Day 5

Cell Division

Cell Cycle & Mitosis

Why Do Cells Divide?

• Cell growth– Larger cell is, the harder

it is for cell to take in nutrients and eliminate waste.

• Replace damaged or old cells

• Form gametes (sex cells)

Cell Division

Cell Cycle

• Beginning of one cell until time that one cell divides into two cells

• Interphase – stage between divisions• Mitosis is division of the nucleus• Cytokinesis is division of cytoplasm and

organellesOften the whole cell cycle is called mitosis,

although this is not technically accurate

Interphase

Interphase

• Longest stage of Cell’s life

• Time spent between divisions

• Produces all materials required for growth (metabolism)

• Preparation for division

• Chromosomes aren’t visible, in form of chromatin

• Centrioles(microtuble-organizing centers) replicate and one centriole moves to each pole.

• 3 phases: G1, S Phase, and G2

G1 Phase of the Cell Cycle

•Growth Phase

•Cell increases in size

S Phase

•Synthesis Phase

• DNA duplicates

•Chromosomes duplicated

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G2

•checkpoint to make sure the DNA is correct

•Cell prepares to divide

Next step –

Mitosis

Interphase

Terms to Know• Chromosome - DNA coiled with

proteins.• Chromatid - one side of the two

strands a chromosome.• Centromere - point at which the

two chromatid attach.• Spindle – cell structures made up

of centrioles and microtubules fibers that move chromosomes during cell division.

• Homologous Chromosomes – pair of like chromosomes that code for same trait.

Homologous Chromosomes

Mitosis:Cell Division

The last part of the Cell Cycle is Mitosis.

-4 phases.

-Takes place in somatic cells (body cells)

Phases of Mitosis

Cytokinesis

1.ProphaseThe Cell begins the

division process

• Nucleolus disappears

• Nuclear membrane breaks apart

• Chromosomes become visible

• Spindle apparatus forms from centrioles and attaches to centromeres.

Prophase

Pair of Centrioles

Spindle Fibers

Chromosomes consisting of 2 Sister Chromatids

2. Metaphase

The Second Phase of Mitosis

• Nuclear Membrane completely gone

• Duplicated chromosomes line up along the cell's equator.

Metaphase

Spindle Fibers

Chromosomes

Equator, or Metaphase Plate

3. Anaphase

The third phase of Mitosis

•Diploid (pair) sets of daughter chromosomes separate

•They are pushed and pulled toward opposite poles of the cell by the spindle fibers

Anaphase

Daughter Chromosomes

Chromosome

Chromatid

Spindle Fibers

4. Telophase

Separation of chromosomes completedCell Plate forms (plants)Cleavage furrow forms(animals)Nucleus & nucleolus reformChromosomes uncoil

Telophase

Cleavage Furrow

Cytokinesis – The final stage of Cell Cycle and Mitosis

The cytoplasm, organelles, and nuclear material are evenly split and two new cells are formed.

Cell Plate

Animals - cell pinches inwardPlants - a new cell wall forms between the two new cells

Cancer

What is Cancer?

• Cancer - disease where cells grow out of control and invade, erode and destroy normal tissue

• Cancer cells lack differentiation (not specialized)

• Normal cells enter the cell cycle only about 50 times; cancer cells can enter the cell cycle repeatedly.

• Normal cells undergo Apoptosis which is a programmed cell death to prevent overgrowth of cells.

•Abnormal cell growth called neoplasm•Abnormal growth results from the mutation of genes that regulate the cell cycle•Carcinogenesis, the development of cancer is gradual—it may take decades before a cell has the characteristics of a cancer cell.

Cancer Development

•Mutations in genes for repair enzymes of DNA can cause cancer.

•If proteins that start cell cycle or inhibit cell cycle are changed (mutated) it can cause cancer.

•Normal DNA segments have ends that shorten with each replication, eventually signaling the cell to end division; cancer cells have enzymes that keep their DNA segments at a constant length and thus the cells to continue dividing.

Origin of Cancer

Characteristics of Cancer Cells• Have abnormal nuclei• Lack differentiation• Chromosomes mutated;

may be duplicated or deleted.

