Chapter 4: Cell Chapter 4: Cell ReproductionReproduction

Aim: Why is cell division Aim: Why is cell division important?important?

The Cell CycleThe Cell CycleSeries of events that takes place

from one cell division to the nextLength of time to complete a cell

cycle is different in all cellsMost of the life of any eukaryotic

cell is spent in interphase-period of growth and development

Nerve and muscles cells are always in interphase (no longer divide)

During interphase, hereditary material is copied and the cell prepares for cell division

Cell division begins after interphase

Cells need to copy hereditary material before dividing so the new cells have a complete set of hereditary material to carry out life functions

Aim: What is the process Aim: What is the process of mitosis?of mitosis?

MitosisMitosisProcess in which the nucleus

divides to form two identical nucleiNew nuclei are identical to original

nucleusInterphase:

◦nucleus divides and chromosomes duplicate forming chromatids-two identical DNA strands

4 stages of mitosis4 stages of mitosis::1. Prophase:

◦ Chromatids fully visible◦ Nucleolus and nuclear membrane

disintegrate◦ Centrioles move to opposite ends

of cell (not in plants)◦ Spindle fibers begin to form

2. Metaphase:◦ Chromatids line up across the

center of the cell◦ Centromere of each chromatids

attaches to spindle fibers from each side

3. Anaphase:◦ Each centromere divides◦ Chromatids separate and move to

opposite ends of cell and become chromosomes

4. Telophase:◦ Spindle fibers disappear◦ Nucleus forms◦ Cytoplasm being divided◦ 2 new cells form: Animal Cell-cell membrane pinches in

middle Plant Cell- cell plate appears forming

a new cell wall

Results of MitosisResults of MitosisEach new nucleus has the same

number and types of chromosomes as the original

Humans:◦Every cell has 46 chromosomes-23

pairs, except sex cells◦All the trillion of cells have the same

hereditary material◦Use DNA to become different types of

cells◦Cell division allows growth and

replaces damaged or worn out cells

Aim: What is asexual Aim: What is asexual reproduction?reproduction?

Asexual ReproductionAsexual ReproductionNew organism is produced from one

organismNew organism’s hereditary material is

identical to the parent’s hereditary material3 forms of Asexual Reproduction

1. Cellular: Used by organisms with eukaryotic cells Ex: sweet potato growing in jar of water

(mitosis) Bacteria reproduce asexually by fission Can’t use mitosis because they don’t

have a nucleus

2. Budding◦Bud grows from the body of the parent organism

◦Made possible by mitosis

3. Regeneration◦Uses cell division (mitosis) to regrow body parts

◦Examples: sponges, sea stars

Aim: What is sexual Aim: What is sexual reproduction?reproduction?

Sexual ReproductionSexual ReproductionTwo sex cells come togetherFormed from cells in reproductive

organsSperm-maleEggs-femaleFertilization-joining of egg and

sperm◦Forms a zygote

Following fertilization, cell division begins

Diploid Cells:◦Cells have pairs of similar chromosomes

◦Human body cells-23 pairs, 46 chromosomes

◦Skin, bones, tissues and organs form from diploid cells

Haploid Cells:◦Do not have pairs of chromosomes◦Sex cells◦Have only 23 chromosomes-one from each of the 23 pairs

Aim: Why is meiosis Aim: Why is meiosis needed for sexual needed for sexual

reproduction?reproduction?

MeiosisMeiosisProduces hapliod sex cellsAfter 2 haploid sex cells combine-a

diploid zygote formsTwo divisions of the nucleus occur

◦Meiosis 1◦Meiosis 2

Results in four sex cells

MeiosisMeiosis 1 1Chromosome is duplicatedProphase 1Each duplicated chromosome comes near its similar duplicated chromosome

Metaphase 1◦Pairs of duplicated chromosomes line up in center of cell

Anaphase 1◦Each chromatid pair attaches to one spindle fiber

◦2 pairs of chromatids move away to opposite ends of cell

Telophase 1◦Cytoplasm divides◦2 new cells form◦Each new cell has one duplicated chromosome from each similar pair

Meiosis 2Meiosis 2Chromatids of each cell will be duplicated

Prophase 2◦Duplicated chromosomes and spindle fibers reappear

Metaphase 2◦Duplicated chromosomes move to middle of the cell

◦Each centromere attaches to 2 spindle fibers instead of 1

Anaphase 2◦Chromatids separate and move to opposite ends of the cell

◦Chromatids now chromosomes

Telophase 2◦Spindle fibers disappear◦Nuclear membrane forms around the chromosomes

After meiosis 2 cytokenisis occurs-the division of the cytoplasm

Aim: What are the parts of Aim: What are the parts of a DNA molecule?a DNA molecule?

DNADNADeoxyribonucleic AcidContains information for an

organism’s growth and functionDNA code is copied when the cell

divides1952- Rosalind Franklin discovered

it is 2 chains of molecules in a spiral form

1953 DNA model created by James Watson & Francis Crick

Similar to a twisted ladderEach side of ladder is made up of

sugar-phosphate moleculesRungs of ladder-made of nitrogen

bases4 kinds of nitrogen bases:

1. Adenine (A)2. Guanine (G)3. Cytosine (C)4. Thymine (T)

Cytosine=GuanineAdenine=ThymineThese bases occur as pairs

Aim: What is the function Aim: What is the function and structure of RNA?and structure of RNA?

GenesGenesMost of your characteristics depend on

the kinds of proteins your cells makeThe instructions for making a specific

protein are found in your genesAre a section of DNA on a chromosomeDetermine the order of amino acids in

a proteinChanging the order makes a different

proteinFound in the nucleus

Proteins are made on ribosomesCodes for making proteins are

carried from the nucleus to the ribosomes by RNA

RNA:◦Made in the nucleus on a DNA pattern

◦4 bases: adenine, guanine, cytosine and uracil (U)

◦Molecules contain the sugar ribose

◦3 types of RNA

1. mRNA:◦ Messenger RNA◦ Protein production begins when it

moves into the cytoplasm◦ Carries codes to make the amino acids

bond

2. rRNA:◦ Ribsosomal RNA◦ Ribosomes made of it

3. tRNA:◦ Transfer RNA◦ Bring amino acids to the ribosomes◦ Attach with the mRNA to make a protein

Aim: How do mutations Aim: How do mutations occur?occur?

MutationsMutationsHappens when DNA is not copied

correctlyAre any permanent change in the

DNA sequence of a gene or chromosome of a cell

X-rays, sunlight, and some chemicals may cause mutations

Examples:◦Having an extra chromosome◦Missing a chromosome

Without correctly coded proteins an organism can not grow, repair or maintain itself

Can cause deathMutations in body cells may or

may not be life threateningMutations in sex cells cause all the

cells that are formed to have the mutation

Some mutations have no effectSome can be beneficial