell Size
● Cell size varies widely despite the general smallness of cells.
● Large cells often contain multiple copies of DNA (ploidy) to combat DNA overload:
● Haploid: One set of chromosomes (e.g., egg and sperm cells)
● Diploid: Two matching sets of chromosomes (most body cells)
● Polyploid: More than two sets of chromosomes
● Some cells grow large because they function as storage cells (e.g., adipocytes storing lipids).
● Cells generally grow until reaching an optimal size, then duplicate their DNA and divide.
● Cells may also divide for reasons beyond size, such as repair, reproduction, or replacing
damaged cells.
The Cell Cycle Overview
The cell cycle consists of three main stages:
Stage Description
Interphase The longest phase where the cell grows, duplicates DNA, and prepares for
division.
, Unit 6 cell growth and regulation
Mitosis Nuclear division, subdivided into Prophase, Metaphase, Anaphase, and
Telophase.
Cytokinesis Division of the cytoplasm, resulting in two daughter cells.
Interphase Details
● Most of a cell’s life is spent in Interphase, which has sub-phases:
● G1 (Gap 1): Cell grows and synthesizes proteins.
● S (Synthesis): DNA replication occurs; chromosomes are duplicated.
● G2 (Gap 2): Additional growth and preparation for mitosis; organelles and molecules
are duplicated.
● G0: A resting phase some cells enter during G1 where they temporarily or
permanently cease division.
● Checkpoints at G1 and G2 phases ensure the cell is ready to proceed. Once past the G2
checkpoint, the cell is committed to division.
Mitosis Phases (IPMAT)
Phase Key Events
Prophase Longest mitosis phase; chromosomes condense and become visible (DNA coils);
centrioles move to poles; spindle fibers form; nuclear envelope breaks down.
Metaphase Chromosomes align at the cell center on spindle fibers; lasts only a few minutes.
Anaphase Sister chromatids split and move to opposite poles of the cell.
Telophase Chromosomes begin to uncoil (DNA uncoils); nuclear envelope reforms;
nucleolus reappears; spindle fibers break down.
● After telophase, cytokinesis occurs, dividing the cytoplasm:
● Animal cells: Cytoplasm pinches inward forming two cells.
● Plant cells: A cell plate forms between nuclei and develops into a cell wall.
Regulation of Cell Growth
● Cell growth and division are controlled by internal and external factors:
Summary of Cell Growth and Regulation
This content provides a comprehensive overview of cell size, the cell cycle, mechanisms regulating
cell growth, and disorders related to cell growth. It explains why cells remain small, how they grow
and divide, the phases of the cell cycle, regulatory proteins involved, and consequences when
regulation fails.
Cell Size and Its Importance
● Cells are small to maintain a high surface area to volume ratio, which is critical for efficient
transport of substances in and out of the cell.
● As a cell grows larger, the DNA becomes overloaded because it must manage more cellular
functions, and transport across the membrane becomes less efficient.
● Surface area to volume ratio decreases as cell size increases, limiting the cell’s ability to
sustain itself if it becomes too large.
Variation in Cell Size
● Cell size varies widely despite the general smallness of cells.
● Large cells often contain multiple copies of DNA (ploidy) to combat DNA overload:
● Haploid: One set of chromosomes (e.g., egg and sperm cells)
● Diploid: Two matching sets of chromosomes (most body cells)
● Polyploid: More than two sets of chromosomes
● Some cells grow large because they function as storage cells (e.g., adipocytes storing lipids).
● Cells generally grow until reaching an optimal size, then duplicate their DNA and divide.
● Cells may also divide for reasons beyond size, such as repair, reproduction, or replacing
damaged cells.
The Cell Cycle Overview
The cell cycle consists of three main stages:
Stage Description
Interphase The longest phase where the cell grows, duplicates DNA, and prepares for
division.
, Unit 6 cell growth and regulation
Mitosis Nuclear division, subdivided into Prophase, Metaphase, Anaphase, and
Telophase.
Cytokinesis Division of the cytoplasm, resulting in two daughter cells.
Interphase Details
● Most of a cell’s life is spent in Interphase, which has sub-phases:
● G1 (Gap 1): Cell grows and synthesizes proteins.
● S (Synthesis): DNA replication occurs; chromosomes are duplicated.
● G2 (Gap 2): Additional growth and preparation for mitosis; organelles and molecules
are duplicated.
● G0: A resting phase some cells enter during G1 where they temporarily or
permanently cease division.
● Checkpoints at G1 and G2 phases ensure the cell is ready to proceed. Once past the G2
checkpoint, the cell is committed to division.
Mitosis Phases (IPMAT)
Phase Key Events
Prophase Longest mitosis phase; chromosomes condense and become visible (DNA coils);
centrioles move to poles; spindle fibers form; nuclear envelope breaks down.
Metaphase Chromosomes align at the cell center on spindle fibers; lasts only a few minutes.
Anaphase Sister chromatids split and move to opposite poles of the cell.
Telophase Chromosomes begin to uncoil (DNA uncoils); nuclear envelope reforms;
nucleolus reappears; spindle fibers break down.
● After telophase, cytokinesis occurs, dividing the cytoplasm:
● Animal cells: Cytoplasm pinches inward forming two cells.
● Plant cells: A cell plate forms between nuclei and develops into a cell wall.
Regulation of Cell Growth
● Cell growth and division are controlled by internal and external factors:
