nucleic acids Flashcards
what is the role of DNA?
hereditary material responsible for passing genetic information from cell to cell.
codes for amino acids and proteins
draw DNA?
draw RNA?
what are the 5 bases in nucleic acid?
guanine, cytosine. adenine, thymine
uracil only in rna replaces thymine
what is the difference between purine bases and pyramidine bases?
purine = bigger 2 rings e.g adenine and guanine
pyramidine = smaller, 1 ring e.g cytosine, thymine and uracil
how is DNA adapted for its function?
- its a stavble molecule - so has the ability to separate so it can be self-replicated
- large molecule - carries lots of information
- base pairing prevents corruption from outside chemicals/physical forces
how is the structure of DNA related to its properties?
- sugar phosphate backbone - gives strength
- coiling - compact shape
- sequence of bases - allows information to be stored
- long molecule/coiling - stores a large amount of information
- complimentary base pairing- infor can be replicaterd
- double helix - protects weak h bonds, makes molecule more stable
- many h bonds - stable molecule and prevents corruption of code
- weak h bonds - allow strands to separate for replication
what is the role of RNA?
transfers genetic information from DNA to ribosomes.
ribosomes are formed from rna and proteins
explain the properties of mrna
- single stranded
- contains ribose
- contains uracil
- shorter than dna
mRNA is complimentary to …?
tRNA
what is the function of tRNA?
carries amino acids that are used to make proteins to the ribosomes.
explain how tRNA is specific?
each tRNA is specific for one amino acid
draw the structure of trna
clover leaf
describe the differences between dna mrna and trna
shape? number of polynucleotide chains? number of nucleotides in chain? base pairs?
DNA - double helix, 2 strands, millions, a-t c-g
mRNA - linear strand , 1 strand, hundreds a- u g-c
tRNA - clover leaf, 1 strands, about 75, a-u g-c
what were the possible mechanisms of DNA replication?
conservative, semi conservative, dispersive
what is conservative replication?
suggested that the original DNA molecule remained intact and that a separate DNA copy was made from new molecules
what is dispersive replication?
little bits from both
who proposed semi-conservative replication?
Watson and Crick
what is semi-conservative replication?
during replication, the strands of DNA separate and each strand acts as a template for the formation of a new strand of DNA
Explain Fully The Process Of DNA Replication.
- replication starts at a specific sequence on the DNA molecule called the replication origin
- the enzyme helicase unwinds and unzips DNA, breaking the hydrogen bonds that join the base pairs, forming 2 separate strands
- the new DNA is built up from the 4 nucleotides ( A,G,C,T) that are abundant in the nucleoplasm
- these nucleotides attach themselves to the bases on the old strands by complimentary base pairing. where there is a T base, only and A nucleotide will bind and so on
- the enzyme DNA polymerase joins the two nucleotides by strong covalent bonds, forming the sugar-phosphate backbone (PHOSPHODIESTER BONDS)
- a winding enzyme winds up the new strands to form double helixes
- the two new moleules are identical to the old molecule
- this is known as semi-conservative replication as each of the parental DNA strands is conserved and acts as a template. the new molecule contains one original parent strand and one new one
Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule? - MSA
- Condensation reaction
- between phosphate and deoxyribose
- Catalysed by DNA polymerase
describe the meselson and stahl experiemnt
Bacterial cells grown in 15N medium for several generations – DNA extracted and subjected to density gradient centrifugation
First generation of bacterial cells after transfer
to 14N medium – DNA extracted and subjected to density gradient centrifugation
Second generation of bacterial cells after transfer to 14N medium – DNA extracted and subjected to density gradient centrifugation
Third generation of bacterial cells after transfer to 14N medium – DNA extracted and subjected to density gradient centrifugation
what is the density gradient diffusion
- Solutions of decreasing density of caesium chloride are placed into centrifuge tubes
- The most dense caesium chloride is at the bottom of the tube
- The extracted DNA molecules are pipetted onto the top of the most dilute caesium chloride solution
- The tubes are spun in a centrifuge
-As the tubes are centrifuged, the DNA molecules move to positions where their density corresponds with that of the caesium chloride solution
Meselson -Stahl results?
bacterial DNA following growth of cells in 15N medium = ALL HEAVY DNA
first generation after transfer to 14N medium = ALL INTERMEDIATE (HYBRID) DNA
second generation after transfer to14N medium = 50% LIGHT – 50% HYBRID
third generation after transfer to14N medium = 75% LIGHT – 25% HYBRID
FINISH
