1.5 Nucleic Acids Flashcards
What is a gene?
Sequence if DNA bases that codes for a specific polypeptide chain. Found on chromosomes in the DNA
What are the two types of nucleic acids?
- DNA (deoxyribonucleic acid)
- RNA (ribonucleic acid)
What do the sequence of bases in DNA code for?
Codes for the sequence of amino acids in a protein
What does protein do in DNA?
Determines all the characteristics of an organism
What are RNA molecules used in?
Used in protein synthesis
What are the monomers that make up nucleic acids? What are they made up of?
Nucleotides
Made up of:
1. Phosphate group - found in DNA AND RNA
2. Pentose (5C) carbon sugar
• DNA contains deoxyribose
• RNA contains ribose
3. Nitrogenous base
• DNA contains A,T,C,G
• RNA contains A,U,C,G
What is the complementary base pair rule?
Adenine is able to base pair through hydrogen bonds with Thymine (Uracil in RNA)
Guanine is able to base pair through hydrogen bonds with Cytosine
How do nucleic acids form?
• Nucleotides link together to form polynucleotides, through condensation reactions.
• a phosphodiester covalent bond is formed between carbon 3 of one nucleotide and the phosphate of the adjacent nucleotide
• this bonding forms a sugar phosphate backbone
What is difference deoxyribose and ribose?
What is the structure and function of DNA?
- Two anti-parallel polynucleotide chains joined together through hydrogen bonds between complementary base pairs (chains twist around each other to form a double helix)
- Stable molecule - allows genetic information to Beto be passed from generation to generation without change unless through mutation
- DNA is a large molecule which allows it to carry a large quantity of genetic information
- quantities of A=T and quantities of C=G as they pair together
- Weak hydrogen bonds join the two strands - allows easy separation during DNA replication and protein synthesis
- There are 2 hydrogen bonds between A&T and 3 hydrogen bonds between C&G
- Strong phosphodiester bonds - protect the nitrogenous bases which form the code in the centre of the molecule
What is the structure of RNA?
- Short, single polynucleotide chain
- Pentose sugar is a ribose
- Contains adenine, uracil, guanine and cytosine
What are the 3 types of RNA and what is there function?
• mRNA - messenger RNA - transfers the genetic information from DNA to the ribosome
• rRNA - ribosomal DNA - together with proteins makes up the ribosome
• tRNA - transfer RNA - transfers specific amino acids to the ribosome for protein synthesis
Explain the process of semi conservative DNA replication
- Double helix is untwisted
- Enzyme DNA helicase breaks the hydrogen bonds between the complementary nitrogenous bases allowing the two strands to separate and expose the unpaired nucleotide bases
- Both strands act as a template
- Free complementary nucleotide bases hydrogen bind to the exposed bases according to the complementary base pairing rule
- Phosphodiester covalent bonds are formed by a condemnation reaction between the nucleotides (NOT BASES)
- The enzyme DNA polymerase joins the sugar phosphate backbone
- Each DNA molecule consists of one ‘old’ strand and one newly built strand
Why is it called semi- conservative replication?
Each DNA molecule consists of one conserved ‘old’ strand and one newly built strand
Why can DNA polymerase only add new nucleotides to the new strand at the 3’ end of the deoxyribose?
The active site of DNA polymerase is only complementary to the 3’ end of the deoxyribose
The strands in the double helix are anti parallel, because DNA polymerase working on one of the template strands works in the opposite direction to the DNA polymerase working on the other template strand
Who carried out the semi-conservative replication experiment?
Meselson and Stahl
What did meselson and stahl do in there experiment?
• grew Escherichia coli bacteria for many generations in a medium in which the only source of nitrogen was the heavy isotope 15^N - heavy nitrogen
• the DNA in the offspring of these bacteria was denser than usual because the bases contained heavy nitrogen
• the bacteria containing heavy nitrogen were transferred to a medium containing only 14^N (light nitrogen) and allowed to replicate for several generations.
• samples of bacteria were taken after each generation, their DNA extracted and centrifuged. The DNA formed visible bands in the tube
• centrifugation separates the DNA on the basis of mass - the DNA with the heaviest mass will be the lowest down the tube
What were the other models of DNA replication disproved by the Meselson-Stahl experiment?
Conservative and dispersive
What was the conservative model?
Each replication results in one DNA molecule that consists of both original strands of DNA, and one DNA molecule that consists of two completely new strands of DNA
What is the dispersive model?
Each replication results in two DNA molecules that are combinations of original and new DNA
