Nucleic acids ( Core concepts ) Flashcards
(44 cards)
What are the components of a nucleotide ?
A pentose sugar, phosphate plus organic base which contains nitrogen ( nitrogenous base )
What are the components of ATP and what does it stand for ?
Adenosine triphosphate
(ATP): ribose sugar, nitrogenous base and three phosphate groups joined together.
What are the components of ADP and what does it stand for ?
Adenosine diphosphate
(ADP): ribose sugar, nitrogenous base and two phosphate groups joined together.
How is ATP formed ? ( condensation )
Energy is required to combine ADP and phosphate to form ATP and this is an endergonic reaction e.g. cell respiration. ADP and Pi can combine in a condensation reaction to form ATP. To synthesise 1 mole of ATP an input of 30.6kJ of energy is required.
What is the addition of phosphate to ADP called ?
phosphorylation
How is ATP converted into ADP and phosphate ? ( hydrolysis )
Energy is released when ATP is hydrolysed to ADP and phosphate; this is linked to energy-requiring (endergonic) reactions e.g. active transport, movement, e.g. muscle contraction, synthesis of organic chemicals, e.g. proteins. ATPase is the enzyme that catalyses the reaction. Energy is released when ATP is hydrolysed to ADP and inorganic phosphate in a exergonic reaction.
What is the importance of ATP and why is it called the ‘universal energy currency in living organisms’ ?
Because ATP is used as a source of energy in all organisms in all/most biochemical reactions.
ATP is required for active transport of molecules across membranes, transport of molecules within the cell and for inducing shape changes in certain molecules giving rise to the necessary reactions in vital metabolic processes.
Found in all cells of all organsims, common source of energy in reactions, high energy bonds, exergonic so energy released when bonds between phosphate hydrolysed / broken.
What are nucleotide bases ?
They are purines or pyrimidines, linked by condensation reactions to form polymers, RNA and DNA, which can be represented in symbolic form.
What is the difference between purines and pyrimidines ?
Purines = double ring - adenine and guanine
Pyrimidines = single ring - cytosine and thymine
What is the bond between 2 nucleotides called ?
Phosphodiester bond is formed, and water is released in a condensation reaction to join 2 nucleotides together.
What does DNA consist of ? And how is RNA different from DNA ?
DNA consists of two chains linked via the base pairs, by hydrogen bonds, to form a double helix. The base pairs are C-G and A –T but in RNA thymine is replaced by uracil.
DNA structure vs RNA structure
DNA : phosphate, deoxyribose, nitrogenous base
RNA : phosphate, ribose, nitrogenous base
DNA nucleotide vs RNA nucleotide
DNA nucleotide : deoxyribose, thymine forms H bonds with adenine
RNA nucleotide : ribose, urecil forms H bonds with adenine
DNA polymer vs RNA polymer
DNA : larger, 2 strands, 1 polymer
RNA : smaller, 1 strand, 3 polymers ( mRNA, tRNA, rRNA )
DNA location vs RNA location
DNA : found in chromosomes in nucleus, extremely long molecule, double stranded molecule as it consists of two polynucleotide strands in a double helix
RNA : found in cytoplasm, relatively short molecule, one polynucleotide strand
What are the three types of RNA ? What is each type’s function and where is this function carried out ?
mRNA : functions in nucleus, migrates to ribosomes in cytoplasm, carries DNA sequence info to ribosomes
tRNA ( clover shaped ) : functions in cytoplasm, provides linkage between mRNA and amino acids to ribosomes - contains binding site for amino acids near the top and contains anticodon near bottom
rRNA : functions in cytoplasm, structural component of ribosomes.
What type and how many bonds form between adenine and thymine ?
They form 2 hydrogen bonds
What type and how many bonds form between cytosine and guanine ?
They form 3 hydrogen bonds
In DNA, what is significant about the polynucleotide strands ?
In DNA, the two polynucleotide strands are anti parallel (“run” in opposite directions, one from the 5 prime end to the 3 prime end, the other from the 3 prime end to 5 the prime end.) Anti-parallel = double stranded helix structure
What are the two main functions of DNA ?
replication, in dividing cells, and carrying the information for protein synthesis in all cells.
What does replication allow ?
Replication allows accurate copying of DNA for cell division. Every time a cell undergoes cell division, all of its DNA is copied
Describe the process of semi conservative replication
- DNA helicase/ polymerase unzips the DNA (double helix)/ breaks hydrogen bonds between (complementary) base pairs
2.{DNA nucleotides} line up along template/ pair up with exposed bases by complementary base pairing - Both strands act as templates
- DNA polymerase joins nucleotides/ catalyses formation of covalent bonds to form (sugar-phosphate backbone of) new strand
- DNA polymerase moves up leading and down lagging strand/ in 5’
to 3’ direction - Semi-conservative replication/ new DNA molecule made of one
original and one new strand
Describe the Meselson Stahl Experiment
The Meselson Stahl Experiment
1. The DNA bases A, C, T and G all contain a form of nitrogen called N14. E .coli bacteria were grown on food containing N14. The bacterial DNA was extracted and centrifuged in a test-tube of caesium chloride. A clear band became visible. The position of the band showed the density of the normal DNA.
2. The bacteria were then grown on food containing the denser form of nitrogen, N15. After several generations, all the DNA bases in the E.coli bacteria contained the N15. When this DNA was extracted and centrifuged, a different band separated out. This band was much denser and lower down in the test-tube (see Figure 16 tube A).
3. The bacteria were returned to a food substrate containing normal N14 nitrogen. The bacteria grew and divided. After one generation, their DNA was extracted and centrifuged. This DNA formed a band which was in between the N14 and N15 (see Figure 16 tube B).
4. A second generation of bacteria was grown on the normal nitrogen. This time, two bands appeared. Both bands were of equal width. One was in the same position as the original N14 bacteria and the other was intermediate between N14 and N15 (see Figure 16 tube C).
5. When a further generation was grown on normal nitrogen, the hybrid layer decreased to 25% and the light layer increased to 75%.
What were the 3 possible forms of DNA replication and describe each type ?
Conservative : completely preserve both of the old strands
Semi conservative : one old strand, one new strand
Dispersive : bit of old DNA and bit of new DNA mixed in strands
