INTRODUCTION TO
CARBOHYDRATES AND GLYCOLYSIS
SAFIYA RANSOME, P3 (safiya.ransome@me.com)
PHARMACY BIOMEDICAL PREVIEW PROGRAM 2014
What are carbohydrates?
• A major class of macromolecules
• Largely composed of carbon, hydrogen, and oxygen.
• Generally, carbohydrates serve two major functions:
• Energy Storage
• Ex: Sucrose is catabolized to glucose which is
converted to ATP via glycolysis. • Structure
• Ex: Cellulose is the major structural component of
plant stems.
Carbohydrate Structure
• Empirical Formula: Cm(H2O)n
• Example: Ribose is C5H10O5
• (But there are exceptions— what’s
deoxyribose?)
• Carbohydrates can exist in either open chain form
or cyclic form. Cyclic form is more common.
Carbohydrate Classification
• Monosaccharide
• Monomeric carbohydrate unit. Also known as a
simple sugar.
• Disaccharide
• Two monomeric sugars linked together form a
disaccharide. • Polysaccharide
• Multiple monomeric units linked together form a
polysaccharide.
Monosaccharides
• Can be further classified by the number of carbons: • Ex: 3 carbons = triose, 6 carbons = hexose
• The most biologically relevant monosaccharide,
glucose, is a hexose.
Disaccharides
• Monomeric units are bonded by O-glycosidic linkages, O
is for oxygen. • Glycosidic linkages are formed by dehydration reactions. • Example: Glucose + Glucose ➔ Maltose + H2O
(byproduct)
• Common disaccharides:
• Glucose + Glucose = Maltose
• Glucose + Fructose = Sucrose
• Glucose + Galactose = Lactose
Polysaccharides
• Composed of multiple monomeric units. • Also bonded by glycosidic linkages. • Common polysaccharides:
• Starch and glycogen - energy storing
polysaccharides
• Cellulose and chitin - structural
polysaccharides
Glycolysis: Introduction
• Glycolysis is the catalytic process by which ATP
(energy) is produced from glucose. • Is an anaerobic process. Oxygen does not need to
be present for it to occur. • Net Reaction: •1 mol glucose ➔ 2 pyruvate + 2 NADH + 2 ATP
• Also known as the Embden-Meyerhof Pathway
Glycolysis Overview:
• Can be divided into two stages:
• Stage 1: Energy Consumption
• 2 ATP consumed
• Energy is used to convert glucose into two
phosphorylated trioses. • Stage 2: Energy Production
• 4 ATP produced • 2 NADH produced • 2 pyruvate produced
Glycolysis Overview
Glycolysis: Step 1
• Enzyme: Hexokinase
• Phosphorylates glucose to produce glucose-6phosphate
•One ATP molecule consumed
• Irreversible Step - Glycolysis process is now committed
to continue.
Glycolysis: Step 2
• Enzyme: Phosphoglucose Isomerase
• Rearranges glucose-6-phosphate to fructose-6phosphate
Glycolysis: Step 3
• Enzyme: Phosphofructokinase (PFK)
• Phosphorylates fructose-6-phosphate to
produce fructose-1,6-bisphosphate
•One ATP Molecule is consumed
• Irreversible Step
Glycolysis: Step 4
• Enzyme: Aldolase
• Cleaves fructose-1,6bisphosphate to two
triose sugars:
dihydroxyacetone
phosphate (DHAP) and
glyceraldehyde-3phosphate (GAP)
• GAP continues through
glycolysis; DHAP is
converted into GAP by triose
phosphate isomerase.
PAUSE!
• We are now moving into stage 2 of glycolysis, the
energy production stage. • Take note! The previous step produced 2
molecules of GAP; individually each molecule will
progress through each of the remaining steps. • You can think of this as stage 2 occurring twice.
Glycolysis: Step 5
• Enzyme: Glyceraldehyde 3-phosphate dehydrogenase
• Converts glyceraldehyde-3-phosphate to 1,3bisphosphoglycerate.
• This step does NOT require ATP; inorganic phosphate is
used to produce the new phosphate. •One molecule of NADH is produced.
Glycolysis: Step 6
• Enzyme: Phosphoglycerate kinase
• 1,3-bisposphoglycerate is de-phosphorylated to
produce 3-phosphoglycerate
•One molecule of ATP is produced.
• This is known as substrate-level phosphorylation.
Glycolysis: Step 7
• Enzyme: Phosphoglycerate mutase
• Rearranges 3-phosphoglycerate to 2phosphoglycerate
Glycolysis: Step 8
• Enzyme: Enolase
• Converts 2-phosphoglycerate to
phosphoenolpyrovate
Glycolysis: Step 9
• Enzyme: Pyruvate kinase
• Phosphoenolpyruvate is de-phosphorylated to produce
pyruvate
• One molecule of ATP is produced.
• Irreversible step.
The Balance Sheet
Consumed
Produced
Net
- 2 mol ATP
4 mol ATP
2 mol ATP
2 NADH
2 NADH
2 pyruvate
2 pyruvate
Learning Tips!
• Pay attention the molecule names, they will help you
understand the order of the steps.
• Pay attention to enzyme names:
• Enzymes that are kinases are responsible for
phosphorylation steps— either ATP consuming or producing. • Ex: hexokinase • Ex: Pyruvate kinase
• Also, enzymes sometimes have similar names to the
molecule that they act on:
• Ex: Phosphoglycerate mutase acts on 3-phosphoglycerate