OCR A Level Biology - Biological molecules

adenosine diphosphate (ADP)

a nucleotide composed of a nitrogenous base (adenine), a pentose sugar and two phosphate groups. Formed by the hydrolysis of ATP, releasing a phosphate ion and energy.

adenosine triphosphate (ATP)

a nucleotide composed of a nitrogenous base (adenine), a pentose sugar and three phosphate groups. The universal energy currency for cells.

amino acids

monomer used to build polypeptides and thus proteins.

anabolism (anabolic)

reactions of metabolism that construct molecules from smaller units. These reactions require energy from the hydrolysis of ATP.

antisense strand

the strand of DNA that runs 3' to 5' and is complementary to the sense strand. It acts as a template strand during transcription.

Benedict's reagent

an alkaline solution of copper(II)sulfate used in the chemical tests for reducing sugars and non-reducing sugars. A brick-red precipitate indicates a positive result.

beta pleated sheet

sheet-like secondary structure of proteins.

biuret test

the chemical test for proteins; peptide bonds form violet coloured complexes with copper ions in alkaline solutions.

carbohydrates

organic polymers composed of the elements carbon, hydrogen and oxygen in the ratio Cx(H2O)y. Also known as saccharides or sugars.

catabolism (catabolic)

reactions of metabolism that break molecules down into smaller units. These reactions release energy.

cellulose

a polysacchardie formed from beta glucose molecules where alternate beta glucose molecules are turned upside down. It is unable to coil or form branches but makes hydrogen bonds with other cellulose molecules to produce strong and insoluble fibres. Major component of plant cell walls.

codon

a three-base sequence of DNA or RNA that codes for an amino acid.

complementary base pairing

specific hydrogen bonding between nucleic acid bases. Adenine (A) binds to thymine (T) or uracil (U) and cytosine (C) binds to guanine (G).

condensation reaction

a reaction between two molecules resulting in the formation of a larger molecule and the release of a water molecule. The opposite reaction to a hydrolysis reaction.

denatured (denaturation)

change in tertiary structure of a protein or enzyme, resulting in loss of normal function.

deoxyribonucleic acid (DNA)

the molecule responsible for the storage of genetic information.

disaccharide

a molecule comprising two monosaccharides, joined together by a glycosidic bond.

DNA helicase

enzyme that catalyses the unwinding and separating of strands in DNA replication.

DNA polymerase

enzyme that catalyses the formation of phosphodiester bonds between adjacent nucleotides in DNA replication.

DNA replication

the semi-conservative process of the production of identical copies of DNA molecules.

emulsion test

laboratory test for lipids using ethanol; a white emulsion indicates the presence of a lipid.

fatty acids

long chain carboxylic acids used in the formation of triglycerides.

fibrous proteins

long, insoluble, structural proteins.

gene

a section of DNA that contains the complete sequence of bases (codons) to code for a protein.

genetic code

the sequences of bases in DNA are the 'instructions' for the sequences of amino acids in the production of proteins.

globular proteins

spherical, water-soluble proteins.

glucose

a monosaccharide with the chemical formula C6H12O6. One of the main products of photosynthesis in plants.

glycerol

alcohol found in triglycerides.

glycogen

a branched polysaccharide formed from alpha glucose molecules. A chemical energy store in animal cells.

glycosidic bond

a covalent bond between two monosaccharides.

hexose monosaccharide

a monosaccharide composed of six carbons.

hydrolysis reaction

the breakdown of a molecule into two smaller molecules requiring the addition of a water molecule. The opposite reaction to a condensation reaction.

hydrophilic

the physical property of a molecule that is attracted to water.

hydrophobic

the physical property of a molecule that is repelled by water.

insulin

a globular protein hormone involved in the regulation of blood glucose concentration.

iodine test

a chemical test for the presence of starch using a potassium iodide solution. A colour change to purple/black indicates a positive result.

