BIOLOGICAL MOLECULES - nucleic acids and DNA, ATP, evidence for semi conservative replication Flashcards
draw the structure of a nucleotide?
phosphate-sugar-base
name the pentose sugars in RNA and DNA?
RNA - ribose
DNA - deoxyribose
state the role of DNA in living cells?
The base sequence of genes codes for functional RNA and amino acid sequence of polypeptides.
Contains genetic information which determines inherited characteristics which influences structure and function of organisms.
State the role of RNA in living cells?
mRNA - carries the genetic code from the DNA to the ribosome, where it’s used to make a protein during translation.
rRNA -involved in synthesisising proteins and catalyses the peptide bond formation
tRNA- supplies complementary amino acids to mRNA codons during translation.
How do polynucleotides form?
condensation reactions between nucleotides forming strong phosphodiester bonds ( sugar phosphate backbone)
describe the structure of DNA
double helix of 2 polynucleotide strands
Hydrogen bonds between complementary purine and pyrimidine base pairs on opposite strands.
A and T
C and G
which bases are purine and which bases are pyrimidine?
A and G - 2 ring purine bases
T and C - 1 ring pyrimidine base
Name the complementary base pairs in DNA?
adenine thymine - 2 h bonds
cytosine guanine - 3 h bonds
Name the complementary base pairs in RNA?
Adenine and Uracil - 2 h bonds
Guanine and cytosine - 3 h bonds
relate the structure of DNA to its functions?
- sugar phosphate backbone and many hydrogen bonds provides stability
- long molecules stores a lot of information
- helix is compact for storage in nucleus
- base sequence in triplets codes for amino acids
- double stranded for semi- conservative replication
- complementary base pairing for accurate replication
- weak h bonds so strands separate for replication
describe the structure of messenger RNA?
long ribose polynucleotide
shorter than DNA
contains uracil instead of thymine
single stranded and linear
relate the structure of mRNA to its function?
- breaks down quickly so no excess polypeptide forms
- ribosome can move along strand and tRNA can bind to exposed bases
- can be translated into a specific polypeptide by ribosomes
why is DNA replication described as ‘semiconservative’?
- strands from original DNA act as a template
- new DNA molecule contains one old strand and one new strand
outline the process of semiconservative DNA replication?
- DNA helicase breaks the H-bonds between base pairs. Each strand acts as a template.
- free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
- DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
- Hydrogen bonds reform
describe the meselson-stahl experiment?
- bacteria were grown in a medium containing heavy isotopes of 15-Nitrogen for many generations.
- some bacteria were moved to another medium containing light isotope 14-N.
- samples were extracted after 1 and 2 cycles of DNA replication
- centrifugation formed a pellet. Heavier DNA (15N) settled closer to the bottom of the tube.
