Cell Division and Mitosis Chapter 9

Understanding Cell Division What instructions are necessary for inheritance? What instructions are necessary for inheritance? How are those instructions duplicated for distribution into daughter cells? How are those instructions duplicated for distribution into daughter cells? By what mechanisms are instructions parceled out to daughter cells? By what mechanisms are instructions parceled out to daughter cells?

Reproduction Parents produce a new generation of cells or multicelled individuals like themselves Parents produce a new generation of cells or multicelled individuals like themselves Parents must provide daughter cells with hereditary instructions, encoded in DNA, and enough metabolic machinery to start up their own operation Parents must provide daughter cells with hereditary instructions, encoded in DNA, and enough metabolic machinery to start up their own operation

Division Mechanisms Eukaryotic organisms Mitosis Mitosis Meiosis Meiosis Prokaryotic organisms Prokaryotic fission Prokaryotic fission

Roles of Mitosis Multicelled organisms Multicelled organisms Growth Growth Cell replacement Cell replacement Some protistans, fungi, plants, animals Some protistans, fungi, plants, animals Asexual reproduction Asexual reproduction

Chromosome A DNA molecule & attached proteins A DNA molecule & attached proteins Duplicated in preparation for mitosis Duplicated in preparation for mitosis one chromosome (unduplicated) one chromosome (duplicated)

Chromosome Number Sum total of chromosomes in a cell Sum total of chromosomes in a cell Somatic cells Somatic cells Chromosome number is diploid (2n) Chromosome number is diploid (2n) Two of each type of chromosome Two of each type of chromosome Gametes Gametes Chromosome number is haploid (n) Chromosome number is haploid (n) One of each chromosome type One of each chromosome type

Human Chromosome Number Diploid chromosome number (n) = 46 Diploid chromosome number (n) = 46 Two sets of 23 chromosomes each Two sets of 23 chromosomes each One set from father One set from father One set from mother One set from mother Mitosis produces cells with 46 chromosomes--two of each type Mitosis produces cells with 46 chromosomes--two of each type

Organization of Chromosomes DNA and proteins arranged as cylindrical fiber DNA histone one nucleosome Figure 9.2 Page 153

The Cell Cycle G1 S G2 Mitosis telophase anaphase metaphase prophase interphase Figure 9.4 Page 154

Interphase Interphase Usually longest part of the cycle Usually longest part of the cycle Cell increases in mass Cell increases in mass Number of cytoplasmic components doubles Number of cytoplasmic components doubles DNA is duplicated DNA is duplicated

Mitosis Period of nuclear division Period of nuclear division Usually followed by cytoplasmic division Usually followed by cytoplasmic division Four stages: Four stages:ProphaseMetaphaseAnaphaseTelophase

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

Stopping the Cycle Some cells normally stop in interphase Some cells normally stop in interphase Neurons in human brain Neurons in human brain Arrested cells do not divide Arrested cells do not divide Adverse conditions can stop cycle Adverse conditions can stop cycle Nutrient-deprived amoebas get stuck in interphase Nutrient-deprived amoebas get stuck in interphase

The Spindle Apparatus The Spindle Apparatus Consists of two distinct sets of microtubules Consists of two distinct sets of microtubules Each set extends from one of the cell poles Each set extends from one of the cell poles Two sets overlap at spindle equator Two sets overlap at spindle equator Moves chromosomes during mitosis 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 Figure 9.5 Page 155

Maintaining Chromosome Number mitosis, cytoplasmic division chromosome (unduplicated) in daughter cell at interphase chromosome (unduplicated) in daughter cell at interphase chromosome (unduplicated) in cell at interphase same chromosome (duplicated) in interphase prior to mitosis Stepped Art Figure 9.6 Page 155

Stages of Mitosis Prophase ProphaseMetaphaseAnaphaseTelophase

Early Prophase - Mitosis Begins Duplicated chromosomes begin to condense Figure 9.7 Page 156

Late Prophase Late Prophase New microtubules are assembled New microtubules are assembled One centriole pair is moved toward opposite pole of spindle One centriole pair is moved toward opposite pole of spindle Nuclear envelope starts to break up Nuclear envelope starts to break up Figure 9.7 Page 156

Transition to Metaphase Spindle forms Spindle forms Spindle microtubules become attached to the two sister chromatids of each chromosome Spindle microtubules become attached to the two sister chromatids of each chromosome Figure 9.7 Page 156

Metaphase All chromosomes are lined up at the spindle equator All chromosomes are lined up at the spindle equator Chromosomes are maximally condensed Chromosomes are maximally condensed Figure 9.7 Page 156

Anaphase Sister chromatids of each chromosome are pulled apart Sister chromatids of each chromosome are pulled apart Once separated, each chromatid is a chromosome Once separated, each chromatid is a chromosome Figure 9.7 Page 156

Telophase Chromosomes decondense Chromosomes decondense Two nuclear membranes form, one around each set of chromosomes Two nuclear membranes form, one around each set of chromosomes Figure 9.7 Page 156

Results of Mitosis Two daughter nuclei Two daughter nuclei Each with same chromosome number as parent cell Each with same chromosome number as parent cell Figure 9.7 Page 156

Cytoplasmic Division Usually occurs between late anaphase and end of telophase Usually occurs between late anaphase and end of telophase Two mechanisms Two mechanisms Cell plate formation (plants) Cell plate formation (plants) Cleavage (animals) Cleavage (animals)

Cell Plate Formation Cell Plate Formation Figure 9.8 Page 158

Animal Cell Division Figure 9.9 Page 159

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