Key Concepts in Biochemistry: Carbohydrates, Lipids, Proteins

What are some key functions of carbohydrates in living organisms?

Primary energy source (e.g. glucose)

Short-term energy storage (e.g. glycogen, starch)

Structural support (e.g. cellulose in plants, chitin in fungi)

What is glycogen?

Branched, energy storage in animals (liver/muscles)

What is cellulose used for?

Straight chains, structural in plants (cell walls), not digestible by humans

State the functions of lipids.

Long-term energy storage, Insulation and cushioning, Major component of cell membranes (phospholipids), Hormone production (e.g. steroids)

What is the structure of triglyceride and how is it formed?

1 glycerol + 3 fatty acids linked by ester bonds via dehydration synthesis;

Saturated = no double bonds (solid), Unsaturated = ≥ 1 double bond (liquid)

What are the four levels of protein structure?

Primary - Sequence of amino acids

Secondary - Alpha helices & beta sheets (hydrogen bonds)

Tertiary - 3D folding (R-group interactions)

Quaternary - Multiple polypeptides forming one protein

What is dipeptide bond? What kind of bond and reaction?

Formed when amino acids (e.g. leucine + glycine) create a peptide bond through dehydration synthesis (releases water)

What are the functions of proteins?

Speed up chemical reactions, provide structural support and strength to cells and tissues, carries substances through body/membranes

Define enzyme-substrate complex.

A temporary structure formed when an enzyme binds to its specific substrate, allowing the reaction to proceed.

What is enzyme inhibition?

A process that reduces enzyme activity (e.g., competitive inhibitor blocks active site)

What is enzyme activation?

A process that increases enzyme activity (e.g., cofactors or allosteric activators enhance enzyme function)

How do enzymes speed up chemical reactions?

They lower the activation energy by providing an alternate reaction pathway and bringing reactants together.

What is the function of the cell membrane?

It controls the movement of substances in and out of the cell; composed of a phospholipid bilayer with proteins.

Describe the fluid mosaic model of the plasma membrane.Describe the fluid mosaic model of the plasma membrane."

A flexible lipid bilayer with scattered proteins that move freely, like tiles in a mosaic — dynamic and selectively permeable.

State endocytosis and exocytosis.

Cell takes in material ; Cell releases material

State phagocytosis and pinocytosis.

Phagocytosis: The process by which a cell engulfs solid particles; Pinocytosis: The process by which a cell takes in liquid droplets

What is simple diffusion?

The passive movement of uncharged molecules from an area of higher concentration to an area of lower concentration across the cell membrane ; doesn't require energy

What is facilitated diffusion?

The passive movement of charged substances from an area of higher concentration to an area of lower concentration through specific membrane proteins; does not require energy.

Differentiate between active and passive transport.

Requires energy to move substances against their concentration gradient (low to high) : Doesn't require energy to move substances with their concentration gradient (high to low)

Hypotonic Solution

A solution with fewer solutes than inside the cell; water enters the cell → cell swells and may burst (lysis).

Hypertonic Solution

A solution with more solutes outside the cell ; water moves out of the cell → cell shrinks and undergoes crenation/plasmolysis

Isotonic Solution

Equal solute concentration inside and outside; water moves equally in both directions → cell remains the same size.