Nucleic Acid L1 Flashcards
GREGOR MENDEL = 3
- In the 19th century, Gregor Mendel uncovered the fundamental principles that would become the MODERN science of GENETICS.
- Mendel demonstrated that heritable
properties are parcelled out in discrete units, that are INDEPENDENTLY INHERITED. - HEREDITY is the transfer of characteristics from generation to generation.
How is the information to make a new individual organism is passed on?
- through the reproductive cells’ DNA
(for example in human sperm & ovum).
What are GENES?
DNA information is contained in genes.
Genes: are part of
our genetic material – DNA
– found in the nucleus
(& also in MITOCHONDRIA & CHLOROPLASTS) as part of the chromosomes…
While many genes encode proteins, lots do not.
How do we convert sequences of ‘nt’ bases into sequences of AA in proteins?
= 4
- DNA = two strands
- RNA one strand
- DNA is transcribed
into RNA - RNA is translated
into protein
How was the nucleus founded?
Fredrich Miescher (1860’s) took leukocytes (WBC) &
isolated a phosphorous containing substance he called “nuclein”
- he believed this was important in inheritance…
Major components of the nucleus = 2
- BASIC (+vely charged) COMPOUNDS
= Polymers of AMINO ACIDS ….PROTEINS - ACIDIC (-vely charged) COMPOUNDS = polymers of NUCLEOTIDES …NUCLEIC ACIDS
In eukaryotic cells …. Protein vs DNA
In eukaryotic cells, nuclear
chromosomes contain about TWICE as much PROTEIN AS DNA.
These PROTEINS (including
histones) PACKAGE THE DNA…
Macromolecule:
polymers of nucleotides
2 TYPES OF MACROMOLECULES
Deoxyribonucleic acid (DNA)
& Ribonucleic acid (RNA)
What are DNA and RNA? = 7
- Found in all living cells & viruses
- Information storage & retrieval
- Determine protein AA sequence
- Cell communication
- Cellular energy
- Structural (rRNAs)
- Functional (tRNA, snRNA …)
What are the 3 Components of Nucleotides?
- Nitrogenous Base
- Pentose Monosaccharide
- Phosphate
Nucleotides are either
deoxyribonucleotides or ribonucleotides
What is the Phosphate?
Simple organic molecule - phosphorous & oxygen atoms only
- At physiological pH (7-7.5),
- the hydroxyl groups are completely
dissociated - WHY?
…pKa very low, H+ readily dissociate
Hence the phosphate has a net charge of -2
Since nucleotides have a negative charge, so do nucleic acids (as these are polymers of nucleotides)
SUGAR:
In nucleotides, this is either DEOXYRIBOSE or RIBOSE
C atoms are numbered 1 to 5 in a clockwise direction and they are designated 1’, 2’, 3’, 4’, 5’.
This is to distinguished them from C and N in the bases.
Pentose Monosaccharides … IN SOLUTION?
When free in solution,
RIBOSE exists as a STRAIGHT CHAIN ALDEHYDE in EQUILIBRIUM
WITH A RING B-furanose form.
Deoxyribose & ribose in a nucleotide, RING form …why
——1’C bond to the BASE.
——5’C bond to the PHOSPHATE.
Recall the C atoms are numbered 1 to 5 in a
clockwise direction, and they are designated 1’, 2’
,3’, 4’, 5’ to distinguish them from C & N in the bases
The pentose ring is not planar….
NOT PLANAR & can OCCURS IN A VARIETY IN A CONFORMATIONS ….
The POSITIONING of the CARBONS in the PENTOSE CAN IMPACT THE SHAPE OF NUCLEIC ACID.
What are the NITROGENOUS BASES?
The bases are HETEROCYCLIC AROMATIC AMINES AND &
fundamental to coding information of nucleic acids.
TWO categories of bases: Note the double bonds
Pyrimidine AND Purine
Nitrogenous Bases structure:
- PYRIMIDINE = N1 in pyrimidines
- PURINE = N9 in purines
- heterocyclic aromatic amines
- C & N are numbered clockwise as 1, 2, 3, 4, 5
(note: no primes here!).
BASES CHEMICAL PROPERTIES AFFECT?
- STRUCTURE & hence
FUNCTION of nucleic acids. - Due to their AROMATIC CHARACTER
- BASES ARE HYDROPHOBIC AND RELATIVELY INSOLUBLE IN WATER AT CELLULAR pH.
SIGNIFICANCE OF THE DOUBLE BONDS?
Result in bases being highly CONJUGATED…
RESONANCE involving many atoms of the ring
gives most bonds a partial double bond character
Resonance Results in Stabilisation
Double bonds of bases make pyrimidines PLANAR &
purines NEARLY PLANAR …
resonance in benzene ring makes it
very STABLE & explains why it does not undergo additions
typical of other alkenes …
Absorption Spectra of Nucleotides
Due to resonance, all bases absorb UV light
Strong absorption near 260nm wavelength
Bond between pentose & base
Note the bond is between 1’C & N9 in purines
& N1 in pyrimidines
AKA GLYCOSIDIC LINKAGE
Linkages in nucleosides & nucleotides
- BASE + SUGAR =
NUCLEOSIDE
- joined by a glycosidic bond
- Condensation reaction - form water
2.BASE + SUGAR + PHOSPHATE = NUCLEOTIDE
Deoxyribonucleotides =
Deoxyribonucleoside monophosphates
- Can add one or two additional phosphate groups to get
diphosphate and triphosphate, e.g., dAMP, dADP & dATP..
Ribonucleotides =
Ribonucleoside monophosphates
-Can add one or two additional phosphate groups to get
diphosphate and triphosphate, e.g., UMP, UDP & UTP…
Bases may be modified? How?
Methylation and Demethylation.
Cells also have Minor bases? = 3
- Inosine monophosphate
- Inosine
- Hypoxanthine
Cells also have nucleotides where the P group is
NOT on the 5’C, & also that form CYCLIC structures.
- Adenosime 5’ - monophosphate
- Adenosine 2’ - monophosphate
- Adenosine 3’ -monophosphate
- adenosine 2’, 3’’, -cyclic monophosphate.
Nucleotides Derivatives = 4
- Not only INFORMATION STORAGE - making RNAs & proteins
- METABOLIC – ATP (adenosine triphosphate) is the cellular energy
“currency”. - COFACTORS IN BIOCHEMICAL REACTIONS – NADH & NAD+
- CELL SIGNALLING – cAMP (cyclic adenosine monophosphate)
