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Home , Anaphase, Prophase, Telophase

Chapter 9: How Cells Reproduce Division Mechanisms

• Eukaryotic organisms – –

• Prokaryotic organisms

– Prokaryotic fission or Binary fission Roles of Mitosis

• Multicelled organisms – Growth – replacement

• Some protistans, fungi, plants, animals – Asexual reproduction

• A DNA molecule & attached • Duplicated in preparation for mitosis

one chromosome (unduplicated)

one chromosome (duplicated) Chromosome

a One chromosome (unduplicated)

one two sister one chromatid b One chromosome (duplicated)

Stepped Art

Fig. 9-3a, p.142 Chromosome

Fig. 9-3b, p.142

Chromosome multiple levels of coiling of DNA and (constricted region) proteins

fiber

beads DNA double helix on a string

core of

nucleosome Fig. 9-4, p.143 Chromosome Number

• Sum total of in a cell • Somatic cells – Chromosome number is diploid (2n) – Two of each type of chromosome • Gametes – Chromosome number is haploid (n) – One of each chromosome type Organization of Chromosomes

DNA

DNA and proteins one nucleosome arranged as cylindrical fiber histone The

G1 S

Mitosis G2 Interphase

• Usually longest part of the cycle

• Cell increases in mass

• DNA is duplicated Mitosis

• Period of nuclear division • Usually followed by cytoplasmic division • Four stages: – Prophase – Metaphase – Anaphase – Telophase Control of the Cycle

• Once S begins, the cycle automatically runs through G2 and mitosis • The cycle has a built-in molecular brake in G1 • Cancer involves a loss of control over the cycle, malfunction of the “brakes” The

• Consists of two distinct sets of – Each set extends from one of the cell poles – Two sets overlap at spindle equator • Moves chromosomes during mitosis Spindle Apparatus

one spindle pole

one of the condensed chromosomes

spindle equator microtubules organized as a spindle apparatus

one spindle pole Maintaining chromosome (unduplicated) Chromosome in cell at interphase Number

same chromosome (duplicated) in interphase prior to mitosis

mitosis, cytoplasmic division chromosome chromosome (unduplicated) (unduplicated) in daughter cell in daughter cell at interphase at interphase Maintaining Chromosome Number 1 2 3 4 5

6 7 8 9 10 11 12

13 14 15 16 17 18

19 20 21 22 XX (or XY)

Fig. 9-6a, p.145 Maintaining Chromosome Number

a Two of the b The same two c Two chromosomes chromosomes chromosomes, now (unduplicated) in the (unduplicated) duplicated, in that parent cell’s daughter in a parent cell at cell at interphase, cells, which both start interphase prior to mitosis life in interphase

Fig. 9-6b, p.145 pole Maintaining Chromosome Number

pole

of bipolar spindle p.145 Stages of Mitosis

Prophase

Metaphase

Anaphase

Telophase Early Prophase - Mitosis Begins

Duplicated chromosomes begin to condense

Figure 9.7 Page 146 Late Prophase

• New microtubules are assembled • One pair is moved toward opposite pole of spindle • starts to break up

Figure 9.7 Page 146 Transition to Metaphase

• Spindle forms • Spindle microtubules become attached to the two of each chromosome

Figure 9.7 Page 146 Metaphase

• All chromosomes are lined up at the spindle equator • Chromosomes are maximally condensed

Figure 9.7 Page 147 Anaphase

• Sister chromatids of each chromosome are pulled apart • Once separated, each chromatid is a chromosome

Figure 9.7 Page 147 Telophase

• Chromosomes decondense • Two nuclear membranes form, one around each set of unduplicated chromosomes

Figure 9.7 Page 147 Results of Mitosis

• Two daughter nuclei • Each with same chromosome number as parent cell • Chromosomes in unduplicated form

Figure 9.7 Page 147 Interphase Early Prophase Late Prophase

pair of

nuclear envelope

Stepped Art

Fig. 9-7a, p.146 Metaphase Anaphase Telophase Interphase

Stepped Art

Fig. 9-7b, p.146 Animal Animal Cell Division

1 Mitosis is 2 At the former 3 As its diameter 4 Contractions over, and the spindle equator, a shrinks, it pulls continue; the spindle is now ring of micro- the cell surface cell is pinched disassembling. filaments attached inward. in two. to the plasma membrane contracts.

Fig. 9-8a, p.148 Animal Cell Division

Mitosis is over, and Band of microfilaments at the The contractions the spindle is now former spindle equator contracts. continue and cut disassembling. the cell in two.

Stepped Art

Fig. 9-8a, p.148 Cell Plate Formation Cell Plate Formation

cell plane forming

1 As mitosis 2 Vesicle membranes 3 Cellulose is 4 A cell plate grows ends, vesicles fuse. The wall material deposited inside the at its margins until cluster at the is sandwiched sandwich. In time, it fuses with the spindle equator. between two new these deposits will parent cell plasma They contain membranes that form two cell walls. membrane. The materials for lengthen along the Others will form the primary wall of anew primary cell plane of a newly middle lamella growing plant cells wall. forming cell plate. between the walls is still thin. New and cement them material is together. deposited on it.

Fig. 9-8b, p.148 Cell Plate Formation

cell wall

former vesicles spindle converging equator

cell plate

Stepped Art

Fig. 9-8b, p.148 Tumors

• Sometimes a checkpoint mutates and control over cell division is lost.

• Cells uncontrollable division forms an abnormal mass called a tumor.

• Neoplasms Cancer

Fig. 9-12, p.150 Cancer

benign tumor malignant tumor

1 Cancer cells slip of out 2 The metastasizing cells their home tissue become attached to the wall of a blood or lymph vessel. They secrete digestive enzymes onto it. Then they cross the wall at the breach.

3 Cancer cells creep or tumble along inside blood vessels, then leave the bloodstream the same way they got in. They start new tumors in new tissues.

Fig. 9-13, p.151 Cancer

Fig. 9-14a, p.151 Cancer

Fig. 9-14b, p.151 Cancer

Fig. 9-14c, p.151 HeLa Cells

• Line of human cancer cells that can be grown in culture • Descendents of tumor cells from a woman named Henrietta Lacks • Lacks died at 31, but her cells continue to live and divide in labs around the world cell at interphase nucleus cytoplasm

telophase prophase

anaphase metaphase

Fig. 9-15, p.153