Bio- 2.9,2.10 Protein and Enzymes

A level- Keeley

What is a protein?

A polymer made up of amino acids linked together by peptide chains.

Describe the components of an amino acid. (5)

A carbon with

1. An amino group (NH₂)

2. A carboxylic group (COOH)

3. A functional group (R)

4. A hydrogen

What reaction forms a polypeptide chain? (2)

Condensation reaction, where amino acid monomers linked by peptide chains in condensation reaction with the waste product being water.

Describe what happens when two amino acids link together. (3)

• The end of an amine group and a carboxylic acid join together with peptide chain

• Water forms as a waste product with one of the hydrogen from (NH₂) and an OH group coming from the carboxylic acid.

Name the four levels of the structures of protein.

1. Primary

2. Secondary

3. Tertiary

4. Quaternary

Define primary protein structure.

A sequence of amino acid in a polypeptide chain held by peptide bonds.

Define secondary protein structure.

The regualr folding patterns of the polypeptide backbone held by hydrogen bonds.

Describe the two types of shapes of a secondary protein structure. (draw out) (4)

1. Alpha helix- where every backbone of N-H group donates a hydrogen bond to the C=O group within every four intervals

2. Beta - pleated sheet- chains of amino acids are anti-parallel, hydrogen bonds with hydrogen bonds forming between N-H and C=O group in adjacent polypeptide strands

Describe tertiary protein structure (name 4 R groups). (5)

A 3D shape of a single polypeptide chain held by various types of bonds between R groups.

R Groups involved- Disulfide, Ionic, hydrogen and hydrophobic interactions

Describe the four bonds involved in tertiary protein structure and how they could be denatured. (3 for each)

1. Disulfide bonds- bonds between cysteine- denatured by reducing agents

2. Ionic bonds- between positive (NH3⁺) and negative (CH₂COO^-), denatured by pH

3. Hydrogen bonds- between polarised oxygen and hydrogen molecules, denatured by temperature or pH

4. hydrophobic interactions- between uncharged/ non polar R groups in amino acids which repel water and found in the interier part of the protein- denatured by alcohol

Describe quaternary protein structure and name 3 examples.

The combination of more than one polypeptide chain into one unit.

Examples: Haemoglobin, Antibody and Actin

Describe the three examples of a quaternary protein structure. (3)

1. Haemoglobin- tetrahedral structure that contains 4 globins/ subunits and each contains iron atom.

2. Antibody- Four polypeptide chain forms a Y shape which is held by sulfur bridges. It’s shape is adapted for linking with antigens

3. Actin- Protein find in muscles which consist many gobular subunits arranged in double helix to form long ligaments.

What are the two types of proteins based on their shapes and functions. (2)

Globular and Fibrous

Descirbe haemoglobin in terms of what type of protein, number of polypeptide chains, its shape, structure, components, type of bond, any prosthetic groups, solubiltity, function and sensitivity to pH (9)

A type of gobular protein

• Consist four polypeptide chains fold into a compact, spherical shape

• Complex tertiary/ quaternary structures

• Contain subunits that are called globin proteins- alpha and beta

• Held by disulfide bonds

• contain prosthetic group (haem group), containing iron that binds with oxyegn reversibly

• Soluble, as hydrophillic R groups facing outwards and hydrophobic R groups facing inwards

• Physiological function- allow protein to be transported in fluids- involving in metabolic reactions

• Sensitive to temp and pH so could be denatured

Why does oxygen bind to iron reversibly?

Easier for oxygen transport

How does the hydrophillic R group facing outwards and hydrophobic R group facing inwards help with functions of globular proteins? (2)

• Hydrophillic R group - interact with water, maintaining solubility

• Hydrophobic R group- keeping 3D spherical shape

Descirbe collagen in terms of what type of protein, number of polypeptide chains, its shape, structure, components, type of bond, any prosthetic groups, solubiltity, function and sensitivity to pH (9)

A type of fibrous protein

• Consist of 3 polypeptide chains forming a triple helix that is long, straight, parallel chain

• Little or no tertiary or quaternary structures

• made up of alpha chains and have cross link hold to form collagen fibrils - every third amino acid is glycine

• held by hydrogen and disulfide bondings

• no prosthetic groups

• Insoluble due to large numbers of hydrophobic R group in amino acids and have great tensil strength and stable that are hard to be seperated by water molecules

• Structural function- which have staggered ends which leaves no gaps as weak spot- collagen found in connective tissues of teeths, bones, ligaments, tendons

• Not very sentisitve to temperature or pH