DNA

• process of semi conservative replication experiment (4)

  -Bacteria grown in a nutrient solution containing heavy nitrogen (15N) for several generations

  -Nitrogen incorporated into bacterial DNA bases

  -Bacteria then transferred to a nutrient solution containing light nitrogen (14N) and allowed to grow and divide twice

  -During this process, DNA from different samples of bacteria was extracted, suspended in a solution in separate tubes and spun in a centrifuge
• how does the mehlson and stahl experiment provide evidence for semi conservative replication?


  -Sample 1. DNA from bacteria grown for several generations in

  a nutrient solution containing 15N

  DNA molecules contain 2 'heavy' strands so at bottom of test tube because highly dense

  -Sample 2. DNA from bacteria grown originally in a nutrient

  solution containing 15N, then transferred for one division

  to a solution containing 14N

  DNA molecules contain 1 original 'heavy' and 1 new

  'light strand so medium density

  -Sample 3. DNA from bacteria grown originally in a nutrient

  solution 15N, then transferred for two divisions to a solution containing 14N

  50% DNA molecules contain 1 original 'heavy' and 1 new 'light' strand, 50% contain both 'light' so one band high up because lights density and one band at same as sample two

  strands
• who proved the semi conservative replication theory?

  meselson and stahl
• who came up with the theory of semi conservative replication?

  Watson and Crick
• why does DNA polymerase move in opposite directions along the DNA strands? (3)


  -DNA strands are anti-parallel

  -DNA polymerase is an enzyme with a specific shaped active site/ active site has a specific tertiary structure which can only bind to substrate with complementary shape

  -can only bind to/ add nucleotides to phosphate 3 end end so works in a 5'3' direction because not complementary to 5' end so no ES complexes

  -5 prime and 3 prime indicate carbon numbers on DNA's sugar backbone; 5' carbon has a phosphate group attached and 3' carbon has a hydroxyl/ OH group attached
• benefit of DNA replication (1)

  ensures genetic continuity between generations of cells
• why is DNA replication semi conservative?

  each DNA molecule is composed of one parent/original/template strand and one new strand
• describe the process of DNA replication (4)

  -DNA helicase unzips two DNA strand in double helix/ unwinds double helix by breaking hydrogen bonds between specific complementary base pairs

  -allows two strands to act as a template

  -free floating DNA nucleotides are attracted to exposed bases via specific complementary base pairing and form hydrogen bonds with their specific complementary base pairs (A=T, C=G)

  -DNA polymerase joins adjacent nucleotides on new strand together by condensation reaction between phosphate group and deoxyribose pentose sugar of another nucleotide, forming phosphodiester bond and sugar phosphate backbone
• describe how the structure of DNA is adapted for its function of storing genetic information (8)

  -base sequence of genes codes for proteins

  -double helix (coiled)- compact

  -double stranded- both strands can act as templates for semi conservative replication

  -weak hydrogen bonds between specific complementary base pairs- strands can be easily unzipped by DNA helicase for semi conservative replication

  -complementary base pairing for accurate replication

  -many hydrogen bonds between bases to provide stability

  -double helix with sugar phosphate backbone for strength/ protection of bases/ hydrogen bonds

  -long molecule so can store lots of genetic information to code for polypeptides
• describe and explain how nitrogen containing bases pair up with each other (4)

  -purine and purine bases don't have enough space in-between them to form hydrogen bonds

  -pyrimidine and pyrimidine have too much space in-between so hydrogen bonds can't form

  -purine and pyrimidine have just the right amount of space in-between them for hydrogen bonds to form

  -purine and pyrimidine is the only complementary pair
• what is a purine base and what structure do these bases have?

  -adenine and guanine

  -double ring structure
• what is a pyrimidine base and what structure do these bases have?

  -cytosine, thymine, uracil

  -single ring structure
• what type bond bond is a phosphodiester bond?

  strong covalent bond
• DNA structure (4)

  -two strands joined in anti parallel

  -held together by hydrogen bonds

  -between specific complementary base pairs

  -twisting into a double helix
• difference between DNA and RNA molecules (2)

  -DNA is longer WHERE AS RNA is shorter

  -DNA is double stranded (double helix) WHERE AS RNA is single stranded
• structure of RNA?


  single polynucleotide strand
• how are DNA/ RNA nucleotides joined together?

  condensation reaction between phosphate group of one nucleotide and pentose sugar of another nucleotide, forming a phosphodiester bond, catalysed by DNA polymerase
• monomers and polymers of DNA

  monomer= nucleotide

  polymer= nucleic acid
• difference between RNA and DNA nucleotides (2)

  -uracil vs thymine base

  -ribose vs deoxyribose pentose sugar
• component of RNA nucleotide (3)

  -ribose pentose sugar

  -organic nitrogen containing base (adenine= uracil, cytosine=-guanine)

  -phosphate group
• component of DNA nucleotide (3)

  -deoxyribose pentose sugar

  -organic nitrogen containing base (adenine= thymine, cytosine=- guanine)

  -phosphate group
• what are ribosomes made of?

  proteins and ribosomal RNA
• RNA function?

  transfers genetic information from DNA to ribosomes
• DNA function

  carries genes/ genetic code to make proteins
• what does DNA stand for?

  deoxyribonucleic acid