Proteins?

Protein structureWALT: To understand the composition and various structures of proteins.

WILF: ~ Identify the basic structures of proteins. ~ Describe how proteins are formed from amino acids.~ Describe the differences between the primary, secondary, tertiary and quaternary structures of proteins.

Keywords

Peptide bondCondensation reactionPolypeptide Hydrogen bondsDisulphide bondsIonic bonds

Thursday 13 April 2023

TranscriptionWhat? The weak hydrogen bonds between the DNA strands are broken and the strands separate.One DNA strand is used as a template.Complementary bases pair up to the template, forming messenger RNA (mRNA).mRNA does not have the base thymine (T). Adenine (A) pairs with uracil (U) instead.

Where? Inside the nucleus.

mRNA

Translation Where? In the cytoplasm.

ribosome

mRNA

The mRNA is decoded in groups of 3 (triplet or codon)

tRNA Protein (polypeptide)

amino acids

Polymer: Protein or polypeptide

Monomer: Amino acid

All Amino Acids have an alkaline amino group (-NH2) and an acid carboxyl group (-COOH).

There are just 20 naturally occurring Amino Acids, each with a different -R group.

Amino acids

The 20 naturally occurring amino acids.

Condensation reaction

Molecule of water

removed

Peptide bond formed dipeptide

Primary StructureThe sequence of amino acids in the polypeptide chain.

This structure determines shape and function of the protein.

Genetic mutations.

Primary Structure

Secondary StructureWeak hydrogen bonds form between the polypeptide chains.

Chain folds, 3d shape

Alpha helix

Beta pleated sheet

Secondary Structure

The Alpha helix

The Beta pleated sheet

------------ weak hydrogen bonds _________ strong covalent bonds

Tertiary StructureFurther twisting and folding of secondary structures.

Unique 3d structure.

Disulphide bonds

Ionic bonds

Hydrogen bonds

Tertiary Structure

Quaternary StructureFurther complexity.

Pairs of chains may bind together or other inorganic substances may be incorporated into the molecule. (Prosthetic Groups)

e.g. haemoglobin

Quaternary Structure

Primary structure

Secondary structure

Tertiary structure

Quaternary structure

Task 1: Fold A3 paper into four and assign a title for each. Cut out and stick the relevant statements and diagrams for each structure in the correct box.

Task 2: Add further detail to each box by answering the questions.

Primary structure: 1. Explain how amino acids are joined together to form the primary structure. 2. Explain how one single change in the amino acid chain can affect the protein from carrying out it’s function. Secondary structure: 3. Explain how the weak hydrogen bonds are formed in the secondary structure of proteins. Tertiary structure:4. Name and describe the different bonds that can form in the formation of a tertiary structure. 5. Explain how the 3D shape of a protein is important to its function. Quaternary structure:6. Explain what a prosthetic group is and name an example.

Prosthetic Groups

Further complexity.

Further twisting and folding of secondary structures.

Unique 3d structure.

Weak hydrogen bonds form between the polypeptide chains.

Alpha helix

Beta pleated sheet

The sequence of amino acids in the polypeptide chain.

Test for proteinsThe Biuret test.1.Place a sample in solution in a test

tube.2.Add an equal volume of sodium

hydroxide.3.Add a few drops of dilute copper

sulphate solution and gently mix.4.Positive purple or negative blue.