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Flashcards in DNA Structure and Organisation Deck (22):

What are 3 essential properties of genetic material?

-Be able to replicate accurately
-Stable and not easily broken down
-Capable of change (in order for evolution and variation to occur)


Describe Griffith's transformation experiment to show that DNA was the genetic material.
(Hint: R and S bacteria in mice).

-Showed that bacteria can get DNA through transformation.
-He infected mice with smooth and rough strains of bacteria. The smooth strain covers itself with a polysaccharide capsule that protects it from the immune defences of the host meaning the host will be infected and die.
-S strain bacteria were killed with heat and their remains were added to R strain bacteria
-Neither R strain nor heat treated S strain killed mice on their own, when together, the DNA containing the gene to produce the polysaccharide had been taken up by the R strain and was able to kill the mice.


Describe Oswald T Avery's experiment that showed that DNA is the transforming principle. (Hint: still using S and R bacteria but this time comparing RNA and DNA).

Showed that DNA is the transforming principle
-Treated a mixture of DNA and RNA with RNAase. Add DNA remains to R bacteria and put on plate of growth medium which resulted in S transformants produced
-Treated a mixture of DNA and RNA with DNase and added RNA remains to R bacteria which resulted in no S transformants


What types of sugar are glucose and ribose?

Glucose is a hexose sugar. Ribose is a pentose sugar.


Describe how deoxyribose differs from ribose sugar.

Deoxyribose is the same as ribose but with a hydroxyl group missing from the second carbon.


Which bases are purines and which are pyrimidines?

(-Both have double rings)

(-Remember this because only C and T have Y in them, like pYrimidine.)
(-Single ring structure)


What is mean by the term 'nucleoside'?

A compound (e.g. adenosine or cytidine) consisting of a purine or pyrimidine base linked to a sugar.


How are nucleotides joined to each other?

Nucleotides are joined by the 3 prime hydroxyl group of one nucleotide and the 5 prime phosphate of the other nucleotide to form a phosohodiester bond in a condensation reaction.


Which bases form two hydrogen bonds between them and which form three hydrogen three hydrogen bonds?

A-T= two hydrogen bonds

C-G= three hydrogen bonds


How is the DNA stack held together?

Van der Waals forces between stacked bases.


Describe the two common secondary structures of DNA.

-Major groove is wider than minor groove

-Minor groove is wider than the major groove
-Found in dehydrated conditions
-Base pairs are more tilted away from the axis


At which end is the start of the gene? The three prime end or the five prime end?

Start of the gene is always at the 5’ end.


What are HU and H1 binding proteins in DNA?

* HU binding proteins are bacterial histone like proteins that also bind to DNA and RNA
* H1 binding proteins are unlike other histones in that they do not make up the nucleosome “bead”. It sits on top of the structure and keeps the DNA in place that has wrapped around the nucleosome.


What is a nucleosome?

A structural unit of eukaryotic DNA which is made of a length of DNA coiled around a core of histones.


How are eukaryotic genomes packaged in by supercoiling? (Hint: which class of enzymes). How do they do this?

Topoisomerases supercoil the DNA. They do this by cutting one or both of the DNA strands, winding or unwinding the helix and resealing the ends


What is chromatin?

A complex of DNA and proteins (histones).


What is a centromere?

centre of chromosome with specialised sequences that form microtubules and spindle apparatus.


What are polytene and lamp brush chromosomes?

-Composed of many DNA strands

Lamp brush:
-Found in oocytes in meiosis.
-Large and have lots of DNA looping.
-Activates the transcription of genes


How are histones modified?

Histones are modified by attaching proteins to the ends of the histones. Histone tails are important for histone modifications such as phosphorylation, acetylation, methylation etc...


What is euchromatin?

-LOOSELY PACKED AND GENE RICH- because of this, it is more likely to contain lots of G and C residues because they are bound more tightly together as they have 3 hydrogen bonds between them.
-Chromosome material which does not stain strongly except during cell division.
-Represents major genes
-Involved in transcription


What is heterochromatin?

-Condensed and inactive DNA.
-More dense than normal
-Activity of genes is modified or suppressed
-Stains strongly (because it is so tightly packed).


Describe how mRNA is modified during/ after transcription.

-During transcription, whilst the mRNA strand is still being formed, a methylated cap is added to the 5' end
-After transcription, two cleavage factors attach to specific RNA sequences and move the 3'end into the correct configuration
- PolyA polymerase attaches to the complex and cleaves the 3' end
-Poly A polymerase now synthesises the polyadenylated tail by adding lots of A residues
-Additional proteins then bind to the tail, increasing the rate at which it grows.