Biological molecules- DNA

Question 1

What are Nucleic Acids?

Answer 1

Polymers made from Nucleotides (2 types = DNA and RNA)

Question 2

What is DNA?

Answer 2

 DeoxyriboNucleic Acid
 found in all organisms (animals, plants, microorganisms)
 carries genes
 genes = section of DNA that codes for a protein
 all organisms are built of proteins

Question 3

Building block of DNA?

Answer 3

 DNA nucleotide (made of phosphate, deoxyribose sugar, nitrogenous base)
 4 types of nucleotides (each has a different base, either
Adenine/Thymine/Cytosine/Guanine)

Question 4

DNA structure?

Answer 4

 DNA Double Helix
 join nucleotides by condensation reaction between sugar and phosphate to form a polynucleotide
 join 2 polynucleotides by hydrogen bond between the bases
 A joins with T, C joins with G (complementary base pairing)
 produces double strand
 then coil double strand into Double Helix

Question 5

Properties of DNA Structure?

Answer 5

Double Stranded = makes DNA more stable & 2 strands act as templates in semi-conservative replication
 Coil into Helix = more compact
 Sugar-phosphate backbone = protects bases (bases code for protein)
 Hydrogen bonds between bases = weak, so double strand separates more easily for semi-conservative
replication
 Complementary Base Pairing = ensures identical copies of DNA made by semi-conservative replication

Question 6

DNA Replication?

Answer 6

occurs in interphase before mitosis & meiosis

occurs by semi-conservative replication

Question 7

Describe Semi-Conservative Replication?

Answer 7

 DNA double strand separate and act as templates, producing 2 identical copies of the DNA, each has half
the original strand and half the new strand
process:
 DNA Helicase breaks hydrogen bonds between the complementary bases
 double strand separates, leaves 2 template stands
 free complementary nucleotides bind to exposed bases on template strands (A to T, C to G)
 DNA Polymerase joins the sugar-phosphate backbone of the new strand

Question 8

Evidence for SCR?

Answer 8

 Replicating Bacterial DNA in 2 types of Nitrogen Isotopes, 15N and 14N
 15N = heavy isotope
 14N = light isotope
 Nitrogen found in nitrogenous bases of DNA
 Bacterial DNA made from 15N will have a Heavy Density
 Bacterial DNA made from 14N will have a Light Density
 Experiment = Bacterial DNA made of 15N is replicated in an environment of 14N – produces DNA
molecules with half 15/half 14 (semi-conservative replication, original strand = 15N & new strand = 14N),
therefore, DNA molecule has medium density

Question 9

What is RNA?

Answer 9

 RiboNucleic Acid
 2 types (mRNA and tRNA)
 mRNA = messenger RNA
 tRNA = transfer RNA
 both single stranded
 both made of RNA Nucleotides (phosphate, ribose sugar, nitrogenous bases - AUCG)