1 Biological Molecules- Nucleic Acids Flashcards
What are DNA and RNA and how are their functions different?
Deoxyribonucleic acid and ribonucleic acid are important information carrying molecules and polymers of nucleotides. DNA holds genetic information in all living cells, and RNA transfers it from DNA to the ribosomes
What are ribosomes formed from?
RNA and proteins
How are both RNA and DNA formed?
A pentose sugar, nitrogen-containing organic base and a phosphate group
What are the components of a DNA nucleotide?
A deoxyribose, phosphate group and one of the organic bases adenine, thymine, cytosine or guanine
What are the components of an RNA nucleotide?
A ribose, phosphate, and one of the organic bases adenine, uracil, cytosine or guanine
How is a phosphodiester bond formed?
Through a condensation reaction between 2 nucleotides; phosphate and deoxyribose
What does a DNA molecule contain?
A double helix of 2 polynucleotide chains (anti-parallel) held together by hydrogen bonds between specific complementary base pairs.
What does an RNA molecule contain?
A relatively short polynucleotide chain
What does the semi-conservative replication of DNA ensure?
Genetic continuity between generations of cells
What is the process of semi-conservative replication?
-DNA helicase binds to DNA and breaks the hydrogen bonds between the 2 strands
-The DNA helix unwinds and the two strands separate
-Free-floating nucleotides form hydrogen bonds with the complementary bases
-Each strand is used as a template to make complementary strands
-DNA polymerase catalyses the condensation of the nucleotides into a new DNA strand, making a phosphodiester bond
-2 new DNA strands are synthesised
What did Watson and Crick do?
Found that specific base pairing was involved in a way of copying sequences of genetic information , thought that each strand acts as a template from which the new complementary strand is copied. However, they didn’t know how replication took place and proposed 3 models
What did Meselson and Stahl do, explain experiment?
Grew E. coli for several generations in a medium with a “heavy” nitrogen 15N isotope and a “light” 14N one (during replication, nitrogen is included into nitrogenous bases and eventually DNA)
After each of the first few generations, cells were harvested and was DNA isolated & centrifuged
DNA formed separate bands according to density, the heavy one lower down
They moved the E. Coli from the 15N batch to a broth with only 14N, after 1 generation of growth the single band observed was in the space between DNA of cells grown exclusively in 15N and 14N- suggesting semi-conservative replication
After 2 generations- 1 band corresponding to 14N and the other in between
