1-B Biological molecules Flashcards
what does DNA stand for?
deoxyribosenucleic acid
what does RNA stand for?
ribonucleic acid
what is the function of DNA?
stores generic info
-all instructions for growth and development
what is the function of RNA?
info carrying molecule
- transfers generic info from DNA to ribosomes to make polypeptides
- makes ribosomes with proteins
what is the structure of a nucleotide?
phosphate group
pentode sugar
nitrogen containing organic base
what is the structure of a DNA nucleotide?
phosphate group
deoxyribose sugar
nitrogen containing organic base
-adenine thymine cytosine guanine
what is the structure of a RNA nucleotide?
phosphate group
ribose sugar
nitrogen containing organic base
-adenine uracil thymine guanine
how are two nucleotides joined?
condensation reaction between two nucleotides forming a phosphodiester bone
- catalysed by DNA polymerase
describe the structure of a single polynucleotide strand?
sugar phosphate backbone
what is the structure of DNA?
- double helix structure - two polynucleotides which wind around each other forming a spiral
- long and tightly coiled so genetic material can fit in small space
what is complementary base pairing?
hydrogen bonding between complementary pairs of bases on opposing polynucleotide strands
(A and T) (G and C)
what is the structure of RNA?
single stranded polynucleotide
shorter strands
compare DNA and RNA
DNA -double strand -deoxyribose -ATCG -long RNA -single strand -ribose -AUCG -shorter
When as DNA first observed and why did scientists doubt it could carry the genetic code?
1800s
has a relatively simple chemical composition
when and who discovered DNA the structure of DNA?
1953 Watson and Crick
discovered the double helix structure, which helps DNA to carry out its function
what process does DNA replicate by?
semi conservative replication
why does DNA replicate?
- DNA copies itself before cell division
- half the strands in each new DNA are from the original molecule
- allows genetic continuity between generations of cells
what is the first stage of semi conservation replication?
- DNA helicase breaks hydrogen bonds between bases on two strands
- helix unwinds forming two single strands
what is the second stage of semi conservation replication?
- each original strand acts as template for new strand
- free floating nucleotides are attracted to complementary exposed bases
what is the third stage of semi conservation replication?
-DNA catalysed condensation reaction joining adjacent nucleotides of new strand together
—> phosphodiester bond
-hydrogen bonds form between complementary bases
how does DNA polymerase work?
- active site is complementary to 3’ end
- new strand is made in 5’ to 3’ direction
who carried out an experiment that gave evidence for semi conservative replication?
Meselson and Stahl
what is an isotope?
different forms of the same element
what is stage one of Meselson and Stahls experiment?
-two samples of bacteria were grown for many generations in nutrient broth
—> one containing light nitrogen (14N)
—> one containing heavy nitrogen (15N)
- as the bacteria reproduced they took up nitrogen from the broth to make nucleotides
-nitrogen became part of the DNA
what is stage two of Meselson and Stahls experiment?
- a sample of DNA was taken from each bacteria and spun in a centrifuge
- heavy nitrogen DNA settles lower
what is stage three of Meselson and Stahls experiment?
- bacteria in heavy nitrogen was taken out and put in broth of light nitrogen
- left for one round of DNA replication
- another sample was taken and spun in centrifuge
what is stage four of Meselson and Stahls experiment?
-if replication was conservative the heavy DNA would settle and the bottom and light DNA would settle at the top
