nucleic acid and nucleotides Flashcards
Nucleic acid : elements, monomer, function
CHONP , nucleotides, contains genetic information required for growth, reproduction, repair/replacement and protein manufacture
What is the timeline of DNA?
1869 - miescher found DNA contained HONP
1910 - levene found a contained sugar and phosphate which formed repeating units called nucleotides
1940 - chargraff suggested complimentary pairing of A=T and C-=G
1950 - Franklin and Wilkins formed the first picture of a double helix
1953 - Watson and Crick found arrangement of double helix and complementary pairing
What are nucleotides the monomers to?
nucleic acid: RNA ATP DNA
What happens when condensation reaction happens to nucleotides?
Phosphodiester bonds are formed (found between the phosphate group of one nucleotide and the pentose sugar of another) forming a sugar phosphate backbone to the polynucleotide chain
What are the similarities between RNA and DNA?
They both contain nitrogenous bases ACG
They both contain a phosphate group
They both contain Pentose sugars (5 ring)
What are the three differences between a DNA and RNA
DNA contains two strands, nitrogenous base T and a deoxyribose sugar (C2 has 2 H)
RNA contains one strand, nitrogenous base U and ribose sugar (C2 has H over OH)
What is the structure of DNA?
double helix structure - two polynucleotide chains that are anti-parallel from each other linked by hydrogen bonds between nitrogenous bases ATCG
Contains deoxyribose sugar
What is the structure of RNA?
Single helix - one polynucleotide chain containing ribose sugar and nitrogenous base U instead of T
Explain about the hydrogen bonds between nitrogenous bases and why they are important?
There are two between AT and three between CG
purine always bonds to a pyrimidine
Hydrogen bonds make DNA very strong and stable structure which helps limit the number of mistakes/mutations in the genetic instructions
What does three prime and five prime mean in the DNA structure?
The three prime polynucleotide chain is where the third carbon is at top (inverted)
The five prime polynucleotide chain is fifth carbon is on the top (non invited chain)
What are the different ways RNA can be found And what are its functions
mRNA A template strands that carries a copy of the gene out of the nuclear pores to ribosome for protein synthesis
tRNA bring specific amino acid to the codons
rRNA catalyses the formation of peptide bonds between amino acids forming proteins
How many hydrogen bonds are there between A and T?
Two
How many hydrogen bonds are there between C and G
Three
What is a phosphodiester bond?
2 Esther Bonds
Both coming from the phosphorus group, 1 to C5 on the Pentose, sugar of its own nucleotide and another to a C3 from a Pentose sugar in a different nucleotide
What are purines?
Two carbon nitrogen rings
Adenine guanine
Larger
What are pyrimidines?
One carbon nitrogen ring so are smaller
Cytosine thymine Uracil
What is the structure of ATP?
- Contains an adenosine (ribose and adenine)
- And 1-3 phosphate groups Each one added or removed by condensation or hydrolysis- (which releases lots of energy used for cellular processes like synthesis, transport and movement)
Properties of ATP
- small and soluble so can be moved easily
- contains unstable bonds between phosphates = lots of energy released
- as each bond is broken, energy is released in small quantities so this is more efficient as there is minimal waste as heat
- easily regenerated (renewable energy) so meets high demands of organisms
What does the enzyme DNA helicase do
Unwinds the double helix by breaking the hydrogen bonds between complementary nitrogenous base pairs
What is a gene
A sequence of DNA nucleotides bases that code for a specific protein
How many possible amino acids could there be and how many are there actually
4x4x4=64 actually 20
Why is an advantage to have less possible amino acids (degenerate)
Possible mutation may result in the same amino acid therefore there will be no effect on the protein formed
What does genetic code being universal mean?
same 4 nucleotide bases, same base triplet codons for the same amino acids in all living things but organisms differ due to the different arrangement of the bases
What does degenerate code mean? Give an example to show how the genetic code is degenerate
Multiple codes code for the same amino acid, There are 6 codon options for leucine
Why is genetic code non overlapping
So each nucleotide is only part of one triplet codon
What is the result of DNA replication and when does it occur?
1 parent double helix strand to 2 polynucleotide stands to 2 identical daughter double helix stands (occurs in S phase of cycle)
DNA replication in detail
- DNA uncoils and is unziped by the enzyme helicase which breaks the hydrogen bonds separating the 2 polynucleotide chains
- free DNA nucleotides bind to the template strands, complementary base pairing occurs A=T C-=G, new hydrogen bonds are formed between the exposed bases on the template and nucleotides
- DNA polymerase (which only goes from 3’ to 5’) catalyses the formation of polydiester bonds between adjacent nucleotides, sealing the sugar phosphate backbone and forming two new polynucleotide chains attached to templates.
