Lecture Power Point to accompany Inquiry into Life

Lecture Power. Point to accompany Inquiry into Life Twelfth Edition Sylvia S. Mader Chapter 5 Copyright © The Mc. Graw-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 • G 1 • S • G 2 – Mitotic Stage • Mitosis and Cytokinesis

5. 1 Cell Increase and Decrease • The Cell Cycle – Interphase • G 1 • S • G 2 – 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 • G 1 • G 2 • 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 (2 n): 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 (2 n): Cells have two (a pair) of each type of chromosome – Haploid (1 n): 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 equatorsynapsis • 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 (2 n) divide in meiosis I to form two secondary spermatocytes (1 n) – 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 (2 n) divides in meiosis I to produce one secondary oocyte (1 n) 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