ion

an atom or molecule with an overall electric charge because the total number of electrons is not equal to the total number of protons. See anion and cation.

ionic bond

a chemical bond that involves the donating of an electron from one atom to another, forming positive and negative ions held together by the attraction of the opposite charges.

lactose

a disaccharide made up of a galactose and glucose monosaccharide.

lipids

non-polar macromolecules containing the elements carbon, hydrogen and oxygen. Commonly known as fats (solid at room temperature) and oils (liquid at room temperature).

macromolecules

large complex molecules with a large molecular weight.

maltose

two glucose molecules linked by a 1, 4 glycosidic bond.

messenger (m)RNA

short strand of RNA produced by transcription from the DNA template strand. It has a base sequence complementary to the DNA from which it is transcribed, except it has uracil (U) in place of thymine (T).

monomers

individual molecules that make up a polymer.

monosaccharide

a single sugar molecule. mRNA see messenger (m)RNA.

nucleic acids

large polymers formed from nucleotides. Contain the elements carbon, hydrogen, nitrogen , phosphorus, and oxygen.

nucleotides

the monomers used to form nucleic acids. Made up of a pentose monosaccharide, a phosphate group and a nitrogenous base.

pentose monosaccharide

a monosaccharide composed of five carbons.

peptide bond

bond formed between two amino acids.

peptides

chains of two or more amino acid molecules.

phosphodiester bonds

covalent bonds formed between the phosphate group of one nucleotide and the hydroxyl (OH) group of another.

phospholipids

modified triglycerides, where one fatty acid has been replaced with a phosphate group.

polymers

long-chain molecules composed of linked (bonded) multiple individual molecules (monomers) in a repeating pattern.

polypeptide

chains of three or more amino acids.

polysaccharide

a polymer made up of many sugar monomers (monosaccharides).

prosthetic group

non-protein component of a conjugated protein.

proteins

one or more polypeptides arranged as a complex macromolecule.

purines

double-ringed, nitrogenous bases that form part of a nucleotide.

pyrimidines

single-ringed, nitrogenous bases that form part of a nucleotide.

quaternary structure

the association of two or more protein subunits.

R-groups

variable groups on amino acids.

reducing sugars

saccharides (sugars) that donate electrons resulting in the reduction (gain of electrons) of another molecule.

ribonucleic acid (RNA)

molecules involved in the copying and transfer of genetic information from DNA. Polynucleotides consisting of a ribose sugar and one of four bases; uracil (U), cytosine (C), adenine (A), and guanine (G).

ribose

the pentose monosaccharide present in RNA molecules.

ribosomal (r)RNA

form of RNA that makes up the ribosome.

RNA polymerase

enzyme that catalyses the formation of phosphodiester bonds between adjacent RNA nucleotides.

semi-conservative replication

DNA replication results in one old strand and one new strand present in each daughter DNA molecule.

sense strand

the strand of DNA that runs 5' to 3' and contains the genetic code for a protein.

starch

a polysaccharide formed from alpha glucose molecules either joined to form amylose or amylopectin.

sucrose

a disaccharide made up of a fructose and glucose monosaccharides.

template strand

the antisense strand of DNA that acts as template during transcription so that the complementary RNA strand formed carries the same code for a protein as the DNA sense strand.

tertiary structure

further folding of the secondary structure of proteins involving interactions between R-groups.

transcription

the process of copying sections of DNA base sequence to produce smaller molecules of mRNA, which can be transported out of the nucleus via the nuclear pores to the site of protein synthesis.

transfer (t)RNA

form of RNA that carries an amino acid specific to its anticodon to the correct position along mRNA during translation.

translation

the process by which the complementary code carried by mRNA is decoded by tRNA into a sequence of amino acids. This occurs at a ribosome.

triglyceride

a lipid composed of one glycerol molecule and three fatty acids.

triplet code

the genetic code is a sequence of three nucleic acid bases, called a codon. Each codon codes for one amino acid.