the cellular basis of reproduction and...

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for!Biology: Concepts and Connections, Fifth Edition! – Campbell, Reece, Taylor, and Simon

Lectures by Chris Romero

Chapter 8

The Cellular Basis of Reproduction and Inheritance

• Objective: • a. Recognize the chromosomes of daughter

cells, formed through the processes of asexual reproduction and mitosis, the formation of somatic (body) cells in multicellular organisms, are identical to the chromosomes of the parent


!

•Reproduction is one phase of an organism's life cycle!– Sexual reproduction!• Fertilization of sperm and egg produces

offspring


– Asexual reproduction!• Offspring are produced by a single parent,

without the participation of sperm and egg!• Cell division is at the heart of organismal

reproduction

CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION

Like begets like, more or less!• Asexual reproduction!– Chromosomes are duplicated and cell divides !– Each daughter cell is genetically identical to

the parent and the other daughter!• Sexual reproduction!– Each offspring inherits a unique combination

of genes from both parents!– Offspring can show great variation



Cells arise only from preexisting cells!• 1858 Rudolf Virchow: "Every cell from a cell" !• This is at the heart of the perpetuation of life !– Can reproduce an entire unicellular organism!– Is the basis of sperm and egg formation!– Allows for development from a single fertilized

egg to an adult organism!– Functions in an organism's renewal and repair


Prokaryotes reproduce by binary fission!• Prokaryotic cells reproduce asexually by a type

of cell division called binary fission!– Genes are on one circular DNA molecule!– The cell replicates its single chromosome!– The chromosome copies move apart!– The cell elongates!– The plasma membrane grows inward

(cleaves), dividing the parent into two daughter cells

LE 8-3a

Continued elongation of the !cell and movement of copies

Duplication of chromosome!and separation of copies

Plasma!membrane

Cell wall

Prokaryotic!chromosome

Division into!two daughter cells

LE 8-3b

Prokaryotic chromosomes

Col

oriz

ed T

EM 3

2,50

0

×


THE EUKARYOTIC CELL CYCLE AND MITOSIS

The large, complex chromosomes of eukaryotes duplicate with each cell division!• Eukaryotic genes !– Many more than in prokaryotes!– Grouped into multiple chromosomes in the

nucleus


• Eukaryotic chromosomes !– Contain a very long DNA molecule associated

with proteins!– Most of the time occur in the form of thin,

loosely packed chromatin fibers!– Condense into visible chromosomes just

before cell division


• Eukaryotic cell division!1. Chromosomes replicate!• Sister chromatids joined together at the

centromere!2. Sister chromatids separate!• Now called chromosomes!

3. Cell divides into two daughter cells!• Each with a complete and identical set of

chromosomes

LE 8-4bSister chromatids

Centromere

TEM

36,

600×

LE 8-4c

Centromere

Chromosome!duplication

Sister !chromatids

Chromosome!distribution!

to!daughter!

cells


The cell cycle multiplies cells!• The cell cycle: an ordered series of events

extending from the time a cell is formed until it divides into two !

• 3 Major processes:!I. Interphase!II. Mitosis!III. Cytokinesis


• Most of the time of cell cycle is in interphase!• 3 Stages:!– G1: cell grows in size!– S: DNA synthesis (replication) occurs!– G2: Cell continues to grow and prepare for

division!


• The cell actually divides in mitotic (M) phase!– Mitosis: nuclear division!– Cytokinesis: cytoplasmic division!– Duplicated chromosomes evenly distributed

into two daughter nuclei

LE 8-5

INTERPHASE

G1

G2

S!(DNA synthesis)

CytokinesisMito

sis

MITOTIC!PHASE (M)


Cell division is a continuum of dynamic changes!• Interphase: Duplication of the genetic material

ends when chromosomes begin to become visible !

• Prophase (the first stage of mitosis): The mitotic spindle is forming. Centrosomes migrate to opposite ends of the cell Chromatins completely coil into chromosomes; nucleoli and nuclear membrane disperse


• Metaphase: The spindle is fully formed; chromosomes are aligned single file with centromeres on the metaphase plate !

• Anaphase: Chromosomes separate from the centromere, dividing to arrive at poles!

