The Life Cycle of Cells

Cell Growth A cell is limited by its cell size The larger the cell the harder it is to move through tissue and get nutrients In order to stay alive and not grow continuously, the cell will divide

Reasons why to divide DNA Transport Genetic information stored Found in the nucleus of the cell DNA would not be able to keep up with demand of the cell Transport Rate decreases as the cell size increases Takes too long for nutrients and wastes to move in and out of cell

Surface Area to Volume Surface Area Area on outside of cell where reactions can occur As a cell increases, the surface area decreases

DNA Structure Monomer of DNA is a nucleotide 5-carbon sugar Phosphorous group Nitrogenous base 4 Nitrogenous bases in DNA Adenine Guanine Thymine Cytosine

DNA Structure Backbone of DNA is the sugar and phosphate Nitrogenous bases stick out of side to form latter rungs These bases are repeated in a pattern that form our genetic code

DNA Structure Chargaff’s Rule Scientist that discovered a peculiar trend between the 4 bases Same percentage of Adenine as Thymine Same percentage of Guanine as Cytosine Scientists still not sure how they match up though

DNA Structure Rosalind Franklin Scientist that worked with X-ray diffraction Used X-rays on a portion of DNA and the results showed an X pattern

DNA Structure Watson & Crick Scientists that were able to figure out what Rosalind’s X-ray pattern Result: DNA has a double helix pattern where the nitrogenous bases face each other

DNA Structure DNA has a double helix pattern Looks like a ladder twisted up The sides of the ladder are the sugar and phosphate and the rungs of the ladder are the nitrogenous bases paired up The adenine binds to thymine The guanine binds to cytosine This concluded Chargaffs’s rule  base pairing

DNA and Chromosomes Prokaryotes Eukaryotes Lack nucleus and organelles DNA floats as a circle in the cytoplasm Eukaryotes 1000 times more DNA than prokaryotes DNA is located in nucleus Specific number of chromosomes Ex: Humans have 46 chromosomes

DNA and Chromosomes DNA Length Chromosome Structure DNA is very long DNA is coiled up into a very small space because it is in chromatin form Chromosome Structure Tightly packed chromatin is wrapped around small proteins called histones When chromatin gets super coiled you create a chromosome

Chromosomes Made up of our DNA Holds genetic information Tight coils or rod like structures Organisms have a specific amount of chromosomes. Humans have 46 chromosomes of DNA in every somatic cell

Chromosome Structure Histones are proteins that DNA wraps around to make the chromosome shape Chromosomes are made of two sister chromatids Identical to each other

Chromosomes Centromeres are in the center of a chromosome Chromosomes are tightly coiled strings of DNA called chromatin Chromatin is the string-like form of DNA

Chromosome Numbers A diploid cell contains 2 sets of each chromosome Prefix di = 2 A haploid cell contains only 1 set of each chromosome Half of the total number Usually sex cells

Chromosome Numbers There is a specific number of chromosomes in each organism Humans autosomes and sex chromosomes We have 2 sex chromosomes Either X or Y We also have 22 autosomes Which do not code for gender

Karyotype A karyotype is a lab picture of one set of chromosomes

How Replication Occurs Enzymes help make new strands of DNA One enzyme “unzips” the DNA, separating the base pairs DNA polymerase adds new bases to pair up with the template This enzyme also proofreads to make sure everything matches What would be the matching bases to the part of DNA shown below?

DNA Replication Each strand of DNA is needed to be a template for a new strand of DNA to be produced Since you can use one strand to make the other side, they are said to be complementary

Duplicating DNA Before mitosis occurs, DNA needs to be duplicated first during interphase When DNA duplicates, its called replication DNA molecules separates into two strands, then produces two new complementary strands following the rules of base pairing Each strand serves as a template for the new strand

Cell Division in Prokaryotes No nucleus No organelles Ex: Bacteria Reproduction is VERY fast Copy DNA Split into two cells Cell division is called binary fission

Eukaryotic Cell Reproduction Eukaryotes Have a nucleus Have organelles Ex: Humans, plants Complex reproduction Everything needs to be controlled! Much longer process – about 18 hours!

Cell Reproduction A cell splits to make 2 identical copies If asexual reproduction Only 1 cell involved This occurs in 3 main stages Interphase – Growth Mitosis – Splitting of the cell Cytokinesis – Splitting of the cytoplasm

Interphase Cell growth 90% of cell’s life is spent in interphase. 3 Part of Interphase: G1, S, G2

G1 Phase The cell is growing The organelles are doubling

S Phase Takes place when cells are too big S = Synthesis of DNA DNA is replicated so there is a set for each new cell

DNA replicates in Interphase so the daughter cells exact copies of the DNA

G2 Phase Cell growth again Replication of organelles Last stage of interphase Cell prepares for cell division

Interphase cell is not dividing cell is growing, performing respiration, producing, photosynthesizing, doing whatever functions it is supposed to do At some point, the cell can’t diffuse fast enough and that signals the end of interphase At the very end of interphase, the chromatin makes an exact copy of itself in a process called DNA replication.

How is DNA copied? Each cell has an protein called helicase Enzyme the unwinds the DNA making 2 identical strands http://www.youtube.com/watch?v=zdDkiRw1PdU

Mitosis The part of a cell’s life cycle when the cell divides it nuclear contents into 2 nuclei which are identical Mitosis consists of 4 steps: Prophase Metaphase Anaphase Telophase

Prophase all sub-cellular organelles disappear centrioles separate and move to opposite poles chromatin become chromosomes centrioles shoot off spindle fibers (short and long)

chromosomes line up at the equator Metaphase

Anaphase centromere splits sister chromatids attach to the short spindle fibers short spindle fibers shorten and bring the sister chromatids to opposite poles.

Telophase chromatids become chromatin (one at each pole) spindle disappears subcellular organelles reappear

Cytokinesis Once mitosis has finished! Last stage of cellular reproduction This process is when the cytoplasm splits apart There are now 2 identical cells

Cytokinesis in Plant Cells Cell plate forms at equator and grows out to the cell wall Cell plate

Cytokinesis in Animal Cells Cell membrane pinches in at equator Cleavage furrow

Interphase

Prophase

Metaphase

Anaphase

Telophase

Prophase

Metaphase

Anaphase

Telophase

Interphase

Prophase

Metaphase

Anaphase

Telophase

Control of Cell Division G1 Checkpoint Enzymes will kick in if cell is large enough and conditions are favorable to reproduce G2 Checkpoint DNA repair enzymes will fix any mutations, if checkpoint is passed mitosis will occur Mitosis checkpoint – if all is correct, the 2 daughter cells will enter G1 phase and start over again

Uncontrolled Mitosis is cancer.

When Control is Lost Enzyme proteins are not functioning properly causing cell to reproduce out of control Could cause cancer Cancer cells do not respond to body’s signals that control mechanisms

Some Cancer Statistics: 1 in 7 people will have some form of cancer in their lifetimes. 1 in 8 women will get breast cancer. Lung cancer is the leading cause of cancer deaths in the U.S. There are approx. ½ million deaths from cancer in the U.S. per year.

Compare/Contrast

How else can our body control cancer?