Nucleic acids Flashcards
general nucleotide formation
Phosphate group
Pentose sugar
Nitrogenous Base
RNA nucleotide formation
Phosphate group
Nitrogenous Base ( A,C,G,U)
Pentose sugar (ribose)
DNA nucleotide formation
Phosphate group
Nitrogenous Base (A,C,G,T)
Pentose Sugar (dexoyribose)
Explain why DNA and RNA examples of polymers.
They are made from small, soluble, repeating units called nucleotides (DNA or RNA nucleotides).
MANY nucleotides can be linked together to for the much larger polymers.
Detail the structural features of DNA.
Polynucleotide (polymer) made from many DNA nucleotides (monomers).
Double stranded helix.
Anti-parallel strands.
Complementary base pairing between strands / nitrogenous bases.
Via hydrogen bonding.
A-T, C-G
Nucleotides are linked via strong, phosphodiester bonds forming a “sugar-phosphate” backbone.
N.B. In eukaryotic (nucleated) cells DNA molecules / chromosomes are linear, coiled and associated with proteins called histones.
What is 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!
Complementary base pairing between strands allows for DNA replication / transcription of genes.
Both strands can be separated for acting as templates for DNA replication and also transcription.
Explain the stability of DNA.
The 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 complementary 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. A,T, C and G.
Whereas there are many different proteins!
Detail semi-conservative replication
DNA helicase unwinds the DNA helix.
Breaks (not hydrolyses!) the hydrogen bonds.
Separates the 2 strands.
Both strands act as a template for forming new strands.
Free, activated DNA nucleotides complementary base pair via hydrogen bonding.
A-T, T-A, C-G, G-C
DNA polymerase forms phosphodiester bonds between the nucleotide monomers.
Condensation reaction, using ATP, water released.
Creates 2 identical DNA molecules, identical to the original DNA molecule.
Each new DNA molecule consists of one strand from the original double helix and one newly synthesised strand.
This Is termed semiconservative replication.
Why can nucleotides (monomers) only be attached to the 3-prime end of a polynucleotide?
DNA nucleotides (monomers) are only added to the 3’ end of a lengthening strand.
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.
Explain how scientist can prove semi-coservate replication.
The scientist took from bacteria of Nitrogen 14 and extracted the DNA. Then they placed the DNA in a solution and spun at very high speeds in a centrifuge. The DNA then moved down the solution and formed a band which the scientist could detect depending on how heavy the DNA is. The band formed can therefore be seen as Nitrogen 14. Next the scientist cultured the bacteria in a growth medium which contained only nitrogen 15. Once the Nitrogen reproduced many times it was really all Nitrogen 15. When the DNA was extracted and centrifuged it formed a band near the bottom of the tube. The sceintist placed Nitrogen 14 into bacteria which had been growing on Nitrogen 15 and allowed it to replicate only once. Once they extrated the DNA and spun it in a centrifuged it produces a band in-between the two band before. Therefore, it contained one strand of Nitrogen 14 and one strand of Nitrogen 15 therefore the DNA replicated semi-conservatively. Then they allowed the bacteria to replicate one more time and once it was ectratced and spun it produces a band pattern with the indermatite band and a nitrogen 14 band.
The difference between DNA and RNA
Pentose sugar:
DNA- dexyribose RNA-ribose
Nitrogenous bases:
DNA- A, T, C, G RNA- A, U, C, G
Length:
DNA-very long RNA-relatively short
Shape:
DNA-linear, double helix, coiled
RNA-
mRNA - linear single strand
rRNA - bulky, with proteins
tRNA - bulky, t - shaped
Cell location:
DNA- nucleus RNA-mRNA in nucleus and cytoplasm
rRNA in cytoplasm attached to RER
tRNA in cytoplasm attaching to amino acids
Lifespan:
DNA-long (stable)
RNA-short (often broken down)
Role:
DNA-Storage of genetic information / code for building proteins
RNA-Protein synthesis
Describe ATP structure
ATP is formed from one adenine base, a ribose (5C) sugar and three phosphate groups.
Aerobic respiration - ATP synthase catalyses a condensation reaction between ADP + inorganic phosphate.
What is the 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 cannot be stored so it is constantly being re-generated (ATP cycle).
More active cells have a faster ATP cycle!
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.
