Ch 8 DNA: The Chemical Nature of the Gene Flashcards
nucleotides
a large, number of linked, repeating units
each contains a sugar, a phosphate, and a base
ribose
RNA’s sugar, has a hydroxyl group (–OH) attached to the 2’-carbon atom
deoxyribose
DNA’s sugar, has a hydrogen atom (–H) at this position and therefore contains one oxygen atom fewer over all
two purines found in DNA and RNA
adenine and guanine (A and G), which differ in the positions of their double bonds and in the groups attached to the six-member ring
three pyrimidines common in nucleic acids
cytosine (C), thymine (T), and uracil (U)
cytosine is present in both DNA and RNA; however, thymine is restricted to DNA, and uracil is found only in RNA
nucleoside
a deoxyribose or a ribose sugar and a base together
phosphate group
consists of a phosphorus atom bonded to four oxygen atoms
frequently carry a negative charge, which makes DNA acidic
phosphodiester linkages
strong covalent bonds that link the 5’-phosphate group of one nucleotide to the 3’-hydroxyl group of the next nucleotide
polynucleotide strand
a series of nucleotides linked in phosphodiester linkages
5’ end
a free phosphate group (meaning that it’s unattached on one side) is attached to the 5’-carbon atom of the sugar in the nucleotide
3’ end
the other end has a free OH group attached to the 3’-carbon atom of the sugar
antiparallel
the two polynucleotide strands run in the opposite directions; the 5’ end of one strand is opposite the 3’ end of the other strand
complementary DNA strands
the two polynucleotide strands of a DNA molecule are therefore not identical; provides for efficient and accurate DNA replication
transcription
the information is transferred from DNA to RNA, information remains in the language of nucleic acids
translation
the information must be translated from the language of nucleotides into the language of amino acids
info passes from RNA to protein
replication
information passes from one DNA molecule to other DNA molecules
reverse transcription
transfer from RNA to DNA
RNA replication
some RNA viruses transfer information from RNA to RNA
supercoiling
a type of DNA structure which takes place when the DNA helix is subjected to strain by being overwound or underwound
relaxed state
a stretch of 100 bp of DNA would assume about 10 complete turns
positive supercoiling
molecules that are overrotated
negative supercoiling
underrotated molecules
topoisomerases
supercoiling relies on enzymes that add or remove rotations from the DNA helix by temporarily breaking the nucleotide strands, rotating the ends around each other, and then rejoining the broken ends
two advantages for DNA being negatively supercoiled
1) makes the separation of the two strands of DNA easier during replication and transcription
2) the supercoiled DNA can be packed into a smaller space than can relaxed DNA
nucleoid
bacterial cell DNA appears as a distinct clump which is confined to a definite region of the cytoplasm
chromatin
the combination of DNA and protein
two basic types of chromatin
euchromatin and heterochromatin
euchromatin
undergoes the normal process of condensation and decondensation in the cell cycle
heterochromatin
remains in a highly condensed state throughout the cell cycle, even during interphase
most of the centromere is made up of this
histones
most abundant proteins in chromatin
small, positively charged proteins of five major types: H1, H2A, H2B, H3, and H4
nucleosome
the repeating core of protein and DNA produced by digestion with nuclease enzymes is the simplest level of chromatin structure
linker DNA
nucleosomes are located at regular intervals along the DNA molecule and are separated from one another by this, which varies in size among cell types; in most cells, it comprises from about 30 to 40 bp
epigenetic changes or epigenetics
alterations of chromatin structure that are passed on to descendant cells or individuals
telomeric sequences
usually repeated units of a series of adenine or thymine nucleotides followed by several guanine nucleotides
shelterin
a multiprotein complex binds to telomeres and protects the ends of the DNA from being inadvertently repaired as a double-strand break in the DNA
repetitive DNA
exist in many copies
deoxyribonucleotides
DNA nucleotides are properly known as this
ribonucleotides
equivalent RNA nucleotides are this
central dogma
states that genetic information passes from DNA to protein in a one-way information pathway
nonhistone chromosomal proteins
a heterogeneous assortment, also found in eukaryotic chromosomes
also called chromosome scaffold proteins
core DNA
DNA wrapped around the core particle (histone octamer)
10-nm fiber
electron micrographs of DNA in its least condensed state
solenoid structure
6-8 nucleosomes per turn and histones H1 stabilizing
300-nm fiber
interphase chromosomes have variably sized loops of 30-nm fibers that form this
metaphase chromatin
compacted 250-fold; condensed chromatin 1400-nm
radial loop scaffold model
nonhistone proteins anchor chromatin loops (20 to 100 kb) to MARs (matrix attachment regions)
