Nucleic acids

What are the three components of a nucleotide?

• pentose sugar (5 carbons)

• phosphate group

• nitrogen containing organic base (A, T, C, G, U)

What reaction are these joined by?

Condensation reaction

What are the names of the bases?

A = adenine

C = cytosine

T = thymine

G = guanine

U = uracil

What bond are two mononucleotides joined by?

phosphodiester - forms dinucleotide

RNA structure (ribonucleic acid)

• single, short chain

• ribose sugar

• bases are A, G, C, U

• three types of RNA

Structure of DNA

• deoxyribose sugar

• bases are A, T, G, C

• two strands of nucleotides

• long strands

• joined by H bonds

• bases paired

Base pairing

• A—T

• C—G

• complementory bases

Stability of DNA

• phosphodiester backbone - protects chemically reactive organic bases inside double helix

• hydrogen bonds - link organic bases

• 3 H bonds between C & G - more C—G = more stable DNA molecule

Function and adaptation of DNA

• passes on genetic information from cell to cell and generation to generation

• stable structure - persistent mutation rare

• strands joined with hydrogen bonds so can separate during DNA replication/protein synthesis

• large = carries lots of info

• info protected

• base pairing leads to DNA being able to replicate and translate info as mRNA

What are the two stages of cell division?

• nuclear division - mitosis and meiosis

• cytokinesis - the process by which the whole cell divides

Process of semi-conservative replication

1. DNA helicase breaks hydrogen bonds linking base pairs of DNA

2. double helix separates & unwinds

3. each exposed polynucleotide strand acts as a template - complementary free nucleotides bind by specific base pairing

4. nucleotides joined in condensation reactions by DNA polymerase

5. each of the new DNA molecules contains one of the og DNA strands - ‘semi conservative’

Structure of ATP

• adenine - nitrogen containing organic base

• ribose - sugar with 5 carbon ring structure (backbone)

• phosphates - chain of three phosphate groups

Synthesis of ATP

• ATP —> ADP + Pi (reversible reaction)

• ADP + Pi —> ATP = catalysed by ATP synthase

• condensation reaction

Why is ATP a better immediate energy store than glucose?

• ATP molecules release less energy than glucose molecules

  • energy released in smaller, more manageable quanitites

• hydrolysis of ATP to ADP is a single reaction that releases energy whereas breakdown of glucose is a long series of reactions and therefore takes longer

What processes is ATP used in?

• metabolic processes - build macromolecules from their basic units e.g. starch from glucose

• movement - energy for muscle contraction

• active transport - provides energy to change shape of carrier proteins

• secretion - ATP needed to form lysosomes necessary for secretion of cell products

• activation of molecules

Water and hydrogen bonding

• hydrogen bonds between molecules - sticks molecules together

Properties of water

• is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions

• is an important solvent in which metabolic reactions occur

• has a relatively high heat capacity, buffering changes in temperature

• has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation

• 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.

Inorganic ions

• found in organisms where they occur in solution in the cytoplasm of cells and in body fluids as well as part of larger molecules

• may be in concentrations that range from very high to very low

Roles of inorganic ions

• iron ions - in haemoglobin - play role in transport of oxygen

• phosphate ions - structural component in DNA

• hydrogen ions - important in determining the pH of solutions

• sodium ions - important in co-transport of glucose and amino acids