Nucleic acids Flashcards
Name the four nitrogenous bases in DNA
- adenine
- thymine
- cytosine
- guanine
Name the four nitrogenous bases in RNA
- adenine
- cytosine
- uracil
- guanine
List 3 properties of DNA and explain how they are related to its function
- DNA is very stable so it passes from generation to generation without changing (only rarely does it mutate)
- The two polynucleotide strands are linked only by hydrogen bonds which means that it is easy for the strands to seperate during DNA replication and protein synthesis
- DNA is a huge molecule so can store vast amounts of information
How many hydrogen bonds form between base pairs?
A-T: two
C-G: three
What type of protein is found in chromosomes?
Histone
What molecules are DNA and RNA made up from?
- phosphate group
- nitrogenous bases
- pentose sugar (deoxyribose in DNA and ribose in RNA)
What are the monomers of DNA and RNA called?
Nucleotides
How many chromosomes are usually found in a human cell?
46
Why is there variability in the stability of different sections of DNA?
- The base pairings account for this as there are 3 hydrogen bonds between cytosine and guanine but only 2 between adenine and thymine
- So the higher the proportion of of C-G pairings, the more stable the DNA molecule
How are the two polynucleotide chains that make up a DNA molecule held together?
Hydrogen bonds between the complementary bases of the nucleotides
What bond is formed between nucleotides?
Phosphodiester bonds
What conditions need to be met in order for DNA replication to occur?
- The enzymes, DNA helicase and DNA polymerase must be present
- ATP is required to drive the process
- A ‘pool’ of the four nucleotides (free nucleotides)
- Both strands of DNA need to be present so they can be copied
What are the two main stages of cell division?
- Nuclear division (mitosis and meiosis)
- Cell division
Explain why DNA replication is described as semi-conservative
Because the two daughter DNA molecules formed are genetically identical to the parent DNA molecule and each daughter DNA molecule contains one old and one new polynucleotide strand
Explain the process of DNA replication
- DNA helicase unwinds the parent DNA molecule and breaks the hydrogen bonds between the complementary base pairs, exposing the nitrogenous bases on the two polynucleotide strands
- Hydrolysis of ATP activates the free nucleotides that are free and abundant in the nucleus
- The activated nucleotides attach themselves to the bases on the parent polynucleotide strands by complementary base pairing, forming hydrogen bonds
- DNA polymerase catalyses the condensation reaction that joins adjacent nucleotides, forming the sugar-phosphate backbone
What is an ATP molecule made up of?
- three phosphates
- ribose sugar
- adenine
List 3 of the main biological functions of ATP
- Metabolic processes such as the building of macromolecules (e.g. starch and polypeptides)
- Active transport. The ATP changes the shape of carrier proteins which allows the movement of molecules against their concentration gradient
- Movement, muscles need ATP so they have energy to contract
Explain why ATP is an immediate source of energy
- ATP releases its energy very rapidly
- The energy is released in a single step and is transferred directly to the reaction requiring it
- The energy containing phosphate bond is easily broken down to release the energy it holds
- ATP is too unstable to be a long term energy store
Explain how surface tension in water occurs
- Where water molecules meet air, they tend to be pulled back into the body of water rather than escaping it (this force is surface tension)
- Means that water surface acts like a skin and is strong enough to support small organisms
Give 5 reasons water is important to living organisms
- Has a relatively high specific heat capacity and so acts as a buffer against sudden temperature variations which makes the aquatic environment a temperature stable one
- Is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions
- Is an important solvent in which metabolic reactions occur
- Has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation
- Has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air
