Nucleic Acids Flashcards
DNA nucleotide structure and RNA nucleotide structure
DNA:
Phosphate group, nitrogenous base (ACGT), pentose sugar (ribose).
RNA:
Phosphate group, nitrogenous base (ACG and uracil), pentose sugar (deoxyribose)
Structural features of DNA
Polynucleotide (polymer) made from many DNA nucleotide monomers.
Double-stranded helix
Anti-parallel strands
Complimentary base pairing between strands
Via hydrogen bonding
A-T C-G
Nucleotides are linked via strong phosphodiester bonds forming a sugar phosphate backbone.
In eukaryotic cells, chromosomes are linear, coiled and associated with proteins called histones.
What’s the function of DNA
DNA molecules hold genetic information
Hereditary information can be passed to the next generation
Genes (sections of chromosomes) hold instructions for synthesising proteins
Complimentary base pairing between strands allow for DNA replication
Both strands can be separated for acting as templates for DNA replication and transcription.
Stability of DNA
Stable structure means mutations (changes to the genetic code) are rare.
Phosphodiester bonds protect the more chemically reactive nitrogenous bases inside the double helix
Hydrogen bonding links the 2 complimentary strands together
Why were scientists originally doubtful DNA carried the genetic code?
DNA is only made from 4 nucleotides. There are only 4 nitrogenous bases. ATCG. DNA is too simple a molecule.
Whereas there are many different proteins and proteins show much more variation.
Semi-conservative replication
DNA helicase unwinds the DNA helix by breaking the hydrogen bonds.
The two strands separate and each acts as a template for the synthesis of a new strand.
Free activated DNA nucleotides complimentary base pair via hydrogen bonding.
DNA polymerase catalyses formation of phosphodiester bonds between the nucleotide monomers (condensation reaction using ATP, water released)
Nucleotide monomers are always added onto the 3’ end of a lengthening new strand.
Two identical DNA molecules are created, identical to the original DNA molecule ( each new DNA molecules consist of one strand from the original double helix and one newly synthesised strand)
This is semi-conservative replication.
Why can nucleotide monomers only be attached to the 3-prime end of a polynucleotide.
The phosphate group attached to C5 on the nucleotide reacts with the hydroxyl group on C3 of the last nucleotide in the chain.
Because the DNA polymerase is an enzyme with a specifically shaped active site.
Basic role of ATP
Immediate source of energy
Small, manageable quantities of energy are released when ATP is hydrolysed
Hydrolysis of ATP is a single, one step reaction so energy release is very rapid
ATP can’t be stored so it’s constantly being regenerated
More active cells have a faster ATP cycle
Chemical equation showing the hydrolysis of ATP
ATP + H2O= ADP + Pi
Why is ATP referred to as the universal currency of energy?
ATP is used by all cells in all living organisms
It is used to drive processes that require an input of energy (endergonic)
All organisms must convert their source of energy (e.g. carbohydrates) into ATP.
What is meant by ATP having low activation energy
Only a little energy is needed to hydrolyse ATP’s 3rd ester bond.
But then
A lot of energy is released
Example of an endergonic (energy out) reaction.
3 ways ATP is synthesised in biology.
- phosphorylation (part of the light dependent reaction on thylakoids)
- oxidative phosphorylation (aerobic respiration on the mitochondria cristae)
- substrate level phosphorylation (enzyme action)
5 uses for ATP in cells
Anabolism- synthesis of complex molecules e.g. protein synthesis, DNA replication Active transport- forced movement of charged ions across a membrane e.g. nerves Muscle contraction (myosin pulling against actin filaments) Maintaining body temperature (ATPase hydrolyses ATP releasing heat energy) Activating biochemistry through phosphorylation e.g. glycolysis
DNA vs RNA
DNA Deoxyribose ATCG Very long Shape: Linear, double helix, coiled Cell location: nucleus Lifespan: long (stable) Role: storage of genetic information/ code for building proteins
RNA: Ribose sugar AUCG Relatively short Shape: mRNA-linear single strand rRNA- bulky with proteins tRNA- bulky, t-shaped Cell location: mRNA in nucleus and cytoplasm rRNA in cytoplasm and attached to RER tRNA in cytoplasm attaching to amino acids Lifespan: short (often broken down) Role: protein synthesis
