Unit 6 Cell Division

Reproduction and Development

Cell Division

• A complex series of changes in the nucleus of a cell that leads to the production of two new cells.

• The new cells are called daughter cells.

Why do cell divide??

• DNA overload- The cell’s DNA would no longer be able to serve the increasing needs of the growing cell.

• Exchange of Materials -If cells grow to large, its more difficult to get rid of waste and take in nutrients.

Why do cells divide?

• Growth- Humans start off as one cell by the time they are adults they have over 10 trillion cells.

• Repair- tissue damage

• Reproduction – Asexual or Sexual

What is inside of the Nucleus?

• Genetic information that is passed on from one generation of cells to the next.

• Chromosomes are made up of DNA which carries that genetic information

• Chromosomes only visible during cell division

Chromosomes

Parts of the chromosome

• Centromere - the part of a chromosome that links sister chromatids

• Chromatid - one copy of a duplicated chromosome, which is generally joined to the other copy by a single centromere.

Homologous ChromosomesHomologous Chromosomes

• Pair of chromosomeschromosomes (maternalmaternal and paternalpaternal) that are similar in shape and size.

• Homologous pairs (tetrads) (tetrads) carry genes controlling the same inherited traits.

• Each locuslocus (position of a gene) (position of a gene) is in the same position on homologues.

• Humans have 23 pairs of homologous chromosomes.homologous chromosomes.

22 pairs of autosomesautosomes

1 pair of sex chromosomessex chromosomes

Homologous ChromosomesHomologous Chromosomes((because a homologous pair consists of 4 chromatids it is called a “Tetrad”)because a homologous pair consists of 4 chromatids it is called a “Tetrad”)

Paternal Maternal

eye color locus

eye color locus

hair color locus

hair color locus

“Sex Chromosomes” …….the 23rd set

23

This person has 2 “X” chromosomes… and is a

female.

Cell Cycle

• Hormones send signals to cells to prepare for division when it is needed.

How do Cells divide?

• Two Stages to a Cell Dividing

• INTERPHASE – growth and preparation

• CELL DIVISION - involves a complex series of changes in the nuclei of body cells that produce identical daughter cells – Mitosis– Cytokinesis

Mitosis

• Prophase – Nuclear Membrane becomes invisible and chromosomes condense

• Metaphase – Chromosomes line up in the middle• Anaphase – Chromosomes are pulled apart by

spindle fibers that attach at the centromere• Telophase – Cell membrane pinches in and

cytokinesis occurs (Cell plate forms in plant cell only)

Cytokinesis

• Dividing of the Cytoplasm and the creation of two daughter cells.

Stages of Mitosis

Same as mitosis in animals except:

• Plants have no centrioles – spindle fibers take their place

• Cell wall does not pinch because it is too rigid

• Cell plate divides the cell into two

The Cell Cycle and Cancer

Cancer

• Cells lose the ability to control growth

• Uncontrolled growth of cells lead to tumors that can damage the surrounding tissue.

There are several factors that regulate the cell cycle and assure a cell divides correctly.

1.Before a cell divides, the DNA is checked to make sure it has replicated correctly. (If DNA does not copy itself correctly, a gene mutation occurs.)

DNA replication Animation:click on DNA picture

2. Chemical Signals tell a cell when to start and stop dividing.

(Target cells animation: click on go sign)

3. Neighboring cells communicate with dividing cells to regulate their growth also.

(Normal contact inhibition animation: click on petri dish)

Cancer is a disease of the cell cycle. Some of the body’s cells divide uncontrollably and tumors form.

Tumors in Liver

Tumor in Colon

Causes that disrupt the cell cycle.

Mutations may be caused by:

1. radiation 2. smoking 3. Pollutants 4. chemicals 5. viruses

While normal cells will stop dividing if there is a mutation in the DNA, cancer cells will continue to divide with mutation.

Due to DNA mutations, cancer cells cannot communicate with neighboring cells. Cells continue

to grow and form tumors.

(cancer cells dividing: click on picture.)

Skin cancer

SUMMARY

Normal Cell Division

1. DNA is replicated properly.

2. Chemical signals start and stop the cell cycle.

3. Cells communicate with each other so they don’t become overcrowded.

Cancer Cells

1. Mutations occur in the DNA when it is replicated.

2. Chemical signals that start and stop the cell cycle are ignored.

3. Cells do not communicate with each other and tumors form.

Estimated Cancer Deaths in the US in 2013

Treating Cancers

Cancer treatments include drugs that can stop cancer cells from dividing.

Mitosis and Asexual Reproduction

Occurs only through the process of mitosis

•Each offspring has the same genetic information

Where can asexual reproduction be found?

BACTERIA YEAST PLANTS

There are 5 different types of asexual reproduction.

