Lesson 2 - DNA and RNA Flashcards
- informational molecules of all living organisms
- long, chain-like polymers assembeld from repeating subunits, nucleotides
nucleic acids
Two types of nucleic acids
- Deoxyribonucleic Acid (DNA)
- Ribonucleic Acid (RNA)
a unit of only the base and sugar without phosphates
nucleoside
nucleosides of DNA
- deoxyadenosine
- deoxyguanosine
- deoxycytidine
- deoxythymidine
nucleosides of RNA
- adenosine
- guanosine
- cytidine
- uridine
Three components of nucleotides
- nitrogenous base
- five-carbon sugar
- phosphate group
two types of nitrogenous bases
- purine
- pyrimidine
six membered ring made up of carbon and nitrogen atoms
pyrimidines
uracil
2,4-dioxypyrimidine
thymine
- 2,4-dioxy-5-methylpyrimidine or
- 5-methyluracil
cytosine
2-oxy-4-aminopyrimidine
six-membered ring fused to a five-memberd ring
purines
adenine
6-aminopurine
guanine
2-amino-6-oxypurine
- reversible change of one DNA base isomer to another
- shift in the location of H atoms and double bonds
tautomeric shift in DNA bases
2 forms of the same molecule differing only in the location of a proton and a double bond
tautomers
in DNA bases, what are the usual forms
- amino (NH2)
- keto (C=O)
in DNA bases, what are the rare forms
- imino (NH)
- enol (C-OH)
links covalently to nitrogenous bases
five-carbon sugar (pentose)
a chain of 1,2, or 3 phosphates linked to the pentose sugar at its 5’ carbon
phosphate group
where is the phosphate group linked to
5’ carbon
bonds between base pairs in the interior of the molecule
numerous hydrogen bonds
- β-N-glycosidic bond (sugar to base)
- phosphodiester bond (nt to nt)
covalent bonds
sugar to base bond
β-N-glycosidic bond
phosphate to sugar base bond
phosphodiester bond
Primary Structure of DNA
- linear sequence of nucleotides
- sugar-phosphate backbone on the outside
Secondary Structure of DNA
- two intertwined antiparellel strands
- major and minor grooves
- right-handed helix
- constant diameter of 20 Å
- base pases are perpendicular to axis
- hydrophobic associations form stable non-polar environment
essential for binding of proteins
major and minor grooves
length between bases
0.34 nm
One complete turn of the double helix
- 3.4 nm long
- 10 base pairs
what is formed between the hydrophobic associations of base pairs
stable non-polar environment
Different DNA conformations
- A DNA
- B DNA
- C DNA
- D DNA
- Z DNA
Why are there different DNA conformations
adapt to stress
most common DNA conformation in nature
B DNA
A DNA: overall proportion
short and broad
A DNA: helix rotation
right
A DNA: bp per turn
11
A DNA: conditions of occurrence
- 75% humidity
- K+, Na+, Ca++
B DNA: overall proportion
long and thin
B DNA: helix rotation
right
B DNA: bp per turn
10
B DNA: conditions of occurrence
- 92% humidity
- low salt
C DNA: overall proportion
long and thin
C DNA: helix rotation
right
C DNA: bp per turn
9.33
C DNA: conditions of occurrence
66% humidity
Z DNA: overall proportion
elongated and slim
Z DNA: helix rotation
left
Z DNA: bp per turn
12
A DNA: helix diameter
23 A
A DNA: major groove
extremely narrow, very deep
A DNA: minor groove
very broad, shallow
A DNA: found in
- dsRNA
- RNA-DNA duplexes
- rRNA
- tRNA
- viral RNA
- polypurine strand
B DNA: helix diameter
20 A
B DNA: major groove
wide, intermed
B DNA: minor groove
narrow, intermed
B DNA: found in
- biologically dominant
- polypyrimidine strand
C DNA: helix diameter
20 A
C DNA: found in
- in vitro
- dehydrated conditions
Z DNA: helix diameter
18 A
Z DNA: major groove
flattened out on helix surface
Z DNA: minor groove
extremely narrow, very deep
Z DNA: found in
- dCGCGCG in vitro
- in vivo
- methylated DNA
- exists largely as single-stranded chains in living cells
- genetic material of some viruses
ribonucleic acid (RNA)
bases in RNA
- cytosine
- guanine
- adenine
- uracil
Segments of RNA molecules may
- form RNA-DNA hybrid
- pair temporaily in double-helical form
- fold back on themselves to set up extensive double-helical regions
where can RNA-DNA hybrid repeat be found
during transcription
Peculiar NA sequences
- mirror repeat
- inverted repeat
symmetrical sequence within each strand
mirror repeat
two copies of an identical sequence present in the reverse orientation
inverted repeats = palindrome
More Secondary Structures of DNA and RNA
- internal loops
- bulge loops
- cruciform
- hairpin
- stem-and-loop
- cloverleaf
when there are bases that cannot pair on both sides of the helix
interal loops
unpaired bases occur only on one side of the helix
bulge loops
- non-B DNA structure characterized by cross-shaped conformations that are observed in inverted repeat sequence features.
- in DNA with a region of dyad symmetry in which the axis of symmetry separates the inverted repeats
cruciform
- when it folds back on itself to form a double-helical segment in the region of the sequence
- in ssDNA molecule with an inverted repeat or
- in an RNA molecule copied from a palindromic DNA
hairpin
- similar with hairpin structure but occurs when the loop at the end would have many unpaired bases
- plays an important role in attenuation
stem-and-loop structure
- characteristic conformation of the tRNA molecule
- made up of three stem-loops
- has four arms
cloverleaf structure
four base-paired arms of tRNA
- Acceptor arm
- D-arm
- TΨC arm
- Anticodon arm
- end of a tRNA molecule to which an amino acid becomes bound
- contains both the 5’ and 3’ ends of the tRNA.
acceptor arm
- recognition process is the primary purpose
- serves as a recognition site for the enzyme aminoacyl-tRNA synthetase
- contains the modified nucleotide dihydrouridine.
D-loop
specialized region on the tRNA molecule which acts as a special recognition site for the ribosome
TΨC arm
- a trinucleotide sequence located at one end of a transfer RNA (tRNA) molecule
- complementary to a corresponding codon in a messenger RNA (mRNA) sequence.
anticodon arm
Significance of other secondary and tertiary structures of DNA/RNA
- stabilize genome structure
- serve as recognition site for initiation and termination
- important in the function of the nucleic acid made from it
- form core of catalytic RNA molcules as binding sites for substrates and cofactors
catalytic RNA molecules
ribozymes