nucleic acids

biochem

chromosomes

From the end of the 19th century, biologists suspected that the transmission of hereditary information took place in the nucleus, more specifically in structures called

histones and nucleic acids

Chemical analysis of nuclei showed chromosomes are made up largely of proteins called

DNA

By the 1940s, it became clear that _ carry the hereditary information.

RNA and DNA

two kinds of nucleic acidsincells

nucleotides

Both RNA and DNA are polymers built from monomers called 

base, monosaccharide, and a phosphate

nucleotide is composed of

Purine Adenine Guanine

PUAG

Pyrimidine Cytosine Thymine Uracil

PYCTU

nucleosides

a compound that consists of D-ribose or 2-deoxy-D-ribose bonded to a purine or pyrimidine base by a -N-glycosidic bond.

nucleotide

a nucleoside in which a molecule of phosphoric acid is esterified with an -OH of the monosaccharide, most commonly either the 3’ or the 5’ -OH.

adenosine 5’-triphosphate (atp)

serves as a common currency into which energy gained from food is converted and stored.

secondary structure

the ordered arrangement of nucleic acid strands.
the double helix model of DNA2° structure was proposed by James Watson and Francis Crick in 1953.

double helix

a type of 2° structure of DNA in which two polynucleotide strands are coiled around each other in a screw-like fashion.

nucleosome

a core of eight histone molecules around which the DNA helix is wrapped.

histones

DNA is coiled around proteins called

chromatin

Nucleosomes are further condensed into

chromosomes

Chromatin fibers are organized into loops, and the loops into the bands that provide the superstructure of

2-deoxy-D-ribose

sugar in dna

D-ribose

sugar in rna

replication

yields into two DNA molecules identical to the original one, ensuring transmission of genetic information to daughter cells with exceptional fidelity.

transcription

the sequence of bases in DNA is recorded as a sequence of complementary bases in a single-stranded mRNA molecule.

translation

three base codons on the mRNA corresponding to specific amino acids direct the sequence of building a protein. these codons are recognizes by the tRNAs carrying the appropriate amino acids. ribosomes are the machinery for protein synthesis.

Transfer RNA

Small

Transports amino acids to site of protein synthesis

Ribosomal RNA (rRNA)

Several kinds; variable in size

Combines with proteins to form ribosomes, the site of protein synthesis

Messenger RNA

Variable

Directs amino sequence of proteins.

Small Nuclear RNA

from 100-200 nucleotides

Pocesses initial mRNA to its mature form in eukaryotes.

Small Inefering RNA

Small

Affects gene expression ; used by scientists to knock out gene being studied.

Micro RNA

Small

Affects gene expressions; important in growth and development

Ribozymes (catalytic RNA)

Very large

catalyze cleavage of part of their own sequences in mRNA and tRNA

gene

a segment of DNA that carries a base sequence that directs the synthesis of a particular protein, tRNA, or mRNA.

continuous

the gene in bacteria

discontinuous

the gene in higher beings

exon

a section of DNA that, when transcribed, codes for a protein or RNA

intron

a section of DNA or mRNA that does not code for a protein

replication

involves separation of the two original strands and synthesis of two new daughter strands using the original strands as templates.

origin of replication

DNA double helix unwinds at a specific point called an

bidirectional

Polynucleotide chains are synthesized in both directions from the origin of replication; that is, DNA replication is

replication forks

At each origin of replication, there are two __ ,points at which new polynucleotide strands are formed.

leading strand

is synthesized continuously in the 5’->3’ direction toward the replication fork

lagging strand

is synthesized semidiscontinuously as a series of okazaki fragments, also in the 5’ ->3’ direction, but away from the replication fork.

DNA ligase

Okazaki fragments of the lagging strand are joined by the enzyme

semiconservative

Replication is _, each daughter strand contains one template strand and one newly synthesized strand.

tropoisomerase (gyrases)

facilitate the relaxation of supercoiled DNA by introducing either single strand or double strand breaks in the DNA.

primers

are short oligonucleotides—4to15nucleotideslong. they are required to start the synthesisof bothdaughterstrands.

primases

are enzymes that catalyze the synthesis of primers. they also are placed at about every 50nucleotidesinthelagging strand synthesis.

base excision repair (ber)

one of the most common repair mechanisms.

nucleotide excision repair (ner)

removes and repairs up to 24-32 units by a similar mechanism involving a number of repair enzymes

clone

a genetically identical population.

cloning

a process whereby DNA is amplified by inserting it into a host and having the host replicate it along with the host’s own DNA.

polymerase chain reaction (pcr)

an automated technique for amplifying DNA using a heat-stable DNA polymerase from a thermophilic bacterium.