Chapter 8 DNA Replication, Binary Fission,

and Mitosis

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What are the 2 forms of reproduction?

1) Asexual2) Sexual

Human family: © Corbis RF; Amoeba reproducing by binary fission: © Carolina Biological Supply

Company/Phototake; Mother cat and kittens: © Jane Burton/Dorling Kindersley/Getty Images

Two Types of Cell Division Interact in the Sexual Life Cycle

Sex cells combine at fertilization.

DNA Replication Precedes Cell Division

Section 8.2

Semi conservative:½ old

&½ new

Figure 8.6

The image at right shows a cell’s DNA before replication. Which of the following best represents the position of the newly created (red) DNA strands after replication is complete?

A.B.

Flower: © Doug Sherman/Geofile/RF

Binary FissionBinary fission

Why is binary fission an asexual process?

A. It occurs only in prokaryotes.B. It does not require DNA replication.C. It produces two identical cells.D. The chromosome is circular.

Flower: © Doug Sherman/Geofile/RF

Cell Cycle

• Interphase

• Mitotic phase (karyokinesis)

– Prophase

– Prometaphase

– Metaphase

– Anaphase

– Telophase

• Cytokinesis

Section 8.5

• What are cells doing when they are not dividing?

• What phase are the majority of your cells in?

• What’s occurring during G1, S & G2 phases of Interphase?

The Cell Cycle

Figure 8.10

Section 8.4

Prophase chromosomes condensed for mitosis

Replicated Chromosomes Condense Before Eukaryotic Cell Division

Figure 8.8Cell division: © Clouds Hill Imaging Ltd./Corbis

• Divide by mitosis

Interphase (chromatin, DNA replication)

Section 8.4

Naked DNA wraps nucleosomes, groups of histone proteins.

Figure 8.9

Replicated Chromosomes Condense Before Eukaryotic Cell Division

Section 8.4

Chromatin

Replicated Chromosomes Condense Before Eukaryotic Cell Division

Figure 8.9

Section 8.4

Condensing into a replicated chromosome

Replicated Chromosomes Condense Before Eukaryotic Cell Division

Figure 8.9

Interphase

• G1

• S DNA replication or DNA synthesis

• G2

Section 8.5 Figure 8.22

Chromosomes Divide During Mitosis

Mitosis is divided into several steps, summarized here and shown in more detail on the following slides.

Section 8.5 Figure 8.11

Chromosomes Divide During Mitosis

Animal cells © Ed Reschke/Peter Arnold/Getty Images; Plant cells © Ed Reschke

Section 8.5

Chromosomes Divide During Mitosis

Figure 8.11Animal cells: © Ed Reschke/Peter Arnold/Getty Images; Plant cells: © Ed Reschke

Prophase/Prometaphase

• Longest of mitotic phases

• Centrioles move to poles

• Nuclear envelop disappears

• Nucleolus disappears

Early Prophase

Late Prophase

Figure 12.5-3

ChromosomesChromosomal

DNA molecules

Centromere

Chromosomearm

Chromosome duplication(including DNA replication)and condensation

Sisterchromatids

Separation of sisterchromatids intotwo chromosomes

1

2

3

If you could

see chromosomes in

interphase

Figure 12.4

0.5 mCentromere

Sisterchromatids

Replicated chromosome

Centromere

Sister chromatids

Section 8.5

Chromosomes Divide During Mitosis

Figure 8.21

This figure summarizes the changes that occur to one chromosome during a cell cycle.

Metaphase

• Duplicated chromosomes line up

• Metaphase plate

Anaphase

• Sister chromatids separate

• Chromosomes

Telophase & Cytokinesis

• Nuclear envelop reforms

• Nucleolus reappears

• Cell pinches in two

• Animal cells:

– Cleavage furrow

• Plant cells:

– Cell plate

Section 8.5 Figure 8.12

Cytoplasm Splits in Cytokinesis

In an animal cell, the first sign of cytokinesis is the cleavage furrow.

Cleavage furrow: © Dr. David M. Phillips/Visuals Unlimited

Concept Check

The diagram represents the cell cycle through time of a eukaryotic organism. During which of the phases of the cell cycle will you copy or replicate your DNA?

a) G1 phase

b) S phase

c) G2 phase

d) M phase

e) Cytokinesis

© 2012 Pearson Education, Inc.

Concept Check

The diagram represents the cell cycle through time of a eukaryotic organism.

During which of the phases of the cell cycle will sister chromatids separate?

a) G1 phase

b) S phase

c) G2 phase

d) M phase

e) Cytokinesis

© 2012 Pearson Education, Inc.

TelophaseAnimal & Plant

Animal Mitosis

Plant Mitosis

Figure 17.16

The nucleus is removedfrom an unfertilized eggtaken from a female.

A body cell from theadult animal to becloned is inserted intothe egg.

Electrical current isapplied to fuse the cells.

The nucleus of theanimal to be clonedis now the nucleus ofthe egg.

