Nucleic Acids Flashcards
Differences between RNA and DNA
DNA: - Double stranded - Deoxyribonucleic acid - Thymine, Adenine, Cytosine and Guanine - Base pairs RNA: - Single stranded - Ribonucleic acid - Adenine, Uracil, Cytosine and Guanine
Nucleotide
Is made up of 3 components:
- deoxyribose sugar
- phosphate group
- nitrogenous base e.g cytosine, guanine, adenine, uracil and thymine
How nucleotides are formed
The deoxyribose sugar, phosphate group and organic base are joined as a result of condensation reactions to form a nucleotide
- Two nucleotides may be joined by a condensation reaction between the deoxyribose of one nucleotide and the phosphate of another. The bond formed between is called a phosphodiester bond
The new structure is called a dinucleotide.
> The continued linking of nucleotides is known as a polynucleotide
Double helix
the two polynucleotide chains being twisted. In this way, the uprights of phosphate and deoxyribose wind around one another to form a double helix. They form the back bone
DNA is a stable molecule:
- The phosphodiester bacbone protects the chemically reactive organic bases inside the double helix
- Hydrogen bonds link the organic base pairs forming bridges between the phosphodiester uprights. As there are 3 hydrogen bonds between cytosine and guanine, the higher the proportion of C-G, the more stable to DNA molecule
Function of DNA
- its two separate strands are joined only by hydrogen bonds, which allow them to separate during DNA replication and protein synthesis
- It’s an extremely large molecule and therefore carries an immense amount of genetic information
- By having base pairs within the helical cylinder of the deoxyribose-phosphate backbone, the genetic info is protected
- Base pairing leads to DNA being able to replicate and transfer info as mRNA
3’ and 5’ carbon atoms
The 5’ carbon has an attached phosphate group, while the 3’ has a hydroxyl group.
One strand runs in the 5’ to 3’ direction while the other runs the opposite way in the 3’ to 5’ direction. the two stands are antiparallel.
Nucleic acids can only be synthesised in the 5’ to 3’ direction. This is because DNA Polymerase that assembles nucleotides into DNA molecule can only attach nucleotides to the hydroxyl group on the 3’ carbon molecule
Cell division occurs in two main stages:
- Nuclear Division: is the process by which the nucleus divides. The are two types of nuclear division: mitosis and meiosis
- Cytokinesis: follows nuclear division and is the process by which the whole cell divides
Semi Conservative Replication requirements:
- 4 types of nucleotide each with their bases of adenine, guanine, cytosine or thymine
- Both strands of the DNA molecule act as a template for the attachment of these nucleotides
- The enzyme DNA polymerase
- source of chemical energy to drive the process
Process of semi-conservative replication
- The enzyme DNA helicase breaks the hydrogen bonds linking base pairs of DNA
- As a result, the double helix separates into two strands
- Each exposed nucleotide strand then acts as a template to which complementary free nucleotides bind by specific base pairing
- Nucleotides are joined together in a condensation reaction by the enzyme DNA polymerase to form the missing polynucleotide strand
- Each of the new DNA molecules contains on the of original DNA strands that is, half the original DNA has been saved and built into each of the new DNA molecules
Structure of ATP
- Adenine: a nitrogen containing base
- Ribose: a sugar molecule with a 5 carbon ring structure that acts as a backbone
- phosphates: a chain of 3 phosphates group
How ATP stores energy
- ATP has 3 phosphate groups
- The bonds between these phosphate groups are unstable and so have a low activation energy, which means they are easily broken
- ATP + H20 –> ADP + Pi + E
- As water is used to convert ATP to ADP, this is known as a hydrolysis reaction. This reaction is catalysed by the enzyme ATP hydrolase
Synthesis of ATP
This reaction is catalysed by the enzyme ATP synthase. As water is removed in this process, the reaction is known as a condensation reaction.
The synthesis of ATP from ADP involves the addition of phosphate molecule to ADP. It occurs in three ways:
- in chloropyll containing plant cells during photosynthesis (photophosphorylation)
- in plant and animal cells during respiration (oxidative phosphorylation)
- In plant and animal cells when phosphate groups are transferred from donor molecules to ADP
Roles of ATP
ATP is a better immediate energy source than glucose because:
- Each ATP molecule releases less energy than each glucose molecule but the energy for reactions is released in smaller quantities rather than greater quantities
- The hydrolysis of ATP to ADP is a single reaction that releases immediate energy s
ATP is used in energy- requiring processes in cells including:
- metabolic processes: ATP provides the energy needed to build up macromolecules e.g making starch from glucose or polypeptides
- movement: ATP provides the energy for muscle contraction. In muscle contraction , ATP provides the energy for the filaments of muscle to slide past one another
- Active transport: ATP provides the energy to change the shape of carrier proteins in plasma membranes. This allows molecules or ions to be moved against a concentration gradient
- Secretion: ATP is needed to form the lysosomes necessary for the secretion of cell products
- Activation of molecules: The inorganic phosphate released during the hydrolysis of ATP can be used to make other compounds more reactive
