DNA Flashcards
Deoxyribonucleic acid
Codes for sequence if amino acid in the primary structure of a protein which in turn determine the final 3D structure
Bases bonds
AUT has two hydrogen bondin
CG has three hydrogen bonding
Common nuleotide Bases
AG - purines - base found in nucleotide has two nitrogen - containing group
CT -pyramidines - base found in nucleotides has one nitrogen - containing group
Mononucleotide contains
Phosphate group
Pentose sugar
Nitrogenous containg base
Structure of RNA
Phosphate group
Ribose sugar
AUCG
Single stranded
No hydrogen bonds
What is a polynucleotide
A polynucleotide is a polymer of mononucleotides
How does mononucleotide join together to form polynucleotide
The mononucleotdie are joined through condensation reactions between the phosphate of one mononucleotide and the sugar group of another.
How is DNA formed
The two strands of DNA double helix are held togther by hydrogen bond between the complementary base pair
These hydrogen bonds form between the amino and carboxyl groups the purines adn pyramidines bases on the opposite strand
—> 10 bases pairs for each complete twist
Describe the process of DNA replication
DNA helicase will cause the two strands of DNA to unwind by breaking the hydrogen bonds between the nitrogen bases
DNA polymerase will stimulate the free mononucleotises to align in front of the template strand according to complementary base pairs
Enzyme ligase will stimulate the formation of phosphodiester bonds between the mononucleotides on the new strand
Two strands automactically coil up through formation of hydrogen bonds forming a new DNA strand identical to the original
Structure of DNA
Double stranded
Contains hydrogen bonds
ATCG
Deoxyribose sugar
Structure of mRNA
Straight and unbranched shape
Codon
No amino binding site
No hydrogen bonds
Structure of tRNA
Clover leaf shape
Anticodon
Amino acid binding site
Has hydrogen bonds
Define semi conservative replication
When new DNA is synthesized out of the old DNA but the new DNA will have half of the original strand, and half of the free mononucleotide in the nucleus
Experimental evidence of melsonson and stahls DNA replication theory
DNA is in an N15 medium, casuing all of it to be made put of N15.
It is placed in an N14 medium and allow to replicate where half of the strands will be made out of N15 and the otehr half N14
The strand will be allowed to replicate again in teh N14 medium causing 3 quarter of them to be made out of N14 and 1 quarter of them to be made of N14 and N15
Explain why a triplet code is required for syntehsis of a protein
Since there are only 4 bases to code for 20 amino acids, if every base coded for one amino acid it wouldnt be enough. Moreover even if the code was a double code it would still only code for 16 amino acids, which is less than 20 . However if it were to use a triplet code, 64 combination would be formed which is more than enough
Explain the nature of a genetic code
Triplet code where 3 bases will code for one amino acid
Degenerate meaning each codon can code for more than one amino acid
Non over lapping each codon will be read separately and doesnt interfere with triple codins that are before it or after it
Describe the process of ttransciption
Part of the DNA unwinds
RNA polymerase will stimulate free mononucleotides to align in frint of the antisense strand according to complementary base pairs to transcribe a copy of the sense strand
Enzyme ligase stimulates formatiob of phosphodiester bonds between the mononucleotides on the mRNA
mRNA detaches from the DNA antisense strand and exits the nucleus
Describe the process of translation
mRNA carries a copy of genetic code from the nucleus to the ribosome for translation
tRNA attaches to the amino acid to the ribosome, tRNA has anticodon that will be complementary to the codon on mRNA
Peptide bond forms via condensatiob reaction between two amino acid
tRNA detaches from the mRNA
Ribosome moves along the mRNA molecule synthesizing a polypeptide chains until it reaches stop codon
A polypeptide chain from ribosome -> fold into 3D shape -> determine formation of protein
Define gene mutation
It the change in base sequences in the DNA
How can gene mutation be increased by
X-rays
Ionising radiation
Certain chemicals
Results of mutayion
Mutation alter the genes they can result in a differetn amino acid sequence in the encoded polypeptide
If the amino acid sequence changes then when protein is modified into the teritary structure it will form hydorgen and ionic conds in different places and fold differently. This will result in a different 3D shape and therefore non-functioning protein
What is insertion
When one extra base being added to the sequence
Affect of insertion
The impact of adding one base is that all subsequent codons are altered. This is known as a frame shift . This type of mutation can be harmful because all the altered codon could potentially code for different amino acids and result in a very different polypeptide chain resulting in a non-functioning protein
Define delection
Where a base is comepletely lost from the sequence
Affect of delection
This causes a frame shift to the left. This causes all the codons to be altered which potentially could code for a different sequence of amino acid chain resulting in a different polypeptide chain resulting in a non-functioning protein
Define substitution
Where one base substitues for another
Affect of substitution
One base has been changed for a different base but the number of bases remains the same and there is no frame shift . This result in only one codon changing , due to the genetic code being degenerate it may still code for the same amino acid and therefore have no impact
Define point mutation
Due to the change of ine base in one codon changes a single amino acid which results in a different polypeptide in a different primary strcutude of proteins
Cause of sickle cell anaemia
Cant carry oxygen efficiently
Prevent blood flowing in the capillaries