The egg is implantedinto a surrogatemother.

The surrogate mothergives birth to a clone.

Somatic Cell Nuclear Transfer: Cloning an Adult

The Cell Cycle Creates New Cells

• Complete cell cycle takes 18–24 hours

• Mitosis and cytokinesis < 1 hr

• Many cells enter a nondividing state, G0, either temporarily or permanently

– Liver cells will divide when stimulated

– Neurons, osteocytes enter G0 after adolescence

Asexual Cell Division1. Growth

2. Repair/replace

3. Regenerate body parts

• All somatic (body) cells

• Nerve & muscle

• Exception:

– Certain nerve cells

Asexual Cell Division

1. Growth

2. Repair/replace

3. Regenerate body parts

4. Reproduction

• Budding

• Fragmentation

• All somatic (body) cells

• Nerve & muscle

• Exception:

– Certain nerve cells

Factors that influence cell division

1. Growth factors

2. Density dependent inhibition (contact)

Figure 17.13

M checkpoint

G2 checkpoint

M

G2

S

G1

G1 checkpoint

Factors that influence cell division

3. Restriction points

4. Cell size

Factors that influence cell division

5. Regulatory proteins

cyclical changes

Section 8.6

Cancer Arises When Cells Divide Out of Control

Chemical checkpoints regulate the cell cycle.

Figure 8.13

Section 8.6

Cancer Arises When Cells Divide Out of Control

But what if the body loses control of cell division?

Figure 12.20

Glandulartissue

Tumor

Lymph vessel

Bloodvessel

Cancercell

Metastatictumor

A tumor growsfrom a singlecancer cell.

Cancer cells invade neighboringtissue.

Cancer cells spreadthrough lymph andblood vessels to other parts of the body.

Cancer cells may survive and establisha new tumor in another part of the body.

4321

Mitosis & CancerCancer cells

• Divide uncontrollably

• No “normal” regulation

• Stimulates angiogenesis

Benign tumor

Malignant tumor

Metastasis

Benign vs malignant tumors

benign tumor cancer in situ

capsule

How Cancer Develops

• Mutated or damaged genes• Proto-oncogenes

– Normal regulatory genes

• Oncogenes– Mutated or damaged proto-oncogenes

• Mutator genes– Involved in DNA repair during replication

– May be mutated themselves and not function

• Tumor suppressor genes– Regulatory genes repress cell growth, division, differentiation,

and adhesion

– May be turned off, damaged, or mutated in cancers

Section 8.6 Figure 8.14

Cancer Arises When Cells Divide Out of Control

A tumor is an abnormal mass of tissue. The cells of a tumor divide out of control. Tumors are either benign or malignant.

Section 8.6

Cancer Arises When Cells Divide Out of Control

Genes and the environment both can increase cancer risk.

Figure 8.18

Section 8.6

Cancer Arises When Cells Divide Out of Control

A tumor may arise from overactive proto-oncogenes or from underactive tumor suppressor genes.

Figure 8.16

No cancer

Tumor Suppressors

p53 genep21 geneBRCA1BRCA2

Tumor Suppressors

Telomeres

• Repetitive DNA

• Tips of chromosomes

• Shorten during division

• Limit # of divisions

Telomerase

• Immortalizing enzyme

• Replaces telomeres

• Allows for more cell division

Fig. 20BSelf exams

fingerpads

Self exams

Fig. 20CSelf exams

8.6 Mastering Concepts

What keeps cells from dividing when they are not supposed to?

World’s tallest man © Frederic J. Brown/AFP/Getty Images

Cancer Development

Figure 18.2

Genetically

altered

epithelial cell

Hyperplasia

• Cell divides

more rapidly

than normal

Dysplasia

• Cells change

form

In situ cancer

• Cells stay in

one place

Malignant tumor (cancer)

• Cancer cells invade normal tissue

and enter blood and lymph

• Metastases form at distant sites

Normal underlying connective

or muscle tissueBlood vessel

Invasion

Metastases

Cancer Development

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malignant

tumor

Colon Cancer

Advances in Diagnosis: Early Detection

• Tumor imaging

– X-rays

• Example: mammogram

– Positron emission tomography (PET)

– Magnetic resonance imaging (MRI)

• Genetic testing

– Identify mutated genes

– Privacy and treatment issues

• Enzyme tests for cancer markers

– Screening large numbers of people

Tumor-Busting Viruses

•Virotherapy uses scientifically-engineered viruses to target cancer cells.

Tying topics together - Comprehension

Tumor-Busting Viruses

How do viruses selectively attach to target cells?

a) target cells display unique cell-surface receptors

b) target cells secrete unique identification proteins

c) viruses attach to specific materials engulfed by cells

d) viruses are not selective about target cells

Apoptosis Is Programmed Cell Death

Section 8.7

Apoptosis has two

functions:

• Eliminates

excess cells,

carving out

structures

• Weeds out aging

or defective cells

Figure 8.19Syndactyly: © Imaginechina/Corbis