Nucleic Acids Flashcards
Summary 1
- The DNA molecule exists to be a store of information. It encodes the
blueprint for making all living organisms. - The complete DNA sequence in an organism is called its genome.
- Some parts of DNA contain genes, which are sections of DNA that contain
information required to make other molecules. Humans have around 20,000
genes. - RNA is transcribed from DNA and used a template for the synthesis of
proteins. - Proteins carry out thousands of functions inside a living organism –
everything to do with the structure, activity and regulation of cells, tissues
and organs.
SUMMARY – 2 – BUILDING BLOCKS
The term “nucleic acids” includes the molecules deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA).
Nucleic acids are built from monomers called nucleotides.
The 3 components of a nucleotide are:
Sugar (monosaccharide)
Nitrogenous base
Phosphate group
Note: a nucleoside has base and sugar but NO phosphate.
SUMMARY - 3
Pyrimidines have a single ring structure (mnemonic: long name → smaller structure).
Purines have a double ring structure (mnemonic: short name → bigger structure).
SUMMARY - 4
Individual DNA (and RNA) strands are ALWAYS synthesised in a 5′ to
3′ direction.
In all double stranded nucleic acids the stands are antiparallel (i.e. they
run in opposite directions).
A always pairs with T; G always pairs with C
Differences between DNA and RNA
DNA
The permanent store of
genetic information
contained in the
nucleus of the cell.
Deoxyribose.
Uses the bases A, C, G,
T.
Forms a double helix
from 2 complementary
strands
RNA
Transferring genetic
information from the
nucleus to the
cytoplasm. Also protein
synthesis.
Ribose.
Uses the bases A, C, G,
U.
Usually present as a
single-stranded
molecule
DNA and RNA are polymers made of monomers called
Nucleotides
Pyramidines
Cytosine Thymine
Purines and pyrimidines are
heterocyclic hydrocarbons
Nucleotides can have one,
two or three phosphate groups
mono/di/triphosphate
Sugar + base =
Nucleoside
Sugar + base + phosphate group
Nucleotide
If the base is Adenine Adenosine triphosphate ATP
If the base is Guanine Guanosine triphosphate GTP
PURINE
If the base is Cytosine Cytidine triphosphate CTP
If the base is Thymine Thymidine triphosphate TTP
If the base is Uracil Uridine triphosphate
PYRAMIDINE
Secondary messengers
cAMP (cyclic adenosine monophosphate) – secondary messengers
cGMP (cyclic guanosine monophosphate) – secondary messengers
The general term for nucleoside triphosphates with deoxyribose
sugar: dNTP
Oligonucleotides
Short (~20 nucleotides long)
Examples:
* RNA molecules that function as
“primers” to begin the duplication of
DNA;
* RNA molecules that regulate the
expression of genes;
* Synthetic DNA molecules used for
amplifying and analysing other,
longer nucleotide sequences (PCR
primers).
Polynucleotides
Long (these are called nucleic acids)
Examples:
* Include DNA and some RNA.
* Are the longest polymers in the living
world. (Some DNA molecules in plants
and animals contain hundreds of millions
of nucleotides)
Double Stranded Helix
with a sugar–phosphate
backbone on the outside and base pairs lined up on the inside
Held together by CBP
In DNA:
Thymine pairs with adenine (T-A)
(T and A are complementary bases)
Cytosine pairs with guanine (C-G)
(C and G are complementary bases)
Formation of hydrogen bonds between a purine and a pyrimidine.
2 hydrogen bonds between T and A.
3 hydrogen bonds between C and G.
Chargaff’s Rules
Rule 1
There is a 1:1 ratio of purine bases to pyrimidine bases in double-
stranded DNA.
Amount of A = amount of T.
Amount of G = amount of C.
Rule 2
The relative amounts of A-T and C-G vary between different
species.
e.g. E. coli has a GC content of 51%; humans, 41%; yeast, 38%.
Other than hydrogen bonds, what kind
of forces hold the two strands
together?
2- Hydrophobic interactions
3- Van der Waals interactions
These interactions are called the ‘base stacking interactions’
Reversible Reaction
However, heat will ‘denaturate’ DNA.
But this is a reversible
reaction.
Cooling down will
‘renaturate’ DNA.
