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DNA consists of what?
Nucleotides: each nucleotide has a deoxyribose, a phosphate group and a nitrogenous base.
differ in their nitrogenous bases: Thymine (T), Cytosine (C), Adenine (A) and Guanine (G).
Nucleotides are joined by the sugar-phosphate backbone which alternates deoxyribose and phosphate bonded by a covalent bond.
a rope like ladder twisted into a spiral: James Watson and Francis Crick determined that DNA took the form of a double helix.
the sugar-phosphate backbones of each strand run in opposite directions: one strand reads 5' to 3' and the other reads 3' to 5'.
hold two nitrogenous bases together: the bonds are weak so they can be easily broken and put back together. The double helix makes the bonds harder to break.
produces a complete copy of the DNA from one parent cell to two daughter cells. Watson and Crick's model suggests DNA replicates by a template mechanism.
Process of replication
1. Helicase attaches to a "point of orgin" on the DNA
2. Helicase unwinds and unzips two strands from eachother- replications "bubbles" are formed
3. DNA polymerase attaches to each half of the DNA
4. DNA polymerase attaches "free floating" nucleotides to each strand of DNA.
DNA replication in eukaryotes
begin at a specific "point of orgin" on the double helix (there are many working together) the polymerase proceed in opposite directions.
reproduction of a cell: first the chromosomes are duplicated- each daughter cell gets one set of chromosomes.
the one parent and two daughters have identical genes through mitosis. Mitosis is used for asexual reproduction and growth and maintenance of mutlicellular organisms.
requires fertilization of an egg by sperm, using meiosis. Sexually reproducing organisms use meiosis for reproduction and mitosis for growth and development.
Cell Cycle and Mitosis
most genes are located on chromosomes in the nucleus; a few genes are found in the mitochondria or chloroplasts.
are made of chromatin, a combination of DNA and protein molecules; they're not visible until cell division.
the proteins used to package DNA in eukaryotes; nucleosomes consist of DNA wound around histene molecules.
before a cell divides it duplicates all of its chromosomes resulting in 2 coplies: the sister chromatids are joined together at a narrow "waist" with a protein called a centromere.
each chromatid is considered a chomosome and is identical to the original chromosome.
the orderly sequence of events that extend from the time a cell is fromed from to divison to when it divides into 2.
90% of life/ G1: normal functions and grows S-phase: DNA replication G2: everything is doubled
Two phases of the mitotic phase
Mitosis: the nucleus and its contents divide into two daughter nuclei Cytokinesis: cytoplasm is divided in 2
the mitotic spindle guides the separation of 2 sets of daughter chromosomes; spindle microtubules grow from 2 centrosomes.
occurs during telophase, divides the cytoplasm, is different in plants and animals: animals- cleavage furrow, plants- cell plate
Cell control system
consists of specialized proteins which send "stop" and "go-ahead" signals at certain keys points in the cycle.
What is caner?
a disease of the cell cycle; cells that don't respond normally to the control system; can form tumors
can spread to other parts of the body and interrupt normal body functions. A person with a malignant tumor is said to have cancer.
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