DNA: Nucleic Acid Structure And function Flashcards
Most common nucleic acids are
DNA & RNA
Is a macromolecule composed of nucleotide chains. These molecules carry genetic information within cells. Are universal in living things, and are also found in viruses.
Nucleic acid
Are compounds are structurally similar to naturally occurring RNA & DNA, used as a research tool in molecular biology and/or as cure in medicine
Nucleic acid analogues
Is a polymeric molecule composed of 4 types of monomeric units that contains the genetic information of an organism.
DNA
The discovery that genetic formation is coded along the length of polymeric molecule composed of only four types of _____________.
Monomeric units
The genetic code in DNA depends on how ______ & ______ are arranged in a ______.
Purines & Pyrimidines. DNA strand.
The DNA structure was proposed by whom. They were able to form a model of double-stranded DNA in helical form held together by ________.
James Watson & Francis Crick. Hydrogen bonds.
One turn of B-DNA includes ________. The ________ of the double helix is indicated by the vertical cord.
10 base pairs. Central axis.
Occurs where the backbones are far apart
Major groove
Occurs where they are close together
Minor groove
In major and minor grooves, certain protein binds to DNA to alter its structure or regulate ______(copying DNA to RNA) or _______(copying DNA to DNA)
Transcription. Replication.
In major and minor grooves, It is easier for DNA binding proteins to interact with these bases (the internal parts of the DNA molecule) on the _________ side because the _______ are not in the way.
Major groove. Backbones.
The purine and pyrimidine bases G, C, T & A are held together by a __________ backbone between 2’ deoxyribosyl moieties attached to the nucleobases by an _________.
Phosphodiester. N-glycosylic bond.
In major and minor grooves, The backbone has _______. Convention dictates that a single stranded DNA sequence is written in the __ to __ direction.
Polarity. 5’ to 3’.
The common DNA form is said to be ______ because as one looks down the double helix, the base residues from a ________ in a _______ direction.
Right-handed. Spiral. Clockwise.
The two strands of the double-helical molecule, each of which possesses a polarity, are ________; ie, on strand runs in the 5’ to 3’ direction and the other in the 3’ to 5’ direction.
Antiparallel
the strand that is copied during nucleic acid synthesis.
Template/non-coding strand
Matches the RNA transcript that encodes the protein ( but containing _______ in place of thymine)
Coding strand. Uracil.
2 DNA strands
Coding strand and Non-coding/Template strand
In RNA strand segment, Double stranded DNA exists in at least
Six forms: A-E and Z
In RNA strand segment, is usually found under physiologic conditions (low salt, high degree of hydration)
B form
In RNA strand segment: are much more resistant to denaturation, or “melting” than A-T rich regions. This is because three hydrogen bonds hold the __________ to the _________, whereas the other pair, the A-T pair, is held together by ________ only.
G-C bonds. Deoxyguanosine nucleotide. Deoxycytidine nucleotide. Two hydrogen bonds.
The double stranded DNA structure can be separated in a solution by
Increasing the temp & decreasing the salt concentration
Separated strands of DNA will renature or will reassociate when appropriate physiologic temperature and salt conditions are achieved in a process called
Hybridization
In some organisms such as bacteria, bacteriophages, many DNA-containing animal viruses, as well as organelles such as mitochondria, the ends of the DNA molecules are joined to create a closed circle _________. This does not destroy the polarity of molecules, but it eliminates all free ___________.
No covalently free ends. 3’ and 5’ hydroxyl and phosphoryl groups.
Closed circles exist in
Relaxed/Supercoiled forms
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
Enzymes that catalyze topologic changes of DNA. Can relax or insert supercoils. Best example is BDG.
Topoisomerase
Introduces negative supercoils (or relaxes positive supercoils) using ATP as energy source.
DNA gyrase
The ability of gyrase to relax positive supercoils comes into play during
DNA replication
Drugs like _______ that inhibit DNA gyrase are used as antibacterial.
Quinolones
Provides a template for replication and transcription. It is the source of info for protein synthesis. It provides info for inheritance.
DNA
Complementarity of DNA strands suggest that replication is done in a ___________, where each strand is used to create a new daughter strand.
Semi-conservative manner
During a round of replication, each of the two strands of DNA is used as a template for synthesis of a new
Complementary strand
Is a polymer of purine and pyrimidine ribonucleotides linked together by a __________ analogous to those in DNA.
