Mitosis & Meiosis

SB2.e – Compare the advantages of sexual reproduction and asexual reproduction in

different situations.

The cell cycle has four main stages.

• The cell cycle is the regular pattern of growth, DNA replication, and cell division that occurs in eukaryotic cells.

The cell cycle has four main stages.

• Phases:– Interphase – cell appears to be at rest• Gap 1 (G1) – cell grows, carry out normal

functions, and replicate their organelles.• Synthesis (S) – DNA synthesis• Gap 2 (G2) – additional growth

–Mitosis – division of the nucleus and its contents• Cytokinesis – process that divides the cells

cytoplasm

Cells divide at different rates.

• Prokaryotic cells typically divide much faster than eukaryotic cells.

• Skin Cells – 2 weeks• Red Blood Cells – 4 months• Liver Cells – 300-500 days• Intestine-internal lining – 4-5 days• Intestine-muscle and other lining – 16 years

Cell size is limited.

• If cells were too small, they could not contain all of the necessary organelles and molecules.

• If cells were too large, the ratio of the surface area to the volume would be too small.–An increase in size could result in a surface

area too small for the adequate exchange of materials, such as oxygen, nutrients, and wastes.

Chromosomes condense at the start of mitosis.

• DNA is a double-stranded molecule made up of four different subunits called nucleotides.

• A chromosome is a long continuous thread of DNA that consists of numerous genes along with regulatory information.

• During interphase, DNA is loosely organized (like spaghetti).

Chromosomes condense at the start of mitosis.

• During mitosis, your chromosomes are tightly condensed.–Duplicated chromosomes must condense to

divide between two nuclei.• The “spaghetti” stage, or loose combination of

DNA and proteins, is called chromatin.

Chromosomes condense at the start of mitosis.

• As the cell progresses to mitosis, chromatin further condenses, eventually forming small thick rods.–The chromosome looks similar to an “X” in

which the left and right halves have two identical DNA double helixes.–One half of a duplicated chromosome is

called a chromatid.

Chromosomes condense at the start of mitosis.

–Together, two identical chromatids are called sister chromatids.–Sister chromatids are held together at the

centromere, a region of the condensed chromosome that looks pinched.–The ends of DNA molecules form structures

called telomeres. They prevent the ends of chromosomes from accidently attaching to each other, and they help prevent the loss of genes.

Label the parts of a chromosome.

telomere

telomere

centromere

chromatid

Mitosis and cytokinesis produce two genetically identical daughter

cells.• Interphase plays an important role in

preparing the cell to divide.• Mitosis divides the cell’s nucleus into two

genetically identical nuclei, each with its own single, full set of DNA.

Mitosis and cytokinesis produce two genetically identical daughter

cells.• Interphase–Cell copies its DNA and grows in preparation

for division.

Mitosis and cytokinesis produce two genetically identical daughter

cells.

• Mitosis–Prophase•DNA and proteins condense into tightly

coiled chromosomes. The nuclear envelope breaks down, centrioles begin to move opposite poles, and spindle fibers form.

Mitosis and cytokinesis produce two genetically identical daughter

cells.

• Mitosis–Metaphase• Spindle fibers attach to each

chromosome. They align the chromosomes along the cell equator.

Mitosis and cytokinesis produce two genetically identical daughter

cells.

• Mitosis–Anaphase• Sister chromatids separate to opposite

sides of the cell.

Mitosis and cytokinesis produce two genetically identical daughter

cells.

• Mitosis–Telophase•Nuclear membranes start to form,

chromosomes begin to uncoil, and spindle fibers fall apart.

Mitosis and cytokinesis produce two genetically identical daughter

cells.• Cytokinesis–Divides the cytoplasm between two

daughter cells, each with a genetically identical nucleus. The cells enter interphase and begin the cycle again.

Cell division is uncontrolled in cancer.

• Cancer is the common name for a class of diseases characterized by uncontrolled cell division.–Divide much more often than healthy cells

do.

Cell division is uncontrolled in cancer.

• Cancer cells form disorganized clumps called tumors.–Benign tumors remain clustered together

and can easily be removed.–Malignant tumors can have cells that break

away, or metastasize and can be carried into the bloodstream and other parts of the body. These are more difficult to get rid of.