On the leading strand, It stalks the helicase and connects all nucleotides but on the lagging strand it has to go the opposite direction due to the 3’ to 5’ rule so leaves gaps (called okazaki fragments) when trying catch up with helicase. - ligase seals the gaps, completing the stand
- semi conservative replication has occurred,
two identical strands are formed
what are the roles of the enzyme in DNA replication
helicase - breaks the hydrogen bonds and splits double helix,
DNA polymerase - forms new phosphodiester bonds and links nucleotides to form a sugar phosphate backbone,
ligase - Seals the gaps (Okazaki fragments) DNA polymerase has made on the lagging strand
When extracting DNA the mixture is placed in a water bath at 30 degrees what effect will this temperature have on the results
The temperature is too low the white precipitate of DNA might not form as the enzymes have not stopped working as they have not denatured this means enzymes breakdown the dna and less dna will be available to form precipitate
how to purify and extract DNA
- break down mixture To break down to cell wall
- add Detergent To dissolve the membrane By attracting phospholipids Away from their bilayer structure
- add salt To isolate the DNA And allow it to precipitate
- incubate at a water bath at 60 degrees for 15 minutes then put in an ice bath to cool down So enzymes don’t break up their DNA
- filter the mixture and transfer a sample into a boiling tube
- add protease to break down histones
- dribble some cold (so DNA doesn’t break down) ethanol down the side of the mixture so it forms a layer on top of the DNA and allow precipitation Of DNA
- leave the tube for a few minutes and remove any white precipitate of DNA that has formed using a glass rod
What is the Meselson Stahl experiment
It is evidence for semi-conservative DNA
they labelled bacterial DNA with different isotopes of nitrogen. the bacteria was exposed to 15N in a Growth medium first then the 14N isotope. as the bacteria grew and replicated the free nucleotides containing N14 were incorporated but still contained strands of N15
what does semi conservative DNA mean
That the two identical daughter cells contain 1 strand of the parent strand which has acted as a template joined to a new strand made from free nucleotides
How would Meselson Stahl check their results for validity
Had a negative control EG grown in a medium with no nitrogen
What is the method of which DNA replicates Itself
Semi conservative replication
how does a mutation in the gene affect the protein produced
amino acid sequence would change causing different folding of a protein which may cause the protein to not work or work the same
What is ATP and how is it used for energy
- It is the universal energy currency,
- A store of chemical potential energy,
- The molecule has to be hydrolyzed (bonds are broken) to release the chemical energy to be used in reactions.
- A small amount of energy is used to break the bond but more is released
why is ATP better than glucose for releasing of energy
As each phosphate breaks off energy is released slowly, This means no energy is wasted and is more efficient for Reactions in the body
Describe how two nucleotide chains in DNA are bonded together
A T with two hydrogen bonds or C G with three hydrogen bonds,
the complementary bases pair together- a purine and a pyrimidine always
Name the components in a nucleotide of DNA
Deoxyribose Pentose sugar, phosphate group and nitrogenous base adenine
what is a stop codon
a codon that doesn’t code for anything
Why does transcription have to take place
DNA can’t leave the nucleus so mRNA is produced to copy the DNA and transfer into ribosome for protein to be made
what is the difference between DNA and MRNA
DNA is long-term
mRNA is short-term
DNA only stays in the nucleus
mRNA is a copy which leaves the nucleus
what happens in Transcription
DNA to mRNA (in the nucleus)
- dna has been unwound from histones and helicase unzips DNA breaking hydrogen bonds exposing genetic code
- RNA polymerase lines up free RNA nucleotides along the template strand forming temporary hydrogen bond with complementary base pairs c=-g a=u
- RNA polymerase catalyses formation of phosphodiester bonds between RNA nucleotides forming a new sugar phosphate backbone for mRNA strand
- once RNA polymerase reaches a stop codon, it detaches and mRNA leaves the nucleus through the nuclear pores
- The hydrogen bonds between the DNA strands reform and their coil back together into double helix
Post transcriptional modification
- mRNA undergoes some editing which will make it more stable in the cytoplasm so it survives longer and is ready for translation
What happens in translation
mRNA to protein
- tRNA brings unique anticodon and specific amino acid to each codon on the mRNA strand
- Complementary base pairing C=-G U=T
- rRNA catalyses the Condensation of peptide bonds between amino acids
- The amino acid chain can now be folded into a protein
Post translational modification
- Proteins are modified to ensure they are functional this can happen automatically or be controlled e.g. enzymes often require activation before they can work (for efficiency)
How does complementary base structure help DNA to replicate semiconservative?
It means the original DNA strand can act as a template for a new strand, free floating DNA nucleotides join up with exposed bases on the original strand by complementary base pairing
Suggest how the meselson and stahl experiment shows evidence for semiconservative replication
It contained 50-50 of the different nitrogens suggesting half of the new strand are from the original nitrogen and the other half are made newly from the template of the original strand proving semiconservative replication
What is a mutation?
A random change to the DNA base sequence
How do tRNA molecules pair up with mRNA?
A tRNA molecule with an anticodon that’s complementary to the a codon on the mRNA attaches itself to the mRNA by complementary base pairing, temporary hydrogen bonds are formed
Which stain is used to make chromosome more visible by dying phosphate groups of dna
Methylene blue
How does uracil differ from thymine
It has a ribose sugar ( 2 oh at the bottom)