• Gene amplification, extra copies of genes

• Do not undergo apoptosis

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•Do not have contact inhibition•Normal cells are anchored and stop dividing when in contact with other cells;

•Growth not inhibited and will invade and destroy normal tissue•Cancer cells pile on top of each other to form a tumor.•Cancer cells undergo metastasis and angiogenesis•Metastasis – cancer spreads throughout body; new tumors away from primary tumor.•Angiogenesis - formation of new blood vessels to bring nutrients and oxygen to tumor.

Characteristics cont.

Types of Tumors

• Benign: slow growth, non-invasive, no metastasis (not cancerous)

• Malignant: rapid growth, invasive, potential for metastasis (cancerous)

Types of Cancers

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Is cancer a heritable disease?

• There are heritable cancer syndromes but a majority are not.

• Cancer is a genetic disease, but the majority of mutations that lead to cancer are somatic (body cell)

What causes the mutations that lead to cancer?

• Viruses: HPV --> cervical cancer• Bacteria: H. pylori --> gastric cancer• Chemicals --> B[a]P --> lung cancer• UV and ionizing radiation --> skin cancer– What do these agents have in common? They are

all Mutagens

Treatments• Surgery• Chemotherapy• Radiation Therapy• Targeted Therapy• Immunotherapy• Hyperhermia• Bone Marrow and Peripheral Blood Stem Cell Transplant• Laser Therapy• Molecular Targeted Therapy

– http://www.cancer.org/Treatment/TreatmentsandSideEffects/TreatmentTypes/index

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7 ways to Reduce Risk

1. Don’t use tobacoco2. Eat healthy diet – fruits, veggies, limit alcohol3. Maintain healthy weight; physical activity4. Protect yourself from the sun5. Get immunized – Hepatitis B and HPV6. Avoid Risky behaviors – safe sex and no shared needles7. Take early detection seriously

1. Self exams2. Regular doctor visits

Meiosis

Creating Cells for Sexual Reproduction

Meiosis• Takes place in Gametes(sex cells)

• Produces a haploid cell (represented by N)

• People have 46 Chromosome or 23 pairs (2N)– When an egg joins a sperm the count must stay at 46 to

remain human

– egg can only have 23

– sperm can only have 23

• How does this happen?

Definitions

• Diploid Cells- (2N)cells that have pairs of chromosomes. There are 2 of each chromosome in diploid cells.

• Haploid Cells- (N)cells that have only one of each chromosome. Haploid cells are used for sexual reproduction.

• Somatic Cells – body cells that are Diploid.

• Gametes or germ cells – sex cells that are Haploid.

•During Meiosis gamete (sex) cells undergo a “double division”, called Meiosis I and Meiosis II.

•This maintains the DNA, but reducing the chromosomal count to 23.

+ =

Sperm (23) + Egg (23) = Fertilized Cell (46)

Haploid Cells (N) Haploid Cells (N) Diploid Cells (2N)

Meiosis I

Prophase I• Chromosomes

already copied• Centrioles separate• Nuclear membrane

breaks down• Crossing over occurs

here

Crossing Over

• Synapsis- Homologous Pairs line up = Tetrad• During synapsis the chromatids within a homologous pair

may twist around each other and break off and attach to the other homologous pair = Crossing Over

• Results in exchange of genetic material between maternal and paternal chromosomes = genetic recombination

