Nucleic acids Flashcards
DNA meaning, structure and function
Deoxyribonucleic acid holds genetic information.
Consists of a phosphate group, nitrogenous base and a pentose sugar (deoxyribose)
RNA meaning, structure and function
Ribonucleic acid transfers genetic information from DNA to ribosomes
Consists of a phosphate group, nitrogenous base and a pentose sugar (ribose)
what are ribosomes formed from
RNA and proteins
Bases in DNA
Adenine-Thymine,
Guanine-Cytosine
Bases in RNA
Adenine-Uracil,
Guanine-Cytosine
how do nucleotides form nucleic acids?
DNA or RNA nucleotides are joined together by condensation reactions
Forms phosphodiester bonds
DNA structure
2 strands joined in anti-parallel, held together by hydrogen bonds (between specific complementary base pairs; A-T, G-C)
Double helix
RNA structure
Single RNA polynucleotide strand
Differences between RNA and DNA
DNA molecules are double-stranded (double helix), whereas RNA molecules are single-stranded
DNA is longer whereas RNA is shorter
Structure of DNA related to its functions (hydrogen bonds)
Weak hydrogen bonds between bases: can be unzipped easily for replication
Many hydrogen bonds between bases: stable/strong molecule
Structure of DNA related to its functions (helical)
Double helix with a sugar-phosphate backbone: protects bases and hydrogen bonds
Double helix (coiled): compact
Long molecule: store lots of genetic information that codes for polypeptides
Structure of DNA related to its functions (shape)
Complementary base pairing: accurate replication
Double-stranded: both strands can act as templates for semi-conservative replication
Process of DNA replication
DNA helicase breaks hydrogen bonds between bases and unwinds the double helix.
Results in two strands which both act as templates.
Free-floating DNA nucleotides are attracted to the exposed bases via specific complementary base pairing
Hydrogen bonds form: adenine-thymine, guanine-cytosine
DNA polymerase joins adjacent nucleotides on new strand by condensation, which forms phosphodiester bonds (sugar-phosphate backbone)
Replication is semi-conservative: each new strand formed contains one template strand and one new strand.
Ensures genetic continuity between generations of cells.
How does DNA polymerase join adjacent nucleotides?
DNA polymerase moves in opposite directions along the DNA strands (DNA has anti-parallel strands)
DNA polymerase is an enzyme with a specific active site which can only bind to substrates with complementary shapes.
It can only bind to and add nucleotides to the phosphate (3’) end of the developing strand.
Works in a 5’ to 3’ direction
5’ carbon has a phosphate group attached
3’ carbon has a hydroxyl (-OH) group attached
What is ATP
Adenosine triphosphate
Ribose, a molecule of adenine and 3 phosphate groups
What is ADP
Adenosine diphosphate
Ribose, a molecule of adenine and 2 phosphate groups
ATP hydrolysis
(ATP -> ADP + Pi)
Catalysed by the enzyme ATP hydrolase
Can be coupled with energy-requiring reactions to provide energy for active transport, protein synthesis, etc (energy is released when the bonds between inorganic phosphate groups are broken)
The inorganic phosphate released can be used to phosphorylate other compounds eg glucose, often making them more reactive (ie lowers activation energy)
ATP/ADP condensation (ADP + Pi -> ATP)
Catalysed by the enzyme ATP synthase
Happens during respiration or photosynthesis
Also called phosphorylation of ADP
Formation of a water molecule
Properties of ATP
(that makes it a suitable immediate source of energy; ATP cannot be stored)
ATP releases energy in small, manageable amounts (no energy is wasted)
Only one bond is hydrolysed (single reaction) to release energy (which is why energy release is immediate)
Evidence for semi-conservative replication (Meselson and Stahl) process
Bacteria is grown in a nutrient containing heavy nitrogen (15N) for several generations
Nitrogen is therefore incorporated into bacterial DNA bases
Bacteria then transferred to a nutrient solution containing light nitrogen (14N) and allowed to grow and divide twice
During this process, DNA from different samples of bacteria was extracted, suspended in a solution in separate tubes and spun in a centrifuge
Evidence for semi-conservative replication (Meselson and Stahl)
results
Sample 1: DNA from bacteria grown for several generations in a nutrient solution containing 15N. DNA molecules contain two heavy strands
Sample 2: DNA from bacteria grown originally in a nutrient solution containing 15N, then transferred for one division to a solution containing 14N. DNA molecules contain 1 original heavy strand, and one new light strand
Sample 3: DNA from bacteria grown originally in nutrient solution containing 15N, then transferred for two divisions to a solution containing 14N. 50% DNA molecules contained 1 heavy and 1 light strand, other 50% contained both light strands