• Telophase: Cell elongation continues, a nuclear envelope forms around chromosomes, chromosomes uncoil, and nucleoli reappear!

• Cytokinesis: The cytoplasm divides

LE 8-6a

INTERPHASE PROPHASE PROPHASE

KinetochoreFragments!of nuclear!envelope

CentrosomeEarly mitotic!spindleChromatin

Centrosomes!(with centriole pairs)

LM 2

50 ×

Nucleolus Nuclear!envelope!

Plasma!membrane!

Chromosome, consisting!of two sister chromatids!

Centromere! Spindle !microtubules!

LE 8-6b

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

Metaphase!plate

Spindle Daughter!chromosomes

Nuclear!envelope!forming

Cleavage!furrow

Nucleolus!forming


Cytokinesis differs for plant and animal cells!• Animals !– Ring of microfilaments contracts into cleavage

furrow!– Cleavage occurs!

• Plants !– Vesicles fuse into a membranous cell plate !– Cell plate develops into a new wall between

two daughter cells

Animation: Cytokinesis

LE 8-7a

Cleavage furrow

Cleavage!furrow

Daughter cells

Cleavage!furrow

Contracting ring of!microfilaments

SEM

140×

LE 8-7bCell plate!forming

Wall of!parent cell

Daughter!nucleus

New cell wallCell wall

TEM

7,5

00×

Daughter cellsVesicles containing!cell wall material

Cell plate


8.8 Anchorage, cell density, and chemical growth factors affect cell division!• An organism must be able to control the timing

of cell division!• Anchorage dependence ! !– Most animal cells must be in contact with a

solid surface to divide


• Density-dependent inhibition!– Cells form a single layer!– Cells stop dividing when they touch one

another!– Inadequate supply of growth factor causes

division to stop

LE 8-8aCells anchor to!dish surface!

and divide.

When cells have!formed a complete!single layer, they!stop dividing!(density-dependent!Inhibition).

If some cells are!scraped away, the!remaining cells!divide to fill the dish!with a single layer!and then stop!(density-dependent!inhibition).

LE 8-8b

After forming a!single layer,!cells have!stopped dividing.

Providing an!additional supply of!growth factors!stimulates!further cell division.


8.9 Growth factors signal the cell cycle control system!• The cell cycle control system regulates the

events of the cell cycle!• If a growth factor is not released at three major

checkpoints, the cell cycle will stop!– G1 of interphase !– G2 of interphase!– M phase




LE 8-9a

G1 checkpointG0

G1

G2

G2 checkpoint

M checkpoint

M

SControl!system


• How a growth factor might affect the cell cycle control system!– Cell has receptor protein in plasma

membrane!– Binding of growth factor to receptor triggers a

signal transduction pathway!• Molecules induce changes in other molecules!

– Signal finally overrides brakes on the cell cycle control system




LE 8-9b

G1 checkpoint

G1

G2M

SControl!system

Growth factor

Plasma membrane

Relay!proteins

Signal!transduction!pathway

Receptor!protein


CONNECTION

8.10 Growing out of control, cancer cells produce malignant tumors!• Cancer cells do not respond normally to the cell

cycle control system!– Divide excessively!– Can invade other tissues!– May kill the organism


• If an abnormal cell avoids destruction by the immune system, it may form a tumor!– Benign: abnormal cells remain at original site!– Malignant: abnormal cells can spread to other

tissues and parts of the body!– Metastasis: spread of cancer cells through the

circulatory system




LE 8-10

Tumor

Glandular!tissue!

Lymph!vessels!

Blood vessel!

A tumor grows from a!single cancer cell. !

Cancer cells invade!Neighboring tissue. !

Cancer cells spread through!lymph and blood vessels to!other parts of the body. !


• Cancers are named according to location of origin!– Carcinoma: external or internal body

coverings!– Sarcoma: tissues that support the body!– Leukemia and lymphoma: blood-forming

tissues!• Radiation and chemotherapy are effective as

cancer treatments because they interfere with cell division


8.11 Review of the functions of mitosis: growth, cell replacement, and asexual reproduction!• When the cell cycle operates normally, mitotic

cell division functions in!– Growth!– Replacement of damaged or lost cells!– Asexual reproduction

Video: Hydra Budding

the cellular basis of reproduction and...

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