Metaphase I

• Chromosome pairs line up at equator

Anaphase I

• Chromosome pairs split

• Sister chromatids stay connected

Telophase I

• Cell starts to divide in two

• Nuclear membranes start to form again

Meiosis II

Prophase II

• Chromosomes do not replicate again

• Cells have one set of sister chromatids

• Nuclear membrane breaks down

• Centrioles separate

Metaphase II

• Sister chromatids line up at the middle of the cell

Anaphase II

• Sister chromatids divide

Telophase II

• Cells start to split in two

• Each cell has one set of chromosomes—it is a haploid

• 4 cells form

Original Gamete Metaphase Anaphase Telophase Cytokinesis

2 Daughter Cells Metaphase 2 Anaphase 2 Telophase 2 Cytokinesis – 4 Gametes

SPERMATOGENESIS- Meiosis in Males

OOGENESIS – Meiosis in females

Meiosis ensures that

all living organisms

maintain both Genetic

Diversity and Genetic Integrity

Cell Division in Prokaryotes

Lack a nucleus Have a single

chromosomeReproduce by

binary fissionInclude bacteria

Steps in Binary Fission

Cells increase their cell mass slightly

the single, circular bacterial chromosome is replicated

Each cell divides into 2 daughter cells

Mutations

Ch. 10. pg. 219-220

Mutations

• Changes in nucleotide sequence of DNA

• May occur in somatic cells (body cells)– not passed to offspring

• May occur in gametes (eggs & sperm)– passed to offspring

Causes• Mutations happen regularly• Any agent that causes a change in DNA is

called a mutagen.• Mutagens include radiation, chemicals,

and even high temperatures.– Ex. of radiation: X rays, cosmic rays, ultraviolet

light, and nuclear radiation.– Chemicals: Benzene

• Many mutations are repaired by enzymes.

Are Mutations Helpful or Harmful?

• Some harmful - Skin cancers and some leukemias result from somatic mutations

• Most mutations have no affect, some have detrimental affects and a few mutations may improve an organism’s survival (beneficial)

Types of Mutations

• 2-Types– 1. Gene mutations - change in one DNA sequence

of a gene.– 2.Chromosomal mutations – change in structure

or loss or gain of part of a chromosome.

Gene mutation- 2 types1. Point Mutation

• A change in a single base pair in DNA.• Changes the amino acid in the protein• Does not always cause a problem.

• THE DOG BIT THE CAT• THE DOG BIT THE CAR

2. Frameshift Mutation

• A single base is added or deleted from the DNA causing all the other bases to be out of position.

• More harmful than a regular point mutation.

• THE DOG BIT THE CAT• THE DOB ITT HEC AT

Chromosome Mutations

• Five types exist:–Deletion–Inversion–Translocation–Nondisjunction–Duplication

DeletionPart of a chromosome is lost/deleted.

A B C D E F G H A B C E F G H

Duplication/InsertionA part of the chromosome repeats

A B C D E F G H A B C B C D E F G H

InversionPart of a chromosome breaks off;

reattaches backward

A B C D E F G H H A D C B E F G

TranslocationPart of a chromosome breaks off; attaches

to a different chromosome that is not homologous

W X Y Z Y ZTranslocation

A B E FDCBX AWC HGGE HD F

W X Y Z Y ZTranslocation

Chromosome Mutation Animation

Karyotyping

Ch. 6 pg. 122-123

• Some mutations that cause chromosomal abnormalities can be detected by analyzing a karyotype.

• Karyotype – photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size, number, and shape.– Identifies gender and genetic disorders

• Amniocentesis – medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections– small amount of amniotic fluid, which has fetal

tissues, is extracted from the amniotic sac surrounding a developing fetus

• Autosomal abnormalities – abnormalities of chromosomes not directly involved in determining gender

• Sex Chromosomal abnormalities – abnormalities that affect the gender of an individual

How Scientists Read Chromosomes?

1) Size. This is the easiest way to tell two different chromosomes apart.

2) Banding pattern. The size and location of Giemsa bands on chromosomes make each chromosome pair unique.

3) Centromere position. Centromeres are regions in chromosomes that appear as a constriction. They have a special role in the separation of chromosomes into daughter cells during mitosis cell division (mitosis and meiosis).

Using these key features, scientists match up the 23 pairs – one set from the mother and one set from the father.

To "read" a set of human chromosomes, scientists first use three key features to identify their similarities and differences:

Image taken from: http://learn.genetics.utah.edu/content/begin/traits/scientists/

Typical Karyotype

Typical Karyotype

Trisomy 21- Down’s Syndrome - Karyotype

47 Total Chromosomes

Three Chromosomes at the 21st Pair Image taken from: http://worms.zoology.wisc.edu/zooweb/Phelps/karyotype.html

Monosomy X - Turner Syndrome - Karyotype

45 Total Chromosomes

One “X” Chromosome Image taken from: http://worms.zoology.wisc.edu/zooweb/Phelps/karyotype.html

XYY Karyotype

One “X” and Two “Y” Chromosomes

47 Total Chromosomes

Image taken from: http://worms.zoology.wisc.edu/zooweb/Phelps/karyotype.html