Lect4: Biological Molecules, Enzymes & Energy

What are the major functions of proteins in cells?

Proteins:

• Move materials

• Send signals

• Provide structure

• Transport molecules

• Carry out chemical reactions

What are enzymes?

Proteins that speed up (catalyze) chemical reactions in cells.

How do enzymes speed up chemical reactions?

They lower the activation energy needed for the reaction to occur.

Why are enzymes important at body temperature?

Many reactions happen too slowly on their own at body temperature. Enzymes allow them to occur fast enough to support life.

What is an example of an enzyme-assisted reaction involving glucose?

Glucose + O₂ → CO₂ + H₂O + energy

What are proteins made of?

Amino acids, which are the monomers (building blocks) of proteins.

What is the general structure of an amino acid?

A central carbon bonded to:

• Amino group (–NH₂)

• Carboxyl group (–COOH)

• Hydrogen (H)

• R group (side chain)

What makes one amino acid different from another?

The R group (side chain) varies between amino acids and gives each one its unique properties.

How many different amino acids are used to make proteins?

20 different amino acids.

What are non-essential amino acids?

Amino acids that your cells can make on their own. Most amino acids (11) are non-essential.

What are essential amino acids?

The 9 amino acids your cells cannot make, so they must come from your diet.

What are conditionally essential amino acids?

Amino acids that can be made by cells, but sometimes not fast enough to meet the body's needs, so getting them from food can be important.

What is a peptide bond?

A covalent bond that joins two amino acids together.

How is a peptide bond formed?

Through dehydration synthesis, where two amino acids join and a water molecule (H₂O) is removed.

What is a polypeptide?

A long chain of amino acids connected by peptide bonds.

How do amino acids form a polypeptide chain?

Amino acids → dehydration synthesis → peptide bonds → polypeptide chain

What happens after a polypeptide chain is made?

The polypeptide folds into a specific 3D shape, becoming a functional protein.

Why is a protein's shape important?

A protein's shape determines its function. Proper folding allows the protein to do its job.

What are the main levels of protein structure shown here?

• Primary: amino acid sequence

• Secondary: local folding (α-helices & β-sheets)

• Tertiary: overall 3D shape of one polypeptide

What is an enzyme's active site?

The specific region where the substrate binds and the reaction occurs.

How does a folded enzyme interact with a substrate?

The substrate binds to the active site → enzyme-substrate complex forms → reaction occurs → products are released.

What are cofactors?

Non-protein substances that help proteins/enzymes function properly.

Where do most cofactors in the body come from?

From the diet, especially vitamins and minerals.

What are examples of cofactors?

• Minerals such as copper (Cu) and iron (Fe)

• Vitamins, especially B-complex vitamins

What are examples of B vitamins that act as cofactors?

• B1 (Thiamine) → TPP: carbohydrate breakdown for energy

• B2 (Riboflavin) → FAD/FMN: electron transfer during ATP production

• B3 (Niacin) → NAD⁺/NADP⁺: carries electrons/H⁺ during metabolism

• B6 (Pyridoxine) → PLP: helps process amino acids/proteins

How does vitamin C function as a cofactor?

Its active form, ascorbate, helps enzymes make collagen for connective tissues.

What are the two main steps for breaking down dietary proteins?

• Denaturation – protein unfolds

• Cleavage – polypeptide is cut into smaller peptides/amino acids

What happens to proteins in the stomach?

The stomach's acidic, low-pH environment denatures (unfolds) proteins.

What does it mean to cleave a polypeptide?

To cut the polypeptide into smaller peptides or individual amino acids.

What happens after proteins are broken down?

The resulting small peptides and amino acids are absorbed in the intestines.