chapter 4: cell reproduction. aim: why is cell division important?
TRANSCRIPT
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