Cell division is uncontrolled in cancer.

• Carcinogens are substances known to produce or promote the development of cancer.–Name three carcinogens:• tobacco smoke• air pollution•UV light

Cell division is uncontrolled in cancer.

• Standard cancer treatment often involves both radiation and chemotherapy.–Radiation therapy is the use of radiation to kill

cancer cells or shrink tumors. It works by damaging a cell’s DNA so much that the cell cannot divide. Radiation is usually targeted at a specific area.–Chemotherapy uses certain drugs to kill actively

dividing cells. It kills both cancerous and healthy cells. It travels though the whole body.

Binary fission is similar in function to mitosis.

• Reproduction is a process that makes new organisms from one or more parent organisms. It happens in two ways:–Sexual reproduction - the joining of two

specialized cells called gametes (sex cells), one from each of two parents.•Offspring are genetically unique.

Binary fission is similar in function to mitosis.

• Reproduction is a process that makes new organisms from one or more parent organisms. It happens in two ways:–Asexual reproduction - the creation of

offspring from a single parent and does not involve the joining of gametes.•Offspring are genetically identical.•Most prokaryotes reproduce through

binary fission.

Multicellular organisms depend on interactions among different cell types.

Cells

Tissues

OrgansOrgan

Systems

Organism

Specialized cells perform specific functions.

• Cell differentiation is the process by which unspecialized cells develop into their mature forms and functions.

Stem cells develop into different cell types.

• Stem cells are a unique type of body cell that have the ability to:–divide and renew themselves for long

periods of time–remain undifferentiated in form–develop into a variety of specialized cell

types

You have body cells and gametes.

• Body cells are called somatic cells.• Sex cells are celled gametes.

Your cells have autosomes and sex chromosomes.

• Homologous chromosomes are two chromosomes – one inherited from the mother, one from the father – that have the same length and general appearance.

• Chromosomes 1-22 make up your autosomes, chromosomes that contain genes for characteristics not directly related to the sex of an organism.

Your cells have autosomes and sex chromosomes.

• Sex chromosomes directly control the development of sexual characteristics.–Humans have two very different sex

chromosomes, X and Y.–Female sex chromosomes are XX.–Male sex chromosomes are XY.

Body cells are diploids; gametes are haploid.

• Sexual reproduction involves the fusion of two gametes that result in offspring that are a genetic mixture of both parents.

*Fusion is called fertilization.• Diploid means a cell has two copies of each

chromosome (2n).• Haploid means a cell has one copy of each

chromosome (1n).

Body cells are diploids; gametes are haploid.

• Maintaining the correct number of chromosomes is important to the survival of organisms. A change in the chromosome number can be harmful.

• Germ cells in your reproductive organs undergo a process of meiosis to form gametes.

• Meiosis is a form of nuclear division that creates 4 haploid cells from one diploid cell.

Body cells are diploids; gametes are haploid.

• Homologous chromosomes are two separate chromosomes: one from the mother and one from the father.– They are very similar to each other; but

they are not copies of each other.– Each half of a duplicated chromosome is

called a chromatid. Together they make up a sister chromatid. They are copies of each other.

Meiosis I

• Prophase I–Nuclear membrane breaks down,

duplicated chromosomes condense and homologous chromosomes pair up.

Meiosis I

• Metaphase I–Homologous chromosome pairs are

randomly lined up along the middle of the cell. Chromosomal combinations occur to help give genetic variability.

Meiosis I

• Anaphase I–Paired homologous chromosomes

separate from each other and move towards opposite sides of the cell. Sister chromatids remain together.

Meiosis I

• Telophase I–Nuclear membrane forms again;

results in 2 cells that each have a unique combination of duplicated chromosomes.

Meiosis I

Meiosis II

• Prophase II–Nuclear membrane breaks down.

• Metaphase II–Sister chromatids line up along the

middle of the cell. Chromosomal combinations occur to help give genetic variability.

Meiosis II

• Anaphase II–Sister chromatids are pulled apart from

each other and move towards opposite sides of the cell.

Meiosis II

• Telophase II–Nuclear membrane forms again;

results in 4 haploid cells that each have a unique combination of chromosomes from both the mother and father.

Meiosis II