Inquiry into LifeTwelfth Edition

Chapter 5

Lecture PowerPoint to accompany

Sylvia S. Mader

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5.1 Cell Increase and Decrease

• Cell division increase the number of somatic cells (body cells)

5.1 Cell Increase and Decrease

• Cell division increase the number of somatic cells (body cells)

Zygote Trillions of cells

5.1 Cell Increase and Decrease

• Cell division increase the number of somatic cells (body cells)

– Mitosis: Division of the nucleus

5.1 Cell Increase and Decrease

• Cell division increase the number of somatic cells (body cells)

– Mitosis: Division of the nucleus

– Cytokinesis: Division of the cytoplasm

5.1 Cell Increase and Decrease

• Cell division increase the number of somatic cells (body cells)

– Mitosis: Division of the nucleus

– Cytokinesis: Division of the cytoplasm

– Apoptosis: Programmed cell death

5.1 Cell Increase and Decrease

• The Cell Cycle– Orderly set of stages that occur between

the time a cell divides and the time the resulting daughter cells divide

5.1 Cell Increase and Decrease

• The Cell Cycle– Interphase

• G1

• S• G2

– Mitotic Stage• Mitosis and Cytokinesis

5.1 Cell Increase and Decrease

• The Cell Cycle– Interphase

• G1

• S• G2

– Mitotic Stage• Mitosis and Cytokinesis

The Cell Cycle

5.1 Cell Increase and Decrease

• Control of the Cell Cycle– Internal and External Signals

• Signaling proteins called cyclins increase and decrease as the cell cycle continues

– Three Checkpoints• G1

• G2

• M

The Cell Cycle

5.1 Cell Increase and Decrease

• Apoptosis– Cells undergo programmed cell death

when they cannot complete mitosis or in response to external signals.

Apoptosis

5.2 Maintaining the Chromosome Number

5.2 Maintaining the Chromosome Number

• Terms:– Chromatin: tangled mass of threadlike DNA in a

non-dividing cell

5.2 Maintaining the Chromosome Number

• Terms:– Chromatin: tangled mass of threadlike DNA in a

non-dividing cell– Chromosomes: condensed DNA molecules

observed in dividing cells

5.2 Maintaining the Chromosome Number

• Terms:– Chromatin: tangled mass of threadlike DNA in a

non-dividing cell– Chromosomes: condensed DNA molecules

observed in dividing cells– Diploid (2n): Cells have two (a pair) of each type

of chromosome

5.2 Maintaining the Chromosome Number

• Terms:– Chromatin: tangled mass of threadlike DNA in a

non-dividing cell– Chromosomes: condensed DNA molecules

observed in dividing cells– Diploid (2n): Cells have two (a pair) of each type

of chromosome– Haploid (1n): Cells have half the diploid number of

chromosomes

5.2 Maintaining the Chromosome Number

• Overview of Mitosis– Nuclear division in which chromosome number

stays constant– DNA replication produces duplicated

chromosomes– Each duplicated chromosome is composed of 2

sister chromatids held together by a centromere– Sister chromatids are genetically identical– During mitosis, the centromere divides and each

chromatid becomes a daughter chromosome

Chromosomes and Chromatids

Mitosis Overview

5.2 Maintaining the Chromosome Number

• Mitosis in Detail - Animal Cells– Prophase-nuclear membrane disappears,

centrosomes migrate, spindle fibers appear– Metaphase-chromosomes line up at metaphase

plate, associated with spindle fibers– Anaphase-centromeres divide, sister chromatids

migrate to opposite poles, cytokinesis begins– Telophase-nuclear membranes form, spindle

disappears, cytokinesis occurs

Mitosis in Detail - Animal Cells

5.2 Maintaining the Chromosome Number

• How Plant Cells Divide– Occurs in meristematic tissues– Same phases as animal cells– Plant cells do not have centrioles or asters

Mitosis in Detail - Plant Cells

5.2 Maintaining the Chromosome Number

• Cytokinesis in Plant Cells– Flattened, small disk appears between daughter

cells– Golgi apparatus produces vesicles which move to

disk– Release molecules which build new cell walls – Vesicle membranes complete plasma membranes

Cytokinesis in Plant Cells

5.2 Maintaining the Chromosome Number

• Cytokinesis in Animal Cells• Cleavage furrow forms between daughter

nuclei• Contractile ring contracts deepening the furrow• Continues until separation is complete

Cytokinesis in Animal Cells

5.2 Maintaining the Chromosome Number

• Cell Division in Prokaryotes: Binary Fission– Prokaryotes have a single chromosome– Chromosomal replication occurs before division– Cell begins to elongate to twice its length– Cell membrane grows inward until division is

complete

Binary Fission

5.3 Reducing the Chromosome Number

5.3 Reducing the Chromosome Number

• Meiosis– Occurs in the life cycle of sexually reproducing

organisms– Reduces the chromosome number– Provides offspring with a different combination of

traits from that of either parent

5.3 Reducing the Chromosome Number

• Overview of Meiosis– 2 divisions, 4 daughter cells– Cells are diploid at beginning of meiosis– Pairs of chromosomes are called homologues

