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Deoxyribonucleic Acid/Ribonucleic Acid

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).


larger molecules-- Adenine and Guanine


smaller molecules-- Thymine and Cytosine

Sugar-phosphate backbone

Nucleotides are joined by the sugar-phosphate backbone which alternates deoxyribose and phosphate bonded by a covalent bond.

Double Helix

a rope like ladder twisted into a spiral: James Watson and Francis Crick determined that DNA took the form of a double helix.

DNA base pairs

Adenine pairs with Thymine and Cytosine pairs with Guanine.


the sugar-phosphate backbones of each strand run in opposite directions: one strand reads 5' to 3' and the other reads 3' to 5'.

Hydrogen bonds

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.

DNA replication

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.

Cell divison

reproduction of a cell: first the chromosomes are duplicated- each daughter cell gets one set of chromosomes.

Importance of cell divison

replaces damaged or lost cells; permits growth; allows for reproduction

Asexual reproduction

the one parent and two daughters have identical genes through mitosis. Mitosis is used for asexual reproduction and growth and maintenance of mutlicellular organisms.

Sexual reproduction

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.


the recipe for a protein


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.

Sister chromatids

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.

Once separated...

each chromatid is considered a chomosome and is identical to the original chromosome.

Humans have...

46 total chromosomes: sex cells have 23 chromosomes

Cell cycle

the orderly sequence of events that extend from the time a cell is fromed from to divison to when it divides into 2.

Two distinct phases

interphase and the mitotic phase


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.

Mitosis consists of 4 distinct phases:

Prophase, Metaphase, Anaphase, Telophase


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


abnormally growing masses of body cells


the spread of cancer cells beyond their original site of orgin

Malignant 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.

Radiation therapy

damages DNA and disrupts cell division.


uses drugs that disrupt cell division.

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