nucleic acids

Question 1

what is the role of DNA?

Answer 1

hereditary material responsible for passing genetic information from cell to cell.
codes for amino acids and proteins

Question 2

draw DNA?

Question 3

draw RNA?

Question 4

what are the 5 bases in nucleic acid?

Answer 4

guanine, cytosine. adenine, thymine
uracil only in rna replaces thymine

Question 5

what is the difference between purine bases and pyramidine bases?

Answer 5

purine = bigger 2 rings e.g adenine and guanine
pyramidine = smaller, 1 ring e.g cytosine, thymine and uracil

Question 6

how is DNA adapted for its function?

Answer 6

• 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

Question 7

how is the structure of DNA related to its properties?

Answer 7

• 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

Question 8

what is the role of RNA?

Answer 8

transfers genetic information from DNA to ribosomes.
ribosomes are formed from rna and proteins

Question 9

explain the properties of mrna

Answer 9

• single stranded
• contains ribose
• contains uracil
• shorter than dna

Question 10

mRNA is complimentary to …?

Answer 10

tRNA

Question 11

what is the function of tRNA?

Answer 11

carries amino acids that are used to make proteins to the ribosomes.

Question 12

explain how tRNA is specific?

Answer 12

each tRNA is specific for one amino acid

Question 13

draw the structure of trna

Answer 13

clover leaf

Question 14

describe the differences between dna mrna and trna
shape? number of polynucleotide chains? number of nucleotides in chain? base pairs?

Answer 14

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

Question 15

what were the possible mechanisms of DNA replication?

Answer 15

conservative, semi conservative, dispersive

Question 16

what is conservative replication?

Answer 16

suggested that the original DNA molecule remained intact and that a separate DNA copy was made from new molecules

Question 17

what is dispersive replication?

Answer 17

little bits from both

Question 18

who proposed semi-conservative replication?

Answer 18

Watson and Crick

Question 19

what is semi-conservative replication?

Answer 19

during replication, the strands of DNA separate and each strand acts as a template for the formation of a new strand of DNA

Question 20

Explain Fully The Process Of DNA Replication.

Answer 20

• 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

Question 21

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule? - MSA

Answer 21

• Condensation reaction
• between phosphate and deoxyribose
• Catalysed by DNA polymerase

Question 22

describe the meselson and stahl experiemnt

Answer 22

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

Question 23

what is the density gradient diffusion

Answer 23

• 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

Question 24

Meselson -Stahl results?

Answer 24

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

Question 25

FINISH