Ribonucleic Acid. Phosphodiester bridges.
Sugar: Deoxyribose
DNA
Sugar: Ribose
RNA
Pyrimidines: cytosine & uracil
RNA
Strand: double
DNA
Hydrolysis by alkaline solution: not possible
DNA
Pyrimidines: cytosine & thymine
DNA
Strand: single
RNA
Hydrolysis by alkaline solution: possible
RNA
Base content: A =/ T & G =/ C
RNA
Base content: A=T & G=C
DNA
The ________ with a 5’ to 3’ polarity is complementary to the template strand with its 3’ to 5’ polarity.
RNA transcript
The sequence in the RNA transcript and its polarity is the same as that in ________, except that the __ of the transcript replaces the __ of the gene.
Coding strand. U. T.
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 _________ that is linked to an adjacent _________ at its 5’-hydroxyl through the three phosphates.
7-methylguanosine triphosphate. 2’-O-methyl ribonucleoside.
The 3’ end of mRNA has an attached polymer of adenylate residues 20-250 nucleotides in length called
Poly (A) Tail
In eukaryotic organisms, __________ is the mechanism by which most messenger RNA molecules are terminated at their 3’ ends.
Polyadenylation
Protects the mRNA molecule from exonucleases and is important for transcription termination, for export of the mRNA from the nucleus, and for translation.
Polyadenosine tail
Some mRNAs, including those for some _____, do not contain poly(A) tails.
Histones
Both the mRNA cap and poly(A) tail are added _________ by _______ enzymes.
Post transcriptionally. Nontemplate-directed.
In mammalian cells, including cells of humans, the mRNA molecules present in the cytoplasm are not RNA products immediately synthesized from the __________.
DNA template
In mammalian nuclei, the immediate products of gene transcription constitute a
Fourth class of RNA molecules
Nuclear RNA molecules that are precursors to the mature, fully processed mRNAs.
Heterogenous nuclear RNA (hnRNA)
Serve as adapters for the translation of mRNA to AA. There are atleast __ species of tRNA in each cell, at least 1 corresponding to each of the 20 AA required for protein synthesis.
Transfer RNA (tRNA)
Although tRNAs are quite stable in _______, they are somewhat unstable in _______. The opposite is true for mRNAs, which are quite unstable in ________ but generally more stable in _______ organism.
Prokaryotes. Eukaryotes. Prokaryotes. Eukaryotic.
Allows extensive folding and intra-strand complementarity to generate a secondary structure that appears in two dimensions like a cloverleaf.
Primary structure of all tRNA molecules
A unit made up of three nucleotides that correspond to the three bases of the codon on the mRNA.
Anticodon/Nodoc
Each tRNA contains a specific anticodon __________ that can base pair to one or more codons for an AA. Ex: one codon for lysine is AAA; the anticodon of a lysine tRNA might be UUU.
Triplet sequence.
A cytoplasmic nucleoprotein that acts as the machinery for the synthesis of proteins from mRNA templates.
Ribosomal RNA (rRNA)
On the ribosomes, the _____ & _____ molecules interact to translate into a specific protein molecule info transcribed from the gene.
mRNA and tRNA
In ribosomes, larger subunit
60s
In ribosomes, smaller
40s
In ribosomes, The 60s subunit contains
5s, 5.8s & 28s
In ribosomes, The 40s subunit contains a single
18s subunit
In ribosomes, all rRNA molecules except the ______ are processed from a single ___ precursor RNA molecule in the nucleolus.
5srRNA. 45s.
In ribosomes, it is independently transcribed
5sRNA
Ribosomal RNA molecules are packaged in the
Nucleolus
Is the target of several clinically relevant antibiotics: Erythromycin & etc.
rRNA
Is the most conserved(least variable) gene in all cells. For this reason, genes that encode the rRNA (rDNA) are sequenced to identify an organism’s _______, calculate related groups, and estimate rates of species divergence.
rRNA. Taxonomic group.
Found within the nucleus of eukaryotic cells. They are involved in a variety of important processes such as ________, regulation of transcription factors and maintaining telomeres. These elements are rich in ________ content.
Small nuclear RNA (snRNA). RNA splicing. Uridine content.
Region of highly repetitive DNA at the end of a linear chromosome.
Telomeres
Removal of introns from hnRNA
RNA splicing
