biological molecules (DNA and RNA) Flashcards
what does DNA stand for?
deoxyribonucleic acid
what does RNA stand for?
ribonucleic acid
what is the purpose of DNA?
stores genetic information
what is the purpose of RNA?
transfers genetic information from DNA to ribosomes
what is a nucleotide?
type of biological molecule
what is a nucleotide made from?
pentose sugar, nitrogen containing base, phosphate group
what is the pentose sugar in DNA?
deoxyribose
what bases are present in DNA?
adenine, thymine, cytosine, guanine
what is the pentose sugar in RNA?
ribose
what bases are present in RNA?
adenine, uracil, cytosine, guanine
what is a polynucleotide?
polymer of nucleotides
how do nucleotides join?
condensation reaction between phosphate of one molecule, and the sugar of another
phosphodiester bond
what is a chain of sugars and phosphates called?
sugar phosphate backbone
what is the structure of DNA?
double helix, 2 polynucleotide strands that are antiparallel
what bonds form between DNA bases?
hydrogen
what is complementary base pairing?
the idea that each base can only join with its complementary base
how many hydrogen bonds form between A and T?
2
how many hydrogen bonds form between C and G?
3
who proposed the structure of the DNA double helix?
Watson and Crick
what is the structure of RNA?
short polynucleotide chain
how does semi conservative DNA replication occur?
1) DNA helicase breaks hydrogen bonds between bases on polynucleotide strands
2) DNA helix unwinds to form 2 strands
3) original strand acts as a template
4) complementary base pairing occurs- free nucleotides are attracted to their exposed bases
5) condensation reaction joins nucleotides (catalysed by DNA polymerase)
which end of the newly forming strand is the active site of DNA polymerase complementary to?
3’ end (enzyme can only add nucleotides at this end)
which direction is a new strand of DNA made in?
5’ to 3’ direction
DNA polymerase moves down the template strand in the 3’ to 5’ direction
as strands are antiparallel, DNA polymerase works in opposite directions on either strand
who proposed evidence for semi conservative replication?
Meselson and Stahl
what isotopes of nitrogen did Meselson and Stahl use?
heavy nitrogen= 15N
light nitrogen= 14N
how did Meselson and Stahl provide evidence for semi conservative replication?
initial DNA samples contained light or heavy nitrogen
heavy nitrogen bacteria were replicated in light nitrogen broth
spun in a centrifuge
DNA with a combination of heavy original strands and light new strands settled in the middle of the test tube
