proteins main

Amino acid

The monomer of a protein formed from C,H,O,N

contains a carboxyl group, amine group, an H, a central carbon and an R group

Polypeptide

Polymer chain of a protein made up of amino acids bonded together by peptide bonds via condensation reactions

Peptide bond

Covalent bond joining amino acids together in proteins C–N link between an amine and carboxyl group of two different amino acid molecules formed by a condensation reaction

Primary structure

The sequence of amino acids on a polypeptide chain peptide bonds between amino acids

Secondary structure

The folding or coiling of polypeptide to create a β pleated sheet or an α helix held in place by hydrogen bonds

Tertiary structure

The further folding to create a unique 3D shape held in place by hydrogen, ionic and sometimes disulfide bonds

Quaternary structure

More than one polypeptide chain in a protein

α helix

A secondary structure in proteins the polypeptide chain coiled up and held in place by hydrogen bonds

β pleated sheet

A secondary structure in proteins the polypeptide chain folded into pleated sheets held in place by hydrogen bonds

Hydrogen bonds

Weak bond forms between H and O in many biological molecules e.g. proteins, DNA, tRNA

Ionic bonds

A bond that forms between the R groups of different amino acids in the tertiary structure of proteins

Disulfide bonds

A strong covalent bond between two sulfur atoms in the R groups of different amino acids in the tertiary structure of proteins

Amine group

NH2 group found on amino acids

Carboxyl group

COOH group made up of a C with hydroxyl (OH) and carbonyl (double-bonded O) group bonded to it found in amino acids and fatty acids

R group on amino acids

The variable group the part of each of the 20 amino acids that is different

Active site

Unique-shaped part of an enzyme that the substrate binds to

Enzyme-substrate complex

forms when an enzyme and substrate collide and bind resulting in a lowered activation energy

Activation energy

The minimum amount of energy required for a reaction to occur

Denature

when the active site changes shape so the substrate can no longer bind and no enzyme-substrate complexes form

Competitive inhibitor

A molecule that is a similar shape to the substrate binds to the active site prevents enzyme-substrate complexes from forming forms enzyme-inhibitor complex

Non-competitive inhibitor

A molecule that binds to an enzyme at the allosteric site causing the active site to change shape preventing enzyme-substrate complexes from forming forms enzyme-inhibitor complex

Induced-fit model

The enzyme active site is not initially complementary to the substrate the active site moulds around the substrate this puts tension on bonds lowers the activation energy

Effect of temperature on enzyme-controlled reaction

At low temperatures, there is not enough kinetic energy for successful collisions between the enzyme and substrate. At too high a temperature, enzymes denature, the active site changes shape and enzyme-substrate complexes cannot form.

Effect of pH on enzyme-controlled reaction

Too high or too low a pH will interfere with the charges in the amino acids in the active site. This breaks the ionic and hydrogen bonds holding the tertiary structure in place therefore the active site changes shape and the enzyme denatures Different enzymes have a different optimal pH

Effect of substrate concentration on enzyme-controlled reaction

At low substrate concentrations, there will be fewer collisions between the enzyme and substrate. At high substrate concentrations, the rate plateaus because all the enzyme active sites are saturated

Effect of enzyme concentration on enzyme-controlled reaction

At low enzyme concentrations, there will be fewer collisions between the enzyme and substrate. At high enzyme concentrations, the rate plateaus because there are more enzymes than the substrate, so there are empty active sites.

Nucleotide

The monomer of DNA and RNA contains a pentose sugar, a phosphate group and a nitrogenous base

DNA nucleotide

The monomer of DNA contains a deoxyribose sugar, a phosphate group and a nitrogenous base

RNA nucleotide

monomer of RNA composed of a phosphate group, ribose and a nitrogenous base has the base uracil instead of thymine

Nitrogenous base

Part of a nucleotide adenine, guanine, cytosine, thymine and uracil

Polynucleotide

DNA polymer many nucleotides joined together via a condensation reaction joined by phosphodiester bonds

Phosphodiester bond

Bond joining two adjacent nucleotides together formed via condensation reaction forms between a phosphate group and the pentose sugar

Complementary base pairs

The base pairs that align opposite each other and form hydrogen bonds adenine and thymine (in DNA) / uracil (in RNA) guanine and cytosine

Ribose

pentose sugar found in RNA nucleotide and ATP

Uracil

Nitrogenous base found in RNA instead of thymine

Role of DNA and RNA in cells

DNA holds genetic information in all living cells RNA transfers genetic information from DNA to the ribosomes for protein synthesis

Ribosomes formed from

RNA proteins

Structure of DNA

nucleotide monomer DNA is a polymer double helix made of two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs

DNA template strand

A DNA strand that is used to make a new DNA copy from both DNA strands in the double helix are used as templates in DNA replication

Semi-conservative replication

DNA replication is semi-conservative replication each new DNA molecule contains one original (parental) strand and one newly synthesised strand

DNA helicase

Enzyme that breaks hydrogen bonds between the two chains of DNA in a double helix causes the two strands to separate involved in DNA replication

DNA polymerase

An enzyme in DNA replication joins together adjacent nucleotides

Describe DNA replication

DNA helicase in unwinds DNA double helix and breaks its hydrogen bonds new DNA nucleotides attracted to complementary base pairs on exposed template strand. DNA polymerase joins adjacent nucleotides.

Structure of RNA

relatively short single polynucleotide chain It contains the base uracil instead of thymine and the sugar ribose instead of deoxyribose