Chapter 4

Cell Reproduction

Ch 4.1 – Cell Division & Mitosis

A. Cell Division – increases the # of cells and causes many-celled organisms to grow

1. Cells have periods of formation, growth & development, and death called life cycles

B. Cell Cycle – series of events that takes place from one cell division to the next

InterphaseGrowth & Development

MitosisNucleus Divides

CytokinesisCytoplasm Splits

1. Interphase – most of the life of eukaryotic cells is spent in this period of growth and development

a) First the cell grows larger in size and makes extra organelles

b) Then the cell duplicates its DNA and coils it into chromosomes

Interphase

Interphase

2. Mitosis – process in which the nucleus divides to form 2 identical nuclei

a) Mitosis is a very complex process that is divided into 4 distinct stages:

Prophase

Metaphase

Anaphase

Telophase

1) Prophase

- Nuclear membrane disintegrates

- Centrioles move to opposite ends of the cell

- Spindle fibers begin to stretch across the cell

Prophase

2) Metaphase

- Pairs of chromosomes line up across the center of the cell attached to the spindle

fibers

Metaphase

3) Anaphase

- Each chromosome divides at its centromere (middle part)

- Each pair of chromatids separate and move to opposite ends of the cell

Anaphase

4) Telophase

- spindle fibers disappear and a new nucleus forms in each side of the cell

Telophase

3. Cytokinesis (Division of the Cytoplasm) – for most cells the cytoplasm separates after the nucleus divides

a) In animal cells the cell membrane pinches in the middle and eventually splits

b) In plant cells a cell plate forms

Cell Cycle/Mitosis Animationhttp://encarta.msn.com/media_701765262_761553491_-1_1/Mitosis.html

C. Results of mitosis

1. Each cell in your body (except sex cells) has a nucleus with 46 chromosomes

2. Allows for growth and replaces worn out or damaged cells

D. Asexual Reproduction – a new organism is produced from one parent organism

1. Fission – a cell/organism divides into 2 identical organisms

2. Budding – a small exact copy of the adult grows from the body of the parent

3. Regeneration – a whole new organism grows from each piece of the parent

Ch 4.2 – Sexual Reproduction & Meiosis

A. Sexual Reproduction – 2 sex cells (one egg cell and one sperm cell) come together

1. Fertilization – the joining of an egg and a sperm from 2 different organisms of the same species

a) Sperm forms in the male repro. organs

b) Eggs form in the female repro. Organs

c) The cell that forms from the 2 during fertilization is called a zygote

2. Following fertilization cell division begins and a new organism develops

3. Human body cells are diploid because they have 46 chromosomes (23 pairs)

4. Human sex cells are haploid because they have 23 chromosomes

B. Meiosis – a process that produces (haploid) sex cells to ensure that offspring have the same diploid number as its parents

1. In meiosis I the nucleus divides producing two new cells with identical sets of chromosomes (same as mitosis)

2. In meiosis II each of those nuclei divide (without copying the chromosomes first) producing 4 new cells, each with half the number of chromosomes in the original cell

Mitosis Meiosis

Egg Sperm

Zygote

+ =

Ch 4.3 - DNA

A. DNA (deoxyribonucleic acid) – a chemical in the nucleus of cells that contains information that an organism needs to grow and function

1. Watson and Crick made an accurate model of DNA in 1953

2. The structure of DNA is similar to a twisted ladder

a) The sides of the ladder are made up of sugar-phosphate molecules (deoxyribose)

Deoxyribose (sugar)

Phosphate

b) The rungs of the ladder are made up of nitrogen bases

(Adenine) A - T (Thymine)

(Guanine) G - C (Cytosine)

c) Before a cell divides, its DNA duplicates itself by unwinding and separating its sides. Then each side becomes a pattern on which a new side forms

B. Genes – sections of DNA on a chromosome

1. Contain instructions for making specific proteins coded for specific traits

C. RNA – carries codes for making proteins from the DNA in the nucleus to the ribosomes in the cytoplasm

1. RNA has the bases A, G, C like DNA but

U (uracil) instead of T

2. Shaped like half a ladder

a) mRNA (messenger RNA) – carries the code that directs the order in which the amino acids bond

b) rRNA (ribosomal RNA) – makes up ribosomes where proteins are built

c) tRNA (transfer RNA) – brings amino acids to the ribosomes to build a protein

D. Mutations – any permanent change in the DNA sequence of a cell’s gene or chromosome

1. Can be caused by an outside factor such as x-rays, sunlight and some chemicals

2. A change in a gene or chromosome can change the traits of an organism