Leyland 4 Catabolism Flashcards
Stage 1
- Extracellular (GI tract)
- Complex molecules à building block molecules (bbm)
- bbm absorbed into circulation
- No energy produced.
Stage II
• Intracellular (cytoplasmic & mitochondrial) • Many pathways (not all in all tissues) • bbm à even simpler molecules • Oxidative (require NAD+, NADP+, FAD) • Some energy (as ATP) produced
Stage III
Mitochondria
• A single pathway –
Citric acid (Tricarboxylic acid)
cycle
- Oxidative
- Acetyl converted to 2CO2
- Produces precursors for
biosynthesis
• Oxidative phosphorylation
(Electron transport and ATP
synthesis)
• NADH & FAD2H re-oxidised
• O2 required (reduced to H2O)
• Lots of energy (ATP) producedCarbohydrates
- General formula (CH2O)n
- Contain aldehyde (-CHO) or keto (-C=O) groups
- Multiple –OH gps
- Monosaccharide – single sugar units (3-9 C-atoms)
trioses
3-carbon monosaccharides
Differ in spatial organization of the asymmetric carbon atom furthest from the aldehyde or ketone group
5-carbon monosaccharides ( Pentoses )
6-carbon monosaccharides (hexoses)
Hexoses usually exist in cyclic forms
Pentoses
5-carbon monosaccharides
hexoses
6-carbon monosaccharides
Hexoses usually exist in cyclic forms
Types of Carbs
Aldohexoses: aldose sugars
Aldopentose: aldose sugars
Ketohexose: ketose sugar
Epimers:
Differ at one of several different asymmetric carbon atoms
Sugar molecules are not planar…
…assume a ‘chair’ (or ‘boat’) conformation.
axial bonds
equatorial bonds
Most important monosaccharide metabolically in mammals …
glucose.
Monosaccharides are linked to form
complex carbohydrates
Disaccharides
alpha 1,4, glycosidic bond between 2 monosaccharides
Maltose
glucose + glucose
Sucrose
Glucose + fructose
Lactose
galactose + glucose
Polysaccharides
(10 – 1000 units)
Glycogen
- main storage polysaccharide of animal cells (liver & skeletal muscle)
- a1-4 and a1-6 glycosidic bonds
- highly branched
Starch
- plants
- a1-4 and a1-6 glycosidic bonds
- less branched
Cellulose
- plants
- b1-4 glycosidic bonds
- unbranched
Dietary CHO
Starch, glycogen lactose maltose sucrose glucose fructose
a-1,4 bonds of glycogen & starch digested in the mouth by:
salivary amylase to produce dextrins
Other enzymes in small intestine (attached to brush border membrane of epithelial cells)
pancreatic amylase (a-1,4 bonds)
isomaltase (a-1,6 bonds)
sucrase (sucrose)
lactase (lactose)
Absorption of monosaccharides (sugars)
• Actively transported into intestinal epithelial cells & then, via blood supply, to target tissues.
• Uptake into cells via facilitated diffusion using transport proteins (GLUT1 - GLUT5).
- different distribution and affinities
- can be hormonally controlled (insulin)
Glucose requirements of tissues.
• All tissues can metabolise glucose
• Blood [glucose] regulated (~5mM).
- because some tissues (rbc, wbc, kidney medulla, lens of the eye) have an absolute requirement &
uptake by these tissues depends on [blood]
• CNS (brain) prefers glucose
