Copyright © 2010 Pearson Education, Inc. Figure 5.2 Chapter 5 Cancer DNA Synthesis, Mitosis, and...

Chapter 5

Cancer DNA Synthesis, Mitosis, and Meiosis

Figure 5.2

Chapter 5 Section 1

What Is Cancer?

5.1 What Is Cancer?

What Is Cancer? Unregulated cell division Tumor: mass of cells with no function

Figure 5.2

Benignif tumor has noeffect onsurrounding tissue(noncancerous)

Metastaticif individual cells breakaway and start a newtumor elsewhere(cancerous)

Malignantif tumor invadessurrounding tissue(cancerous)

Normal cell division Unregulated cell division

Potentiallycancerous

Normalcell

5.1 What Is Cancer?

Benign tumor: doesn’t affect surrounding tissues

Malignant tumor: invades surrounding tissues; cancerous

Metastasis: cells break away from a malignant tumor and start a new cancer at another location

Figure 5.2

Benignif tumor has noeffect onsurrounding tissue(noncancerous)

Metastaticif individual cells breakaway and start a newtumor elsewhere(cancerous)

Malignantif tumor invadessurrounding tissue(cancerous)

Normal cell division Unregulated cell division

Potentiallycancerous

Normalcell

5.1 What Is Cancer?

Metastatic cells Metastatic cells can travel throughout the

body via the circulatory system or the lymphatic system. Lymphatic system collects fluid that leaks

from capillaries. Lymph nodes filter the lymph. Cancer cells found in lymph nodes indicate

metastasis has taken place.

5.1 What Is Cancer?

Cancer cells differ from normal cells:1. Divide when they shouldn’t

2. Invade surrounding tissues

3. Move to other locations in the body

5.1 What Is Cancer?

Risk factors: increase a person’s risk of developing a disease Tobacco use: tobacco contains many

carcinogens (chemicals that can cause cancer)

Alcohol consumption: alcohol and tobacco increase risk in multiplicative manner

High-fat, low-fiber diet

5.1 What Is Cancer? - Risk factors

Risk factors continuedLack of exercise increases risk in two ways

Exercise keeps immune system healthy Exercise helps prevent obesity

Increasing age Immune system declines with age Cumulative damage from carcinogens

Cells that divide frequently

Figure 5.2

End of Chapter 5 Section 1

What Is Cancer?

Figure 5.2

Chapter 5 Section 2

Passing Genes and Chromosomes to Daughter Cells

5.2 Passing Genes and Chromosomes to Daughter Cells

Asexual reproduction: Only one parent Offspring are genetically identical to parent

Sexual reproduction Gametes are combined from two parents Offspring are genetically different from one

another and from the parents

Before dividing, cells must copy their DNA Gene: section of DNA that has the

instructions for making one protein One molecule of DNA is wrapped around

proteins to form a chromosome containing hundreds of genes.

Different species have different numbers of chromosomes (we have 46).

Chromosomes are uncondensed before cell division

They are duplicated through DNA replication Duplicated chromosomes, held together at the

centromere, are called sister chromatids

Figure 5.6

Unduplicatedchromosome

Duplicatedchromosome

Sisterchromatids

Centromere

Replication

DNA Replication DNA molecule is split up the

middle of the helix Nucleotides are added to each

side Result is two identical daughter

molecules, each with one parental strand and one new strand (semiconservative replication)

Figure 5.5a

(a) DNA replication

New strands

Parental strands

DNA polymerase: the enzyme that replicates DNA

Forms covalent bonds between nucleotides on the new strands

Forms hydrogen bond between nitrogenous bases

Figure 5.5b

(b) The DNA polymerase enzyme facilitates replication.

Unwound DNA helix

Free nucleotides

DNA polymerase

Animation—The Structure of DNAPLAY

Figure 5.2

Passing Genes and Chromosomes to Daughter Cells

Figure 5.2

Chapter 5 Section 3

The Cell Cycle and Mitosis

5.3 The Cell Cycle and Mitosis

Cell cycle: the “lifecycle” of the cell Three steps:

