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38 terms

DNA

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DNA/RNA
Deoxyribonucleic Acid/Ribonucleic Acid
DNA consists of what?
Nucleotides: each nucleotide has a deoxyribose, a phosphate group and a nitrogenous base.
Nucleotides...
differ in their nitrogenous bases: Thymine (T), Cytosine (C), Adenine (A) and Guanine (G).
Purines
larger molecules-- Adenine and Guanine
Pyrmidines
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.
Anti-parallel
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.
Genes
the recipe for a protein
Chromosomes
are made of chromatin, a combination of DNA and protein molecules; they're not visible until cell division.
Histones/Nucleosomes
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
Interphase
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
Mitosis
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
Cytokinesis
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
Tumors
abnormally growing masses of body cells
Metastasis
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.
Chemotherapy
uses drugs that disrupt cell division.