IAL Biology (Edexcel) Topic 2B - Proteins and DNA

catalyst

a substance that speeds up a reaction without changing the substances produced or being changed itself

enzymes

proteins that act as biological catalysts for a specific reaction or group of reactions

specificity

the characteristic of enzymes that means that each enzyme will catalyse only a specific reaction or group of reactions; this is due to the very specific shapes which come from the tertiary and quaternary structures

anabolic reaction

a reaction that builds up (synthesises) new molecules in a cell

catabolic reaction

a reaction which breaks down substances within a cell

metabolism

the sum of the anabolic and catabolic processes in a cell

metabolic chain (metabolic pathway)

a series of linked reactions in the metabolism of a cell

intracellular enzymes

enzymes that catalyse reactions within the cell

extracellular enzymes

enzymes that catalyse reactions outside of the cell in which they were made

activation energy

the energy needed for a chemical reaction to get started

substrate

the molecule or molecules on which an enzyme acts

lock-and-key hypothesis

a model that explains enzyme action by an active site in the protein structure that has a very specific shape; the enzyme and substrate slot together to form a complex in the same way as a key fits in a lock

active site

the area of an enzyme that has a specific shape into which the substrate(s) of a reaction fit

induced-fit hypothesis

a modified version of the lock and-key model of enzyme action where the active site is considered to have a more flexible shape; after the substrate enters the active site, the shape of that site changes around it to form the active complex; after the products have left the complex, the enzyme returns to its inactive, relaxed form

molecular activity (turnover number)

the number of substrate molecules transformed per minute by a single enzyme molecule

temperature coefficient (Q10)

the measure of the effect of temperature on the rate of a reaction

denaturation

the loss of the three-dimensional shape of a protein (e.g. caused by changes in temperature or pH)

initial rate of reaction

the measure taken to compare the rates of enzyme-controlled reactions under different conditions

mononucleotides

molecules with three parts - a 5-carbon pentose sugar, a nitrogen-containing base and a phosphate group - joined by condensation reactions

adenosine triphosphate (ATP)

a molecule that acts as the universal energy supply molecule in cells; it is made up of the base adenine, the pentose sugar ribose and three phosphate groups

deoxyribonucleic acid (DNA)

a nucleic acid that is the genetic material in many organisms

ribonucleic acid (RNA)

a nucleic acid which is the genetic material in some organisms and is involved in protein synthesis

ribose

a pentose sugar that is part of the structure of RNA

deoxyribose

a pentose sugar that is part of the structure of DNA

purine base

a base found in nucleotides that has two nitrogen-containing rings

pyrimidine base

a base found in nucleotides that has one nitrogen-containing ring

adenine

a purine base found in DNA and RNA

guanine

a purine base found in DNA and RNA

cytosine

a pyrimidine base found in DNA and RNA

thymine

a pyrimidine base found in DNA

uracil

a pyrimidine base found in RNA

nucleic acids

polynucleotides /polymers made up of many nucleotide monomer units that carry all the information needed to form new cells

phosphodiester bond

bond formed between the phosphate group of one nucleotide and the sugar of the next nucleotide in a condensation reaction

complementary base pairs

complementary purine and pyrimidine bases which align in a DNA helix, with hydrogen bonds holding them together (C-G, A-T)

genome

the entire genetic material of an organism

conservative replication

a model of DNA replication which suggests that the original double helix remains intact and in some way instructs the formation of a new, identical double helix made up entirely of new material

semiconservative replication

the accepted model of DNA replication in which the DNA 'unzips' and new nucleotides align along each strand; each new double helix contains one strand of the original DNA and one strand made up of new material

isotopes

different atoms of the same element, with the same number of protons but a different number of neutrons; isotopes have the same chemical properties

DNA helicase

an enzyme involved in DNA replication that 'unzips' the two strands of the DNA molecules

DNA polymerase

an enzyme involved in DNA replication that lines up the new nucleotides along the DNA template strands

DNA ligase

an enzyme involved in DNA replication that catalyses the formation of phosphodiester bonds between the nucleotides

translation

the process by which proteins are produced, via RNA, using the genetic code found in the DNA; it takes place on the ribosomes

ribosomes

the site of protein synthesis in the cell

triplet code

the code of three bases that is the basis of the genetic information in the DNA

gene

a sequence of bases on a DNA molecule; it contains coding for a sequence of amino acids in a polypeptide chain that affects a characteristic in the phenotype of the organism

codon

a sequence of three bases in DNA or mRNA

messenger RNA (mRNA)

the RNA formed in the nucleus that carries the genetic code out into the cytoplasm

complementary strand

the strand of RNA formed that complements the DNA acting as the coding strand

non-overlapping code

a code where each codon codes for only one thing with no overlap between codons

degenerate code

a code containing more information than is needed

point mutation

a change in a single base of the DNA code

sense strand

the DNA strand that carries the code for the protein to be produced

antisense strand (template strand)

the DNA strand which acts as a template for an mRNA molecule

start codon

the sequence of bases which indicates the start of an amino acid chain - TAC; this is the code for the amino acid methionine

RNA polymerase

the enzyme that polymerises nucleotide units to form RNA in a sequence determined by the antisense strand of DNA

stop codon

one of three sequences of bases which indicate the end of an amino acid chain

transfer RNA (tRNA)

small units of RNA that pick up specific amino acids from the cytoplasm and transport them to the surface of the ribosome to align with the mRNA

anticodon

a sequence of three bases on tRNA that are complementary to the bases in the mRNA codon

translation

the process by which the DNA code is converted into a protein from the mRNA strand made in the nucleus

transcription

the process by which the DNA sequence is used to make a strand of mRNA in the nucleus

polysomes

groups of ribosomes, joined by a thread of mRNA, that can produce large quantities of a particular protein