Structure and function Flashcards
universal in living things, and are also found in viruses
Nucleic acid
compounds structurally similar to naturally occuring RNA and DNA, used as a research tool in molecular biology and/or as cure in medicine
Nucleic acid analogue
polymeric molecule composed of 4 types of monomeric units that contains the genetic information of an organism
DNA
The DNA structure as we know today was proposed by ____________ and _________ who were able to form a model of double-stranded DNA in helical form held together by hydrogen bonds
James watson and francis crick
occurs where the backbones are far apart
Major grooves
occurs where they are close together
Minor grooves
The purine and pyrimidine bases guanine (G), cytosine (C), thymine (T), and adenine (A) are held together by a phosphodiester backbone between _______________ attached to the nucleobases by an N-glycosidic bond
2 deoxyribosyl moieties
Convention dictates that a single-stranded DNA sequence is written in the _____________
5-3 direction
The common form of DNA is said to be right-handed because as one looks down the double helix, the base residues form a spiral in a __________
Clockwise direction
one strand runs in the 5’ to 3’ direction and the other in the 3’ to 5’ direction
Antiparallel
Of the 2 DNA strands, 1 is a template strand (the strand that is copied during nucleic acid synthesis), also called the
Non coding strand
The other strand is the coding strand which matches the RNA transcript that encodes the proteins
but containing uracil in place of thymine
Double-stranded DNA exists in at least six forms
A-E and Z
The G–C bonds are much more resistant to denaturation, or “melting,” than
A-T regions
G-C bonds have three hydrogen bonds hold the ______________ to ____________, whereas the other pair, the A–T pair, is held together by two hydrogen bonds only
Deoxyguanosine nucleotide
Deoxycytidine nucleotide
The double-stranded DNA structure can be separated in a solution by
Increasing the temperature 2. Decreasing the salt concentration
Separated strands of DNA will renature or will reassociate when appropriate physiologic temperature and salt conditions are achieved
Hybridization
are formed when the molecule is twisted in the direction opposite from the clockwise turns of the right-handed double helix found in B-DNA. Such DNA is said to be underwound
Negative supercoils
Negative super coil
Right handed
Positive super coil
Left handed
Enzymes that catalyze topologic changes of DNA are called
Topoisomerases
The best-characterized example topoisomerases
Bacterial DNA gyrase
DNA gyraseintroduces negative supercoils (or relaxes positive supercoils) using
ATP
The ability of gyrase to relax positive supercoils comes into play during
DNA replication
Drugs like _____________ that inhibit DNA gyrase are used as antibacterial agents
Quinolones
DNA provides a template for replication and transcription •It is the source of information for
Protein synthesis
Complementarity of DNA strands suggests that replication is done in a semi-conservative manner, where each strand is used to create a new
Daughter strand
During a round of replication, each of the two strands of DNA is used as a _________________ of a new, complementary strand
Template for synthesis
polymer of purine and pyrimidine ribonucleotides linked together by phosphodiester bridges analogous to those in DNA
Ribonucleic acid RNA
Serves as template for protein synthesis
Messenger RNA
For mRNA recognition prior to translation •Stabilizes mRNA
CAP
The 5’ terminal of mRNA is “capped” by a
7methylguanosine triphosphate
The 3’ end of mRNA has an attached polymer of adenylate residues 20-250 nucleotides in length called the
Poly A tail
mechanism by which most messenger RNA molecules are terminated at their 3’ ends
Polyadenelation
The polyadenosine (poly-A) tail protects the mRNA molecule from
Exonucleases
important for transcription termination, for export of the mRNA from the nucleus, and for translation
Polyadenosine
do not contain poly(A) tails
Histones
Both the mRNA “cap” and “poly(A) tail” are added post-transcriptionally by
Nontemplate directed enzyme
In mammalian cells, including cells of humans, the mRNA molecules present in the cytoplasm are not the RNA products immediately synthesized from the DNA template •Thus, in mammalian nuclei, the immediate products of gene transcription constitute a fourth class of RNA molecules. •These nuclear RNA molecules, called
Heterogenous nuclear RNA
Serve as adapters for the translation of mRNA to amino acids
Transfer RNA
There are at least 20 species of tRNA in each cell, at least 1 corresponding to each of the 20 amino acids required for protein synthesis
20 1 20
Although tRNAs are quite stable in prokaryotes, they are somewhat less stable in
Eukaryotes
tRNA stabel in________ mRNA stable in______
Prokaryotes
Eukaryotes
The primary structure of all tRNA molecules allows extensive folding and intra-strand complementarity to generate a secondary structure that appears in two dimensions like a
Cloverleaf
Sometimes called nodocfrom the reversed letters of the word codon •A unit made up of three nucleotides that correspond to the three bases of the codon on the mRNA •Each tRNA contains a specific anticodon triplet sequence that can base-pair to one or more codons for an amino acid •For example, one codon for lysine is AAA; the anticodon of a lysine tRNA might be UUU
Aicodon
A cytoplasmic nucleoprotein that acts as the machinery for the synthesis of proteins from mRNA templates
rRNA
The 60s subunit contains subunits
5s, 5.8s, & 28s
The 40s subunit contains a single
18 sub units
All rRNA molecules except the _____________ are processed from a single 45s precursor RNA molecule in the nucleolus
5sRNA
Found within the nucleus of eukaryotic cells. •They are involved in a variety of important processes such as RNA splicing (removal of introns from hnRNA), regulation of transcription factors and maintaining the telomeres (region of highly repetitive DNA at the end of a linear chromosome) •These elements are rich in Uridine content
Small nuclear RNA
