B1.2 Proteins

Question 1

Generalized structure of an amino acid

Answer 1

Be able to draw diagram (check notes). Alpha carbon atom with amine group, carboxyl group, R-group and hydrogen attached.

Question 1

R-group importance

Answer 1

Varies and makes amino acids different from each other. Also affect the way amino acids bond with each other. Also determine properties of assembled polypeptides.

Question 2

Peptides

Answer 2

Formed by joining amino acids together in condensation reactions. Carboxyl of 1 amino acid reacts with amine of another forming a peptide bond and water.

Question 3

Explain the infinite variety of possible peptide chains

Answer 3

20 different amino acids: 11 made in body, 9 cannot so are called essential amino acids as they are needed and obtained from diet. Amino acids can be combined and be arranged in any order. Polypeptides vary in length and can have any number of amino acids from a few to thousands long.

Question 4

Effect of pH on protein structure

Answer 4

Proteins each have pH ranges where they function optimally which will depend on their amino acid sequence and the intramolecular forces present such as ionic bonds between positive and negative R-groups. A change in pH can alter chemical properties of the R-groups, namely their charge. Change in charge can break ionic bonds within protein, altering its shape and causing it to denature.

Question 5

Effects of Temperature on protein structure.

Answer 5

Proteins each have temperature ranges where they function optimally which will depend on their amino acid sequence and the intramolecular forces present. Above this temperature, the increased energy will cause the polypeptide to vibrate/move so much that weak intramolecular bonds can break, altering its shape causing it to denature.

Question 6

Primary protein structure

Answer 6

Linear sequence of amino acids in a polypeptide linked together by peptide bonds.

Question 7

Importance of DNA in formation of a polypeptide sequence

Answer 7

DNA gene provides instructions for a polypeptide sequence including its length, composition, and placement giving proteins a precise, predictable and repeatable structure.

Question 8

Secondary protein structure

Answer 8

Plating and coiling of a polypeptide into alpha-helices and beta-pleated sheets due to hydrogen bonding between carboxyl groups and amines.

Question 9

Effect of R-group structure on the properties of an amino acid

Answer 9

Two types of groups: Hydrophobic and Hydrophilic.
Hydrophobic: uncharged and non-polar so repel and are insoluble in water.
Hydrophilic: Either charged (negatively: acidic; positively: basic) or polar; both soluble in water.

Question 10

Tertiary protein structure

Answer 10

Overall 3-dimensional shape of the protein due to intramolecular interactions/bonds between R-groups: Hydrogen bonds formed between the D- and D+ atoms of polar groups. Ionic bonds formed between ionized R-groups. Hydrophobic interaction where non-polar R-groups interact and move closer with each other to avoid water. Covalent bond formed with the sulfur atoms from two cysteine R-groups.

Question 11

Quaternary protein structure

Answer 11

Protein complex composed of 2 or more polypeptides.

Question 12

Hemoglobin structure and function.

Answer 12

An example of a conjugated protein. Made up of 4 subunits, 2 alpha globins, 2 beta globins, each a polypeptide folded into many helices and each globin is bound to a hem prosthetic group.
The hem group contains an Fe2+ which binds reversibly to O2 in the lungs and deliver it to cells around the body.

Question 13

Conjugated protein

Answer 13

Composed of both protein and non-protein prosthetic group(s) such as carbohydrates, lipids, metal ions, and other organic groups.

Question 14

Non-conjugated protein

Answer 14

Composed of proteins only.

Question 15

Insulin structure and function

Answer 15

An example of a non-conjugated protein. Made of 2 polypeptides. After initial synthesis it is a single polypeptide but is then modified to two chains linked by covalent disulfide bridges. It is a hormone which promotes synthesis and storage of glycogen in the liver and muscle cells, reducing blood glucose levels.

Question 16

Collagen structure and function

Answer 16

An example of a non-conjugated protein. Made of 3 left-handed helices wound together into a right-handed triple helix, forms strong fibers. It is a structural protein making up connective tissue, giving tensile strength to tendons and ligaments and elasticity to skin.

Question 17

Difference between Fibrous and Globular proteins

Answer 17

Insulin is a non-conjugated globular protein whilst Collagen is a non-conjugated fibrous protein.
Structure: Globular - Round/spherical, typically composed of variable, irregular amino acid sequences. Fibrous - long and narrow, typically composed of repeating amino acid sequences.
Properties: Globular - generally soluble in water, sensitive to temp and pH changes. Fibrous - generally insoluble in water, stable in a large range of conditions.
Function: Globular - Physiological/functional/specialized role. Fibrous - structural role (strength and support).