Cellular Reproduction

Chapter 2:

pp. 32-35

Chapter 3:

pp. 49-56

Fat Cells

Chromosomes-

DNA tightly coiled around proteins

Humans have 46

The Cell Cycle (figs. 2.14 & 2.17)

Interphase: 90% of time

1. First Growth (G1)

2. Synthesis Phase (S)

3. Second Growth (G2) Prepare for Mitosis

G1

Cell Grows Rapidly Length varies greatly depending on cell type

Liver cells enter G0 and may be there for yrs.

Bone marrow only in G1 for hrs. Early cells in embryo skip this phase all together

S

Cell’s DNA copied Each chromosome consists of 2 copies

(2 chromatids) joined together by a centromere

~ 8-10 hrs.

More protein synthesis Membranes formed and stored in vesicles

near cell membrane to be used for daughter cells

G2

Cell Division

Surface area to volume ratios Surface area ÷ Volume =

Cells must divide because Volume of cell becomes greater than the Surface Area or the ratio is too low.

Big cells are inefficient

Skin Cells

Mitosis –(Fig 2.16)

Occurs in Somatic Cells- all cells but sperm & egg cells.

Nucleus of cell divides

Nuclear Division

In your book

Cellular Reproduction

Link!Mitosis

animation

Cellular Reproduction

•Begins with division of nucleus

Prophase

DNA coils up and thickens and tightens the chromosomes. Enables them to separate easier

Microtubules assemble to form spindle fibers

The nuclear envelope begins to break down

Nucleolus no longer visible

Aster- fasten centrioles to cell membrane

Metaphase

Chromosomes move to the middle of the cell and line up along the equator.

Spindle fibers link the chromatids of each chromosome to opposite poles.

Centrioles (Centrosome)

Anaphase

•Centromeres divide

•Chromatids (now called chromosomes) move toward opposite poles

•Very brief phase

Telophase

A nuclear envelope forms around the chromosomes at each pole

Chromosomes uncoil LAST step in mitosis

Cytokinesis

•Cytoplasm is divided in ½

•Organelles distributed to 2 daughter cells

•Microfilament contracts like a drawstring

•Cell membrane encloses each cell

Control of the Cell Cycle

Groups of interacting proteins function at times called checkpoints- ensure correct replication of chromosomes

1. DNA damage -repair DNA

2. Apoptosis -keep cell alive (survivins)

3. Spindle Assembly - oversees spindle construction

When do divisions stop?

Telomeres- act as fuses 100s-1000s of nucleotides 50-200 used during mitosis Mitosis stops

Cell may die or live long

Apoptosis

Cell Death Rapidly dismantles cell into membrane

bound pieces that other cells (phagocytes) can pick up

Death receptor Mitosis and Apoptosis are synchronized

Except in Cancer

?’s 1-14

Production of sex cells

1/2 the number of Chromosomes

Gametes-reproductive cells

Meiosis: (Fig. 3.3)

Link!-video

In your book

Definitions for Meiosis

Occurs in germ cells- inherited sex cells (gametes) Homologous Chromosomes-

Chromosomes that are similar

in size, shape and content

Crossing Over- Portions of one chromatid are

shared with a chromatid on

another (Homologous

Chromosome)Tetrad

Definitions for Meiosis

Haploid- containing one set of chromosomes 23 for humans (sex cells)

Diploid- containing two sets of chromosomes Zygote- fertilized egg

46 chromosomes in humans 78 chromosomes in dogs Some plants have thousands

Definitions for Meiosis

Asexual Reproduction-a single parent passes copies of all of its genes to each of its offspring. (Clones)

Sexual Reproduction-two parents, each donating a haploid reproductive cell

Meiosis

Two divisions Reduction division (Meiosis 1)

Reduces chromosomes from 46 -23Separates Homologous Chromosomes

Equational division (Meiosis 2)2 cells become 4 cellsSeparates sister chromatids

Prophase 1

90% of meiosis The chromosomes. become

visible Nuclear envelope breaks down Homologs line up-Synapsis Crossing over- Homologous

chromosomes (homologs) exchange parts

Metaphase 1:

Pairs of homologous chromosomes move to the equator of the cell

Independent Assortment- Random arrangement of

the members of homolog pairs in metaphase

Anaphase 1:

Homologous chromosomes move to opposite poles of cell

Telophase 1:

Chromosomes gather at the poles of the cell

Cytoplasm divides Short Interphase after

Telophase 1 NO REPLICATION!

Prophase 2:

A new spindle forms around the chromosomes

Metaphase 2:

Chromosomes line up at the equator

Anaphase 2

Centromeres divide. Chromatids are now

called chromosomes Chromosomes move to

opposite poles of the cell.

Telophase 2:

Cells begin split Cell membrane between cells Four gametes are formed 4 HAPLOID gametes All cells different

Comparison of Mitosis

and Meiosis

Table 3.1!!

46 Chromosomes (Diploid)-23 pairs

Trisomy 21 or Downs Syndrome

Extra Chromosome

?’s 14-20

Compare Mitosis and Meiosis

1. What kind of cells?

2. # of nuclear divisions

3. Compare daughter cells and parent cells

4. Chromosome # after division

5. Do homologous chromosomes pair?

6. Does Crossing over occur

7. When do the centromeres divide?

8. When is each type of cell division used?

Answer these on a clean sheet of paper

Comparison of Mitosis and MeiosisMitosis

1. Somatic Cells

2. 1 nuclear division

3. Daughter cells identical to parent cells

4. Diploid (remain constant)

5. No pairing of homologous Chromosomes

6. Crossing over rare

7. Centromeres divide at Anaphase

8. Growth, repair, asexual repro

Meiosis

1. Germ Cells

2. 2 nuclear divisions

3. Daughter cells differ from parent cells

4. Haploid (Halved)

5. Pairing of homologous Chromosomes

6. Crossing over

7. Centromeres Divide at Anaphase 2

8. Sexual repro., new gene combinations arise

KEY