The life of cells

What limits cell growth?

&

The Cell Cycle: Mitosis

Section 8.2

What limits cell size?

Diffusion 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.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

a-inter.jpg

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)

img005.GIF

a-pro.jpg

Metaphase (M is for middle)

Chromosomes attached to spindle fibers by centromeres

Line up on midline

or equator

a-meta.jpg

Anaphase

Centromeres split Sister chromatids separate

Pulled apart by shortening of spindle fibers

a-ana.jpg

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

img009.GIF

a-telo.jpg

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

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

1. 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?

A. 23 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