Proteins

What are proteins?

large biological molecules found in all living cells.

→ made of amino acids linked in long chains by peptide bonds.

What are amino acids linked by?

Peptide bonds.

→ this is a condensation reaction - same principle as ester bonds in lipids. Water is released each time.

Where are proteins produced in the cell?

At the ribosomes, during protein synthesis

→ the process: DNA → RNA → Protein

What elements do proteins contain?

• Carbon

• Hydrogen

• Oxygen

• Nitrogen

→ ALWAYS contain nitrogen (unlike lipids/carbohydrates)

Name 5 functions of proteins

• Enzymes (spped up reactions)

• structural support (muscles, hair)

• transport (haemoglobin)

• Signalling (hormones/ receptors)

• Defence (aantibodies)

Primary structure of a protein?

exact sequence of amino acids in the polypeptide chain

→ sequence is determined by DNA code (even one wrong acid can change whole protein!)

Secondary structure of a protein?

local folding of the polypeptide cahin into regular shapes

→ e.g.: alpha-helix (spiral)

Tertiary structure of a protein?

overall 3D shape of shingle polypeptide chain

→ determined by interactions between side chains: hydrogen bonds, hydrophobic interactions,…

Quaternary structure of a protein?

Formed when two are more polypeptide chains combine

What is a base triplet? (codon)

sequence of 3 DNA/RNA bases that codes for one specific amino acid

→ e.g.: GGG → one specific amino acid. There are 20 essential amino acids.

What are the 4 DNA bases?

• Guanine (G)

• Cytosine (C)

• Adenine (A)

• Thymine (T)

What is an enzyme?

A biological catalyst - a protein that speeds up chemical reactions in cells

→ ALL enzymes are proteins, but NOT ALL proteins are enzymes!!

Name 4 specific proteins + functions

1. Haemoglobin (carries O2)

2. Collagen (bones/ arteries)

3. Keratin (skin/hair/nail)

4. Insulin (regulates blood sugar)

Difference between haemoglobin and myoglobin?

Both carry oxygen, BUT:

→ haemoglobin in red blood cells (carries O2 through body)

→ myoglobin stores O2 in muscle tissue

What bonds stabilise the tertiary structure?

• Hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges