Nucleus 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 ~8cm 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, it 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 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: 1. Interphase: : longest stage; preparation for cell division 2. Mitosis: : nucleus divides into 2 nuclei, each with the same # and kind of chromosomes (DNA) as the parent cell 2. 3. 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? (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
Every organism has a specific number of chromosomes ex #1: carrots = 18 chromosomes; 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 interphase, the DNA and protein molecules that make up chromosomes is spread throughout the nucleus being used during cell division? (a.k.a. CHROMATIN)
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 CHROMATIN centromere 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!
Mitosis is one, continuous event, but it can be described as happening in 4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. 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:
chromosomes uncoil into chromatin; new nuclear envelope forms around the chromatin spindle breaks apart nucleolus reappears in each new nucleus TELOPHASE
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
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
Finally CYTOKINESIS
and back to INTERPHASE