Chapter 10 Cell Growth

10.1 Cell Growth Living things grow by producing more cells. Cells of an adult are the same size as the cells of a baby, adults just have more cells. Cells divide rather than growing indefinitely for 2 reasons: 1. the larger the cell become the more demands the cell places on it’s DNA 2. the larger the cell the more problems it has moving nutrients and wastes across the cell membrane.

DNA “overload” As cells increase in size they often cannot make enough copies of their DNA.

Exchanging Materials Rate at which exchange takes place depends on the surface area of the cell (the total area of the cells membrane) Rate at which food and oxygen are used up depends on the cells volume

Ratio of Surface Area to Volume SA = length x width x # of surfaces (cube =6) Volume = length x width x height Volume increase more rapidly than surface area – creates serious problems for the cell if it gets too big.

So what do we do now? Before the cell gets too large – it will divide forming 2 daughter cells – this process is called CELL DIVISION Before a cell divides it replicates, or copies all of its DNA (that’s why the chromatin has to become organized into chromosomes)

Prokaryotic Cell Division Prokaryotes do not have a nucleus or multiple chromosomes. To reproduce, the single circular strand of DNA duplicates itself. The cell elongates and the two circular strands of DNA separate The cell divides in to two cells This is called BINARY FISSION

Eukaryotic Cell Division Cell division is more complex and occurs in two stages: 1. MITOSIS – the division of the cells nucleus 2. CYTOKINESIS – the division of the cytoplasm

Chromosomes Made up of DNA and proteins Cells have a specific number or chromosomes Human cells have 46, fruit flies have 8, etc. Only visible during cell division Called chromatin before they become organized Before division the chromosomes replicate forming “sister” chromatids which are identical in structure – they will separate from each other when the cell divides

The Cell Cycle A series of events during a cell’s life in which a cell grows, prepares for division and divides to form 2 daughter cells, each of which will begin the cycle again 3 total phases 1. Interphase 2. Mitosis 3. Cytokinesis

Overview of the Cell Cycle 1.Interphase G1-G2 growth, DNA replication, prep for mitosis 2. Mitotic phase

INTERPHASE – everyday activity technically not part of mitosis, but it is included in the cell cycle Cell is in a resting phase, performing cell functions DNA replicates (copies) Organelles double in number, to prepare for division G1 – growth, make proteins and organelles S - synthesis (copy DNA) G2 - Second growth - shortest

MITOSIS BEGINS… 4 phases 1. prophase 2. metaphase 3. anaphase 4. telophase

PROPHASE Longest phase Chromosomes become visible Centrioles (two tiny structures near the nuclear envelope, separate) Spindle (structure that helps separate the chromosomes) begins to form Nuclear envelope breaks down

Metaphase Chromosomes line up along the equator Each chromosome is connected to a spindle fiber at it’s centromere.

Anaphase Centromeres divide Shortest stage Sister chromatids split and move to opposite poles becoming individual chromosomes

Telophase Opposite of prophase Chromosomes turn back into chromatin Nuclear envelope re- forms Spindle breaks down

Cytokinesis Division of the cytoplasm Results in two identical cells called daughter cells Plants form a cell plate Animals form a cell furrow Occurs at the end of telophase

Regulating the Cell Cycle Some cells divide and grow rapidly Some cells never divide after maturity (nerve cells) Cell cycle is carefully controlled When cells come in to contact with other cells they respond by not growing Cells at the edges of a cut grow rapidly until the wound is healed (they come in contact with other cells)

Cell Cycle Regulators Proteins called cyclins regulates the cell cycle in eukaryotic cell

Uncontrolled Cell Growth Results in cancer – cells lose ability to control growth, no longer respond to signals

Warm Up #1 Write a paragraph (at least 5 sentences) explaining why a human cell does not grow as large as a fist.

Warm Up #2