1. Budding

Parent divides unequally; new individuals develop from budsex – yeast & hydra

2. Binary Fission

Most simple form of asexual reproduction; Parent divides equally and results in two separate individualsEx.-paramecium

3. Spore Formation

Single specialized cells that germinate when released from parent. Usually covered by a protective coating for preservation.

4. Regeneration/fragmentation

Ability to regrow new body parts/ability to grow new Organism from parts.ex – hyrda, planaria, starfish, the bad guy from Terminator 2

5. Vegetative Reproduction/Propagation

Refers to roots, stems, and leaves. Cells divide then differentiateto produce the same organismEx.- strawberry plant, pick-a-back plant

MEIOSISMEIOSIS

Organisms that reproduce Sexually are made up of two different types of cells.

1. Somatic Cells are “body” cells and contain the normal number of chromosomes ….called the “Diploid” number (the symbol is 2n). Examples would be … skin cells, brain cells, etc. (Mitosis Cell Division)

2. Gametes are the “sex” cells and contain only ½ the normal number of chromosomes…. called the “Haploid” number (the symbol is n)….. Sperm cells and ova are gametes. (Meiosis Cell Division)

Meiosis Cell Division

• Formation of sex cells (gamates)

• Egg cell and Sperm cell (gamates)

• 4 daughter cells are made with each having half the number of chromosomes as parent cell (n) Haploid

• Reduction of chromosomes

• Cells are NOT identical to parent

Meiosis is the process by which is the process by which ”gametes” (sex cells) , ”gametes” (sex cells) , with halfhalf the

number of chromosomes,chromosomes, are produced.

During Meiosis diploid cells are reduced to haploid cells

Diploid (2n) Diploid (2n) Haploid (n)Haploid (n)

If Meiosis did not occur the chromosome number If Meiosis did not occur the chromosome number in each new generation would double…. The in each new generation would double…. The

offspring would die.offspring would die.

Stages of Meiosis

Crossing OverCrossing Over creates variation (diversity) in the offspring’s traits.creates variation (diversity) in the offspring’s traits.

nonsister chromatids

variation

Tetrad

Question:Question:

• A cell containing 20 chromosomes20 chromosomes (diploid)(diploid) at the beginning of meiosis would, at its completion,

produce cells containing how many chromosomeschromosomes?

Answer:Answer:

• 10 chromosomes (haploid)10 chromosomes (haploid)

Sexual Reproduction

Sexual Development• Puberty is a period of rapid growth

and sexual maturation during which the reproductive system becomes fully functional.

• When puberty ends, reproductive organs are fully developed.

• Puberty usually begins between the ages of 9 and 15, and usually starts one year earlier in females than in males.

Sexual Development

• Puberty begins when the hypothalamus signals the pituitary to produce increased levels of two hormones that affect the gonads.

• These hormones are follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

The Male Reproductive System

• The Male Reproductive System• Release of FSH and LH stimulates cells in the testes

to produce testosterone.

• FSH and testosterone stimulate the development of sperm.

The Male Reproductive System

• A sperm cell consists of:

• a head, which contains the nucleus

• a midpiece, which contains energy-releasing mitochondria

• a tail, which propels the cell forward

Head

Nucleus

Midpiece

Mitochondria

Tail

The Male Reproductive System

• Male Reproductive SystemUrinary bladder

Vas deferens

Pubic bone

Urethra

Penis

Seminal vesicle

Rectum

Prostate gland

Bulbourethral gland

Scrotum

Testis

Epididymis

The Female Reproductive System

• Puberty in females starts when the hypothalamus signals the pituitary gland to release FSH and LH.

• FSH stimulates cells within the ovaries to produce estrogen.

The Female Reproductive System

• The Female Reproductive System• The primary reproductive organs in the female are

the ovaries.

• The ovaries are located in the abdominal cavity.

The Female Reproductive System

Fallopian tube

Ovary

Uterus

Urinary bladder

Pubic bone

Urethra Vagina

Rectum

Cervix

The Menstrual Cycle

• The Menstrual Cycle• The menstrual cycle is controlled by internal

feedback mechanisms between the reproductive system and the endocrine system.

• The cycle takes an average of 28 days.

The Menstrual Cycle

• During the menstrual cycle, an egg develops and is released from an ovary.

• The uterus is prepared to receive a fertilized egg.

• If the egg is fertilized, it is implanted in the uterus and embryonic development begins.

• If the egg is not fertilized, it is discharged.

Fertilization and Development of an Offspring

• Gametes – reproductive cells (egg and sperm)

• When sperm and egg unite, new cell is called zygote

• Fertilization occurs in the oviduct (fallopian tubes)

• 1st 8 weeks - Embryo

• Development of fetus occurs in uterus