1. Interphase: the DNA replicates

2. Mitosis: the copied chromosomes are moved into daughter cells

3. Cytokinesis: the cell is split into 2 daughter cells

5.3 The Cell Cycle and Mitosis - Interphase

Interphase has three phases:1. G1: cell grows, organelles duplicate

2. S: DNA replicates

3. G2: cell makes proteins needed to complete mitosis

Most of the cell cycle

5.3 The Cell Cycle and Mitosis - Mitosis

Mitosis Produces genetically-identical daughter

cells Sister chromatids are pulled apart Four stages:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

5.3 The Cell Cycle and Mitosis - Mitosis Prophase: cell prepares for division

Replicated chromosomes condense Nuclear envelope disappears Microtubules pull the chromosomes toward

the middle of the cell In Animal cells, microtubules are attached

to centrosomes at the poles of the cell

Metaphase: chromosomes prepare for separation chromosomes are aligned across the middle

of the cell

Anaphase: chromotids separate centromeres split, sister chromatids are pulled apart toward

opposite poles

Telophase: cells finalize nuclear division Nuclear envelopes reform around

chromosomes Chromosomes revert to uncondensed form

Animation—MitosisPLAY

5.3 The Cell Cycle and Mitosis - Cytokinesis

Cytokinesis Stage in which two daughter cells are

formed from the original one In Plants, a new cell wall forms between the

cells, built from cellulose

5.3 The Cell Cycle and Mitosis - Cytokinesis

Cytokinesis Animals:

Don’t have a cell wall Proteins pinch the original cell into two new

After cytokinesis, cells reenter interphase.

Mitosis

Figure 5.2

The Cell Cycle and Mitosis

Figure 5.2

Chapter 5 Section 4

Cell Cycle Control and Mutation

5.4 Cell Cycle Control and Mutation

Control of the Cell Cycle Cell division is a tightly controlled process Normal cells halt at checkpoints Proteins survey the condition of the cell Cell must pass the survey to proceed with

cell division

3 checkpoints during the cell cycle

1.G1 checkpoint: are growth factors present? Cell must also be large enough and have

enough nutrients

2.G2 checkpoint: has DNA replicated properly?

3.Metaphase checkpoint: have all chromosomes attached properly to microtubules?

5.4 Cell Cycle Control

Animation—The Cell CyclePLAY

Cell Cycle Control and Cancer

Two important genes

1.Proto-oncogenes

2.Tumor-suppressor genes

Proto-oncogenesProto-oncogenes are genes that code for the cell cycle control proteins

Many proto-oncogenes encode for growth factors

Mutation: a change in the sequence of DNA

This changes the structure and function of the protein

Mutations may be inherited or caused by carcinogens

OncogenesWhen proto-oncogenes mutate, they become oncogenes

Their proteins no longer properly regulate cell division

They usually over stimulate cell division

Figure 5.12a

(a) Mutations to proto-oncogenes

Functional proteinstimulates celldivision only whenconditions are right.

Mutated proteinmay overstimulatecell division byoverridingcheckpointcontrol.

Mutation Mutation

Protein

Proto-oncogeneMutated proto-oncogene(oncogene)

Tumor suppressor genes: genes for proteins that stop cell division if conditions are not favorable

When mutated, can allow cells to override checkpoints

Figure 5.12b

(b) Mutations to tumor-suppressor genes

Tumor-suppressorprotein stops tumorformation by suppressingcell division.

Mutated tumor-suppressorprotein fails to stop tumor growth.

Mutation

Protein

MutationDNA

Tumor suppressorMutated tumorsuppressor

5.4 Cell Cycle Control and Mutation –

Many Mutations Are Required for Cancer to Develop

Angiogenesis: tumor gets its own blood supply Loss of contact inhibition: cells will now pile up

on each other

Loss of anchorage dependence: enables a cancer cell to move to another location

Immortalized: cells no longer have a fixed number of cell divisions

Multiple hit model: process of cancer development requires multiple mutations

Some mutations may be inherited (familial risk)

Most are probably acquired during a person’s lifetime

Figure 5.2

Cell Cycle Control and Mutation

Figure 5.2

Chapter 5 Section 5

Cancer Detection and Treatment

5.5 Cancer Detection and Treatment

Cancer Detection Early detection and treatment is best

Different detection methods for different cancers1. Some cancers produce increased amount

of a characteristic protein2. Biopsies

5.5 Cancer Detection and Treatment

Biopsy: surgical removal of cells or fluid for analysis Needle biopsy: removal is made using a

needle Laparoscope: surgical instrument with a

light, camera, and small scalpel

5.5 Cancer Detection and Treatment -

Treatment Methods Chemotherapy: drugs that selectively kill

dividing cells Combination of different drugs used

(“cocktail”) Interrupt cell division in different ways Helps prevent resistance to the drugs

from arising Normal dividing cells are also killed (hair

follicles, bone marrow, stomach lining)

