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Lecture 2.4

Element 2- Biochemistry

QuestionAnswer
What charge does DNA have and why? Negative because the phosphate in the backbone is negatively charged due to the _O-
In what form do free DNA nucleotides float around in the cell? With a triphosphate attached onto them
What happens when a nucleotide is added to a growing chain of DNA? The outer two phosphates are cleaved off and are called pyrophosphates (like a little diphosphate). This is split into two phosphates bt a pyrophosphatase enzyme which makes the addition of the nucleotide to the DNA irreversible.
Explain the difference between a purine and a pyramidine Purines are double ringed and pyramidines are single ringed
Which bases are purines and which are pyramidines? Adenine and Guanine are purines. Cytosine, uracil and thymine are pyramidines
What is the role of exonuclease Cleave nucleotides one at a time from the ends of the polynucleotide chain
What is the role of endonuclease Recognise a restriction site and break the phosphodiester bond in the backbone there, separating the polynucleotide chain
How many hydrogen bonds are there between cytosine and it's complementary base on the other strand of DNA Cytosine's complementary base pair is guanine and they have 3 hydrogen bonds between them
What can go wrong with cytosine? It can deaminate and turn into uracil, but a special repair pathway reanimated it.
Why do bacteria use uracil and not thymine? It is easier to manufacture
Why is the deamination of cytosine not a problem for humans? In DNA it is repaired through a special repair pathway and in RNA its not an issue because there so many mRNA molecules around in the cell
Why do humans have thymine instead of uracil in their DNA? If uracil was involved then the body would think it was a deaminated cytosine and reanimated it.
What is a nucleoside? A nucleotide without the phosphate group
What type of bond links the nitrogenous base to the sugar? Glycosidic bond
Describe the structure of the DNA helix A double stranded right hand helix that rotates around a common axis. The strands are antiparallel (they run in opposite directions)
What are the differences between major and minor grooves? The distance between the two strands of backbone in a DNA molecule differs along the strong. The minor groove occurs when the strands are close together and the major groover is when they're far apart.
What is the major groove's function? Allow for more space for the proteins that alter the DNA shape to interact with the bases because the backbone isn't in the way.
What bond is present in the backbone of a DNA molecule? Phosphodiester bond
What is the definition of a genome? Genetic info of an organism. Divides into chromosomes
Define gene Basic unit of inheritance. e.g. protein structure
Created by: macdonkr
 

 



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