Lecture 1 - DNA Structure Flashcards
why are nucleic acids useful in forensics
they are found in everyone and can have identifiable features for specific individuals within the base pair sequence
what is DNA
a polymer made of two polynucleotide chains that coil around one another
what are the three core components of nucleic acids in DNA
bases
deoxyribose sugar
phosphate groups - these make phosphodiester bonds with the sugar
name the 4 types of bases
what is the base seen in RNA but not DNA
thymine
guanine
cytosine
adenine
uracil
what bases are purines
adenine
guanine
AG
what bases are pyrimidines
cytosine
thymine
uracil
CUT
which bases pair together and how many hydrogen bonds do they form
AT = 2 hydrogen bonds
CG = 3 hydrogen bonds
why does a deoxyribose sugar come from
from a ribose sugar that has undergone deoxygenation by an enzyme called ribonucleotide reductase
what is a phosphate group
PO4 - one oxygen is double bonded to phosphorus
there is an overall negative charge
what are the two possible structures of ribose
linear or cyclic
an equilibrium lies between the two as it can exist in either form
where do the phosphate groups attach to the deoxyribose sugar
what does this linkage drive
at carbon 3 and 5
the helical structure of DNA, this asymmetric linkage gives DNA a direction and if more stable in a twisted form
what is the difference between a nucleobase, nucleoside and nucleotide
nucleobase = the base alone
nucleoside = the base + sugar
nucleotide = base, sugar + phosphate
how is the anti-parallel structure of DNA formed
the two strands are connected via hydrogen bonds between the bases
the strands run 5’-3’ so as there are two of them in order to connect the bases they need to run anti parallel to one another
what is the primary structure of DNA
the nucleotide sequence
is the CG or AT base paring more stable
CG due to their being more hydrogen bonds between them
name 3 features that DNA has in a double helix
a major groove
a minor groove
right handed twist
why does DNA form a double helix (4 reasons)
1- to allow hydrogen bonding between the complimentary bases
2 - the negatively charged phosphate groups repel each other so they are furthest apart in the helix (reducing electrostatic repulsion)
3 - pi pi stacking is seen for the rings of the bases (hydrophobic and Van der Waals interactions) allowing a tight helix
4 - the bases being closely packed prevent water getting in and causing the hydrogen bonds to break and the structure to fall = entropically favourable
what are the three structure the double helix could be and where are they commonly seen
- B-DNA - right handed = most common and seen in cells
- A-DNA - right handed = seen in dehydrated conditions or hybrid DNA-RNA
- Z-DNA - left handed = seen in diseases when DNA has undergone methylation
what is the secondary structure of DNA
the double helix formed by two complimentary strands coming together
could be B, A or Z DNA
or triplex or quadruplex
what are triplex and quadruplex DNA
triplex = the addition of a third strand of DNA strand binding into the major groove
quadruplex = 4 DNA strands held round a metal ion, found in telomeres, protects DNA ends and allows ends to be copied
what is the tertiary structure of DNA
the 3D folded shape of the polymer
give three ways in which DNA and RNA differ structurally
DNA has T, RNA has U
DNA is normally double stranded and RNA single stranded
DNA has deoxyribose sugar and RNA has ribose (so RNA has more hydrogen bonding sites so the phosphodiesters are more easily hydrolysed)
What type of structures does RNA exist in
give 4 examples of what the structure of RNA might be
complex structures
such as:
hairpin
stem loop
bulge
bubble
how is DNA packaged into the nucleus
in structures called nucleosomes
DNA is wound round histone proteins = nucleosomes and these are packed in chromosomes
8 histones are needed to make 1 nucleosome
how can RNA be beneficial in Nanotechnology
can use RNA to create structures for desired uses
e.g cages or tubes
especially useful for getting things into the body as our body is less likely to reject it and can target certain areas