5.5 Cancer Detection and Treatment - Treatment Methods

Radiation therapy: use of high-energy particles to destroy cancer cells Damages their DNA so they can’t continue

to divide or grow Usually used on cancers close to the surface Typically performed after surgical removal of

Figure 5.2

Cancer Detection and Treatment

Figure 5.2

Chapter 5 Section 6

Meiosis – cell division for reproduction

5.6 MeiosisChromosomes of Somatic Cells Humans have 46 chromosomes Chromosomes come in homologous pairs

Diploid – cells have a pair of each chromosome 22 pairs of autosomes 1 pair of sex chromosomes

5.6 Meiosis

Homologous pairs of chromosomes carry the same genes.

Alleles But each chromosomes may carry a different

version of the gene, called alleles Alleles code for a different version of the same protein

Figure 5.22

5.6 MeiosisMeiosis Specialized form of cell division in gonads to

produce gametes Meiosis reduces number of chromosomes in

each cell by one-half Gamete gets one of each pair Somatic cells are diploid (2n), but gametes are

haploid (1n)

•Eggs and sperm fuse to form diploid Zygote

5.6 Meiosis

Chromosome Replicaton Before meiosis can occur, DNA is duplicated DNA is duplicated in the S phase Creates 2 sister chromotids

Held together by centromere

Figure 5.22

5.6 Meiosis

MeiosisCell division that reduces diploid to haploid Meiosis takes place in two stages:

meiosis I and meiosis II

Figure 5.22

Cell growth andpreparation fordivision

End of previousmitotic event

S and G phasessimilar to the S and Gphases of mitosis

Interphase andMeiosis Cell growth

Interphase(G1, S, G2) DNA is copied

5.6 Meiosis

Steps of Meiosis Meiosis I separates the members of a

homologous pair from each other. After meiosis I, the resulting cells are haploid (n) Meiosis I is therefore called ‘reduction division’

Meiosis II is essentially like mitosis; it separates the sister chromatids

5.6 Meiosis

Four Steps of Meiosis I Meiosis I separates the members of a

homologous pair from each other.1. During prophase I there may be crossing

over between members of homologous pairs

5.6 Meiosis

Four Steps of Meiosis I

2.Metaphase I homologous pairs line up at the equator of cell Microtubules attach to centromere

5.6 Meiosis

Four Steps of Meiosis I

3.Anaphase I Homologous pairs are separated by shortening

microtubules

4.Telophase I – nuclear envelop reforms

5.6 Meiosis

Meiosis II Consists of Prophase II, Metaphase II,

Anaphase II, and Telophase II Virtually identical to mitosis Sister chromatids are separated

5.6 Meiosis

Two events create millions of different gametes from each parent1. Crossing over during prophase I

2. Random alignment during metaphase I

> Both increase the variation of next generation

5.6 Meiosis

1. Crossing over during prophase I exchange of equivalent portions of

chromosomes between members of a homologous pair

Results in new assortment of genes in gametes

5.6 Meiosis

1. Random Assortment during metaphase I Homologous pairs of chromosomes arrange

arbitrarily at cell equator

Results in new assortment of genes in gametes

5.6 Meiosis

Meiosis

5.6 Meiosis - Mistakes in Meiosis

Mistakes in Meiosis Nondisjunction: failure of homologues to

separate normally during meiosis Results in a gamete having one too many

chromosomes (trisomy) or one too few chromosomes (monosomy)

Human Nondisjunction of autosomes

Human Nondisjunction of sex chromosomes

5.6 Meiosis

Inheriting Cancer For cancer mutations to be passed on to

offspring, they must occur in cells that give rise to gametes.

Mutations in somatic cells (e.g., skin cancer) are not heritable.

Comparison of Mitosis & Meiosis – Fig 5.27

Figure 5.2

Meiosis – cell division for reproduction

Figure 5.2

End of Chapter 5

Copyright © 2010 Pearson Education, Inc. Figure 5.2 Chapter 5 Cancer DNA Synthesis, Mitosis, and...

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