Nucleic Acid 3 Flashcards
(39 cards)
There are only 4 bases commonly found in DNA/RNA:
A, C, G, T/U
So have some common “motifs” (sequences of bases).
Palindromes:
- read same in both directions,
e.g. ROTATOR
- In DNA are really “inverted repeats”
Note: self-complementary sequences within strands
What About Base Sequence?
If the inverted repeat is within one individual
strand, it’s called a mirror repeat:
Self-complementary sequences within each single strand of DNA or a strand of RNA can form intra- strand H bonds between complementary bases…
What are Hairpins?
- Hairpins form when a SINGLE DNA or RNA strand FORMS BASE PAIRS:
- ISOLATED DNA SOLUTIONS with
such SEQUENCES
can FORM COMPLEX
STRUCTURES WITH MULTIPLE HAIRPINS. - Note: base-pairs within strands are ANTIPARALLEL
What is CRUCIFORM?
- When BOTH STRANDS of
DNA are involved, in
INTRA-STRAND H bonding,
get a CRUCIFORM. - Cruciform DNA has
been found in some
BACTERIA, but not (yet?)
in human cells.
What is RNA? = 4
- RNA is INTERMEDIARY in CONVERTING GENETIC INFORMATION INTON THE PRODUCTION OF FUNCTIONAL PROTEINS….
- SECOND MAJOR FORM OF NUCLEIC ACID IN CELLS.
- In eukaryotes, DNA = NUCLEUS;
whereas RNA = NUCLEUS AND CYTOPLASM. - Since 1950’s thought RNA had role as a MESSENGER & INFORMATION RELAY FROM THE NUCLEUS TO THE CYTOPLASMrelay from the nucleus to the cytoplasm
RNA – polymer of ribonucleotides
EXPLAIN THE RNA PRIMARY STRUCTURE:
- Polymer of
ribonucleotides, joined
by POSPHODIESTER BONDS - Sugar = ribose
- Uracil replaces the
thymine found in DNA - RNA = SINGLE STRANDED
Understanding RNA primary Structure…..3
- same as DNA primary structure
- sequence of
ribonucleotides from 5’ to 3’ - Many RNAs have SEQUENCES THAT ENABLE FORMATION OF INTRA-STRAND COMPLEMENTARY BASE PAIRS…
Understanding RNA Secondary Structure
- RNA is synthesised as a SINGLE STRAND BUT this
does NOT mean RNA has a RANDOM STRUCTURE. - Single strands tend to make up a RIGHT-HANDED HELIX DOMINATED BY BASE-STACKING INTERACTIONS, WITH
*****PURINE-PURINE STACKS BEING THE STRONGEST. - RNA can for INTRA-STRAND H BONDS AND MANY RNAs have COMPLEX SECONDARY STRUCTURES, ENABLING VARIOUS FUNCTIONS THAT RNAs perform.
RNA Secondary Structure - Self-complementary sequences can lead to….
- RNA Secondary Structure - Self-complementary sequences can lead to COMPLEX AND SPECIFIC STRUCTURES.
- RNA can Base pair complementary strands of DNA or RNA….
- Standard base pairs C:G, A:T or A:U and ANTIPARALLEL.
- single strand, bulge, internal loop, hairpin
Uracil rather than Thymine
CHEMICAL DIFFERENCE does NOT IMPACT U-A base-pairing.
Important for transcription of RNA (DNA:RNA hybrid).
But uracil CAN BASE PAIR with OTHER RIBONUCLEOTIDES INCLUDING ITSELF. ….
Explain RNA STRUCTURE is Essential to FUNCTION….
- RNA can BASE PAIR CONVENTIONALLY (A-U & G-C),
& also UNUSUAL base-pairing such as U-U or G-U
2.The unusual base pairings = RNAs to form EXTENSIVE, COMPLICATED STRUCTURES.
3.Note: H bonds in U-G/U-U are WEAKER than those in U-A.
4.FOLDED RNA can have
ENZYMATIC ACTIVITY (ribozyme) & various STRUCTURAL ROLES.
RNA grouped into two “classes”
1.CODING: Encodes PROTEIN PRIMARY STRUCTURE
—- mRNA (messenger) “code”.
- NONCODING: Functional RNAs, i.e. RNA itself is
the final functional product
- tRNA (transfer) - “one” for each AA
- rRNA (ribosomal) - part of ribosomes
Majority of RNAs are Noncoding…
Majority of RNAs are Noncoding
mRNA
Messenger RNAs = code for Protein
rRNA
Ribosomal RNA, form the
- basic structure of the ribosome and
- catalyze protein synthesis
tRNA
Transfer RNAs, central to protein synthesis as ADAPTORS between mRNA and Amino Acids
snRNAs
small nuclear RNAs, function in a variety of nuclear processes, including the spicing of pre-mRNA.
These 3 RNA types are essential FOR
PROTEIN SYNTHESIS
Noncoding snRNAs are essential for
JOINING EXONS
Transfer RNAs deliver amino acids to the
ribosome (where proteins are made)
— AA attachment is very specific & is at the 3’-OH of the tRNA.
—- Single stranded tRNA = “cloverleaf” structure of “hairpins”.
—- Four double-helical stems & three single stranded loops.
Why does DNA have deoxyribose?
- RNA in solution with
high pH … ionisation
of OH; eventually
forming 2’,3’-cyclic
mono-nucleotides. - In contrast: alkali is an
excellent denaturant
for DNA.
Why have DNA and RNA??
- DNA is more stable & less reactive than RNA
= a better long term genetic store! - The GROOVES in RNA LARGER than in DNA, allowing ACCESS to DEGRADING ENZYMES, so RNA isLESS STABLE than DNA.
- DEOXYRIBOSE in SUGAR-PHOSPHATE backbone MORE STABLE = greater length.
- DOUBLE HELIX & THYMINE instead of URACIL= STABLE &
errors during replication
easier to RECOGNISE/REPAIR.
Hypothesis – RNA preceded DNA & proteins in evolution
- If nucleic acids needed to synthesise proteins & proteins in turn required to synthesise nucleic acids – how did
interdependent components arise? - Maybe RNA both stored genetic material & catalysed chemical reactions, only later did DNA take over as genetic material & proteins become major catalyst & structural component
of cells… - Do RNAs with catalytic activity in modern day cells – yes! Ribozymes for example rRNA catalyses peptide bond formation!
