2 - ICH - DNA Flashcards
What type of molecule is DNA?
Name it’s monomer?
Nucleic acid
Monomer = nucleotide
`What does DNA stand for?
Deoxyribonucleic acid
Name the 3 components of a nucleotide.
What are the differences for RNA and DNA?
Contains:
- Pentose sugar (deoxyribose for DNA and ribose for RNA)
- Phosphate group (from H3PO4)
- Nitrogenous organic base (DNA = Adenine, thymine, guanine, cytosine. RNA = Adenine, uracil, cytosine, guanine)
Name the complementary base pairings?
Adenine - Thymine
Cytosine - Guanine
What is a:
Purine
Pyrimidine
Which bases are purines and which are pyrimidines in DNA?
Purine = Double ringed nitrogenous bases that form a part of a nucleotide
Pyrimidine = Single ringed nitrogenous bases that form a part of a nucleotide
DNA:
- Purines = A and G*
- Pyrimidines = C and T*
Name the type of reaction and bond formed by the joining on nucleotides.
What do you use to hydrolyse it?
Condentation reaction
Phosphodiester bond
Nuclease
What are nucleic acids?
Polynucleotides made from monomers called nucleotides
How does a phosphodiester bond form?
H of the OH on carbon 3 of the pentose sugar in one nucleotide reacts with the OH in the phosphate group of the other nucleotide.
H2O is condensed.
Property of the phosphodiester bond?
The sugar phosphate bond is very strong and helps to maintain the sequence of nucleotides in the chain
The number of hydrogen bonds between:
- A-T
- C-G
- 2
- 3
What direction do the chains of the polynucleotide run?
ANTIPARALLEL
One strand runs from 5’ → 3’ and the other 3’ → 5’
What is the structure of DNA often referred to as?
Double helix
What do these do in DNA replication?
DNA Helicase
DNA Ligase
DNA Polymerase
DNA Helicase = Enzyme that breaks hydrogen bonds holding the complementary base pairings together to unzip the 2 DNA strands.
DNA Ligase = Joins okazaki fragments of lagging strand together.
DNA Polymerase = Joins the nucleotide bases back together to form 2 new molecules of DNA which are identical to each othe and te original parent molecule.
Descibe an experiment to purify DNA
STRAWBERRIES!
- Break up a bit of strawberry in a test tube.
- Make a solution of detergent (washing up liquid), salt and distilled water. Add broken up cells to beaker containing detergent solution.
- Heat in hot water bath for 15 mins at 60°C. Detergent breaks down cell membranes, salt binds to DNA and causes it to clump together. Temperture denatures enzymes in cells.
- Place beaker in ice bath to cool. Filter the mixture into a new test tube.
- Add protease enzymes - This breaks down proteins in the mixture.
- Slowly dribble some cold ethanol down the side of the tube so a layer forms on top of the DNA-detergent mixture.
- Leave for a few minutes. DNA forms a white ppt (solid).
How does DNA replicate?
Semi conservatively = Half of the strands of the new daughter strands are from the parent strands
How does DNA replicate itself?
- DNA helicase breaks hydrogen bonds (unzips the double helix).
- Each original strand acts as template for the 2 new strands. Free floating nucleotides join to exposed bases by complementary base pairings.
- DNA polymerase joins the nucleotides together (by the hydrogen bonds).
- The 2 new daughter strands have half the DNA of the parent strand.
DNA self replication and mutation
Generally it’s very accurate - makes sure that genetic information is conserved.
Sometimes:
Random, spontaneous mutations happen.
Mutations don’t always have an effect, but they alter the sequence of amino acids in a protein.
This can cause an abnormal protein to be produced. This can work better/ worse/ not work at all compared to the original
Adaptations of DNA (4)
- Can store large amounts of information.
- Self replicate accurately
- Stable (strong sugar phosphate backbone and lots of hydrogen bonds) so information isn’t easily altered.
- Able to repair itself. If one polynucleotide strand is damaged as long as the complementary strand is intact the missing nucleotides can be replaced.
Why is DNA called the genetic code?
DNA codes for the sequence of amino acids in a polypeptide chain
List 5 characteristics of the genetic code
Triplet code
Code is universal
It’s a degenerate code
It’s non-overlapping
It has nonsense triplets
Why does it mean?
Genetic code:
It’s a triplet code
- Each amino acid is coded for by a sequence of 3 DNA bases.
- Sequence is always read in ONE direction.
- Sequence is always read from one of the 2 strands of DNA (coding strand/reference strand)
- Non coding strand is important, makes DNA very stable and allow accurate copying by semi-conservative replication.
- Must code for all 20 amino acids. (44 = 64 combinations)
Why does it mean?
Genetic code:
Universal
+ example?
The same DNA triplets code for the same amino acids in nearly all organisms
E.g.
CGT codes for arginine in ALL living organisms
Why does it mean?
Genetic code:
Degenerate code
+ example?
- There’s 64 combinations of the 4 bases (44 = 64) but there’s only 20 amino acids.
- Some amino acids are coded for by more than one triplet code. Only the first 2 bases are important!
E.g.
The 4 codes in the picture all code for Arginine but all begin with CG
Why does it mean?
Genetic code:
Non-overlapping
- Each sequence of 3 base codes for a seperate amino acid.
- There’s NO overlap in the base sequence
