What limits cell growth? & The Cell Cycle: Mitosis Section 8.2 The life of cells What limits cell growth? & The Cell Cycle: Mitosis Section 8.2

What limits cell size? Diffusion DNA Surface area-to-volume ratio Slow & inefficient over long distances DNA Copying DNA takes time Must be enough DNA to support cell’s protein needs Surface area-to-volume ratio Volume increases much faster than surface area If cell were too big, it couldn’t process nutrients and wastes properly – would starve or be poisoned

Cell Reproduction Cells can’t grow forever Stop growing or divide Reproduction (division) is necessary for life to continue

Reproduction in prokaryotes Very simple Binary fission cell pinches in two Each has its own DNA http://www.lakemichigancollege.edu/liberal/bio/pics2/fission_an.gif

Reproduction in Eukaryotes Much more complicated DNA in membrane-bound nucleus Chromosomes – contain DNA material Come in pairs (sister chromatids), joined by a centromere Chromatin – long strands of DNA Most of the time, chromosomes exist as chromatin See page 205

http://micro. magnet. fsu http://micro.magnet.fsu.edu/cells/nucleus/images/chromatinstructurefigure1.jpg

Chromosome Terms Diploid (2n) – cell contains pairs of homologous chromosomes Body cells AKA somatic cells Haploid (n) – cell has only one chromatid from each pair Sex cells AKA gametes AKA egg & sperm

Karyotype of a human somatic cell

Cell Cycle Sequence of growth and division Interphase Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis

Interphase Majority of cell’s life Very busy time Cell grows in size Carries on metabolism DNA synthesis & replication student.ccbcmd.edu/.../DNArep/pcinterphase.html

Activity Look at problem-solving lab on page 204

Mitosis Nuclear division Result: two daughter cells, each with a set of chromosomes 4 stages Prophase Metaphase Anaphase Telophase

Prophase stringy chromatin coils up  chromosomes Nucleus begins to disappear Nuclear envelope & nucleolus disintegrate *In animal cells* - centrioles migrate to opposite ends of cell Spindle – forms between centrioles (in plant cells, spindle forms without the centrioles)

Metaphase (M is for middle) Chromosomes attached to spindle fibers by centromeres Line up on midline or equator

Anaphase Centromeres split Sister chromatids separate Pulled apart by shortening of spindle fibers

Telophase (think telephone – requires two people to talk) Chromatids reach opposite poles of cell Prophase changes are reversed Chromosomes unwind Spindle breaks down Nucleolus reappears New nuclear envelope forms around each set of chromosomes

Cytokinesis Cytoplasm divides Animals – plasma membrane pinches in at equator Plants – cell plate is laid down across equator New cell walls form

Results of mitosis **Cellular heirarchy** Cells  tissues  organs  Guarantees genetic continuity Two new cells with identical sets of chromosomes Unicellular organisms – more identical organisms are produced Multicellular organisms – groups of cells **Cellular heirarchy** Cells  tissues  organs  organ systems  organism

Quiz: Cell cycle

Division in prokaryotes is called? A. Binary fission B. Metaphase C. Replication D. Binary fusion

2. Pairs of chromosomes are homologous which means

3. How is cytokinesis different in animal and plant cells?

4. Somatic cells are A. 4n B. 2n C. n D. 3n

5. Humans have how many pairs of chromosomes? B. 46 C. 4 D. 2

6. What are the organelles that produce spindle fibers called? A. Microtubules B. Centrioles C. Nucleoli D. Cytoplasm

7. ____ is the specific region where chromatids are held. A. Centrioles B. Telomeres C. Centromeres D. Spindle fibers

8. Name the missing phase. Interphase, Prophase, _________, Anaphase, Telophase

9. Cells spend most of their time in which phase mitosis? A. Telophase B. Anaphase C. Metaphase D. Prophase E. Interphase

10. The phase at which the chromosomes are pulled to the poles of the cells. A. Prophase B. Anaphase C. Interphase D. Metaphase E. Telophase