Exam questions

Compare and contrast the structure and function of globular vs fibrous proteins.

Globular proteins

• Compact, rounded shape

• Water-soluble

• Complex tertiary (and sometimes quaternary) structure

• Functions: metabolic roles

• Examples: enzymes, haemoglobin, insulin

Fibrous proteins

• Long, thin strands

• Insoluble in water

• Mostly secondary structure (repeating)

• Functions: structural roles

• Examples: collagen, keratin

Comparison

• Both are made of amino acids joined by peptide bonds

• Different shapes → different functions

Describe the gross structure of cellulose.

• Cellulose is a polysaccharide

• Made of β-glucose monomers

• Monomers joined by β-1,4 glycosidic bonds

• Chains are long, straight, and unbranched

• Parallel chains form microfibrils

• Microfibrils are held together by hydrogen bonds

• Provides strength and rigidity to plant cell walls

Define the 4 levels of protein structure including any key bonding / features.

Primary

• Sequence of amino acids

• Held by peptide bonds

Secondary

• Folding into α-helices or β-pleated sheets

• Stabilised by hydrogen bonds

Tertiary

• Overall 3D shape

• Bonds include:

  • Hydrogen bonds

  • Ionic bonds

  • Disulfide bridges

  • Hydrophobic interactions

Quaternary

• Multiple polypeptide chains combined

• Example: haemoglobin

Define the term validity.

Validity is how well an experiment measures what it is supposed to measure.

High validity means:

• Only the independent variable affects the result

• Control variables are kept constant

Explain the difference between a reducing and non-reducing sugar as well as how we test for them both.

Reducing sugars

• Have a free aldehyde or ketone group

• Examples: glucose, maltose

• Test: Benedict’s test

  • Blue → green/yellow/orange/brick-red

Non-reducing sugars

• No free aldehyde or ketone group

• Example: sucrose

• Test:

  1. Heat with dilute HCl

  2. Neutralise with sodium hydrogencarbonate

  3. Then add Benedict’s solution

Explain why we should not extrapolate data points on our graphs.

• Extrapolation goes beyond measured data

• Relationships may change outside the tested range

• Leads to unreliable and invalid conclusions

Explain why there is an issue with viewing colours with the human eye as indicators of concentration and how we would resolve this.

Problem

• Human perception of colour is subjective

• Light conditions and eyesight vary

• Small differences are hard to detect

Solution

• Use a colorimeter

• Measures absorbance quantitatively

• Produces more accurate and reliable data