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Single -stranded polynucleotide, contains the pentose sugar ribose, contains purine bases: adenine and guanine and pyrimidine bases: uracil and cytosine.  Three types:

Messenger RNA, mRNA: long, single-stranded molecule. Synthesised in the nucleus and carries the genetic code from DNA to the ribosomes in nucleus. Different mRNA have different lengths based on the genes which they are synthesised.

Ribosomal RNA, rRNA: found in the cytoplasm and comprises large complex molecules. Ribosome are composed of rRNA and protein. Site of translation of the genetic code into protein.

Transfer RNA, tRNA: small single-stranded molecule. Folds so that in places, complementary base pairs can form. Shape: cloverleaf. The 3' end of the molecule has base sequence: cytosine-cytosine-adenine, where the specific amino acid the molecule carries is attached. Carries a sequence of three bases: anticodon. Molecules of tRNA transport specific amino acids to the ribosomes in protein synthesis.

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Composed of two polynucleotide strands wound around each other in a double helix. Pentose sugar: deoxyribose. DNA contains four organic bases, two purines: adenine & guanine and two pyrimidines: cytosine & thymine. deoxyribose sugar and phosphate groups: outside of DNA and form the backbone. Bases of two strands face each other: adenine is always opposite thymine and guanine is always opposite cytosine, AT and CG are 'complementary pairs.' Hydrogen bonds maintain the shape of het double helix and form between the bases. DNA molecule is very long & thin and is tightly coiled within the chromosome. Double helix: 2nm in diameter, DNA molecule is 85mm. Nucleotides in one strand are arranged in the opposite direction from those in the complementary strand. The strands are antiparallel.
Suited to its functions:

Base pairs are on the inside of the double helix, within the deoxyribose-phosphate backbones therefore the genetic information is protected.

Very stable & info. content passes essentially unchanged from generation to generation.

Very large molecule so carries a large amount of genetic information.

Two strands separate as they are held together by hydrogen bonds.

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Provides the necessary energy for cellular activity:

Metabolic processes: to build large molecules from smaller molecule i.e. nucleotides to DNA

Active transport: to change the shape of a carrier proteins in membranes and allow molecules or ions to moved agains a concentration gradient.

Movement: muscle contraction

Nerve transmission: sodium-potassium pumps actively transport sodium & potassium ions across the axon membrane.

Secretion: the packaging and transport of secretory products into vesicles in cells.

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When energy is needed, the enzyme ATPase hydrolyses the bond between the 2nd and 3rd phosphate, removing the 3rd phosphate and leaving 2. ATP is hydrolysed into ADP: Adenosine diphosphate and an inorganic ion. it also releases 30.6kJ of chemical energy. the reaction is exergonic.
ATP + H2O <=> ADP + inorganic phosphate (Pi) + ΔH= -30.6kJ Double arrows: reversible reaction. Every mole of ATP synthesised requires 30.6kJ and reaction is endergonic. The addition of phosphate to ADP is called phosphorylation. ATP transfers free energy from energy-rich compounds e.g. glucose. ATP as a supplier of energy:

Hydrolysis of ATP to ADP is a single reaction & releases energy immediately. The breakdown of glucose involves many intermediates and it takes longer for energy to be released.

ATP only needs 1 enzyme to be broken down, ATPase. Many enzymes are needed to breakdown glucose.

ATP releases energy in small amounts when its needed whereas glucose releases energy in large amounts at once.

ATP provides a common source of energy that can be used for many chemical reactions which increases the efficiency and control by the cell.

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ATP is the molecule that makes the energy available when it is needed. We make and break down about 50kg ATP everyday but the body only contains 5g of it therefore its not an energy store. It may be called the energy currency of the cell because it is involved in energy changes. ATP is synthesised when energy is made available e.g. in mitochondria. It is broken down when energy is needed e.g. muscle contraction.
Structure: ATP contains adenine, ribose and 3 phosphate groups.

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Chemical energy and biological processes

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Chemical energy and biological processes

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Chemical energy causes reactions to happen as chemical bonds must be made or broken.  Heterotrophic organisms (animals)  derive their chemical energy from food. Auto trophic organisms (green plants) derive chemical energy from light energy & convert it.

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Nucleic acids: polymers made of monomers called nucleotides. A molecule containing many nucleotides: polynucleotide. Nucleotide has 3 components which are combined by condensation reactions:

A phosphate group,same structure in all nucleotides

A pentose sugar: deoxyribose in DNA and ribose in RNA

An organic base: may be called a 'nitrogenous' base

Two groups of organic bases:
Pyrimidines: thymine, cytosine & uracil
Purines: adenine & guanine.