Cell Reproduction

Cell Division

• Increases the number of cells and causes many-celled organisms to grow

• Cell cycle- series of events that take place from one cell division to the next

Interphase

• Most of the life of a eukaryotic cell, or cell with a nucleus, is spent in this period of growth and development– During interphase, a cell duplicates its

chromosomes and prepares for cell division– After interphase, the nucleus divides, and then the

cytoplasm separates to form two new cells• Muscle and nerve cells no longer divide so

they are always in interphase

Chromosomes

• Chromosome- structure in the nucleus that contains hereditary material

Mitosis

• Process in which the nucleus divides to form two identical nuclei

Prophase

• Nucleolus and nuclear membrane disintegrate• Centrioles move to the opposite ends of the

cell• Spindle fibers begin to stretch across the cell

Metaphase

• Pairs of chromatids line up across center of cell

Anaphase

• Each centromere divides• Each pair of chromatids separates and moves

to opposite ends of the cell

Telophase

• Spindle fibers disappear and a new nucleus forms

Cytokinesis

• For most cells, the cytoplasm separates after the nucleus divides– In animal cells, the cell membrane pinches in the

middle and the cell membrane divides– In plant cells, a cell plate forms

Results

• Each cell in your body, except for sex cells, has a nucleus with 46 chromosomes– People with conditions

such as Down Syndrome, have extra or less chromosomes.

• Allows growth and replaces worn out or damaged cells

Asexual Reproduction

• A new organism is produced from one parent organism– An organism with no

nucleus divides into two identical organisms by fission

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

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

Sexual Reproduction

• Two sex cells, called the sperm and egg, come together– Sperm formed in male

reproductive organs– Egg formed in female

reproductive organs

• Fertilization the joining of the sperm and egg– The new cell that forms

after fertilization is called the zygote.

Cells

• Your body forms 2 types of cells– Diploid cells that have 23 pairs of chromosomes.

Includes brain, skin, bone cells.– Haploid only 23 individual chromosomes, NOT

PAIRS. These are the sperm and egg cells.

Meiosis

• Process that produces haploid cells. • Insures that offspring will have same total

amount of chromosomes as parent because after two haploid cells combine, a diploid zygote is produced

• During meiosis, two nucleus divisions occur– Meiosis I– Meiosis II

Interphase

• Before meiosis starts, each chromosome is duplicated (just like in mitosis)

Prophase I

• Nucleolus and nuclear membrane disintegrate

• Centrioles move to the opposite ends of the cell

• Spindle fibers begin to stretch across the cell

• Each duplicated chromosome comes near its duplicate

Metaphase I

• Pairs of duplicated chromosomes line up in center of cell

• The centromere of each chromatid pair attaches to a spindle fiber

Anaphase I

• Two pairs of chromatids of each similar pair move away from each other to opposite ends of the cell.

• Each duplicated chromosome still has two chromatids.

Telophase I

• Cytoplasm divides and two new cells form• Each new cell has one duplicated chromosome

from each similar pair

Prophase II

• The duplicated chromosomes and spindle fibers reappear in each cell

Metaphase II

• Duplicated chromosomes move to the center of the cell

• Each centromere attached to two spindle fibers instead of one

Anaphase II

• Centromere divides• Chromatids separate and move to opposite

sides of the cell• Each chromatid is individual chromosome

Telophase II

• Spindle fibers disappear.• New nuclear membrane forms around each

set of chromosomes at each end of the cell

Meiosis

• At the end of meiosis II, the cytoplasm divides.• SUMMARY– Two cells form during meiosis I– Those two cells form two new cells in meiosis II– Results in FOUR SEX CELLS, each with one half the

number of chromosomes in its nucleus as in the original nucleus

Let’s Review Meiosis!

DNA

• Deoxyribonucleic acid (a chemical)

• Contains information for organism’s growth and function

• When a cell divides, DNA code is copied and passed to new cell

• Watson and Crick made accurate model of DNA in 1953

DNA Structure• Similar to twisted ladder• Sides of ladder are made up of

sugar-phosphate molecules• The rungs of ladder made of

nitrogen bases– Adenine and Thymine are base

pairs– Guanine and Cytosine are base

pairs

• Before cell divides, DNA duplicates itself by unwinding and separating its sides, then each side becomes a pattern on which new side forms

Genes and RNA

• Genes sections of DNA on a chromosome• RNA carries the codes for making proteins from

the nucleus to the ribosomes in the cytoplasm– Messenger RNA carries the code that directs the

order in which amino acids bond– Ribosomal RNA makes up ribosomes, where

proteins are built– Transfer RNA brings amino acids to the ribosomes to

build proteins

Codons

• Every 3 base pairs (such as UGA) on the messenger RNA are a CODON

• Each codon represents a specific amino acid

• The ribosome reads the messenger RNA by each codon, then adds the correct amino acid to the protein chain

RNA

RNA

• DNA vs. RNA• DNA to RNA to Proteins

Mutations

• Any permanent change in the DNA sequence of a cell’s genes or chromosome– Can be caused by

outside factors like X rays, sunlight, and chemicals

– A change in the gene or chromosome can change traits of the organism