L4 - Amino Acids and Proteins

What are essential amino acids

• obtained from food sources

• cant be made by body

• e.g. Leucine + Isoleucine

What are non-essential Amino Acids?

• Made by the body

• not obtained from food source

• e.g. alanine + aspartate

The general structure of a protein

Where do plants amino acids from?

From nitrates in the soil which is converted

Amino acids are joined together using what reaction

Condensation reactions, bonded with peptide bonds and releases water

What are polypeptides?

Proteins consisting on one or more polypeptide chains folded into a very specific 3D shape.

What are the 4 types of structure in Proteins?

Primary, Secondary, Tertiary and Quaternary

What is the primary structure in proteins?

The order of amino acids according to bonds

• amino acids held together by peptide bonds

What is the secondary structure in proteins?

It is the coiling/folding of the amino acid chain.

• it is due to the hydrogen bonded between amino acids.

• Forms either:

  • Alpha Helix

  • Beta Pleated Sheet

What determines if the Amino acid chain is alpha helix?

Coiled structure

• Intra-chain hydrogen bonds within the same chain

What determines if the Amino acid chain is Beta Pleated Sheet?

Pleated/folded structure.

• hydrogen bonds form between different sections of the chain (or different chains), forming sheet-like layers.

What is the Tertiary structure of a protein?

The overall 3D shape of a single polypeptide chain.

• formed by further folding of secondary structure

What kind of different bonds occur in Tertiary Structure of proteins?

Stabilised by interactions between R Groups:

• Disulphide bonding

• Ionic Bonding

• Hydrogen Bonding

• Hydrophobic and Hydrophilic

Explain Disulphide bonds in Tertiarty Structure

Cysteine contains sulphur

• if two cysteine are close together, a strong covalent bond forms

Explain Ionic Bonds in Tertiarty Structure

Positive and negative part of R groups can form ionic bonds.

Explain Hydrogen Bonds in Tertiarty Structure

Hydrogen bonds can form between polar parts of the R group.

Explain Hydrophobic and Hydrophilic interactions in Tertiarty Structure

Some parts of R-group are hydrophobic, some are hydrophilic

• In water based environment, hydrophobic areas will cluster together.

What is the Quaternary Structure?

The quaternary structure is the association of two or more polypeptide chains into a functional protein.

What holds the quaternary structure together

Interactions between R groups, including hydrogen bonds, ionic bonds, disulfide bonds, and hydrophobic interactions.

Do all proteins have a quaternary structure?

No, only proteins made of more than one polypeptide chain have quaternary structure.

Give an example of a protein with quaternary structure

Haemoglobin, which has four polypeptide chains (haem groups)

What are the 2 Types of Proteins?

• Globular - Insulin, Catalase, Haemoglobin

• Fibrous - Collagen, Keratin

Properties of Globular Proteins?

Spherical shape - tightlty folded polypeptide chains.

3 Types:

• transport proteins (haemoglobin)

• enzymes (catase)

• Hormones (insulin)

Properties of Insulin

Globular Protein

• Hormone secreted by pancreas

• Quaternary structure - two polypeptide chains

  • Insulin soluble - hormone that travels in blood plasma

Properties of Haemoglobin

Globular protein

• Four polypeptide chains

• Each chain wrapped around atoms called haem groups (type of prosthetic group)

  • Prosthetic group - parts of proteins not made up of amino acids

  • Holds Fe²⁺ ion in the centre

• Each ion is able to bond with 1 oxygen molecule

4 Haem groups x O₂ = 8 Oxygen Atoms per Hb

What are proteins that have Prosthetic groups called?

Conjugated proteins (e.g. haemoglobin)

Properties of Catalase?

Globular protein

• Common enzyme in nearly all living organisms

• Catalyses decomposition of hydrogen peroxide → water + oxygen

Contains 4 polypeptide chains and 4 haem prosthetic groups

Properties of Fibrous proteins?

Formed from parallel polypeptide chains held by cross links

• Generally insoluble in water.

Examples:

• Elastin, Silk, Collagen and Keratin.

Properties of Keratin?

Fibrous protein

• Group of Fibrous proteins found in hair, skin and nails

• The degree of sulphide bonds determines flexibility.

  • Hair would have more sulphide bonds than nails

Properties of Collagen?

Fibrous protein

• Found in connective tissues (e.g. skin, muscles, tendons)

• Consists of 3 helical polypeptide chains that twist around eachother.

  • 1 in every 3 Amino acids is Glycine to allow the chains to pack closely together.

• Huge tensile strength - can withstand pulling pressure.

Glycine (amino acid type) forms a high proportion of the collagen molecule.