Biology AS Chapter 2 - Nucleic Acids Flashcards
What are the three components of a nucleotide?
- A pentose sugar
- A phosphate group
- A nitrogen containing organic base
How is a nucleotide formed?
Through condensation reactions
What is the bond between 2 nucleotides called, and where does it form?
A phosphodiester bond and it forms through a condensation reaction between the deoxyribose sugar of one nucleotide and the phosphate group of another
What is RNA?
A polymer made up of nucleotides. It is a single, short chain in which the pentose sugar is always ribose and the organic bases are A,G,C and U
What must be complementary for bases to pair?
Size, shape and hydrogen bonding
Why is DNA a stable molecule?
- The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
- Hydrogen bonds link the organic base pairs forming bridges between the phosphodiester uprights, the more CG pairings, the more stable the molecule
How many hydrogen bonds are between C and G, and A and T?
- C and G –> 3
- A and T - -> 2
How is DNA adapted to carry out its function?
- Stable which normally passes from generation to generation without change
- Two separate strands joined by hydrogen bonds which allow them to separate during DNA replication
- Large so carries lots of genetic information
- The bases are in the helical cylinder of the backbone and so are protected from being corrupted by outside chemicals and forces
- Base pairing leads to DNA being able to replicate and transfer its information as mRNA
What are the two stages of cell division and what happens in them?
- Nuclear division - process by which the nucleus divides
- Cytokinesis - process by which whole cell divides
What are the 4 requirements for semi-conservative replication to occur?
- The four types of nucleotide must be present
- Both strands of the DNA molecule act as a template for the attachment of nucleotides
- The enzyme DNA polymerase
- A source of chemical energy to drive the process
How does the process of semi-conservative replication occur?
- The enzyme DNA helicase breaks the hydrogen bonds linking the base pairs of DNA
- As a result the double helix separates into its 2 strands and unwinds
- Each exposed polynucleotide stand then acts as a template to which complementary free nucleotides bind by specific base pairing
- Nucleotides are joined in a condensation reaction by the enzyme DNA polymerase (forms the phosphodiester bonds) to form the ‘missing’ polynucleotide strand on each of the two original strands of DNA
- Each of the new DNA molecules contains one of the original strands and one of the ‘new’ strands
What is the difference between the conservative and semi-conservative models?
Conservative suggested that the original DNA molecule remained intact and a separate daughter DNA molecule was built from new molecules of deoxyribose, phosphate and organic bases
Semi-conservative proposed the original strand split into two separate strands and each acted as a template
What is the structure of ATP?
Three parts:
- adenine
- ribose
- phosphates (chain of 3 phosphate groups)
What does ATP form when it reacts with water?
ADP, energy and an inorganic phosphate
What is the re-synthesis of ATP catalysed by?
ATP synthase
The synthesis of ATP from ADP involves the addition of a phosphate molecule to ADP. It occurs in 3 ways. What are these?
- in chlorophyll 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 (substrate level phosphorylation)
Why is ATP a better immediate energy source than glucose?
- Each ATP molecule releases less energy than each glucose molecule, meaning the energy is released in smaller, more manageable quantities
- The hydrolysis of ATP to ADP is a single reaction which releases immediate energy, rather than a long series of reactions
What are the 5 roles of ATP? Briefly explain each
- Metabolic processes - ATP provides the energy needed to build up macromolecules from their basic units
- Movement - ATP provides energy for muscle contraction
- Active transport - ATP provides energy to change the shape of carrier proteins in plasma membranes
- Secretion - ATP is needed to form the lysosomes needed for secretion of cell products
- Activation of molecules - inorganic phosphate can be used to phosphorylate other molecules to make them more reactive
Why is it good that water has a high specific heat capacity?
It takes lots of energy to heat a given mass of water and so it acts as a buffer against sudden temperature changes, making the aquatic environment temperature stable
What is the latent heat of vapourisation and why is this important?
Requires a lot of energy to evaporate 1 gram of water due to hydrogen bonding between water molecules. Evaporation of water, such as sweat, in mammals is a very effective means of cooling because body heat is used to evaporate water
Why is cohesion of water molecules important?
Hydrogen bonding causes large cohesive forces between water molecules which is useful when water needs to be pulled up through the xylem vessel. Also means water is pulled back to the body of water rather than escaping (surface tension)
How is water used in metabolsim?
- to break down complex molecules by hydrolysis
- chemical reactions occur in an aqueous medium
- water is a major raw material in photosynthesis
Why is water good when used as a solvent?
Readily dissolves other substances such as gases, wastes, inorganic ions and enzymes
Why is the fact that water is transparent useful?
Aquatic plants can photosynthesise as light can pass through the water, and light rays can penetrate the jelly like fluid that fills the eye and so reach the retina
