Core Concepts: Necleic Acids and Protein Synthesis Flashcards
What is a nucleotide
A pentose sugar bonded to phosphate and a nitrogenous base
What is DNA (structure)
DNA is an abbreviation for deoxyribonucleic acid. In DNA the sugar is deoxyribose, and the base is one of these four: adenine, thymine, guanine or cytosine
A DNA molecule is composed of two complementary polynucleotide strands. A polynucleotide is a polymer of nucleotides.
The sugar-phosphate molecules are joined by condensation reactions, making a phosphodiester linkage.
The sugar-phosphate molecules form the two sugar-phosphate ‘backbones’ of the molecule. The bases project into the centre of the molecule.
The two strands are joined by hydrogen bonds between the complementary base pairs (A-T and C-G).
What is DNA (structure)
DNA is an abbreviation for deoxyribonucleic acid. In DNA the sugar is deoxyribose, and the base is one of these four:
* adenine
* thymine
* guanine
* cytosine
What is RNA
RNA is an abbreviation for ribonucleic acid. In RNA, the sugar is ribose, and the base is one of these four:
* adenine
* uracil
* guanine
* cytosine
What is ATP Structure)
ATP is an abbreviation for adenosine triphosphate. In ATP, the sugar is ribose, the base is adenine and there are three phosphate groups
What nucleotides have ribose as a component
ATP
RNA
What is ATP
ATP is the ‘universal energy currency’. This means it provides energy to all reactions in all cells in all species.
ATP is important to organisms as this energy is released in a single hydrolysis reaction that is catalysed by ATPase. This energy is released in small useable quantities; 30.6kJ mol-1 is released as the terminal phosphate bond is broken forming ADP and Pi
How does ATP release energy
ATP can be hydrolysed to ADP and Pi, this reaction releases energy. The enzyme that catalyses this reaction is ATPase. 30.6 kJmol-1 energy is released when ATP is converted to ADP and Pi
How is ATP formed
- ATP is formed in an endergonic reaction
- ADP and phosphate (Pi) are combined to form ATP
- The energy to form the bond comes from exergonic (energy releasing reactions) in cellular respiration
- The reaction is a condensation reaction; water is eliminated when the bond is formed
- An enzyme that catalyses this reaction is ATP synthetase
What are the two main categories of base in nucleic acids
- Purines
- Pyridimines
Is a purine base a single ring or double ring
double ring
Is a pyridimine base a single ring or double ring
single ring
What are the purine bases
- Guanine
- Adenine
what are the pyridimine bases
- Thymine
- Cytosine
- Uracil
Out of A C G T bases, which complementary base pair
A T
C G
What are the two functions of DNA in cells
- As the base sequence codes for amino acid sequences in protein synthesis
- Replicating prior to cell division so that each daughter cell gets equal DNA
What is the structure of DNA and how do the two DNA strands run relative to eachother
DNA is a double helix
The two strands run antiparalell
What are the types of RNA
- Ribosomal RNA (rRNA)
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
What were Meselson and Stahl’s 3 possible mechanisms for DNA replication
- Conservative replication - the DNA molecule would be copied from the original, leaving the original DNA molecule as it was and having a new copy.
- Dispersive replication - sections of the DNA molecule would be copied and spliced together, making each new DNA molecule a mix of original and new DNA.
- Semi-conservative replication - the two polynucleotide chains would part, and new nucleotides attach to each of the chains, leading to each new molecule having one original chain and one new one.
How did Meselson and Stahl’s experiment work
Meselson and Stahl used E.coli bacteria as the source of DNA. E.coli are easily grown in a flask of culture medium and replicate their cells (and DNA) every 20 minutes under optimal conditions.
‘New’ and ‘original’ nucleotides were distinguished by the isotope of nitrogen (N) in the nitrogenous bases. 15N is heavier in mass than 14N, so DNA molecules containing bases with 15N and DNA molecules containing 14N can be separated by mass in centrifugation.
First, the scientists grew E.coli in a culture medium with only 15N isotopes until, after many generations, all of the bases contained 15N. When a sample was centrifuged, the band of DNA molecules was near the bottom of the tube, as shown in the diagram below. This is because 15N is heavier, so it settles at the bottom of the tube
A sample of the E.coli was then transferred to a new culture medium containing 14N (light) nucleotides and allowed to replicate once
Finally, a sample was withdrawn from the flask and centrifuged. The DNA was found at an intermediate position between 15N molecules and 14N molecules, as shown below
This first generation showed that replication was not conservative but that each new DNA molecule produced by replication consisted of half new (14N) nucleotides and half original (15N) nucleotides
What mechanism does DNA replicate from
Semi-Conservative
