VOCABULARY: chromatid centromere interphase cell cycle mitosis NOTES: 10.1 – 10.2 Cell Growth and Division VOCABULARY: chromatid centromere interphase cell cycle mitosis centriole spindle prophase metaphase anaphase telophase cytokinesis

How big do you think the largest cell is? Yolk of ostrich egg ~8 cm in diameter Average cell size range from 2-200µm in diameter Why aren’t there more large cells like the ostrich’s?

When a living organism grows… On average, the cells of an adult animal are the same size as those of a young animal So what’s the difference between a young animal and adult animal? The difference is that there are a lot MORE cells in an adult animal!

3 Factors Limiting Cell Size Diffusion DNA Surface Area-to-Volume Ratio Why do you think these factors would influence cell size?

Diffusion as a limiting factor: Remember…the cell membrane allows for nutrients and gases to diffuse into and out of cell Diffusion is fast and efficient but only over short distances As distance increases, diffusion becomes slow and inefficient

DNA as Limiting Factor: As a cell grows in size, more demands are placed on the cell’s DNA ● It takes time to make proteins that play a critical role in cell function ● Ex: a small town library has enough books for people to borrow but if a lot of people move into the town, some people may have to wait for popular books; DNA is like a “genetic library”

Surface Area-to-Volume Ratio: As a cell increases in size, volume increases much faster than S.A.

In other words….if a cell size were to double in size, there would be 8 times more waste to get rid of! A cell can’t get rid of wastes that quickly…it would poison itself! The lower the SA:Volume ratio, the harder it is to get materials into/out of the cell

The Cell Cycle

3 main stages of the cell cycle: Interphase: longest stage; includes preparation for cell division Mitosis: nucleus divides into 2 nuclei, each with the same # and kind of chromosomes (DNA) as the parent cell Cytokinesis: cytoplasm divides forming 2 distinct cells

Cell Cycle Overview Interphase: quite long… most of the cell’s time spent here Cell Division: occurs quickly

Parts of Interphase: G1 phase— cells GROW, make organelles and proteins; perform their JOB(S)!...basically, they have a life! S phase — DNA is copied (S stands for SYNTHESIS!) G2 phase — more organelles are produced than are needed in preparation for cell division

MITOSIS: MITOSIS = division of the NUCLEUS

Why is it so important that the nucleus divides in mitosis Why is it so important that the nucleus divides in mitosis? (for DNA to be copied and divided?) it stores the DNA (information of life) all new cells need this information!

Chromosomes Genetic information is passed on from one generation to the next through chromosomes

Chromosomes: Every organism has a specific number of chromosomes ex #1: carrots = 18 chromosomes; ex #2: humans = 46  23 came from MOM & 23 came from DAD Chromosomes are not visible in most cells except in cell division

Why are chromosomes only visible during cell division? During interphase, the DNA and protein molecules that make up chromosomes is spread throughout the nucleus being used to direct cell activities / protein synthesis (a.k.a. CHROMATIN)

Chromosome Structure: At the beginning of cell division, the chromosomes condense into compact visible structures (CHROMOSOMES) Before cell division (in the S phase of interphase), each chromosome is replicated (copied) Each chromosome is made up of 2 identical “sister” chromatids held together by a centromere

CHROMOSOME centromere chromatin DNA

Mini-Summary (up to this point) During a cell’s life, its DNA is being used/ giving instructions to make proteins; Cell gets too big so the cell prepares to divide; DNA replicates; DNA condenses into visible structures (chromosomes); Chromosomes are now ready for division!

Prophase Metaphase Anaphase Telophase Mitosis is one, continuous event, but it can be described as happening in 4 phases: Prophase Metaphase Anaphase Telophase

**Remember, the cell is coming out of Interphase…

PROPHASE chromatin condenses & chromosomes become visible centrioles separate and move to opposite sides of the nucleus;

Centrioles:

PROPHASE continued… spindle fibers (from centrioles) connect to chromosomes at their centromeres; nuclear envelope breaks down and the nucleolus disappears

PROPHASE (early & late) EARLY PROPHASE LATE PROPHASE

METAPHASE **chromosomes line up in the center of the cell;   **fibers connect from the poles (end) of the spindle to the centromere of each chromosome

METAPHASE:

ANAPHASE centromeres split, causing the sister chromatids to separate, becoming individual chromosomes   individual chromosomes are pulled apart to opposite ends of the cell

ANAPHASE:

TELOPHASE chromosomes uncoil into chromatin;   new nuclear envelope forms around the chromatin spindle breaks apart nucleolus reappears in each new nucleus

TELOPHASE:

**Often, telophase overlaps with cytokinesis.

CYTOKINESIS: CYTOKINESIS = division of the cytoplasm

Finally… CYTOKINESIS in animal cells: cell membrane pinches in & divides in plant cells: a cell plate (new cell wall) forms

Then each new cell returns to interphase… and the process continues… One More Time!

PROPHASE

METAPHASE

ANAPHASE

TELOPHASE

Finally… CYTOKINESIS

and back to INTERPHASE