5.3 Reducing the Chromosome Number

• Overview of Meiosis– Meiosis I

• Homologues line up side by side at equator-synapsis

• When pairs separate, each daughter cell receives one member of the pair

• Cells are now haploid

Meiosis

5.3 Reducing the Chromosome Number

• Overview of Meiosis– Meiosis II

• No replication of DNA occurs in this division• Centromeres divide and sister chromatids

migrate to opposite poles to become individual chromosomes

• Each of the four daughter cells produced has the haploid chromosome number and each chromosome is composed of one chromatid

Meiosis

5.3 Reducing the Chromosome Number

• Overview of Meiosis– Fertilization

• Fertilization restores the diploid number of chromosomes in a cell that will develop into a new individual.

5.3 Reducing the Chromosome Number

• Meiosis in Detail– Genetic Recombination Occurs in Two Ways

• Crossing Over• Independent Assortment

Crossing Over

Independent Assortment

5.3 Reducing the Chromosome Number

• Phases of Meiosis I

– Prophase I• Synapsis occurs, nuclear membrane breaks

down• Homologues line up side by side and crossing

over occurs– Metaphase I

• Homologous pairs line up at metaphase plate such that maternal or paternal member may be oriented toward either pole

5.3 Reducing the Chromosome Number

• Phases of Meiosis I

• Anaphase I• Homologous chromosomes (each still

consisting of 2 chromatids) undergo independent assortment into daughter cells

– Telophase I• Cytokinesis produces 2 daughter cells which

are haploid

Phases of Meiosis I

• Fig 5.12

5.3 Reducing the Chromosome Number

• Interkinesis - period of time between Meiosis I and Meiosis II

• Phases of Meiosis II

– Prophase II-• Cells have one member of each homologous

pair– Metaphase II

• Chromosomes line up at the metaphase plate

5.3 Reducing the Chromosome Number

• Phases of Meiosis II

– Anaphase II• Centromeres divide and daughter

chromosomes migrate– Telophase II

• Nuclei form, cytokinesis

Phases of Meiosis II

• Fig 5.13

5.3 Reducing the Chromosome Number

• Nondisjunction

– The failure of paired chromosomes or chromatids to separate during cell division

– Results in cells with an abnormal number of chromosomes

– Trisomy 21 (Down syndrome) is an example

5.3 Reducing the Chromosome Number

• Genetic Recombination– Promotes genetic variability– Independent assortment of paired chromosomes

during metaphase I– Crossing over in prophase I– Both assure that gametes will contain different

combinations of chromosomes– When fertilization occurs, the resulting offspring

will be genetically unique

Comparison of Meiosis to Mitosis

• DNA replication occurs only once prior to either meiosis and mitosis

• Meiosis requires two divisions, mitosis only one

• Meiosis produces four daughter cells, mitosis produces two

• Daughter cells from meiosis are haploid, those from mitosis are diploid

• Daughter cells from meiosis are genetically variable, while those from mitosis are genetically identical

Comparison of Meiosis to Mitosis

5.5 The Human Life Cycle

• Requires both mitosis and meiosis• Meiosis in the female is called oogenesis• Meiosis in the male is called

spermatogenesis• At fertilization, the resulting zygote divides by

mitosis for the processes of growth and development

• Mitosis is used for repair throughout life

Life Cycle of Humans

5.5 The Human Life Cycle

• Spermatogenesis– Begins at puberty and continues throughout life– Primary spermatocytes (2n) divide in meiosis I to

form two secondary spermatocytes (1n)– Secondary spermatocytes divide in meiosis II to

produce four sperm

5.5 The Human Life Cycle

• Oogenesis– Begins in the fetus

• Primary oocytes are arrested in prophase I

– At puberty, one primary oocyte continues the process of meiosis during each menstrual cycle

– Primary oocyte (2n) divides in meiosis I to produce one secondary oocyte (1n) and one polar body• Division is unequal as secondary oocyte receives most

of the cell contents and half the chromosomes

5.5 The Human Life Cycle

• Oogenesis– If the secondary oocyte is fertilized, meiosis II will

proceed.• Another unequal division will occur, the egg receiving

most of the cytosplasm. A second polar body is also formed.

– The unequal divisions allows the egg to have all the cellular “machinery” it needs for embryonic development

Spermatogenesis and Oogenesis in Mammals

5.5 The Human Life Cycle• Summary

– Spermatogenesis and oogenesis both utilize meiosis– Spermatogenesis begins at puberty and continues

throughout life– Spermatogenesis produces one sperm per primary

spermatocyte• Results in production of many sperm

– Oogenesis results in one oocyte and up to three polar bodies per primary oocyte• Divisions are unequal, ovum receives most cell contents

– Oogenesis begins prior to birth, stops until puberty, then resumes in a cyclic pattern

– Cyclic release of oocytes continues until menopause when the process stops