3.5 - Lipids and Proteins

Question 1

What make up triglycerides?

Answer 1

Fatty acid and glycerol molecules

Question 2

Describe the structure and function of cholesterol

Answer 2

• steroid structure of 4 hydrocarbon rings
• hydrocarbon tail on one side hydroxyl group on the other side
• adds stability to cell surface phospholipid bilateral by connecting molecules and reducing fluidity
• molecules of cholesterol are synthesised in the liver and transported via the blood
• acts as a barrier fitting in spaces between phospholipids- prevents water soluble substances from diffusing across the membrane

Question 3

What’s the general structure of an amino acid?

Answer 3

• COOH carboxyl/ carboxylic acid group
• R variable side groups consists of carbon chain and may include other functional groups
• amine group

Question 4

How do polypeptides form?

Answer 4

Condensation reactions between amino acids form peptide bonds

Question 5

What are lipids ?

Answer 5

•They’re macromolecules that contain C,H and O atoms
• non polar and hydrophobic

Question 6

What is glycerol?

Answer 6

an alcohol that contains a OH group bonded to a carbon atom

Question 7

What are fatty acids?

Answer 7

• contain a methyl group at one end of a hydrocarbon chain known as a R group and a carbonyl group at another end

Question 8

Name 2 ways a fatty acid Can vary

Answer 8

1. Length of the hydrocarbon chain (R group )
2. The fatty acid chain may be saturated or unsaturated

Question 9

How are triglycerides formed?

Answer 9

By esterification

Question 10

How does a ester bond form?

Answer 10

When the hydroxyl group from the glycerol bonds react with the carboxyl group of the fatty acids

Question 11

What type of reaction is a formation of a ester bond?

Answer 11

Condensation reaction

Question 12

Define primary structure of a protein

Answer 12

Sequence, number & type of amino acids in the polypeptide determines by the sequence of codons on mRNA

Question 13

Define the secondary structure of a protein

Answer 13

Hydrogen bonds form between O delta negative attached to C=O and H delta positive attached to -NH

Question 14

Describe the 2 types of secondary protein structure

Answer 14

• alpha helix
- all N-H bonds on the same side of protein chain
- spiral shape
- H- binds parallel to helical axis

• beta pleated sheet
- N-H & C=O groups alternate from one side to the other

Question 15

In what circumstance does the secondary structure occur ?

Answer 15

Occurs when weak negatively charged nitrogen and oxygen atom’s interact with weak positively charged hydrogen atoms to form hydrogen bonds

Question 16

Describe the tertiary structure of a protein and describe the bonds present

Answer 16

3D structure formed by further folding
Disulfude bonds - string covalent S-S bonds between molecules acid Cysteine
Ionic bonds- relatively strong bonds between charged R groups
Hydrogen bonds - numerous and easily broken

Question 17

Define quaternary structure of a protein

Answer 17

• functional proteins may consist of more than one polypeptide
• precise 3D structure held together by the same types of bond as tertiary structure
• may involve the addition of prosthetic groups eg. Metal ions or phosphate groups

Question 18

Define the structure and function of globular proteins

Answer 18

• compact, circular shape, soluble in water
• hydrophilic R groups face outwards and hydrophobic R groups face inwards = usually water soluble
• involved in metabolic processes eg. Enzymes such as amylase , insulin and haemoglobin

Question 19

Describe the structure of haemoglobin

Answer 19

• quaternary structure = 4 polypeptide chains
• 2 alpha chains , 2 beta chains and 4 prosthetic haem groups
• these chains are subunits are globular proteins and each subunit has a prosthetic haem group
• these 4 globin subunits are held together by disulphide bonds and are arranged so that their hydrophobic R groups are facing outwards- helping maintain its solubility
• prosthetic haem group contains iron ( iI) which reversible combines with an oxygen molecule forming an oxyhemoglobin and results in the haemoglobin appearing bright red

Question 20

Describe the structure and function of fibrous proteins

Answer 20

• long strands of polypeptide chains that have cross linkages due to hydrogen bonds
• due to large number of hydrophobic R groups they’re insoluble in water
• useful for structure and support eg. Collagen in skin

Question 21

What is the function of collagen?

Answer 21

Component of bones , cartilage, connective tissues and tendon’s

Question 22

What’s the function of elastin?

Answer 22

Provides elasticity to connective tissue , arteries, skin , lungs , cartilage, ligaments

Question 23

What’s the function of keratin?

Answer 23

Structural component of hair, nails, epithelial cells of outer layer of skin